Concerning the Motion and Orientation of Flux Transfer Events Produced by Component and Antiparallel Reconnection

NASA Technical Reports Server (NTRS)

Sibeck, D. G.; Lin, R.-Q.

2011-01-01

We employ the Cooling et al. (2001) model to predict the location, orientation, motion, and signatures of flux transfer events (FTEs) generated at the solstices and equinoxes along extended subsolar component and high ]latitude antiparallel reconnection curves for typical solar wind plasma conditions and various interplanetary magnetic field (IMF) strengths and directions. In general, events generated by the two mechanisms maintain the strikingly different orientations they begin with as they move toward the terminator in opposite pairs of magnetopause quadrants. The curves along which events generated by component reconnection form bow toward the winter cusp. Events generated by antiparallel reconnection form on the equatorial magnetopause during intervals of strongly southward IMF orientation during the equinoxes, form in the winter hemisphere and only reach the dayside equatorial magnetopause during the solstices when the IMF strength is very large and the IMF points strongly southward, never reach the equatorial dayside magnetopause when the IMF has a substantial dawnward or duskward component, and never reach the equatorial flank magnetopause during intervals of northward and dawnward or duskward IMF orientation. Magnetosheath magnetic fields typically have strong components transverse to events generated by component reconnection but only weak components transverse to the axes of events generated by antiparallel reconnection. As a result, much stronger bipolar magnetic field signatures normal to the nominal magnetopause should accompany events generated by component reconnection. The results presented in this paper suggest that events generated by component reconnection predominate on the dayside equatorial and flank magnetopause for most solar wind conditions.

Double Magnetic Reconnection Driven by Kelvin-Helmholtz Vortices

NASA Astrophysics Data System (ADS)

Horton, W., Jr.; Faganello, M.; Califano, F.; Pegoraro, F.

2017-12-01

Simulations and theory for the solar wind driven magnetic reconnection in the flanks of the magnetopause is shown to be intrinsically 3D with the secular growth of couple pairs of reconnection regions off the equatorial plane. We call the process double mid-latitude reconnection and show supporting 3D simulations and theory descripting the secular growth of the magnetic reconnection with the resulting mixing of the solar wind plasma with the magnetosphere plasma. The initial phase develops Kelvin-Helmholtz vortices at low-latitude and, through the propagation of Alfven waves far from the region where the stresses are generated, creates a standard quasi-2D low latitude boundary layer magnetic reconnection but off the equatorial plane and with a weak guide field component. The reconnection exponential growth is followed by a secularly growing nonlinear phase that gradually closes the solar wind field lines on the Earth. The nonlinear field line structure provides a channel for penetration of the SW plasma into the MS as observed by spacecraft [THEMIS and Cluster]. The simulations show the amount of solar wind plasma brought into the magnetosphere by tracing the time evolution of the areas corresponding to double reconnected field lines with Poincare maps. The results for the solar wind plasma brought into the magnetosphere seems consistent with the observed plasma transport. Finally, we have shown how the intrinsic 3D nature of the doubly reconnected magnetic field lines leads to the generation of twisted magnetic spatial structures that differ from the quasi-2D magnetic islands structures.

Model development of supersonic trough wind with shocks

NASA Technical Reports Server (NTRS)

Grebowsky, J. M.

1972-01-01

The time dependent one dimensional hydrodynamic equations describe the evolution of the thermal plasma flow along closed magnetic field lines outside of the plasmasphere. The convection of the supersonic polar wind onto a closed fieldline results in the assumed formation of collisionless plasma shocks. These shocks move earthward as the field line with its frozen-in plasma remains fixed or contracts with time to smaller L coordinates. The high equatorial plasma temperature (of the order of electron volts) produced by the shock process decreases with time if the flow is isothermal but it will increase if the contraction is under adiabatic conditions. Assuming adiabaticity a peak in the temperature forms at the equator in conjunction with a depression in the ion density. After an initial contraction, if the flux tube drifts to higher L coordinates the direction of the shock motion can be reversed so that the supersonic region will expand along the field line towards the state characterizing the supersonic polar wind. A rapid expansion will lower the equatorial density while the temperature decreases with time under adiabatic but not isothermal conditions.

Poster 17: Methane storms as a driver of Titan's dune orientation.

NASA Astrophysics Data System (ADS)

Charnay, Benjamin; Barth, Erika; Rafkin, Scot; Narteau, Clement; Lebonnois, Sebastien; Rodriguez, Sebastien; Courech Du Pont, Sylvain; Lucas, Antoine

2016-06-01

Titan's equatorial regions are covered by eastward oriented linear dunes [1,2]. This direction is opposite to mean surface winds simulated by Global Climate Models (GCMs) at these latitudes, oriented westward as trade winds on Earth. We propose that Titan's dune orientation is actually determined by equinoctial tropical methane storms producing a coupling with superrotation and dune formation [3]. Using meso-scale simulations of convective methane clouds [4] with a GCM wind profile featuring the superrotation [5,6], we show that Titan's storms should produce fast eastward gust fronts above the surface. Such gusts dominate the aeolian transport. Using GCM wind calculations and analogies with terrestrial dune fields [7], we show that Titan's dune propagation occurs eastward under these conditions. Finally, this scenario combining global circulation winds and methane storms can explain other major features of Titan's dunes as the divergence from the equator or the dune size and spacing. It also implies an equatorial origin of Titan's dune sand and a possible occurence of dust storms.

Response of the Equatorial Ionosphere to the Geomagnetic DP 2 Current System

NASA Technical Reports Server (NTRS)

Yizengaw, E.; Moldwin, M. B.; Zesta, E.; Magoun, M.; Pradipta, R.; Biouele, C. M.; Rabiu, A. B.; Obrou, O. K.; Bamba, Z.; Paula, E. R. De

2016-01-01

The response of equatorial ionosphere to the magnetospheric origin DP 2 current system fluctuations is examined using ground-based multiinstrument observations. The interaction between the solar wind and fluctuations of the interplanetary magnetic field (IMF) Bz, penetrates nearly instantaneously to the dayside equatorial region at all longitudes and modulates the electrodynamics that governs the equatorial density distributions. In this paper, using magnetometers at high and equatorial latitudes, we demonstrate that the quasiperiodic DP 2 current system penetrates to the equator and causes the dayside equatorial electrojet (EEJ) and the independently measured ionospheric drift velocity to fluctuate coherently with the high-latitude DP 2 current as well as with the IMF Bz component. At the same time, radar observations show that the ionospheric density layers move up and down, causing the density to fluctuate up and down coherently with the EEJ and IMF Bz.

Pacific decadal variability in the view of linear equatorial wave theory

NASA Astrophysics Data System (ADS)

Emile-Geay, J. B.; Cane, M. A.

2006-12-01

It has recently been proposed, within the framework of the linear shallow water equations, that tropical Pacific decadal variability can be accounted for by basin modes with eigenperiods of 10 to 20 years, amplifying a mid- latitude wind forcing with an essentially white spectrum (Cessi and Louazel 2001; Liu 2003). We question this idea here, using a different formalism of linear equatorial wave theory. We compute the Green's function for the wind forced response of a linear equatorial shallow water ocean, and use the results of Cane and Moore (1981) to obtain a compact, closed form expression for the motion of the equatorial thermocline, which applies to all frequencies lower than seasonal. At very low frequencies (decadal timescales), we recover the planetary geostrophic solution used by Cessi and Louazel (2001), as well as the equatorial wave solution of Liu (2003), and give a formal explanation for this convergence. Using this more general solution to explore more realistic wind forcings, we come to a different interpretation of the results. We find that the equatorial thermocline is inherently more sensitive to local than to remote wind forcing, and that planetary Rossby modes only weakly alter the spectral characteristics of the response. Tropical winds are able to generate a strong equatorial response with periods of 10 to 20 years, while midlatitude winds can only do so for periods longer than about 50 years. Since the decadal pattern of observed winds shows similar amplitude for tropical and midlatitude winds, we conclude that the latter are unlikely to be responsible for the observed decadal tropical Pacific SST variability. References : Cane, M. A., and Moore, D. W., 1981: A note on low-frequency equatorial basin modes. J. Phys. Oceanogr., 11(11), 1578 1584. Cessi, P., and Louazel, S., 2001: Decadal oceanic response to stochastic wind forcing. J. Phys. Oceanogr., 31, 3020 3029. Liu, Z., 2003: Tropical ocean decadal variability and resonance of planetary wave basin modes. J. Clim., 16(18), 1539 1550.

Solar Cycle Effects on Equatorial Electrojet Strength and Low Latitude Ionospheric Variability (P10)

NASA Astrophysics Data System (ADS)

Veenadhari, B.; Alex, S.

2006-11-01

veena_iig@yahoo.co.in The most obvious indicators of the activity of a solar cycle are sunspots, flares, plages, and soon. These are intimately linked to the solar magnetic fields, heliospheric processes which exhibit complex but systematic variations. The changes in geomagnetic activity, as observed in the ground magnetic records follow systematic correspondence with the solar activity conditions. Thus the transient variations in the magnetic field get modified by differing solar conditions. Also the solar cycle influences the Earth causing changes in geomagnetic activity, the magnetosphere and the ionosphere. Daily variations in the ground magnetic field are produced by different current systems in the earth’s space environment flowing in the ionosphere and magnetosphere which has a strong dependence on latitude and longitude of the location. The north-south (Horizontal) configuration of the earth’s magnetic field over the equator is responsible for the narrow band of current system over the equatorial latitudes and is called the Equatorial electrojet (EEJ) and is a primary driver for Equatorial Ionization anomaly (EIA). Equatorial electric fields and plasma drifts play the fundamental roles on the morphology of the low latitude ionosphere and strongly vary during geomagnetically quiet and disturbed periods. Quantitative study is done to illustrate the development process of EEJ and its influence on ionospheric parameters. An attempt is also made to examine and discuss the response of the equatorial electrojet parameters to the fast varying conditions of solar wind and interplanetary parameters.

Lagrangian mixed layer modeling of the western equatorial Pacific

NASA Technical Reports Server (NTRS)

Shinoda, Toshiaki; Lukas, Roger

1995-01-01

Processes that control the upper ocean thermohaline structure in the western equatorial Pacific are examined using a Lagrangian mixed layer model. The one-dimensional bulk mixed layer model of Garwood (1977) is integrated along the trajectories derived from a nonlinear 1 1/2 layer reduced gravity model forced with actual wind fields. The Global Precipitation Climatology Project (GPCP) data are used to estimate surface freshwater fluxes for the mixed layer model. The wind stress data which forced the 1 1/2 layer model are used for the mixed layer model. The model was run for the period 1987-1988. This simple model is able to simulate the isothermal layer below the mixed layer in the western Pacific warm pool and its variation. The subduction mechanism hypothesized by Lukas and Lindstrom (1991) is evident in the model results. During periods of strong South Equatorial Current, the warm and salty mixed layer waters in the central Pacific are subducted below the fresh shallow mixed layer in the western Pacific. However, this subduction mechanism is not evident when upwelling Rossby waves reach the western equatorial Pacific or when a prominent deepening of the mixed layer occurs in the western equatorial Pacific or when a prominent deepening of the mixed layer occurs in the western equatorial Pacific due to episodes of strong wind and light precipitation associated with the El Nino-Southern Oscillation. Comparison of the results between the Lagrangian mixed layer model and a locally forced Eulerian mixed layer model indicated that horizontal advection of salty waters from the central Pacific strongly affects the upper ocean salinity variation in the western Pacific, and that this advection is necessary to maintain the upper ocean thermohaline structure in this region.

Theoretical study of the ionospheric plasma cave in the equatorial ionization anomaly region

NASA Astrophysics Data System (ADS)

Chen, Yu-Tsung; Lin, C. H.; Chen, C. H.; Liu, J. Y.; Huba, J. D.; Chang, L. C.; Liu, H.-L.; Lin, J. T.; Rajesh, P. K.

2014-12-01

This paper investigates the physical mechanism of an unusual equatorial electron density structure, plasma cave, located underneath the equatorial ionization anomaly by using theoretical simulations. The simulation results provide important new understanding of the dynamics of the equatorial ionosphere. It has been suggested previously that unusual E>⇀×B>⇀ drifts might be responsible for the observed plasma cave structure, but model simulations in this paper suggest that the more likely cause is latitudinal meridional neutral wind variations. The neutral winds are featured by two divergent wind regions at off-equator latitudes and a convergent wind region around the magnetic equator, resulting in plasma divergences and convergence, respectively, to form the plasma caves structure. The tidal-decomposition analysis further suggests that the cave related meridional neutral winds and the intensity of plasma cave are highly associated with the migrating terdiurnal tidal component of the neutral winds.

Feedback process responsible for intermodel diversity of ENSO variability

NASA Astrophysics Data System (ADS)

An, Soon-Il; Heo, Eun Sook; Kim, Seon Tae

2017-05-01

The origin of the intermodel diversity of the El Niño-Southern Oscillation (ENSO) variability is investigated by applying a singular value decomposition (SVD) analysis between the intermodel tropical Pacific sea surface temperature anomalies (SSTA) variance and the intermodel ENSO stability index (BJ index). The first SVD mode features an ENSO-like pattern for the intermodel SSTA variance (74% of total variance) and the dominant thermocline feedback (TH) for the BJ index (51%). Intermodel TH is mainly modified by the intermodel sensitivity of the zonal thermocline gradient response to zonal winds over the equatorial Pacific (βh), and the intermodel βh is correlated higher with the intermodel off-equatorial wind stress curl anomalies than the equatorial zonal wind stress anomalies. Finally, the intermodel off-equatorial wind stress curl is associated with the meridional shape and intensity of ENSO-related wind patterns, which may cause a model-to-model difference in ENSO variability by influencing the off-equatorial oceanic Rossby wave response.

On the day-to-day variation of the equatorial electrojet during quiet periods

NASA Astrophysics Data System (ADS)

Yamazaki, Y.; Richmond, A. D.; Maute, A.; Liu, H.-L.; Pedatella, N.; Sassi, F.

2014-08-01

It has been known for a long time that the equatorial electrojet varies from day to day even when solar and geomagnetic activities are very low. The quiet time day-to-day variation is considered to be due to irregular variability of the neutral wind, but little is known about how variable winds drive the electrojet variability. We employ a numerical model introduced by Liu et al. (2013), which takes into account weather changes in the lower atmosphere and thus can reproduce ionospheric variability due to forcing from below. The simulation is run for May and June 2009. Constant solar and magnetospheric energy inputs are used so that day-to-day changes will arise only from lower atmospheric forcing. The simulated electrojet current shows day-to-day variability of ±25%, which produces day-to-day variations in ground level geomagnetic perturbations near the magnetic equator. The current system associated with the day-to-day variation of the equatorial electrojet is traced based on a covariance analysis. The current pattern reveals return flow at both sides of the electrojet, in agreement with those inferred from ground-based magnetometer data in previous studies. The day-to-day variation in the electrojet current is compared with those in the neutral wind at various altitudes, latitudes, and longitudes. It is found that the electrojet variability is dominated by the zonal wind at 100-120 km altitudes near the magnetic equator. These results suggest that the response of the zonal polarization electric field to variable zonal winds is the main source of the day-to-day variation of the equatorial electrojet during quiet periods.

Global Specification of the Post-Sunset Equatorial Ionization Anomaly

NASA Astrophysics Data System (ADS)

Coker, C.; Dandenault, P. B.; Dymond, K.; Budzien, S. A.; Nicholas, A. C.; Chua, D. H.; McDonald, S. E.; Metzler, C. A.; Walker, P. W.; Scherliess, L.; Schunk, R. W.; Gardner, L. C.; Zhu, L.

2012-12-01

The Special Sensor Ultraviolet Limb Imager (SSULI) on the Defense Meteorological Satellite Program (DMSP) is used to specify the post-sunset Equatorial Ionization Anomaly. Ultraviolet emission profiles of 135.6 nm and 91.1 nm emissions from O++ e recombination are measured in successive altitude scans along the orbit of the satellite. The overlapping sample geometry provides for a high resolution reconstruction of the ionosphere in altitude and latitude for each pass of the satellite. Emission profiles are ingested by the Global Assimilation of Ionospheric Measurements (GAIM) space weather model, which was developed by Utah State University and is run operationally at the Air Force Weather Agency (AFWA). The resulting specification of the equatorial ionosphere reveals significant variability in the postsunset anomaly, which is reflective of the driving space weather processes, namely, electric fields and neutral winds. Significant longitudinal and day-to-day variability in the magnitude (or even existence) of the post-sunset anomaly reveal the influence of atmospheric tides and waves as well as geomagnetic disturbances on the pre-reversal enhancement of the electric field. Significant asymmetry between anomaly crests reveals the influence of atmospheric tides and waves on meridional neutral winds. A neutral wind parallel to the magnetic field line pushes plasma up (or down) the field lines, which raises (or lowers) the altitude of the crests and modifies the horizontal location and magnitude of the crests. The variability in the post-sunset anomaly is one of the largest sources of error in ionospheric specification models. The SSULI instrument provides critical data towards the reduction of this specification error and the determination of key driver parameters used in ionospheric forecasting. Acknowledgements: This research was supported by the USAF Space and Missile Systems Center (SMC), the Naval Research Laboratory (NRL) Base Program, and the Office of Naval Research (ONR).

Observations of Equatorial Kelvin Waves and their Convective Coupling with the Atmosphere/Ocean Surface Layer

NASA Astrophysics Data System (ADS)

Conry, Patrick; Fernando, H. J. S.; Leo, Laura; Blomquist, Byron; Amelie, Vincent; Lalande, Nelson; Creegan, Ed; Hocut, Chris; MacCall, Ben; Wang, Yansen; Jinadasa, S. U. P.; Wang, Chien; Yeo, Lik-Khian

2016-11-01

Intraseasonal disturbances with their genesis in the equatorial Indian Ocean (IO) are an important component of global climate. The disturbances, which include Madden-Julian Oscillation and equatorial Kelvin and Rossby waves in the atmosphere and ocean, carry energy which affects El Niño, cyclogenesis, and monsoons. A recent field experiment in IO (ASIRI-RAWI) observed disturbances at three sites across IO with arrays of instruments probing from surface layer to lower stratosphere. During the field campaign the most pronounced planetary-scale disturbances were Kelvin waves in tropical tropopause layer. In Seychelles, quasi-biweekly westerly wind bursts were documented and linked to the Kelvin waves aloft, which breakdown in the upper troposphere due to internal shear instabilities. Convective coupling between waves' phase in upper troposphere and surface initiates rapid (turbulent) vertical transport and resultant wind bursts at surface. Such phenomena reveal linkages between planetary-scale waves and small-scale turbulence in the surface layer that can affect air-sea property exchanges and should be parameterized in atmosphere-ocean general circulation models. Funded by ONR Grants N00014-14-1-0279 and N00014-13-1-0199.

An evidence for prompt electric field disturbance driven by changes in the solar wind density under northward IMF Bz condition

DOE PAGES

Rout, Diptiranjan; Chakrabarty, D.; Sekar, R.; ...

2016-05-26

Before the onset of a geomagnetic storm on 22 January 2012 (Ap = 24), an enhancement in solar wind number density from 10/cm 3 to 22/cm 3 during 0440–0510 UT under northward interplanetary magnetic field (IMF Bz) condition is shown to have enhanced the high-latitude ionospheric convection and also caused variations in the geomagnetic field globally. Some conspicuous changes in ΔX are observed not only at longitudinally separated low-latitude stations over Indian (prenoon), South American (midnight), Japanese (afternoon), Pacific (afternoon) and African (morning) sectors but also at latitudinally separated stations located over high and middle latitudes. The latitudinal variation ofmore » the amplitude of the ΔX during 0440–0510 UT is shown to be consistent with the characteristics of prompt penetration electric field disturbances. Most importantly, the density pulse event caused enhancements in the equatorial electrojet strength and the peak height of the F layer (h mF 2) over the Indian dip equatorial sector. Furthermore, the concomitant enhancements in electrojet current and F layer movement over the dip equator observed during this space weather event suggest a common driver of prompt electric field disturbance at this time. Such simultaneous variations are found to be absent during magnetically quiet days. In the absence of significant change in solar wind velocity and magnetospheric substorm activity, these observations point toward perceptible prompt electric field disturbance over the dip equator driven by the overcompression of the magnetosphere by solar wind density enhancement.« less

Revised Atmospheric Angular Momentum Series Related to Earth's Variable Rotation under Consideration of Surface Topography

NASA Technical Reports Server (NTRS)

Zhou, Y. H.; Salstein, D. A.; Chen, J. L.

2006-01-01

The atmospheric angular momentum is closely related to variations in the Earth rotation. The atmospheric excitation function (AEF), or namely atmospheric effective angular momentum function, is introduced in studying the atmospheric excitation of the Earth's variable rotation. It may be separated into two portions, i.e, the "wind" terms due to the atmospheric motion relative to the mantle and the "pressure" terms due to the variations of atmospheric mass distribution evident through surface pressure changes. The AEF wind terms during the period of 1948-2004 are re-processed from the NCEP/NCAR (National Centers for Environmental Prediction-National Center for Atmospheric Research) reanalysis 6-hourly wind and pressure fields. Some previous calculations were approximate, in that the wind terms were integrated from an isobaric lower boundary of 1000 hPa. To consider the surface topography effect, however, the AEF is computed by integration using the winds from the Earth's surface to 10 hPa, the top atmospheric model level, instead of from 1000 hPa. For these two cases, only a minor difference, equivalent to approx. 0.004 milliseconds in length-of-day variation, exists with respect to the axial wind term. However, considerable differences, equivalent to 5-6 milliarcseconds in polar motion, are found regarding equatorial wind terms. We further compare the total equatorial AEF (with and without the topographic effect) with the polar motion excitation function (PMEF) during the period of 1980-2003. The equatorial AEF gets generally closer to the PMEF, and improved coherences are found between them when the topography effect is included. Keywords: Atmospheric angular momentum, Atmospheric excitation function, Earth rotation, Topography, Wind, Pressure.

Southern Oscillation in surface circulation and climate over the tropical Atlantic, eastern Pacific, and Indian Oceans as captured by cluster analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wolter, K.

Clusters of sea level pressure (SLP), surface wind, cloudiness, and sea surface temperature (SST) in the domain of the tropical Atlantic, eastern Pacific, and Indian Oceans are introduced and discussed in terms of general circulation and climate. They appear to capture well the large-scale degrees of freedom of the seasonal fields. In the Atlantic, and, to a lesser extent, in the eastern Pacific, most analyzed fields group into zonally oriented trade wind clusters. These are separated distinctly by the near-equatorial trough axis. By contrast, the Indian Ocean features strong interhemispheric connections associations with the monsoon systems of boreal summer and,more » to a lesser degree, of boreal winter. The usefulness of clusters thus established is elucidated with respect to the Southern Oscillation (SO). General circulation changes associated with this planetary pressure seesaw are deduced from the correlation maps of surface field clusters for January/February and July/August. During the positive SO phase (i.e., anomalously high pressure over the eastern Pacific and anomalously low pressure over Indonesia), both the Atlantic and eastern Pacific near-equatorial troughs are inferred to be shifted towards the north from July/August SLP, wind, and cloudiness fields. While eastern Pacific trade winds are weakened in both seasons in the positive PO phase, the Atlantic trades appear strengthened at the same time in the winter hemisphere only. Over the Indian Ocean, the monsoon circulation seems to be strengthened during the positive SO phase, with the summer monsoon displaying a more complex picture. Its SLP, cloudiness, and SST fields support an enhanced southwest monsoon, while its surface winds appear largely inconclusive. SST is lowered during the positive SO phase in all three tropical oceans.« less

The climatology of low latitude ionospheric currents derived from CHAMP observations

NASA Astrophysics Data System (ADS)

Stolle, Claudia; Alken, Patrik

2010-05-01

The multi-year data base of magnetic field and ionospheric measurements from the CHAMP satellite contain enormous potential to investigate the behaviour and the origin of currents in the E and F region ionosphere. Special advantage is drawn from the satellite's near polar orbit and the full data coverage over all longitudes and local times. This paper will present findings about two prominent features of the low latitude ionosphere: equatorial plasma irregularities and the equatorial electrojet (EEJ). Equatorial plasma irregularities (commonly known as "bubbles") severely disturb the post sunset F region ionosphere and cause the strongest radio wave scintillations globally during solar maximum years. Using CHAMP vector magnetic field data, it was possible for the first time to show on a long term basis that equatorial plasma irregularities have signatures in all components of the magnetic field. The first ever global climatology of the occurrence rate of these magnetic signatures has been compiled. Such a data base of disturbed orbits is especially useful for core and crustal magnetic field modellers. The magnetic field observations of CHAMP, Ørsted, and SAC-C were employed to develop a climatological model of the EEJ. Measurements of the EEJ and empirical values from electron density and thermospheric density and winds have in addition enabled the development of a climatological model of the equatorial electric field. These results provide excellent opportunity to investigate the seasonal/longitudinal characteristics of the EEJ and the influence of atmospheric waves on E region dynamics.

Magnetospheric disturbance effects on the Equatorial Ionization Anomaly (EIA) : an overview

NASA Astrophysics Data System (ADS)

Abdu, M. A.; Sobral, J. H. A.; de Paula, E. R.; Batista, I. S.

1992-12-01

The Equatorial lonization Anomaly (EIA) development can undergo drastic modification in the form of an anomalous occurrence at local times outside that of its quiet time development and/or inhibition/enhancement at local times of its normal occurrences. This happens for disturbed electrodynamic conditions of the global ionosphere-thermosphere-magnetosphere system, consequent upon the triggering of a magnetospheric storm event. Direct penetration to equatorial latitudes of the magnetospheric electric fields and the thermospheric disturbances involving winds, electric fields and composition changes produce significant alteration in the EIA morphology and dynamics. Results on statistical behaviour based on accumulated ground-based data sets, and those from recent theoretical modelling efforts and from satellite and ground-based observations, are reviewed. Some outstanding problems of the EIA response to magnetospheric disturbances that deserve attention in the coming years are pointed out.

Wintertime Phytoplankton Blooms in the Western Equatorial Indian Ocean Associated With the Madden-Julian Oscillation

NASA Astrophysics Data System (ADS)

Liao, Xiaomei; Du, Yan; Zhan, Haigang; Wang, Tianyu; Feng, Ming

2017-12-01

This study investigated boreal wintertime phytoplankton blooms in the western equatorial Indian Ocean (WEIO) and the underlying physical mechanisms. The Sea viewing Wide field of View sensor (SeaWiFS) chlorophyll-a (Chla) concentrations show that phytoplankton blooms occur in the WEIO during December-March. The development of these blooms is not only a seasonal process but also consists of 2-3 intraseasonal events induced by the Madden-Julian Oscillation (MJO). During a typical intraseasonal event, enhanced cross-equatorial wind induces strong upwelling and ocean mixing, thus increasing the supply of nutrients to the surface in equatorial regions. Argo profiles clearly show various responses to the intraseasonal wind bursts, including shoaling of the thermocline and deepening of the mixed layer. Further analysis reveals that the former is the dominant mechanism for the blooms along the equator, while the latter controls the high Chla concentrations off the coast of Somalia. Surface ocean circulations not only account for the blooms south of the equator but also modulate the thermocline depth in the WEIO. The shallower thermocline during the early period of the northeast monsoon season provides favorable conditions for a stronger Chla response to intraseasonal forcing.

Evolution of the Equatorial Oscillation in Saturn's Stratosphere Between 2005 and 2010 from Cassini/CIRS Limb Data Analysis

NASA Technical Reports Server (NTRS)

Guerlet, S.; Fouchet, T.; Bezard, B.; Flasar, F. M.; Simon-Miller, A. A.

2011-01-01

We present an analysis of thermal infrared spectra acquired in limb viewing geometry by Cassini/CIRS in February 2010. We retrieve vertical profiles of Saturn's stratospheric temperature from 20 hPa to 10 (exp -2) hPa, at 9 latitudes between 20 deg N and 20 deg S. Using the gradient thermal wind equation, we derive a map of the zonal wind field. Both the temperature and the zonal wind vertical profiles exhibit an oscillation in the equatorial region. These results are compared to the temperature and zonal wind maps obtained from 2005-2006 CIRS limb data, when this oscillation was first reported. In both epochs, strong temperature anomalies at the equator (up to 20K) are consistent with adiabatic heating (cooling) due to a sinking (rising) motion at a speed of 0.1 - 0.2 mm/s. Finally, we show that the altitude of the maximum eastward wind has moved downwards by 1.3 scale heights in 4.2 years, hence with a 'phase' speed of approximately 0.5 mm/s. This rate is consistent with the estimated period of 14.7 years for the equatorial oscillation, and requires a local zonal acceleration of 1.1 x 10(exp -6) m.s(exp -2) at the 2.5 hPa pressure level. This downward propagation of the oscillation is consistent with it being driven by absorption of upwardly propagating waves.

Recent developments in the understanding of equatorial ionization anomaly: A review

NASA Astrophysics Data System (ADS)

Balan, N.; Souza, J.; Bailey, G. J.

2018-06-01

A brief review of the recent developments in the understanding of the equatorial plasma fountain (EPF) and equatorial ionization anomaly (EIA) under quiet and active conditions is presented. It is clarified that (1) the EPF is not upward ExB plasma drift at the equator followed by downward plasma diffusion, but it is field perpendicular ExB plasma drift and field-aligned plasma diffusion acting together all along the field lines at all altitudes and plasma flowing in the direction of the resultant. (2) The EIA is formed not from the accumulation of plasma at the crests but mainly from the removal of plasma from around the equator by the upward ExB drift with small accumulations when the crests are within approximately ±20° magnetic latitude. The accumulations reduce with increasing latitude and become zero by approximately ±25°. (3) An asymmetric neutral wind makes EPF and EIA asymmetric with stronger fountain and stronger crest usually occurring in opposite hemispheres especially at equinoxes when winter anomaly is absent. (4) During the early stages of daytime main phase of major geomagnetic storms, the plasma fountain becomes a super fountain and the EIA becomes strong not due to the eastward prompt penetration electric field (PPEF) alone but due to the combined effect of eastward PPEF and storm-time equatorward winds (SEW). (5) During the later stages of the storms when EIA gets inhibited a peak sometimes occurs around the equator not due to westward electric fields but mainly due to the convergence of plasma from both hemispheres due to SEW.

Response of the equatorial and polar magnetosphere to the very tenuous solar wind on May 11, 1999

NASA Astrophysics Data System (ADS)

Farrugia, C. J.; Singer, H. J.; Evans, D.; Berdichevsky, D.; Scudder, J. D.; Ogilvie, K. W.; Fitzenreiter, R. J.; Russell, C. T.

2000-12-01

We examine effects in the equatorial and polar magnetosphere during 9-13 May, 1999. Earth's field at geostationary orbit became closely dipolar for ˜16 hours when solar wind densities nsw were <1 cm-3. Electron precipitation in the northern polar cap intensified as nsw decreased, with significant fluxes up to ˜15 keV energy on May 11. The simultaneous precipitation void in the southern polar cap implies a very pronounced north-south asymmetry, also reflected in the hemispherical power deposition. With an intense and collimated strahl, these observations support the ideas of Fairfield and Scudder [1985] on the preferential entry of the strahl into the northern hemisphere under the observed IMF away sector as a source of the north-south precipitation asymmetry. The polar rain north-south asymmetry argues against an ejecta source for the solar wind drop-out. The temporal profiles of solar wind parameters were very asymmetric with respect to the time of minimum nsw, and strong compressions and substorm activity prevailed as nsw recovered.

Line formation in winds with enhanced equatorial mass-loss rates and its application to the Wolf-Rayet star HD 50896

NASA Technical Reports Server (NTRS)

Rumpl, W. M.

1980-01-01

A model having a spherically symmetric velocity distribution with a higher density at the equatorial region was developed to simulate the UV spectrum of the Wolf-Rayet star HD 50896. The spectrum showed P Cygni-shaped profiles whose emissions are stronger than expected in a spherically symmetric stellar wind. The model was studied varying the inclination angle of the star-wind system and the polar to equatorial density ratios; it was shown that HD 50896 could possess a nonspherically symmetric wind and that its symmetry axis is inclined between 60 and 90 deg. It is possible that the velocity distribution of the wind could include an inner constant velocity plateau beyond which the wind accelerates to its terminal velocity as indicated by infrared continuum investigations.

Equatorial oceanography. [review of research

NASA Technical Reports Server (NTRS)

Cane, M. A.; Sarachik, E. S.

1983-01-01

United States progress in equatorial oceanography is reviewed, focusing on the low frequency response of upper equatorial oceans to forcing by the wind. Variations of thermocline depth, midocean currents, and boundary currents are discussed. The factors which determine sea surface temperature (SST) variability in equatorial oceans are reviewed, and the status of understanding of the most spectacular manifestation of SST variability, the El Nino-Southern Oscillation phenomenon, is discussed. The problem of observing surface winds, regarded as a fundamental factor limiting understanding of the equatorial oceans, is addressed. Finally, an attempt is made to identify those current trends which are expected to bear fruit in the near and distant future.

Dynamics of upwelling annual cycle in the equatorial Atlantic Ocean

NASA Astrophysics Data System (ADS)

Wang, Li-Chiao; Jin, Fei-Fei; Wu, Chau-Ron; Hsu, Huang-Hsiung

2017-04-01

The annual upwelling is an important component of the equatorial Atlantic annual cycle. A simple theory is proposed using the framework of Zebiak-Cane (ZC) ocean model for insights into the dynamics of the upwelling annual cycle. It is demonstrated that in the Atlantic equatorial region this upwelling is dominated by Ekman processing in the west, whereas in the east it is primarily owing to shoaling and deepening of the thermocline resulting from equatorial mass meridional recharge/discharge and zonal redistribution processes associated with wind-driven equatorial ocean waves. This wind-driven wave upwelling plays an important role in the development of the annual cycle in the sea surface temperature of the cold tongue in the eastern equatorial Atlantic.

How predictable are equatorial Atlantic surface winds?

NASA Astrophysics Data System (ADS)

Richter, Ingo; Doi, Takeshi; Behera, Swadhin

2017-04-01

Sensitivity tests with the SINTEX-F general circulation model (GCM) as well as experiments from the Coupled Model Intercomparison Project phase 5 (CMIP5) are used to examine the extent to which sea-surface temperature (SST) anomalies contribute to the variability and predictability of monthly mean surface winds in the equatorial Atlantic. In the SINTEX-F experiments, a control experiment with prescribed observed SST for the period 1982-2014 is modified by inserting climatological values in certain regions, thereby eliminating SST anomalies. When SSTs are set to climatology in the tropical Atlantic only (30S to 30N), surface wind variability over the equatorial Atlantic (5S-5N) decreases by about 40% in April-May-June (AMJ). This suggests that about 60% of surface wind variability is due to either internal atmospheric variability or SSTs anomalies outside the tropical Atlantic. A further experiment with climatological SSTs in the equatorial Pacific indicates that another 10% of variability in AMJ may be due to remote influences from that basin. Experiments from the CMIP5 archive, in which climatological SSTs are prescribed globally, tend to confirm the results from SINTEX-F but show a wide spread. In some models, the equatorial Atlantic surface wind variability decreases by more than 90%, while in others it even increases. Overall, the results suggest that about 50-60% of surface wind variance in AMJ is predictable, while the rest is due to internal atmospheric variability. Other months show significantly lower predictability. The relatively strong internal variability as well as the influence of remote SSTs suggest a limited role for coupled ocean-atmosphere feedbacks in equatorial Atlantic variability.

Equatorial E Region Electric Fields and Sporadic E Layer Responses to the Recovery Phase of the November 2004 Geomagnetic Storm

NASA Astrophysics Data System (ADS)

Moro, J.; Resende, L. C. A.; Denardini, C. M.; Xu, J.; Batista, I. S.; Andrioli, V. F.; Carrasco, A. J.; Batista, P. P.; Schuch, N. J.

2017-12-01

Equatorial E region electric fields (EEFs) inferred from coherent radar data, sporadic-E (Es) layers observed from a digital ionosonde data, and modeling results are used to study the responses of the equatorial E region over São Luís (SLZ, 2.3°S, 44.2°W, -7° dip angle), Brazil, during the super storm of November 2004. The EEF is presented in terms of the zonal (Ey) and vertical (Ez) components in order to analyze the corresponding characteristics of different types of Es seen in ionograms and simulated with the E region ionospheric model. We bring out the variabilities of Ey and Ez components with storm time changes in the equatorial E region. In addition, some aspects of the electric fields and Es behavior in three cases of weak, very weak, and strong Type II occurrences during the recovery phase of the geomagnetic storm are discussed. The connection between the enhanced occurrence and suppressions of the Type II irregularities and the q-type Es (Esq) controlled by electric fields, with the development or disruption of the blanketing sporadic E (Esb) layers produced by wind shear mechanism, is also presented. The mutual presence of Esq along with the Esb occurrences is a clear indicator of the secular drift of the magnetic equator and hence that of the equatorial electrojet (EEJ) over SLZ. The results show evidence about the EEJ and Es layer electrodynamics and coupling during geomagnetic disturbance time electric fields.

Study of Geomagnetic Field Response to Solar Wind Forcing

NASA Astrophysics Data System (ADS)

Kim, S.; Li, X.; Damas, M. C.; Ngwira, C.

2017-12-01

The solar wind is an integral component of space weather that has a huge impact on the near-Earth space conditions, which can in turn adversely impact technological infrastructure. By analyzing solar wind data, we can investigate the response of the Earth's magnetic field to changes in solar wind conditions, such as dynamic pressure, speed, and interplanetary magnetic fields (IMF). When a coronal mass ejection (CME) hits the Earth's magnetosphere, it compresses the dayside magnetosphere, which leads to SSC (Sudden Storm Commencement) seen in Dst or SYM-H index. Dst and SYM-H index are a measure of geomagnetic storm intensity that represents the magnetic field perturbations in the equatorial region originating from ring current. In this study, we focused on SSC intervals with sudden density increase, density, greater than 10 n/cc from 2000 to 2015 using data obtained from the NASA CDAWEB service. A total of 1,049 events were picked for this project. Then using INTERMAGNET service, corresponding horizontal component of magnetic field data were collected from several stations located in equatorial region, mid-latitude region, high-latitude region on the day-side and night-side of Earth. Using MATLAB, we calculated the rate of change of magnetic fields (dB/dt) for each station and each event. We found that in most cases, the sudden increase in proton density is associated with large changes in magnetic fields, dB/dt. The largest magnetic field changes were observed on the day-side than night-side at high latitudes. Interestingly, some exceptions were found such that greater dB/dt was found on night-side than day-side during some events, particularly at high latitudes. We suspect these are driven by magnetospheric substorms, which are manifested by an explosive release of energy in the local midnight sector. The next step will be creating the statistical form to see the correlation between proton density changes and magnetic field changes.

Coronal holes as sources of solar wind

NASA Technical Reports Server (NTRS)

Nolte, J. T.; Krieger, A. S.; Timothy, A. F.; Gold, R. E.; Roelof, E. C.; Vaiana, G.; Lazarus, A. J.; Sullivan, J. D.; Mcintosh, P. S.

1976-01-01

We investigate the association of high-speed solar wind with coronal holes during the Skylab mission by: (1) direct comparison of solar wind and coronal X-ray data; (2) comparison of near-equatorial coronal hole area with maximum solar wind velocity in the associated streams; and (3) examination of the correlation between solar and interplanetary magnetic polarities. We find that all large near-equatorial coronal holes seen during the Skylab period were associated with high-velocity solar wind streams observed at 1 AU.

First observational evidence for the connection between the meteoric activity and occurrence of equatorial counter electrojet

NASA Astrophysics Data System (ADS)

Vineeth, C.; Mridula, N.; Muralikrishna, P.; Kumar, K. K.; Pant, T. K.

2016-09-01

This paper presents the first direct observational evidence for the possible role of meteoric activity in the generation of the equatorial Counter Electrojets (CEJ), an enigmatic daytime electrodynamical process over the geomagnetic equatorial upper atmosphere. The investigation carried out using the data from Proton Precession Magnetometer and Meteor Wind Radar over a geomagnetic dip equatorial station, Trivandrum (8.5°N, 77°E, 0.5°N dip lat.) in India, revealed that the occurrence of the afternoon CEJ events during a month is directly proportional to the average monthly meteor counts over this location. The observation is found to be very consistent during the considered period of study, i.e the years 2006 and 2007. The study vindicates that the meteor showers play a major role in setting up the background condition conducive for the generation of CEJ by reducing the strength of the upward polarization field.

Sensitivity of Pacific Cold Tongue and Double-ITCZ Bias to Convective Parameterization

NASA Astrophysics Data System (ADS)

Woelfle, M.; Bretherton, C. S.; Pritchard, M. S.; Yu, S.

2016-12-01

Many global climate models struggle to accurately simulate annual mean precipitation and sea surface temperature (SST) fields in the tropical Pacific basin. Precipitation biases are dominated by the double intertropical convergence zone (ITCZ) bias where models exhibit precipitation maxima straddling the equator while only a single Northern Hemispheric maximum exists in observations. The major SST bias is the enhancement of the equatorial cold tongue. A series of coupled model simulations are used to investigate the sensitivity of the bias development to convective parameterization. Model components are initialized independently prior to coupling to allow analysis of the transient response of the system directly following coupling. These experiments show precipitation and SST patterns to be highly sensitive to convective parameterization. Simulations in which the deep convective parameterization is disabled forcing all convection to be resolved by the shallow convection parameterization showed a degradation in both the cold tongue and double-ITCZ biases as precipitation becomes focused into off-equatorial regions of local SST maxima. Simulations using superparameterization in place of traditional cloud parameterizations showed a reduced cold tongue bias at the expense of additional precipitation biases. The equatorial SST responses to changes in convective parameterization are driven by changes in near equatorial zonal wind stress. The sensitivity of convection to SST is important in determining the precipitation and wind stress fields. However, differences in convective momentum transport also play a role. While no significant improvement is seen in these simulations of the double-ITCZ, the system's sensitivity to these changes reaffirm that improved convective parameterizations may provide an avenue for improving simulations of tropical Pacific precipitation and SST.

Relationship of boreal summer 10-20-day and 30-60-day intraseasonal oscillation intensity over the tropical western North Pacific to tropical Indo-Pacific SST

NASA Astrophysics Data System (ADS)

Wu, Renguang; Cao, Xi

2017-06-01

The present study contrasts interannual variations in the intensity of boreal summer 10-20-day and 30-60-day intraseasonal oscillations (ISOs) over the tropical western North Pacific and their factors. A pronounced difference is found in the relationship of the two ISOs to El Niño-Southern Oscillation. The 10-20-day ISO intensity is enhanced during El Niño developing summer, whereas the 30-60-day ISO intensity is enhanced during La Niña decaying summer. The above different relationship is interpreted as follows. The equatorial central and eastern Pacific SST anomalies modify vertical wind shear, lower-level moisture, and vertical motion in a southeast-northwest oriented band from the equatorial western Pacific to the tropical western North Pacific where the 10-20-day ISOs originate and propagate. These background field changes modulate the amplitude of 10-20-day ISOs. Preceding equatorial central and eastern Pacific SST anomalies induce SST anomalies in the North Indian Ocean in summer, which in turn modify vertical wind shear and vertical motion over the tropical western North Pacific. The modified background fields influence the amplitude of the 30-60-day ISOs when they reach the tropical western North Pacific from the equatorial region. A feedback of ISO intensity on local SST change is identified in the tropical western North Pacific likely due to a net effect of ISOs on surface heat flux anomalies. This feedback is more prominent from the 10-20-day than the 30-60-day ISO intensity change.

Sources of magnetic fields in recurrent interplanetary streams

NASA Technical Reports Server (NTRS)

Burlaga, L. F.; Behannon, K. W.; Hansen, S. F.; Pneuman, G. W.; Feldman, W. C.

1977-01-01

The sources of magnetic fields in recurrent streams were examined. Most fields and plasmas at 1 AU were related to coronal holes, and the magnetic field lines were open in those holes. Some of the magnetic fields and plasmas were related to open field line regions on the sun which were not associated with known coronal holes, indicating that open field lines are more basic than coronal holes as sources of the solar wind. Magnetic field intensities in five equatorial coronal holes ranged from 2G to 18G. Average measured photospheric magnetic fields along the footprints of the corresponding unipolar fields on circular equatorial arcs at 2.5 solar radii had a similar range and average, but in two cases the intensities were approximately three times higher than the projected intensities. The coronal footprints of the sector boundaries on the source surface at 2.5 solar radii, meandered between -45 deg and +45 deg latitude, and their inclination ranged from near zero to near ninety degrees.

Observation of El Nino by the Nimbus-7 SMMR

NASA Technical Reports Server (NTRS)

Hwang, P. H.; Macmillan, D. S.; Fu, C. C.; Kim, S. T.; Han, Daesoo; Gloersen, P.

1986-01-01

The quality of Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) derived SST, water vapor, and windspeed are assessed, and these parameters are used to study the El Nino event of 1982-1983 in the equatorial Pacific region from 120 deg to the South American coast. The features of the anomaly fields for these parameters, and the connections between these fields, are discussed. Anomaly fields are found to be qualitatively consistent with outgoing longwave radiation anomaly fields and wind vector anomaly fields.

A search for the coronal origins of fast solar wind streams during the whole sun month period

NASA Technical Reports Server (NTRS)

Lazarus, A. J.; Steinberg, J. T.; Biesecker, D. A.; Forsyth, R. J.; Galvin, A. B.; Ipavich, F. M.; Gibson, S. E.; Lecinski, A.; Hassler, D. M.; Hoeksema, J. T.;

Impact of effective ocean optical properties on the Pacific subtropical cell: a CGCM study

NASA Astrophysics Data System (ADS)

Yamanaka, G.; Tsujino, H.; Ishizaki, H.; Nakano, H.; Hirabara, M.

2012-12-01

The choice of ocean radiant scheme is important for modeling the upper ocean. According to the ocean-only simulation (Yamanaka et al., 2012), introduction of the chlorophyll-a dependent ocean radiant scheme results in the decreased mixed layer depth (MLD), the enhanced subtropical cell (STC), and the cooling of the eastern tropical Pacific sea surface temperature (SST). They also found that the enhanced STC results from the velocity profile change associated with the decreased Ekman boundary layer. However, the impact is not well understood when the air-sea feedback process is at work. This study examines the impact of the effective ocean optical properties on the Pacific mean fields, especially focusing on the STC, using a coupled general circulation model (CGCM). The CGCM we employed is the Meteorological Research Institute Earth System Model (MRI-ESM1). The atmospheric model is TL159L48, and the ocean model has a horizontal resolution of 1 x 0.5 deg. with 51 levels in vertical. Experimental design basically follows the CMIP5 protocol. Two experiments (CTL and SLR runs) are performed to investigate the impact of the effective ocean optical properties. In the CTL run, a conventional ocean radiant heating scheme (Paul and Simpson, 1977) is used, whereas a new ocean radiant heating scheme is used in the SLR run, where the satellite-derived chlorophyll-a distribution is taken into consideration based on Morel and Antoine (1994) as well as the effect of the varying solar angle (Ishizaki and Yamanaka, 2010). Each experiment is integrated during the period from 1985 to 2005. It is found that introduction of the new ocean radiant scheme (SLR run) changes the long-term mean wind pattern in the Pacific: easterly winds are strengthened in the equatorial Pacific, but weakened in the off-equatorial region. In the tropical Pacific, the enhanced equatorial upwelling cools the equatorial SST and the MLD becomes shallower. This is similar to the ocean-only simulation, but is more reinforced due to the Bjerknes feedback. On the other hand, unlike the ocean-only simulation, the STC is enhanced only in the equatorial band from 5 S to 5 N. Analysis of meridional volume transport in the upper 300 m indicates that poleward Ekman transport forced by the enhanced trade winds is balanced by the interior flow in the equatorial region. Apart from the equatorial region, the decreased Ekman transport due to the decreased easterly wind weakens the increased poleward transport associated with the velocity profile change in the Ekman boundary layer.

Mariner 9 evidence for wind erosion in the equatorial and mid-latitude regions of Mars

NASA Technical Reports Server (NTRS)

Mccauley, J. F.

1973-01-01

Evidence for extensive wind erosion principally in the equatorial and mid-latitude regions of Mars is presented and compared with selected erosional landforms from the coastal desert of Peru known to be of eolian origin. The evidence for widespread erosion on Mars prompted an examination of certain aspects of its wind regime that are thought to be significant geologically.

Steady hydromagnetic flows in open magnetic fields. II - Global flows with static zones

NASA Technical Reports Server (NTRS)

Tsinganos, K.; Low, B. C.

1989-01-01

A theoretical study of an axisymmetric steady stellar wind with a static zone is presented, with emphasis on the situation where the global magnetic field is symmetrical about the stellar equator and is partially open. In this scenario, the wind escapes in open magnetic fluxes originating from a region at the star pole and a region at an equatorial belt of closed magnetic field in static equilibrium. The two-dimensional balance of the pressure gradient and the inertial, gravitational, and Lorentz forces in different parts of the flow are studied, along with the static interplay between external sources of energy (heating and/or cooling) distributed in the flow and the pressure distribution.

The tropical tropopause inversion layer: variability and modulation by equatorial waves

NASA Astrophysics Data System (ADS)

Pilch Kedzierski, Robin; Matthes, Katja; Bumke, Karl

2016-09-01

The tropical tropopause layer (TTL) acts as a transition layer between the troposphere and the stratosphere over several kilometers, where air has both tropospheric and stratospheric properties. Within this region, a fine-scale feature is located: the tropopause inversion layer (TIL), which consists of a sharp temperature inversion at the tropopause and the corresponding high static stability values right above, which theoretically affect the dispersion relations of atmospheric waves like Rossby or inertia-gravity waves and hamper stratosphere-troposphere exchange (STE). Therefore, the TIL receives increasing attention from the scientific community, mainly in the extratropics so far. Our goal is to give a detailed picture of the properties, variability and forcings of the tropical TIL, with special emphasis on small-scale equatorial waves and the quasi-biennial oscillation (QBO).We use high-resolution temperature profiles from the COSMIC satellite mission, i.e., ˜ 2000 measurements per day globally, between 2007 and 2013, to derive TIL properties and to study the fine-scale structures of static stability in the tropics. The situation at near tropopause level is described by the 100 hPa horizontal wind divergence fields, and the vertical structure of the QBO is provided by the equatorial winds at all levels, both from the ERA-Interim reanalysis.We describe a new feature of the equatorial static stability profile: a secondary stability maximum below the zero wind line within the easterly QBO wind regime at about 20-25 km altitude, which is forced by the descending westerly QBO phase and gives a double-TIL-like structure. In the lowermost stratosphere, the TIL is stronger with westerly winds. We provide the first evidence of a relationship between the tropical TIL strength and near-tropopause divergence, with stronger (weaker) TIL with near-tropopause divergent (convergent) flow, a relationship analogous to that of TIL strength with relative vorticity in the extratropics.To elucidate possible enhancing mechanisms of the tropical TIL, we quantify the signature of the different equatorial waves on the vertical structure of static stability in the tropics. All waves show, on average, maximum cold anomalies at the thermal tropopause, warm anomalies above and a net TIL enhancement close to the tropopause. The main drivers are Kelvin, inertia-gravity and Rossby waves. We suggest that a similar wave modulation will exist at mid- and polar latitudes from the extratropical wave modes.

The dynamo of the diurnal tide and its effect on the thermospheric circulation

NASA Technical Reports Server (NTRS)

Mayr, H. G.; Harris, I.; Herrero, F. A.

1990-01-01

A theoretical multiconstituent model (including O, N2, and O2) which describes the interactions between neutral winds, dynamo electric fields, and ion drifts is used to interpret observations that revealed a dominance of the fundamental diurnal tide in the upper thermosphere and at equatorial latitudes, and its effect on the thermospheric circulation. The model is shown to reproduce reasonably well the magnitudes of the neutral winds, ion drift velocities, and the ratio between the two. A solution for the neutral winds in which the dynamo electric field is forced to zero shows that the dynamo-induced ion drift is very important in accelerating the neutral atmosphere at higher altitudes. The dynamo interaction primarily affects the curl component of the field; its effect on the temperature and density perturbations is small.

The Role of Storm Time Electrodynamics in Suppressing the Equatorial Plasma Bubble Development in the Recovery Phase of a Geomagnetic Storm

NASA Astrophysics Data System (ADS)

Sripathi, S.; Banola, S.; Emperumal, K.; Suneel Kumar, B.; Radicella, Sandro M.

2018-03-01

We investigate the role of storm time electrodynamics in suppressing the equatorial plasma bubble (EPB) development using multi-instruments over India during a moderate geomagnetic storm that occurred on 2 October 2013 where Dst minimum reached -80 nT. This storm produced unique signatures in the equatorial ionosphere such that equatorial electrojet strength showed signatures of an abrupt increase of its strength to 150 nT and occurrence of episodes of counter electrojet events. During the main phase of the storm, the interplanetary magnetic field Bz is well correlated with the variations in the equatorial electrojet/counter electrojet suggesting the role of undershielding/overshielding electric fields of magnetospheric origin. Further, observations showed the presence of strong F3 layers at multiple times at multiple stations due to undershielding electric field. Interestingly, we observed simultaneous presence of F3 layers and suppression of EPBs in the dusk sector during the recovery phase. While strong EPBs were observed before and after the day of the geomagnetic storm, suppression of the EPBs on the storm day during "spread F season" is intriguing. Our further analysis using low-latitude station, Hyderabad, during the time of prereversal enhancement suggests that intense Esb layers were observed on the storm day but were absent/weak on quiet days. Based on these results, we suggest that the altitude/latitude variation of disturbance dynamo electric fields/disturbance winds may be responsible for simultaneous detection of F3 layers, occurrence of low-latitude Es layers, and suppression of EPBs during the storm day along the sunset terminator.

Competition between winds and electric fields in the formation of blanketing sporadic E layers at equatorial regions

NASA Astrophysics Data System (ADS)

Resende, Laysa Cristina Araújo; Batista, Inez Staciarini; Denardini, Clezio Marcos; Carrasco, Alexander José; de Fátima Andrioli, Vânia; Moro, Juliano; Batista, Paulo Prado; Chen, Sony Su

2016-12-01

In the present work, we analyze the competition between tidal winds and electric fields in the formation of blanketing sporadic E layers (Esb) over São Luís, Brazil (2° 31' S, 44° 16' W), a quasi-equatorial station. To investigate this competition, we have used an ionospheric E region model (MIRE) that is able to model the Esb layers taking into account the E region winds and electric fields. The model calculates the densities for the main molecular and metallic ions by solving the continuity and momentum equations for each of the species. Thus, the main purpose of this analysis is to verify the electric fields role in the occurrence or disruption of Esb layers through simulations. The first results of the simulations show that the Esb layer is usually present when only the tidal winds were considered. In addition, when the zonal component of the electric field is introduced in the simulation, the Esb layers do not show significant changes. However, the simulations show the disruption of the Esb layers when the vertical electric field is included. In this study, we present two specific cases in which Esb layers appear during some hours over São Luís. We can see that these layers appear when the vertical electric field was weak, which means that the tidal components were more effective during these hours. Therefore, the vertical component of the electric field is the main agent responsible for the Esb layer disruption. [Figure not available: see fulltext. Caption: Ionograms from São Luís on January 5, 2005, show a clear case of the competition between electric fields and wind effects in the Es layer formation. In ionograms, the Esq trace is clearly seen and identified by a blue arrow. Besides the Esq, we can identify another Es trace at 1415 UT (identified by a black arrow) that persists until 1600 UT. This layer becomes stronger in each ionogram, as can be seen by its effect on partially blocking the reflection from the low-frequency end of F region above. This is indicated in the ionograms by a black vertical line, and the corresponding minimum frequency reflected from the F layer, f minF, is listed in the right upper corner of each frame of Figure. This minimum frequency increases from 3.62 MHz at 1415 UT to 3.7 MHz, at 1500 UT, after which it can be considered a blanketing Es layer (indicated by the red arrow). The fminF reaches a maximum value of 3.93 MHz at 1545 UT after which it decreases until the Esb layer vanishes at 1615 UT. Therefore, this day is an interesting case because São Luís lies in a transition region, since the geomagnetic equator is being driven away due to the secular variation of the Earth's magnetic field. This drift, in turn, provides an apparent northwestward movement of the geomagnetic equator at a rate of 9'/year ( 16 km/year). Therefore, in this event, we can observe two different types of Es layers: a diffuse, Esq; and the Esb layers formed by wind shear. This competition was simulated using an E region model, MIRE, for which the input parameters, winds and electric fields, for the equatorial region were included.

Free and Convectively Coupled Equatorial Waves Simulated by CMIP5 Climate Models

NASA Astrophysics Data System (ADS)

Marques, Carlos A. F.; Castanheira, José M.

2015-04-01

It is well known that precipitation in the equatorial belt does not occur randomly, but is often organized into synoptic to planetary-scale disturbances with time scales smaller than a season. Several studies have shown that a large fraction of the convection variability in such disturbances is associated with dynamical Equatorial Waves, such as the Kelvin, Equatorial Rossby, Mixed Rossby-Gravity, Eastward and Westward Inertio-Gravity waves (e.g. Kiladis et al., Rev. Geophys., 2009). The horizontal structures and dispersion characteristics of such Convectively Coupled Equatorial Waves (CCEWs) correspond to the solutions of the shallow water (SW) equations on an equatorial β-plane obtained by Matsuno (J. Meteor. Soc. Japan, 1966). CCEWs have broad impacts within the tropics, but their simulation in general circulation models is still problematic. Using space-time spectral analyses of a proxy field for tropical convection (e.g. outgoing long wave radiation (OLR)), it has been shown the existence of spectral peaks aligned along the dispersion curves of equatorially trapped wave modes of SW theory, which have been interpreted as the effect of equatorial wave processes (e.g. Takayabu, J. Meteor. Soc. Japan, 1994; Wheeler and Kiladis, JAS, 1999). However, different equatorial modes may not be well separated in the wavenumber-frequency domain due to a vertical variation of the horizontal basic flow, that may introduce Doppler shiftings and changes in the vertical heating profiles which may distort the theoretical dispersion curves (Yang et al., JAS, 2003). In this communication, we present a new methodology for the diagnosis of CCEWs, which is based on a pre-filtering of the geopotential and horizontal wind, via three-dimensional (3-D) normal mode functions of the adiabatic linearized equations of a resting atmosphere, followed by a space-time power and cross spectral analysis applied to the 3-D normal mode filtered fields and the OLR (or other fields that may be proxies of tropical convection) to identify the spectral regions of coherence. The advantage of such an approach is that the theoretical vertical as well as horizontal structure functions are taken into account in the projection method, and so the structures obtained are better defined with respect to the theoretical normal modes of a 3-D atmosphere compared to other approaches. The methodology has been applied to the (u,v,φ) and OLR fields simulated by various of the most recent climate models (CMIP5). The methodology has been also applied to the ERA-Interim geopotential and horizontal wind fields and to the interpolated OLR data produced by the National Oceanic and Atmospheric Administration, against which model simulations are evaluated. This new diagnosis method permits a direct detection of various types of equatorial waves, compares the dispersion characteristics of the coupled waves with the theoretical dispersion curves and allows an identification of which vertical modes are more involved in the convection. Moreover, it is able to show the existence of free dry waves and moist coupled waves with a common vertical structure, which is in conformity with the effect of convective heating/cooling on the effective static stability, as deduced from the gross moist stability concept (Kiladis et al., Rev. Geophys., 2009). The methodology is also sensitive to wave's interactions. Deficiencies found in the models' simulations should help the identification of which physical processes need to be improved in climate models.

Investigating Perturbation Electric Fields and Their Effects on the Coupled Low-, Mid- and High-latitude Ionosphere

DTIC Science & Technology

2015-08-14

stream (SAPS) E field had been strong. During these E field events, the repeated development of equatorial ionization anomaly ( EIA ), storm-enhanced...density (SED) bulge and SED plume occurred in those longitude sectors that covered the local dusk-midnight hours. Thus, a well-formed EIA - SED...Observational results and CTIPe simulated wind vector maps suggest that 1) the enhanced growth of the EIA transported solar produced plasma to the

Shape of the equatorial magnetopause affected by the radial interplanetary magnetic field

NASA Astrophysics Data System (ADS)

Grygorov, K.; Šafránková, J.; Němeček, Z.; Pi, G.; Přech, L.; Urbář, J.

2017-11-01

The ability of a prediction of the magnetopause location under various upstream conditions can be considered as a test of our understanding of the solar wind-magnetosphere interaction. The present magnetopause models are parametrized with the solar wind dynamic pressure and usually with the north-south interplanetary magnetic field (IMF) component. However, several studies pointed out an importance of the radial IMF component, but results of these studies are controversial up to now. The present study compares magnetopause observations by five THEMIS spacecraft during long lasting intervals of the radial IMF with two empirical magnetopause models. A comparison reveals that the magnetopause location is highly variable and that the average difference between the observed and predicted positions is ≈ + 0.7 RE under this condition. The difference does not depend on the local times and other parameters, like the upstream pressure, IMF north-south component, or tilt angle of the Earth dipole. We conclude that our results strongly support the suggestion on a global expansion of the equatorial magnetopause during intervals of the radial IMF.

Spatio-temporal evolutions of non-orthogonal equatorial wave modes derived from observations

NASA Astrophysics Data System (ADS)

Barton, Cory

Equatorial waves have been studied extensively due to their importance to the tropical climate and weather systems. Historically, their activity is diagnosed mainly in the wavenumber-frequency domain. Recently, many studies have projected observational data onto parabolic cylinder functions (PCFs), which represent the meridional structure of individual wave modes, to attain time-dependent spatial wave structures. The non-orthogonality of wave modes has yet posed a problem when attempting to separate data into wave fields where the waves project onto the same structure functions. We propose the development and application of a new methodology for equatorial wave expansion of instantaneous flows using the full equatorial wave spectrum. By creating a mapping from the meridional structure function amplitudes to the equatorial wave class amplitudes, we are able to diagnose instantaneous wave fields and determine their evolution. Because all meridional modes are shared by some subset of the wave classes, we require constraints on the wave class amplitudes to yield a closed system with a unique solution for all waves' spatial structures, including IG waves. A synthetic field is analyzed using this method to determine its accuracy for data of a single vertical mode. The wave class spectra diagnosed using this method successfully match the correct dispersion curves even if the incorrect depth is chosen for the spatial decomposition. In the case of more than one depth scale, waves with varying equivalent depth may be similarly identified using the dispersion curves. The primary vertical mode is the 200 m equivalent depth mode, which is that of the peak projection response. A distinct spectral power peak along the Kelvin wave dispersion curve for this value validates our choice of equivalent depth, although the possibility of depth varying with time and height is explored. The wave class spectra diagnosed assuming this depth scale mostly match their expected dispersion curves, showing that this method successfully partitions the wave spectra by calculating wave amplitudes in physical space. This is particularly striking because the time evolution, and therefore the frequency characteristics, is determined simply by a timeseries of independently-diagnosed instantaneous horizontal fields. We use the wave fields diagnosed by this method to study wave evolution in the context of the stratospheric QBO of zonal wind, confirming the continuous evolution of the selection mechanism for equatorial waves in the middle atmosphere. The amplitude cycle synchronized with the background zonal wind as predicted by QBO theory is present in the wave class fields even though the dynamics are not forced by the method itself. We have additionally identified a time-evolution of the zonal wavenumber spectrum responsible for the amplitude variability in physical space. Similar to the temporal characteristics, the vertical structures are also the result of a simple height cross-section through multiple independently-diagnosed levels.

Saturn's equatorial jet structure from Cassini/ISS

NASA Astrophysics Data System (ADS)

García-Melendo, Enrique; Legarreta, Jon; Sánchez-Lavega, Agustín.; Pérez-Hoyos, Santiago; Hueso, Ricardo

2010-05-01

Detailed wind observations of the equatorial regions of the gaseous giant planets, Jupiter and Saturn, are crucial for understanding the basic problem of the global circulation and obtaining new detailed information on atmospheric phenomena. In this work we present high resolution data of Saturn's equatorial region wind profile from Cassini/ISS images. To retrieve wind measurements we applied an automatic cross correlator to image pairs taken by Cassini/ISS with the MT1, MT2, MT3 filters centred at the respective three methane absorbing bands of 619nm, 727nm, and 889nm, and with the adjacent continuum CB1, CB2, and CB3 filters. We obtained a complete high resolution coverage of Saturn's wind profile in the equatorial region. The equatorial jet displays an overall symmetric structure similar to that shown the by same region in Jupiter. This result suggests that, in accordance to some of the latest compressible atmosphere computer models, probably global winds in gaseous giants are deeply rooted in the molecular hydrogen layer. Wind profiles in the methane absorbing bands show the effect of strong vertical shear, ~40m/s per scale height, confirming previous results and an important decay in the wind intensity since the Voyager era (~100 m/s in the continuum and ~200 m/s in the methane absorbing band). We also report the discovery of a new feature, a very strong and narrow jet on the equator, about only 5 degrees wide, that despite the vertical shear maintains its intensity (~420 m/s) in both, the continuum and methane absorbing band filters. Acknowledgements: Work supported by the Spanish MICIIN AYA2009-10701 with FEDER and Grupos Gobierno Vasco IT-464-07.

Shape, zonal winds and gravitational field of Jupiter: a fully self-consistent, multi-layered model

NASA Astrophysics Data System (ADS)

Schubert, Gerald; Kong, Dali; Zhang, Keke

2016-10-01

We construct a three-dimensional, finite-element, fully self-consistent, multi-layered,non-spheroidal model of Jupiter consisting of an inner core, a metallic electrically conducting dynamo region and an outer molecular electrically insulating envelope. We assume that the Jovian zonal winds are on cylinders parallel to the rotation axis but, due to the effect of magnetic braking, are confined within the outer molecular envelope. Two related calculations are carried out. The first provides an accurate description of the shape and internal density profile of Jupiter; the effect of rotational distortion is not treated as a small perturbation on a spherically symmetric state. This calculation determines the density, size and shape of the inner core, the irregular shape of the 1-bar pressure level, and the internal structure of Jupiter; the full effect of rotational distortion, without the influence of the zonal winds, is accounted for. Our multi-layered model is able to produce the known mass, the known equatorial and polar radii, and the known zonal gravitational coefficient J2 of Jupiter within their error bars; it also yields the coefficients J4 and J6 within about 5% accuracy, and the core equatorial radius 0.09RJ containing 3.73 Earth masses.The second calculation determines the variation of the gravitational field caused solely by the effect of the zonal winds on the rotationally distorted non-spheroidal Jupiter. Four different cases, ranging from a deep wind profile to a very shallow profile, are considered and implications for accurate interpretation of the zonal gravitational coefficients expected from the Juno mission are discussed.

Electrodynamics of ionospheric weather over low latitudes

NASA Astrophysics Data System (ADS)

Abdu, Mangalathayil Ali

2016-12-01

The dynamic state of the ionosphere at low latitudes is largely controlled by electric fields originating from dynamo actions by atmospheric waves propagating from below and the solar wind-magnetosphere interaction from above. These electric fields cause structuring of the ionosphere in wide ranging spatial and temporal scales that impact on space-based communication and navigation systems constituting an important segment of our technology-based day-to-day lives. The largest of the ionosphere structures, the equatorial ionization anomaly, with global maximum of plasma densities can cause propagation delays on the GNSS signals. The sunset electrodynamics is responsible for the generation of plasma bubble wide spectrum irregularities that can cause scintillation or even disruptions of satellite communication/navigation signals. Driven basically by upward propagating tides, these electric fields can suffer significant modulations from perturbation winds due to gravity waves, planetary/Kelvin waves, and non-migrating tides, as recent observational and modeling results have demonstrated. The changing state of the plasma distribution arising from these highly variable electric fields constitutes an important component of the ionospheric weather disturbances. Another, often dominating, component arises from solar disturbances when coronal mass ejection (CME) interaction with the earth's magnetosphere results in energy transport to low latitudes in the form of storm time prompt penetration electric fields and thermospheric disturbance winds. As a result, drastic modifications can occur in the form of layer restructuring (Es-, F3 layers etc.), large total electron content (TEC) enhancements, equatorial ionization anomaly (EIA) latitudinal expansion/contraction, anomalous polarization electric fields/vertical drifts, enhanced growth/suppression of plasma structuring, etc. A brief review of our current understanding of the ionospheric weather variations and the electrodynamic processes underlying them and some outstanding questions will be presented in this paper.

Polarization cancellation in the two-component winds from Wolf-Rayet stars

NASA Technical Reports Server (NTRS)

Taylor, M.; Cassinelli, J. P.

1992-01-01

In this paper we explore the possibility that there can be at least partial cancellation of the equatorial disk polarization as a result of scattering from the electrons that are present in the strong polar wind of WR stars. In order to achieve the cancellation necessary to explain the wavelength-dependent polarization, the polar wind must have a mass-loss rate that is near the maximum that is supported by radiation-driven wind theory. In addition, we find that it is possible to derive important new information regarding the relative column masses of the polar and equatorial winds.

Response of the Surface Circulation of the Arabian Sea to Monsoonal Forcing

NASA Astrophysics Data System (ADS)

Beal, L. M.; Hormann, V.; Lumpkin, R.; Foltz, G. R.

2014-12-01

We use two decades of drifter and satellite data to examine the monthly evolution of the surface circulation of the Arabian Sea, which reverses annually in response to the Indian monsoon winds. Most significantly, we find that in the transition from winter to summer circulations, northward flow appears along the length of the western boundary as early as March or April, one or two months before the onset of the southwest monsoon winds. This reversal is initiated by annual Rossby waves, which in turn are initiated by wind curl forcing during the previous southwest monsoon. These results lead us to speculate that there is an oceanic mechanism through which one monsoon may precondition the next. Previous studies of monsoon circulations with lower temporal resolution have highlighted basin-wide currents and connections that are not found to exist in the monthly fields. In particular, we find that the Northeast Monsoon Current does not reach the western boundary and there is no counter-rotating gyre system during boreal winter. South of the equator, the eastward-flowing South Equatorial Counter Current (SECC) is present year-round, even though equatorial winds are strongly influenced by the monsoons. Semi-annual variability of the SECC is governed by Ekman pumping over the south equatorial gyre (or Seychelles dome) and, surprisingly, it is weakest during the northeast monsoon. This region has important influence on the atmosphere and its link to the monsoons deserves further investigation. The East African Coastal Current feeds into the SECC from the boundary. During the southwest monsoon it overshoots the equator and splits, feeding both northward into the Somali Current and eastward into the SECC after looping back across the equator. This apparent retroflection of the EACC is what was previously known as the southern gyre and is obscured at the surface by strong, locally wind-driven, cross-equatorial Ekman transport. Finally, there is broad, strong eastward flow at the mouth of the Gulf of Aden throughout the southwest monsoon, which is influenced by the curvature and bifurcation of the atmospheric monsoon jet.

Wave Forcing of Saturn's Equatorial Oscillation

NASA Technical Reports Server (NTRS)

Flasar, F. M.; Schlinder, P. J.; Guerlet, S.; Fouchet, T.

2011-01-01

Ground-based measurements and Cassini data from CIRS thermal-infrared spectra and radio-occultation soundings have characterized the spatial structure and temporal behavior of a 15-year equatorial oscillation in Saturn's stratosphere. The equatorial region displays a vertical pattern of alternating warm and cold anomalies and, concomitantly, easterly and westerly winds relative to the cloud-top winds, with a peak-to-peak amplitude of 200 m/s. Comparison of the Cassini data over a four-year period has established that the pattern of mean zonal winds and temperatures descends at a rate of roughly I scale height over 4 years. This behavior is reminiscent of the equatorial oscillations in Earth's middle atmosphere. Here the zonal-mean spatial structure and descending pattern are driven by the absorption of vertically propagating waves. The maximum excursions in the pattern of easterly and westerly winds is determined by the limits of the zonal phase velocities of the waves. Here we report on the characterization of the waves seen in the temperature profiles retrieved from the Cassini radio-occultation soundings. The equatorial profiles exhibit a complex pattern of wavelike structure with dimensions one pressure scale height and smaller. We combine a spectral decomposition with a WKBJ analysis, where the vertical wavelength is assumed to vary slowly with the ambient static stability and doppler-shifted phase velocity of the wave. Use of the temperature and zonal wind maps from CIRS makes this approach viable. On Earth, the wave forcing associated with the equatorial oscillations generates secondary meridional circulations that affect the mean flow and planetary wave ducting well away from the equator. This may relate to the triggering of the recently reported mid-latitude storms on Saturn.

Quasi-two-day wave coupling of the mesosphere and lower thermosphere-ionosphere in the TIME-GCM: Two-day oscillations in the ionosphere

NASA Astrophysics Data System (ADS)

Yue, Jia; Wang, Wenbin; Richmond, Arthur D.; Liu, Han-Li

2012-07-01

The Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) is used to simulate the quasi-two-day wave (QTDW) modulation of the ionospheric dynamo and electron density. The QTDW can directly penetrate into the lower thermosphere and modulate the neutral winds at a period of two days. The QTDW modulation of the tidal amplitudes is not evident. The QTDW in zonal and meridional winds results in a quasi-two-day oscillation (QTDO) of the dynamo electric fields at southern midlatitudes, which is mapped into the conjugate northern magnetic midlatitudes. The QTDO of the electric fields in the E region is transmitted along the magnetic field lines to the F region and leads to the QTDOs of the vertical ion drift and total electron content (TEC) at low and mid latitudes. The QTDO of the vertical ion drift near the magnetic equator leads to the 2-day oscillation of the fountain effect. The QTDO of the TEC has two peaks at ±25 magnetic latitude (Mlat) and one near the dip equator. The equatorial peak is nearly out of phase with the ones at ±25 Mlat. The vertical ion drift at midlatitudes extends the QTDW response of the TEC to midlatitudes from the Equatorial Ionospheric Anomaly (EIA). Most differently from previous reports, we discover that the QTDW winds couple into the F region ionosphere through both the fountain effect and the middle latitude dynamos.

Daytime and Nighttime Neutral Wind and Temperature Measurements from Incoherent Scatter Radar at 300 KM over Arecibo.

DTIC Science & Technology

1985-12-01

Incoherent *scatter observations and their interpretation, 3. Atmos. Tarr. Phys., 34, 351-364, 1972. Bohnk&,R., and Harper,R., Vector measurements of F...equatorial F-region, 3. Atmos. Terr. Phys., 39, 1159-1168, 1977. Rishbeth, H., Ganguly,S., Walker,3.C., Feild -aligned and field-perpendicular velocities

Equatorial ionospheric response to the 2015 St. Patrick's Day magnetic storm

NASA Astrophysics Data System (ADS)

Huang, C.; Wilson, G. R.; Hairston, M. R.; Zhang, Y.; Wang, W.; Liu, J.

2016-12-01

The geomagnetic storm on 17 March 2015 was the strongest storm during solar cycle 24 and caused significant disturbances in the global ionosphere. We present measurements of the Defense Meteorological Satellite Program satellites and identify the dynamic response of the equatorial ionosphere to the storm. Large penetration and disturbance dynamo electric fields are detected in both the dusk and the dawn sectors, and the characteristics of the electric fields are dramatically different in the two local time sectors. Penetration electric field is strong in the evening sector, but disturbance dynamo electric field is dominant in the dawn sector. The dynamo process is first observed in the post-midnight sector 4 hours after the beginning of the storm main phase and lasts for 31 hours, covering the major part of the storm main phase and the initial 20 hours of the recovery phase. The dynamo vertical ion drift is upward (up to 200 m/s) in the post-midnight sector and downward (up to 80 m/s) in the early morning sector. The dynamo zonal ion drift is westward at these locations and reaches 100 m/s. The dynamo process causes large enhancements of the oxygen ion concentration, and the variations of the oxygen ion concentration are well correlated with the vertical ion drift. The observations suggest that disturbance dynamo becomes dominant in the post-midnight equatorial ionosphere even during the storm main phase when disturbance neutral winds arrive there. The results provide new insight into storm-time equatorial ionospheric dynamics.

Observed variability in the upper layers at the Equator, 90°E in the Indian Ocean during 2001-2008, 1: zonal currents

NASA Astrophysics Data System (ADS)

Rao, R. R.; Horii, T.; Masumoto, Y.; Mizuno, K.

2017-08-01

The observed variability of zonal currents (ZC) at the Equator, 90°E shows a strong seasonal cycle in the near-surface 40-350 m water column with periodic east-west reversals most pronounced at semiannual frequency. Superposed on this, a strong intraseasonal variability of 30-90 day periodicity is also prominently seen in the near-surface layer (40-80 m) almost throughout the year with the only exception of February-March. An eastward flowing equatorial undercurrent (EUC) is present in the depth range of 80-160 m during March-April and October-November. The observed intraseasonal variability in the near-surface layer is primarily determined by the equatorial zonal westerly wind bursts (WWBs) through local frictional coupling between the zonal flow in the surface layer and surface zonal winds and shows large interannual variability. The eastward flowing EUC maintained by the ZPG set up by the east-west slope of the thermocline remotely controlled by the zonal wind (ZW) and zonally propagating wave fields also shows significant interannual variability. This observed variability on interannual time scales appears to be controlled by the corresponding variability in the alongshore winds off the Somalia coast during the preceding boreal winter, the ZW field along the equator, and the associated zonally propagating Kelvin and Rossby waves. The salinity induced vertical stratification observed in the near-surface layer through barrier layer thickness (BLT) effects also shows a significant influence on the ZC field on intraseasonal time scale. Interestingly, among all the 8 years (2001-2008), relatively weaker annual cycle is seen in both ZC in the 40-350 m water column and boreal spring sea surface temperature (SST) only during 2001 and 2008 along the equator caused through propagating wave dynamics.

The 630 nm MIG and the vertical neutral wind in the low latitude nighttime thermosphere

NASA Technical Reports Server (NTRS)

Herrero, F. A.; Meriwether, J. W., Jr.

1994-01-01

It is shown that large negative divergences (gradients) in the horizontal neutral wind in the equatorial thermosphere can support downward neutral winds in excess of 20 m/s. With attention to the meridional and vertical winds only, the pressure tendency equation is used to derive the expression U(sub z0) approximately equals (Partial derivative U(sub y)/Partial derivative y)H for the vertical wind U(sub z0) at the reference altitude for the pressure tendency equation; H is the atmospheric density scale height, and (Partial derivative U(sub y)/Partial derivative y) is the meridional wind gradient. The velocity gradient associated with the Meridional Intensity Gradient (MIG) of the O((sup 1)D) emission (630 nm) at low latitudes is used to estimate the vertical neutral wind in the MIG region. Velocity gradients derived from MIG data are about 0.5 (m/s)/km) or more, indicating that the MIG region may contain downward neutral winds in excess of 20 m/s. Though direct measurements of the vertical wind are scarce, Fabry-Perot interferometer data of the equatorial F-region above Natal, Brazil, showed downward winds of 30 m/s occurring during a strong meridional wind convergence in 1982. In-situ measurements with the WATS instrument on the DE-2 satellite also show large vertical neutral winds in the equatorial region.

Effects of the Solar Wind Pressure on Mercury's Exosphere: Hybrid Simulations

NASA Astrophysics Data System (ADS)

Travnicek, P. M.; Schriver, D.; Orlando, T. M.; Hellinger, P.

2017-12-01

We study effects of the changed solar wind pressure on the precipitation of hydrogen on the Mercury's surface and on the formation of Mercury's magnetosphere. We carry out a set of global hybrid simulations of the Mercury's magnetosphere with the interplanetary magnetic field oriented in the equatorial plane. We change the solar wind pressure by changing the velocity of injected solar wind plasma (vsw = 2 vA,sw; vsw = 4 vA,sw; vsw = 6 vA,sw). For each of the cases we examine proton and electron precipitation on Mercury's surface and calculate yields of heavy ions released from Mercury's surface via various processes (namely: Photo-Stimulated Desorption, Solar Wind Sputtering, and Electron Stimulated Desorption). We study circulation of the released ions within the Mercury's magnetosphere for the three cases.

Winds in the meteor zone over Trivandrum

NASA Astrophysics Data System (ADS)

Reddi, C. R.; Rajeev, K.; Ramakumar, Geetha

1991-04-01

The height profiles of the zonal and meridional wind obtained from the meteor wind radar data recorded at Trivandrum (8 deg 36 min N, 77 deg E) are presented. Large wind shears were found to exist in the meteor zone over Trivandrum. The profiles showed quasi-sinusoidal variations with altitude and vertical wavelength of the oscillation in the range 15-25 km. Further, there was a large day-to-day variability in the profiles obtained for the same local time on consecutive days. The results are discussed in the light of the winds due to tides and equatorial waves in the low latitudes. The implications of the large wind shears with reference to the local wind effects on the equatorial electrojet are outlined.

Dynamics of Monsoon-Induced Biennial Variability in ENSO

NASA Technical Reports Server (NTRS)

Kim, Kyu-Myong; Lau, K.-M.; Einaudi, Franco (Technical Monitor)

2000-01-01

The mechanism of the quasi-biennial tendency in El Nino Southern Oscillation (ENSO)-monsoon coupled system is investigated using an intermediate coupled model. The monsoon wind forcing is prescribed as a function of Sea Surface Temperature (SST) anomalies based on the relationship between zonal wind anomalies over the western Pacific to sea level change in the equatorial eastern Pacific. The key mechanism of quasi-biennial tendency in El Nino evolution is found to be in the strong coupling of ENSO to monsoon wind forcing over the western Pacific. Strong boreal summer monsoon wind forcing, which lags the maximum SST anomaly in the equatorial eastern Pacific approximately 6 months, tends to generate Kelvin waves of the opposite sign to anomalies in the eastern Pacific and initiates the turnabout in the eastern Pacific. Boreal winter monsoon forcing, which has zero lag with maximum SST in the equatorial eastern Pacific, tends to damp the ENSO oscillations.

Moisture dynamics of the northward and eastward propagating boreal summer intraseasonal oscillations: possible role of tropical Indo-west Pacific SST and circulation

NASA Astrophysics Data System (ADS)

Pillai, Prasanth A.; Sahai, A. K.

2016-08-01

Boreal summer intraseasonal oscillation (BSISO) has complex spatial structure due to the co-existence of equatorial eastward and off-equatorial northward propagation in the equatorial Indian Ocean. As a result, equatorial Indian Ocean convection has simultaneous northward and eastward (NE), northward only (N-only) and eastward only (E-only) propagations. It is well established that the convection propagates in the direction of increasing moist static energy (MSE). The moisture and MSE budget analysis reveals that the horizontal advection of anomalous MSE contributes to positive MSE tendency, which is in agreement with the horizontal advection of column integrated moisture anomaly. Northward movement of warm SST and the anomalous moisture advected by zonal wind are the major initiative for the northward propagation of convection from the equatorial Indian Ocean in both NE and N-only category. At the same time warm SST anomaly in the equatorial west Pacific along with moisture advection caused by anomalous meridional wind is important for the equatorial eastward branch of NE propagation. As these anomalies in the west Pacific moves northward, equatorial Indian Ocean convection establishes over the equatorial west Pacific. The absence of these processes confines the BSISO in northward direction for N-only category. In the case of E-only movement, warm SST anomaly and moisture advection by zonal component of wind causes the eastward propagation of convection. Boundary layer moisture convergence always remains east of convection center in E-only propagation, while it coincides with convection centre in other two categories. Thus the present study concludes that the difference in underlying SST and atmospheric circulation in tropical Indo-west Pacific oceanic regions encourage the differential propagation of BSISO convection through moisture dynamics.

Easterly and westerly wind events in the equatorial Pacific ocean and their oceanic response

NASA Astrophysics Data System (ADS)

Puy, martin; Lengaigne, matthieu; Vialard, jerome; Guilyardi, eric

2014-05-01

Intraseasonal wind variability is known to influence the onset and evolution of the El Niño Southern Oscillation (ENSO), in particular through the occurrence of Westerly Wind Events (WWEs) in the western Equatorial Pacific. For predictability purposes, it is important to identify the large scale atmospheric controls of the occurrences of those WWEs. We hence carefully assess the link between equatorial WWEs and large-scale atmospheric waves. We find that WWEs preferably occur during convectively active phases associated to equatorial atmospheric Rossby waves (74% against 15% if the distribution was random) and to the MJO (60% against 15%). We also find that WWEs that occur in relation with those atmospheric waves tend to be stronger. The results also show that WWEs that occur in relation with the MJO tend to be longer than others, and tend to have a larger impact on SST, both on the eastern edge of the warm pool and in the eastern Pacific. We further show that the central and eastern equatorial Pacific is home to frequent easterly wind events (EWEs). These EWEs are further shown to be influenced by atmospheric Rossby waves and the MJO, but to a lesser extent than WWEs. We will discuss the potential influence of EWEs on the ENSO cycle, and propose a modeling strategy to test the influence of these EWEs / WWEs on the ENSO evolution.

Disruption of Saturn's quasi-periodic equatorial oscillation by the great northern storm

NASA Astrophysics Data System (ADS)

Fletcher, Leigh N.; Guerlet, Sandrine; Orton, Glenn S.; Cosentino, Richard G.; Fouchet, Thierry; Irwin, Patrick G. J.; Li, Liming; Flasar, F. Michael; Gorius, Nicolas; Morales-Juberías, Raúl

2017-11-01

The equatorial middle atmospheres of the Earth1, Jupiter2 and Saturn3,4 all exhibit a remarkably similar phenomenon—a vertical, cyclic pattern of alternating temperatures and zonal (east-west) wind regimes that propagate slowly downwards with a well-defined multi-year period. Earth's quasi-biennial oscillation (QBO) (observed in the lower stratospheric winds with an average period of 28 months) is one of the most regular, repeatable cycles exhibited by our climate system1,5,6, and yet recent work has shown that this regularity can be disrupted by events occurring far away from the equatorial region, an example of a phenomenon known as atmospheric teleconnection7,8. Here, we reveal that Saturn's equatorial quasi-periodic oscillation (QPO) (with an 15-year period3,9) can also be dramatically perturbed. An intense springtime storm erupted at Saturn's northern mid-latitudes in December 201010-12, spawning a gigantic hot vortex in the stratosphere at 40° N that persisted for three years13. Far from the storm, the Cassini temperature measurements showed a dramatic 10 K cooling in the 0.5-5 mbar range across the entire equatorial region, disrupting the regular QPO pattern and significantly altering the middle-atmospheric wind structure, suggesting an injection of westward momentum into the equatorial wind system from waves generated by the northern storm. Hence, as on Earth, meteorological activity at mid-latitudes can have a profound effect on the regular atmospheric cycles in Saturn's tropics, demonstrating that waves can provide horizontal teleconnections between the phenomena shaping the middle atmospheres of giant planets.

A high-resolution OGCM simulation of the Tropical Pacific Ocean during the 1985-1994 TOGA period. Part I: Long equatorial waves

NASA Technical Reports Server (NTRS)

Boulanger, J. P.; Delecluse, F.; Maes, C.; Levy, C.

1995-01-01

A high resolution oceanic general circulation model of the three topical oceans is used to investigate long equatorial wave activity in the Pacific Ocean during the 1985-1994 TOGA period. Zonal wind stress forcing and simulated dynamic height are interpreted using techniques previously applied to data. Kelvin and first Rossby waves are observed propagating during all the period. A seasonal cycle and interannual anomalies are computed for each long equatorial wave. The east Pacific basin is mainly dominated by seasonal cycle variations while strong interannual anomalies are observed west of the dateline. Long wave interannual anomalies are then compared to wave coefficients simulated by a simple wind-forced model. Our results outline the major role played by wind forcing on interannual time scales in generating long equatorial waves. However, near both eastern and western boundaries, some differences can be attributed to long wave reflections. A comparison to wave coefficients calculated from GEOSAT sea-level data gives some insight of the model behavior.

Magnetohydrodynamic simulations of hot jupiter upper atmospheres

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trammell, George B.; Li, Zhi-Yun; Arras, Phil, E-mail: gbt8f@virginia.edu, E-mail: zl4h@virginia.edu, E-mail: arras@virginia.edu

Two-dimensional simulations of hot Jupiter upper atmospheres including the planet's magnetic field are presented. The goal is to explore magnetic effects on the layer of the atmosphere that is ionized and heated by stellar EUV radiation, and the imprint of these effects on the Lyα transmission spectrum. The simulations are axisymmetric, isothermal, and include both rotation and azimuth-averaged stellar tides. Mass density is converted to atomic hydrogen density through the assumption of ionization equilibrium. The three-zone structure—polar dead zone (DZ), mid-latitude wind zone (WZ), and equatorial DZ—found in previous analytic calculations is confirmed. For a magnetic field comparable to thatmore » of Jupiter, the equatorial DZ, which is confined by the magnetic field and corotates with the planet, contributes at least half of the transit signal. For even stronger fields, the gas escaping in the mid-latitude WZ is found to have a smaller contribution to the transit depth than the equatorial DZ. Transmission spectra computed from the simulations are compared to Hubble Space Telescope Space Telescope Imaging Spectrograph and Advanced Camera for Surveys data for HD 209458b and HD 189733b, and the range of model parameters consistent with the data is found. The central result of this paper is that the transit depth increases strongly with magnetic field strength when the hydrogen ionization layer is magnetically dominated, for dipole magnetic field B {sub 0} ≳ 10 G. Hence transit depth is sensitive to magnetic field strength, in addition to standard quantities such as the ratio of thermal to gravitational binding energies. Another effect of the magnetic field is that the planet loses angular momentum orders of magnitude faster than in the non-magnetic case, because the magnetic field greatly increases the lever arm for wind braking of the planet's rotation. Spin-down timescales for magnetized models of HD 209458b that agree with the observed transit depth can be as short as ≅ 30 Myr, which is much shorter than the age of the system.« less

Multiscale empirical modeling of the geomagnetic field: From storms to substorms

NASA Astrophysics Data System (ADS)

Stephens, G. K.; Sitnov, M. I.; Korth, H.; Gkioulidou, M.; Ukhorskiy, A. Y.; Merkin, V. G.

2017-12-01

An advanced version of the TS07D empirical geomagnetic field model, herein called SST17, is used to model the global picture of the geomagnetic field and its characteristic variations on both storm and substorm scales. The new SST17 model uses two regular expansions describing the equatorial currents with each having distinctly different scales, one corresponding to a thick and one to a thin current sheet relative to the thermal ion gyroradius. These expansions have an arbitrary distribution of currents in the equatorial plane that is constrained only by magnetometer data. This multi-scale description allows one to reproduce the current sheet thinning during the growth phase. Additionaly, the model uses a flexible description of field-aligned currents that reproduces their spiral structure at low altitudes and provides a continuous transition from region 1 to region 2 current systems. The empirical picture of substorms is obtained by combining magnetometer data from Geotail, THEMIS, Van Allen Probes, Cluster II, Polar, IMP-8, GOES 8, 9, 10 and 12 and then binning this data based on similar values of the auroral index AL, its time derivative and the integral of the solar wind electric field parameter (from ACE, Wind, and IMP-8) in time over substorm scales. The performance of the model is demonstrated for several events, including the 3 July 2012 substorm, which had multi-probe coverage and a series of substorms during the March 2008 storm. It is shown that the AL binning helps reproduce dipolarization signatures in the northward magnetic field Bz, while the solar wind electric field integral allows one to capture the current sheet thinning during the growth phase. The model allows one to trace the substorm dipolarization from the tail to the inner magnetosphere where the dipolarization of strongly stretched tail field lines causes a redistribution of the tail current resulting in an enhancement of the partial ring current in the premidnight sector.

The relationship between significant wave height and Indian Ocean Dipole in the equatorial North Indian Ocean

NASA Astrophysics Data System (ADS)

Fu, Chen; Wang, Dongxiao; Yang, Lei; Luo, Yao; Zhou, Fenghua; Priyadarshana, Tilak; Yao, Jinglong

2018-05-01

Based on reanalysis data, we find that the Indian Ocean Dipole (IOD) plays an important role in the variability of wave climate in the equatorial Northern Indian Ocean (NIO). Significant wave height (SWH) in the equatorial NIO, especially over the waters southeast to Sri Lanka, exhibits strong interannual variations. SWH anomalies in the waters southeast to Sri Lanka correlate well with dipole mode index (DMI) during both summer and autumn. Negative SWH anomalies occur over the oceanic area southeast to Sri Lanka during positive IOD events and vary with different types of IOD. During positive prolonged (unseasonable) IOD, the SWH anomalies are the strongest in autumn (summer); while during positive normal IOD, the SWH anomalies are weak in both summer and autumn. Strong easterly wind anomalies over the southeast oceanic area of Sri Lanka during positive IOD events weaken the original equatorial westerly wind stress, which leads to the decrease in wind-sea waves. The longer wave period during positive IOD events further confirms less wind-sea waves. The SWH anomaly pattern during negative IOD events is nearly opposite to that during positive IOD events.

The relationship between significant wave height and Indian Ocean Dipole in the equatorial North Indian Ocean

NASA Astrophysics Data System (ADS)

Fu, Chen; Wang, Dongxiao; Yang, Lei; Luo, Yao; Zhou, Fenghua; Priyadarshana, Tilak; Yao, Jinglong

2018-06-01

Based on reanalysis data, we find that the Indian Ocean Dipole (IOD) plays an important role in the variability of wave climate in the equatorial Northern Indian Ocean (NIO). Significant wave height (SWH) in the equatorial NIO, especially over the waters southeast to Sri Lanka, exhibits strong interannual variations. SWH anomalies in the waters southeast to Sri Lanka correlate well with dipole mode index (DMI) during both summer and autumn. Negative SWH anomalies occur over the oceanic area southeast to Sri Lanka during positive IOD events and vary with different types of IOD. During positive prolonged (unseasonable) IOD, the SWH anomalies are the strongest in autumn (summer); while during positive normal IOD, the SWH anomalies are weak in both summer and autumn. Strong easterly wind anomalies over the southeast oceanic area of Sri Lanka during positive IOD events weaken the original equatorial westerly wind stress, which leads to the decrease in wind-sea waves. The longer wave period during positive IOD events further confirms less wind-sea waves. The SWH anomaly pattern during negative IOD events is nearly opposite to that during positive IOD events.

Understanding the El Niño-like Oceanic Response in the Tropical Pacific to Global Warming

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Yiyong; Lu, Jian; Liu, Fukai

The enhanced central and eastern Pacific SST warming and the associated ocean processes under global warming are investigated using the ocean component of the Community Earth System Model (CESM), Parallel Ocean Program version 2 (POP2). The tropical SST warming pattern in the coupled CESM can be faithfully reproduced by the POP2 forced with surface fluxes computed using the aerodynamic bulk formula. By prescribing the wind stress and/or wind speed through the bulk formula, the effects of wind stress change and/or the wind-evaporation-SST (WES) feedback are isolated and their linearity is evaluated in this ocean-alone setting. Result shows that, although themore » weakening of the equatorial easterlies contributes positively to the El Niño-like SST warming, 80% of which can be simulated by the POP2 without considering the effects of wind change in both mechanical and thermodynamic fluxes. This result points to the importance of the air-sea thermal interaction and the relative feebleness of the ocean dynamical process in the El Niño-like equatorial Pacific SST response to global warming. On the other hand, the wind stress change is found to play a dominant role in the oceanic response in the tropical Pacific, accounting for most of the changes in the equatorial ocean current system and thermal structures, including the weakening of the surface westward currents, the enhancement of the near-surface stratification and the shoaling of the equatorial thermocline. Interestingly, greenhouse gas warming in the absence of wind stress change and WES feedback also contributes substantially to the changes at the subsurface equatorial Pacific. Further, this warming impact can be largely replicated by an idealized ocean experiment forced by a uniform surface heat flux, whereby, arguably, a purest form of oceanic dynamical thermostat is revealed.« less

Mars Global Digital Dune Database (MGD3): Global dune distribution and wind pattern observations

USGS Publications Warehouse

Hayward, Rosalyn K.; Fenton, Lori; Titus, Timothy N.

2014-01-01

The Mars Global Digital Dune Database (MGD3) is complete and now extends from 90°N to 90°S latitude. The recently released south pole (SP) portion (MC-30) of MGD3 adds ∼60,000 km2 of medium to large-size dark dune fields and ∼15,000 km2 of sand deposits and smaller dune fields to the previously released equatorial (EQ, ∼70,000 km2), and north pole (NP, ∼845,000 km2) portions of the database, bringing the global total to ∼975,000 km2. Nearly all NP dunes are part of large sand seas, while the majority of EQ and SP dune fields are individual dune fields located in craters. Despite the differences between Mars and Earth, their dune and dune field morphologies are strikingly similar. Bullseye dune fields, named for their concentric ring pattern, are the exception, possibly owing their distinctive appearance to winds that are unique to the crater environment. Ground-based wind directions are derived from slipface (SF) orientation and dune centroid azimuth (DCA), a measure of the relative location of a dune field inside a crater. SF and DCA often preserve evidence of different wind directions, suggesting the importance of local, topographically influenced winds. In general however, ground-based wind directions are broadly consistent with expected global patterns, such as polar easterlies. Intriguingly, between 40°S and 80°S latitude both SF and DCA preserve their strongest, though different, dominant wind direction, with transport toward the west and east for SF-derived winds and toward the north and west for DCA-derived winds.

AN ADJOINT-BASED METHOD FOR THE INVERSION OF THE JUNO AND CASSINI GRAVITY MEASUREMENTS INTO WIND FIELDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galanti, Eli; Kaspi, Yohai, E-mail: eli.galanti@weizmann.ac.il

2016-04-01

During 2016–17, the Juno and Cassini spacecraft will both perform close eccentric orbits of Jupiter and Saturn, respectively, obtaining high-precision gravity measurements for these planets. These data will be used to estimate the depth of the observed surface flows on these planets. All models to date, relating the winds to the gravity field, have been in the forward direction, thus only allowing the calculation of the gravity field from given wind models. However, there is a need to do the inverse problem since the new observations will be of the gravity field. Here, an inverse dynamical model is developed tomore » relate the expected measurable gravity field, to perturbations of the density and wind fields, and therefore to the observed cloud-level winds. In order to invert the gravity field into the 3D circulation, an adjoint model is constructed for the dynamical model, thus allowing backward integration. This tool is used for the examination of various scenarios, simulating cases in which the depth of the wind depends on latitude. We show that it is possible to use the gravity measurements to derive the depth of the winds, both on Jupiter and Saturn, also taking into account measurement errors. Calculating the solution uncertainties, we show that the wind depth can be determined more precisely in the low-to-mid-latitudes. In addition, the gravitational moments are found to be particularly sensitive to flows at the equatorial intermediate depths. Therefore, we expect that if deep winds exist on these planets they will have a measurable signature by Juno and Cassini.« less

Effects of the intense geomagnetic storm of September-October 2012 on the equatorial, low- and mid-latitude F region in the American and African sector during the unusual 24th solar cycle

NASA Astrophysics Data System (ADS)

de Jesus, R.; Fagundes, P. R.; Coster, A.; Bolaji, O. S.; Sobral, J. H. A.; Batista, I. S.; de Abreu, A. J.; Venkatesh, K.; Gende, M.; Abalde, J. R.; Sumod, S. G.

2016-02-01

The main purpose of this paper is to investigate the response of the ionospheric F layer in the American and African sectors during the intense geomagnetic storm which occurred on 30 September-01 October 2012. In this work, we used observations from a chain of 20 GPS stations in the equatorial, low- and mid-latitude regions in the American and African sectors. Also, in this study ionospheric sounding data obtained during 29th September to 2nd October, 2012 at Jicamarca (JIC), Peru, São Luis (SL), Fortaleza (FZ), Brazil, and Port Stanley (PST), are presented. On the night of 30 September-01 October, in the main and recovery phase, the h´F variations showed an unusual uplifting of the F region at equatorial (JIC, SL and FZ) and mid- (PST) latitude stations related with the propagations of traveling ionospheric disturbances (TIDs) generated by Joule heating at auroral regions. On 30 September, the VTEC variations and foF2 observations at mid-latitude stations (American sector) showed a long-duration positive ionospheric storm (over 6 h of enhancement) associated with large-scale wind circulations and equatorward neutral winds. Also, on 01 October, a long-duration positive ionospheric storm was observed at equatorial, low- and mid- latitude stations in the African sector, related with the large-scale wind circulations and equatorward neutral winds. On 01 and 02 October, positive ionospheric storms were observed at equatorial, low- and mid-latitude stations in the American sector, possibly associated with the TIDs and an equatorward neutral wind. Also, on 01 October negative ionospheric storms were observed at equatorial, low- and mid-latitude regions in the American sector, probably associated with the changes in the O/N2 ratio. On the night of 30 September-01 October, ionospheric plasma bubbles were observed at equatorial, low- and mid- latitude stations in the South American sector, possibly associated with the occurrence of geomagnetic storm.

Geomagnetically Induced Currents Around the World During the 17 March 2015 Storm

NASA Technical Reports Server (NTRS)

Carter, B. A.; Yizengaw, E.; Pradipta, R.; Weygand, J. M.; Piersanti, M.; Pulkkinen, Antti Aleksi; Moldwin, M. B.; Norman, R.; Zhang, K.

2016-01-01

Geomagnetically induced currents (GICs) represent a significant space weather issue for power grid and pipeline infrastructure, particularly during severe geomagnetic storms. In this study, magnetometer data collected from around the world are analyzed to investigate the GICs caused by the 2015 St. Patricks Day storm. While significant GIC activity in the high-latitude regions due to storm time substorm activity is shown for this event, enhanced GIC activity was also measured at two equatorial stations in the American and Southeast Asian sectors. This equatorial GIC activity is closely examined, and it is shown that it is present both during the arrival of the interplanetary shock at the storm sudden commencement (SSC) in Southeast Asia and during the main phase of the storm approximately 10 h later in South America. The SSC caused magnetic field variations at the equator in Southeast Asia that were twice the magnitude of those observed only a few degrees to the north, strongly indicating that the equatorial electrojet (EEJ) played a significant role. The large equatorial magnetic field variations measured in South America are also examined, and the coincident solar wind data are used to investigate the causes of the sudden changes in the EEJ approximately 10 h into the storm. From this analysis it is concluded that sudden magnetopause current increases due to increases in the solarwind dynamic pressure, and the sudden changes in the resultant magnetospheric and ionospheric current systems, are the primary drivers of equatorial GICs.

CO/sub 2/ fluxes in the tropical Atlantic during FOCAL cruises

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrie, C.; Oudot, C.; Genthon, C.

1986-10-15

CO/sub 2/ partial pressures in the atmosphere and in surface seawater have been measured in the equatorial Atlantic Ocean during Programme Francais Ocean-Climat en Atlantique Equatorial cruises extending from July 1982 to August 1984 along the 4/degree/W, 22/degree/W, and 35/degree/W meridians. Gas transfer coefficients based on recently reported field data combined with information deduced from wind tunnel experiments are used to compute the CO/sub 2/ fluxes. The global mean net flux between 5/degree/N and 5/degree/S is equal to 1.05 mmol m/sup /minus/2/ d/sup /minus/1/ and is from the ocean to the atmosphere. The escape of CO/sub 2/ increases strongly frommore » the east to the west and is always lower in the north than in the south. The importance of wind speed, pCO/sub 2/ in atmosphere, PCO/sub 2/ in surface seawater, and temperature on the flux variability is discussed. The relative influence of the equatorial upwelling on one hand and of the advection and warming of surface waters on the other hand is studied in order to explain high partial pressure in seawater. 59 refs., 15 figs., 5 tabs.« less

The response of an ocean general circulation model to surface wind stress produced by an atmospheric general circulation model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, B.; Schneider, E.K.

1995-10-01

Two surface wind stress datasets for 1979-91, one based on observations and the other from an investigation of the COLA atmospheric general circulation model (AGCM) with prescribed SST, are used to drive the GFDL ocean general circulation model. These two runs are referred to as the control and COLA experiments, respectively. Simulated SST and upper-ocean heat contents (HC) in the tropical Pacific Ocean are compared with observations and between experiments. Both simulation reproduced the observed mean SST and HC fields as well as their annual cycles realistically. Major errors common to both runs are colder than observed SST in themore » eastern equatorial ocean and HC in the western Pacific south of the equator, with errors generally larger in the COLA experiment. New errors arising from the AGCM wind forcing include higher SST near the South American coast throughout the year and weaker HC gradients along the equator in boreal spring. The former is associated with suppressed coastal upwelling by weak along shore AGCM winds, and the latter is caused by weaker equatorial easterlies in boreal spring. The low-frequency ENSO fluctuations are also realistic for both runs. Correlations between the observed and simulated SST anomalies from the COLA simulation are as high as those from the control run in the central equatorial Pacific. A major problem in the COLA simulation is the appearance of unrealistic tropical cold anomalies during the boreal spring of mature El Nino years. These anomalies propagate along the equator from the western Pacific to the eastern coast in about three months, and temporarily eliminate the warm SST and HC anomalies in the eastern Pacific. This erroneous oceanic response in the COLA simulation is caused by a reversal of the westerly wind anomalies on the equator, associated with an unrealistic southward shift of the ITCZ in boreal spring during El Nino events. 66 refs., 16 figs.« less

Multiproxy Reduced-Dimension Reconstruction of Holocene Tropical Pacific SST Fields and Indian Monsoon Variability

NASA Astrophysics Data System (ADS)

Gill, E.; Rajagopalan, B.; Molnar, P. H.; Marchitto, T. M., Jr.; Kushnir, Y.

2016-12-01

We develop a multiproxy reduced-dimension methodology that blends magnesium calcium (Mg/Ca) and alkenone (UK'37) paleo sea surface temperature (SST) records from the eastern and western equatorial Pacific to recreate snapshots of full field SSTs and zonal wind anomalies from 10 to 2 ka BP in 2000-year increments. In the reconstruction, the zonal SST difference (average west Pacific SST minus average east Pacific SST) is largest at 10 ka (0.26°C), with coldest SST anomalies of -0.9°C in the eastern equatorial Pacific and concurrent easterly maximum zonal wind anomalies of 7 m s-1 throughout the central Pacific. From 10 to 2 ka, the entire equatorial Pacific warms, but at a faster rate in the east than in the west. These patterns are broadly consistent with previous inferences of reduced El Niño-Southern Oscillation variability associated with a cooler and/or "La Niña-like" state during the early to middle Holocene. At present there is a strong negative correlation between tropical pacific SSTs and Indian summer monsoon strength. Assuming ENSO-monsoon teleconnections were the same during early Holocene, we would expect a cooler tropical Pacific to enhance the summer Indian monsoon. To test this idea, we used the same tropical Pacific SST proxy records and a similar reduced-dimension technique to reconstruct fields of Arabian Sea wind-stress curl and Indian summer monsoon precipitation. Reconstructions for 10 ka reveal wind-stress curl anomalies of 30% greater than present day off the coastlines of Oman and Yemen, which suggest greater coastal upwelling and an enhanced monsoon jet during this time. Spatial rainfall reconstructions reveal the greatest difference in precipitation at 10 ka over the core monsoon region ( 20-60% greater than present day). Specifically, reconstructions from 10 ka reveal 40-60% greater rainfall over North West India, a region home to abundant paleo-lake records spanning the Holocene but is at present remarkably dry ( 200-450 mm of annual rainfall). These findings advance the hypothesis that teleconnections from the tropical Pacific contributed to, if not accounted for, greater early to middle Holocene wetness over India as recorded by various (e.g., cave, lacustrine, river discharge) paleoclimate proxies throughout the monsoon region.

Wind-Stress Simulations and Equatorial Dynamics in an AGCM. Part 1; Basic Results from a 1979-1999 Forced SST Experiment

NASA Technical Reports Server (NTRS)

Bacmeister, Julio T.; Suarez, Max J.; Einaudi, Franco (Technical Monitor)

2001-01-01

This is the first of a two part study examining the connection of the equatorial momentum budget in an AGCM (Atmospheric General Circulation Model), with simulated equatorial surface wind stresses over the Pacific. The AGCM used in this study forms part of a newly developed coupled forecasting system used at NASA's Seasonal- to-Interannual Prediction Project. Here we describe the model and present results from a 20-year (1979-1999) AMIP-type experiment forced with observed SSTs (Sea Surface Temperatures). Model results are compared them with available observational data sets. The climatological pattern of extra-tropical planetary waves as well as their ENSO-related variability is found to agree quite well with re-analysis estimates. The model's surface wind stress is examined in detail, and reveals a reasonable overall simulation of seasonal interannual variability, as well as seasonal mean distributions. However, an excessive annual oscillation in wind stress over the equatorial central Pacific is found. We examine the model's divergent circulation over the tropical Pacific and compare it with estimates based on re-analysis data. These comparisons are generally good, but reveal excessive upper-level convergence in the central Pacific. In Part II of this study a direct examination of individual terms in the AGCM's momentum budget is presented. We relate the results of this analysis to the model's simulation of surface wind stress.

On the importance of Sri Lanka for sea-level variability along the west coast of India

NASA Astrophysics Data System (ADS)

Suresh, I.; Vialard, J.; Izumo, T.; Lengaigne, M.; Han, W.; McCreary, J. P., Jr.; Pillathu Moolayil, M.

2015-12-01

Earlier studies have illustrated the strong influence of remote forcing from the equator and the Bay of Bengal on the sea-level variability off the west coast of India, especially at the seasonal timescale. More recently, Suresh et al. [2013] demonstrated with a simple, linear, continuously-stratified (LCS) model that the equatorial zonal winds contribute to more than 60% of intraseasonal sea-level variability along the Indian west coast. In the present study, we quantify the contributions from various processes to the sea-level variability along the west coast of India at different timescales with the help of a LCS model through both idealized and realistic sensitivity experiments. We demonstrate that remote forcing dominates the sea-level variability along the west coast of India at intraseasonal to interannual timescales. Sri Lanka and the southern tip of India play an important role on Indian west coast sea-level variability at all timescales for two reasons: First, the geometry of the coast favors a strong alongshore wind-stress forcing of coastal Kelvin waves across timescales there. Second, Sri Lanka interacts with low-order meridional mode equatorial Rossby waves forced by equatorial winds or southern Bay of Bengal wind- stress curl. This interaction of coastal waveguide with equatorial waveguide creates a new pathway for the equatorial signals to arrive at the west coast of India, alternative to the "classical" coastal waveguide around the rim of the Bay of Bengal. Reference: Suresh, I., J. Vialard, M. Lengaigne, W. Han, J. McCreary, F. Durand, and P. M. Muraleedharan (2013), Origins of wind-driven intraseasonal sea level variations in the North Indian Ocean coastal waveguide, Geophys. Res. Lett., 40, 5740-5744, doi:10.1002/2013GL058312.

The influence of tidal winds in the formation of blanketing sporadic e-layer over equatorial Brazilian region

NASA Astrophysics Data System (ADS)

Resende, Laysa Cristina Araujo; Batista, Inez Staciarini; Denardini, Clezio Marcos; Batista, Paulo Prado; Carrasco, Alexander José; Andrioli, Vânia Fátima; Moro, Juliano

2018-06-01

This work analysis the blanketing sporadic layers (Esb) behavior over São Luís, Brazil (2° 31‧ S, 44° 16‧ W, dip: -4.80) which is classified as a transition region between equatorial and low-latitude. Hence, some peculiarities can appear as Esb occurrence instead of the common Esq, which is a non-blanketing irregularity layer. The analysis presented here was obtained using a modified version of a theoretical model for the E region (MIRE), which computes the densities of the metallic ions (Fe+ and Mg+) and the densities of the main molecular ions (NO+, O2+, N2+) by solving the continuity and momentum equations for each one of them. In that model, the Es layer physics driven by both diurnal and semidiurnal tidal winds are taken into account and it was extended in height coverage by adding a novel neutral wind model derived from the all-sky meteor radar measurements. Thus, we provide more trustworthy results related to the Es layer formation in the equatorial region. We verified the contribution of each tidal wind component to the Esb layer formation in this equatorial region. Additionally, we compared the Es layer electron density computed by MIRE with the data obtained by using the blanketing frequency parameter (fbEs) deduced from ionograms. The results show that the diurnal component of the tidal wind is more important in the Esb layer formation whereas the semidiurnal component has a little contribution in our simulations. Finally, it was verified that the modified MIRE presented here can be used to study the Esb layers occurrence over the equatorial region in the Brazilian sector.

Sensitivity of the Mid-Winter Arctic Stratosphere to QBO Width in a Simplified Chemistry-Climate Model

NASA Technical Reports Server (NTRS)

Hurwitz, M. M.; Braesicke., P.; Pyle, J. A.

2011-01-01

In the stratosphere, equatorial winds continually alternate between easterly (westward) and westerly (eastward). This phenomenon is called the quasi-biennial oscillation (QBO). The average QBO cycle (Le. easterly to westerly to easterly) lasts approximately 27 months. Large-scale 'planetary' waves can only travel upward through the atmosphere when equatorial winds are westerly, and below a critical threshold. Thus, the amount of wave energy that reaches the middle atmosphere depends on the wind direction. When equatorial winds are easterly, wave energy is concentrated at higher latitudes, weakening the high-latitude eastward wind feature known as the 'polar jet' during the Northern Hemisphere winter season. Holton and Tan (1980) used atmospheric observations to show the dependence of the strength of the northern polar jet on the phase (easterly vs. westerly) of the QBO. This modeling study finds that the width of the quasi-biennial oscillation (QBO) varies from one cycle to the next, and that variation in QBO width may exert equal influence on the Arctic stratosphere as does the QBO wind direction. High latitude winds are weaker and ozone values are higher in a wide-QBO model simulation, as compared with a realistic simulation. This result implies that a relatively wider QBO acts like a preferential shift toward the easterly phase of the QBO.

New observations of Yanai waves and equatorial inertia-gravity waves in the Pacific Ocean

NASA Astrophysics Data System (ADS)

Farrar, J. T.; Durland, T.

2011-12-01

In the 1970's and 1980's, there was a great deal of research activity on near-equatorial variability at periods of days to weeks associated with oceanic equatorial inertia-gravity waves and Yanai waves. At that time, the measurements available for studying these waves were much more limited than today: most of the available observations were from island tide gauges and a handful of short mooring records. We use more than a decade of the extensive modern data record from the TAO/TRITON mooring array in the Pacific Ocean to re-examine the internal-wave climate in the equatorial Pacific, with a focus on interpretation of the zonal-wavenumber/frequency spectrum of surface dynamic height relative to 500-m depth. Many equatorial-wave meridional modes can be identified, for both the first and second baroclinic mode. We also estimated zonal-wavenumber/frequency spectra for the zonal and meridional wind stress components. The location and extent of spectral peaks in dynamic height is readily rationalized using basic, linear theory of forced equatorial waves and the observed wind stress spectrum.

Remote forcing at the Last Glacial Maximum in the Tropical Pacific Ocean

NASA Astrophysics Data System (ADS)

Andreasen, Dyke H.; Ravelo, A. Christina; Broccoli, Anthony J.

2001-01-01

We present results of a Last Glacial Maximum (LGM) wind stress sensitivity experiment using a high-resolution ocean general circulation model of the tropical Pacific Ocean. LGM wind stress, used to drive the ocean model, was generated using an atmospheric general circulation model simulation forced by LGM boundary conditions as part of the Paleoclimate Modeling Intercomparison Project (PMIP) [Broccoli, 2000]. LGM wind stress anomalies were large in the western half of the basin, yet there was a significant hydrographic response in the eastern half. This ocean model experiment hind casts changes that are in close agreement with paleoceanographic data from the entire region, even without the explicit modeling of the air-sea interactions. Data and model both predict that the annual average thermocline tilt across the basin was enhanced. Data and model are consistent with a stronger equatorial undercurrent which shoaled to the west of where it does today, and stronger advection of water from the Peru Current into the east equatorial Pacific and across the equator. Paleoproductivity and sea surface temperature (SST) data are interpreted in light of the modeling results, indicating that paleoproductivity changes were related to wind-forced dynamical changes resulting from LGM boundary conditions, while SST changes were related to independent, possibly radiative, forcing. Overall, our results imply that much of the dynamic response of the tropical Pacific during the LGM can be explained by wind field changes resulting from global LGM boundary conditions.

Constraints on Wave Drag Parameterization Schemes for Simulating the Quasi-Biennial Oscillation. Part I: Gravity Wave Forcing.

NASA Astrophysics Data System (ADS)

Campbell, Lucy J.; Shepherd, Theodore G.

2005-12-01

Parameterization schemes for the drag due to atmospheric gravity waves are discussed and compared in the context of a simple one-dimensional model of the quasi-biennial oscillation (QBO). A number of fundamental issues are examined in detail, with the goal of providing a better understanding of the mechanism by which gravity wave drag can produce an equatorial zonal wind oscillation. The gravity wave driven QBOs are compared with those obtained from a parameterization of equatorial planetary waves. In all gravity wave cases, it is seen that the inclusion of vertical diffusion is crucial for the descent of the shear zones and the development of the QBO. An important difference between the schemes for the two types of waves is that in the case of equatorial planetary waves, vertical diffusion is needed only at the lowest levels, while for the gravity wave drag schemes it must be included at all levels. The question of whether there is downward propagation of influence in the simulated QBOs is addressed. In the gravity wave drag schemes, the evolution of the wind at a given level depends on the wind above, as well as on the wind below. This is in contrast to the parameterization for the equatorial planetary waves in which there is downward propagation of phase only. The stability of a zero-wind initial state is examined, and it is determined that a small perturbation to such a state will amplify with time to the extent that a zonal wind oscillation is permitted.

Explaining the features of the Bipolar Nebulae of η-Carinae through gas dynamical simulations

NASA Astrophysics Data System (ADS)

de Gouveia dal Pino, E. M.; Gonzalez, R. F.; Raga, A. C.; Velezquez, P. F.

2005-09-01

Employing an alternative scenario to previous interacting stellar wind models that is supported both by theoretical and observational evidence, we let a nonspherical outburst wind (with a latitudinal velocity dependence that matches the observations of the large Homunculus) interact with a preeruptive slow wind also with a toroidal density distribution but with a much smaller equator-to-polar density contrast than that assumed in previous models. A second eruptive wind with spherical shape is ejected about 50 years after the first outburst and causes the development of the little internal nebula. We find that as a result of an appropriate combination of the parameters that control the degree of asymmetry of the interacting winds, the model is able to produce not only the structure and kinematics of both Homunculi but also the high-velocity components of the equatorial ejecta. These latter arise from the impact between the nonspherical outburst and the preoutburst winds in the equatorial plane (see Figs. 1 and 2 in Gonzalez, de Gouveia Dal Pino, Raga & Velazquez 2004a). Our model predicts that most of the features of the bipolar winds of eta-Carinae and the source ejection mechanism are directly linked to the central star only, therefore without requiring to invoke the secondary wind of the companion star to explain, e.g., the equatorial ejecta (Gonzalez, de Gouveia Dal Pino, Raga & Velazquez 2004b).

Magnetic field of jupiter and its interaction with the solar wind.

PubMed

Smith, E J; Davis, L; Jones, D E; Colburn, D S; Coleman, P J; Dyal, P; Sonett, C P

1974-01-25

Jupiter's magnetic field and its interaction with the magnetized solar wind were observed with the Pioneer 10 vector helium magnetometer. The magnetic dipole is directed opposite to that of the earth with a moment of 4.0 gauss R(J)(3) (R(J), Jupiter radius), and an inclination of 15 degrees lying in a system III meridian of 230 degrees . The dipole is offset about 0.1 R(J) north of the equatorial plane and about 0.2 R(J) toward longitude 170 degrees . There is severe stretching of the planetary field parallel to the equator throughout the outer magnetosphere, accompanied by a systematic departure from meridian planes. The field configuration implies substantial plasma effects inside the magnetosphere, such as thermal pressure, centrifugal forces, and differential rotation. As at the earth, the outer boundary is thin, nor diffuse, and there is a detached bow shock.

Opportunities investigating the thermosphere/ionosphere system by low Earth orbiting satellite missions (Invited)

NASA Astrophysics Data System (ADS)

Stolle, C.; Park, J.; Luhr, H.

2013-12-01

New opportunities for investigating the thermosphere/ionosphere interactions arise from in situ measurements on board low Earth orbiting satellites. Ten years of successful operation of the CHAMP satellite mission at a unique orbit altitude of about 400 km revealed many interesting features of the coupling between the thermosphere and ionosphere and the different atmospheric layers. Examples are the investigations of signatures of stratospheric warming events that are known to change significantly the dynamics of the equatorial ionosphere. It was shown that these modifications are due to an enhancement of lunar tidal effects, e.g. reflected in the thermospheric zonal wind, in the equatorial electroje or in the eastward electric field. Another topic concerns the energy deposit in the F-region though cooling of the thermal electron gas caused by elastic and inelastic processes (Schunk and Nagy, 2009). We find that a significant deposition is present during day at mid latitudes. At low latitudes the energy flux remain important until midnight. Observed heating rates depend on the satellite altitudes, but they are globally available from the CHAMP data. Further enhanced investigations are expected from ESA's three-satellite Swarm mission with a launch planned in 2014. The mission will provide observations of electron density, electron and ion temperature, ion drift and the electric field together with neutral density and winds. High-precision magnetic field observations will allow monitoring ionospheric currents.

The growth and decay of equatorial backscatter plumes

NASA Astrophysics Data System (ADS)

Tsunoda, R. T.

1980-02-01

During the past three years, a series of rocket experiments from the Kwajalein Atoll, Marshall Islands, were conducted to investigate the character of intense, scintillation-producing irregularities that occur in the nighttime equatorial ionosphere. Because the source mechanism of equatorial irregularities, believed to be the Rayleigh-Taylor instability, is analogous to that which generates plasma-density striations in a nuclear-induced environment, there is considerable interest in the underlying physics that controls the characteristics of these irregularities. A primary objective of ALTAIR investigations of equatorial irregularities is to seek an understanding of the underlying physics by establishing the relationship between meter-scale irregularities (detected by ALTAIR), and the large-scale plasma-density depletions (or 'bubbles') that contain the kilometer-scale, scintillation-producing irregularities. We describe the time evolution of backscatter 'plumes' produced by one meter equatorial field-aligned irregularities. Using ALTAIR, a fully steerable backscatter radar, to repeatedly map selected plumes, we characterize the dynamic behavior of plumes in terms of growth and a decay phase. Most of the observed characteristics are found to be consistent with equatorial-irregularity generation predicted by current theories of Rayleigh-Taylor and gradient-drift instabilities. However, other characteristics have been found that suggest key roles played by the eastward neutral wind and by altitude-modulation of the bottomside F layer in establishing the initial conditions for plume growth.

New results on equatorial thermospheric winds and temperatures from Ethiopia, Africa

NASA Astrophysics Data System (ADS)

Tesema, Fasil; Mesquita, Rafael; Meriwether, John; Damtie, Baylie; Nigussie, Melessew; Makela, Jonathan; Fisher, Daniel; Harding, Brian; Yizengaw, Endawoke; Sanders, Samuel

2017-03-01

Measurements of equatorial thermospheric winds, temperatures, and 630 nm relative intensities were obtained using an imaging Fabry-Perot interferometer (FPI), which was recently deployed at Bahir Dar University in Ethiopia (11.6° N, 37.4° E, 3.7° N magnetic). The results obtained in this study cover 6 months (53 nights of useable data) between November 2015 and April 2016. The monthly-averaged values, which include local winter and equinox seasons, show the magnitude of the maximum monthly-averaged zonal wind is typically within the range of 70 to 90 ms-1 and is eastward between 19:00 and 21:00 LT. Compared to prior studies of the equatorial thermospheric wind for this local time period, the magnitude is considerably weaker as compared to the maximum zonal wind speed observed in the Peruvian sector but comparable to Brazilian FPI results. During the early evening, the meridional wind speeds are 30 to 50 ms-1 poleward during the winter months and 10 to 25 ms-1 equatorward in the equinox months. The direction of the poleward wind during the winter months is believed to be mainly caused by the existence of the interhemispheric wind flow from the summer to winter hemispheres. An equatorial wind surge is observed later in the evening and is shifted to later local times during the winter months and to earlier local times during the equinox months. Significant night-to-night variations are also observed in the maximum speed of both zonal and meridional winds. The temperature observations show the midnight temperature maximum (MTM) to be generally present between 00:30 and 02:00 LT. The amplitude of the MTM was ˜ 110 K in January 2016 with values smaller than this in the other months. The local time difference between the appearance of the MTM and a pre-midnight equatorial wind was generally 60 to 180 min. A meridional wind reversal was also observed after the appearance of the MTM (after 02:00 LT). Climatological models, HWM14 and MSIS-00, were compared to the observations and the HWM14 model generally predicted the zonal wind observations well with the exception of higher model values by 25 ms-1 in the winter months. The HWM14 model meridional wind showed generally good agreement with the observations. Finally, the MSIS-00 model overestimated the temperature by 50 to 75 K during the early evening hours of local winter months. Otherwise, the agreement was generally good, although, in line with prior studies, the model failed to reproduce the MTM peak for any of the 6 months compared with the FPI data.

Dynamics of Andaman Sea circulation and its role in connecting the equatorial Indian Ocean to the Bay of Bengal

NASA Astrophysics Data System (ADS)

Chatterjee, Abhisek; Shankar, D.; McCreary, J. P.; Vinayachandran, P. N.; Mukherjee, A.

2017-04-01

Circulation in the Bay of Bengal (BoB) is driven not only by local winds, but are also strongly forced by the reflection of equatorial Kelvin waves (EKWs) from the eastern boundary of the Indian Ocean. The equatorial influence attains its peak during the monsoon-transition period when strong eastward currents force the strong EKWs along the equator. The Andaman Sea, lying between the Andaman and Nicobar island chains to its west and Indonesia, Thailand, and Myanmar to the south, east, and north, is connected to the equatorial ocean and the BoB by three primary passages, the southern (6°N), middle (10°N), and northern (15°N) channels. We use ocean circulation models, together with satellite altimeter data, to study the pathways by which equatorial signals pass through the Andaman Sea to the BoB and associated dynamical interactions in the process. The mean coastal circulation within the Andaman Sea and around the islands is primarily driven by equatorial forcing, with the local winds forcing a weak sea-level signal. On the other hand, the current forced by local winds is comparable to that forced remotely from the equator. Our results suggest that the Andaman and Nicobar Islands not only influence the circulation within the Andaman Sea, but also significantly alter the circulation in the interior bay and along the east coast of India, implying that they need to be represented accurately in numerical models of the Indian Ocean.

Signature of 3-4 day planetary waves in the equatorial ionospheric F layer height and medium frequency radar winds over Tirunelveli (8.7oN)

NASA Astrophysics Data System (ADS)

Sundararaman, Sathishkumar

Signature of 3-4 day planetary waves in the equatorial ionospheric F layer height and medium frequency radar winds over Tirunelveli (8.7oN) S. Sathishkumar1, R. Dhanya1, K. Emperumal1, D. Tiwari2, S. Gurubaran1 and A. Bhattacharyya2 1. Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Tirunelveli, India 2. Indian Institute of Geomagnetism, Navi Mumbai, India Email: sathishmaths@gmail.com Abstract The equatorial atmosphere-ionosphere system has been studied theoretically and observationally in the past. In the equatorial atmosphere, oscillations with periods of 3-4 days are often observed in the medium frequency (MF) radar over Tirunelveli (8.7oN, 77.8oE, 1.34oN geomag. lat.). Earlier observations show the clear evidence that these waves can propagate from the stratosphere to ionosphere. A digital ionosonde has been providing useful information on several ionospheric parameters from the same site. Simultaneous observations of mesospheric winds using medium frequency radar and F-layer height (h'F) from ionosonde reveal that the 3-4 day wave was evident in both the component during the 01 June 2007 and 31 July 2007. The 3-4 day wave could have an important role in the day to day variability of the equatorial ionosphere evening uplift. Results from an extensive analysis that is being carried out in the direction of 3-4 day wave present in the ionosphere will be presented.

Solar wind and coronal structure near sunspot minimum - Pioneer and SMM observations from 1985-1987

NASA Technical Reports Server (NTRS)

Mihalov, J. D.; Barnes, A.; Hundhausen, A. J.; Smith, E. J.

1990-01-01

Changes in solar wind speed and magnetic polarity observed at the Pioneer spacecraft are discussed here in terms of the changing magnetic geometry implied by SMM coronagraph observations over the period 1985-1987. The pattern of recurrent solar wind streams, the long-term average speed, and the sector polarity of the interplanetary magnetic field all changed in a manner suggesting both a temporal variation, and a changing dependence on heliographic latitude. Coronal observations during this epoch show a systematic variation in coronal structure and the magnetic structure imposed on the expanding solar wind. These observations suggest interpretation of the solar wind speed variations in terms of the familiar model where the speed increases with distance from a nearly flat interplanetary current sheet, and where this current sheet becomes aligned with the solar equatorial plane as sunspot minimum approaches, but deviates rapidly from that orientation after minimum.

Simultaneous observation of Pc 3-4 pulsations in the solar wind and in the earth's magnetosphere

NASA Technical Reports Server (NTRS)

Engebretson, M. J.; Zanetti, L. J.; Potemra, T. A.; Baumjohann, W.; Luehr, H.; Acuna, M. H.

1987-01-01

The equatorially orbiting Active Magnetospheric Particle Tracer Explorers CCE and IRM satellites have made numerous observations of Pc 3-4 magnetic field pulsations (10-s to 100-s period) simultaneously at locations upstream of the earth's bow shock and inside the magnetosphere. These observations show solar wind/IMF control of two categories of dayside magnetospheric pulsations. Harmonically structured, azimuthally polarized pulsations are commonly observed from L = 4 to 9 in association with upstream waves. More monochromatic compressional pulsations are clearly evident on occasion, with periods identical to those observed simultaneously in the solar wind. The observations reported here are consistent with a high-latitude (cusp) entry mechanism for wave energy related to harmonically structured pulsations.

Faraday rotation fluctuations of MESSENGER radio signals through the equatorial lower corona near solar minimum

NASA Astrophysics Data System (ADS)

Wexler, D. B.; Jensen, E. A.; Hollweg, J. V.; Heiles, C.; Efimov, A. I.; Vierinen, J.; Coster, A. J.

2017-02-01

Faraday rotation (FR) of transcoronal radio transmissions from spacecraft near superior conjunction enables study of the temporal variations in coronal plasma density, velocity, and magnetic field. The MESSENGER spacecraft 8.4 GHz radio, transmitting through the corona with closest line-of-sight approach 1.63-1.89 solar radii and near-equatorial heliolatitudes, was recorded soon after the deep solar minimum of solar cycle 23. During egress from superior conjunction, FR gradually decreased, and an overlay of wave-like FR fluctuations (FRFs) with periods of hundreds to thousands of seconds was found. The FRF power spectrum was characterized by a power law relation, with the baseline spectral index being -2.64. A transient power increase showed relative flattening of the spectrum and bands of enhanced spectral power at 3.3 mHz and 6.1 mHz. Our results confirm the presence of coronal FRF similar to those described previously at greater solar offset. Interpreted as Alfvén waves crossing the line of sight radially near the proximate point, low-frequency FRF convey an energy flux density higher than that of the background solar wind kinetic energy, but only a fraction of that required to accelerate the solar wind. Even so, this fraction is quite variable and potentially escalates to energetically significant values with relatively modest changes in estimated magnetic field strength and electron concentration. Given the uncertainties in these key parameters, as well as in solar wind properties close to the Sun at low heliolatitudes, we cannot yet confidently assign the quantitative role for Alfvén wave energy from this region in driving the slow solar wind.

Global ionospheric dynamics and electrodynamics during geomagnetic storms (Invited)

NASA Astrophysics Data System (ADS)

Mannucci, A. J.; Tsurutani, B.; Verkhoglyadova, O. P.; Komjathy, A.; Butala, M. D.

2013-12-01

Globally distributed total electron content (TEC) data has become an important tool for exploring the consequences of storm-time electrodynamics. Magnetosphere-ionosphere coupling during the main phase is responsible for the largest ionospheric effects observed during geomagnetic storms, mediated by global scale electrodynamics. Recent research using case studies reveals a complex picture of M-I coupling and its relationship to interplanetary drivers such as the solar wind electric field. Periods of direct coupling exist where the solar wind electric field is strongly correlated with prompt penetration electric fields, observed as enhanced vertical plasma drifts or an enhanced electrojet in the daytime equatorial ionosphere. Periods of decoupling between low latitude electric fields and the solar wind electric field are also observed, but the factors distinguishing these two types of response have not been clearly identified. Recent studies during superstorms suggest a role for the transverse (y-component) of the interplanetary magnetic field, which affects magnetospheric current systems and therefore may affect M-I coupling, with significant ionospheric consequences. Observations of the global ionospheric response to a range of geomagnetic storm intensities are presented. Scientific understanding of the different factors that affect electrodynamic aspects of M-I coupling are discussed.

The spiral field inhibition of thermal conduction in two-fluid solar wind models

NASA Technical Reports Server (NTRS)

Nerney, S.; Barnes, A.

1978-01-01

The paper reports on two-field models which include the inhibition of thermal conduction by the spiraling interplanetary field to determine whether any of the major conclusions obtained by Nerney and Barnes (1977) needs to be modified. Comparisons with straight field line models reveal that for most base conditions, the primary effect of the inhibition of thermal conduction is the bottling-up of heat in the electrons as well as the quite different temperature profiles at a large heliocentric radius. The spiral field solutions show that coronal hole boundary conditions do not correspond to states of high-speed streams as observed at 1 AU. The two-fluid models suggest that the spiral field inhibition of thermal conduction in the equatorial plane will generate higher gas pressures in comparison with flows along the solar rotation axis (between 1 and 10 AU). In particular, massive outflows of stellar winds, such as outflow from T Tauri stars, cannot be driven by thermal conduction. The conclusions of Nerney and Barnes remain essentially unchanged.

Influence of El Niño and Indian Ocean Dipole on sea level variability in the Bay of Bengal

NASA Astrophysics Data System (ADS)

Sreenivas, P.; Gnanaseelan, C.; Prasad, K. V. S. R.

2012-01-01

Zonally oscillating seasonal equatorial winds generate pairs of upwelling and downwelling Kelvin waves in the Equatorial Indian Ocean, which then advance in to the coastal Bay of Bengal. The first (second) equatorial upwelling Kelvin wave has its origin in the western (eastern) basin, whereas the downwelling Kelvin waves originate in the central basin. The observed interannual variability of these Kelvin waves is highly governed by the associated zonal wind changes in the central and eastern equatorial Indian Ocean during the anomalous years. The second downwelling (upwelling) Kelvin wave is absent (weak) during El Niño (La Niña) years, whereas the second upwelling Kelvin wave strengthened during El Niño years both in the equatorial Indian Ocean and Bay of Bengal. The large scale off equatorial Rossby waves occasionally feedback the equatorial Kelvin waves, which then strengthen the Bay of Bengal coastal Kelvin waves. The coastal Kelvin waves and the associated radiated Rossby waves from east play a dominant role in the mesoscale eddy generation in Bay of Bengal. The analysis of cyclogenesis characteristics in the bay over the past 65 years revealed that the active (suppressed) phases of cyclogenesis are coinciding with the downwelling (upwelling) planetary waves which influence the cyclone heat potential by altering the thermocline depth.

On the average configuration of the geomagnetic tail

NASA Technical Reports Server (NTRS)

Fairfield, D. H.

1978-01-01

Over 3000 hours of IMP-6 magnetic field data obtained between 20 and 33 R sub E in the geomagnetic tail have been used in a statistical study of the tail configuration. A distribution of 2.5 minute averages of B sub Z as a function of position across the tail reveals that more flux crosses the equatorial plane near the dawn and dusk flanks than near midnight. The tail field projected in the solar magnetospheric equatorial plane deviates from the X axis due to flaring and solar wind aberration by an angle alpha = -0.9 y sub SM - 1.7 where Y sub SM is in earth radii and alpha is in degrees. After removing these effects the Y component of the tail field is found to depend on interplanetary sector structure. During an away sector the B sub Y component of the tail field is on average 0.5 gamma greater than that during a toward sector, a result that is true in both tail lobes and is independent of location across the tail.

The generation of post noon F3 layers over the dip equatorial location of Thiruvananthapuram- A new perspective

NASA Astrophysics Data System (ADS)

Mridula, N.; Pant, Tarun Kumar

2018-05-01

In the present paper, occurrence of post noon F3 layers over Thiruvananthapuram (8.5°N; 77°E; dip latitude ∼ 1.5 °N), a dip equatorial station in India have been investigated. F3 layers that occur beyond 13 IST and as observed using ground based ionosonde, for the years 2004-2008 have been studied. Our analysis shows that post noon F3 layers occur mostly on CEJ days around 16 IST to 18 IST. It is found that the time of the ionospheric E-region electric field reversal as inferred from collocated ground based magnetometer observations plays a crucial role in the generation of post noon F3 layers. In fact an early reversal of electric field emerged to be the necessary condition for the formation of post noon F3 layers. A time delay of three to 4 h is observed between the electric field reversal and the formation of F3 layer. It is proposed that this early reversal causes enhanced ionization over dip equatorial region, providing an additional ion drag to the flow of thermospheric zonal wind. This leads to accumulation of more ionization and neutrals culminating in the generation of post noon F3 layers as in the case of pre noon F3 layers. These results reveal that the generation of post noon F3 layers over the dip equatorial region is a natural consequence of the variability associated with the spatio-temporal evolution of EIA and prevailing thermospheric and ionospheric dynamics, and adds a new perspective to the present understanding.

Interannual variability in equatorial Kelvin waves in the upper troposphere and lower stratosphere, and relation to the background equatorial wind

NASA Astrophysics Data System (ADS)

Suzuki, J.; Nishi, N.; Fujiwara, M.; Yoneyama, K.

2016-12-01

We investigated the influence of the background wind regime on interannual variability in equatorial Kelvin waves in the upper troposphere and lower stratosphere using the European Centre for Medium-Range Weather Forecasts 40-year reanalysis data. We focused on variability in the number of Kelvin wave events as a function of the background westerly wind, given by the zonal wind index (ZWI) in the equatorial western hemisphere. The ZWI measures the strength of the upper branch of the Walker circulation in the western hemisphere. Although the ZWI is well correlated with the sea surface temperature in the Niño-3.4 region, nearly half of the peaks of positive (negative) ZWI cases occurred outside of the typical La Niña (El Niño) season (December to February), respectively. In the positive ZWI (stronger westerly) cases, both convective activity over the western Pacific and extratropical Rossby waves were enhanced. Kelvin waves over the western hemisphere appeared frequently at 200 hPa but barely reached 100 hPa due to the strong westerly wind under this level. In the negative ZWI period, on the other hand, the number of Kelvin waves at 200 hPa decreased due to the weaker convection; Kelvin waves reached 100 hPa and propagated even farther upward. We also investigated the relationship between the ZWI and the phase speed of Kelvin waves. Kelvin waves with relatively slow phase speeds are found in negative ZWI cases, but are not found in positive ZWI cases due to the westerly background wind below the altitudes where Kelvin waves commonly propagate.

Ocean-state dependency of the equatorial Pacific response to Westerly Wind Events

NASA Astrophysics Data System (ADS)

Puy, martin; Lengaigne, matthieu; Madec, gurvan; Vialard, jerome; Guilyardi, eric

2015-04-01

Short-lived wind events in the equatorial Pacific strongly influence the El Niño/Southern Oscillation (ENSO) evolution. In the first part of this study, we found in observations that both westerly wind events (WWEs) and their easterly wind events (EWEs) counterpart are unambiguously associated with increased Madden Julian oscillation and atmospheric equatorial Rossby waves activity, i.e. that the atmospheric state influences the occurrence probability of WWEs. In the second part, we investigate how the oceanic state modulates the response to these WWEs by applying the same WWE forcing over a interannually-varying ocean state in an OGCM simulation. We find that the amplitude of the SST response, both at the warm pool eastern edge and in the eastern Pacific, can vary by a factor of up to two depending on the ocean state. The sea level and current response are also clearly modulated, with varying contributions of the second and third baroclinic modes depending on the oceanic stratification. We will discuss the mechanisms by which the oceanic state modulates the response to the WWE, and how this could contribute to their impact on ENSO

Recent Advances in Atmospheric, Solar-Terrestrial Physics and Space Weather From a North-South network of scientists [2006-2016] PART A: TUTORIAL

NASA Astrophysics Data System (ADS)

Amory-Mazaudier, C.; Menvielle, M.; Curto, J-J.; Le Huy, M.

2017-12-01

This paper reviews scientific advances achieved by a North-South network between 2006 and 2016. These scientific advances concern Solar Terrestrial Physics, Atmospheric Physics and Space Weather. In this part A, we introduce knowledge on the Sun-Earth system. We consider the physical process of the dynamo which is present in the Sun, in the core of the Earth and also in the regions between the Sun and the Earth, the solar wind-magnetosphere and the ionosphere. Equations of plasma physics and Maxwell's equations will be recalled. In the Sun-Earth system there are permanent dynamos (Sun, Earth's core, solar wind - magnetosphere, neutral wind - ionosphere) and non-permanent dynamos that are activated during magnetic storms in the magnetosphere and in the ionosphere. All these dynamos have associated electric currents that affect the variations of the Earth's magnetic field which are easily measurable. That is why a part of the tutorial is also devoted to the magnetic indices which are indicators of the electric currents in the Sun-Earth system. In order to understand some results of the part B, we present some characteristics of the Equatorial region and of the electrodynamics coupling the Auroral and Equatorial regions.

Association of whale sharks (Rhincodon typus) with thermo-biological frontal systems of the eastern tropical Pacific.

PubMed

Ryan, John P; Green, Jonathan R; Espinoza, Eduardo; Hearn, Alex R

2017-01-01

Satellite tracking of 27 whale sharks in the eastern tropical Pacific, examined in relation to environmental data, indicates preferential occupancy of thermo-biological frontal systems. In these systems, thermal gradients are caused by wind-forced circulation and mixing, and biological gradients are caused by associated nutrient enrichment and enhanced primary productivity. Two of the frontal systems result from upwelling, driven by divergence in the current systems along the equator and the west coast of South America; the third results from wind jet dynamics off Central America. All whale sharks were tagged near Darwin Island, Galápagos, within the equatorial Pacific upwelling system. Occupancy of frontal habitat is pronounced in synoptic patterns of shark locations in relation to serpentine, temporally varying thermal fronts across a zonal expanse > 4000 km. 80% of shark positions in northern equatorial upwelling habitat and 100% of positions in eastern boundary upwelling habitat were located within the upwelling front. Analysis of equatorial shark locations relative to thermal gradients reveals occupancy of a transition point in environmental stability. Equatorial subsurface tag data show residence in shallow, warm (>22°C) water 94% of the time. Surface zonal current speeds for all equatorial tracking explain only 16% of the variance in shark zonal movement speeds, indicating that passive drifting is not a primary determinant of movement patterns. Movement from equatorial to eastern boundary frontal zones occurred during boreal winter, when equatorial upwelling weakens seasonally. Off Peru sharks tracked upwelling frontal positions within ~100-350 km from the coast. Off Central America, the largest tagged shark (12.8 m TL) occupied an oceanic front along the periphery of the Panama wind jet. Seasonal movement from waning equatorial upwelling to productive eastern boundary habitat is consistent with underlying trophic dynamics. Persistent shallow residence in thermo-biological frontal zones suggests the role of physical-biological interactions that concentrate food resources.

Association of whale sharks (Rhincodon typus) with thermo-biological frontal systems of the eastern tropical Pacific

PubMed Central

Green, Jonathan R.; Espinoza, Eduardo; Hearn, Alex R.

2017-01-01

Satellite tracking of 27 whale sharks in the eastern tropical Pacific, examined in relation to environmental data, indicates preferential occupancy of thermo-biological frontal systems. In these systems, thermal gradients are caused by wind-forced circulation and mixing, and biological gradients are caused by associated nutrient enrichment and enhanced primary productivity. Two of the frontal systems result from upwelling, driven by divergence in the current systems along the equator and the west coast of South America; the third results from wind jet dynamics off Central America. All whale sharks were tagged near Darwin Island, Galápagos, within the equatorial Pacific upwelling system. Occupancy of frontal habitat is pronounced in synoptic patterns of shark locations in relation to serpentine, temporally varying thermal fronts across a zonal expanse > 4000 km. 80% of shark positions in northern equatorial upwelling habitat and 100% of positions in eastern boundary upwelling habitat were located within the upwelling front. Analysis of equatorial shark locations relative to thermal gradients reveals occupancy of a transition point in environmental stability. Equatorial subsurface tag data show residence in shallow, warm (>22°C) water 94% of the time. Surface zonal current speeds for all equatorial tracking explain only 16% of the variance in shark zonal movement speeds, indicating that passive drifting is not a primary determinant of movement patterns. Movement from equatorial to eastern boundary frontal zones occurred during boreal winter, when equatorial upwelling weakens seasonally. Off Peru sharks tracked upwelling frontal positions within ~100–350 km from the coast. Off Central America, the largest tagged shark (12.8 m TL) occupied an oceanic front along the periphery of the Panama wind jet. Seasonal movement from waning equatorial upwelling to productive eastern boundary habitat is consistent with underlying trophic dynamics. Persistent shallow residence in thermo-biological frontal zones suggests the role of physical-biological interactions that concentrate food resources. PMID:28854201

Sensitivity of Coupled Tropical Pacific Model Biases to Convective Parameterization in CESM1

NASA Astrophysics Data System (ADS)

Woelfle, M. D.; Yu, S.; Bretherton, C. S.; Pritchard, M. S.

2018-01-01

Six month coupled hindcasts show the central equatorial Pacific cold tongue bias development in a GCM to be sensitive to the atmospheric convective parameterization employed. Simulations using the standard configuration of the Community Earth System Model version 1 (CESM1) develop a cold bias in equatorial Pacific sea surface temperatures (SSTs) within the first two months of integration due to anomalous ocean advection driven by overly strong easterly surface wind stress along the equator. Disabling the deep convection parameterization enhances the zonal pressure gradient leading to stronger zonal wind stress and a stronger equatorial SST bias, highlighting the role of pressure gradients in determining the strength of the cold bias. Superparameterized hindcasts show reduced SST bias in the cold tongue region due to a reduction in surface easterlies despite simulating an excessively strong low-level jet at 1-1.5 km elevation. This reflects inadequate vertical mixing of zonal momentum from the absence of convective momentum transport in the superparameterized model. Standard CESM1simulations modified to omit shallow convective momentum transport reproduce the superparameterized low-level wind bias and associated equatorial SST pattern. Further superparameterized simulations using a three-dimensional cloud resolving model capable of producing realistic momentum transport simulate a cold tongue similar to the default CESM1. These findings imply convective momentum fluxes may be an underappreciated mechanism for controlling the strength of the equatorial cold tongue. Despite the sensitivity of equatorial SST to these changes in convective parameterization, the east Pacific double-Intertropical Convergence Zone rainfall bias persists in all simulations presented in this study.

Seasonal influence of ENSO on the Atlantic ITCZ and equatorial South America

NASA Astrophysics Data System (ADS)

Münnich, M.; Neelin, J. D.

2005-11-01

In late boreal spring, especially May, a strong relationship exists in observations among precipitation anomalies over equatorial South America and the Atlantic intertropical convergence zone (ITCZ), and eastern equatorial Pacific and central equatorial Atlantic sea surface temperature anomalies (SSTA). A chain of correlations of equatorial Pacific SSTA, western equatorial Atlantic wind stress (WEA), equatorial Atlantic SSTA, sea surface height, and precipitation supports a causal chain in which El Niño/Southern Oscillation (ENSO) induces WEA stress anomalies, which in turn affect Atlantic equatorial ocean dynamics. These correlations show strong seasonality, apparently arising within the atmospheric links of the chain. This pathway and the influence of equatorial Atlantic SSTA on South American rainfall in May appear independent of that of the northern tropical Atlantic. Brazil's Nordeste is affected by the northern tropical Atlantic. The equatorial influence lies further to the north over the eastern Amazon and the Guiana Highlands.

Numerical modeling of the equatorial ionization anomaly (EIA), equatorial temperature and wind anomaly (ETWA) and equatorial electron temperature anomaly (EETA) on the basis of the GSM TIP

NASA Astrophysics Data System (ADS)

Klimenko, M. V.; Klimenko, V. V.; Bryukhanov, V. V.

On the basis of Global Self-consistent Model of Thermosphere Ionosphere and Protonosphere GSM TIP developed in WD IZMIRAN the calculations of the behavior of thermosphere F-region and upper ionosphere parameters at middle and low geomagnetic latitudes are carried out The calculations were carried out with use the new block of the calculation of electric fields in the ionosphere in which the decision of the three-dimensional equation describing the law of the conservation of the full current density in the ionosphere of the Earth is realized by adduction it to the two-dimensional by integration on the thickness of the current conductive layer of the ionosphere along equipotential geomagnetic field lines The calculations of the neutral atmosphere composition and temperature were executed with use of the MSIS model The quite geomagnetic conditions of the equinox were considered in the minimum of the solar activity There are presented the calculated global distributions of the critical frequency of the F2-layer of ionosphere for the different moments UT the latitudinal course of the N e and T e in the F-region and upper ionosphere in the vicinity of geomagnetic equator and unrolling on UT of the calculated velocities of zonal component of the thermospheric wind and ion temperature in the F-region of ionosphere as well as critical frequency and height of the F2-layer maximum of the ionosphere at three longitude chains of the stations Brazilian -- Fortaleza 4 0 r S 38 0 r W Jicamarca 11 9 r S 76 0 r W Cachoeira

Low-latitude thermospheric neutral winds determined from AE-E measurements of the 6300-A nightglow at solar maximum

NASA Technical Reports Server (NTRS)

Burrage, M. D.; Abreu, V. J.; Fesen, C. G.

1990-01-01

Atmosphere Explorer E (AE-E) measurements of the O(1D) 6300-A emission in the nighttime equatorial thermosphere are used to infer the height of the F2 layer peak as a function of latitude and local time. The investigation is conducted both for northern hemisphere winter solstice and for spring equinox, under solar maximum conditions. The layer heights are used to derive magnetic meridional components of the transequatorial neutral wind, in conjunction with the MSIS-86 model and previous Jicamarca incoherent scatter measurements of the zonal electric field. The AE-E wind estimates indicate a predominant summer to winter flow for the winter solstice case. Comparisons are made with the empirical horizontal wind model HWM87 and with winds generated by the thermospheric general circulation model. The model predictions and experimental results are generally in good agreement, confirming the applicability of visible airglow data to studies of the global neutral wind pattern.

Ω-slow Solutions and Be Star Disks

NASA Astrophysics Data System (ADS)

Araya, I.; Jones, C. E.; Curé, M.; Silaj, J.; Cidale, L.; Granada, A.; Jiménez, A.

2017-09-01

As the disk formation mechanism(s) in Be stars is(are) as yet unknown, we investigate the role of rapidly rotating radiation-driven winds in this process. We implemented the effects of high stellar rotation on m-CAK models accounting for the shape of the star, the oblate finite disk correction factor, and gravity darkening. For a fast rotating star, we obtain a two-component wind model, I.e., a fast, thin wind in the polar latitudes and an Ω-slow, dense wind in the equatorial regions. We use the equatorial mass densities to explore Hα emission profiles for the following scenarios: (1) a spherically symmetric star, (2) an oblate star with constant temperature, and (3) an oblate star with gravity darkening. One result of this work is that we have developed a novel method for solving the gravity-darkened, oblate m-CAK equation of motion. Furthermore, from our modeling we find that (a) the oblate finite disk correction factor, for the scenario considering the gravity darkening, can vary by at least a factor of two between the equatorial and polar directions, influencing the velocity profile and mass-loss rate accordingly, (b) the Hα profiles predicted by our model are in agreement with those predicted by a standard power-law model for following values of the line-force parameters: 1.5≲ k≲ 3,α ˜ 0.6, and δ ≳ 0.1, and (c) the contribution of the fast wind component to the Hα emission line profile is negligible; therefore, the line profiles arise mainly from the equatorial disks of Be stars.

Convectively Coupled Equatorial Waves in Reanalysis and CMIP5 Simulations

NASA Astrophysics Data System (ADS)

Castanheira, J. M.; Marques, C. A. F.

2014-12-01

Convectively coupled equatorial waves (CCEWs) are a result of the interplay between the physics and dynamics in the tropical atmosphere. As a result of such interplay, tropical convection appears often organized into synoptic to planetary-scale disturbances with time scales matching those of equatorial shallow water waves. CCEWs have broad impacts within the tropics, and their simulation in general circulation models is still problematic. Several studies showed that dispersion of those waves characteristics fit the dispersion curves derived from the Matsuno's (1966) solutions of the shallow water equations on the equatorial beta plane, namely, Kelvin, equatorial Rossby, mixed Rossby-gravity, and inertio-gravity waves. However, the more common methodology used to identify those waves is yet controversial. In this communication a new methodology for the diagnosis of CCEWs will be presented. It is based on a pre-filtering of the geopotential and horizontal wind, using 3--D normal modes functions of the adiabatic linearized equations of a resting atmosphere, followed by a space--time spectral analysis to identify the spectral regions of coherence. The methodology permits a direct detection of various types of equatorial waves, compares the dispersion characteristics of the coupled waves with the theoretical dispersion curves and allows an identification of which vertical modes are more involved in the convection. Moreover, the proposed methodology is able to show the existence of free dry waves and moist coupled waves with a common vertical structure, which is in conformity with the effect of convective heating/cooling on the effective static stability, as traduced in the gross moist stability concept. The methodology is also sensible to Doppler shifting effects. The methodology has been applied to the ERA-Interim horizontal wind and geopotential height fields and to the interpolated Outgoing Longwave Radiation (OLR) data produced by the National Oceanic and Atmospheric Administration. The same type of data (i.e. u, v, Φ and OLR) from CMIP5 historical experiments (1976-2005) were analyzed. The obtained results provide examples of the aforementioned effects and points deficiencies in the models.

Analysis of Venusian Atmospheric Two-Dimensional Winds and Features Using Venus Express, Akatsuki, and Ground-Based Images

NASA Astrophysics Data System (ADS)

McCabe, Ryan M.; Gunnarson, Jacob; Sayanagi, Kunio M.; Blalock, John J.; Peralta, Javier; Gray, Candace L.; McGouldrick, Kevin; Imamura, Takeshi; Watanabe, Shigeto

2017-10-01

We investigate the horizontal dynamics of Venus’s atmosphere at cloud-top level. In particular, we focus on the atmospheric superrotation, in which the equatorial atmosphere rotates with a period of approximately 4-5 days (~60 times faster than the solid planet). The superrotation’s forcing and maintenance mechanisms remain to be explained. Temporal evolution of the zonal (latitudinal direction) wind could reveal the transport of energy and momentum in/out of the equatorial region, and eventually shed light on mechanisms that maintain the Venusian superrotation. As a first step, we characterize the zonal mean wind field of Venus between 2006 and 2013 in ultraviolet images captured by the Venus Monitoring Camera (VMC) on board the ESA Venus Express (VEX) spacecraft which observed Venus’s southern hemisphere. Our measurements show that, between 2006 and 2013, the westward wind speed at mid- to equatorial latitudes exhibit an increase of ~20 m/s; these results are consistent with previous studies by Kouyama et al. 2013 and Khatuntsev et al. 2013. The meridional component of the wind could additionally help us characterize large-scale cloud features and their evolution that may be connected to such superrotation. We also conduct ground-based observations contemporaneously with JAXA’s Akatsuki orbiter at the 3.5 m Astrophysical Research Consortium (ARC) telescope at the Apache Point Observatory (APO) in Sunspot, NM to extend our temporal coverage to present. Images we have captured at APO to date demonstrate that, even under unfavorable illumination, it is possible to see large features that could be used for large-scale feature tracking to be compared to images taken by Akatsuki. Our work has been supported by the following grants: NASA PATM NNX14AK07G, NASA MUREP NNX15AQ03A, NSF AAG 1212216, and JAXA’s ITYF Fellowship.Kouyama, T. et al (2013), J. Geophys. Res. Planets, 118, 37-46, doi:10.1029/2011JE004013.Khatuntsev et al. (2013), Icarus, 226, 140-158, doi:10.1016/j.icarus.2013.05.018

Vertical transport of Kelut volcanic stratospheric aerosols observed by the equatorial lidar and the Equatorial Atmosphere Radar

NASA Astrophysics Data System (ADS)

Nagasawa, C.; Abo, M.; Shibata, Y.

2017-12-01

The transport of substance between stratosphere and troposphere in the equatorial region makes an impact to the global climate change, but it has a lot of unknown behaviors. We have performed the lidar observations for survey of atmospheric structure of troposphere, stratosphere, and mesosphere over Kototabang (0.2S, 100.3E), Indonesia in the equatorial region since 2004. Kelut volcano (7.9S, 112.3E) in the Java island of Indonesia erupted on 13 February 2014. The CALIOP observed that the eruption cloud reached 26km above sea level in the tropical stratosphere, but most of the plume remained at 19-20 km over the tropopause. By CALIOP data analysis, aerosol clouds spread in the longitude direction with the lapse of time and arrived at equator in 5 days. After aerosol clouds reached equator, they moved towards the east along the equator by strong eastward equatorial wind of QBO. In June 2014 (4 months after the eruption), aerosol transport from the stratosphere to the troposphere were observed by the polarization lidar at Kototabang. At the same time, we can clearly see down phase structure of vertical wind velocity observed by EAR (Equatorial Atmosphere Radar) generated by the equatorial Kelvin wave. We investigate the transport of substance between stratosphere and troposphere in the equatorial region by data which have been collected by the polarization lidar at Kototabang and the EAR after Kelut volcano eruption. Using combination of ground based lidar, satellite based lidar, and atmosphere radar, we can get valuable evidence of equatorial transport of substance between the troposphere and the lower stratosphere. This work was supported by Collaborative Research based on MU Radar and Equatorial Atmosphere Radar.

Variation of Equatorial F-region Vertical Neutral Wind and Neutral Temperature during Geomagnetic Storms: Brazil FPI Observations

NASA Astrophysics Data System (ADS)

Sheng, C.; De La Garza, J. L.; Deng, Y.; Makela, J. J.; Fisher, D. J.; Meriwether, J. W.; Mesquita, R.

2015-12-01

An accurate description of vertical neutral winds in the thermosphere is essential to understand how the upper atmosphere responds to the geomagnetic storms. However, vertical wind measurements are difficult to obtain and there are still limited data. Recent observation deployments now permit substantial progress on this issue. In this paper, neutral vertical wind data from Brazil FPI observations at around 240 km altitude during 2009 to 2015 are used for the study of the equatorial vertical wind and neutral temperature variation during geomagnetic activity times. First, the observations during several particular storm periods will be analyzed. Secondly, Epoch analysis will be used to bin all the observed events together to investigate the climatological features of vertical wind and temperature during storms. The results will give us an unprecedented view of the nighttime vertical wind and neutral temperature variations at low latitudes, which is critical to specify the dynamics of the upper atmosphere.

Quiet Time Depression of the Equatorial Electrojet and Dynamics of the F-layer Ionosphere

NASA Astrophysics Data System (ADS)

Khadka, S.; Valladares, C. E.; Doherty, P.

2017-12-01

The depression of the equatorial electrojet (EEJ) is marked by a westward current due to streaming movement of laterally limited (±3°) charged particles in the ionospheric E region during the day along the magnetic equator. It is a complex low-latitude phenomenon and driven by various sources of electric fields associated with global neutral wind, solar tidal force, Interplanetary magnetic Field (IMF), etc. This unique physical property of the equatorial ionosphere holds a great promise for sorting out the governing mechanism of the dayside ionospheric electrodynamics and the onset of the enigmatic plasma structures in the ionospheric layers. Present study provides an overview of the special sequence of the longitudinal, seasonal, and occurrence rate variability of the depression of the EEJ, including its temporal variation, using data from an excellent chain of magnetic and ionospheric observatories along the low-latitude regions. A case and statistical study of the geomagnetically quiet time depression of EEJ strengths is presented using a pair of magnetometers, one located at the dip equator and another off the dip equator (±6° to ±9° away) in the American low-latitude regions. The significance of the variability of the depression of the EEJ current observed in the scenario of vertical drifts, sporadic E-layer, the equatorial F region plasma fountain, and height of the peak ionization in the F-layer, as well as GPS-TEC distributions, will be investigated.

A general circulation model study of the solar and QBO modulation of the stratospheric circulation during the northern hemisphere winter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kodera, Kunihiko; Chiba, Masaru; Shibata, Kiyotaka

1991-07-01

A general circulation model has been used to study the modulation of north-polar temperatures during winter by both solar activity and the equatorial quasi-biennial oscillation (QBO). The variation of solar activity was simulated by changing the heating rate due to the absorption of ultraviolet (UV) radiation by ozone, while the QBO zonal wind fields were reproduced by incorporating zonal-momentum sources in the equatorial stratosphere. A total of 10 experiments were conducted by changing the heating rate from 70 to 110% for each of the simulated QBO easterly and westerly cases. The results of the numerical experiments show modulation effects similarmore » to those found by Labitzke (1987) in the 30-mb temperatures at the North Pole.« less

Equatorial Oscillations in Jupiter's and Saturn's Atmospheres

NASA Technical Reports Server (NTRS)

Flasar, F. Michael; Guerlet, S.; Fouchet, T.; Schinder, P. J.

2011-01-01

Equatorial oscillations in the zonal-mean temperatures and zonal winds have been well documented in Earth's middle atmosphere. A growing body of evidence from ground-based and Cassini spacecraft observations indicates that such phenomena also occur in the stratospheres of Jupiter and Saturn. Earth-based midinfrared measurements spanning several decades have established that the equatorial stratospheric temperatures on Jupiter vary with a cycle of 4-5 years and on Saturn with a cycle of approximately 15 years. Spectra obtained by the Composite Infrared Spectrometer (CIRS) during the Cassini swingby at the end of 2000, with much better vertical resolution than the ground-based data, indicated a series of vertically stacked warm and cold anomalics at Jupiter's equator; a similar structurc was seen at Saturn's equator in CIRS limb measurements made in 2005, in the early phase of Cassini's orbital tour. The thermal wind equation implied similar patterns of mean zonal winds increasing and decreasing with altitude. On Saturn the peak-to-pcak amplitude of this variation was nearly 200 meters per second. The alternating vertical pattern of wanner and colder cquatorial tcmperatures and easterly and westerly tendencies of the zonal winds is seen in Earth's equatorial oscillations, where the pattern descends with time, The Cassini Jupiter and early Saturn observations were snapshots within a limited time interval, and they did not show the temporal evolution of the spatial patterns. However, more recent Saturn observations by CIRS (2010) and Cassini radio-occultation soundings (2009-2010) have provided an opportunity to follow the change of the temperature-zonal wind pattern, and they suggest there is descent, at a rate of roughly one scale height over four years. On Earth, the observed descent in the zonal-mean structure is associated with the absorption of a combination of vertically propagating waves with easlerly and westerly phase velocities. The peak-to-peak zonal wind amplitude in the oscillation pattern and the rate of descent constrain the absorbed wave flux of zonal momentum. On Saturn this is approximately 0.05 square meters per square seconds, which is comparable to if not greater than that associated with the terrestrial oscillations. We discuss possible candidates for the absorbed waves on Saturn. On Earth the wave forcing of the equatorial oscillation generales secondary circulations that can affcct the temperature and wind structure at latitudes well away from the equator, and we discuss possible evidence of that on Saturn.

Acceleration region of the slow solar wind in corona

NASA Astrophysics Data System (ADS)

Abbo, L.; Antonucci, E.; Mikić, Z.; Riley, P.; Dodero, M. A.; Giordano, S.

We present the results of a study concerning the physical parameters of the plasma of the extended corona in the low-latitude and equatorial regions, in order to investigate the sources of the slow solar wind during the minimum of solar activity. The equatorial streamer belt has been observed with the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO from August 19 to September 1, 1996. The spectroscopic diagnostic technique applied in this study, based on the OVI 1032, 1037 Ålines, allows us to determine both the solar wind velocity and the electron density of the extended corona. The main result of the analysis is the identification of the acceleration region of the slow wind, whose outflow velocity is measured in the range from 1.7 up to 3.5 solar radii.

Ocean Color and the Equatorial Annual Cycle in the Pacific

NASA Astrophysics Data System (ADS)

Hammann, A. C.; Gnanadesikan, A.

2012-12-01

The presence of chlorophyll, colored dissolved organic matter (CDOM) and other scatterers in ocean surface waters affect the flux divergence of solar radiation and thus the vertical distribution of radiant heating of the ocean. While this may directly alter the local mixed-layer depth and temperature (Martin 1985; Strutton & Chavez 2004), non-local changes are propagated through advection (Manizza et al. 2005; Murtugudde et al. 2002; Nakamoto et al. 2001; Sweeny et al. 2005). In and coupled feedbacks (Lengaigne et al. 2007; Marzeion & Timmermann 2005). Anderson et al. (2007), Anderson et al. (2009) and Gnanadesikan & Anderson (2009) have performed a series of experiments with a fully coupled climate model which parameterizes the e-folding depth of solar irradiance in terms of surface chlorophyll-a concentration. The results have so far been discussed with respect to the climatic mean state and ENSO variability in the tropical Pacific. We extend the discussion here to the Pacific equatorial annual cycle. The focus of the coupled experiments has been the sensitivity of the coupled system to regional differences in chlorophyll concentration. While runs have been completed with realistic SeaWiFS-derived monthly composite chlorophyll ('green') and with a globally chlorophyll-free ocean ('blue'), the concentrations in two additional runs have been selectively set to zero in specific regions: the oligotrophic subtropical gyres ('gyre') in one case and the mesotrophic gyre margins ('margin') in the other. The annual cycle of ocean temperatures exhibits distinctly reduced amplitudes in the 'blue' and 'margin' experiments, and a slight reduction in 'gyre' (while ENSO variability almost vanishes in 'blue' and 'gyre', but amplifies in 'margin' - thus the frequently quoted inverse correlation between ENSO and annual amplitudes holds only for the 'green' / 'margin' comparison). It is well-known that on annual time scales, the anomalous divergence of surface currents and vertical upwelling acting on a mean temperature field contribute the largest term to SST variability (Köberle & Philander 1994; Li & Philander 1996). We examine whether it is changes in the surface currents (driven by the annual cycle of winds) or changes in the mean temperature fields (driven by enhanced penetration of solar radiation) that drive the differences between the coupled models. We do this using a simple linear equatorial-wave model, which, when forced with an annual harmonic of wind stresses, reproduces the essential characteristics of annual ocean current anomalies. The model solves the linearized Boussinesq equations by expansion into discrete modes in all spatial dimensions (McCreary 1981; Lighthill 1969). Both the wind forcing and the (laterally homogeneous) background density profile are constructed as approximations to the coupled model fields. The annual perturbation currents from the wave model are then used to advect the mean temperature fields from the coupled model experiments. While the difference in the mean stratification explains the difference between the 'green' and 'blue' cases. For the other two cases, it appears that changes in the annual wind fields need also be taken into account. An initial hypothesis is that the hemispheric asymmetry in the annual amplitude of wind stress curl that is most important in setting the amplitude of the annual cycle on the equator.

Equatorial superrotation in a thermally driven zonally symmetric circulation

NASA Technical Reports Server (NTRS)

Mayr, H. G.; Harris, I.

1981-01-01

Near the equator where the Coriolis force vanishes, the momentum balance for the axially symmetric circulation is established between horizontal and vertical diffusion, which, a priori, does not impose constraints on the direction or magnitude of the zonal winds. Solar radiation absorbed at low latitudes is a major force in driving large scale motions with air rising near the equator and falling at higher latitudes. In the upper leg of the meridional cell, angular momentum is redistributed so that the atmosphere tends to subrotate (or corotate) at low latitudes and superrotate at high latitudes. In the lower leg, however, the process is reversed and produces a tendency for the equatorial region to superrotate. The outcome depends on the energy budget which is closely coupled to the momentum budget through the thermal wind equation; a pressure (temperature) maximum is required to sustain equatorial superrotation. Such a condition arises in regions which are convectively unstable and the temperature lapse rate is superadiabatic. It should arise in the tropospheres of Jupiter and Saturn; planetary energy from the interior is carried to higher altitudes where radiation to space becomes important. Upward equatorial motions in the direct and indirect circulations (Ferrel-Thomson type) imposed by insolation can then trap dynamic energy for equatorial heating which can sustain the superrotation of the equatorial region.

Role of atmosphere-ocean interactions in supermodeling the tropical Pacific climate

NASA Astrophysics Data System (ADS)

Shen, Mao-Lin; Keenlyside, Noel; Bhatt, Bhuwan C.; Duane, Gregory S.

2017-12-01

The supermodel strategy interactively combines several models to outperform the individual models comprising it. A key advantage of the approach is that nonlinear improvements can be achieved, in contrast to the linear weighted combination of individual unconnected models. This property is found in a climate supermodel constructed by coupling two versions of an atmospheric model differing only in their convection scheme to a single ocean model. The ocean model receives a weighted combination of the momentum and heat fluxes. Optimal weights can produce a supermodel with a basic state similar to observations: a single Intertropical Convergence zone (ITCZ), with a western Pacific warm pool and an equatorial cold tongue. This is in stark contrast to the erroneous double ITCZ pattern simulated by both of the two stand-alone coupled models. By varying weights, we develop a conceptual scheme to explain how combining the momentum fluxes of the two different atmospheric models affects equatorial upwelling and surface wind feedback so as to give a realistic basic state in the tropical Pacific. In particular, we propose a mechanism based on the competing influences of equatorial zonal wind and off-equatorial wind stress curl in driving equatorial upwelling in the coupled models. Our results show how nonlinear ocean-atmosphere interaction is essential in combining these two effects to build different sea surface temperature structures, some of which are realistic. They also provide some insight into observed and modelled tropical Pacific climate.

Role of atmosphere-ocean interactions in supermodeling the tropical Pacific climate.

PubMed

Shen, Mao-Lin; Keenlyside, Noel; Bhatt, Bhuwan C; Duane, Gregory S

2017-12-01

The supermodel strategy interactively combines several models to outperform the individual models comprising it. A key advantage of the approach is that nonlinear improvements can be achieved, in contrast to the linear weighted combination of individual unconnected models. This property is found in a climate supermodel constructed by coupling two versions of an atmospheric model differing only in their convection scheme to a single ocean model. The ocean model receives a weighted combination of the momentum and heat fluxes. Optimal weights can produce a supermodel with a basic state similar to observations: a single Intertropical Convergence zone (ITCZ), with a western Pacific warm pool and an equatorial cold tongue. This is in stark contrast to the erroneous double ITCZ pattern simulated by both of the two stand-alone coupled models. By varying weights, we develop a conceptual scheme to explain how combining the momentum fluxes of the two different atmospheric models affects equatorial upwelling and surface wind feedback so as to give a realistic basic state in the tropical Pacific. In particular, we propose a mechanism based on the competing influences of equatorial zonal wind and off-equatorial wind stress curl in driving equatorial upwelling in the coupled models. Our results show how nonlinear ocean-atmosphere interaction is essential in combining these two effects to build different sea surface temperature structures, some of which are realistic. They also provide some insight into observed and modelled tropical Pacific climate.

The Onset of the 1997-1998 El Nino and its Impact on the Phytoplankton Community of the Central Equatorial Pacific

NASA Technical Reports Server (NTRS)

Chavez, F. P.; Strutton, P. G.; McPhaden, M. J.

1996-01-01

Using physical and bio-optical data from moorings in the central equatorial Pacific, the perturbations to phytoplankton biomass and productivity associated with the onset of the 1997-98 El Nino event were investigated. The data presented depict the physical progression of El Nino onset, from reversal of the trade winds in the western equatorial Pacific, through eastward propagation of equatorially trapped Kelvin waves and advection of waters from the nutrient-poor western equatorial warm pool. The physical perturbations led to fluctuations in phytoplankton biomass, quantum yield of fluorescence and a 50% reduction in primary productivity.

Latitude-dependent delay in the responses of the equatorial electrojet and Sq currents to X-class solar flares

NASA Astrophysics Data System (ADS)

Nogueira, Paulo A. B.; Abdu, Mangalathayil A.; Souza, Jonas R.; Denardini, Clezio M.; Barbosa Neto, Paulo F.; Serra de Souza da Costa, João P.; Silva, Ana P. M.

2018-01-01

We have analyzed low-latitude ionospheric current responses to two intense (X-class) solar flares that occurred on 13 May 2013 and 11 March 2015. Sudden intensifications, in response to solar flare radiation impulses, in the Sq and equatorial electrojet (EEJ) currents, as detected by magnetometers over equatorial and low-latitude sites in South America, are studied. In particular we show for the first time that a 5 to 8 min time delay is present in the peak effect in the EEJ, with respect that of Sq current outside the magnetic equator, in response to the flare radiation enhancement. The Sq current intensification peaks close to the flare X-ray peak, while the EEJ peak occurs 5 to 8 min later. We have used the Sheffield University Plasmasphere-Ionosphere Model at National Institute for Space Research (SUPIM-INPE) to simulate the E-region conductivity enhancement as caused by the flare enhanced solar extreme ultraviolet (EUV) and soft X-rays flux. We propose that the flare-induced enhancement in neutral wind occurring with a time delay (with respect to the flare radiation) could be responsible for a delayed zonal electric field disturbance driving the EEJ, in which the Cowling conductivity offers enhanced sensitivity to the driving zonal electric field.

Equatorial ion composition, 140-200 km, based on Atmosphere Explorer E data

NASA Technical Reports Server (NTRS)

Miller, N. J.; Grebowsky, J. M.; Hedin, A. E.; Spencer, N. W.

1993-01-01

We have used in situ measurements of ion composition and horizontal winds, taken from equatorial orbiting Atmosphere Explorer E in eccentric orbit during 1975-1976 to investigate the bottomside ionosphere at altitudes 140-200 km. Representative daytime altitude profiles of ionization were stable against wide variations in horizontal wind patterns. Special features that sometimes appeared in the structured nightside ionization were apparent ion composition waves, intermediate layers of enhanced ionization, and ionization depletions similar to equatorial ionization bubbles. Apparent ion composition waves displayed a horizontal wave length of about 650 km. Enhanced layers of ionization appeared to be newly separated from the bottomside midnight F layer; its ions were primarily NO(+) and O2(+) without significant densities of metallic ions, an indication that metallic ions are not required to produce the layers at altitudes above 140 km. Equatorial ionization depletions were observed at lower altitudes than previously reported and displayed molecular ion depletions as well as O(+) depletions.

Four-peak longitudinal distribution of the equatorial plasma bubbles observed in the topside ionosphere: Possible troposphere tide influence

NASA Astrophysics Data System (ADS)

Sidorova, L. N.; Filippov, S. V.

2018-03-01

In this paper we consider an idea of the troposphere tide influence on the character of the longitudinal variations in the distribution of the equatorial plasma bubbles (EPBs) observed in the topside ionosphere. For this purpose, the obtained EPB longitudinal patterns were compared with the thermosphere and ionosphere characteristics having the prominent "wave-like" longitudinal structures with wave number 4, which are uniquely associated with the influence of the troposphere DE3 tides. The characteristics of the equatorial mass density anomaly (EMA), equatorial ionization anomaly (EIA), zonal wind and pre-reversal E × B drift enhancement (PRE) were used for comparison. The equinox seasons during high solar activity were under consideration. It was obtained that the longitudinal patterns of the EMA and zonal wind show the surprising similarity with the EPB distributions (R ≅ 0.8, R ≅ 0.72). On the other hand, the resemblance with the ionosphere characteristics (EIA, PRE) is rather faint (R ≅ 0.37, R ≅ 0.12). It was shown that the thermosphere zonal winds are the most possible transfer mediator of the troposphere DE3 tide influence. The most successful moment for the transfer of the troposphere DE3 tide energy takes place in the beginning of the EPB production, namely, during the seed perturbation development.

A Simulation Study of the Equatorial Ionospheric Response to the October 2013 Geomagnetic Storm

NASA Astrophysics Data System (ADS)

Ren, Dexin; Lei, Jiuhou

2017-09-01

The ionospheric observation from ionosonde at Sao Luis (2.5°S, 44.2°W; 6.68°S dip latitude) around the magnetic equator showed that the nighttime ionospheric F2 layer was uplifted by more than 150 km during the October 2013 geomagnetic storm. The changes of the F2 peak height (hmF2) at the magnetic equator were generally attributed to the variations of vertical drift associated with zonal electric fields. In this paper, the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulation results are utilized to explore the possible physical mechanisms responsible for the observed increase of hmF2 at Sao Luis. The TIEGCM generally reproduced the changes of F2 peak electron density (NmF2) and its height (hmF2) during the main and recovery phases of the October 2013 storm. A series of controlled simulations revealed that storm time hmF2 changes at the magnetic equator are not purely associated with the changes of electric fields; horizontal plasma transport due to meridional winds and thermospheric expansion also contributed significantly to the profound increase of nighttime hmF2 observed at Sao Luis on 2 October. Moreover, the changes of meridional winds and neutral temperature in the equatorial region are associated with storm time traveling atmospheric disturbances originating from high latitudes.

Substorm-associated large-scale magnetic field changes in the magnetotail: a prerequisite for magnetotail deflation events

NASA Astrophysics Data System (ADS)

Nakai, H.; Kamide, Y.

2003-04-01

An attempt is made to search for a critical condition in the lobe magnetic field to initiate large-scale magnetic field changes associated with substorm expansions. Using data from ISEE-1 for 1978, sudden decreases in the lobe magnetic field accompanied by magnetic field dipolarizations are identified. In this study, such events are designated as the magnetotail deflation. The magnetic field component parallel to the equatorial plane, BE , is normalized to a fixed geocentric distance, BEN , and is corrected for the compression effect of the solar wind dynamic pres-sure, BENC . It is shown that the BENC value just prior to a magnetotail deflation correlates well with the Dst index; BENC = 37.5 - 0.217 Dst0, where Dst0 denotes the Dst value corrected for the solar wind dynamic pressure. This regression function appears to delineate the upper limit of BENC values, when they are sorted by the Dst0 index. On the basis of this finding it is suggested that a prerequisite condition for magnetotail deflations must exist in the magnetosphere.

Large enhancements in low latitude total electron content during 15 May 2005 geomagnetic storm in Indian zone

NASA Astrophysics Data System (ADS)

Dashora, N.; Sharma, S.; Dabas, R. S.; Alex, S.; Pandey, R.

2009-05-01

Results pertaining to the response of the equatorial and low latitude ionosphere to a major geomagnetic storm that occurred on 15 May 2005 are presented. These results are also the first from the Indian zone in terms of (i) GPS derived total electron content (TEC) variations following the storm (ii) Local low latitude electrodynamics response to penetration of high latitude convection electric field (iii) effect of storm induced traveling atmospheric disturbances (TAD's) on GPS-TEC in equatorial ionization anomaly (EIA) zone. Data set comprising of ionospheric TEC obtained from GPS measurements, ionograms from an EIA zone station, New Delhi (Geog. Lat. 28.42° N, Geog. Long. 77.21° E), ground based magnetometers in equatorial and low latitude stations and solar wind data obtained from Advanced Composition Explorer (ACE) has been used in the present study. GPS receivers located at Udaipur (Geog. Lat. 24.73° N, Geog. Long. 73.73° E) and Hyderabad (Geog. Lat. 17.33° N, Geog. Long. 78.47° E) have been used for wider spatial coverage in the Indian zone. Storm induced features in vertical TEC (VTEC) have been obtained comparing them with the mean VTEC of quiet days. Variations in solar wind parameters, as obtained from ACE and in the SYM-H index, indicate that the storm commenced on 15 May 2005 at 02:39 UT. The main phase of the storm commenced at 06:00 UT on 15 May with a sudden southward turning of the Z-component of interplanetary magnetic field (IMF-Bz) and subsequent decrease in SYM-H index. The dawn-to-dusk convection electric field of high latitude origin penetrated to low and equatorial latitudes simultaneously as corroborated by the magnetometer data from the Indian zone. Subsequent northward turning of the IMF-Bz, and the penetration of the dusk-to-dawn electric field over the dip equator is also discernible. Response of the low latitude ionosphere to this storm may be characterized in terms of (i) enhanced background level of VTEC as compared to the mean VTEC, (ii) peaks in VTEC and foF2 within two hours of prompt penetration of electric field and (iii) wave-like modulations in VTEC and sudden enhancement in hmF2 within 4-5 h in to the storm. These features have been explained in terms of the modified fountain effect, local low latitude electrodynamic response to penetration electric field and the TIDs, respectively. The study reveals a strong positive ionospheric storm in the Indian zone on 15 May 2005. Consequences of such major ionospheric storms on the systems that use satellite based navigation solutions in low latitude, are also discussed.

A simple inertial model for Neptune's zonal circulation

NASA Technical Reports Server (NTRS)

Allison, Michael; Lumetta, James T.

1990-01-01

Voyager imaging observations of zonal cloud-tracked winds on Neptune revealed a strongly subrotational equatorial jet with a speed approaching 500 m/s and generally decreasing retrograde motion toward the poles. The wind data are interpreted with a speculative but revealingly simple model based on steady gradient flow balance and an assumed global homogenization of potential vorticity for shallow layer motion. The prescribed model flow profile relates the equatorial velocity to the mid-latitude shear, in reasonable agreement with the available data, and implies a global horizontal deformation scale L(D) of about 3000 km.

Geomagnetic conjugate observations of plasma bubbles and thermospheric neutral winds at equatorial latitudes

NASA Astrophysics Data System (ADS)

Fukushima, D.; Shiokawa, K.; Otsuka, Y.; Nishioka, M.; Kubota, M.; Tsugawa, T.; Nagatsuma, T.

2012-12-01

Plasma bubbles are plasma-density depletion which is developed by the Rayleigh-Taylor instability on the sunset terminator at equatorial latitudes. They usually propagate eastward after the sunset. The eastward propagation of the plasma bubbles is considered to be controlled by background eastward neutral winds in the thermosphere through the F-region dynamo effect. However, it is not clear how the F-region dynamo effect contributes to the propagation of the plasma bubbles, because plasma bubbles and background neutral winds have not been simultaneously observed at geomagnetic conjugate points in the northern and southern hemispheres. In this study, geomagnetic conjugate observations of the plasma bubbles at low latitudes with thermospheric neutral winds were reported. The plasma bubbles were observed at Kototabang (0.2S, 100.3E, geomagnetic latitude (MLAT): 10.0S), Indonesia and at Chiang Mai (18.8N, 98.9E, MLAT: 8.9N), Thailand, which are geomagnetic conjugate stations, on 5 April, 2011 from 13 to 22 UT (from 20 to 05 LT). These plasma bubbles were observed in the 630-nm airglow images taken by using highly-sensitive all-sky airglow imagers at both stations. They propagated eastward with horizontal velocities of about 100-125 m/s. Background thermospheric neutral winds were also observed at both stations by using two Fabry-Perot interferometers (FPIs). The eastward wind velocities were about 70-130 m/s at Kototabang, and about 50-90 m/s at Chiang Mai. We estimated ion drift velocities by using these neutral winds observed by FPIs and conductivities calculated from the IRI and MSIS models. The estimated velocities were about 60-90 % of the drift velocities of plasma bubbles. This result shows that most of the plasma bubble drift can be explained by the F-region dynamo effect, and additional electric field effect may come in to play.

Absolute wind measurements in the lower thermosphere of Venus using infrared heterodyne spectroscopy

NASA Technical Reports Server (NTRS)

Goldstein, Jeffrey J.

1990-01-01

The first absolute wind velocities above the Venusian cloud-tops were obtained using NASA/Goddard infrared heterodyne spectrometers at the NASA Infrared Telescope Facility (IRTF) and the McMath Solar Telescope. Beam-integrated Doppler displacements in the non-thermal emission core of (12)C(16)O2 10.33 micron R(8) sampled the line of sight projection of the lower thermospheric wind field (100 to 120 km). A field-usable Lamb-dip laser stabilization system, developed for spectrometer absolute frequency calibration to less than + or - 0.1 MHz, allowed S/N-limited line of sight velocity resolution at the 1 m/s level. The spectrometer's diffraction-limited beam (1.7 arc-second HPBW at McMath, 0.9 arc-second HPBW at IRTF), and 1 to 2 arc-second seeing, provided the spatial resolution necessary for circulation model discrimination. Qualitative analysis of beam-integrated winds provided definitive evidence of a dominant subsolar-antisolar circulation in the lower thermosphere. Beam-integrated winds were modelled with a 100x100 grid over the beam, incorporating beam spatial rolloff and across-the-beam gradients in non-thermal emission intensity, line of sight projection geometry, and horizontal wind velocity. Horizontal wind velocity was derived from a 2-parameter model wind field comprised of subsolar-antisolar and zonal components. Best-fit models indicated a dominant subsolar-antisolar flow with 120 m/s cross-terminator winds and a retrograde zonal component with a 25 m/s equatorial velocity. A review of all dynamical indicators above the cloud-tops allowed development of an integrated and self-consistent picture of circulation in the 70 to 200 km range.

The modeled latitudinal distribution of the ozone quasi-biennial oscillation using observed equatorial winds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gray, L.J.; Ruth, S.

1993-04-15

A simulation of precise years of the quasi-biennial oscillation (QBO) is achieved in a two-dimensional model by relaxing the modeled equatorial winds in the lower stratosphere toward radiosonde observations. The model has been run for the period 1971-90. A QBO signal in column ozone is produced in the model that agrees reasonably well with observational data from the BUV, TOMS, and SAGE II satellite datasets. The model results confirm previous indications of the importance of the interaction of the QBO with the annual cycle in the determination of the subtropical ozone anomaly. The low-frequency modulation of the subtropical ozone anomalymore » is now particularly clear. The low-frequency modulation of the subtropical ozone anomaly in the model arises as a result of the interaction of the QBO with the annual cycle in the vertical advection by the Hadley circulation. The possibility of a further, similar modulation arising from the interaction of the equatorial wind QBO and the annual cycle in midlatitude eddy activity is discussed, with particular emphasis on the implications for the eddy transfer of ozone to high latitudes and on the ability to predict the severity of the Antarctic ozone hole. A link is proposed between the QBO signal in the severity of the Antarctic ozone hole and the amount of ozone observed in the subtropical/midlatitude springtime maximum in the Southern Hemisphere. On the basis of this relationship, the reliability of the model as a predictor of the severity of the ozone hole is explored. A conclusion of the study is that a reliable predictor of the severity of the ozone hole must take into account the timing of the descent of the equatorial wind QBO at the equator with respect to the annual cycle and that the use, as in previous studies, of a single parameter, such as the sign of the 50-mb equatorial wind, will not be entirely reliable because it cannot do this. 31 refs., 11 figs.« less

The Role of the Indian Ocean Sector for Prediction of the Coupled Indo-Pacific System: Impact of Atmospheric Coupling

NASA Technical Reports Server (NTRS)

Hackert, E. C.; Busalacchi, A. J.; Carton, J.; Murtugudde, R.; Arkin, P.; Evans, M. N.

2017-01-01

Indian Ocean (IO) dynamics impact ENSO predictability by influencing wind and precipitation anomalies in the Pacific. To test if the upstream influence of the IO improves ENSO validation statistics, a combination of forced ocean, atmosphere, and coupled models are utilized. In one experiment, the full tropical Indo-Pacific region atmosphere is forced by observed interannual SST anomalies. In the other, the IO is forced by climatological SST. Differences between these two forced atmospheric model experiments spotlight a much richer wind response pattern in the Pacific than previous studies that used idealized forcing and simple linear atmospheric models. Weak westerlies are found near the equator similar to earlier literature. However, at initialization strong easterlies between 30 deg. S to 10 deg. S and 0 deg. N to 25 deg. N and equatorial convergence of the meridional winds across the entire Pacific are unique findings from this paper. The large-scale equatorial divergence west of the dateline and northeasterly-to-northwesterly cross-equatorial flow converging on the equator east of the dateline in the Pacific are generated from interannual IO SST coupling. In addition, off-equatorial downwelling curl impacts large-scale oceanic waves (i.e., Rossby waves reflect as western boundary Kelvin waves). After 3 months, these downwelling equatorial Kelvin waves propagate across the Pacific and strengthen the NINO3 SST. Eventually Bjerknes feedbacks take hold in the eastern Pacific which allows this warm anomaly to grow. Coupled forecasts for NINO3 SST anomalies for 1993-2014 demonstrate that including interannual IO forcing significantly improves predictions for 3-9 month lead times.

The role of the Indian Ocean sector for prediction of the coupled Indo-Pacific system: Impact of atmospheric coupling

NASA Astrophysics Data System (ADS)

Hackert, E. C.; Busalacchi, A. J.; Carton, J.; Murtugudde, R.; Arkin, P.; Evans, M. N.

2017-04-01

Indian Ocean (IO) dynamics impact ENSO predictability by influencing wind and precipitation anomalies in the Pacific. To test if the upstream influence of the IO improves ENSO validation statistics, a combination of forced ocean, atmosphere, and coupled models are utilized. In one experiment, the full tropical Indo-Pacific region atmosphere is forced by observed interannual SST anomalies. In the other, the IO is forced by climatological SST. Differences between these two forced atmospheric model experiments spotlight a much richer wind response pattern in the Pacific than previous studies that used idealized forcing and simple linear atmospheric models. Weak westerlies are found near the equator similar to earlier literature. However, at initialization strong easterlies between 30°S-10°S and 0°N-25°N and equatorial convergence of the meridional winds across the entire Pacific are unique findings from this paper. The large-scale equatorial divergence west of the dateline and northeasterly-to-northwesterly cross-equatorial flow converging on the equator east of the dateline in the Pacific are generated from interannual IO SST coupling. In addition, off-equatorial downwelling curl impacts large-scale oceanic waves (i.e., Rossby waves reflect as western boundary Kelvin waves). After 3 months, these downwelling equatorial Kelvin waves propagate across the Pacific and strengthen the NINO3 SST. Eventually Bjerknes feedbacks take hold in the eastern Pacific which allows this warm anomaly to grow. Coupled forecasts for NINO3 SST anomalies for 1993-2014 demonstrate that including interannual IO forcing significantly improves predictions for 3-9 month lead times.

Wind Patterns in Jupiter's Equatorial Region (Time set 1)

NASA Technical Reports Server (NTRS)

1997-01-01

Wind patterns of Jupiter's equatorial region. This mosaic covers an area of 34,000 kilometers by 22,000 kilometers and was taken using the 756 nanometer (nm) near-infrared continuum filter. The dark region near the center of the mosaic is an equatorial 'hotspot' similar to the Galileo Probe entry site. The near-infrared continuum filter shows the features of Jupiter's main visible cloud deck.

Jupiter's atmospheric circulation is dominated by alternating jets of east/west (zonal) winds. The bands have different widths and wind speeds but have remained constant as long as telescopes and spacecraft have measured them. The top half of these mosaics lies within Jupiter's North Equatorial Belt, a westward (left) current. The bottom half shows part of the Equatorial Zone, a fast moving eastward current. The clouds near the hotspot are the fastest moving features in these mosaics, moving at about 100 meters per second, or 224 miles per hour.

Superimposed on the zonal wind currents is the Jovian 'weather'. The arrows show the winds measured by an observer moving eastward (right) at the speed of the hotspot. (The observer's perspective is that the hotspot is 'still' while the rest of the planet moves around it.) Clouds south of the hotspot appear to be moving towards it, as seen in the flow aligned with cloud streaks to the southwest and in the clockwise flow to the southeast. Interestingly, there is little cloud motion away from the hotspot in any direction. This is consistent with the idea that dry air is converging over this region and sinking, maintaining the cloud-free nature of the hotspot.

North is at the top. The mosaic covers latitudes 1 to 19 degrees and is centered at longitude 336 degrees West. The smallest resolved features are tens of kilometers in size. These images were taken on December 17, 1996, at a range of 1.5 million kilometers by the Solid State Imaging system aboard NASA's Galileo spacecraft.

The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

Modulation of quasi-biennial ozone oscillations in the equatorial stratosphere by the solar cycle

NASA Astrophysics Data System (ADS)

Bezverkhnii, Viacheslav; Gruzdev, Aleksandr

Analysis of variation in ozone concentration, temperature, and zonal wind velocity in the equatorial stratosphere at the quasi-biennial (QB) and quasi-decadal (QD) time scales and their relation to the QB and 11-year variations in solar activity is made with the help of wavelet, cross-wavelet and cross-spectral techniques using SBUV/SBUV 2 (ozone), NMC, ERA-40, ERA-Interim (wind and temperature), and radiosonde (wind) data. Sunspot number and 10.7 cm solar radio flux data are used as indices of solar activity. The QD mode with the mean period of 128 months and the QB mode with 28-29 month period are derived from variations in ozone concentration , ozone meridional gradient, temperature and wind velocity. Local maxima of amplitudes of the QD variation in the ozone meridional gradient occur in 4-5 and 20-30 hPa layers. The amplitude of the QB mode of the ozone meridional gradient in 30-50 hPa layer is modulated by the solar cycle in such a way that the amplitude maximum corresponds approximately to the solar cycle maximum. Similar modulation is not found in the QB mode of ozone concentration. While the QD variations in ozone and zonal wind velocity are weak compared to the QB oscillation, the amplitudes of the QD and QB modes of temperature oscillations in the lower and middle stratosphere are close to each other. The modulation of the QB oscillations in the ozone meridional gradient in the lower stratosphere by the 11-year solar cycle is an additional evidence of solar activity influence on the stratosphere, which extends results by Soukharev and Hood (2001), Bezverkhnii and Gruzdev (2007), and Gruzdev and Bezverkhnii (2010). References: 1. Bezverkhnii, V.A., and A.N. Gruzdev. Relation between quasi-decadal and quasi-biennial oscillations of solar activity and the equatorial stratospheric wind. Doklady Earth Sciences, 2007, Vol. 415A, No 6, pp. 970-974. 2. Gruzdev, A.N., and V.A. Bezverkhnii. Possible ozone influence on the quasi-biennial oscillation in the equatorial stratosphere. Doklady Earth Sciences, 2010, Vol. 434, Part 1, pp. 1279-1284. 3. Soukharev, B.E., and L.L. Hood. Possible solar modulation of the equatorial quasi-biennisl oscillation: Additional statistical evidence. J. Geophys. Res., 2001, Vol. 106, No D14, pp. 14855-14868.

Equatorial Oscillation and Planetary Wave Activity in Saturn's Stratosphere Through the Cassini Epoch

NASA Astrophysics Data System (ADS)

Guerlet, S.; Fouchet, T.; Spiga, A.; Flasar, F. M.; Fletcher, L. N.; Hesman, B. E.; Gorius, N.

2018-01-01

Thermal infrared spectra acquired by Cassini/Composite InfraRed Spectrometer (CIRS) in limb-viewing geometry in 2015 are used to derive 2-D latitude-pressure temperature and thermal wind maps. These maps are used to study the vertical structure and evolution of Saturn's equatorial oscillation (SEO), a dynamical phenomenon presenting similarities with the Earth's quasi-biennal oscillation (QBO) and semi-annual oscillation (SAO). We report that a new local wind maximum has appeared in 2015 in the upper stratosphere and derive the descent rates of other wind extrema through time. The phase of the oscillation observed in 2015, as compared to 2005 and 2010, remains consistent with a ˜15 year period. The SEO does not propagate downward at a regular rate but exhibits faster descent rate in the upper stratosphere, combined with a greater vertical wind shear, compared to the lower stratosphere. Within the framework of a QBO-type oscillation, we estimate the absorbed wave momentum flux in the stratosphere to be on the order of ˜7 × 10-6 N m-2. On Earth, interactions between vertically propagating waves (both planetary and mesoscale) and the mean zonal flow drive the QBO and SAO. To broaden our knowledge on waves potentially driving Saturn's equatorial oscillation, we searched for thermal signatures of planetary waves in the tropical stratosphere using CIRS nadir spectra. Temperature anomalies of amplitude 1-4 K and zonal wave numbers 1 to 9 are frequently observed, and an equatorial Rossby (n = 1) wave of zonal wave number 3 is tentatively identified in November 2009.

Long waves in the eastern equatorial pacific ocean: a view from a geostationary satellite.

PubMed

Legeckis, R

1977-09-16

During 1975, westward-moving long waves with a period of about 25 days and a wavelength of 1000 kilometers were observed at a sea surface temperature front in the equatorial Pacific on infrared images obtained by a geostationary environmental satellite system. The absence of these waves during 1976, and the above-average equatorial sea surface temperatures during 1976, may be related to a decrease in the southeasterly trade winds during that year.

Auroral activity associated with Kelvin-Helmholtz instability at the inner edge of the low-latitude boundary layer

NASA Technical Reports Server (NTRS)

Farrugia, C. J.; Sandholt, P. E.; Burlaga, L. F.

1994-01-01

Auroral activity occurred in the late afternoon sector (approx. 16 MLT) in the northern hemisphere during the passage at Earth of an interplanetary magnetic cloud on January 14, 1988. The auroral activity consisted of a very dynamic display which was preceded and followed by quiet auroral displays. During the quiet displays, discrete rayed arcs aligned along the geomagnetic L shells were observed. In the active stage, rapidly evolving spiral forms centered on magnetic zenith were evident. The activity persisted for many minutes and was characterized by the absence of directed motion. They were strongly suggestive of intense filaments of upward field-aligned currents embedded in the large-scale region 1 current system. Distortions of the flux ropes as they connect from the equatorial magnetosphere to the ionosphere were witnessed. We assess as possible generating mechanisms three nonlocal sources known to be associated with field-aligned currents. Of these, partial compressions of the magnetosphere due to variations of solar wind dynamic pressure seem an unlikely source. The possibility that the auroral forms are due to reconnection is investigated but is excluded because the active aurora were observed on the closed field line region just equatorward of the convection reversal boundary. To support this conclusion further, we apply recent results on the mapping of ionospheric regions to the equatorial plane based on the Tsyganenko 1989 model (Kaufmann et al., 1993). We find that for comparable magnetic activity the aurora map to the equatorial plane at X(sub GSM) = approx. 3 R(sub E) and approx. 2 R(sub E) inward of the magnetopause, that is, the inner edge of the boundary layer close to dusk. Since the auroral forms are manifestly associated with magnetic field shear, a vortical motion at the equatorial end of the flux rope is indicated, making the Kelvin-Helmholtz instability acting at the inner edge of the low-latitude boundary layer the most probable generating source.

The Equatorial Pacific Cold Tongue Simulated by IPCC AR4 Coupled GCMs: Upper Ocean Heat Budget and Feedback Analysis

DTIC Science & Technology

2012-05-15

ET AL .: THE PACIFIC COLD TONGUE BIAS ANALYSIS C05024 circulation, which intensifies the surface easterly winds over the Pacific Basin, further...productivity, and in carbon cycling since it is the major oceanic source of C02 for the atmosphere [Field et al , 1998; Calvo et al , 2011]. Large SST anomalies...used for climate predictions and projec- tions [Neelin et al , 1992; Mechoso et al , 1995; Delecluse et al , 1998; Laufet al , 2001; Davey

Modeling the hook depth distribution of pelagic longlining in the equatorial area of Indian Ocean

NASA Astrophysics Data System (ADS)

Song, Liming; Li, Jie; Gao, Panfeng; Zhou, Ji; Xu, Liuxiong

2012-12-01

A survey was conducted in the equatorial area of Indian Ocean for a better understanding of the dynamics of hook depth distribution of pelagic longline fishery. We determined the relationship between hook depth and vertical shear of current coefficiency, wind speed, hook position code, sine of wind angle, sine of angle of attack and weight of messenger weight. We identified the hook depth models by the analysis of covariance with a general linear model. The results showed that the wind effect on the hook depth can be ignored from October to November in the survey area; the surface current effect on the hook depth can be ignored; the equatorial undercurrent is the key factor for the hook depth in Indian Ocean; and there is a negative correlation between the hook depth and vertical shear of current and angle of attack. It was also found that the deeper the hook was set, the higher hook depth shoaling was. The proposed model improves the accuracy of the prediction of hook depth, which can be used to estimate the vertical distribution of pelagic fish in water column.

Analysis of the disturbed electric field effects in the sporadic E-layers at equatorial and low latitude regions

NASA Astrophysics Data System (ADS)

Araujo Resende, Laysa Cristina; Moro, Juliano; Denardini, Clezio Marcos; Carrasco, Alexander J.; Batista, Paulo; Chen, Sony Su; Batista, Inez S.; Andrioli, Vania Fatima

2016-07-01

In the present work we analyze the disturbed electric field effects in the sporadic E-layers at equatorial regions, Jicamarca (11.57°S, 76.52°O, I: -2°) and São Luís (2°S, 44° O, I: -2.3°), and at low latitude regions, Fortaleza (3.9°S, 38.45°O, I: -9°) and Cachoeira Paulista (22.42°S, 45°O, I: -15°). We have conducted a deep analysis to investigate these effects using a theoretical model for the ionospheric E region, called MIRE. This model is able to simulate the Es layers taking into account the E region winds and electric fields. It calculates the densities for the main molecular (NO^{+}, O_{2}^{+}, N_{2}^{+}) and metallic ions (Fe^{+}, Mg^{+}) by solving the continuity and momentum equations for each species. The main purpose of this analysis is to verify the disturbed electric fields role in the occurrence or disruption of Es layers through simulations. The analysis show that the Es layer formation and dynamics can be influenced by the prompt penetration electric fields that occur during magnetic disturbances. Therefore, the simulations present interesting results that helps to improve the understanding of Es layer behavior during the disturbed periods.

A theoretical study of the global F region for June solstice, solar maximum, and low magnetic activity

NASA Technical Reports Server (NTRS)

Sojka, J. J.; Schunk, R. W.

1985-01-01

A time-dependent, three-dimensional, multi-ion model of the ionospheric F region at 120-800 km altitude is presented. Account is taken of field-aligned diffusion, cross-field electrodynamic drifts in equatorial and high latitude regions, interhemispheric flow, thermospheric winds, polar wind escape, energy-dependent chemical reactions and neutral composition changes. Attention is also given to the effects of ion production by solar EUV radiation and auroral precipitation, thermal conduction, diffusion-thermal heat flow, local heating and cooling processes, offsets between the geomagnetic and geographic poles, and bending of field lines near the magnetic equator. The model incorporates all phenomena described by previous models and can be applied to tracing magnetic storm and substorm disturbances from high to low latitudes on a global scale. Sample results are provided for ionospheric features during a June solstice, the solar maximum and in a period of low geomagnetic activity. The model will eventually be used to study coupled ionosphere-thermosphere activity.

On the association between the recent episode of the quasi-biennial oscillation and the strong El Niño event

NASA Astrophysics Data System (ADS)

Varotsos, Costas A.; Sarlis, Nikos V.; Efstathiou, Maria

2017-07-01

Since February 2016, the equatorial quasi-biennial oscillation (QBO) in zonal wind of the lower stratosphere exhibited anomalous behavior. In more detail, it broke down from its typical pattern and the eastward stratospheric winds unexpectedly reversed to a westward direction. We herewith attempt to detect whether this unprecedented event could be considered as a result of plausible long-range correlations in the QBO temporal evolution. The analyses performed using all the available QBO data sets showed that such an interpretation could not be inferred, because the temporal evolution of the equatorial zonal wind in the lower stratosphere does not exhibit power-law behavior. Further, the natural time analysis of the QBO data indicates precursory behavior before the maximization of the zonal wind velocity and that the recent strong El Niño event might be related with the aforementioned unprecedented behavior.

Sources of magnetic fields in recurrent interplanetary streams

NASA Technical Reports Server (NTRS)

Burlaga, L. F.; Behannon, K. W.; Hansen, S. F.; Pneuman, G. W.; Feldman, W. C.

1978-01-01

The paper examines sources of magnetic fields in recurrent streams observed by the Imp 8 and Heos spacecraft at 1 AU and by Mariner 10 en route to Mercury between October 31, 1973 and February 9, 1974, during Carrington rotations 1607-1610. Although most fields and plasmas at 1 AU were related to coronal holes and the magnetic field lines were open in those holes, some of the magnetic fields and plasmas at 1 AU were related to open field line regions on the sun which were not associated with known coronal holes, indicating that open field lines may be more basic than coronal holes as sources of the solar wind. Magnetic field intensities in five equatorial coronal holes, certain photospheric magnetic fields, and the coronal footprints of the sector boundaries on the source surface are characterized.

Future wave and wind projections for United States and United-States-affiliated Pacific Islands

USGS Publications Warehouse

Storlazzi, Curt D.; Shope, James B.; Erikson, Li H.; Hegermiller, Christine A.; Barnard, Patrick L.

2015-01-01

Changes in future wave climates in the tropical Pacific Ocean from global climate change are not well understood. Spatially and temporally varying waves dominate coastal morphology and ecosystem structure of the islands throughout the tropical Pacific. Waves also impact coastal infrastructure, natural and cultural resources, and coastal-related economic activities of the islands. Wave heights, periods, and directions were forecast through the year 2100 using wind parameter outputs from four atmosphere-ocean global climate models from the Coupled Model Inter-Comparison Project, Phase 5, for Representative Concentration Pathways (RCP) scenarios 4.5 and 8.5 that correspond to moderately mitigated and unmitigated greenhouse gas emissions, respectively. Wind fields from the global climate models were used to drive a global WAVEWATCH-III wave model and generate hourly time-series of bulk wave parameters for 25 islands in the mid to western tropical Pacific for the years 1976–2005 (historical), 2026–2045 (mid-century projection), and 2085–2100 (end-of-century projection). Although the results show some spatial heterogeneity, overall the December-February extreme significant wave heights, defined as the mean of the top 5 percent of significant wave height time-series data modeled within a specific period, increase from present to mid-century and then decrease toward the end of the century; June-August extreme wave heights increase throughout the century within the Central region of the study area; and September-November wave heights decrease strongly throughout the 21st century, displaying the largest and most widespread decreases of any season. Peak wave periods increase east of the International Date Line during the December-February and June-August seasons under RCP4.5. Under the RCP8.5 scenario, wave periods decrease west of the International Date Line during December-February but increase in the eastern half of the study area. Otherwise, wave periods decrease throughout the study area during other seasons. Extreme wave directions in equatorial Micronesia during June-August undergo an approximate 30° clockwise rotation from primarily west to northwest. September-November RCP4.5 extreme mean wave directions rotate counterclockwise by approximately 30 to 45° in equatorial Micronesia; September-November RCP8.5 extreme mean wave directions within equatorial Micronesia rotate clockwise by approximately 20 to 30°. Extreme wind speeds decreased within both scenarios, with the largest decreases occurring in the September-November season. Extreme wind directions under RCP4.5 rotated clockwise by more than 60° in equatorial Micronesia during the September-November season and by approximately 30° during June-August. RCP8.5 extreme wind directions rotated counterclockwise during September-November within the same region by 30 to 50° and clockwise by 30 to 40° at one island. The spatial patterns and trends are similar between the two different greenhouse gas emission scenarios, with the magnitude and extent of the trends generally greater for the higher (RCP8.5) scenario.

Modeling ionospheric pre-reversal enhancement and plasma bubble growth rate using data assimilation

NASA Astrophysics Data System (ADS)

Rajesh, P. K.; Lin, C. C. H.; Chen, C. H.; Matsuo, T.

2017-12-01

We report that assimilating total electron content (TEC) into a coupled thermosphere-ionosphere model by using the ensemble Kalman filter results in improved specification and forecast of eastward pre-reversal enhancement (PRE) electric field (E-field). Through data assimilation, the ionospheric plasma density, thermospheric winds, temperature and compositions are adjusted simultaneously. The improvement of dusk-side PRE E-field over the prior state is achieved primarily by intensification of eastward neutral wind. The improved E-field promotes a stronger plasma fountain and deepens the equatorial trough. As a result, the horizontal gradients of Pedersen conductivity and eastward wind are increased due to greater zonal electron density gradient and smaller ion drag at dusk, respectively. Such modifications provide preferable conditions and obtain a strengthened PRE magnitude closer to the observation. The adjustment of PRE E-field is enabled through self-consistent thermosphere and ionosphere coupling processes captured in the model. The assimilative outputs are further utilized to calculate the flux tube integrated Rayleigh-Taylor instability growth rate during March 2015 for investigation of global plasma bubble occurrence. Significant improvements in the calculated growth rates could be achieved because of the improved update of zonal electric field in the data assimilation forecast. The results suggest that realistic estimate or prediction of plasma bubble occurrence could be feasible by taking advantage of the data assimilation approach adopted in this work.

Effects of southeastern Pacific sea surface temperature on the double-ITCZ bias in NCAR CESM1

NASA Astrophysics Data System (ADS)

Song, F.; Zhang, G. J.

2016-12-01

The double-intertropical convergence zone (ITCZ) is a long-standing bias in the coupled general circulation models (CGCMs). The warm biases in southeastern Pacific (SEP) sea surface temperature (SST) are also evident in many CGCMs. In this study, the role of SEP SST in the double-ITCZ is investigated by prescribing the observed SEP SST in the Community Earth System Model version 1 (CESM1). Both the double-ITCZ and dry equator problems are significantly improved with SEP SST prescribed. The colder SST over the SEP increases the southeasterly winds extending outside the prescribed SST region, cooling the ocean there via increased evaporation. The enhanced descending motion over the SEP strengthens the Walker circulation, so the low-level wind convergence in the tropical western Pacific is increased. The reduced wind speed leads to warmer SST and stronger convection there. The stronger convection in turn leads to more cloud and reduces the incoming solar radiation, cooling the SST. These competing effects between radiative heat flux and latent heat flux make the atmospheric heat flux secondary to the ocean dynamics in the western Pacific warming. The increased easterly winds over the equatorial Pacific enhance upwelling and shoal the thermocline over the eastern Pacific. This Bjerknes feedback plays an important role in the improvement of dry equator. The changes of surface wind and wind curl also lead to weaker South Equatorial Countercurrent and stronger South Equatorial Current, preventing the warm water from expanding eastward, thereby improving both the double-ITCZ and dry equator.

Structure of magnetopause layers formed by a radial interplanetary magnetic field

NASA Astrophysics Data System (ADS)

Safrankova, Jana; Simunek, Jiri; Nemecek, Zdenek; Prech, Lubomir; Grygorov, Kostiantyn; Shue, Jih-Hong; Samsonov, Andrey; Pi, Gilbert

2016-07-01

The magnetopause location is generally believed to be determined by the solar wind dynamic pressure and by the sign and value of the interplanetary magnetic field (IMF) vertical (Bz) component. A contribution of other parameters is usually assumed to be minor or negligible near the equatorial plane. However, recent papers have shown a magnetopause expansion during intervals of a nearly radial IMF (large IMF Bx component). Under such conditions, the total pressure exerted on the subsolar magnetopause is significantly lower than the solar wind dynamic pressure as demonstrate both MHD simulations and statistical investigations. During a long-duration radial IMF, all parameters - the IMF magnitude, solar wind speed, density, and especially the temperature are depressed in comparison with their yearly averages. Moreover, in this case, the structures of the LLBL change; the LLBL shows different profiles at both hemispheres for negative and positive IMF Bx polarities. This asymmetry changes over time and influences the LLBL structures due to magnetic reconnection. We present an overview of important physical quantities controlling the magnetopause compression and new results that deal with the structure of the magnetopause and adjacent layers.

The Heliotail: Theory and Modeling

DOE PAGES

Pogorelov, N. V.

2016-05-31

Physical processes are discussed related to the heliotail which is formed when the solar wind interacts with the local interstellar medium. Although astrotails are commonly observed, the heliotail observations are only indirect. As a consequence, the direct comparison of the observed astrophysical objects and the Sun is impossible. This requires proper theoretical understanding of the heliotail formation and evolution, and numerical simulations in sufficiently large computational boxes. In this paper, we review some previous results related to the heliotail flow and show new simulations which demonstrate that the solar wind collimation inside the Parker spiral field lines diverted by themore » heliopause toward the heliotail is unrealistic. On the contrary, solar cycle effects ensure that the solar wind density reaches its largest values near the solar equatorial plane. We also argue that a realistic heliotail should be very long to account for the observed anisotropy of 1-10 TeV cosmic rays.« less

The stratospheric QBO signal in the NCEP reanalysis, 1958-2001

NASA Astrophysics Data System (ADS)

Ribera, Pedro; Gallego, David; Peña-Ortiz, Cristina; Gimeno, Luis; Garcia-Herrera, Ricardo; Hernandez, Emiliano; Calvo, Natalia

2003-07-01

The spatiotemporal evolution of the zonal wind in the stratosphere is analyzed based on the use of the NCEP reanalysis (1958-2001). MultiTaper Method-Singular Value Decomposition (MTM-SVD), a frequency-domain analysis method, is applied to isolate significant spatially-coherent variability with narrowband oscillatory character. A quasibiennial oscillation is detected as the most intense coherent signal in the stratosphere, the signal being less intense in the lower levels. There is a clear downward propagation of the signal with time at low latitudes, not evident at mid and high latitudes. There are differences in the behavior of the signal over both hemispheres, being much weaker over the SH. In the NH an anomaly in the zonal wind field, in phase with the equatorial signal, is detected at approximately 60°N. Two different areas at subtropical latitudes are detected to be characterized by wind anomalies opposed to that of the equator.

Annual, orbital, and enigmatic variations in tropical oceanography recorded by the Equatorial Atlantic amplifier

NASA Technical Reports Server (NTRS)

Mcintyre, Andrew

1992-01-01

Equatorial Atlantic surface waters respond directly to changes in zonal and meridional lower tropospheric winds forced by annual insolation. This mechanism has its maximum effect along the equatorial wave guide centered on 10 deg W. The result is to amplify even subtle tropical climate changes such that they are recorded by marked amplitude changes in the proxy signals. Model realizations, NCAR AGCM and OGCM for 0 Ka and 126 Ka (January and July), and paleoceanographic proxy data show that these winds are also forced by insolation changes at the orbital periods of precession and obliquity. Perhelion in boreal summer produces a strengthened monsoon, e.g., increase meridional and decrease zonal wind stress. This reduces oceanic Ekman divergence and thermocline/nutricline shallowing. The result, in the equatorial Atlantic, is reduced primary productivity and higher euphotic zone temperatures; vice versa for perihelion in boreal winter. Perihelion is controlled by precession. Thus, the dominant period in spectra from a stacked SST record (0-252 Ka BP) at the site of the equatorial Atlantic amplifier is 23 Ky (53 percent of the total variance). This precessional period is coherent (k = 0.920) and in phase with boreal summer insolation. Oscillations of shorter period are present in records from cores sited beneath the amplifier region. These occur between 12.5 and 74.5 Ka BP, when eccentricity modulation of precession is at a minimum. Within this time interval there are 21 cycles with mean periods of 3.0 plus or minus 0.5 Ky. Similar periods have been documented from high latitude regions, e.g., Greenland ice cores from Camp Century. The Camp Century signal in this same time interval contains 21 cycles. A subjective correlation was made between the Camp Century and the equatorial records; the signals were statistically similar, r = 0.722 and k = 0.960.

Earth observations taken by the Expedition Seven crew

NASA Image and Video Library

2003-09-21

ISS007-E-15177 (21 September 2003) --- This view, photographed by an Expedition 7 crewmember onboard the International Space Station (ISS), features a small part of the coastal dune field which is now protected as the Lencois Maranhenses National Park, on Brazil’s north coast, about 700 kilometers east of the Amazon River mouth. Persistent winds blow off the equatorial Atlantic Ocean onto Brazil from the east, driving white sand inland from 100 kilometers stretch of coast, to form a large field of dunes. The dark areas between the white dunes are fresh water ponds that draw fishermen to this newly established park.

The Effect of Neutral Winds on Simulated Inner Magnetospheric Electric Fields During the 17 March 2013 Storm

NASA Astrophysics Data System (ADS)

Chen, M.; Lemon, C.; Walterscheid, R. L.; Hecht, J. H.; Sazykin, S. Y.; Wolf, R.

2017-12-01

We investigate how neutral winds and particle precipitation affect the simulated development of electric fields including Sub-Auroral Polarization Streams (SAPS) during the 17 March 2013 storm. Our approach is to use the magnetically and electrically self-consistent Rice Convection Model - Equilibrium (RCM-E) to simulate the inner magnetospheric electric field. We use parameterized rates of whistler-generated electron pitch-angle scattering from Orlova and Shprits [JGR, 2014] that depend on equatorial radial distance, magnetic activity (Kp), and magnetic local time (MLT) outside the simulated plasmasphere. Inside the plasmasphere, parameterized scattering rates due to hiss [Orlova et al., GRL, 2014] are used. Ions are scattered at a fraction of strong pitch-angle scattering where the fraction is scaled by epsilon, the ratio of the gyroradius to the field-line radius of curvature, when epsilon is greater than 0.1. The electron and proton contributions to the auroral conductance in the RCM-E are calculated using the empirical Robinson et al. [JGR, 1987] and Galand and Richmond [JGR, 2001] equations, respectively. The "background" ionospheric conductance is based on parameters from the International Reference Ionosphere [Bilitza and Reinisch, JASR, 2008] but modified to include the effect of specified ionospheric troughs. Neutral winds are modeled by the empirical Horizontal Wind Model (HWM07) in the RCM-E. We compare simulated precipitating particle energy flux, E x B velocities with DMSP observations during the 17 March 2013 storm with and without the inclusion of neutral winds. Discrepancies between the simulations and observations will aid us in assessing needed improvements in the model.

Characteristics of Quasi-Biennial Oscillation simulation in the Meteorological Research Institute earth system model

NASA Astrophysics Data System (ADS)

Yoshida, K.; Naoe, H.

2016-12-01

Whether climate models drive Quasi-Biennial Oscillation (QBO) appropriately is important to assess QBO impact on climate change such as global warming and solar related variation. However, there were few models generating QBO in the Coupled Model Intercomparison Project Phase 5 (CMIP5). This study focuses on dynamical structure of the QBO and its sensitivity to background wind pattern and model configuration. We present preliminary results of experiments designed by "Towards Improving the QBO in Global Climate Models (QBOi)", which is derived from the Stratosphere-troposphere processes and their role in climate (SPARC), in the Meteorological Research Institute earth system model, MRI-ESM2. The simulations were performed in present-day climate condition, repeated annual cycle condition with various CO2 level and sea surface temperatures, and QBO hindcast. In the present climate simulation, zonal wind in the equatorial stratosphere generally exhibits realistic behavior of the QBO. Equatorial zonal wind variability associated with QBO is overestimated in upper stratosphere and underestimated in lower stratosphere. In the MRI-ESM2, the QBO behavior is mainly driven by gravity wave drag parametrization (GWDP) introduced in Hines (1997). Comparing to reanalyses, shortage of resolved wave forcing is found especially in equatorial lower stratosphere. These discrepancies can be attributed to difference in wave forcing, background wind pattern and model configuration. We intend to show results of additional sensitivity experiments to examine how model configuration and background wind pattern affect resolved wave source, wave propagation characteristics, and QBO behavior.

A study of Equartorial wave characteristics using rockets, balloons, lidar and radar

NASA Astrophysics Data System (ADS)

Sasi, M.; Krishna Murthy, B.; Ramkumar, G.; Satheesan, K.; Parameswaran, K.; Rajeev, K.; Sunilkumar, S.; Nair, P.; Krishna Murthy, K.; Bhavanikumar, Y.; Raghunath, K.; Jain, A.; Rao, P.; Krishnaiah, M.; Nayar, S.; Revathy, K.

Dynamics of low latitude middle atmosphere is dominated by the zonal wind quasi- biennial oscillation (QBO) in the lower stratosphere and zonl wind semiannual oscillation (SAO) in the stratopause and mesopause regions. Equatorial waves play a significant role in the evolution of QBO and SAO through wave- mean flow interactions resulting in momentum transfer from the waves to the mean flow in the equatorial middle atmosphere. With the objective of characterising the equatorial wave characteristics and momentum fluxes associated with them a campaign experiment was conducted in 2000 using RH-200 rockets, balloons, Raleigh lidar and MST radar. Winds and temperatures in the troposphere, stratosphere and mesosphere over two low latitude stations Gadanki (13.5°N, 79.2°E) and SHAR (13.7°N, 80.2°E) were measured, using MST Radar, Rayleigh Lidar, balloons and RH-200 rockets, for 40 consecutive days from 21 February to 01 April 2000 and were used for the study of equatorial waves and their interactions with the background mean flow in various atmospheric regions. The study shows the occurrence of a strong stratospheric cooling (~25 K) anomaly along with a zonal wind anomaly and this low-latitude event appears to be linked to high-latitude stratospheric warming event and leads to subsequent generation of short period (~5 days) oscillations lasting for a few cycles in the stratosphere. A slow Kelvin wave (~18 day period), fast Kelvin wave (~8 days) and ultra fast Kelvin wave (~3.3 day period) and RG wave (~4.8 day period) have been identified. There are indications of slow and ultra fast Kelvin waves, in addition to fast Kelvin waves, contributing to the evolution of the westerly phase of the stratopause SAO.

Longitudinal Variation and Waves in Jupiter's South Equatorial Wind Jet

NASA Technical Reports Server (NTRS)

Simon-Miller, Amy A.; Choi, David; Rogers, John H.; Gierasch, Peter J.; Allison, Michael D.; Adamoli, Gianluigi; Mettig, Hans-Joerg

2012-01-01

A detailed study of the chevron-shaped dark spots on the strong southern equatorial wind jet near 7.5 S planetographic latitude shows variations in velocity with longitude and time. The presence of the large anticyclonic South Equatorial Disturbance (SED) has a profound effect on the chevron velocity, causing slower velocities to its east and accelerations over distance from the disturbance. The chevrons move with velocities near the maximum wind jet velocity of approx 140 m/s, as deduced by the history of velocities at this latitude and the magnitude of the symmetric wind jet near 7 N latitude. Their repetitive nature is consistent with a gravity-inertia wave (n = 75 to 100) with phase speed up to 25 m/s, relative to the local flow, but the identity of this wave mode is not well constrained. However, for the first time, high spatial resolution movies from Cassini images show that the chevrons oscillate in latitude with a 6.7 +/- 0.7-day period. This oscillating motion has a wavelength of approx 20 and a speed of 101 +/- 3 m/s, following a pattern similar to that seen in the Rossby wave plumes of the North Equatorial Zone, and possibly reinforced by it. All dates show chevron latitude variability, but it is unclear if this larger wave is present during other epochs, as there are no other suitable time series movies that fully delineate it. In the presence of mUltiple wave modes, the difference in dominant cloud appearance between 7 deg N and 7.5 deg S is likely due to the presence of the Great Red Spot, either through changes in stratification and stability or by acting as a wave boundary.

Space-time interpolation of satellite winds in the tropics

NASA Astrophysics Data System (ADS)

Patoux, Jérôme; Levy, Gad

2013-09-01

A space-time interpolator for creating average geophysical fields from satellite measurements is presented and tested. It is designed for optimal spatiotemporal averaging of heterogeneous data. While it is illustrated with satellite surface wind measurements in the tropics, the methodology can be useful for interpolating, analyzing, and merging a wide variety of heterogeneous and satellite data in the atmosphere and ocean over the entire globe. The spatial and temporal ranges of the interpolator are determined by averaging satellite and in situ measurements over increasingly larger space and time windows and matching the corresponding variability at each scale. This matching provides a relationship between temporal and spatial ranges, but does not provide a unique pair of ranges as a solution to all averaging problems. The pair of ranges most appropriate for a given application can be determined by performing a spectral analysis of the interpolated fields and choosing the smallest values that remove any or most of the aliasing due to the uneven sampling by the satellite. The methodology is illustrated with the computation of average divergence fields over the equatorial Pacific Ocean from SeaWinds-on-QuikSCAT surface wind measurements, for which 72 h and 510 km are suggested as optimal interpolation windows. It is found that the wind variability is reduced over the cold tongue and enhanced over the Pacific warm pool, consistent with the notion that the unstably stratified boundary layer has generally more variable winds and more gustiness than the stably stratified boundary layer. It is suggested that the spectral analysis optimization can be used for any process where time-space correspondence can be assumed.

The Detectability of Radio Auroral Emission from Proxima b

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burkhart, Blakesley; Loeb, Abraham

Magnetically active stars possess stellar winds whose interactions with planetary magnetic fields produce radio auroral emission. We examine the detectability of radio auroral emission from Proxima b, the closest known exosolar planet orbiting our nearest neighboring star, Proxima Centauri. Using the radiometric Bode’s law, we estimate the radio flux produced by the interaction of Proxima Centauri’s stellar wind and Proxima b’s magnetosphere for different planetary magnetic field strengths. For plausible planetary masses, Proxima b could produce radio fluxes of 100 mJy or more in a frequency range of 0.02–3 MHz for planetary magnetic field strengths of 0.007–1 G. According tomore » recent MHD models that vary the orbital parameters of the system, this emission is expected to be highly variable. This variability is due to large fluctuations in the size of Proxima b’s magnetosphere as it crosses the equatorial streamer regions of dense stellar wind and high dynamic pressure. Using the MHD model of Garraffo et al. for the variation of the magnetosphere radius during the orbit, we estimate that the observed radio flux can vary nearly by an order of magnitude over the 11.2-day period of Proxima b. The detailed amplitude variation depends on the stellar wind, orbital, and planetary magnetic field parameters. We discuss observing strategies for proposed future space-based observatories to reach frequencies below the ionospheric cutoff (∼10 MHz), which would be required to detect the signal we investigate.« less

A case study of ionospheric storm effects during long-lasting southward IMF Bz-driven geomagnetic storm

NASA Astrophysics Data System (ADS)

Liu, Jing; Liu, Libo; Nakamura, Takuji; Zhao, Biqiang; Ning, Baiqi; Yoshikawa, A.

2014-09-01

Multiple instrumental observations including GPS total electron content (TEC), foF2 and hmF2 from ionosondes, vertical ion drift measurements from Communication/Navigation Outage Forecasting System, magnetometer data, and far ultraviolet airglow measured by Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (TIMED/GUVI) are used to investigate the profound ionospheric disturbances at midlatitude and low latitude during the 14-17 July 2012 geomagnetic storm event, which was featured by prolonged southward interplanetary geomagnetic field component for about 30 h below -10 nT. In the East Asian/Australian sector, latitudinal profile of TEC variations in the main phase were characterized by three bands of increments and separated by weak depressions in the equatorial ionospheric anomaly (EIA) crest regions, which were caused by the combined effects of disturbance dynamo electric fields (DDEF) and equatorward neutral winds. In the recovery phase, strong inhibition of EIA occurred and the summer crest of EIA disappeared on 16 July due to the combined effects of intrusion of neutral composition disturbance zone as shown by the TIMED/GUVI O/N2 measurements and long-lasting daytime westward DDEF inferred from the equatorial electrojet observations. The transit time of DDEF over the dip equator from westward to eastward is around 2200 LT. In the American longitude, the salient ionospheric disturbances in the summer hemisphere were characterized by daytime periodical intrusion of negative phase for three consecutive days in the recovery phase, preceded by storm-enhanced density plume in the initial phase. In addition, multiple short-lived prompt penetration electric fields appeared during stable southward interplanetary magnetic field (IMF) Bz in the recovery phase and were responsible for enhanced the EIA and equatorial ionospheric uplift around sunset.

Longitudinal Variation of the Lunar Tide in the Equatorial Electrojet

NASA Astrophysics Data System (ADS)

Yamazaki, Yosuke; Stolle, Claudia; Matzka, Jürgen; Siddiqui, Tarique A.; Lühr, Hermann; Alken, Patrick

2017-12-01

The atmospheric lunar tide is one known source of ionospheric variability. The subject received renewed attention as recent studies found a link between stratospheric sudden warmings and amplified lunar tidal perturbations in the equatorial ionosphere. There is increasing evidence from ground observations that the lunar tidal influence on the ionosphere depends on longitude. We use magnetic field measurements from the CHAMP satellite during July 2000 to September 2010 and from the two Swarm satellites during November 2013 to February 2017 to determine, for the first time, the complete seasonal-longitudinal climatology of the semidiurnal lunar tidal variation in the equatorial electrojet intensity. Significant longitudinal variability is found in the amplitude of the lunar tidal variation, while the longitudinal variability in the phase is small. The amplitude peaks in the Peruvian sector (˜285°E) during the Northern Hemisphere winter and equinoxes, and in the Brazilian sector (˜325°E) during the Northern Hemisphere summer. There are also local amplitude maxima at ˜55°E and ˜120°E. The longitudinal variation is partly due to the modulation of ionospheric conductivities by the inhomogeneous geomagnetic field. Another possible cause of the longitudinal variability is neutral wind forcing by nonmigrating lunar tides. A tidal spectrum analysis of the semidiurnal lunar tidal variation in the equatorial electrojet reveals the dominance of the westward propagating mode with zonal wave number 2 (SW2), with secondary contributions by westward propagating modes with zonal wave numbers 3 (SW3) and 4 (SW4). Eastward propagating waves are largely absent from the tidal spectrum. Further study will be required for the relative importance of ionospheric conductivities and nonmigrating lunar tides.

Vertical structure and characteristics of 23-60 day (zonal) oscillations over the tropical latitudes during the winter months of 1986 - Results of equatorial wave campaign-II

NASA Technical Reports Server (NTRS)

Raghavarao, R.; Suhasini, R.; Sridharan, R.; Krishnamurthy, B. V.; Nagpal, O. P.

1990-01-01

Results are presented of the equatorial wave campaign-II, a meteorological rocket study which was part of the Indian Middle Atmosphere Program. The equatorial wave campaign-II was conducted from Shar, India (13.7 deg N, 80.2 deg E) from January 15-February 28, 1986. By means of high altitude balloon and the RH-200 meteorological rocket, winds were measured from ground level up to 60 km altitude once each day during the 45-day period. The oscillation frequencies of the deviations in the east-west component of the winds from their mean at each 1-km height interval are obtained by the maximum entropy method. The phases and amplitudes of these frequencies are determined by use of the least squares method on the wind variation time series. Enhanced wave activity is shown to take place in the troposphere and lower mesosphere. The tropospheric waves observed suggest themselves to be Rossby waves of extratropical origin penetrating to tropical latitudes. The observed stratospheric/mesospheric waves appear to emanate from a source around the stratopause.

Intraseasonal Variability of the Equatorial Indian Ocean Observed from Sea Surface Height, Wind, and Temperature Data

NASA Technical Reports Server (NTRS)

Fu, Lee-Lueng

2007-01-01

The forcing of the equatorial Indian Ocean by the highly periodic monsoon wind cycle creates many interesting intraseasonal variabilities. The frequency spectrum of the wind stress observations from the European Remote Sensing Satellite scatterometers reveals peaks at the seasonal cycle and its higher harmonics at 180, 120, 90, and 75 days. The observations of sea surface height (SSH) from the Jason and Ocean Topography Experiment (TOPEX)/Poseidon radar altimeters are analyzed to study the ocean's response. The focus of the study is on the intraseasonal periods shorter than the annual period. The semiannual SSH variability is characterized by a basin mode involving Rossby waves and Kelvin waves traveling back and forth in the equatorial Indian Ocean between 10(deg)S and 10(deg)N. However, the interference of these waves with each other masks the appearance of individual Kelvin and Rossby waves, leading to a nodal point (amphidrome) of phase propagation on the equator at the center of the basin. The characteristics of the mode correspond to a resonance of the basin according to theoretical models. The theory also calls for similar modes at 90 and 60 days.

On the Fluctuating Component of the Sun's Large-Scale Magnetic Field

NASA Astrophysics Data System (ADS)

Wang, Y.-M.; Sheeley, N. R., Jr.

2003-06-01

The Sun's large-scale magnetic field and its proxies are known to undergo substantial variations on timescales much less than a solar cycle but longer than a rotation period. Examples of such variations include the double activity maximum inferred by Gnevyshev, the large peaks in the interplanetary field strength observed in 1982 and 1991, and the 1.3-1.4 yr periodicities detected over limited time intervals in solar wind speed and geomagnetic activity. We consider the question of the extent to which these variations are stochastic in nature. For this purpose, we simulate the evolution of the Sun's equatorial dipole strength and total open flux under the assumption that the active region sources (BMRs) are distributed randomly in longitude. The results are then interpreted with the help of a simple random walk model including dissipation. We find that the equatorial dipole and open flux generally exhibit multiple peaks during each 11 yr cycle, with the highest peak as likely to occur during the declining phase as at sunspot maximum. The widths of the peaks are determined by the timescale τ~1 yr for the equatorial dipole to decay through the combined action of meridional flow, differential rotation, and supergranular diffusion. The amplitudes of the fluctuations depend on the strengths and longitudinal phase relations of the BMRs, as well as on the relative rates of flux emergence and decay. We conclude that stochastic processes provide a viable explanation for the ``Gnevyshev gaps'' and for the existence of quasi periodicities in the range ~1-3 yr.

Equatorial waves in the NCAR stratospheric general circulation model

NASA Technical Reports Server (NTRS)

Boville, B. A.

1985-01-01

Equatorially trapped wave modes are very important in the tropical stratospheric momentum balance. Kelvin waves and mixed Rossby-gravity waves are believed to be responsible for the quasi-biennial oscillation of the zonal winds in the equatorial lower stratosphere. Both Kelvin and mixed Rossby-gravity waves have been identified in observations and in numerical models. Kelvin and mixed Rossby-gravity waves are identified in a general circulation model extending from the surface into the mesosphere and looks at the effect on the waves of lowering the top of the model.

Solar activity variations of nocturnal thermospheric meridional winds over Indian longitude sector

NASA Astrophysics Data System (ADS)

Madhav Haridas, M. K.; Manju, G.; Arunamani, T.

2016-09-01

The night time F-layer base height information from ionosondes located at two equatorial stations Trivandrum (TRV 8.5°N, 77°E) and Sriharikota (SHAR 13.7°N, 80.2°E) spanning over two decades are used to derive the climatology of equatorial nocturnal Thermospheric Meridional Winds (TMWs) prevailing during High Solar Activity (HSA) and Low Solar Activity (LSA) epochs. The important inferences from the analysis are 1) Increase in mean equatorward winds observed during LSA compared to HSA during pre midnight hours; 25 m/s for VE (Vernal Equinox) and 20 m/s for SS (Summer Solstice), AE (autumnal Equinox) and WS (Winter Solstice). 2) Mean wind response to Solar Flux Unit (SFU) is established quantitatively for all seasons for pre-midnight hours; rate of increase is 0.25 m/s/SFU for VE, 0.2 m/s/SFU for SS and WS and 0.08 m/s/SFU for AE. 3) Theoretical estimates of winds for the two epochs are performed and indicate the role of ion drag forcing as a major factor influencing TMWs. 4) Observed magnitude of winds and rate of flux dependencies are compared to thermospheric wind models. 5) Equinoctial asymmetry in TMWs is observed for HSA at certain times, with more equatorward winds during AE. These observations lend a potential to parameterize the wind components and effectively model the winds, catering to solar activity variations.

Nonmigrating tidal modulation of the equatorial thermosphere and ionosphere anomaly

NASA Astrophysics Data System (ADS)

Lei, Jiuhou; Thayer, Jeffrey P.; Wang, Wenbin; Yue, Jia; Dou, Xiankang

2014-04-01

The modulation of nonmigrating tides on both the ionospheric equatorial ionization anomaly (EIA) and the equatorial thermosphere anomaly (ETA) is investigated on the basis of simulations from the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM). Our simulations demonstrate the distinct features of the EIA and ETA seen in observations after the inclusion of field-aligned ion drag in the model. Both the EIA and the ETA in the constant local time frame display an obvious zonal wave-4 structure associated with the modulation of nonmigrating tides. However, the modeled EIA and ETA show a primary zonal wave-1 structure when only the migrating tides are specified at the model lower boundary. Our simulations reveal that the zonal wave-4 structure of the ETA under both low and high solar activity conditions is mainly caused by the direct response of the upper thermosphere to the diurnal eastward wave number 3 and semidiurnal eastward wave number 2 nonmigrating tides from the lower atmosphere. There is a minor contribution from the ion-neutral coupling. The zonal wave-4 structure of the EIA is also caused by these nonmigrating tides but through the modulation of the neutral wind dynamo.

Seasonal variation of the South Indian tropical gyre

NASA Astrophysics Data System (ADS)

Aguiar-González, Borja; Ponsoni, Leandro; Ridderinkhof, Herman; van Aken, Hendrik M.; de Ruijter, Will P. M.; Maas, Leo R. M.

2016-04-01

Based on satellite altimeter data and global atlases of temperature, salinity, wind stress and wind-driven circulation we investigate the seasonal variation of the South Indian tropical gyre and its associated open-ocean upwelling system, known as the Seychelles-Chagos Thermocline Ridge (SCTR). Results show a year-round, altimeter-derived cyclonic gyre where the upwelling regime appears closely related to seasonality of the ocean gyre, a relationship that has not been previously explored in this region. An analysis of major forcing mechanisms suggests that the thermocline ridge results from the constructive interaction of basin-scale wind stress curl, local-scale wind stress forcing and remote forcing driven by Rossby waves of different periodicity: semiannual in the west, under the strong influence of monsoonal winds; and, annual in the east, where the southeasterlies prevail. One exception occurs during winter, when the well-known westward intensification of the upwelling core, the Seychelles Dome, is shown to be largely a response of the wind-driven circulation. At basin-scale, the most outstanding feature is the seasonal shrinkage of the ocean gyre and the SCTR. From late autumn to spring, the eastward South Equatorial Countercurrent (SECC) recirculates early in the east on feeding the westward South Equatorial Current, therefore closing the gyre before arrival to Sumatra. We find this recirculation longitude migrates over 20° and collocates with the westward advance of a zonal thermohaline front emerging from the encounter between (upwelled) Indian Equatorial Water and relatively warmer and fresher Indonesian Throughflow Water. We suggest this front, which we call the Indonesian Throughflow Front, plays an important role as remote forcing to the tropical gyre, generating southward geostrophic flows that contribute to the early recirculation of the SECC.

A simulation study of the equatorial ionospheric response to the October 2013 geomagnetic storm

NASA Astrophysics Data System (ADS)

Lei, J.; Ren, D.

2017-12-01

The ionospheric observation from ionosonde at Sao Luis (2.5S, 44.2W; 7S dip latitude) around the magnetic equator showed that the nighttime ionospheric F2 peak height (hmF2) was uplifted by more than 150 km during the October 2013 geomagnetic storm. The changes of hmF2 at the magnetic equator were generally attributed to the variations of vertical drift associated with zonal electric field. In this paper, the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulation results are utilized to explore the possible physical mechanisms responsible for the observed increase of hmF2 at Sao Luis. The TIEGCM reproduced the changes of F2 peak electron density (NmF2) and its height (hmF2) during the main and recovery phases of the October 2013 storm. A series of controlled simulations revealed that, besides the enhancement of vertical plasma drift, the convergence of horizontal neutral winds and thermospheric expansion also contributed significantly to the profound increase of nighttime hmF2 observed at Sao Luis on 2 October. Moreover, the changes of neutral winds and neutral temperature in the equatorial region are associated with the interference of storm time travelling atmospheric disturbances originating from high latitudes.

Storm-Time Meridional Wind Perturbations in the Equatorial Thermosphere

NASA Astrophysics Data System (ADS)

Haaser, R. A.; Davidson, R.; Heelis, R. A.; Earle, G. D.; Venkatraman, S.; Klenzing, J.

2013-12-01

We present observations from the Coupled Ion Neutral Dynamics Investigation (CINDI) of storm-time modifications to the neutral atmosphere at equatorial latitudes near the magnetic equator at 400 km altitude during the active period near solar maximum in 2011 and 2012. Perturbations in the neutral temperature on the dayside and the nightside are consistent with observed increases in the neutral density in accord with hydrostatic equilibrium. In the evening and midnight sectors these modifications are additionally accompanied by perturbations in the meridional neutral wind, which are the focus of the work. The observations are made in the southern hemisphere near the magnetic equator, usually dominated by energy inputs from the southern polar regions that produce south to north (northward) wind perturbations to accompany perturbations in the neutral density and temperature. In one exceptional case when observations are made near midnight and the north magnetic pole rotates through the midnight sector, north to south (southward) meridional wind perturbations are observed.

M-dwarf stellar winds: the effects of realistic magnetic geometry on rotational evolution and planets

NASA Astrophysics Data System (ADS)

Vidotto, A. A.; Jardine, M.; Morin, J.; Donati, J. F.; Opher, M.; Gombosi, T. I.

2014-02-01

We perform three-dimensional numerical simulations of stellar winds of early-M-dwarf stars. Our simulations incorporate observationally reconstructed large-scale surface magnetic maps, suggesting that the complexity of the magnetic field can play an important role in the angular momentum evolution of the star, possibly explaining the large distribution of periods in field dM stars, as reported in recent works. In spite of the diversity of the magnetic field topologies among the stars in our sample, we find that stellar wind flowing near the (rotational) equatorial plane carries most of the stellar angular momentum, but there is no preferred colatitude contributing to mass-loss, as the mass flux is maximum at different colatitudes for different stars. We find that more non-axisymmetric magnetic fields result in more asymmetric mass fluxes and wind total pressures ptot (defined as the sum of thermal, magnetic and ram pressures). Because planetary magnetospheric sizes are set by pressure equilibrium between the planet's magnetic field and ptot, variations of up to a factor of 3 in ptot (as found in the case of a planet orbiting at several stellar radii away from the star) lead to variations in magnetospheric radii of about 20 per cent along the planetary orbital path. In analogy to the flux of cosmic rays that impact the Earth, which is inversely modulated with the non-axisymmetric component of the total open solar magnetic flux, we conclude that planets orbiting M-dwarf stars like DT Vir, DS Leo and GJ 182, which have significant non-axisymmetric field components, should be the more efficiently shielded from galactic cosmic rays, even if the planets lack a protective thick atmosphere/large magnetosphere of their own.

Ubiquitous equatorial accretion disc winds in black hole soft states

NASA Astrophysics Data System (ADS)

Ponti, G.; Fender, R. P.; Begelman, M. C.; Dunn, R. J. H.; Neilsen, J.; Coriat, M.

2012-05-01

High-resolution spectra of Galactic black holes (GBHs) reveal the presence of highly ionized absorbers. In one GBH, accreting close to the Eddington limit for more than a decade, a powerful accretion disc wind is observed to be present in softer X-ray states and it has been suggested that it can carry away enough mass and energy to quench the radio jet. Here we report that these winds, which may have mass outflow rates of the order of the inner accretion rate or higher, are a ubiquitous component of the jet-free soft states of all GBHs. We furthermore demonstrate that these winds have an equatorial geometry with opening angles of few tens of degrees, and so are only observed in sources in which the disc is inclined at a large angle to the line of sight. The decrease in Fe XXV/Fe XXVI line ratio with Compton temperature, observed in the soft state, suggests a link between higher wind ionization and harder spectral shapes. Although the physical interaction between the wind, accretion flow and jet is still not fully understood, the mass flux and power of these winds and their presence ubiquitously during the soft X-ray states suggest they are fundamental components of the accretion phenomenon.

The effect of oblateness and gravity darkening on the radiation driving in winds from rapidly rotating B stars

NASA Technical Reports Server (NTRS)

Cranmer, Steven R.; Owocki, Stanley P.

1995-01-01

We calculate the radiative driving force for winds around rapidly rotating oblate B stars, and we estimate the impact these forces should have on the production of a wind compressed disk. The effects of limb darkening, gravity darkening, oblateness, and an arbitrary wind velocity field are included in the computation of vector 'oblate finite disk' (OFD) factors, which depend on both radius and colatitude in the wind. The impact of limb darkening alone, with or without rotation, can increase the mass loss by as much as 10% over values computed using the standard uniformly bright spherical finite disk factor. For rapidly rotating stars, limb darkening makes 'sub-stellar' gravity darkening the dominant effect in the radial and latitudinal OFD factors, and lessens the impact of gravity darkening at other visible latitudes (nearer to the oblate limb). Thus, the radial radiative driving is generally stronger over the poles and weaker over the equator, following the gravity darkening at these latitudes. The nonradial radiative driving is considerably smaller in magnitude than the radial component, but is directed both away from the equatorial plane and in a retrograde azimuthal direction, acting to decrease the effective stellar rotation velocity. These forces thus weaken the equatorward wind compression compared to wind models computed with nonrotating finite disk factors.

Statistical modeling of Earth's plasmasphere

NASA Astrophysics Data System (ADS)

Veibell, Victoir

The behavior of plasma near Earth's geosynchronous orbit is of vital importance to both satellite operators and magnetosphere modelers because it also has a significant influence on energy transport, ion composition, and induced currents. The system is highly complex in both time and space, making the forecasting of extreme space weather events difficult. This dissertation examines the behavior and statistical properties of plasma mass density near geosynchronous orbit by using both linear and nonlinear models, as well as epoch analyses, in an attempt to better understand the physical processes that precipitates and drives its variations. It is shown that while equatorial mass density does vary significantly on an hourly timescale when a drop in the disturbance time scale index ( Dst) was observed, it does not vary significantly between the day of a Dst event onset and the day immediately following. It is also shown that increases in equatorial mass density were not, on average, preceded or followed by any significant change in the examined solar wind or geomagnetic variables, including Dst, despite prior results that considered a few selected events and found a notable influence. It is verified that equatorial mass density and and solar activity via the F10.7 index have a strong correlation, which is stronger over longer timescales such as 27 days than it is over an hourly timescale. It is then shown that this connection seems to affect the behavior of equatorial mass density most during periods of strong solar activity leading to large mass density reactions to Dst drops for high values of F10.7. It is also shown that equatorial mass density behaves differently before and after events based on the value of F10.7 at the onset of an equatorial mass density event or a Dst event, and that a southward interplanetary magnetic field at onset leads to slowed mass density growth after event onset. These behavioral differences provide insight into how solar and geomagnetic conditions impact mass density at geosynchronous orbit, enabling operators to better anticipate the response to space weather events and magnetosphere models to include mass density effects in magnetosphere simulations. It is shown that it is possible to classify an equatorial mass density event onset as being distinct from the three hours preceding it, indicating that there are distinguishing characteristics of solar wind and geomagnetic conditions surrounding an event. It is also been shown that given four days of solar and geomagnetic conditions, an event can be forecasted a day in advance with reasonable accuracy, but also with a number of false positives. These false positives have similarly distributed values as the true positives, though, indicating more data are needed to distinguish impending events.

A magnetospheric signature of some F layer positive storms

NASA Technical Reports Server (NTRS)

Miller, N. J.; Mayr, H. G.; Grebowsky, J. M.; Harris, I.; Tulunay, Y. K.

1981-01-01

Calculations of electron density distributions in the global thermosphere-ionosphere system perturbed by high-latitude thermospheric heating are presented which indicate a link between the heating and magnetospheric plasma disturbances near the equator. The calculations were made using a self-consistent model of the global sunlit thermosphere-ionosphere system describing the evolution of equatorial plasma disturbances. The heat input is found to cause electron density enhancements that propagate along magnetic field lines from the F2 maximum over mid-latitudes to the equator in the magnetosphere and which correspond to the positive phase of an F layer storm. The positive phase is shown to be generated by the induction of equatorward winds that raise the mid-latitude F layer through momentum transfer from neutral atoms to ionospheric ions, which ions pull electrons with them. Model results are used to identify plasma signatures of equatorward winds and an intensified magnetospheric electric field in Explorer 45 and Arial 4 measurements taken during the positive phase of an F layer storm.

Challenges in Measuring External Currents Driven by the Solar Wind-Magnetosphere Interaction

NASA Technical Reports Server (NTRS)

Le, Guan; Slavin, James A.; Pfaff, Robert F.

2014-01-01

In studying the Earth's geomagnetism, it has always been a challenge to separate magnetic fields from external currents originating from the ionosphere and magnetosphere. While the internal magnetic field changes very slowly in time scales of years and more, the ionospheric and magnetospheric current systems driven by the solar wind -magnetosphere interaction are very dynamic. They are intimately controlled by the ionospheric electrodynamics and ionospheremagnetosphere coupling. Single spacecraft observations are not able to separate their spatial and temporal variations, and thus to accurately describe their configurations. To characterize and understand the external currents, satellite observations require both good spatial and temporal resolutions. This paper reviews our observations of the external currents from two recent LEO satellite missions: Space Technology 5 (ST-5), NASA's first three-satellite constellation mission in LEO polar orbit, and Communications/Navigation Outage Forecasting System (C/NOFS), an equatorial satellite developed by US Air Force Research Laboratory. We present recommendations for future geomagnetism missions based on these observations.

Mapping magnetic field lines between the Sun and Earth

NASA Astrophysics Data System (ADS)

Li, B.; Cairns, Iver H.; Gosling, J. T.; Steward, G.; Francis, M.; Neudegg, D.; Schulte in den Bäumen, H.; Player, P. R.; Milne, A. R.

2016-02-01

Magnetic field topologies between the Sun and Earth are important for the connectivity to Earth of solar suprathermal particles, e.g., solar energetic particles and beam electrons in type III solar radio bursts. An approach is developed for mapping large-scale magnetic field lines near the solar equatorial plane, using near-Earth observations and a solar wind model with nonzero azimuthal magnetic field at the source surface. Unlike Parker's spiral model, which restricts the in-ecliptic angle ΦB in the Geocentric Solar Ecliptic coordinates to (90°-180°, 270°-360°) and so is unable to predict field configurations for the other ΦB values frequently observed in the solar wind, our approach can account for all the observed ΦB values. A set of predicted maps shows that near both minimal and maximal solar activity the field lines are typically open and that loops with both ends either connected to or disconnected from the Sun are relatively rare. The open field lines, nonetheless, often do not closely follow the Parker spiral, being less or more tightly wound, or strongly azimuthally or radially oriented, or inverted. The time-varying classes, e.g., bidirectional electrons, of suprathermal electron pitch angle distributions (PADs) at 1 AU are predicted from the mapped field line configurations and compared with Wind observations for two solar rotations, one each near solar minimum and solar maximum. PAD predictions by our approach agree quantitatively (≈90%) with the PAD observations and outperform (by ≈20%) PAD predictions using Parker's model.

Seasonal variations of the ionospheric total electron content in Asian equatorial anomaly regions

NASA Astrophysics Data System (ADS)

Tsai, Ho-Fang; Liu, Jann-Yenq; Tsai, Wei-Hsiung; Liu, Chao-Han; Tseng, Ching-Liang; Wu, Chin-Chun

2001-12-01

The ionospheric total electron contents (TEC) in both northern and southern equatorial anomaly regions are examined by using the Global Positioning System (GPS) in Asian area. The TEC contour charts obtained at YMSM (25.2°N, 121.6°E 14.0°N geomagnetic) and DGAR (7.3°S, 72.4°E 16.2°S geomagnetic) stations in 1997, solar minimum, are investigated. It is found that the ionospheric crests manifest remarkable seasonal variations. The TEC values on both northern and southern equatorial anomaly crests yield their maximum values during the vernal and autumnal months, but the winter anomaly does not appear in the southern region. Results show that both crests are fully developed around midday in winter, postnoon in equinoxes and late afternoon in summer, and the two crests move significantly equatorward in winter but slightly poleward in summer and autumn. These phenomena can be fully explained by a combined theory of the transequatorial neutral wind, the subsolar point, and the auroral equatorward wind.

Seasonal variation of the South Indian tropical gyre

NASA Astrophysics Data System (ADS)

Aguiar-González, Borja; Ponsoni, Leandro; Ridderinkhof, Herman; van Aken, Hendrik M.; de Ruijter, Will P. M.; Maas, Leo R. M.

2016-04-01

The South Indian tropical gyre receives and redistributes water masses from the Indonesian Throughflow (ITF), a source of Pacific Ocean water which represents the only low-latitude connector between the world oceans and, therefore, a key component in the global ocean circulation and climate system. We investigate the seasonal variation of the South Indian tropical gyre and its associated open-ocean upwelling system, known as the Seychelles-Chagos Thermocline Ridge (SCTR), based on satellite altimeter data (AVISO) and global atlases of temperature and salinity (CARS09), wind stress (SCOW) and wind-driven circulation. Two novel large-scale features governing the upper geostrophic circulation of the South Indian tropical gyre are revealed. First, the seasonal shrinkage of the ocean gyre. This occurs when the South Equatorial Countercurrent (SECC) recirculates before arrival to Sumatra from winter to spring, in apparent synchronization with the annual cycle of the ITF. Second, the open-ocean upwelling is found to vary following seasonality of the overlying geostrophic ocean gyre, a relationship that has not been previously shown for this region. An analysis of major forcing mechanisms suggests that the thermocline ridge results from the constructive interaction of basin-scale wind stress curl, local-scale wind stress forcing and remote forcing driven by Rossby waves of different periodicity: semiannual in the west, under the strong influence of monsoonal winds; and, annual in the east, where the southeasterlies prevail. One exception occurs during winter, when the well-known westward intensification of the upwelling core, the Seychelles Dome, is shown to be largely a response of the wind-driven circulation. Broadly speaking, the seasonal shrinkage of the ocean gyre (and the SCTR) is the one feature that differs most when the geostrophic circulation is compared to the wind-driven Sverdrup circulation. From late autumn to spring, the eastward SECC recirculates early in the east on feeding the westward South Equatorial Current, therefore closing the gyre before arrival to Sumatra. We find this recirculation longitude migrates over 20° and collocates with the westward advance of a zonal thermohaline front emerging from the encounter between (upwelled) Indian Equatorial Water and relatively warmer and fresher Indonesian Throughflow Water. We suggest this front, which we call the Indonesian Throughflow Front, plays an important role as forcing to the tropical gyre, generating southward geostrophic flows that contribute to the early recirculation of the SECC at longitudes more westward than predicted from the barotropic wind-driven circulation. Because our findings are based on time-averaged seasonal fields from 22 years of satellite altimeter data and from about 60 years of non-systematic sampling of ocean temperature and salinity data (CARS09), we stress the importance of further study on the possibility that interanual variability in the seasonal ITF may cause changes in the seasonal resizing of the ocean gyre and its associated upwelling ridge.

Interaction of the Local Interstellar Medium with the Heliosphere: Role of the Interior and Exterior Magnetic Fields

NASA Technical Reports Server (NTRS)

Barnes, Aaron; DeVincenzi, Donald (Technical Monitor)

2000-01-01

A complete model of the global interaction between the solar wind and the local interstellar medium must take account of interstellar neutral atoms, interstellar ionized gas, solar and galactic magnetic fields, galactic and anomalous cosmic rays. For now, however, in view of the many uncertainties about conditions in the interstellar medium, etc., all models must be regarded as highly idealized and incomplete. In the present review I concentrate on the role of magnetic fields of solar and interstellar origin. The former, the interior field, has negligible influence on the unshocked solar wind; the immediate post-shock solar wind is probably low-beta, so that the interior magnetic field is still unimportant, but this situation changes as the plasma flows through the heliosheath, and a ridge of strong magnetic field may form to separate materials of polar and equatorial origin. The exterior (interstellar) field is likely to play an important role in determining the global morphology of the system outside the termination shock. If the exterior field is strong enough, it can compress the heliosphere (although exterior neutral and/or ionized hydrogen may play the dominant role). Even if the interstellar magnetic field does not provide the dominant pressure, its orientation can substantially affect the configuration of the heliosphere, especially the location and orientation of the heliospheric discontinuities. The configurations can be quite different for the situations in which the field and flow are (a) aligned or (b) transverse. Obliquity of the field produces asymmetry in the geometry of the system; in particular the noses of heliopause and interstellar bow shock are shifted away from the interstellar flow direction, and in opposite directions, due to the asymmetric draping of the magnetic field.

High altitude flights in equatorial regions

NASA Astrophysics Data System (ADS)

Redkar, R. T.

A thorough analysis of balloon flights made from Hyderabad, India (Latitude 17°28'N, Longitude 78°35'E), and other equatorial sites has been made. It has been shown that limited success is expected for flights made from equatorial latitudes with balloons made out of natural colour polyethylene film, since the best known balloon film in the world today viz. Winzen Stratofilm is tested for low temperature brittleness only at -80°C., whereas the tropopause temperatures over equatorial latitudes vary between -80°C and -90°C. The success becomes even more critical when flights are made with heavy payloads and larger balloons particularly at night when in the absence of solar radiation the balloon film becomes more susceptible to low temperature brittle failure. It is recommended that in case of capped balloons longer caps should be used to fully cover the inflated protion of the balloon at the higher level equatorial tropopause. It is also advised that the conditions such as wind shears in the tropopause should be critically studied before launching and a day with the tropopause temperature nearer to -80°C should be chosen. Special care also should be taken while handling the balloon on ground and during launching phase. Properties of Winzen Stratofilm have been critically studied and fresh mandates have been recommended on the basis of limiting values of film stresses which caused balloon failures in the equatorial tropopause. It is also emphasized that the data on such flights is still meagre especially for flights with heavy payloads and larger balloons. It has been also shown that it is safest to use balloons made out of grey coloured film which retains its flexibility with the absorption of solar radiation, the success obtained with such balloons so far being 100%. The drawback, however, is that these balloons cannot be used for night flights. Stratospheric wind regimes over Hyderabad are also discussed with a view to determine the period over which long duration flights can be made. The data available, however, is meagre and it is recommended that more frequent special wind ascents be made to collect adequate statistical data from which reliable conclusions could be drawn through critical analysis.

Discovery Of A Rossby Wave In Jupiter's South Equatorial Region

NASA Technical Reports Server (NTRS)

Simon-Miller, Amy A.; Choi, D. S.; Rogers, J. H.; Gierasch, P. J.

2012-01-01

A detailed study of the chevron-shaped dark spots on the strong southern equatorial wind jet near 7.5 deg S planetographic latitude shows variations in velocity with longitude and time. The chevrons move with velocities near the maximum wind jet velocity of approx.140 m/s, as deduced by the history of velocities at this latitude and the magnitude of the symmetric wind jet near 7 deg N latitude. Their repetitive nature is consistent with an inertia-gravity wave (n = 75-100) with phase speed up to 25 m/s, relative to the local flow, but the identity of this wave mode is not well constrained. However, high spatial resolution movies from Cassini images show that the chevrons oscillate in latitude with a approx.7-day period. This oscillating motion has a wavelength of approx.20 deg and a speed of approx.100 m/s, following a pattern similar to that seen in the Rossby wave plumes of the North Equatorial Zone, and possibly reinforced by it, though they are not perfectly in phase. The transient anticyclonic South Equatorial Disturbance (SED) may be a similar wave feature, but moves at slower velocity. All data show chevron latitude variability, but it is unclear if this Rossby wave is present during other epochs, without time series movies that fully delineate it. In the presence of multiple wave modes, the difference in dominant cloud appearance between 7 deg N and 7.5 deg S may be due to the presence of the Great Red Spot, either through changes in stratification and stability or by acting as a wave boundary.

Equatorial Wave Line, Pacific Ocean

NASA Image and Video Library

1993-01-19

STS054-95-042 (13-19 Jan 1993) --- The Equatorial Pacific Ocean is represented in this 70mm view. The international oceanographic research community is presently conducting a program called Joint Global Ocean Flux Study (JGOFS) to study the global ocean carbon budget. A considerable amount of effort within this program is presently being focused on the Equatorial Pacific Ocean because of the high annual average biological productivity. The high productivity is the result of nearly constant easterly winds causing cool, nutrient-rich water to well up at the equator. In this view of the sun glint pattern was photographed at about 2 degrees north latitude, 103 degrees west longitude, as the Space Shuttle passed over the Equatorial Pacific. The long narrow line is the equatorial front, which defines the boundary between warm surface equatorial water and cool, recently upwelled water. Such features are of interest to the JGOFS researchers and it is anticipated that photographs such as this will benefit the JGOFS program.

Late Quaternary surface circulation in the east equatorial South Atlantic: Evidence from Alkenone sea surface temperatures

NASA Astrophysics Data System (ADS)

Schneider, Ralph R.; Müller, Peter J.; Ruhland, GöTz

1995-04-01

Angola Basin and Walvis Ridge records of past sea surface temperatures (SST) derived from the alkenone Uk37 index are used to reconstruct the surface circulation in the east equatorial South Atlantic for the last 200,000 years. Comparison of SST estimates from surface sediments between 5° and 20°S with modern SST data suggests that the alkenone temperatures represent annual mean values of the surface mixed layer. Alkenone-derived temperatures for the warm climatic maxima of the Holocene and the penultimate interglacial are 1 to 4°C higher than latest Holocene values. All records show glacial to interglacial differences of about 3.5°C in annual mean SST, which is about 1.5°C greater than the difference estimated by CLIMAP (1981) for the eastern Angola Basin. At the Walvis Ridge, significant SST variance is observed at all of the Earth's orbital periodicities. SST records from the Angola Basin vary predominantly at 23- and 100-kyr periodicities. For the precessional cycle, SST changes at the Walvis Ridge correspond to variations of boreal summer insolation over Africa and lead ice volume changes, suggesting that the east equatorial South Atlantic is sensitive to African monsoon intensity via trade-wind zonality. Angola Basin SST records lag those from the Walvis Ridge and the equatorial Atlantic by about 3 kyr. The comparison of Angola Basin and Walvis Ridge SST records implies that the Angola-Benguela Front (ABF) (currently at about 14-16°S) has remained fairly stationary between 12° and 20°S (the limits of our cores) during the last two glacial-interglacial cycles. The temperature contrast associated with the ABF exhibits a periodic 23-kyr variability which is coherent with changes in boreal summer insolation over Africa. These observations suggest that surface waters north of the present ABF have not directly responded to monsoon-modulated changes in the trade-wind vector, that the central field of zonally directed trades in the southern hemisphere was not shifted or extended northward by several degrees of latitude during glacials, and that a cyclonic gyre circulation has existed in the east equatorial South Atlantic over the last 200,000 years. This scenario contradicts former assumptions of glacial intensification of the Benguela Current into the eastern Angola Basin and increased coastal upwelling off Angola.

The Atmospheric Dynamics of Jupiter, Saturn, and Titan

NASA Technical Reports Server (NTRS)

Flasar, F. M.

2009-01-01

Comparative studies of Jupiter and Saturn often emphasize their similarities, but recent observations have highlighted important differences. The stratospheres of both planets exhibit an equatorial oscillation reminiscent of that in Earth's middle atmosphere. Jupiter's oscillation has a 4-5 year period, not linked to its season, and it has been modeled as an analog to the terrestrial quasi-biennial oscillation, driven by the stresses associated with vertically propagating waves. Saturn's equatorial oscillation is nearly semiannual, but wave activity may still be a driver. Jupiter's internal rotation rate is inferred from its steady modulated radio emission. Saturn's internal rotation is more enigmatic. It has been inferred from the modulation of the body's kilometric radio emission, but this period has varied by 1% over the last 25 years. Saturn's equatorial winds are also puzzling, as those inferred from cloud tracking by Cassini and more recent HST observations are weaker than those from Voyager. Whether this is attributable to a difference in altitudes of the tracked clouds in winds with vertical shear or a real temporal change in the winds is not known. Both winter and summer poles of Saturn exhibit very compact circumpolar vortices with warm cores, indicating subsidence. Titan's middle atmosphere is characterized by global cyclostrophic winds, particularly the strong circumpolar vortex in the winter hemisphere. In many ways, the spatial distribution of temperature, gaseous constituents, and condensates is reminiscent of conditions in terrestrial winter vortices, albeit with different chemistry. The meridional contrast in Titan's tropospheric temperatures is small, only a few kelvins.

Saturn and Earth polar oval position forecast by IMPEx InfrastructureWeb Services based on the Paraboloid magnetospheric model

NASA Astrophysics Data System (ADS)

Blokhina, M. S.; Alexeev, I. I.; Belenkaya, E. S.; Kalegaev, V. V.; Barinova, V. O.; Khodachenko, M. L.; Topf, F.

2012-09-01

The Saturn and Earth auroral emissions have different generation mechanisms, however, both mechanisms are not understood very well till now (see [1]). Both of these phenomena have a long history of observations. For Saturn these are Hubble images and big onground telescope images, as well as the Cassini ones in recent time. For Earth these are the satellite visible and UV camera images and onground observations. In course of the EU-FP7 Project "Integrated Medium for Planetary Exploration" the Web services based on the paraboloid magnetospheric models were constructed . The model field lines tracing gives us a possibility to distinguish the closed and open field line bundles. Additionally, we can find a boundary between the dipole type field lines and determine a region of the tail-like field lines crossing the equatorial plane tailward from the inner edge of the tail current sheet. Projections of this boundary and of the boundary between open and closed field lines at the ionospheric level mark the terrestrial auroral oval boundaries. The final result depends on the solar wind parameters and the magnetospheric state. In the Earth's case we have the ACE solar wind monitoring data which should be used to determine the magnetospheric state (http://smdc.sinp.msu.ru/index.py? nav=paraboloid/index [Interactive Earth]). For Saturn we use the three levels of the solar wind dynamic pressure (http://smdc.sinp. msu.ru/index.py?nav=paraboloid/index [Interactive Saturn]).

Organized convection over southwest peninsular India during the pre-monsoon season

NASA Astrophysics Data System (ADS)

Sreelekha, P. N.; Babu, C. A.

2018-03-01

The paper addresses observational aspects of widespread rain associated with the organized convection that forms over the southwest peninsular India during the pre-monsoon season. The evolution of the cloud band over the equatorial region, its northward propagation, development of cross equatorial flow near the Somalia coast, and appearance of equatorial westerly wind resemble closely to that of the monsoon organized convection. Low-level convergence, cyclonic vorticity, and ascending motion are other major characteristics of the cloud bands associated with the pre-monsoon organized convection which exhibits similarity with that of monsoon. The ascending motion plays vital role on the formation of cloud band that produces widespread rainfall persisting for more than a week. The vertical shear of meridional winds is found to co-exist with precipitation over the Arabian Sea off the southwest peninsular India. The velocity potential values derived from the winds at 850 and 200 hPa levels confirm the rising motion on the basis of low-level convergence and upper level divergence. Also, shifting of ascending limb of the local Hadley circulation to the north of the equator is observed during the days of the presence of organized convection over the southwest peninsular region. Noticeable shift in the Walker circulation rising limb is also identified during the same time.

The stratospheric QBO signal in the NCEP reanalysis, 1948-2001

NASA Astrophysics Data System (ADS)

Ribera, P.; Gallego, D.; Pena-Ortiz, C.; Gimeno, L.; Garcia, R.; Hernandez, E.; Calvo, N.

2003-04-01

The spatiotemporal evolution of the zonal wind in the stratosphere is analyzed based on the use of the NCEP reanalysis dataset (1948-2001). MTM-SVD, a frequency-domain analysis method, is applied to isolate significant spatially-coherent variability with narrowband, oscillatory character. A quasibiennial oscillation is detected as the most intense coherent signal in the whole mid and high stratosphere, being the signal less intense in the lower levels, closer to the troposphere. There is a clear downward propagation of the signal with time over low latitudes, from 10 to 100 hPa, that is not evident over mid and high latitudes. A different behavior of the signal is detected over the Northern and the Southern Hemisphere. In the NH an anomaly in the zonal wind field, in phase with the equatorial signal, is detected to run around the whole hemisphere at 60º, and two regions in subtropical latitudes show wind anomalies with their sing opposed to that of the equator. In the SH no signal is detected in extratropical areas.

Thermal winds in stellar mass black hole and neutron star binary systems

NASA Astrophysics Data System (ADS)

Done, Chris; Tomaru, Ryota; Takahashi, Tadayuki

2018-01-01

Black hole binaries show equatorial disc winds at high luminosities, which apparently disappear during the spectral transition to the low/hard state. This is also where the radio jet appears, motivating speculation that both wind and jet are driven by different configurations of the same magnetic field. However, these systems must also have thermal winds, as the outer disc is clearly irradiated. We develop a predictive model of the absorption features from thermal winds, based on pioneering work of Begelman, McKee & Shields. We couple this to a realistic model of the irradiating spectrum as a function of luminosity to predict the entire wind evolution during outbursts. We show that the column density of the thermal wind scales roughly with luminosity, and does not shut off at the spectral transition, though its visibility will be affected by the abrupt change in ionizing spectrum. We re-analyse the data from H1743-322, which most constrains the difference in wind across the spectral transition, and show that these are consistent with the thermal wind models. We include simple corrections for radiation pressure, which allows stronger winds to be launched from smaller radii. These winds become optically thick around Eddington, which may even explain the exceptional wind seen in one observation of GRO J1655-40. These data can instead be fit by magnetic wind models, but similar winds are not seen in this or other systems at similar luminosities. Hence, we conclude that the majority (perhaps all) of current data can be explained by thermal or thermal-radiative winds.

Ionospheric Storm Effects and Equatorial Plasma Irregularities During the 17-18 March 2015 Event

NASA Technical Reports Server (NTRS)

Zhou, Yun-Liang; Luhr, Hermann; Xiong, Chao; Pfaff, Robert F.

2016-01-01

The intense magnetic storm on 17-18 March 2015 caused large disturbances of the ionosphere. Based on the plasma density (Ni) observations performed by the Swarm fleet of satellites, the Gravity Recovery and Climate Experiment mission, and the Communications/Navigation Outage Forecasting System satellite, we characterize the storm-related perturbations at low latitudes. All these satellites sampled the ionosphere in morning and evening time sectors where large modifications occurred. Modifications of plasma density are closely related to changes of the solar wind merging electric field (E (sub m)). We consider two mechanisms, prompt penetration electric field (PPEF) and disturbance dynamo electric field (DDEF), as the main cause for the Ni redistribution, but effects of meridional wind are also taken into account. At the start of the storm main phase, the PPEF is enhancing plasma density on the dayside and reducing it on the nightside. Later, DDEF takes over and causes the opposite reaction. Unexpectedly, there appears during the recovery phase a strong density enhancement in the morning/pre-noon sector and a severe Ni reduction in the afternoon/evening sector, and we suggest a combined effect of vertical plasma drift, and meridional wind is responsible for these ionospheric storm effects. Different from earlier studies about this storm, we also investigate the influence of storm dynamics on the initiation of equatorial plasma irregularities (EPIs). Shortly after the start of the storm main phase, EPIs appear in the post-sunset sector. As a response to a short-lived decline of E (sub m), EPI activity appears in the early morning sector. Following the second start of the main phase, EPIs are generated for a few hours in the late evening sector. However, for the rest of the storm main phase, no more EPIs are initiated for more than 12 hours. Only after the onset of recovery phase does EPI activity start again in the post-midnight sector, lasting more than 7 hours.This comprehensive view of ionospheric storm effects and plasma irregularities adds to our understanding of conditions that lead to ionospheric instabilities.

Ionospheric storm effects and equatorial plasma irregularities during the 17-18 March 2015 event

NASA Astrophysics Data System (ADS)

Zhou, Yun-Liang; Lühr, Hermann; Xiong, Chao; Pfaff, Robert F.

2016-09-01

The intense magnetic storm on 17-18 March 2015 caused large disturbances of the ionosphere. Based on the plasma density (Ni) observations performed by the Swarm fleet of satellites, the Gravity Recovery and Climate Experiment mission, and the Communications/Navigation Outage Forecasting System satellite, we characterize the storm-related perturbations at low latitudes. All these satellites sampled the ionosphere in morning and evening time sectors where large modifications occurred. Modifications of plasma density are closely related to changes of the solar wind merging electric field (Em). We consider two mechanisms, prompt penetration electric field (PPEF) and disturbance dynamo electric field (DDEF), as the main cause for the Ni redistribution, but effects of meridional wind are also taken into account. At the start of the storm main phase, the PPEF is enhancing plasma density on the dayside and reducing it on the nightside. Later, DDEF takes over and causes the opposite reaction. Unexpectedly, there appears during the recovery phase a strong density enhancement in the morning/prenoon sector and a severe Ni reduction in the afternoon/evening sector, and we suggest a combined effect of vertical plasma drift, and meridional wind is responsible for these ionospheric storm effects. Different from earlier studies about this storm, we also investigate the influence of storm dynamics on the initiation of equatorial plasma irregularities (EPIs). Shortly after the start of the storm main phase, EPIs appear in the postsunset sector. As a response to a short-lived decline of Em, EPI activity appears in the early morning sector. Following the second start of the main phase, EPIs are generated for a few hours in the late evening sector. However, for the rest of the storm main phase, no more EPIs are initiated for more than 12 h. Only after the onset of recovery phase does EPI activity start again in the postmidnight sector, lasting more than 7 h. This comprehensive view of ionospheric storm effects and plasma irregularities adds to our understanding of conditions that lead to ionospheric instabilities.

A case study of Ionospheric storm effects during long-lasting southward IMF Bz driven geomagnetic storm

NASA Astrophysics Data System (ADS)

Liu, J., Sr.

2014-12-01

Multiple instrumental observations including GPS TEC, foF2 and hmF2 from ionosondes, vertical ion drift measurements from C/NOFS, magnetometer data and far-ultraviolet airglow measured by TIMED/GUVI are used to investigate the profound ionospheric disturbances at mid- and low-latitudes during the 14-17 July 2012 geomagnetic storm event, which was featured by prolonged southward interplanetary geomagnetic field component for about 30 hours below -10 nT. In the East Asian/Australian sector, latitudinal profile of TEC variations in the main phase were characterized by three bands of increments and separated by weak depressions in the Equatorial Ionospheric Anomaly (EIA) crest regions, which were caused by the combined effects of disturbance dynamo electric fields (DDEF) and equatorward neutral winds. In the recovery phase, strong inhibition of EIA occurred and the summer crest of EIA disappeared on 16 July due to the combined effects of intrusion of neutral composition disturbance zone as shown by the TIME/GUVI O/N2 measurements and long-lasting daytime westward DDEF inferred from the equatorial electric electrojet (EEJ) observations. The transit time of DDEF over the dip equator from westward to eastward is around 2200 LT. In the American longitude, the salient ionospheric disturbances in the summer hemisphere were characterized by daytime periodical intrusion of negative phase for three consecutive days in the recovery phase, preceded by storm enhanced density (SED) plume in the initial phase. In addition, multiple short-lived prompt penetration electric fields (PPEF) appeared during stable southward IMF Bz in the recovery phase and were responsible for enhanced the EIA and equatorial ionospheric uplift around sunset.

Equatorial atmospheric Kelvin waves during El Niño episodes and their effect on stratospheric QBO.

PubMed

Das, Uma; Pan, C J

2016-02-15

Equatorial atmospheric Kelvin waves are investigated during a positive El Niño Southern Oscillation (ENSO) episode using temperature data retrieved from GPS Radio Occultation (RO) observations of FORMOSAT-3/COSMIC during the period from August 2006 to December 2013. Enhanced Kelvin wave amplitudes are observed during the El Niño episode of 2009-2010 and it is also observed that these amplitudes correlate with the Niño 3.4 index and also with outgoing longwave radiation and trade wind index. This study indicates that the enhanced equatorial atmospheric Kelvin wave amplitudes might be produced by geophysical processes that were involved in the onset and development of the El Niño episode. Further, easterly winds above the tropopause during this period favored the vertically upward propagation of these waves that induced a fast descending westerly regime by the end of 2010, where the zero-wind line is observed to take only 5 months to descend from 10 to 50 hPa. The current study presents observational evidence of enhanced Kelvin wave amplitudes during El Niño that has affected the stratospheric quasi-biennial oscillation (QBO) through wave-mean flow interactions. Earlier El Niño episodes of 1987 and 1998 are also qualitatively investigated, using reanalysis data. It is found that there might have been an enhancement in the equatorial Kelvin wave amplitudes during almost all El Niño episodes, however, an effect of a fast descending westerly is observed in the QBO only when the ambient zonal winds in the lower stratosphere favor the upward propagation of the Kelvin waves and consequently they interact with the mean flow. This study indicates that the El Niño and QBO are not linearly related and wave mean flow interactions play a very important role in connecting these two geophysical phenomena. Copyright © 2015 Elsevier B.V. All rights reserved.

Dynamical relationship between wind speed magnitude and meridional temperature contrast: Application to an interannual oscillation in Venusian middle atmosphere GCM

NASA Astrophysics Data System (ADS)

Yamamoto, Masaru; Takahashi, Masaaki

2018-03-01

We derive simple dynamical relationships between wind speed magnitude and meridional temperature contrast. The relationship explains scatter plot distributions of time series of three variables (maximum zonal wind speed UMAX, meridional wind speed VMAX, and equator-pole temperature contrast dTMAX), which are obtained from a Venus general circulation model with equatorial Kelvin-wave forcing. Along with VMAX and dTMAX, UMAX likely increases with the phase velocity and amplitude of a forced wave. In the scatter diagram of UMAX versus dTMAX, points are plotted along a linear equation obtained from a thermal-wind relationship in the cloud layer. In the scatter diagram of VMAX versus UMAX, the apparent slope is somewhat steep in the high UMAX regime, compared with the low UMAX regime. The scatter plot distributions are qualitatively consistent with a quadratic equation obtained from a diagnostic equation of the stream function above the cloud top. The plotted points in the scatter diagrams form a linear cluster for weak wave forcing, whereas they form a small cluster for strong wave forcing. An interannual oscillation of the general circulation forming the linear cluster in the scatter diagram is apparent in the experiment of weak 5.5-day wave forcing. Although a pair of equatorial Kelvin and high-latitude Rossby waves with a same period (Kelvin-Rossby wave) produces equatorward heat and momentum fluxes in the region below 60 km, the equatorial wave does not contribute to the long-period oscillation. The interannual fluctuation of the high-latitude jet core leading to the time variation of UMAX is produced by growth and decay of a polar mixed Rossby-gravity wave with a 14-day period.

A Multi-wavelength Study of an Isolated MSP Bow Shock

NASA Astrophysics Data System (ADS)

Romani, Roger W.; Slane, Patrick; Green, Andrew

2017-08-01

PSR J2124-3358 is the only single MSP known to sport an Halpha bow shock. This shock, now also seen in the UV, encloses an unusual X-ray pulsar wind nebula (PWN) with a long off-axis trail. Combining the X-ray and UV images with AAT/KOALA integral field spectroscopy of the Halpha emission, we have an unusually complete picture of the pulsar's (101 km/s transverse) motion and the latitudinal distribution of its wind flux. These images reveal the 3-D orientation of a hard-spectrum PWN jet and a softer equatorial outflow. Within the context of a thin shock model, we can constrain the total energy output of the pulsar and the neutron star moment of inertia. The IFU spectra show extreme Balmer dominance, which also constrains the nature of the UV shock emission.

Equatorial plasma bubbles/range spread F irregularities and the QBO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, P.R.

1993-11-05

This paper reports on a study of plasma bubbles or spread F irregularities, observed at equatorial observation stations, looked at in conjunction with measures of the quasi biennial oscillation (QBO) of the mean lower stratospheric winds. Plasma bubbles and spread F irregularities are thought to be different manifestations of the same basic event, distinguished mainly by the observational method. For the case of range spread F events, ionosonde data has revealed in the past daily and seasonal variations, effects due to the solar cycle, and dependence upon the geomagnetic field and longitudinal location. These relationships have been shown to bemore » statistical in nature, so the authors have looked for other relationships which might be more relational in nature. When correlation with QBO phase variations are investigated, there is an observed increase or decrease in the range spread F, dependent upon whether the QBO is in an easterly or westerly phase, and observed in the American sector or Indian/East African sector.« less

Decay of Mesoscale Flux Transfer Events During Quasi-Continuous Spatially Extended Reconnection at the Magentopause

NASA Technical Reports Server (NTRS)

Hasegawa, H.; Kitamura, N.; Saito, Y.; Nagai, T.; Shinohara, I.; Yokota, S.; Pollock, C. J.; Giles, B. L.; Dorelli, J. C.; Gershman, D. J.;

Longitudinal Variations in Jupiter's Winds

NASA Astrophysics Data System (ADS)

Simon-Miller, Amy A.; Gierasch, P. J.; Tierney, G.

2010-10-01

Long-term studies of Jupiter's zonal wind field revealed temporal variations on the order of 20 to 40 m/s at many latitudes, greater than the typical data uncertainties of 1 to 10 m/s. No definitive periodicities were evident, however, though some latitudinally-confined signals did appear at periods relevant to the Quasi-Quadrennial Oscillation (Simon-Miller & Gierasch, Icarus, in press). As the QQO appears, from vertical temperature profiles, to propagate downward, it is unclear why a signal is not more obvious, unless other processes dominate over possibly weaker forcing from the QQO. An additional complication is that zonal wind profiles represent an average over some particular set of longitudes for an image pair and most data sets do not offer global wind coverage. Even avoiding known features, such as the large anticyclonic vortices especially prevalent in the south, there can be distinct variations in longitude. We present results on the full wind field from Voyager and Cassini data, showing apparent longitudinal variations of up to 60 m/s or more. These are particularly obvious near disruptions such as the South Equatorial Disturbance, even when the feature itself is not clearly visible. These two dates represent very different states of the planet for comparison: Voyagers 1 & 2 flew by Jupiter shortly after a global upheaval, while many regions were in a disturbed state, while the Cassini view is typical of a more quiescent period present during much of the 1990s and early 2000s.

Longitudinal Variations in Jupiter's Winds

NASA Technical Reports Server (NTRS)

Simon-Miller, Amy A.; Gierasch, P. J.; Tierney, G.

2010-01-01

Long-term studies of Jupiter's zonal wind field revealed temporal variations on the order of 20 to 40 m/s at many latitudes, greater than the typical data uncertainties of 1 to 10 m/s. No definitive periodicities were evident, however, though some latitudinally-confined signals did appear at periods relevant to the Quasi- Quadrennial Oscillation (Simon-Miller & Gierasch, Icarus, in press). As the QQO appears, from vertical temperature profiles, to propagate downward, it is unclear why a signal is not more obvious, unless other processes dominate over possibly weaker forcing from the QQO. An additional complication is that zonal wind profiles represent an average over some particular set of longitudes for an image pair and most data sets do not offer global wind coverage. Lien avoiding known features, such as the large anticyclonic vortices especially prevalent in the south, there can be distinct variations in longitude. We present results on the full wind field from Voyager and Cassini data, showing apparent longitudinal variations of up to 60 m/s or more. These are particularly obvious near disruptions such as the South Equatorial Disturbance, even when the feature itself is not clearly visible. These two dates represent very different states of the planet for comparison: Voyagers 1 & 2 flew by Jupiter shortly after a global upheaval, while many regions were in a disturbed state, while the Cassini view is typical of a more quiescent period present during much of the 1990s and early 2000s.

A Reversal of Decadal Trends in the Equatorial and North Indian Ocean

NASA Astrophysics Data System (ADS)

Thompson, P. R.; Merrifield, M. A.; McCreary, J. P., Jr.; Firing, E.; Piecuch, C. G.

2016-02-01

Sea level and upper ocean temperature trends in the Equatorial and North Indian Ocean (ENIO) reversed sign shortly after the turn of the century. The trend reversal is spatially coherent and characterized by subsurface cooling during 1993-2002 followed by subsurface warming during 2003-2012. Here we explore the dynamics and forcing of the decadal trend reversal, with a particular emphasis on the role of the Indian Ocean cross-equatorial cell (CEC) and anomalies transmitted from the Pacific basin to the ENIO via the Indonesian Throughflow (ITF). An examination of reanalysis wind-stress fields suggest that forcing of the CEC is enhanced during the cooling phase of the decadal fluctuation, which may account for the cooling trend below 100m in the ENIO during the first decade. In contrast, the subsurface warming during the second decade occurs at thermocline levels, which suggests a deepening of the thermocline during this period. Enhanced Pacific tradewinds since the early 1990s result in a deepening thermocline in the western tropical Pacific (WTP), which may be transmitted to the Indian Ocean basin via the ITF. We present results from simple model experiments that assess the potential for thermocline anomalies originating in the WTP to account for the deepening thermocline in the ENIO during the warming phase of the decadal fluctuation.

Coordinated observations of postmidnight irregularities and thermospheric neutral winds and temperatures at low latitudes

NASA Astrophysics Data System (ADS)

Dao, Tam; Otsuka, Yuichi; Shiokawa, Kazuo; Nishioka, Michi; Yamamoto, Mamoru; Buhari, Suhaila M.; Abdullah, Mardina; Husin, Asnawi

2017-07-01

We investigated a postmidnight field-aligned irregularity (FAI) event observed with the Equatorial Atmosphere Radar at Kototabang (0.2°S, 100.3°E, dip latitude 10.4°S) in Indonesia on the night of 9 July 2010 using a comprehensive data set of both neutral and plasma parameters. We examined the rate of total electron content change index (ROTI) obtained from GPS receivers in Southeast Asia, airglow images detected by an all-sky imager, and thermospheric neutral winds and temperatures obtained by a Fabry-Perot interferometer at Kototabang. Altitudes of the F layer (h'F) observed by ionosondes at Kototabang, Chiang Mai, and Chumphon were also surveyed. We found that the postmidnight FAIs occurred within plasma bubbles and coincided with kilometer-scale plasma density irregularities. We also observed an enhancement of the magnetically equatorward thermospheric neutral wind at the same time as the increase of h'F at low-latitude stations, but h'F at a station near the magnetic equator remained invariant. Simultaneously, a magnetically equatorward gradient of thermospheric temperature was identified at Kototabang. The convergence of equatorward neutral winds from the Northern and Southern Hemispheres could be associated with a midnight temperature maximum occurring around the magnetic equator. Equatorward neutral winds can uplift the F layer at low latitudes and increase the growth rate of Rayleigh-Taylor instabilities, causing more rapid extension of plasma bubbles. The equatorward winds in both hemispheres also intensify the eastward Pedersen current, so a large polarization electric field generated in the plasma bubble might play an important role in the generation of postmidnight FAIs.

A ‘self-adjustment’ mechanism for mixed-layer heat budget in the equatorial Atlantic cold tongue

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, Yanyan; Wang, Bin; Huang, Wenyu

Wind forcing is one of the most important sources for the oceanic energy cycle and is especially critical to the heat budget of surface mixed layer. The sensitivity of heat budget in the equatorial Atlantic cold tongue (EACT) region (5°S–5°N, 25°W–5°E) to wind forcing and the related mechanism are explored in this study. Based on the experiments forced by different wind forcing from both reanalysis and idealized datasets, it is revealed that the contribution ratio for each of the dominant physical processes in the heat budget is insensitive (the variations within 1% of the mean) to the variations in themore » local winds (the largest variation is about 20% of the mean) over the EACT region. Therefore, a ‘self-adjustment’ mechanism exists in the mixed-layer heat budget: as local zonal winds over the EACT region strengthen (weaken), both the cooling effects of turbulent mixing and the combined warming effects of surface net heat flux and zonal advection simultaneously increase (decrease) by nearly the same percentage and thus their contribution ratios are kept constant. Finally, owing to the impact of meridional winds on each term of heat budget can be neglected, the above mechanism is also tenable under the situation when the local meridional winds change.« less

A ‘self-adjustment’ mechanism for mixed-layer heat budget in the equatorial Atlantic cold tongue

DOE PAGES

Shi, Yanyan; Wang, Bin; Huang, Wenyu

2017-01-20

Wind forcing is one of the most important sources for the oceanic energy cycle and is especially critical to the heat budget of surface mixed layer. The sensitivity of heat budget in the equatorial Atlantic cold tongue (EACT) region (5°S–5°N, 25°W–5°E) to wind forcing and the related mechanism are explored in this study. Based on the experiments forced by different wind forcing from both reanalysis and idealized datasets, it is revealed that the contribution ratio for each of the dominant physical processes in the heat budget is insensitive (the variations within 1% of the mean) to the variations in themore » local winds (the largest variation is about 20% of the mean) over the EACT region. Therefore, a ‘self-adjustment’ mechanism exists in the mixed-layer heat budget: as local zonal winds over the EACT region strengthen (weaken), both the cooling effects of turbulent mixing and the combined warming effects of surface net heat flux and zonal advection simultaneously increase (decrease) by nearly the same percentage and thus their contribution ratios are kept constant. Finally, owing to the impact of meridional winds on each term of heat budget can be neglected, the above mechanism is also tenable under the situation when the local meridional winds change.« less

A 27-month periodicity in the low latitude geomagnetic field and its connection to the stratospheric QBO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Olsen, N.

1994-06-01

Geomagnetic daily variations are produced at a height of about 100 to 130 km due to dynamo action of thermospheric winds in combination with the ionospheric conductivity. They are influenced by longterm variability of thermospheric dynamics and are used as tool for investigating a QBO (Quasi-Biennial-Oscillation) in thermospheric winds. Power spectrum analysis has been applied to monthly means of the daily range of the geomagnetic field. In addition to an annual modulation (and subharmonics) there is clear evidence for a sharp peak at about 27 months in the H-component at low-latitude observatories (delta H approximately equal to 0.5 nT). Atmore » single observatories, statistical significance is at the 99% confidence level, squared coherency between distant observatories is highly significant, too. However, there is no global modulation of the S(sub q) current system because: (1) the D-component contain no 27-month periodicity; and (2) the oscillation is not present at mid-latitude observatories. In order to explain the observations, a 27-month oscillation in the low-latitude prevailing zonal winds with an amplitude of few m/s at a height of about 100-130 km is postulated. Squared Coherency between geomagnetic variations and prevailing winds in the equatorial stratosphere is significant at the 95%-level.« less

A special MJO event with a double Kelvin wave structure

NASA Astrophysics Data System (ADS)

Zhu, Lili; Li, Tim

2017-04-01

The second Madden-Julian Oscillation (MJO) event during the field campaign of the Dynamics of the MJO/Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (DYNAMO/CINDY2011) exhibi ted an unusual double rainband structure. Using a wavenumber-frequency spectral filtering method, we unveil that this double rainband structure arises primarily from the Kelvin wave component. The zonal phase speed of the double rainbands is about 7.9 degree per day in the equatorial Indian Ocean, being in the range of convectively coupled Kelvin wave phase speeds. The convection and circulation anomalies associated with the Kelvin wave component are characterized by two anomalous convective cells, with low-level westerly (easterly) and high (low) pressure anomalies to the west (east) of the convective centers, and opposite wind and pressure anomalies in the upper troposphere. Such a zonal wind-pressure phase relationship is consistent with the equatorial free-wave dynamics. While the free-atmospheric circulation was dominated by the first baroclinic mode vertical structure, moisture and vertical motion in the boundary layer led the convection. The convection and circulation structures derived based on the conventional MJO filter show a different characteristic. For example, the phase speed is slower (about 5.9 degree per day), and there were no double convective branches. This suggests that MJO generally involves multi-scales and it is incomplete to extract its signals by using the conventional filtering technique.

Mechanism for Surface Warming in the Equatorial Pacific during 1994-95

NASA Technical Reports Server (NTRS)

Rienecker, Michele M.; Borovikov, Anna; Schopf, Paul S.

1999-01-01

Mechanisms controlling the variation in sea surface temperature warm event in the equatorial Pacific were investigated through ocean model simulations. In addition, the mechanisms of the climatological SST cycle were investigated. The dominant mechanisms governing the seasonal cycle of SST vary significantly across the basin. In the western Pacific the annual cycle of SST is primarily in response to external heat flux. In the central basin the magnitude of zonal advection is comparable to that of the external heat flux. In the eastern basin the role of zonal advection is reduced and the vertical mixing is more important. In the easternmost equatorial Pacific the vertical entrainment contribution is as large as that of vertical diffusion. The model estimate of the vertical mixing contribution to the mixed layer heat budget compared well with estimates obtained by analysis of observations using the same diagnostic vertical mixing scheme. During 1994- 1995 the largest positive SST anomaly was observed in the mid-basin and was related to reduced latent heat flux due to weak surface winds. In the western basin the initial warming was related to enhanced external heating and reduced cooling effects of both vertical mixing and horizontal advection associated with weaker than usual wind stress. In the eastern Pacific where winds were not significantly anomalous throughout 1994-1995, only a moderate warm surface anomaly was detected. This is in contrast to strong El Nino events where the SST anomaly is largest in the eastern basin and, as shown by previous studies, the anomaly is due to zonal advection rather than anomalous surface heat flux. The end of the warm event was marked by cooling in July 1995 everywhere across the equatorial Pacific.

RACOONs amass wind data

NASA Astrophysics Data System (ADS)

Richman, Barbara T.

Balloons, not furry little animals, are being developed to provide new, inexpensive methods for gathering weather data in the tropics.RACOON—short for radiation-controlled balloon—is a zero-pressure balloon which will be used to provide stratospheric wind data for equatorial regions, according to the National Center for Atmospheric Research. These data are unavailable from satellites. Currently, the global rocket network gathers tropical wind measurements for weather forecasting; however, the network is being phased out.

Global Dayside Ionospheric Uplift and Enhancement Associated with Interplanetary Electric Fields

NASA Technical Reports Server (NTRS)

Tsurutani, Bruce; Mannucci, Anthony; Iijima, Byron; Abdu, Mangalathayil Ali; Sobral, Jose Humberto A.; Gonzalez, Walter; Guarnieri, Fernando; Tsuda, Toshitaka; Saito, Akinori; Yumoto, Kiyohumi;

Main Ionospheric Trough and Equatorial Ionization Anomaly During Substorms With the Different UT Onset Moments

NASA Astrophysics Data System (ADS)

Klimenko, M. V.; Klimenko, V. V.; Bryukhanov, V. V.

2007-05-01

In the given work the numerical calculation results of ionospheric effects of four modeling substorms which have begun in 00, 06, 12 and 18 UT are presented. Calculations are executed on the basis of Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP), developed in WD IZMIRAN, added by the new block of calculation of electric fields in the ionosphere of the Earth for vernal equinox conditions in the minimum of solar activity. In calculations we considered superposition of magnetospheric convection electric field (at set potential differences through polar caps and field aligned currents of the second zone with taking into account of particle precipitation) and dynamo field generated by thermospheric winds without taking into account the tides. It is shown, that in the given statement of problem the substorms cause strong positive disturbances in F-region of ionosphere in night sector. Negative disturbances are much less and arise, mainly, at night in the middle and low latitudes. During substorms longitudinal extent of main ionospheric trough increases. The substorm beginning in 18 UT, causes negative disturbances in high latitudes except for a southern polar cap. Besides there is "stratification" of the main ionospheric trough. As a result in southern hemisphere the additional high-latitude trough which is absent in quiet conditions is formed. "Stratification" of the main ionospheric trough occurs in northern hemisphere at 6 hours after the beginning of the substorm. These "stratifications" are consequence non-stationary magnetospheric convection. Distinction between these events consists that "stratification" in a southern hemisphere occurs in active phase of substorm, and in northern hemisphere in recovery phase. During a substorm beginning in 00 UT, foF2 increases in all northern polar cap. Positive disturbances of foF2 in the equatorial anomaly region cause all presented substorms, except for a substorm beginning in 18 UT. This substorm causes small negative disturbances in the equatorial anomaly region in the Indian longitudinal sector.

A delayed action oscillator shared by biennial, interannual, and decadal signals in the Pacific Basin

USGS Publications Warehouse

White, Warren B.; Tourre, Y.M.; Barlow, M.; Dettinger, M.

2003-01-01

Biennial, interannual, and decadal signals in the Pacific basin are observed to share patterns and evolution in covarying sea surface temperature (SST), 18??C isotherm depth (Z18), zonal surface wind (ZSW), and wind stress curl (WSC) anomalies from 1955 to 1999. Each signal has warm SST anomalies propagating slowly eastward along the equator, generating westerly ZSW anomalies in their wake. These westerly ZSW anomalies produce cyclonic WSC anomalies off the equator which pump baroclinic Rossby waves in the western/central tropical North Pacific Ocean. These Rossby waves propagate westward, taking ???6, ???12, and ???36 months to reach the western boundary near ???7??N, ???12??N, and ???18??N on biennial, interannual, and decadal period scales, respectively. There, they reflect as equatorial coupled waves, propagating slowly eastward in covarying SST, Z18, and ZSW anomalies, taking ???6, ???12, and ???24 months to reach the central/eastern equatorial ocean. These equatorial coupled waves produce a delayed-negative feedback to the warm SST anomalies there. The decrease in Rossby wave phase speed with latitude, the increase in meridional scale of equatorial SST anomalies with period scale, and the associated increase in latitude of Rossby wave forcing are consistent with the delayed action oscillator (DAO) model used to explain El Nin??o. However, this is not true of the western-boundary reflection of Rossby waves into slow equatorial coupled waves. This requires modification of the extant DAO model. We construct a modified DAO model, demonstrating how the various mechanisms and the size and sources of their delays yield the resulting frequency of each signal.

Double-reconnected magnetic structures driven by Kelvin-Helmholtz vortices at the Earth's magnetosphere

NASA Astrophysics Data System (ADS)

Faganello, Matteo; Borgogno, Dario; Califano, Francesco; Pegoraro, Francesco

2015-11-01

In an almost collisionless MagnetoHydrodynamic plasma in a relatively strong magnetic field, stresses can be conveyed far from the region where they are exerted e.g., through the propagation of Alfvèn waves. The forced dynamics of line-tied magnetic structures in solar and stellar coronae is a paradigmatic case. We investigate how this action at a distance develops from the equatorial region of the Kelvin-Helmholtz unstable flanks of the Earth's magnetosphere leading to the onset, at mid latitude in both hemispheres, of correlated double magnetic field line reconnection events that can allow the solar wind plasma to enter the Earth's magnetosphere. This mid-latitude double reconnection process, first investigated in, has been confirmed here by following a large set of individual field lines using a method similar to a Poincarè map.

Comparison of the EIA, EETA and ETWA, received in the model GSM TIP, at the self-consistent approach and with use of the model MSIS-90

NASA Astrophysics Data System (ADS)

Klimenko, M. V.; Klimenko, V. V.; Bryukhanov, V. V.

On the basis of the Global Self-consistent model of the thermosphere ionosphere and protonosphere GSM TIP developed in WD IZMIRAN the calculations for the quiet geomagnetic conditions of the equinox in the minimum of solar activity are carried out In the calculations the new block of the computation of electric fields in the ionosphere briefly described in COSPAR2006-A-00108 was used Two variants of calculations are executed with the account only the dynamo field generated by the thermosphere winds - completely self-consistent and with use of the model MSIS-90 for the calculation of the composition and temperature of the neutral atmosphere The results of the calculations are compared among themselves The global distributions of the foF2 the latitude behavior of the N e and T e on the near-midnight meridian at two height levels 233 and 626 km the latitude-altitude sections on the near-midnight meridian of the T e and time developments on UT of zonal component of the thermosphere wind and ion temperature at height sim 300 km and foF2 and h m F2 for three longitudinal chains of stations - Brazil Pacific and Indian in a vicinity of geomagnetic equator COSPAR2006-A-00109 calculated in two variants are submitted It is shown that at the self-consistent approach the maxima of the crests of the equatorial ionization anomaly EIA in the foF2 are shifted concerning calculated with the MSIS aside later evening hours The equatorial electron temperature anomaly EETA is formed in both variants of calculations However at the

Diurnal, monthly and seasonal variation of mean winds in the MLT region observed over Kolhapur using MF radar

NASA Astrophysics Data System (ADS)

Sharma, A. K.; Gaikwad, H. P.; Ratnam, M. Venkat; Gurav, O. B.; Ramanjaneyulu, L.; Chavan, G. A.; Sathishkumar, S.

2018-04-01

Medium Frequency (MF) radar located at Kolhapur (16.8°N, 74.2°E) has been upgraded in August 2013. Since then continuous measurements of zonal and meridional winds are obtained covering larger altitudes from the Mesosphere and Lower Thermosphere (MLT) region. Diurnal, monthly and seasonal variation of these mean winds is presented in this study using four years (2013-2017) of observations. The percentage occurrence of radar echoes show maximum between 80 and 105 km. The mean meridional wind shows Annual Oscillation (AO) between 80 and 90 km altitudes with pole-ward motion during December solstice and equatorial motion during June solstice. Quasi-biennial oscillation (QBO) with weaker amplitudes are also observed between 90 and 104 km. Zonal winds show semi-annual oscillation (SAO) with westward winds during equinoxes and eastward winds during solstices between 80 and 90 km. AO with eastward winds during December solstice and westward wind in the June solstice is also observed in the mean zonal wind between 100 and 110 km. These results match well with that reported from other latitudes within Indian region between 80 and 90 km. However, above 90 km the results presented here provide true mean background winds for the first time over Indian low latitude region as the present station is away from equatorial electro-jet and are not contaminated by ionospheric processes. Further, the results presented earlier with an old version of this radar are found contaminated due to unknown reasons and are corrected in the present work. This upgraded MF radar together with other MLT radars in the Indian region forms unique network to investigate the vertical and lateral coupling.

Causes of the longitudinal differences in the equatorial vertical E × B drift during the 2013 SSW period as simulated by the TIME-GCM

NASA Astrophysics Data System (ADS)

Maute, A.; Hagan, M. E.; Yudin, V.; Liu, H.-L.; Yizengaw, E.

2015-06-01

During stratospheric sudden warming (SSW) periods large changes in the low-latitude vertical drift have been observed at Jicamarca as well as in other longitudinal sectors. In general, a strengthening of the daytime maximum vertical drift with a shift from prenoon to the afternoon is observed. During the January 2013 stratospheric warming significant longitudinal differences in the equatorial vertical drift were observed. At Jicamarca the previously reported SSW behavior prevails; however, no shift of the daytime maximum drift was exhibited in the African sector. Using the National Center for Atmospheric Research thermosphere-ionosphere-mesosphere electrodynamics general circulation model (TIME-GCM) the possible causes for the longitudinal difference are examined. The timing of the strong SSW effect in the vertical drift (15-20 January) coincides with moderate geomagnetic activity. The simulation indicates that approximately half of the daytime vertical drift increase in the American sector may be related to the moderate geophysical conditions (Kp = 4) with the effect being negligible in the African sector. The simulation suggests that the wind dynamo accounts for approximately 50% of the daytime vertical drift in the American sector and almost 100% in the African sector. The simulation agrees with previous findings that the migrating solar tides and the semidiurnal westward propagating tide with zonal wave number 1 (SW1) mainly contribute to the daytime wind dynamo and vertical drift. Numerical experiments suggest that the neutral wind and the geomagnetic main field contribute to the presence (absence) of a local time shift in the daytime maximum drift in the American (African) sector.

Equatorial magnetic field of the near-Earth magnetotail

NASA Astrophysics Data System (ADS)

Ohtani, S.; Motoba, T.

2017-08-01

The equatorial magnetic field of the nightside magnetosphere is critical for understanding not only the configuration of the magnetotail but also its state and dynamics. The present study observationally addresses various aspects of the equatorial magnetic field, such as its spatial distribution, possible antisunward gradients, and extremely weak magnetic fields, with emphasis on the transition region between dipolar and stretched magnetic configurations. The results are summarized as follows: (1) the transition of the tail magnetic field from a near-Earth dipolar configuration to a stretched one farther out takes place around -12 ≤ Xagsm ≤ -9 RE, although instantaneous configurations can vary significantly; (2) the average equatorial magnetic field in this transition region is noticeably weaker at solar minimum presumably reflecting weaker nightside magnetospheric currents closer to Earth; (3) the statistical comparison of equatorial magnetic fields measured simultaneously at two locations indicates that the gradient of the equatorial magnetic field is directed predominantly earthward, and it is suggested that apparent tailward gradients observed can be very often attributed to other factors such as structures in the Y direction and local fluctuations; (4) however, the gradient can be transiently directed tailward in association with the dipolarization of local magnetic field; (5) extremely weak (≤ 2 nT) magnetic fields are occasionally observed in the transition region during the substorm growth phase and during prolonged quiet intervals, but the association with steady magnetospheric convection, which was suggested before, cannot be confirmed possibly because of its rare occurrence.

Atmospheric Torques on the Solid Earth and Oceans Based on the GEOS-1 General Circulation Model

NASA Technical Reports Server (NTRS)

Sanchez, Braulio V.; Au, Andrew Y.

1998-01-01

The GEOS-1 general circulation model has been used to compute atmospheric torques on the oceans and solid Earth for the period 1980-1995. The time series for the various torque components have been analyzed by means of Fourier transform techniques. It was determined that the wind stress torque over land is more powerful than the wind stress torque over water by 55%, 42%, and 80% for the x, y, and z components respectively. This is mainly the result of power in the high frequency range. The pressure torques due to polar flattening, equatorial ellipticity, marine geoid, and continental orography were computed. The orographic or "mountain torque" components are more powerful than their wind stress counterparts (land plus ocean) by 231% (x), 191% (y), and 77% (z). The marine pressure torques due to geoidal undulations are much smaller than the orographic ones, as expected. They are only 3% (x), 4% (y), and 5% (z) of the corresponding mountain torques. The geoidal pressure torques are approximately equal in magnitude to those produced by the equatorial ellipticity of the Earth. The pressure torque due to polar flattening makes the largest contributions to the atmospheric torque budget. It has no zonal component, only equatorial ones. Most of the power of the latter, between 68% and 69%, is found in modes with periods under 15 days. The single most powerful mode has a period of 361 days. The gravitational torque ranks second in power only to the polar flattening pressure torque. Unlike the former, it does produce a zonal component, albeit much smaller (1%) than the equatorial ones. The gravitational and pressure torques have opposite signs, therefore, the gravitational torque nullifies 42% of the total pressure torque. Zonally, however, the gravitational torque amounts to only 6% of the total pressure torque. The power budget for the total atmospheric torque yields 7595 and 7120 Hadleys for the equatorial components and 966 Hadleys for the zonal. The x-component exhibits a large mean value (1811 H), mainly the result of polar flattening pressure torque acting on the ocean surfaces. Atmospheric torque modes with periods of 408, 440, and 476 days appear in the spectrum of the equatorial components.

Atmospheric Torques on the Solid Earth and Oceans Based on the GEOS-1 General Circulation Model

NASA Technical Reports Server (NTRS)

Sanchez, Braulio

1999-01-01

The GEOS-1 general circulation model has been used to compute atmospheric torques on the oceans and solid Earth for the period 1980-1995. The time series for the various torque components have been analyzed by means of Fourier transform techniques. It was determined that the wind stress torque over land is more powerful than the wind stress torque over water by 55\\%, 42\\%, and 80\\t for the x, y, and z components respectively. This is mainly the result of power in the high frequency range. The pressure torques due to polar flattening, equatorial ellipticity, marine geoid, and continental orography were computed. The orographic or "mountain torque" components are more powerful than their wind stress counterparts (land plus ocean) by 231\\% (x), 191\\% (y), and 77\\% (z). The marine pressure torques due to geoidal undulations are much smaller than the orographic ones, as expected. They are only 3\\% (x), 4\\% (y), and 5\\% (z) of the corresponding mountain torques. The geoidal pressure torques are approximately equal in magnitude to those produced by the equatorial ellipticity of the Earth. The pressure torque due to polar flattening makes the largest contributions to the atmospheric'torque budget. It has no zonal component, only equatorial ones. Most of the power of the latter, between 68\\% and 69 %, is found in modes with periods under 15 days. The single most powerful mode has a period of 361 days. The gravitational torque ranks second in power only to the polar flattening pressure torque. Unlike the former, it does produce a zonal component, albeit much smaller (1\\ ) than the equatorial ones. The gravitational and pressure torques have opposite signs, therefore, the gravitational torque nullifies 42\\% of the total pressure torque. Zonally, however, the gravitational torque amounts to only 6\\% of the total pressure torque. The power budget for the total atmospheric torque yields 7595 and 7120 Hadleys for the equatorial components and 966 Hadleys for the zonal. The x-component exhibits a large mean value (1811 H), mainly the result of polar flattening pressure torque acting on the ocean surfaces. Atmospheric torque modes with periods of 408, 440, and 476 days appear in the spectrum of the equatorial components.

Variations of Sea Surface Temperature, Wind Stress, and Rainfall over the Tropical Atlantic and South America.

NASA Astrophysics Data System (ADS)

Nobre, Paulo; Srukla, J.

1996-10-01

Empirical orthogonal functions (E0Fs) and composite analyses are used to investigate the development of sea surface temperature (SST) anomaly patterns over the tropical Atlantic. The evolution of large-scale rainfall anomaly patterns over the equatorial Atlantic and South America are also investigated. 71e EOF analyses revealed that a pattern of anomalous SST and wind stress asymmetric relative to the equator is the dominant mode of interannual and longer variability over the tropical Atlantic. The most important findings of this study are as follows.Atmospheric circulation anomalies precede the development of basinwide anomalous SST patterns over the tropical Atlantic. Anomalous SST originate off the African coast simultaneously with atmospheric circulation anomalies and expand westward afterward. The time lag between wind stress relaxation (strengthening) and maximum SST warming (cooling) is about two months.Anomalous atmospheric circulation patterns over northern tropical Atlantic are phase locked to the seasonal cycle. Composite fields of SLP and wind stress over northern tropical Atlantic can be distinguished from random only within a few months preceding the March-May (MAM) season. Observational evidence is presented to show that the El Niño-Southern Oscillation phenomenon in the Pacific influences atmospheric circulation and SST anomalies over northern tropical Atlantic through atmospheric teleconnection patterns into higher latitudes of the Northern Hemisphere.The well-known droughts over northeastern Brazil (Nordeste) are a local manifestation of a much larger-scale rainfall anomaly pattern encompassing the whole equatorial Atlantic and Amazon region. Negative rainfall anomalies to the south of the equator during MAM, which is the rainy season for the Nordeste region, are related to an early withdrawal of the intertropical convergence zone toward the warm SST anomalies over the northern tropical Atlantic. Also, it is shown that precipitation anomalies over southern and northern parts of the Nordeste are out of phase: drought years over the northern Nordeste are commonly preceded by wetter years over the southern Nordeste, and vice versa.

Relationship Between Sea Surface Temperature and Surface Heat Balance Trends in the Tropical Oceans: The Crucial Role of Surface Wind Trends

NASA Astrophysics Data System (ADS)

Cook, K. H.; Vizy, E. K.; Sun, X.

2016-12-01

Multiple atmospheric and ocean reanalyses are analyzed for 1980-2015 to understand annual-mean adjustments of the surface heat balance over the tropical oceans as the climate warms. Linear trends are examined, with statistical significance evaluated. While surface heat budgets and sea surface temperatures are mutually adjusted fields, insights into the physical processes of this adjustment and the implications for temperature trends can be identified. Two second-generation reanalyses, ERA-Interim and JRA-55, agree well on the distributions and magnitudes of trends in the net heat flux from the atmosphere to the ocean. Trends in the net longwave and sensible heat fluxes are generally small, and trends in solar radiation absorbed are only influential regionally and vary among the reanalyses. The largest contribution is from latent heat flux trends. Contributions to these trends associated with surface temperature (thermal-driving), 10-m wind (dynamical-driving) and specific humidity (hydrological-driving) trends are estimated. The dynamically-driven latent heat flux dominates and explains much of the regionality of the multi-decadal heat flux trends. However, trends in the net surface heat flux alone do not match the observed SSTs trends well, indicating that the redistribution of heat within the ocean mixed layer is also important. Ocean mixed layer heat budgets in various ocean reanalyses are examined to understand this redistribution, and we again identify a crucial role for changes in the surface wind. Acceleration of the tropical easterlies is associated with strengthening of the equatorial undercurrents in both the tropical Pacific and Atlantic. In the Pacific, where the EUC is also shoaling, the result is enhanced warm-water advection into the central Pacific. This advective warming is superimposed on cooling due to enhanced evaporation and equatorial upwelling, which are also associated with wind trends, to determine the observed pattern of SST trends.

Contributions of the atmosphere-land and ocean-sea ice model components to the tropical Atlantic SST bias in CESM1

NASA Astrophysics Data System (ADS)

Song, Z.; Lee, S. K.; Wang, C.; Kirtman, B. P.; Qiao, F.

2016-02-01

In order to identify and quantify intrinsic errors in the atmosphere-land and ocean-sea ice model components of the Community Earth System Model version 1 (CESM1) and their contributions to the tropical Atlantic sea surface temperature (SST) bias in CESM1, we propose a new method of diagnosis and apply it to a set of CESM1 simulations. Our analyses of the model simulations indicate that both the atmosphere-land and ocean-sea ice model components of CESM1 contain large errors in the tropical Atlantic. When the two model components are fully coupled, the intrinsic errors in the two components emerge quickly within a year with strong seasonality in their growth rates. In particular, the ocean-sea ice model contributes significantly in forcing the eastern equatorial Atlantic warm SST bias in early boreal summer. Further analysis shows that the upper thermocline water underneath the eastern equatorial Atlantic surface mixed layer is too warm in a stand-alone ocean-sea ice simulation of CESM1 forced with observed surface flux fields, suggesting that the mixed layer cooling associated with the entrainment of upper thermocline water is too weak in early boreal summer. Therefore, although we acknowledge the potential importance of the westerly wind bias in the western equatorial Atlantic and the low-level stratus cloud bias in the southeastern tropical Atlantic, both of which originate from the atmosphere-land model, we emphasize here that solving those problems in the atmosphere-land model alone does not resolve the equatorial Atlantic warm bias in CESM1.

Equatorial dynamics in a 2 {1}/{2}- layer model

NASA Astrophysics Data System (ADS)

McCreary, Julian P.; Yu, Zuojun

A nonlinear, 2 {1}/{2}- layer model is used to study the dynamics of wind-driven equatorial ocean circulation, including the generation of mean flows and instabilities. The model allows water to entrain into, and detrain from, the upper layer, and as a consequence the temperatures of the two active layers can vary. The model ocean basin is rectangular, extends 100° zonally, and for most solutions has open boundaries at 15°S and 15°N. All solutions are forced by a switched-on wind field that is an idealized version of the Pacific trades: the wind is westward, uniform in the meridional direction (so it has no curl), located primarily in the central and eastern oceans, and in most cases it has an amplitude of 0.5 dyn cm -2. For reasonable choices of parameters, solutions adjust to have a realistic equatorial circulation with a westward surface jet, an eastward undercurrent, and with upwelling and cool sea surface temperature in the eastern ocean. Most of the meridional circulation (81% of the transport) is part of a closed tropical circulation cell, in which water upwells in the eastern, equatorial ocean and downwells elsewhere in the basin; the rest participates in a mid-latitude circulation cell with lower-layer water entering the basin and upper-layer water leaving it through the open boundaries. Three basic types of unstable disturbances are generated in the eastern ocean: two of them are antisymmetric about the equator, one being surface-trapped with a period of about 21 days (f 1), and the other predominantly a lower-layer oscillation with periods ranging from 35 to 53 days (f 2) that causes the undercurrent to meander; the third is symmetric with a period of about 28 days (f 0) and a structure like that of a first-meridional-mode Rossby wave. The amplitudes of the disturbances are sensitive to model parameters, and as parameter values are varied systematically solutions appear to follow variations of the quasi-periodic route to turbulence, one of the common transitions to chaotic behavior. Realistic mean flows develop only when detrainment and lower-layer cooling are present in the model physics, processes that are necessary for the generation of a tropical circulation cell: without detrainment, water accumulutes in the upper layer until entrainment ceases and the model adjusts to Sverdrup balance, which is a state of rest for a wind without curl; without cooling, the temperature of the lower layer slowly rises until it approaches that of the upper layer. The mean-momentum budget for the upper layer shows that the model's Reynolds-stress terms are not a significant part of the momentum balance, having a maximum amplitude only about 19% of the wind stress. In contrast, the mean-heat budget demonstrates that eddy heating warms the cold tongue significantly, with an amplitude as large as the heating through the surface. Interestingly, the time-averaged continuity equations indicate that the instabilities tend to increase the upward tilt of the upper-layer interface toward the equator. When layer temperatures are kept fixed only a weak version of disturbance f 1 develops, indicating that the equatorial temperature front is an important aspect of instability dynamics. In fact, a frontal instability does exist in the model; it involves the conversion of mean to eddy potential energy, but it is the mean energy associated with the variable upper-layer temperature field, rather than with tilted layer interfaces, as is the case for traditional baroclinic instability. Perturbation-energy budgets suggest that frontal, barotropic and Kelvin-Helmholtz instabilities are energy sources for the disturbances, whereas traditional baroclinic instability is an energy sink. The two, fastest growing, antisymmetric, unstable-wave solutions to a linearized version of the model correspond closely to disturbances f 1 and f 2 from the nonlinear model, and perturbation-energy budgets for these waves indicate that their energy sources are primarily frontal instability and lower-layer barotropic instability, respectively.

Panel 1: A pulsating red giant star and a compact, hot white dwarf star orbit each other.

NASA Technical Reports Server (NTRS)

2002-01-01

Panel 1: A pulsating red giant star and a compact, hot white dwarf star orbit each other. Panel 2: The red giant sheds much of its outer layers in a stellar wind. The white dwarf helps concentrate the wind along a thin equatorial plane. The white dwarf accretes some of this escaping gas forming a disk around the itself. Panel 3: When enough gas accumulates on the white dwarf's surface it explodes as a nova outburst. Most of the hot gas forms a pair of expanding bubbles above and below the equatorial disk. Panel 4: A few thousand years after the bubbles expand into space, the white dwarf goes through another nova outburst and makes another pair of bubbles, which form a distinctive hourglass shape.

Transverse Aeolian Ridges (TARs) on Mars II: Distributions, orientations, and ages

NASA Astrophysics Data System (ADS)

Berman, Daniel C.; Balme, Matthew R.; Rafkin, Scot C. R.; Zimbelman, James R.

2011-05-01

Transverse Aeolian Ridges (TARs), 10 m scale, ripple-like aeolian bedforms with simple morphology, are widespread on Mars but it is unknown what role they play in Mars' wider sediment cycle. We present the results of a survey of all Mars Global Surveyor Narrow angle images in a pole-to-pole study area, 45° longitude wide. Following on from the classification scheme and preliminary surveys of Balme et al. (Balme, M.R., Berman, D.C., Bourke, M.C., Zimbelman, J.R. [2008a]. Geomorphology 101, 703-720) and Wilson and Zimbelman (Wilson, S.A., Zimbelman, J.R. [2004]. J. Geophys. Res. 109 (E10). doi: 10.1029/2004JE002247) we searched more than 10,000 images, and found that over 2000 reveal at least 5% areal cover by TARs. The mean TAR areal cover in the study area is about 7% (3% in the northern hemisphere and 11% in the southern hemisphere) but TARs are not homogenously distributed - they are concentrated in the mid-low latitudes and almost absent poleward of 35°N and 55°S. We found no clear correlation between TAR distribution and any of thermal inertia, kilometer-scale roughness, or elevation. We did find that TARs are less common at extremes of elevation. We found that TARs are most common near the equator (especially in the vicinity of Meridiani Planum, in which area they have a distinctive "barchan-like" morphology) and in large southern-hemisphere impact craters. TARs in the equatorial band are usually associated with outcrops of layered terrain or steep slopes, hence their relative absence in the northern hemisphere. TARs in the southern hemisphere are most commonly associated with low albedo, intercrater dune fields. We speculate that the mid-latitude mantling terrain (e.g., Mustard, J.F., Cooper, C.D., Rifkin, M.K. [2001]. Nature 412, 411-414; Kreslavsky, M.A., Head, J.W. [2002]. J. Geophys. Res. 29 (15). doi: 10.1029/2002GL015392) could also play a role in covering TARs or inhibiting saltation. We compared TAR distribution with general circulation model (GCM) climate data for both surface wind shear stress and wind direction. We performed GCM runs at various obliquity values to simulate the effects of changing obliquity on recent Mars climate. We found good general agreement between TAR orientation and GCM wind directions from present day obliquity conditions in many cases, but found no good correlation between wind shear stress and TAR distribution. We performed preliminary high resolution crater count studies of TARs in both equatorial and southern intracrater dunefield settings and compared these to superposition relationships between TARs and large dark dunes. Our results show that TARs near dunefield appear to be younger than TARs in the equatorial regions. We infer that active saltation from the large dunes keeps TARs active, but that TARs are not active under present day condition when distal to large dunes - perhaps supporting the interpretation that TARs are granule ripples. We conclude that local geology, rather than wind strength, controls TAR distribution, but that their orientation matches present-day regional wind patterns in most cases. We suggest that TARs are likely most (perhaps only) active today when they are proximal to large dark dune fields.

Climate extremes in Malaysia and the equatorial South China Sea

NASA Astrophysics Data System (ADS)

Salahuddin, Ahmed; Curtis, Scott

2011-08-01

The southern extent of the South China Sea (SCS) is an important natural resource epicenter for Malaysia which experiences climate extremes. This paper documents the variability of extremes in the equatorial SCS through selected ground-based observations of precipitation in Malaysia and ship-based observations of wind data in the Maritime Continent region, to elucidate the interrelationship between precipitation variability over Malaysia and wind variability over the ocean. The data have been carefully inspected and analyzed, and related to the real-time multivariate Madden-Julian Oscillation (MJO) time series. The analysis suggests that the northeast or boreal winter monsoon dominates extreme rainfall in eastern Malaysian cities. Further, the west coast of Peninsular Malaysia and Borneo Malaysia are affected by the MJO differently than the east coast of Peninsular Malaysia. From the wind analysis we found that average zonal wind is westerly from May to September and easterly from November to April. When the active (convective) phase of the MJO is centered over the Maritime Continent, the strong westerly wind bursts are more frequent in the South China Sea. While more investigation is needed, these results suggest that the status of the Madden-Julian Oscillation can be used to help forecast climate extremes in areas of Malaysia.

Equatorial jet in the lower to middle cloud layer of Venus revealed by Akatsuki

NASA Astrophysics Data System (ADS)

Horinouchi, Takeshi; Murakami, Shin-Ya; Satoh, Takehiko; Peralta, Javier; Ogohara, Kazunori; Kouyama, Toru; Imamura, Takeshi; Kashimura, Hiroki; Limaye, Sanjay S.; McGouldrick, Kevin; Nakamura, Masato; Sato, Takao M.; Sugiyama, Ko-Ichiro; Takagi, Masahiro; Watanabe, Shigeto; Yamada, Manabu; Yamazaki, Atsushi; Young, Eliot F.

2017-09-01

The Venusian atmosphere is in a state of superrotation where prevailing westward winds move much faster than the planet's rotation. Venus is covered with thick clouds that extend from about 45 to 70 km altitude, but thermal radiation emitted from the lower atmosphere and the surface on the planet's nightside escapes to space at narrow spectral windows of the near-infrared. The radiation can be used to estimate winds by tracking the silhouettes of clouds in the lower and middle cloud regions below about 57 km in altitude. Estimates of wind speeds have ranged from 50 to 70 m s-1 at low to mid-latitudes, either nearly constant across latitudes or with winds peaking at mid-latitudes. Here we report the detection of winds at low latitude exceeding 80 m s-1 using IR2 camera images from the Akatsuki orbiter taken during July and August 2016. The angular speed around the planetary rotation axis peaks near the equator, which we suggest is consistent with an equatorial jet, a feature that has not been observed previously in the Venusian atmosphere. The mechanism producing the jet remains unclear. Our observations reveal variability in the zonal flow in the lower and middle cloud region that may provide clues to the dynamics of Venus's atmospheric superrotation.

Equatorial jet in the lower to middle cloud layer of Venus revealed by Akatsuki.

PubMed

Horinouchi, Takeshi; Murakami, Shin-Ya; Satoh, Takehiko; Peralta, Javier; Ogohara, Kazunori; Kouyama, Toru; Imamura, Takeshi; Kashimura, Hiroki; Limaye, Sanjay S; McGouldrick, Kevin; Nakamura, Masato; Sato, Takao M; Sugiyama, Ko-Ichiro; Takagi, Masahiro; Watanabe, Shigeto; Yamada, Manabu; Yamazaki, Atsushi; Young, Eliot F

2017-01-01

The Venusian atmosphere is in a state of superrotation where prevailing westward winds move much faster than the planet's rotation. Venus is covered with thick clouds that extend from about 45 to 70 km altitude, but thermal radiation emitted from the lower atmosphere and the surface on the planet's night-side escapes to space at narrow spectral windows of near-infrared. The radiation can be used to estimate winds by tracking the silhouettes of clouds in the lower and middle cloud regions below about 57 km in altitude. Estimates of wind speeds have ranged from 50 to 70 m/s at low- to mid-latitudes, either nearly constant across latitudes or with winds peaking at mid-latitudes. Here we report the detection of winds at low latitude exceeding 80 m/s using IR2 camera images from the Akatsuki orbiter taken during July and August 2016. The angular speed around the planetary rotation axis peaks near the equator, which we suggest is consistent with an equatorial jet, a feature that has not been observed previously in the Venusian atmosphere. The mechanism producing the jet remains unclear. Our observations reveal variability in the zonal flow in the lower and middle cloud region that may provide new challenges and clues to the dynamics of Venus's atmospheric superrotation.

A Comparative Examination of Plasmoid Structure and Dynamics at Mercury, Earth, Jupiter, and Saturn

NASA Technical Reports Server (NTRS)

Slavin, James A.

2010-01-01

The circulation of plasma and magnetic flux within planetary magnetospheres is governed by the solar wind-driven Dungey and planetary rotation-driven cycles. The Dungey cycle is responsible for all circulation at Mercury and Earth. Jupiter and Saturn's magnetospheres are dominated by the Vasyliunas cycle, but there is evidence for a small Dungey cycle contribution driven by the solar wind. Despite these fundamental differences, all well-observed magnetospheres eject relatively large parcels of the hot plasma, termed plasmoids, down their tails at high speeds. Plasmoids escape from the restraining force of the planetary magnetic field through reconnection in the equatorial current sheet separating the northern and southern hemispheres of the magnetosphere. The reconnection process gives the magnetic field threading plasmoids a helical or flux rope-type topology. In the Dungey cycle reconnection also provides the primary tailward force that accelerates plasmoids to high speeds as they move down the tail. We compare the available observations of plasmoids at Mercury, Earth, Jupiter, and Saturn for the purpose of determining the relative role of plasmoids and the reconnection process in the dynamics these planetary magnetic tails.

Westerly Wind Bursts: a Synoptic-Dynamic Study

NASA Astrophysics Data System (ADS)

Hartten, Leslie Marie

This research examines the synoptic and climatological settings of westerly wind bursts (WWBs) during the 1980s and the dynamical processes active during them. Probabilities of strong westerly and easterly 1000 mb winds over the western equatorial Pacific are presented. Westerlies exhibit a clear annual cycle, appearing in the north in July, moving southeastward as the year progresses, and disappearing by June. Conditional probabilities, dependent on the value of the SOI, show that strong westerlies are more likely and more geographically extensive when the SOI is low, especially from July through January. A newly developed two-dimensional classification scheme qualitatively describes the near-surface synoptic flow of almost 90% of the 131 WWBs identified during the decade. Only 8% of the WWBs are described by the pattern involving twin cyclonic circulations straddling the equator. The trades, tropical cyclones, and the southeast Asian monsoon are all at times linked to WWBs, and the synoptic patterns often contain a significant barotropic component. Breaks in WWB activity are well correlated with a cooler than normal western Pacific warm pool. However, near-equatorial WWBs do not show a good correlation with the Madden-Julian Oscillation. Four near-equatorial WWBs are examined in detail. All are associated with broad cross-equatorial flow; two also have a cyclonic circulation poleward of the westerlies. Anticyclonic relative vorticity equatorward of the burst displaces the zero line of absolute vorticity, eta, into the burst hemisphere. In the three Southern Hemisphere cases, horizontal advection in a region extending from north of New Guinea east-southeast toward the dateline is crucial to the generation and maintenance of the eta pattern. Vorticity stretching associated with convection helps maintain a tight gradient of eta near and poleward of the burst, but also drives the eta = 0 line back towards the equator as the burst ends. In the Northern Hemisphere case, advection is less efficient because the trades slow and turn further away from the equator. This research indicates that Gill's (1980) solution to the linear shallow -water equations forced by near-equatorial heating is not a good model for WWBs.

Solar wind driving of ionosphere-thermosphere responses during three storms on St. Patrick's Day.

NASA Astrophysics Data System (ADS)

Verkhoglyadova, O. P.; Tsurutani, B.; Mannucci, A. J.; Komjathy, A.; Mlynczak, M. G.; Hunt, L. A.; Paxton, L. J.

2015-12-01

We overview solar wind features of three intense CME-driven storms occurring around the same time in March of 2012, 2013 and 2015 (74 - 80 DOY). Differences in solar wind drivers lead to different ionosphere-thermosphere (IT) responses in time, magnitude, and to different pre-conditioning. The purpose of our study is to establish a correspondence between interplanetary transient structures (parts of a CME or a high-speed-stream) and dynamics of IT parameters over the course of a geomagnetic storm. Detailed analysis will be presented for the St. Patrick's Day storm of 2015. We introduce global metrics of daytime and dusktime average ionospheric response of VTEC estimates from over ~2000 GPS ground stations distributed globally. Nitric oxide and carbon dioxide cooling radiation fluxes measured by TIMED/SABER instrument are calculated in several latitudinal bins throughout the storm phases. In addition, GUVI observations of the dynamical response of the thermosphere (NO and O/N2) are compared. SSUSI observations of the equatorial ionosphere, particularly the magnitude and separation of the equatorial arcs are considered. In our analysis, metrics are inter-compared to get better understanding of the self-consistent IT response to solar wind driving.

Ocean dynamics, not dust, have controlled equatorial Pacific productivity over the past 500,000 years

PubMed Central

Winckler, Gisela; Anderson, Robert F.; Jaccard, Samuel L.; Marcantonio, Franco

2016-01-01

Biological productivity in the equatorial Pacific is relatively high compared with other low-latitude regimes, especially east of the dateline, where divergence driven by the trade winds brings nutrient-rich waters of the Equatorial Undercurrent to the surface. The equatorial Pacific is one of the three principal high-nutrient low-chlorophyll ocean regimes where biological utilization of nitrate and phosphate is limited, in part, by the availability of iron. Throughout most of the equatorial Pacific, upwelling of water from the Equatorial Undercurrent supplies far more dissolved iron than is delivered by dust, by as much as two orders of magnitude. Nevertheless, recent studies have inferred that the greater supply of dust during ice ages stimulated greater utilization of nutrients within the region of upwelling on the equator, thereby contributing to the sequestration of carbon in the ocean interior. Here we present proxy records for dust and for biological productivity over the past 500 ky at three sites spanning the breadth of the equatorial Pacific Ocean to test the dust fertilization hypothesis. Dust supply peaked under glacial conditions, consistent with previous studies, whereas proxies of export production exhibit maxima during ice age terminations. Temporal decoupling between dust supply and biological productivity indicates that other factors, likely involving ocean dynamics, played a greater role than dust in regulating equatorial Pacific productivity. PMID:27185933

Ocean dynamics, not dust, have controlled equatorial Pacific productivity over the past 500,000 years

NASA Astrophysics Data System (ADS)

Winckler, Gisela; Anderson, Robert F.; Jaccard, Samuel L.; Marcantonio, Franco

2016-05-01

Biological productivity in the equatorial Pacific is relatively high compared with other low-latitude regimes, especially east of the dateline, where divergence driven by the trade winds brings nutrient-rich waters of the Equatorial Undercurrent to the surface. The equatorial Pacific is one of the three principal high-nutrient low-chlorophyll ocean regimes where biological utilization of nitrate and phosphate is limited, in part, by the availability of iron. Throughout most of the equatorial Pacific, upwelling of water from the Equatorial Undercurrent supplies far more dissolved iron than is delivered by dust, by as much as two orders of magnitude. Nevertheless, recent studies have inferred that the greater supply of dust during ice ages stimulated greater utilization of nutrients within the region of upwelling on the equator, thereby contributing to the sequestration of carbon in the ocean interior. Here we present proxy records for dust and for biological productivity over the past 500 ky at three sites spanning the breadth of the equatorial Pacific Ocean to test the dust fertilization hypothesis. Dust supply peaked under glacial conditions, consistent with previous studies, whereas proxies of export production exhibit maxima during ice age terminations. Temporal decoupling between dust supply and biological productivity indicates that other factors, likely involving ocean dynamics, played a greater role than dust in regulating equatorial Pacific productivity.

Ocean dynamics, not dust, have controlled equatorial Pacific productivity over the past 500,000 years.

PubMed

Winckler, Gisela; Anderson, Robert F; Jaccard, Samuel L; Marcantonio, Franco

2016-05-31

Biological productivity in the equatorial Pacific is relatively high compared with other low-latitude regimes, especially east of the dateline, where divergence driven by the trade winds brings nutrient-rich waters of the Equatorial Undercurrent to the surface. The equatorial Pacific is one of the three principal high-nutrient low-chlorophyll ocean regimes where biological utilization of nitrate and phosphate is limited, in part, by the availability of iron. Throughout most of the equatorial Pacific, upwelling of water from the Equatorial Undercurrent supplies far more dissolved iron than is delivered by dust, by as much as two orders of magnitude. Nevertheless, recent studies have inferred that the greater supply of dust during ice ages stimulated greater utilization of nutrients within the region of upwelling on the equator, thereby contributing to the sequestration of carbon in the ocean interior. Here we present proxy records for dust and for biological productivity over the past 500 ky at three sites spanning the breadth of the equatorial Pacific Ocean to test the dust fertilization hypothesis. Dust supply peaked under glacial conditions, consistent with previous studies, whereas proxies of export production exhibit maxima during ice age terminations. Temporal decoupling between dust supply and biological productivity indicates that other factors, likely involving ocean dynamics, played a greater role than dust in regulating equatorial Pacific productivity.

Shallow water simulations of Saturn's giant storms at different latitudes

NASA Astrophysics Data System (ADS)

García-Melendo, E.; Sánchez-Lavega, A.

2017-04-01

Shallow water simulations are used to present a unified study of three major storms on Saturn (nicknamed as Great White Spots, GWS) at different latitudes, polar (1960), equatorial (1990), and mid-latitude (2010) (Sánchez-Lavega, 2004; Sánchez-Lavega et al., 2011). In our model, the three GWS are initiated by introducing a Gaussian function pulse at the latitude of the observed phenomena with controlled horizontal size and amplitude. This function represents the convective source that has been observed to trigger the storm. A growing disturbance forms when the pulse reacts to ambient winds, expanding zonally along the latitude band of the considered domain. We then compare the modeled potential vorticity with the cloud field, adjusting the model parameters to visually get the closest aspect between simulations and observations. Simulations of the 2010 GWS (planetographic latitude ∼+40º, zonal velocity of the source ∼-30 m s-1) indicate that the Coriolis forces and the wind profile structure shape the disturbance generating, as observed, a long region to the east of the convective source with a high speed peripheral anticyclonic circulation, and a long-lived anticyclonic compact vortex accompanied by strong zonal advection on the southern part of the storm forming a turbulent region. Simulations of the equatorial 1990 GWS (planetographic latitude +12º-+5º, zonal velocity of the source 365-400 m s-1) show a different behavior because of the intense eastward jet, meridional shear at the equatorial region, and low latitude dynamics. A round shaped source forms as observed, with the rapid growth of a Kelvin-Helmholtz instability on the north side of the source due to advection and to the strong meridional wind shear, whereas at the storm latitude the disturbance grows and propagates eastward. The storm nucleus is the manifestation of a Rossby wave, while the eastward propagating planetary-scale disturbance is a gravity-Rossby wave trapped around the equator. The simulated 1960 GWS disturbance (planetographic latitude +56º, zonal velocity 4 m s-1) formed a chain of periodic oval spots that mimic the few available observations of the phenomenon. For the mid and high latitude storms, simulations predict a strong injection of negative relative vorticity due to divergence of the upwelling storm material, which may produce large anticyclones on the anticyclonic side of the zonal profile, and a quick turbulent expansion on the background cyclonic regions. In general, simulations indicate that negative relative vorticity injected by storms determines the natural reaction to zonal winds at latitudes where Coriolis forces are dominant.

Double-reconnected magnetic structures driven by Kelvin-Helmholtz vortices at the Earth's magnetosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borgogno, D.; Califano, F.; Pegoraro, F.

2015-03-15

In an almost collisionless magnetohydrodynamic plasma in a relatively strong magnetic field, stresses can be conveyed far from the region where they are exerted, e.g., through the propagation of Alfvèn waves. The forced dynamics of line-tied magnetic structures in solar and stellar coronae (see, e.g., A. F. Rappazzo and E. N. Parker, Astrophys. J. 773, L2 (2013) and references therein) is a paradigmatic case. Here, we investigate how this action at a distance develops from the equatorial region of the Kelvin-Helmholtz unstable flanks of the Earth's magnetosphere leading to the onset, at mid latitude in both hemispheres, of correlated doublemore » magnetic field line reconnection events that can allow the solar wind plasma to enter the Earth's magnetosphere.« less

F2 layer characteristics and electrojet strength over an equatorial station

NASA Astrophysics Data System (ADS)

Adebesin, B. O.; Adeniyi, J. O.; Adimula, I. A.; Reinisch, B. W.; Yumoto, K.

2013-09-01

The data presented in this work describes the diurnal and seasonal variation in hmF2, NmF2, and the electrojet current strength over an African equatorial station during a period of low solar activity. The F2 region horizontal magnetic element H revealed that the Solar quiet Sq(H) daily variation rises from early morning period to maximum around local noon and falls to lower values towards evening. The F2 ionospheric current responsible for the magnetic field variations is inferred to build up at the early morning hours, attaining maximum strength around 1200 LT. The Sq variation across the entire months was higher during the daytime than nighttime. This is ascribed to the variability of the ionospheric parameters like conductivity and winds structure in this region. Seasonal daytime electrojet (EEJ) current strength for June solstice, March and September equinoxes, respectively had peak values ranging within 27-35 nT (at 1400 LT) , 30-40 nT (at 1200 LT) and 35-45 nT (at 1500 LT). The different peak periods of the EEJ strength were attributed to the combined effects of the peak electron density and electric field. Lastly, the EEJ strength was observed to be higher during the equinoxes than the solstice period.

On a magnetic reconnection in the Venusian wake. The experimental evidences.

NASA Astrophysics Data System (ADS)

Fedorov, Andrei; Jarvinen, Riku; Volwerk, Martin; Barabash, Stas; Zhang, Tielong; Sauvaud, Jean-Andre

2010-05-01

The Venusian magnetotail is formed by solar wind magnetic flux tubes draping around the planet and stretched antisunward. The magnetotail topology represents two magnetic lobes separated by a thin current sheet. Such a configuration is a free energy reservoir. The accumulated energy is generally released by antisunward acceleration of the planetary ions. But in the case of a magnetic reconnection, hypothetically appeared somewhere in the equatorial current sheet, some part of the planetary ions filling the tail, should be accelerated toward the planet. To check this hypothesis we have performed statistical and case studies based on the data from the IMA mass-spectrometer and the magnetometer onboard ESA Venus Express mission. We found that the distribution function of the planetary ions in the equatorial plane of the wake, near the midnight, and at the distances less than 1.7Rv from the center of the planet contains the significant part moving toward the planet. At the same time the magnetic field statistics and the numerical simulation show the magnetic field minimum similar to an X-line in the current sheet at the distance about 1.7 Rv from the planet center. This could be an evidence for a quasi-permanent reconnection in the Venusian wake.

Alleviating tropical Atlantic sector biases in the Kiel climate model by enhancing horizontal and vertical atmosphere model resolution: climatology and interannual variability

NASA Astrophysics Data System (ADS)

Harlaß, Jan; Latif, Mojib; Park, Wonsun

2018-04-01

We investigate the quality of simulating tropical Atlantic (TA) sector climatology and interannual variability in integrations of the Kiel climate model (KCM) with varying atmosphere model resolution. The ocean model resolution is kept fixed. A reasonable simulation of TA sector annual-mean climate, seasonal cycle and interannual variability can only be achieved at sufficiently high horizontal and vertical atmospheric resolution. Two major reasons for the improvements are identified. First, the western equatorial Atlantic westerly surface wind bias in spring can be largely eliminated, which is explained by a better representation of meridional and especially vertical zonal momentum transport. The enhanced atmospheric circulation along the equator in turn greatly improves the thermal structure of the upper equatorial Atlantic with much reduced warm sea surface temperature (SST) biases. Second, the coastline in the southeastern TA and steep orography are better resolved at high resolution, which improves wind structure and in turn reduces warm SST biases in the Benguela upwelling region. The strongly diminished wind and SST biases at high atmosphere model resolution allow for a more realistic latitudinal position of the intertropical convergence zone. Resulting stronger cross-equatorial winds, in conjunction with a shallower thermocline, enable a rapid cold tongue development in the eastern TA in boreal spring. This enables simulation of realistic interannual SST variability and its seasonal phase locking in the KCM, which primarily is the result of a stronger thermocline feedback. Our findings suggest that enhanced atmospheric resolution, both vertical and horizontal, could be a key to achieving more realistic simulation of TA climatology and interannual variability in climate models.

Response of the surface tropical Atlantic Ocean to wind forcing

NASA Astrophysics Data System (ADS)

Castellanos, Paola; Pelegrí, Josep L.; Campos, Edmo J. D.; Rosell-Fieschi, Miquel; Gasser, Marc

2015-05-01

We use 10 years of satellite data (sea level pressure, surface winds and absolute dynamic topography [ADT]) together with Argo-inferred monthly-mean values of near-surface velocity and water transport, to examine how the tropical system of near-surface zonal currents responds to wind forcing. The data is analyzed using complex Hilbert empirical orthogonal functions, confirming that most of the variance has annual periodicity, with maximum amplitudes in the region spanned by the seasonal displacement of the Inter-Tropical Convergence Zone (ITCZ). The ADT mirrors the shape of the upper isopycnals, hence becoming a good indicator of the amount of water stored in the upper ocean. Within about 3° from the Equator, where the Coriolis force is small, there is year-long meridional Ekman-transport divergence that would lead to the eastward transport of the Equatorial Undercurrent and its northern and southern branches. Beyond 3° of latitude, and at least as far as 20°, the convergence of the Ekman transport generally causes a poleward positive ADT gradient, which sustains the westward South Equatorial Current (SEC). The sole exception occurs in summer, between 8°N and 12°N, when an Ekman-transport divergence develops and depletes de amount of surface water, resulting in an ADT ridge-valley system which reverses the ADT gradient and drives the eastward North Equatorial Countercurrent (NECC) at latitudes 4-9°N; in late fall, divergence ceases and the NECC drains the ADT ridge, so the ADT gradient again becomes positive and the SEC reappears. The seasonal evolution of a tilted ITCZ controls the surface water fluxes: the wind-induced transports set the surface divergence-convergence, which then drive the ADT and, through the ADT gradients, create the geostrophic jets that close the water balance.

On the origin of jets from disc-accreting magnetized stars

NASA Astrophysics Data System (ADS)

Lovelace, Richard V. E.; Romanova, Marina M.; Lii, Patrick; Dyda, Sergei

2014-09-01

A brief review of the origin of jets from disc-accreting rotating magnetized stars is given. In most models, the interior of the disc is characterized by a turbulent viscosity and magnetic diffusivity ("alpha" discs) whereas the coronal region outside the disc is treated using ideal magnetohydrodynamics (MHD). Extensive MHD simulations have established the occurrence of long-lasting outflows in the case of both slowly and rapidly rotating stars. (1) Slowly rotating stars exhibit a new type of outflow, conical winds. Conical winds are generated when stellar magnetic flux is bunched up by the inward motion of the accretion disc. Near their region of origin, the winds have a thin conical shell shape with half opening angle of ˜30°. At large distances, their toroidal magnetic field collimates the outflow forming current carrying, matter dominated jets. These winds are predominantly magnetically and not centrifugally driven. About 10-30% of the disc matter from the inner disc is launched in the conical wind. Conical winds may be responsible for episodic as well as long lasting outflows in different types of stars. (2) Rapidly rotating stars in the "propeller regime" exhibit two-component outflows. One component is similar to the matter dominated conical wind, where a large fraction of the disc matter may be ejected in this regime. The second component is a high-velocity, low-density magnetically dominated axial jet where matter flows along the open polar field lines of the star. The axial jet has a mass flux of about 10% that of the conical wind, but its energy flux, due to the Poynting flux, can be as large as for the conical wind. The jet's magnetically dominated angular momentum flux causes the star to spin down rapidly. Propeller-driven outflows may be responsible for protostellar jets and their rapid spin-down. When the artificial requirement of symmetry about the equatorial plane is dropped, the conical winds are found to come alternately from one side of the disc and then the other, even for the case where the stellar magnetic field is a centered axisymmetric dipole. Recent MHD simulations of disc accretion to rotating stars in the propeller regime have been done with no turbulent viscosity and no diffusivity. The strong turbulence observed is due to the magneto-rotational instability. This turbulence drives accretion in the disc and leads to episodic conical winds and jets.

Seasonal and interannual variability of atmospheric heat sources and moisture sinks as determined from NCEP/NCAR ranalysis. Part I

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yanai, Michio; Tomita, Tomohiko

1997-11-01

In this paper, an analysis of the heat and moisture budgets of the troposphere is revised and extended. The analysis is based on the National Centers for Environmental Prediction (NCEP) and National Center for Atmospheric Research (NCAR) reanalysis from 1980 to 1994. The seasonal and interannual variability of heat sources and sinks and the nature of heating over various geographical locations is examined in detail. Results presented include global distributions of the 15-year mean of the vertically integrated heat source and moisture sink and the outgoing longwave radiation flux for northern winter and northern summer. A time series of monthlymore » mean anomalies of the apparent heat source, the apparent moisture sink, outgoing longwave radiation, sea surface temperature, and divergence at wind fields of 850 hPa and 200 hPa are presented for the equatorial Indian Ocean, the equatorial eastern Pacific Ocean, western Tibet, and eastern Tibet. In the equatorial Indian Ocean, short period oscillation is superimposed upon longer periods. Over the eastern Pacific, a longer periodicity is dominant and the variability of the heat source is very well correlated with similar variations of outgoing longwave radiation, sea surface temperature, and horizontal divergence. The high correlation with these variables suggests that anomalous heating is accompanied by intensified convective activity favored by warmer sea surface temperature. 13 refs., 5 figs.« less

Reassessment of ice-age cooling of the tropical ocean and atmosphere

USGS Publications Warehouse

Hostetler, S.W.; Mix, A.C.

1999-01-01

The CLIMAP project's reconstruction of past sea surface temperature inferred limited ice-age cooling in the tropical oceans. This conclusion has been controversial, however, because of the greater cooling indicated by other terrestrial and ocean proxy data. A new faunal sea surface temperature reconstruction, calibrated using the variation of foraminiferal species through time, better represents ice-age faunal assemblages and so reveals greater cooling than CLIMAP in the equatorial current systems of the eastern Pacific and tropical Atlantic oceans. Here we explore the climatic implications of this revised sea surface temperature field for the Last Glacial Maximum using an atmospheric general circulation model. Relative to model results obtained using CLIMAP sea surface temperatures, the cooler equatorial oceans modify seasonal air temperatures by 1-2??C or more across parts of South America, Africa and southeast Asia and cause attendant changes in regional moisture patterns. In our simulation of the Last Glacial Maximum, the Amazon lowlands, for example, are cooler and drier, whereas the Andean highlands are cooler and wetter than the control simulation. Our results may help to resolve some of the apparent disagreements between oceanic and continental proxy climate data. Moreover, they suggest a wind-related mechanism for enhancing the export of water vapour from the Atlantic to the Indo-Pacific oceans, which may link variations in deep-water production and high-latitude climate changes to equatorial sea surface temperatures.

The use of stellite scatterometer winds to drive a primitive equation model of the Indian Ocean: The impact of bandlike sampling

NASA Technical Reports Server (NTRS)

Barnier, Bernard; Capella, Jorge; O'Brien, James J.

1994-01-01

The aim of this study is to evaluate the impact of the bandlike sampling of spaceborne scatterometers on the ability of scatterometer winds to successfully force the mean flow and seasonal cycle of an ocean model in the context of equatorial and tropical dynamics. The equatorial ocean is simulated with a four-layer, primitive equation, reduced gravity model of the Indian Ocean. The variable wind stress used in this study is derived from one year (1988) of 6-hour analyses of the 10-m wind vector over the Indian Ocean performed at the European Centre for Medium-Range Weather Forecasts (ECMWF). It is applied as a forcing at every grid point of the model to drive a reference circulation. Scatterometer winds are simulated from ECMWF winds, using the nominal configurations and orbital parameters of the European Remote Sensing 1 (ERS-1) and NASA Scatterometer (NSCAT) missions. The model is forced in real time under swaths with the raw scatterometer winds of ERS-1 and NSCAT, with a persistence condition (i.e., the wind is kept constsnt until the next passage of the satellite provides a new value). The circulation obtained for each of the scatterometer experiments is compared with the reference circulation. The seasonal circulation of the Indian Ocean with NSCAT winds is very similar to the reference. The perturbations introduced by the bandlike sampling and the persistance condition have an impact similar to that of a small uncorrelated noise added to the reference forcing. The persistence condition for ERS-1 does not give results which are as good as those obtained for NSCAT.

Relation of large-scale coronal X-ray structure and cosmic rays. I - Sources of solar wind streams as defined by X-ray emission and H-alpha absorption features

NASA Technical Reports Server (NTRS)

Krieger, A. S.; Nolte, J. T.; Sullivan, J. D.; Lazarus, A. J.; Mcintosh, P. S.; Gold, R. E.; Roelof, E. C.

1975-01-01

The large-scale structure of the corona and the interplanetary medium during Carrington rotations 1601-1607 is discussed relative to recurrent high-speed solar wind streams and their coronal sources. Only streams A, C, D, and F recur on more than one rotation. Streams A and D are associated with coronal holes, while C and F originate in the high corona (20-50 solar radii) over faint X-ray emissions. The association of the streams with holes is confirmed by earlier findings that there are no large equatorial holes without an associated high-speed stream and that the area of the equatorial region of coronal holes is highly correlated with the maximum velocity observed in the associated stream near 1 AU.

Interbasin effects of the Indian Ocean on Pacific decadal climate change

NASA Astrophysics Data System (ADS)

Mochizuki, Takashi; Kimoto, Masahide; Watanabe, Masahiro; Chikamoto, Yoshimitsu; Ishii, Masayoshi

2016-07-01

We demonstrate the significant impact of the Indian Ocean on the Pacific climate on decadal timescales by comparing two sets of data assimilation experiments (pacemaker experiments) conducted over recent decades. For the Indian Ocean of an atmosphere-ocean coupled global climate model, we assimilate ocean temperature and salinity anomalies defined as deviations from climatology or as anomalies with the area-averaged changes for the Indian Ocean subtracted. When decadal sea surface temperature (SST) trends are observed to be strong over the Indian Ocean, the equatorial thermocline uniformly deepens, and the model simulates the eastward tendencies of surface wind aloft. Surface winds strongly converge around the maritime continent, and the associated strengthening of the Walker circulation suppresses an increasing trend in the equatorial Pacific SST through ocean thermocline shoaling, similar to common changes associated with seasonal Indian Ocean warming.

A study of equatorial wave characteristics using rockets, balloons, lidar and radar

NASA Astrophysics Data System (ADS)

Sasi, M. N.; Krishna Murthy, B. V.; Ramkumar, Geetha; Satheesan, K.; Parameswaran, K.; Rajeev, K.; Sunilkumar, S. V.; Nair, Prabha R.; Krishna Moorthy, K.; Bhavanikumar, Y.; Raghunath, K.; Jain, A. R.; Rao, P. B.; Krishnaiah, M.; Prabhakaran Nayars, S. R.; Revathy, K.; Devanarayanan, S.

2003-09-01

A co-ordmated experimental campaign was conducted for 40 consecutive days from 21 February to 01 April 2000 using RH-200 rockets, balloons, Rayleigh lidar and MST radar, with the objective of delineating the equatorial waves and estimating momentum fluxes associated with them. Winds and temperatures in the troposphere, stratosphere and mesosphere over two low latitude stations Gadanki (13.5°N, 79.2°E) and SHAR (13.7°N, 80.2°E) were measured and were used for the study of equatorial waves and their interactions with the background mean flow in various atmospheric regions. The study shows the occurrence of a strong stratospheric cooling (˜25 K) anomaly along with a zonal wind anomaly and this low-latitude event appears to be linked to high-latitude stratospheric warming event and followed by subsequent generation of short period (˜5 days) oscillations lasting for a few cycles in the stratosphere. Slow and fast Kelvin waves and RG wave (˜-17-day and ˜7.2-day and ˜4.2-day periods respectively) have been identified. The mean flow acceleration produced by the divergence of the momentum flux due to the observed Kelvin waves in the 35-60 km height region were compared with the zonal flow accelerations computed from the observed zonal winds. Contribution by the slow and fast Kelvin waves was found to be only ˜25 % of the observed acceleration during the evolution of the westerly phase of the semi-annual oscillation.

On the relationship between the stratospheric quasi-biennial oscillation and the tropospheric Southern oscillation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, J.S.

1992-05-01

Two quasi-periodic oscillations in the tropical atmosphere with similar oscillation period-the stratospheric quasi-biennial and the Southern oscillations-and the relationship between these two oscillations are examined using the Principal Oscillation Pattern (POP) analysis technique. The POP analysis of the equatorial stratospheric dataset provides a compact description of the QBO. The oscillation features identified by the POP analysis, namely, the spatial structure, the characteristic times of the oscillation, and the asymmetry in downward propagation, are almost identical to those found by earlier studies using more conventional analyses. The simultaneous POP analysis of the equatorial zonal surface wind and sea surface temperature indicatesmore » a well-defined cyclic behavior of the SO. In contrast to the very regular QBO, the SO appears to be much more noisy with intermittent quiet phases. A spectral analysis of the complex POP coefficient time series and the SO index reveals a negligible correlation between the two processes. A POP analysis of the combined equatorial dataset of stratospheric wind, zonal surface wind, and SST also indicates no relation between the QBO and the SO. Two independent modes are identified, one of them completely describing the QBO and the other representing the entire SO. No linear relationship is found between the two modes either in space or in time. It is concluded that the SO and the QBO are two independent processes in the tropical atmosphere with similar time scales. 26 refs., 17 figs.« less

Modeling the Earth's magnetospheric magnetic field confined within a realistic magnetopause

NASA Technical Reports Server (NTRS)

Tsyganenko, N. A.

1995-01-01

Empirical data-based models of the magnetosphereic magnetic field have been widely used during recent years. However, the existing models (Tsyganenko, 1987, 1989a) have three serious deficiencies: (1) an unstable de facto magnetopause, (2) a crude parametrization by the K(sub p) index, and (3) inaccuracies in the equatorial magnetotail B(sub z) values. This paper describes a new approach to the problem; the essential new features are (1) a realistic shape and size of the magnetopause, based on fits to a large number of observed crossing (allowing a parametrization by the solar wind pressure), (2) fully controlled shielding of the magnetic field produced by all magnetospheric current systems, (3) new flexible representations for the tail and ring currents, and (4) a new directional criterion for fitting the model field to spacecraft data, providing improved accuracy for field line mapping. Results are presented from initial efforts to create models assembled from these modules and calibrated against spacecraft data sets.

Studying Peculiarities of Ionospheric Response to the 2015 March 17-19 Geomagnetic Storm in East Asia: Observations and Simulation

NASA Astrophysics Data System (ADS)

Romanova, Elena; Zherebtsov, Gelii; Polekh, Nelya; Wang, Xiao; Wang, Guojun; Zolotukhina, Nina; Shi, Jiankui

2016-07-01

We report results of the research into effects of the strong geomagnetic storm in the ionosphere of high, middle, and low latitudes on March 17-19, 2015. The research relies on measurements made at the network of ionospheric stations located near the 120°E meridian. The analysis of experimental data has revealed that at the beginning of the main storm phase the equatorial wall of the main ionospheric trough (MIT) shifted towards geographic latitudes 58-60°N, which caused negative disturbances in subauroral latitudes and positive disturbances in middle latitudes. Further displacement of the MIT equatorial wall towards a geographic latitude of 52° N led to a decrease in the F2-layer critical frequency (foF2) up to 2 MHz in middle latitudes during evening and night hours, and to the appearance of sporadic layers in these latitudes due to energetic particle precipitation. Such phenomena are largely specific to the subauroral ionosphere. During the recovery storm phase on March 18, 2015 during daylight hours, negative disturbances were recorded at all the stations. Since prolonged negative disturbances are usually associated with a reduction in the ratio of concentrations of atomic oxygen and molecular nitrogen [O]/[N2] which is transported by disturbed thermospheric wind from auroral latitudes to middle and low ones, we analyzed measurements of [O]/[N2], made by GUVI (Global Ultraviolet Imager, http://guvi.jhuapl.edu/site/gallery/guvi-galleryl3on2.shtml), during this storm. The storm appeared to be characterized by very low values of [O]/[N2] which were recorded in the longitude sector 60 - 150°E up to 15°N on March 18. The discovered peculiarities of the ionospheric response to the storm were interpreted using a theoretical model of ionosphere-plasmosphere coupling developed at ISTP SB RAS. The simulation showed that the displacement of MIT equatorial wall resulted in foF2 variations similar to those observed during the main storm phase in subauroral and middle latitudes. The prolonged negative disturbances during the recovery storm phase in middle latitudes are attributed to variations in the global wind circulation and to [O]/[N2] reduction; in low latitudes, a prolonged negative disturbance is also conditioned by variations in the global wind circulation and, to a lesser extent, by [O]/[N2] reduction as well as by penetration of electric fields to low latitudes; hence there was no equatorial anomaly on March 18. This is confirmed by total electron content data (http://cdaweb.gsfc.nasa.gov/cgi-bin/eval2.cgi). The recovery storm phase lasted until mid-March 25. The work is supported by the Russian Foundation for Basic Research (RFBR grant No. 16-55-53003_DVEH_a).

Is the Critical Rotation of Be Stars Really Critical for the Be Phenomenon?

NASA Astrophysics Data System (ADS)

Stee, Ph.; Meilland, A.

We aim to study the effect of the fast rotation, stellar wind and circumstellar disks around active hot stars and their effects on the formation and evolution of these massive stars. For that purpose, we obtained, for the first time, interferometric measurements of three active hot stars, namely α Arae, κ CMa and Achernar, using the VLTI /AMBER and VLTI/MIDI instruments which allow us to study the kinematics of the central star and its surrounding circumstellar matter. These data coupled with our numerical code SIMECA (SIMulation pour Etoiles Chaudes Actives) seem to indicate that the presence of equatorial disks and polar stellar wind around Be stars are not correlated. A polar stellar wind was detected for α Arae and Achernar whereas κ CMa seems to exhibit no stellar wind. On the other hand, these two first Be stars are certainly nearly critical rotators whereas the last one seems to be far from the critical rotation. Thus a polar stellar wind may be due to the nearly critical rotation which induces a local effective temperature change following the von Zeipel theorem, producing a hotter polar region triggering a polar stellar wind. This critical rotation may also explain the formation of a circumstellar disk which is formed by the centrifugal force balancing the equatorial effective gravity of the central star. Following these results we try to investigate if critical rotation may be the clue for the Be phenomenon.

Influence of interplanetary solar wind sector polarity on the ionosphere

NASA Astrophysics Data System (ADS)

liu, jing

2014-05-01

Knowledge of solar sector polarity effects on the ionosphere may provide some clues in understanding of the ionospheric day-to-day variability. A solar-terrestrial connection ranging from solar sector boundary (SB) crossings, geomagnetic disturbance and ionospheric perturbations has been demonstrated. The increases in interplanetary solar wind speed within three days are seen after SB crossings, while the decreases in solar wind dynamic pressure and magnetic field intensity immediately after SB crossings are confirmed by the superposed epoch analysis results. Furthermore, the interplanetary magnetic field (IMF) Bz component turns from northward to southward in March equinox and June solstice as the Earth passes from a solar sector of outward to inward directed magnetic fields, whereas the reverse situation occurs for the transition from toward to away sectors. The F2 region critical frequency (foF2) covering about four solar cycles and total electron content (TEC) during 1998-2011 are utilized to extract the related information, revealing that they are not modified significantly and vary within the range of 15% on average. The responses of the ionospheric TEC to SB crossings exhibit complex temporal and spatial variations and have strong dependencies on season, latitude, and solar cycle. This effect is more appreciable in equinoctial months than in solstitial months, which is mainly caused by larger southward Bz components in equinox. In September equinox, latitudinal profile of relative variations of foF2 at noon is featured by depressions at high latitudes and enhancements in low-equatorial latitudes during IMF away sectors. The negative phase of foF2 is delayed at solar minimum relative to it during other parts of solar cycle, which might be associated with the difference in longevity of major interplanetary solar wind drivers perturbing the Earth's environment in different phases of solar cycle.

Modulation of equatorial Pacific westerly/easterly wind events by the Madden-Julian oscillation and convectively-coupled Rossby waves

NASA Astrophysics Data System (ADS)

Puy, Martin; Vialard, J.; Lengaigne, M.; Guilyardi, E.

2016-04-01

Synoptic wind events in the equatorial Pacific strongly influence the El Niño/Southern Oscillation (ENSO) evolution. This paper characterizes the spatio-temporal distribution of Easterly (EWEs) and Westerly Wind Events (WWEs) and quantifies their relationship with intraseasonal and interannual large-scale climate variability. We unambiguously demonstrate that the Madden-Julian Oscillation (MJO) and Convectively-coupled Rossby Waves (CRW) modulate both WWEs and EWEs occurrence probability. 86 % of WWEs occur within convective MJO and/or CRW phases and 83 % of EWEs occur within the suppressed phase of MJO and/or CRW. 41 % of WWEs and 26 % of EWEs are in particular associated with the combined occurrence of a CRW/MJO, far more than what would be expected from a random distribution (3 %). Wind events embedded within MJO phases also have a stronger impact on the ocean, due to a tendency to have a larger amplitude, zonal extent and longer duration. These findings are robust irrespective of the wind events and MJO/CRW detection methods. While WWEs and EWEs behave rather symmetrically with respect to MJO/CRW activity, the impact of ENSO on wind events is asymmetrical. The WWEs occurrence probability indeed increases when the warm pool is displaced eastward during El Niño events, an increase that can partly be related to interannual modulation of the MJO/CRW activity in the western Pacific. On the other hand, the EWEs modulation by ENSO is less robust, and strongly depends on the wind event detection method. The consequences of these results for ENSO predictability are discussed.

New Measurements Of Jupiter's Equatorial Region In Visible Wavelengths

NASA Astrophysics Data System (ADS)

Rojas, Jose; Arregi, J.; García-Melendo, E.; Barrado-Izagirre, N.; Hueso, R.; Gómez-Forrellad, J. M.; Pérez-Hoyos, S.; Sanz-Requena, J. F.; Sánchez-Lavega, A.

2010-10-01

We have studied the equatorial region of Jupiter, between 15ºS and 15ºN, on Cassini ISS images obtained during the Jupiter flyby at the end of 2000 and on HST images acquired in May and July 2008. We have found significant longitudinal variations in the intensity of the 6ºN eastward jet, up to 60 m s-1 in Cassini and HST observations. In the HST case we found that these longitudinal variations are associated to different cloud morphology. Photometric and radiative transfer analysis of the cloud features used as tracers in HST images shows that there is only a small height difference, no larger than 0.5 - 1 scale heights at most, between the slow ( 100 m s-1) and fast ( 150 m s-1) moving features. This suggests that speed variability at 6ºN is not dominated by vertical wind shears and we propose that Rossby wave activity is the responsible for the zonal variability. After removing this variability we found that Jupiter's equatorial jet is actually symmetric relative to the equator with two peaks of 140 - 150 m s-1 located at latitudes 6ºN and 6ºS and at a similar pressure level. We also studied a large, long-lived feature called the White Spot (WS) located at 6ºS that turns to form and desapear. The internal flow field in the White Spot indicates that it is a weakly rotating quasi-equatorial anticyclone relative to the ambient meridionally sheared flow. Acknowledgements: This work was supported by the Spanish MICIIN AYA2009-10701 with FEDER and Grupos Gobierno Vasco IT-464-07.

The 4-5 day mode oscillation in zonal winds of Indian middle atmosphere during MONEX-79

NASA Astrophysics Data System (ADS)

Reddy, R. S.; Mukherjee, B. K.; Indira, K.; Murty, B. V. R.

1985-12-01

In the early studies based on time series of balloon observations, the existence of 4 to 5 day period waves and 10 to 20 day wind fluctuations were found in the tropical lower stratosphere, and they are identified theoretically as the mixed Rossby-gravity wave and the Kelvin wave, respectively. On the basis of these studies, it was established that the vertically propagating equatorial waves play an important role in producing the QBO (quasi-biennial oscillation) in the mean zonal wind through the mechanism of wave-zonal interaction. These studies are mainly concentrated over the equatorial Pacific and Atlantic Oceans. Similar prominent wave disturbances have been observed over the region east of the Indian Ocean during a quasi-biennial oscillation. Zonal winds in upper troposphere and lower stratosphere (10 to 20) km of the middle atmosphere over the Indian subcontinent may bear association with the activity of summer monsoon (June-September). Monsoon Experiment (MONEX-79) has provided upper air observations at Balasore (21 deg. 30 min.N; 85 deg. 56 min.E), during the peak of monsoon months July and August. A unique opportunity has, therefore, been provided to study the normal oscillations present in the zonal winds of lower middle atmosphere over India, which may have implication on large scale wave dynamics. This aspect is examined in the present study.

Equatorial jet in the lower to middle cloud layer of Venus revealed by Akatsuki

PubMed Central

Horinouchi, Takeshi; Murakami, Shin-ya; Satoh, Takehiko; Peralta, Javier; Ogohara, Kazunori; Kouyama, Toru; Imamura, Takeshi; Kashimura, Hiroki; Limaye, Sanjay S.; McGouldrick, Kevin; Nakamura, Masato; Sato, Takao M.; Sugiyama, Ko-ichiro; Takagi, Masahiro; Watanabe, Shigeto; Yamada, Manabu; Yamazaki, Atsushi; Young, Eliot F.

2018-01-01

The Venusian atmosphere is in a state of superrotation where prevailing westward winds move much faster than the planet’s rotation. Venus is covered with thick clouds that extend from about 45 to 70 km altitude, but thermal radiation emitted from the lower atmosphere and the surface on the planet’s night-side escapes to space at narrow spectral windows of near-infrared. The radiation can be used to estimate winds by tracking the silhouettes of clouds in the lower and middle cloud regions below about 57 km in altitude. Estimates of wind speeds have ranged from 50 to 70 m/s at low- to mid-latitudes, either nearly constant across latitudes or with winds peaking at mid-latitudes. Here we report the detection of winds at low latitude exceeding 80 m/s using IR2 camera images from the Akatsuki orbiter taken during July and August 2016. The angular speed around the planetary rotation axis peaks near the equator, which we suggest is consistent with an equatorial jet, a feature that has not been observed previously in the Venusian atmosphere. The mechanism producing the jet remains unclear. Our observations reveal variability in the zonal flow in the lower and middle cloud region that may provide new challenges and clues to the dynamics of Venus’s atmospheric superrotation. PMID:29887914

Singapore Haze in June 2013: Consequences of Land-Use Change, Fires, and Anomalous Meteorology for Air Quality in Equatorial Asia

NASA Astrophysics Data System (ADS)

Koplitz, S.; Mickley, L. J.; Jacob, D. J.; Kim, P. S.; DeFries, R. S.; Marlier, M. E.; Schwartz, J.; Buonocore, J.; Myers, S. S.

2014-12-01

Much of Equatorial Asia is currently undergoing extensive burning from agricultural fires and rapid land-use conversion to oil palm plantations, with substantial consequences for air quality and health. In June 2013, Singapore experienced severe smoke levels, with surface particulate matter concentrations greater than ten times average. Unlike past haze events in Singapore (e.g. September 1997 and October 2006), the June 2013 pollution event occurred during El Nino-neutral conditions. Using a combination of observations and chemical transport modeling, we examine relationships between sea surface temperatures, wind fields, fire patterns, and aerosol optical depth during the June 2013 haze event. We find reasonable agreement between satellite measurements of aerosol optical depth (AOD) from the MODIS and MISR instruments and in-situ measurements from the AERONET stations across Equatorial Asia for 2005-2010 (MODIS R2 = 0.39, bias = -1.6%; MISR R2 = 0.27, bias = -42%). However, AOD observations fail to capture the Singapore pollution event of June 2013. Simulations with the GEOS-Chem model suggest that anomalously high dust concentrations during June 2013 may have impaired the ability of MODIS to monitor the haze over Singapore. In contrast, we show that the OMI Aerosol Index can effectively capture these smoke events and may be used to monitor future haze episodes in Equatorial Asia. We find that the June 2013 haze in Singapore may be attributed to anomalously strong westerlies carrying smoke from Riau Province in Indonesia. These westerlies, 5 m s-1 faster than the 2005-2010 mean June winds, are consistent with the phase of the Madden-Julian Oscillation (MJO) crossing the Maritime Continent at that time. These westerlies may have been further enhanced by a negative phase of the Indian Ocean Dipole (IOD), an east-west gradient in sea surface temperature anomalies across the Indian Ocean, with cold sea surface temperature anomalies (-3 C°) off the Arabian coast and warm anomalies (+2 C°) in the East. These conditions appear to provide an important meteorological pathway by which land-use change fires in Indonesia may affect the health of large populations. Our work suggests that this pathway should be taken into account in the development of strategies to curb fire-related air pollution and health effects in Indonesia.

El Ni?o Last Stand?

NASA Image and Video Library

2010-03-16

Recent sea-level height data from NASA Jason-2 oceanography satellite show a weakening of trade winds in western and central equatorial Pacific during late-January through February has triggered yet another strong, eastward-moving Kelvin wave.

Modeling Global Ocean Biogeochemistry With Physical Data Assimilation: A Pragmatic Solution to the Equatorial Instability

NASA Astrophysics Data System (ADS)

Park, Jong-Yeon; Stock, Charles A.; Yang, Xiaosong; Dunne, John P.; Rosati, Anthony; John, Jasmin; Zhang, Shaoqing

2018-03-01

Reliable estimates of historical and current biogeochemistry are essential for understanding past ecosystem variability and predicting future changes. Efforts to translate improved physical ocean state estimates into improved biogeochemical estimates, however, are hindered by high biogeochemical sensitivity to transient momentum imbalances that arise during physical data assimilation. Most notably, the breakdown of geostrophic constraints on data assimilation in equatorial regions can lead to spurious upwelling, resulting in excessive equatorial productivity and biogeochemical fluxes. This hampers efforts to understand and predict the biogeochemical consequences of El Niño and La Niña. We develop a strategy to robustly integrate an ocean biogeochemical model with an ensemble coupled-climate data assimilation system used for seasonal to decadal global climate prediction. Addressing spurious vertical velocities requires two steps. First, we find that tightening constraints on atmospheric data assimilation maintains a better equatorial wind stress and pressure gradient balance. This reduces spurious vertical velocities, but those remaining still produce substantial biogeochemical biases. The remainder is addressed by imposing stricter fidelity to model dynamics over data constraints near the equator. We determine an optimal choice of model-data weights that removed spurious biogeochemical signals while benefitting from off-equatorial constraints that still substantially improve equatorial physical ocean simulations. Compared to the unconstrained control run, the optimally constrained model reduces equatorial biogeochemical biases and markedly improves the equatorial subsurface nitrate concentrations and hypoxic area. The pragmatic approach described herein offers a means of advancing earth system prediction in parallel with continued data assimilation advances aimed at fully considering equatorial data constraints.

Ockham's Razorblade Shaving Wind-Induced Circulation

NASA Astrophysics Data System (ADS)

Bergmann, Juan Carlos

2010-05-01

Terrestrial physical oceanography is fortunate because of the existence of the continents that divide the low-latitude oceans into basins. At first glance, the previous statement appears to be not obvious because an ocean-planet should be much simpler to describe. Simple-case explanation is the central aspect of Ockham's Razorblade: If a theory fails to describe the most-simple case properly, the theory is, at least, ‘not good'. Also Descartes' methodical rules take the most-simple case as starting point. The analysis of wind-induced circulation on an ocean-planet will support the initial statement. Earth's south hemisphere is dominated by the oceans. The continents' influence on the zonal-average zonal-wind climate is relatively small. Therefore, South Hemisphere's zonal wind pattern is a relatively good proxy for that of an ocean planet. Application of this wind-stress pattern to an ocean planet yields reasonable meridional mass-flow results from the polar-regions down to the high-pressure belts: Down-welling and up-welling of water-mass are approximately balanced. However, the entire tropical circulation can in principle not be closed because there is only down-welling - even if the extreme down-welling in the equatorial belt (± 8°, with a singularity at the equator) is disregarded. The only input to the calculations is the observed terrestrial south-hemisphere zonal wind-stress pattern. Meridional stress is irrelevant because it produces a closed zonal Ekman-transport around the ocean planet (sic!). Vertical mass-transport is calculated from the divergence of the wind-induced meridional Ekman-mass-transport, which in its turn is a necessary consequence of angular-momentum conservation. No assumptions are made on how the return-flows at depth are forced because the wind-force equations cannot contribute hereto. This circumstance expresses a fundamental difference to atmospheric circulation, where mechanical forcing is caused by the pressure-fields that result from differential heating/cooling and therefore ‘automatically' comprise the entire circulation system. Wind-caused oceanic flow is exclusively generated by frictional wind-forces at the surface, and other processes in the ocean are not causally connected hereto. In absence of continents it is quite difficult to ‘find' the corresponding forcing for the meridional return-flows - and it can definitely not be wind-force-caused - very strange! The fact that the wind-induced circulation can only be closed by the action of other processes, which are not causally connected to wind-forces, demonstrates that something must be fundamentally wrong. The singularity at the equator and the extreme down-welling in the equatorial belt indicate an additional severe problem that can only be avoided if zonal wind-stress is completely excluded. Escape to additional assumptions is similar to the introduction of the epicycles in order to explain the planets' retrograde motion in maintaining geocentric cosmology. Should the previous analysis be ignored in favour of maintaining the ‘established' ideas of wind-induced circulation or should there be an effort to formulate new ideas that provide closed and balanced circulation without employing other processes than wind-forces?

Influence of Transient Atmospheric Circulation on the Surface Heating of the Pacific Warm Pool

NASA Technical Reports Server (NTRS)

Chou, Ming-Dah; Chou, Shu-Hsien; Chan, Pui-King

2003-01-01

Analyses of data on clouds, winds, and surface heat fluxes show that the transient behavior of basin-wide large-scale circulation has a significant influence on the warm pool sea surface temperature (SST). Trade winds converge to regions of the highest SST in the equatorial western Pacific. These regions have the largest cloud cover and smallest wind speed. Both surface solar heating and evaporative cooling are weak. The reduced evaporative cooling due to weakened winds exceeds the reduced solar heating due to enhanced cloudiness. The result is a maximum surface heating in the strong convective and high SST regions. Data also show that the maximum surface heating in strong convective regions is interrupted by transient atmospheric and oceanic circulation. Due to the seasonal variation of the insolation at the top of the atmosphere, trade winds and clouds also experience seasonal variations. Regions of high SST and low-level convergence follow the Sun, where the surface heating is a maximum. As the Sun moves away from a convective region, the strong trade winds set in, and the evaporative cooling enhances, resulting in a net cooling of the surface. During an El Nino, the maximum SST and convective region shifts eastward from the maritime continent to the equatorial central Pacific. Following the eastward shift of the maximum SST, the region of maximum cloudiness and surface heating also shift eastward. As the atmospheric and oceanic circulation returns to normal situations, the trade winds increase and the surface heating decreases. We conclude that the evaporative cooling associated with the seasonal and interannual variations of trade winds is one of the major factors that modulate the SST distribution of the Pacific warm pool.

On the structure of climate variability near the tropopause and its relationship to equatorial planetary waves

NASA Astrophysics Data System (ADS)

Grise, Kevin M.

The tropopause is an important interface in the climate system, separating the unique dynamical, chemical, and radiative regimes of the troposphere and stratosphere. Previous studies have demonstrated that the long-term mean structure and variability of the tropopause results from a complex interaction of stratospheric and tropospheric processes. This project provides new insight into the processes involved in the global tropopause region through two perspectives: (1) a high vertical resolution climatology of static stability and (2) an observational analysis of equatorial planetary waves. High vertical resolution global positioning system radio occultation profiles are used to document fine-scale features of the global static stability field near the tropopause. Consistent with previous studies, a region of enhanced static stability, known as the tropopause inversion layer (TIL), exists in a narrow layer above the extratropical tropopause and is strongest over polar regions during summer. However, in the tropics, the TIL possesses a unique horizontally and vertically varying structure with maxima located at ˜17 and ˜19 km. The upper feature peaks during boreal winter and has its largest magnitude between 10º and 15º latitude in both hemispheres; the lower feature exhibits a weaker seasonal cycle and is centered at the Equator. The spatial structure of both features resembles the equatorial planetary wave response to the climatological distribution of deep convection. Equatorial planetary waves not only dominate the climatological-mean general circulation near the tropical tropopause but also play an important role in its intraseasonal and interannual variability. The structure of the equatorial planetary waves emerges as the leading pattern of variability of the zonally asymmetric tropical atmospheric circulation. Regressions on an index of the equatorial planetary waves reveal that they are associated with a distinct pattern of equatorially symmetric climate variability characterized by variations in: (1) the distribution of convection in the deep tropics; (2) the eddy momentum flux convergence and the zonal-mean zonal wind in the tropical upper troposphere; (3) the mean meridional circulation of the tropical and subtropical troposphere; (4) temperatures in the tropical upper troposphere, the tropical lower stratosphere, and the subtropical troposphere of both hemispheres; and (5) the amplitude of the upper tropospheric anticyclones that straddle the Equator over the western tropical Pacific Ocean. The pulsation of the equatorial planetary waves in time provides a framework for interpreting a broad range of climate phenomena. Variability in the equatorial planetary waves is associated with variability in the tropical TIL and is linked to both the El Nino-Southern Oscillation and the Madden-Julian Oscillation (MJO). Evidence is presented that suggests that the MJO can be viewed as the linear superposition of: (1) the pulsation of the equatorial planetary waves at a fixed location and (2) a propagating component. Variability in the equatorial planetary waves may also contribute to variability in troposphere/stratosphere exchange and the width of the tropical belt.

The magnetic field of the equatorial magnetotail - AMPTE/CCE observations at R less than 8.8 earth radii

NASA Technical Reports Server (NTRS)

Fairfield, D. H.; Acuna, M. H.; Zanetti, L. J.; Potemra, T. A.

1987-01-01

The MPTE/CCE magnetic field experiment has been used to obtain a quantitative evaluation of the frequency and extent of magnetic field distortion in the near-tail region at less than 8.8 earth radii. The variation of this distortion with Kp, radial distance, longitude, and near-equatorial latitude is reported. It has been found that taillike distortions from the dipole field direction may reach 80 deg near the MPTE/CE apogee of 8.8 earth radii. The Bz field component in dipole coordinates was always positive within 0.5 earth radii of the equatorial current sheet, indicating the neutral lines were never seen inside of 8.8 earth radii. Fields were most taillike near midnight and during times of high Kp. At 8.5 earth radii the equatorial field magnitude depressions were roughly half the dipole field strength of 51 nT. These depressions are larger at lesser distances, reaching -40 nT at 3.4 earth radii for Kp of 2- or less and -80 nT and Kp of 3+ and greater.

Equatorial Dynamics Observed by Rocket, Radar, and Satellite During the CADRE/MALTED Campaign. 1; Programmatics and small-scale fluctuations

NASA Technical Reports Server (NTRS)

Goldberg, Richard A.; Lehmacher, Gerald A.; Schmidlin, Frank J.; Fritts, David C.; Mitchell, J. D.; Croskey, C. L.; Friedrich, M.; Swartz, W. E.

1997-01-01

In August 1994, the Mesospheric and Lower Thermospheric Equatorial Dynamics (MALTED) Program was conducted from the Alcantara rocket site in northeastern Brazil as part of the International Guard Rocket Campaign to study equatorial dynamics, irregularities, and instabilities in the ionosphere. This site was selected because of its proximity to the geographic (2.3 deg S) and magnetic (approx. 0.5 deg S) equators. MALTED was concerned with planetary wave modulation of the diurnal tidal amplitude, which exhibits considerable amplitude variability at equatorial and subtropical latitudes. Our goals were to study this global modulation of the tidal motions where tidal influences on the thermal structure are maximum, to study the interaction of these tidal structures with gravity waves and turbulence at mesopause altitudes, and to gain a better understanding of dynamic influences and variability on the equatorial middle atmosphere. Four (two daytime and two nighttime) identical Nike-Orion payloads designed to investigate small-scale turbulence and irregularities were coordinated with 20 meteorological falling-sphere rockets designed to measure temperature and wind fields during a 10-day period. These in situ measurements were coordinated with observations of global-scale mesospheric motions that were provided by various ground based radars and the Upper Atmosphere Research Satellite (UARS) through the Coupling and Dynamics of Regions Equatorial (CADRE) campaign. The ground-based observatories included the Jicamarca radar observatory near Lima, Peru, and medium frequency (MF) radars in Hawaii, Christmas Island, and Adelaide. Since all four Nike-Orion flights penetrated and overflew the electrojet with apogees near 125 km, these flights provided additional information about the electrodynamics and irregularities in the equatorial ionospheric E region and may provide information on wave coupling between the mesosphere and the electrojet. Simultaneous with these flights, the CUPRI 50-MHz radar (Cornell University) provided local sounding of the electrojet region. A description of the campaign logistics and the measurements performed with the Nike-Orion instrumentation and their implications for turbulence due to gravity waves and tidal instability in the mesosphere and lower thermosphere (MLT) are presented here. From a study of electron density fluctuations measured by rocket probes, we have found evidence for equatorial mesospheric neutral-atmospheric turbulence between 85 and 90 km. Furthermore, falling-sphere data imply that gravity wave breaking was a source for this turbulence. Mean motions and the various planetary, tidal, and gravity wave structures and their coherence and variability are the subjects of a companion paper.

Equatorial dynamics observed by rocket, radar, and satellite during the CADRE/MALTED campaign 1. Programmatics and small-scale fluctuations

NASA Astrophysics Data System (ADS)

Goldberg, Richard A.; Lehmacher, Gerald A.; Schmidlin, Frank J.; Fritts, David C.; Mitchell, J. D.; Croskey, C. L.; Friedrich, M.; Swartz, W. E.

1997-11-01

In August 1994, the Mesospheric and Lower Thermospheric Equatorial Dynamics (MALTED) Program was conducted from the Alca‸ntara rocket site in northeastern Brazil as part of the International Guará Rocket Campaign to study equatorial dynamics, irregularities, and instabilities in the ionosphere. This site was selected because of its proximity to the geographic (2.3°S) and magnetic (~0.5°S) equators. MALTED was concerned with planetary wave modulation of the diurnal tidal amplitude, which exhibits considerable amplitude variability at equatorial and subtropical latitudes. Our goals were to study this global modulation of the tidal motions where tidal influences on the thermal structure are maximum, to study the interaction of these tidal structures with gravity waves and turbulence at mesopause altitudes, and to gain a better understanding of dynamic influences and variability on the equatorial middle atmosphere. Four (two daytime and two nighttime) identical Nike-Orion payloads designed to investigate small-scale turbulence and irregularities were coordinated with 20 meteorological falling-sphere rockets designed to measure temperature and wind fields during a 10-day period. These in situ measurements were coordinated with observations of global-scale mesospheric motions that were provided by various ground based radars and the Upper Atmosphere Research Satellite (UARS) through the Coupling and Dynamics of Regions Equatorial (CADRE) campaign. The ground-based observatories included the Jicamarca radar observatory near Lima, Peru, and medium frequency (MF) radars in Hawaii, Christmas Island, and Adelaide. Since all four Nike-Orion flights penetrated and overflew the electrojet with apogees near 125 km, these flights provided additional information about the electrodynamics and irregularities in the equatorial ionospheric E region and may provide information on wave coupling between the mesosphere and the electrojet. Simultaneous with these flights, the CUPRI 50-MHz radar (Cornell University) provided local sounding of the electrojet region. A description of the campaign logistics and the measurements performed with the Nike-Orion instrumentation and their implications for turbulence due to gravity waves and tidal instability in the mesosphere and lower thermosphere (MLT) are presented here. From a study of electron density fluctuations measured by rocket probes, we have found evidence for equatorial mesospheric neutral-atmospheric turbulence between 85 and 90 km. Furthermore, falling-sphere data imply that gravity wave breaking was a source for this turbulence. Mean motions and the various planetary, tidal, and gravity wave structures and their coherence and variability are the subjects of a companion paper.

Equatorial Plasma Bubbles: Effect of Thermospheric Winds Modulated by DE3 Tidal Waves

NASA Astrophysics Data System (ADS)

Sidorova, L. N.; Filippov, S. V.

2018-03-01

A hypothesis about the effect of the tropospheric source on the longitudinal distributions of the equatorial plasma bubbles observed in the topside ionosphere was proposed earlier. It was supposed that this influence is transferred mainly by the thermospheric winds modulated by the DE3 tropospheric tidal waves. This conclusion was based on the discovered high degree correlation ( R ≅ 0.79) between the variations of the longitudinal distribution of the plasma bubbles and the neutral atmospheric density. In this work, the hypothesis of the effect of the thermospheric tidal waves on the plasma bubbles at the stage of their generation is subjected to further verification. With this purpose, the longitudinal distributions of the frequency of the plasma bubble observations at the different ionospheric altitudes ( 600 km, ROCSAT-1; 1100 km, ISS-b) are analyzed; their principal similarity is revealed. Comparative analysis of these distributions with the longitudinal profile of the deviations of the zonal thermospheric wind ( 400 km, CHAMP) modulated by the DE3 tidal wave is carried out; their considerable correlation ( R ≅ 0.69) is revealed. We conclude that the longitudinal variations of the zonal wind associated with DE3 tidal waves can effect the longitudinal variations in the appearance frequency of the initial "seeding" perturbations, which further evolve into the plasma bubbles.

A Model Study of Zonal Forcing in the Equatorial Stratosphere by Convectively Induced Gravity Waves

NASA Technical Reports Server (NTRS)

Alexander, M. J.; Holton, James R.

1997-01-01

A two-dimensional cloud-resolving model is used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation (QBO) of the zonal winds in the equatorial stratosphere. A simulation with constant background stratospheric winds is compared to simulations with background winds characteristic of the westerly and easterly QBO phases, respectively. In all three cases a broad spectrum of both eastward and westward propagating gravity waves is excited. In the constant background wind case the vertical momentum flux is nearly constant with height in the stratosphere, after correction for waves leaving the model domain. In the easterly and westerly shear cases, however, westward and eastward propagating waves, respectively, are strongly damped as they approach their critical levels, owing to the strongly scale-dependent vertical diffusion in the model. The profiles of zonal forcing induced by this wave damping are similar to profiles given by critical level absorption, but displaced slightly downward. The magnitude of the zonal forcing is of order 5 m/s/day. It is estimated that if 2% of the area of the Tropics were occupied by storms of similar magnitude, mesoscale gravity waves could provide nearly 1/4 of the zonal forcing required for the QBO.

Neutrino-heated winds from millisecond protomagnetars as sources of the weak r-process

NASA Astrophysics Data System (ADS)

Vlasov, Andrey D.; Metzger, Brian D.; Lippuner, Jonas; Roberts, Luke F.; Thompson, Todd A.

2017-06-01

We explore heavy element nucleosynthesis in neutrino-driven winds from rapidly rotating, strongly magnetized protoneutron stars ('millisecond protomagnetars') for which the magnetic dipole is aligned with the rotation axis, and the field is assumed to be a static force-free configuration. We process the protomagnetar wind trajectories calculated by Vlasov, Metzger & Thompson through the r-process nuclear reaction network SkyNet using contemporary models for the evolution of the wind electron fraction during the protoneutron star cooling phase. Although we do not find a successful second or third-peak r-process for any rotation period P, we show that protomagnetars with P ˜ 1-5 ms produce heavy element abundance distributions that extend to higher nuclear mass number than from otherwise equivalent spherical winds (with the mass fractions of some elements enhanced by factors of ≳100-1000). The heaviest elements are synthesized by outflows emerging along flux tubes that graze the closed zone and pass near the equatorial plane outside the light cylinder. Due to dependence of the nucleosynthesis pattern on the magnetic field strength and rotation rate of the protoneutron star, natural variations in these quantities between core collapse events could contribute to the observed diversity of the abundances of weak r-process nuclei in metal-poor stars. Further diversity, including possibly even a successful third-peak r-process, could be achieved for misaligned rotators with non-zero magnetic inclination with respect to the rotation axis. If protomagnetars are central engines for GRBs, their relativistic jets should contain a high-mass fraction of heavy nuclei of characteristic mass number \\bar{A}≈ 100, providing a possible source for ultrahigh energy cosmic rays comprised of heavy nuclei with an energy spectrum that extends beyond the nominal Grezin-Zatsepin-Kuzmin cut-off for protons or iron nuclei.

Precipitation Anomalies in the Tropical Indian Ocean and Possible Links to the Initiation of El Nino

NASA Technical Reports Server (NTRS)

Curtis, Scott; Adler, Robert F.; Huffman, George J.; Starr, David OC. (Technical Monitor)

2001-01-01

A pattern of variability in precipitation and 1000mb zonal winds for the tropical Indian Ocean during, 1979 to 1999 (AtmIO mode) is described using EOFs. The AtmIO mode consists of a cross-equatorial gradient of precipitation anomalies and equatorial wind anomalies of alternating signs on the Equator. The positive phase is defined as enhanced precipitation to the In "n south of the equator, suppressed precipitation to the north, and anomalous westerlies centered on the island of Sumatra. In September-October 1981, February-March 1990, and October-December 1996 the AtmIO mod-, was positive and there was a significant 30-60 day variability in the gradient of precipitation anomalies. These cases coincided with moderate to heavy ,activity in the Madden-Jullan Oscillation (MJO). Links between the AtmIO, MJO, and El Nino are discussed.

Cross-scale transport processes in the three-dimensional Kelvin-Helmholtz instability

NASA Astrophysics Data System (ADS)

Delamere, P. A.; Burkholder, B. L.; Ma, X.; Nykyri, K.

2017-12-01

The Kelvin-Helmholtz (KH) instability is a crucial aspect of the solar wind interaction with the giant magnetospheres. Rapid internal rotation of the magnetodisc produces conditions favorable for the growth of KH vortices along much of the equatorial magnetopause boundary. Pronounced dawn/dusk asymmetries at Jupiter and Saturn indicate a robust interaction with the solar wind. Using three-dimensional hybrid simulations we investigate the transport processes associated with the flow shear-driven KH instability. Of particular importance is small-scale and intermittent reconnection generated by the twisting of the magnetic field into configurations with antiparallel components. In three-dimensions strong guide field reconnection can occur even for initially parallel magnetic field configurations. Often the twisting motion leads to pairs of reconnection sites that can operate asynchronously, generating intermittent open flux and Maxwell stresses at the magnetopause boundary. We quantify the generation of open flux using field line tracing methods, determine the Reynolds and Maxwell stresses, and evaluate the mass transport as functions of magnetic shear, velocity shear, electron pressure and plasma beta. These results are compared with magnetohydrodynamic simulations (Ma et al., 2017). In addition, we present preliminary results for the role of cross-scale coupling processes, from fluid to ion scales. In particular, we characterize small-scale waves and the their role in mixing, diffusing and heating plasma at the magnetopause boundary.

ARC-1979-AC79-7081

NASA Image and Video Library

1979-07-08

P-21747 C Range: 2,200,000 miles This image shows a region of the Jovian atmosphere from approximately 25° N to the equatorial region. The north temperate jet, at approximately 23° N, where the wind speed is about 150 meters per second, is seen as a dark brown line from the left-hand edge to the right-hand corner of the picture. The wispy clouds of the north equatorial belt appear as shades of brown. The lower right-hand corner of the image shows the brighter (white) clouds of the equatorial region. A small blue area is apparent near the lower edge, which corresponds to a region free of the upper clouds, where it is possible to penetrate to cloud layers approximately 60 kilometers below the visible surface.

ARC-1979-A79-7081

NASA Image and Video Library

1979-07-08

P-21747 BW Range: 2,200,000 miles This image shows a region of the Jovian atmosphere from approximately 25° N to the equatorial region. The north temperate jet, at approximately 23° N, where the wind speed is about 150 meters per second, is seen as a dark brown line from the left-hand edge to the right-hand corner of the picture. The wispy clouds of the north equatorial belt appear as shades of brown. The lower right-hand corner of the image shows the brighter (white) clouds of the equatorial region. A small blue area is apparent near the lower edge, which corresponds to a region free of the upper clouds, where it is possible to penetrate to cloud layers approximately 60 kilometers below the visible surface.

Observations of equatorial ionization anomaly over Africa and Middle East during a year of deep minimum

NASA Astrophysics Data System (ADS)

Bolaji, Olawale; Owolabi, Oluwafisayo; Falayi, Elijah; Jimoh, Emmanuel; Kotoye, Afolabi; Odeyemi, Olumide; Rabiu, Babatunde; Doherty, Patricia; Yizengaw, Endawoke; Yamazaki, Yosuke; Adeniyi, Jacob; Kaka, Rafiat; Onanuga, Kehinde

2017-01-01

In this work, we investigated the veracity of an ion continuity equation in controlling equatorial ionization anomaly (EIA) morphology using total electron content (TEC) of 22 GPS receivers and three ground-based magnetometers (Magnetic Data Acquisition System, MAGDAS) over Africa and the Middle East (Africa-Middle East) during the quietest periods. Apart from further confirmation of the roles of equatorial electrojet (EEJ) and integrated equatorial electrojet (IEEJ) in determining hemispheric extent of EIA crest over higher latitudes, we found some additional roles played by thermospheric meridional neutral wind. Interestingly, the simultaneous observations of EIA crests in both hemispheres of Africa-Middle East showed different morphology compared to that reported over Asia. We also observed interesting latitudinal twin EIA crests domiciled at the low latitudes of the Northern Hemisphere. Our results further showed that weak EEJ strength associated with counter electrojet (CEJ) during sunrise hours could also trigger twin EIA crests over higher latitudes.

A quasi-biennial oscillation signal in general circulation model simulations.

PubMed

Cariolle, D; Amodei, M; Déqué, M; Mahfouf, J F; Simon, P; Teyssédre, H

1993-09-03

The quasi-biennial oscillation (QBO) is a free atmospheric mode that affects the equatorial lower stratosphere. With a quasi-regular frequency, the mean equatorial zonal wind alternates from easterly to westerly regimes. This oscillation is zonally symmetric about the equator, has its largest amplitude in the latitudinal band from 20 degrees S to 20 degrees N, and has a mean period of about 27 months. The QBO appears to originate in the momentum deposition produced by the damping in the stratosphere of equatorial waves excited by diabatic thermal processes in the troposphere. The results of three 10-year simulations obtained with three general circulation models are reported, all of which show the development in the stratosphere of a QBO signal with a period and a spatial propagating structure that are in good agreement with observations without any ad hoc parameterization of equatorial wave forcing. Although the amplitude of the oscillation in the simulations is still less than the observed value, the result is promising for the development of global climate models.

Turbulent wind at the equatorial segment of an operating Darrieus wind turbine blade

NASA Astrophysics Data System (ADS)

Connell, J. R.; Morris, V. R.

1989-09-01

Six turbulent wind time series, measured at equally spaced equator-height locations on a circle 3 m outside a 34-m Darrieus rotor, are analyzed to approximate the wind fluctuations experienced by the rotor. The flatwise lower root-bending stress of one blade was concurrently recorded. The wind data are analyzed in three ways: wind components that are radial and tangential to the rotation of a blade were rotationally sampled; induction and wake effects of the rotor were estimated from the six Eulerian time series; and turbulence spectra of both the measured wind and the modeled wind from the PNL theory of rotationally sampled turbulence. The wind and the rotor response are related by computing the spectral response function of the flatwise lower root-bending stress. Two bands of resonant response that surround the first and second flatwise modal frequencies shift with the rotor rotation rate.

On the stability of fast rotating magentodiscs

NASA Astrophysics Data System (ADS)

Neupane, B. R.; Delamere, P. A.; Ma, X.

2016-12-01

In this study, a steady-state, self-consistent magnetodisc model (i.e., Caudal [1986] model based on in-situ observational temperature and density profile) has been developed to systematically investigate the stability of fast rotationing magnetodiscs, which is fundamentally important to the dynamics of Jupiter's and Saturn's magnetospheres. Comparison between model and observational data (magnetic field component normal to the equatorial plane) suggests that Saturn's magnetodisc equilibrium is dominated by the heavy and cold plasma, where the centrifugal force cannot be ignored. In contrast, the hot tenuous plasma contribution, in which the centrifugal force can be ignored, should be small. In general, the stability of the Saturn's magnetosphere is determined by the competition between the radial decrease of flux tube content and radial increase of flux tube entropy. The profiles of flux tube content and flux tube entropy are expected to vary under different solar wind dynamic pressure conditions, consequently changing the stability of the magnetosphere. We will discuss stability during solar wind compression and expansion.

The impact of the 17 March 2015- St. Patrick's Day storm on the evolutionary pattern of Equatorial Ionization Anomaly over the Indian longitudes using high resolution spatio-temporal TEC maps - New insights

NASA Astrophysics Data System (ADS)

Yadav, S.; Sunda, S.; Sridharan, R.

2016-12-01

The impact of the St. Patrick's Day storm (17 March 2015) on the major equatorial electro-dynamical process viz., the Equatorial Ionization Anomaly (EIA) has been assessed using 2D (lat. x long.) total electron content (TEC) maps generated from the ground based SBAS (Satellite Based Augmentation System) enabled receiver data. The various aspects of EIA viz., i) evolution/devolution, ii) longitudinal structure, and iii) its variability during different phases of a geomagnetic storm have been brought out. These 2D TEC maps, which have a large latitudinal (5̊ S-45° N) and longitudinal (55-110° E) coverage, show the complete reversal in the longitudinal structure of EIA during the recovery phase of the storm as compared to the quiet day. These results have been explained in the light of the combined effects of the storm associated processes viz., i) the penetration electric fields of magnetosphere origin, ii) storm induced thermospheric winds, and iii) activation of the consequent disturbance dynamo, effectively distorting the longitudinal wave number 4 (WN4) structure of the EIA. It has been shown unambiguously that even a separation of few degrees in longitude ( 30̊) could experience significantly different forcings. The relevance and the far reaching consequences of the study in the light of the current trends and requirements for reliable satellite based navigation are highlighted.

Annual and longitudinal variations of the Pacific North Equatorial Countercurrent

NASA Technical Reports Server (NTRS)

Lolk, Nina K.

1992-01-01

The climatological annual cycle of the Pacific North Equatorial Countercurrent (NECC) simulated by an ocean general circulation model (OGCM) was studied. The longitudinal variation of transports, degree of geostrophy, and the relationship between Ekman pumping and vertical displacement of the thermocline were emphasized. The longitudinal variation was explored using six sections along 150 deg E, 180 deg, 160 deg W, 140 deg W, 125 deg W, and 110 deg W. A primitive equation OGCM of the Pacific Ocean was run for three years and the fields used were from the third year. The fields consisted of zonal, meridional, and vertical current components and temperature and salinity averaged every three days. The model was forced with the Hellerman and Rosenstein climatological wind stress. The mean annual eastward transport (19.9 Sv) was largest at 160 deg W. The maximum-current boundaries along 160 deg W were 9.2 deg N (1.0 deg), 5.1 deg N (1.1 deg), and 187 m (90.6 m). The annual-cycle amplitude of the NECC was greatest between 160 deg W and 140 deg W. Although the NECC is geostrophic to the first order, deviations from geostrophy were found in the boreal spring and summer near the southern boundary and near the surface. Meridional local acceleration played a role between 3 deg N-5 deg N.

Atmospheric structure favoring high sea surface temperatures in the western equatorial Pacific

NASA Astrophysics Data System (ADS)

Wirasatriya, Anindya; Kawamura, Hiroshi; Shimada, Teruhisa; Hosoda, Kohtaro

2016-10-01

We investigated the atmospheric processes over high sea surface temperature called Hot Event (HE) in the western equatorial Pacific from climatological analysis and a case study of the HE which began on 28 May 2003 (hereafter, HE030528). Climatological analysis shows that during the development stage of HE, solar radiation inside the HE area is higher than its climatology and wind speed is lower than the decay stage. During the decay stage, strong westerly wind often occurs inside HE area. The case study of HE030528 shows that the suppressed convection above high SST area resulted from the deep convection from the northern and southern areas outside HE. The suppressed convection created a band-shaped structure of low cloud cover along HE area increasing solar radiation during the development stage. Thus, the theory of "remote convection" was supported for the HE030528 formation mechanisms. The large sea level pressure gradient magnitude between the southern side of the terrain gap and the northern coast of the Solomon Islands, through which strong wind blew, indicated the role of land topography for the increase of wind speed during the decay of HE030528. Moreover, surface wind had an important role to influence the variability of solar radiation during the occurrence of HE030528 by controlling the water vapor supply in the upper troposphere through surface evaporation and surface convergence variation. Thus, surface wind was the key factor for HE030528 occurrence. The representativeness of HE030528 and the possible relation between HE and Madden-Julian Oscillation are also discussed.

Multidecadal-scale adjustment of the ocean mixed layer heat budget in the tropics: examining ocean reanalyses

NASA Astrophysics Data System (ADS)

Cook, Kerry H.; Vizy, Edward K.; Sun, Xiaoming

2018-03-01

Distributions of ocean mixed layer temperature trends and trends in the net heat flux from the atmosphere differ, indicating the important role of the transport of heat within the ocean for determining temperature trends. Annual-mean, linear trends in the components of the tropical ocean mixed layer heat budget for 1980-2015 are diagnosed in 4 ocean reanalyses to improve our physical understanding of multidecadal-scale SST trends. The well-known temperature trend in the tropical Pacific, with cooling in the east and warming in the west, is reproduced in each reanalysis with high statistical significance. Cooling in the east is associated with negative trends in the net heat flux from the atmosphere and enhanced equatorial upwelling related to a strengthening of the subtropical cells. Negative trends in the net heat flux also occur in the western tropical Pacific, but advective warming associated with a strengthening and shoaling of the equatorial undercurrent overwhelms these negative trends. The strengthening of the equatorial undercurrent is consistent with enhanced easterly wind stress, which is applied to the ocean reanalyses, and differential sea level trends that enhance the negative zonal height gradient across the Pacific. The Pacific North Equatorial countercurrent is also strengthening in all 4 reanalyses in association with a strengthening of the sea level trough at 10°N in the central and eastern Pacific. All 4 ocean reanalyses produce warming of 0.1-0.3 K/decade in the North Atlantic with statistical significance levels ranging from below 90-99%. The Atlantic is similar to the Pacific in having the equatorial undercurrent strengthening, but indications of shoaling are less consistent in the reanalyses and the North Equatorial Countercurrent in the Atlantic is not strengthening. Large-scale ocean mixed layer warming trends in the Indian Ocean in the reanalyses are interrupted by some regional cooling close to the equator. Net surface heat flux trends are mostly negative, indicating increasing heat fluxes from the ocean to the atmosphere. Wind stress trends applied to the ocean reanalyses are weak, but trends in the Indian Ocean equatorial undercurrent are strong. Since the Indian monsoon climate introduces strong seasonality, the annual analysis may not be adequate for studying physical processes in this ocean basin.

Teleconnections between Low and High-Latitude MLT regions during the Southern Hemisphere (SH) Sudden Stratospheric Warmings (SSWs)

NASA Astrophysics Data System (ADS)

Kim, Y.; Lee, J.; Eswaraiah, S.; Ratnam, M. V.

2017-12-01

In the present study, we study the teleconnections between the tropical and polar region during the Southern Hemisphere (SH) Sudden Stratospheric Warmings (SSWs) as well as the effect of SH SSWs on the modification of global mean atmospheric circulation. By analyzing the European Center for Medium-range Weather Forecasts (ECMWF) data and Earth Observing System (EOS) Microwave Limb Sounder (MLS) measurements both at the equatorial and polar region during the SH SSW events of 2002 and 2010, we find that; (i) the zero-wind line in the stratosphere appeared over the tropics ˜90 days prior to the 2002 SSW and progressed toward the south pole, thus satisfying the preconditioning for planetary wave (PW) propagation as suggested in the model study; (ii) an enhanced 16-day PW activity, along with the zero-wind line, is noted from the equator to the south pole, and (iii) during the 2010 SSW strong anti-correlation between the polar and equatorial temperatures occurred both in the stratosphere and the mesosphere. We interpret these characteristics as a possible teleconnection between the two regions through the intensification of 16-day PW. This is the first observational study over SH that reveals some novel features of the SSW and its connection to the equatorial region.

The Role of Reversed Equatorial Zonal Transport in Terminating an ENSO Event

NASA Astrophysics Data System (ADS)

Chen, H. C.; Hu, Z. Z.; Huang, B.; Sui, C. H.

2016-02-01

In this study, we demonstrate that a sudden reversal of anomalous equatorial zonal current at the peaking ENSO phase triggers the rapid termination of an ENSO event. Throughout an ENSO cycle, the anomalous equatorial zonal current is strongly controlled by the concavity of the anomalous thermocline meridional structure near the equator. During the ENSO developing phase, the anomalous zonal current in the central and eastern Pacific generally enhances the ENSO growth through its zonal SST advection. In the mature phase of ENSO, however, the equatorial thermocline depth anomalies are reflected in the eastern Pacific and slowly propagate westward off the equator in both hemispheres. As a result, the concavity of the thermocline anomalies near the equator is reversed, i.e., the off-equatorial thermocline depth anomalies become higher than that on the equator for El Niño events and lower for La Niño events. This meridional change of thermocline structure reverses zonal transport rapidly in the central-to-eastern equatorial Pacific, which weakens the ENSO SST anomalies by reversed advection. More importantly, the reversed zonal mass transport weakens the existing zonal tilting of equatorial thermocline and suppresses the thermocline feedback. Both processes are concentrated in the eastern equatorial Pacific and can be effective on subseasonal time scales. These current reversal effects are built-in to the ENSO peak phase and independent of the zonal wind effect on thermocline slope. It functions as an oceanic control on ENSO evolution during both El Niño and La Niña events.

The Sidebands of the Equatorial Electrojet: General Characteristic of the Westward Currents, as Deduced From CHAMP

NASA Astrophysics Data System (ADS)

Zhou, Yun-Liang; Lühr, Hermann; Alken, Patrick

2018-02-01

Based on 5 years (2001-2005) of magnetic field measurements made by the CHAMP satellite, latitudinal profiles of the equatorial electrojet (EEJ) have been derived. This study provides a comprehensive characterization of the reverse current EEJ sidebands. These westward currents peak at ±5° quasi-dipole latitude with typical amplitudes of 35% of the main EEJ. The diurnal amplitude variation is quite comparable with that of the EEJ. Similarly to the EEJ, the intensity is increasing with solar EUV flux, but with a steeper slope, indicating that not only the conductivity plays a role. For the longitude distribution we find, in general, larger amplitudes in the Western than in the Eastern Hemisphere. It is presently a common understanding that the reverse current EEJ sidebands are generated by eastward zonal winds at altitudes above about 120 km. In particular, a positive vertical gradient of wind speed generates westward currents at magnetic latitudes outside of 2° dip latitude. Interesting information about these features can be deduced from the sidebands' tidal characteristics. The longitudinal variation of the amplitude is dominated by a wave-1 pattern, which can primarily be attributed to the tidal components SPW1 and SW3. In case of the hemispheric amplitude differences these same two wave-1 components dominate. The ratio between sideband amplitude and main EEJ is largely controlled by the tidal features of the EEJ. The longitudinal patterns of the latitude, where the sidebands peak, resemble to some extent those of the amplitude. Current densities become larger when the peaks move closer to the magnetic equator.

Influence of Assimilation of Subsurface Temperature Measurements on Simulations of Equatorial Undercurrent and South Equatorial Current Along the Pacific Equator

NASA Technical Reports Server (NTRS)

Halpern, David; Leetmaan, Ants; Reynolds, Richard W.; Ji, Ming

1997-01-01

Equatorial Pacific current and temperature fields were simulated with and without assimilation of subsurface temperature measurements for April 1992 - March 1995, and compared with moored bouy and research vessel current measurements.

Modulation of low-latitude west wind on abnormal track and intensity of tropical cyclone Nargis (2008) in the Bay of Bengal

NASA Astrophysics Data System (ADS)

Li, Wei-Wei; Wang, Chunzai; Wang, Dongxiao; Yang, Lei; Deng, Yi

2012-03-01

Tropical cyclone (TC) Nargis (2008) made landfall in Myanmar on 02 May 2008, bringing a storm surge, major flooding, and resulting in a significant death toll. TC Nargis (2008) displayed abnormal features, including rare eastward motion in its late stage, rapid intensification before landing. Using reanalysis data and a numerical model, we investigated how a low-latitude westerly wind modulated TC Nargis' (2008) track and provided favorable atmospheric conditions for its rapid intensification. More importantly, we found a possible counterbalance effect of flows from the two hemispheres on the TC track in the Bay of Bengal. Our analysis indicates that a strong westerly wind burst across the Bay of Bengal, resulting in TC Nargis' (2008) eastward movement after its recurvature. This sudden enhancement of westerly wind was mainly due to the rapidly intensified mid-level cross-equatorial flow. Our results show that a high-pressure system in the Southern Hemisphere induced this strong, mid-level, cross-equatorial flow. During the rapid intensification period of TC Nargis (2008), this strong and broad westerly wind also transported a large amount of water vapor to TC Nargis (2008). Sufficient water vapor gave rise to continuously high and increased mid-level relative humidity, which was favorable to TC Nargis' (2008) intensification. Condensation of water vapor increased the energy supply, which eventuated the intensification of TC Nargis (2008) to a category 4 on the Saffir-Simpson scale.

The magnetic field of the equatorial magnetotail from 10 to 40 earth radii

NASA Technical Reports Server (NTRS)

Fairfield, D. H.

1986-01-01

A statistical study of IMP 6, 7, and 8 magnetotail magnetic field measurements near the equatorial plane reveals new information about various aspects of magnetospheric structure. More magnetic flux crosses the equatorial plane on the dawn and dusk flanks of the tail than near midnight, but no evidence is found for a dependence on the interplanetary magnetic field sector polarity. Field magnitudes within 3 earth radii of the equatorial plane near dawn are more than twice as large as those near dusk for Xsm = -20 to -10 earth radii. The frequency of occurrence of southward fields is greatest near midnight, and such fields are seen almost twice as often for Xsm = -20 to -10 earth radii as for Xsm beyond -20 earth radii. This latter result supports the idea that the midnight region of the tail between 10 and 20 is a special location where neutral lines are particularly apt to form. Such a neutral line will approach nearest the earth in the midnight and premidnight region, where substorms are thought to have their onset.

Impacts of the cloud structure's latitudinal variation on the general circulation of the Venus atmosphere as modeled by the LMD-GCM

NASA Astrophysics Data System (ADS)

Garate-Lopez, Itziar; Lebonnois, Sébastien

2017-04-01

A new simulation of Venus atmospheric circulation obtained with the LMD Venus GCM is described and the impact of cloud's latitudinal structure on the general circulation is analyzed. The model used here is based on that presented in Lebonnois et al. (2016). However, in the present simulation we consider the latitudinal variation of the cloud structure (Haus et al., 2014) both for the solar heating and to compute the infrared net-exchange rate matrix used in the radiative transfer module. The new cloud treatment affects mainly the balance in the angular momentum and the zonal wind distribution. Consequently, the agreement between the vertical profile of the modeled mean zonal wind and the profiles measured by different probes, is clearly improved from previous simulations in which zonal winds below the clouds were weak (roughly half the observed values). Moreover, the equatorial jet obtained at the base of the cloud deck is now more consistent with the observations. In Lebonnois et al. (2016) it was too strong compared to mid-latitudes, but in the present simulation the equatorial jet is less intense than the mid-latitude jets, in concordance with cloud-tracking measurements (Hueso et al., 2015). Since the atmospheric waves play a crucial role in the angular momentum budget of the Venus's atmospheric circulation, we analyze the wave activity by means of the Fast Fourier Transform technique studying the frequency spectrum of temperature, zonal and meridional wind fields. Modifications in the activity of the different types of waves present in the Venusian atmosphere compared to Lebonnois et al. (2016) are discussed, in terms of horizontal and vertical transport of the angular momentum by diurnal and semi-diurnal tides, barotropic and baroclinic waves, and Rossby and Kelvin type waves. Haus R., Kappel D. and Arnold G., 2014. Atmospheric thermal structure and cloud features in the southern hemisphere of Venus as retrieved from VIRTIS/VEX radiation measurements. Icarus 232, 232-248. Hueso R., Peralta J., Garate-Lopez I., et al., 2015. Six years of Venus winds at the upper cloud level from UV, visible and near infrared observations from VIRTIS on Venus express. Planet. Space Sci. 113-114, 78-99. Lebonnois S., Sugimoto N., and Gilli G., 2016. Wave analysis in the atmosphere of Venus below 100km altitude, simulated by the LMD Venus GCM. Icarus 278, 38-51.

Influence of the 11-year solar cycle on the effects of the equatorial quasi-biennial oscillation, manifesting in the extratropical northern atmosphere

NASA Astrophysics Data System (ADS)

Sitnov, S. A.

2009-01-01

Using the longest and most reliable ozonesonde data sets grouped for four regions (Japan, Europe, as well as temperate and polar latitudes of Canada) the comparative analysis of regional responses of ozone, temperature, horizontal wind, tropopause and surface pressure on the equatorial quasi-biennial oscillation (QBO effects), manifesting in opposite phases of the 11-year solar cycle (11-yr SC) was carried out. The impact of solar cycle is found to be the strongest at the Canadian Arctic, near one of two climatological centres of polar vortex, where in solar maximum conditions the QBO signals in ozone and temperature have much larger amplitudes, embrace greater range of heights, and are maximized much higher than those in solar minimum conditions. The strengthening of the temperature QBO effect during solar maxima can explain why correlation between the 11-yr SC and polar winter stratospheric temperature is reversed in the opposite QBO phases. At the border of polar vortex the 11-yr SC also modulates the QBO effect in zonal wind, strengthening the quasi-biennial modulation of polar vortex during solar maxima that is associated with strong negative correlation between stratospheric QBO signals in zonal wind and temperature. Above Japan the QBO effects of ozone, temperature, and zonal wind, manifesting in solar maxima reveal the downward phase dynamics, reminding similar feature of the zonal wind in the equatorial stratosphere. Above Europe, the QBO effects in solar maxima reveal more similarity with those above Japan, while in solar minima with the effects obtained at the Canadian middle-latitude stations. It is revealed that the 11-yr SC influences regional QBO effects in tropopause height, tropopause temperature and surface pressure. The influence most distinctly manifest itself in tropopause characteristics above Japan. The results of the accompanying analysis of the QBO reference time series testify that in the period of 1965-2006 above 50-hPa level the duration of the QBO cycle in solar maxima is 1-3 months longer than in solar minima. The differences are more distinct at higher levels, but they are diminished with lengthening of the period.

The roles of vertical mixing, solar radiation, and wind stress in a model simulation of the sea surface temperature seasonal cycle in the tropical Pacfic Ocean

NASA Technical Reports Server (NTRS)

Chen, Dake; Busalacchi, Antonio J.; Rothstein, Lewis M.

1994-01-01

The climatological seasonal cycle of sea surface temperature (SST) in the tropical Pacific is simulated using a newly developed upper ocean model. The roles of vertical mixing, solar radiation, and wind stress are investigated in a hierarchy of numerical experiments with various combinations of vertical mixing algorithms and surface-forcing products. It is found that the large SST annual cycle in the eastern equatorial Pacific is, to a large extent, controlled by the annually varying mixed layer depth which, in turn, is mainly determined by the competing effects of solar radiation and wind forcing. With the application of our hybrid vertical mixing scheme the model-simulated SST annual cycle is much improved in both amplitude and phase as compared to the case of a constant mixed layer depth. Beside the strong effects on vertical mixing, solar radiation is the primary heating term in the surface layer heat budget, and wind forcing influences SST by driving oceanic advective processes that redistribute heat in the upper ocean. For example, the SST seasonal cycle in the western Pacific basically follows the semiannual variation of solar heating, and the cycle in the central equatorial region is significantly affected by the zonal advective heat flux associated with the seasonally reversing South Equatorial Current. It has been shown in our experiments that the amount of heat flux modification needed to eliminate the annual mean SST errors in the model is, on average, no larger than the annual mean uncertainties among the various surface flux products used in this study. Whereas a bias correction is needed to account for remaining uncertainties in the annual mean heat flux, this study demonstrates that with proper treatment of mixed layer physics and realistic forcing functions the seasonal variability of SST is capable of being simulated successfully in response to external forcing without relying on a relaxation or damping formulation for the dominant surface heat flux contributions.

Modeling Study of Planetary Waves in the Mesosphere Lower Thermosphere (MLT)

NASA Technical Reports Server (NTRS)

Mengel, J. G.; Mayr, H. g.; Drob, D.; Porter, H. S.; Hines, C. O.

2003-01-01

For comparison with measurements from the TIMED satellite and coordinated ground based observations, we present results from our Numerical Spectral Model (NSM) that incorporates the Doppler Spread Parameterization (Hines, 1997) for small-scale gravity waves (GWs). We discuss the planetary waves (PWs) that are purely generated by dynamical interactions, i.e., without explicitly specifying excitation sources related for example to tropospheric convection or topography. With tropospheric heating that reproduces the observed zonal jets near the tropopause and the accompanying reversal in the latitudinal temperature variation, which is conducive to baroclinic instability, long period PWs are produced that propagate up into the stratosphere to affect the wave driven equatorial oscillations (QBO and SAO) extending into the upper mesosphere. The PWs in the model that dominate higher up in the MLT region, however, are to a large extent produced by instabilities under the influence of the zonal circulation and temperature variations in the middle atmosphere and they are amplified by GW interactions. Three classes of PWs are generated there. (1) Rossby waves that slowly propagate westward but are carried by the zonal mean (m = 0) winds to produce eastward and westward propagating PWs respectively in the winter and summer hemispheres below 80 km. Depending on the zonal wave number and magnitudes of the zonal winds under the influence of the equatorial oscillations, the PWs typically have periods between 2 and 20 days and their horizontal wind amplitudes can exceed 40 m/s in the lower mesosphere. (2) Rossby gravity waves that propagate westward at low latitudes, having periods around 2 days for zonal wave numbers m = 2 to 4. (3) Eastward propagating equatorial Kelvin waves generated in the upper mesosphere with periods between 2 and 3 days for m = 1 & 2. The seasonal variations of the PWs reveal that the largest wind amplitudes tend to occur below 80 km in the winter hemisphere, but above that altitude in the summer hemisphere to approach magnitudes as large as 50 m/s.

Westward equatorial electrojet during daytime hours. [relation to geomagnetic horizontal field depression

NASA Technical Reports Server (NTRS)

Rastogi, R. G.

1974-01-01

The phenomenon of the depression of the geomagnetic horizontal field during the daytime hours of magnetically quiet days at equatorial stations is described. These events are generally seen around 0700 and 1600 LT, being more frequent during the evening than the morning hours. The evening events are more frequent during periods of low solar activity and in the longitude region of weak equatorial electrojet currents. The latitudinal extent of the phenomenon is limited to the normal equatorial electrojet region, and on some occasions the phenomenon is not seen at both stations, separated by only a few hours in longitude. During such an event, the latitudinal profile of the geomagnetic vertical field across the equator is reversed, the ionospheric drift near the equator is reversed toward the east, the q type of sporadic E layer is completely absent, and the height of the peak ionization in the F2 region is decreased. It is suggested that these effects are caused by a narrow band of current flowing westward in the E region of the ionosphere and within the latitude region of the normal equatorial electrojet, due to the reversal of the east-west electrostatic field at low latitudes.

Hemispherically asymmetric trade wind changes as signatures of past ITCZ shifts

NASA Astrophysics Data System (ADS)

McGee, David; Moreno-Chamarro, Eduardo; Green, Brian; Marshall, John; Galbraith, Eric; Bradtmiller, Louisa

2018-01-01

The atmospheric Hadley cells, which meet at the Intertropical Convergence Zone (ITCZ), play critical roles in transporting heat, driving ocean circulation and supplying precipitation to the most heavily populated regions of the globe. Paleo-reconstructions can provide concrete evidence of how these major features of the atmospheric circulation can change in response to climate perturbations. While most such reconstructions have focused on ITCZ-related rainfall, here we show that trade wind proxies can document dynamical aspects of meridional ITCZ shifts. Theoretical expectations based on angular momentum constraints and results from freshwater hosing simulations with two different climate models predict that ITCZ shifts due to anomalous cooling of one hemisphere would be accompanied by a strengthening of the Hadley cell and trade winds in the colder hemisphere, with an opposite response in the warmer hemisphere. This expectation of hemispherically asymmetric trade wind changes is confirmed by proxy data of coastal upwelling and windblown dust from the Atlantic basin during Heinrich stadials, showing trade wind strengthening in the Northern Hemisphere and weakening in the Southern Hemisphere subtropics in concert with southward ITCZ shifts. Data from other basins show broadly similar patterns, though improved constraints on past trade wind changes are needed outside the Atlantic Basin. The asymmetric trade wind changes identified here suggest that ITCZ shifts are also marked by intensification of the ocean's wind-driven subtropical cells in the cooler hemisphere and a weakening in the warmer hemisphere, which induces cross-equatorial oceanic heat transport into the colder hemisphere. This response would be expected to prevent extreme meridional ITCZ shifts in response to asymmetric heating or cooling. Understanding trade wind changes and their coupling to cross-equatorial ocean cells is key to better constraining ITCZ shifts and ocean and atmosphere dynamical changes in the past, especially for regions and time periods for which few paleodata exist, and also improves our understanding of what changes may occur in the future.

Field Line Mapping of the Polar Cap Neutral Density Anomaly

NASA Astrophysics Data System (ADS)

Sutton, E. K.; Lin, C. S.; Huang, C. Y.; Cooke, D. L.

2016-12-01

Polar cap neutral density anomaly (PCNDA) events of localized density enhancement with a half size around 700-1000 km had been frequently detected by CHAMP satellite at around 400 km during major magnetic storms with Dst < -100 nT. Density enhancement is probably produced via Joule heating of the thermosphere when a significant amount of energy is deposited in the polar cap. We have identified 12 PCNDA events measured by CHAMP during two major magnetic storms including one initiated by a large solar wind pressure pulse. Their density anomaly locations are found to scatter randomly within the polar circle of 80o magnetic latitude in the geomagnetic coordinate. However after transformed to the Geocentric Solar Wind (GSW) coordinates, their locations become aligned in the direction of solar wind velocity. To better understand the polar cap energy deposition we trace magnetic field lines to the magnetosphere up to 30 earth radii from the ionosphere at 400 km using the data-based Tsyganenko T95 and TS05 magnetic field models. Field line tracing is performed in the GSW coordinate along the CHAMP orbit as well as for the whole polar cap. Each traced magnetic field line is classified into one of the three categories, (1) magnetosphere closed field line (MC) crossing the equatorial plane within 30 earth radii, (2) open field line connected to the magnetopause (MP), or (3) open field line connected to the magnetotail lobe (MT). For nine PCNDA events among the 10 events that we are able to conduct tracing, field lines originated from the density anomaly regions are classified as MT. Only one outlier event in association with a very large IMF BZ is classified as MP. Furthermore the separation angle between the density anomaly peak and the MP-MT field line separation point at 400 km on the X- and Z-axes meridian plane varies from -4o to 16o. Based on these results we speculate that convective electric fields and field aligned currents in the ionosphere might be enhanced near the MP-MT separation point during magnetic storms, resulting in intense localized Joule heating of the thermosphere.

THE BALMER-DOMINATED BOW SHOCK AND WIND NEBULA STRUCTURE OF {gamma}-RAY PULSAR PSR J1741-2054

DOE Office of Scientific and Technical Information (OSTI.GOV)

Romani, Roger W.; Shaw, Michael S.; Camilo, Fernando

2010-12-01

We have detected an H{alpha} bow shock nebula around PSR J1741-2054, a pulsar discovered through its GeV {gamma}-ray pulsations. The pulsar is only {approx}1.''5 behind the leading edge of the shock. Optical spectroscopy shows that the nebula is non-radiative, dominated by Balmer emission. The H{alpha} images and spectra suggest that the pulsar wind momentum is equatorially concentrated and implies a pulsar space velocity {approx}150 km s{sup -1}, directed 15{sup 0} {+-} 10{sup 0} out of the plane of the sky. The complex H{alpha} profile indicates that different portions of the post-shock flow dominate line emission as gas moves along themore » nebula and provide an opportunity to study the structure of this unusual slow non-radiative shock under a variety of conditions. CXO ACIS observations reveal an X-ray pulsar wind nebula within this nebula, with a compact {approx}2.''5 equatorial structure and a trail extending several arcminutes behind. Together these data support a close ({<=}0.5 kpc) distance, a spin geometry viewed edge-on, and highly efficient {gamma}-ray production for this unusual, energetic pulsar.« less

Lunar Tidal Modulation of Periodic Meridional Movement of Equatorial Ionization Anomaly Crest During Sudden Stratospheric Warming

NASA Astrophysics Data System (ADS)

Mo, X. H.; Zhang, D. H.

2018-02-01

Using the location of equatorial ionization anomaly (EIA) crest derived from GPS observations in China and Brazilian sector, we investigated the longitudinal dependence of periodic meridional movement of EIA crest during sudden stratospheric warming events in 2003, 2006, and 2009. The solar activity was from high to low for the three events. Results show that the locations of EIA crests in both China and Brazilian sectors exhibit obvious and constant 14- to 15-day periodic oscillation being in-phase in two sectors, which coincide with the half of the lunar revolution period (29.53 days) and the lunar phase. The temporal extent of wave power at 14-15 days is consistent with the temporal extent of stratospheric zonal wind, indicating that 14- to 15-day periodic meridional movement of EIA crest is due to enhanced lunar tide modulated by zonal wind. In addition, it is also found that the amplitude of 14- to 15-day periodic oscillation of EIA crest in China sector is larger than that in Brazilian sector, which may be caused by the longitudinal variation of tides and neutral wind pattern.

Assessment of prediction skill in equatorial Pacific Ocean in high resolution model of CFS

NASA Astrophysics Data System (ADS)

Arora, Anika; Rao, Suryachandra A.; Pillai, Prasanth; Dhakate, Ashish; Salunke, Kiran; Srivastava, Ankur

2018-01-01

The effect of increasing atmospheric resolution on prediction skill of El Niño southern oscillation phenomenon in climate forecast system model is explored in this paper. Improvement in prediction skill for sea surface temperature (SST) and winds at all leads compared to low resolution model in the tropical Indo-Pacific basin is observed. High resolution model is able to capture extreme events reasonably well. As a result, the signal to noise ratio is improved in the high resolution model. However, spring predictability barrier (SPB) for summer months in Nino 3 and Nino 3.4 region is stronger in high resolution model, in spite of improvement in overall prediction skill and dynamics everywhere else. Anomaly correlation coefficient of SST in high resolution model with observations in Nino 3.4 region targeting boreal summer months when predicted at lead times of 3-8 months in advance decreased compared its lower resolution counterpart. It is noted that higher variance of winds predicted in spring season over central equatorial Pacific compared to observed variance of winds results in stronger than normal response on subsurface ocean, hence increases SPB for boreal summer months in high resolution model.

Decadal Variability and Temperature Trends in the Middle Atmosphere From Historical Rocketsonde Data

NASA Technical Reports Server (NTRS)

Dunkerton, Timothy J.

2000-01-01

Observational studies were performed using historical rocketsonde data to investigate long-term temperature trends, solar-cycle variations, and interactions between tropical and extratropical latitudes in the middle atmosphere. Evidence from tropical, subtropical, and midlatitude North American rocketsonde stations indicated a consistent downward trend over 25 years, with a solar cycle component superposed. The trend is about -1.4 to -2.0 K per decade and the amplitude of the decadal oscillation is about 1.1 K. Prior to trend derivation it was necessary for us to correct temperatures for aerodynamic heating in the early years. The empirically derived correction profile agrees well with a theoretical profile of Krumins and Lyons. A study was also performed of the correlation between equatorial winds and north polar temperatures in winter, showing that the entire stratospheric wind profile near the equator -- including the quasi-biennial oscillation (QBO) and stratopause semiannual oscillation (SAO) -- is important to the extratropical flow, not merely the QBO component as previously thought. A strong correlation was discovered between winter polar temperatures and equatorial winds in the upper stratosphere during the preceding September, suggesting a role for the second cycle of the SAO.

Evaluation of observed blast loading effects on NIF x-ray diagnostic collimators.

PubMed

Masters, N D; Fisher, A; Kalantar, D; Prasad, R; Stölken, J S; Wlodarczyk, C

2014-11-01

We present the "debris wind" models used to estimate the impulsive load to which x-ray diagnostics and other structures are subject during National Ignition Facility experiments. These models are used as part of the engineering design process. Isotropic models, based on simulations or simplified "expanding shell" models, are augmented by debris wind multipliers to account for directional anisotropy. We present improvements to these multipliers based on measurements of the permanent deflections of diagnostic components: 4× for the polar direction and 2× within the equatorial plane-the latter relaxing the previous heuristic debris wind multiplier.

Wave transience in a compressible atmosphere. I - Transient internal wave, mean-flow interaction. II - Transient equatorial waves in the quasi-biennial oscillation

NASA Technical Reports Server (NTRS)

Dunkerton, T. J.

1981-01-01

Analytical and numerical solutions are obtained in an approximate quasi-linear model, to describe the way in which vertically propagating waves give rise to mean flow accelerations in an atmosphere due to the effects of wave transience. These effects in turn result from compressibility and vertical group velocity feedback, and culminate in the spontaneous formation and descent of regions of strong mean wind shear. The numerical solutions display mean flow accelerations due to Kelvin waves in the equatorial stratosphere, with wave absorption altering the transience mechanism in such significant respects as causing the upper atmospheric mean flow acceleration to be very sensitive to the precise magnitude and distribution of the damping mechanisms. The numerical simulations of transient equatorial waves in the quasi-biennial oscillation are also considered.

The solar and equatorial QBO influences on the stratospheric circulation during the early northern-hemisphere winter. [Quasi-Biennial Oscillation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kodera, Kunihiko

1991-06-01

A case study was conducted to investigate the mechanism of how the solar cycle and the equatorial quasi-biennial oscillation (QBO) influence the stratospheric circulation during the Northern-Hemisphere winter. It was found that the solar and QBO influences on the stratospheric jet exist rather independently in the upper stratosphere during December. The mean-zonal wind anomalies produced in early winter persist by deformation until late winter through wave-mean flow interactions with planetary waves. The modulation effect of the solar influence by the QBO takes place during this process.

Vertical motions in the equatorial middle atmosphere

NASA Technical Reports Server (NTRS)

Weisman, M. L.

1979-01-01

A single station vertical velocity equation which considers ageostrophic and diabatic effects derived from the first law of thermodynamics and a generalized thermal wind relation is presented. An analysis and verification procedure which accounts for measurement and calculation errors as well as time and space continuity arguments and theoretical predictions are described. Vertical velocities are calculated at every kilometer between 25 and 60 km and for approximately every three hours for the above diurnal period at Kourou (French Guiana), Fort Sherman (Panama Canal Zone), Ascension Island, Antigua (British West Indies) and Natal (Brazil). The results, plotted as time series cross sections, suggest vertical motions ranging in magnitude from 1 or 2 cm/sec at 30 km to as much as 15 cm/sec at 60 km. Many of the general features of the results agree well with atmospheric tidal predictions but many particular features suggest that both smaller time scale gravity waves (periods less than 6 hours) and synoptic type waves (periods greater than 1 day) may be interacting significantly with the tidal fields. The results suggest that vertical motions can be calculated for the equatorial middle atmosphere and must be considered a significant part of the motion for time scales from 8 to 24 hours.

A Saturnian cam current system driven by asymmetric thermospheric heating

NASA Astrophysics Data System (ADS)

Smith, C. G. A.

2011-02-01

We show that asymmetric heating of Saturn's thermosphere can drive a current system consistent with the magnetospheric ‘cam’ proposed by Espinosa, Southwood & Dougherty. A geometrically simple heating distribution is imposed on the Northern hemisphere of a simplified three-dimensional global circulation model of Saturn's thermosphere. Currents driven by the resulting winds are calculated using a globally averaged ionosphere model. Using a simple assumption about how divergences in these currents close by flowing along dipolar field lines between the Northern and Southern hemispheres, we estimate the magnetic field perturbations in the equatorial plane and show that they are broadly consistent with the proposed cam fields, showing a roughly uniform field implying radial and azimuthal components in quadrature. We also identify a small longitudinal phase drift in the cam current with radial distance as a characteristic of a thermosphere-driven current system. However, at present our model does not produce magnetic field perturbations of the required magnitude, falling short by a factor of ˜100, a discrepancy that may be a consequence of an incomplete model of the ionospheric conductance.

Theory for substorms triggered by sudden reductions in convection

NASA Technical Reports Server (NTRS)

Lyons, L. R.

1996-01-01

Many substorm expansions are triggered by interplanetary magnetic field changes that reduce magnetospheric convection. This suggests that expansion onsets are a result of a reduction in the large-scale electric field imparted to the magnetosphere from the solar wind. Such a reduction disrupts the inward motion and energization of plasma sheet particles that occur during the growth phase. It is proposed that the resulting magnetic drift of particles and a large dawn to dusk gradient in the ion energies leads to a longitudinally localized reduction in the plasma pressure, and thus, to the current wedge formation. This theory accounts for the rapid development of the expansion phase relative to growth phase, the magnitude of the wedge currents, the speeds of tailward and westward expansion of the current reduction region in the equatorial plane, and the speeds of the poleward and westward motion of active aurora in the ionosphere.

Development and Utilization of the Regional Oceanic Modeling System (ROMS)

DTIC Science & Technology

2008-09-30

the Peru/ Chile Current system (PCS). Emphasis is put on the PCS due to its direct connection with the equatorial region; this makes it a good...nearshore wind drop-off that occurs in reality. Numerical simulations of the Peru/ Chile (PCS) and the California (CCS) upwelling systems are being... Chile and the USWC 4. More subtle effects of the wind/SST coupling on the mesoscale eddy activity are now investigated. RESULTS Since funds for

High charge state carbon and oxygen ions in Earth's equatorial quasi-trapping region

NASA Technical Reports Server (NTRS)

Christon, S. P.; Hamilton, D. C.; Gloeckler, G.; Eastmann, T. E.

1994-01-01

Observations of energetic (1.5 - 300 keV/e) medium-to-high charge state (+3 less than or equal to Q less than or equal to +7) solar wind origin C and O ions made in the quasi-trapping region (QTR) of Earth's magnetosphere are compared to ion trajectories calculated in model equatorial magnetospheric magnetic and electric fields. These comparisons indicate that solar wind ions entering the QTR on the nightside as an energetic component of the plasma sheet exit the region on the dayside, experiencing little or no charge exchange on the way. Measurements made by the CHarge Energy Mass (CHEM) ion spectrometer on board the Active Magnetospheric Particle Tracer Explorer/Charge Composition Explorer (AMPTE/CCE) spacecraft at 7 less than L less than 9 from September 1984 to January 1989 are the source of the new results contained herein: quantitative long-term determination of number densities, average energies, energy spectra, local time distributions, and their variation with geomagnetic disturbance level as indexed by Kp. Solar wind primaries (ions with charge states unchanged) and their secondaries (ions with generally lower charge states produced from primaries in the magnetosphere via charge exchange)are observed throughout the QTR and have distinctly different local time variations that persist over the entire 4-year analysis interval. During Kp larger than or equal to 3 deg intervals, primary ion (e.g., O(+6)) densities exhibit a pronounced predawn maximum with average energy minimum and a broad near-local-noon density minimum with average energy maximum. Secondary ion (e.g., O(+5)) densities do not have an identifiable predawn peak, rather they have a broad dayside maximum peaked in local morning and a nightside minimum. During Kp less than or equal to 2(-) intervals, primary ion density peaks are less intense, broader in local time extent, and centered near midnight, while secondary ion density local time variations diminish. The long-time-interval baseline helps to refine and extend previous observations; for example, we show that ionospheric contribution to O(+3)) is negligible. Through comparison with model ion trajectories, we interpret the lack of pronounced secondary ion density peaks colocated with the primary density peaks to indicate that: (1) negligible charge exchange occurs at L greater than 7, that is, solar wind secondaries are produced at L less than 7, and (2) solar wind secondaries do not form a significant portion of the plasma sheet population injected into the QTR. We conclude that little of the energetic solar wind secondary ion population is recirculated through the magnetosphere.

A Study of Transport in the Near-Earth Plasma Sheet During A Substorm Using Time-Dependent Large Scale Kinetics

NASA Technical Reports Server (NTRS)

El-Alaoui, M.; Ashour-Abdalla, M.; Raeder, J.; Frank, L. A.; Paterson, W. R.

1998-01-01

In this study we investigate the transport of H+ ions that made up the complex ion distribution function observed by the Geotail spacecraft at 0740 UT on November 24, 1996. This ion distribution function, observed by Geotail at approximately 20 R(sub E) downtail, was used to initialize a time-dependent large-scale kinetic (LSK) calculation of the trajectories of 75,000 ions forward in time. Time-dependent magnetic and electric fields were obtained from a global magnetohydrodynamic (MHD) simulation of the magnetosphere and its interaction with the solar wind and the interplanetary magnetic field (IMF) as observed during the interval of the observation of the distribution function. Our calculations indicate that the particles observed by Geotail were scattered across the equatorial plane by the multiple interactions with the current sheet and then convected sunward. They were energized by the dawn-dusk electric field during their transport from Geotail location and ultimately were lost at the ionospheric boundary or into the magnetopause.

Increased frequency of extreme Indian Ocean Dipole events due to greenhouse warming.

PubMed

Cai, Wenju; Santoso, Agus; Wang, Guojian; Weller, Evan; Wu, Lixin; Ashok, Karumuri; Masumoto, Yukio; Yamagata, Toshio

2014-06-12

The Indian Ocean dipole is a prominent mode of coupled ocean-atmosphere variability, affecting the lives of millions of people in Indian Ocean rim countries. In its positive phase, sea surface temperatures are lower than normal off the Sumatra-Java coast, but higher in the western tropical Indian Ocean. During the extreme positive-IOD (pIOD) events of 1961, 1994 and 1997, the eastern cooling strengthened and extended westward along the equatorial Indian Ocean through strong reversal of both the mean westerly winds and the associated eastward-flowing upper ocean currents. This created anomalously dry conditions from the eastern to the central Indian Ocean along the Equator and atmospheric convergence farther west, leading to catastrophic floods in eastern tropical African countries but devastating droughts in eastern Indian Ocean rim countries. Despite these serious consequences, the response of pIOD events to greenhouse warming is unknown. Here, using an ensemble of climate models forced by a scenario of high greenhouse gas emissions (Representative Concentration Pathway 8.5), we project that the frequency of extreme pIOD events will increase by almost a factor of three, from one event every 17.3 years over the twentieth century to one event every 6.3 years over the twenty-first century. We find that a mean state change--with weakening of both equatorial westerly winds and eastward oceanic currents in association with a faster warming in the western than the eastern equatorial Indian Ocean--facilitates more frequent occurrences of wind and oceanic current reversal. This leads to more frequent extreme pIOD events, suggesting an increasing frequency of extreme climate and weather events in regions affected by the pIOD.

Magnetic Reconnection Controls Impacts of Solar Wind Ions at Mercury's Surface : Investigation By Global Hybrid Simulations

NASA Astrophysics Data System (ADS)

Chanteur, G. M.; Modolo, R.; Leblanc, F.

2014-12-01

MESSENGER has revealed the complexity of the Hermean magnetic field which is dominated by dipolar and quadrupolar components (Anderson et al., 2012 and references therein). By contrast to other magnetized planets having large scale dynamo driven magnetic fields Mercury has a quadrupolar field large enough to reinforce the dipolar field at high northern latitudes and to shape the topology of the planetary field in the equatorial region and the southern hemisphere. Magnetic reconnection at Mercury is extremely effective for all IMF orientations [DiBraccio et al., JGR, 2013]. Global hybrid simulations by Richer et al. (2012) have demonstrated the dramatic influence of the quadrupolar field of Mercury on the topology of the Hermean magnetosphere. Then Chanteur et al. (AOGS 2014) have investigated the impacts of solar wind protons and alphas on Mercury's surface with the same hybrid code and have presented a case study to demonstrate the importance of magnetic reconnection between the IMF and the planetary field in this process. We will present a set of different results corresponding to different configurations depending upon the IMF orientation and solar wind parameters. References Anderson, B. J., C. L. Johnson, H. Korth, R. M. Winslow, J. E. Borovsky, M. E. Purucker, J. A. Slavin, S. C. Solomon, M. T. Zuber, and R. L. McNutt Jr. (2012), Low-degree structure in Mercury's planetary magnetic field, J. Geophys. Res., 117, E00L12, doi:10.1029/2012JE004159. DiBraccio, G. A., J. A. Slavin, S. A. Boardsen, B. J. Anderson, H. Korth, T. H. Zurbuchen, J. M. Raines, D. N. Baker, R. L. McNutt Jr., and S. C. Solomon (2013), MESSENGER observations of magnetopause structure and dynamics at Mercury, J. Geophys. Res. Space Phys., 118, 997-1008, doi:10.1002/jgra50123. Richer, E., R. Modolo, G. M. Chanteur, S. Hess, and F. Leblanc (2012), A global hybrid model for Mercury's interaction with the solar wind: Case study of the dipole representation, J. Geophys. Res., 117, A10228, doi:10.1029/2012JA017898. Chanteur, G.M., R. Modolo, and F. Leblanc (2014), Effect of the Hermean Magnetic quadrupole on Magnetic Reconnection and Penetration of the SW Plasma Inside the Magnetosphere, AOGS, 11th annual meeting, Sapporo, Japan, July 28th - August 1st.

Jason Celebrates 5th Anniversary as El Niño Builds, Warm Kelvin Wave Surges Toward South America

NASA Image and Video Library

2006-12-07

Recent sea-level height data from NASA Jason-1 altimetric satellite show that continuing weaker-than-normal trade winds in the western and central equatorial Pacific have triggered another strong, eastward moving, warm Kelvin wave.

Cloud and Wind Variability in Saturn's Equatorial Jet prior to the Cassini orbital tour

NASA Astrophysics Data System (ADS)

Sánchez-Lavega, A.; Pérez-Hoyos, S.; Hueso, R.; Rojas, J. F.; French, R. G.

2004-11-01

We use ground-based observations (going back to 1876), Pioneer-11 data (1979), Voyager 1 and 2 encounter images in 1980 and 1981, and HST 1990-2004 images, to study the changes that occurred in the vertical cloud structure and morphology and motions, in Saturn's Equatorial Region (approximately the band between latitudes 40 deg North and South). We compare ``calm periods" with ``stormy periods" i. e. those that occur during the development of the phenomenon known as the ``Great White Spots." We discuss different interpretations of the mechanisms that can be involved in the observed changes: vertical wind shears, waves, storm - mean flow interaction and changes in atmospheric angular momentum. Acknowledgements: This work was supported by the Spanish MCYT AYA 2003-03216. SPH acknowledges a PhD fellowship from the Spanish MECD and RH a post-doc fellowship from Gobierno Vasco. RGF was supported in part by NASA's Planetary Geology and Geophysics Program NAG5-10197 and STSCI Grant GO-08660.01A.

Dynamics of the seasonal variation of the North Equatorial Current bifurcation

NASA Astrophysics Data System (ADS)

Chen, Zhaohui; Wu, Lixin

2011-02-01

The dynamics of the seasonal variation of the North Equatorial Current (NEC) bifurcation is studied using a 1.5-layer nonlinear reduced-gravity Pacific basin model and a linear, first-mode baroclinic Rossby wave model. The model-simulated bifurcation latitude exhibits a distinct seasonal cycle with the southernmost latitude in June and the northernmost latitude in November, consistent with observational analysis. It is found that the seasonal migration of the NEC bifurcation latitude (NBL) not only is determined by wind locally in the tropics, as suggested in previous studies, but is also significantly intensified by the extratropical wind through coastal Kelvin waves. The model further demonstrates that the amplitude of the NEC bifurcation is also associated with stratification. A strong (weak) stratification leads to a fast (slow) phase speed of first-mode baroclinic Rossby waves, and thus large (small) annual range of the bifurcation latitude. Therefore, it is expected that in a warm climate the NBL should have a large range of annual migration.

Ocean-Atmosphere Interaction in Climate Changes

NASA Technical Reports Server (NTRS)

Liu, W. Timothy

1999-01-01

The diagram, which attests the El Nino teleconnection observed by the NASA Scatterometer (NSCAT) in 1997, is an example of the results of our research in air-sea interaction - the core component of our three-part contribution to the Climate Variability Program. We have established an interplay among scientific research, which turns spacebased data into knowledge, a push in instrument technology, which improves observations of climate variability, and an information system, which produces and disseminates new data to support our scientific research. Timothy Liu led the proposal for advanced technology, in response to the NASA Post-2002 Request for Information. The sensor was identified as a possible mission for continuous ocean surface wind measurement at higher spatial resolution, and with the unique capability to measure ocean surface salinity. He is participating in the Instrument Incubator Program to improve the antenna technology, and is initiating a study to integrate the concept on Japanese missions. He and his collaborators have set up a system to produce and disseminate high level (gridded) ocean surface wind/stress data from NSCAT and European missions. The data system is being expanded to produce real-time gridded ocean surface winds from Quikscat, and precipitation and evaporation from the Tropical Rain Measuring Mission. It will form the basis for a spacebased data analysis system which will include momentum, heat and water fluxes. The study on 1997 El Nino teleconnection illustrates our interdisciplinary and multisensor approach to study climate variability. The diagram shows that the collapse of trade wind and the westerly wind anomalies in the central equatorial Pacific led to the equatorial ocean warming. The equatorial wind anomalies are connected to the anomalous cyclonic wind pattern in the northeast Pacific. The anomalous warming along the west coast of the United States is the result of the movement of the pre-existing warm sea surface temperature anomalies with the cyclonic wind anomalies toward the coast. The results led to a new study which identifies decadal ocean variations in the Northeast Pacific. Three studies of oceanic responses to wind forcing caused by the seasonal change of monsoons, the passage of a typhoon, and the 1997 El Nino, were successfully conducted. Besides wind forcing, we continue to examine new techniques for estimating thermal and hydrologic fluxes, through the inverse ocean mixed-layer model, through divergence of atmospheric water transport, and by direct retrieval from radiances observed by microwave radiometers. Greenhouse warming has been linked to water vapor measured by two spaceborne sensors in two studies. In the first study, strong baroclinicity and deep convection were found to transport water vapor to the upper atmosphere and increase greenhouse trapping over the storm tracks of the North Pacific and Atlantic. In another study, the annual cycle of greenhouse warming were related to sea surface temperature (SST) and integrated water vapor, and the latitudinal dependence of the magnitudes and phases of the annual cycles were compared.

Wet deposition of trace elements and radon daughter systematics in the South and equatorial Atlantic atmosphere

NASA Astrophysics Data System (ADS)

Kim, Guebuem; Church, Thomas M.

2002-09-01

Atmospheric samples were collected aboard ship in the South and equatorial Atlantic (35°S-10°N) between 19 May and 20 June 1996. We measured 222Rn in air, 210Pb in aerosol, and trace elements (Fe, Mn, Zn, Pb, Cu, Cd, Ni, and Cr), 210Pb, and 210Po in precipitation samples. The large variation of 222Rn in air suggests a significant change in the incursion of continental air with time and latitude in the remote Atlantic. In the equatorial and subtropical Atlantic (20°S-10°N), 222Rn activity was lower but 210Pb/222Rn ratios were higher than those at higher latitudes. The higher 210Pb/222Rn ratios in the equatorial Atlantic appear to be due to prevailing trade easterly winds which transport a supported source of 210Pb in Saharan dust from the African Sahel. The enrichment of noncrustal trace elements in precipitation samples from the remote equatorial Atlantic was small on account of the remoteness from the continental emission regions and as a result of dilution with Saharan dust. The wet depositional fluxes of major crustal elements (Fe and Mn) were two- to three-fold higher, while those of Cd and Zn were two- to ten-fold lower, in the South and equatorial Atlantic relative to the western North Atlantic (Bermuda) or North Atlantic coast (Lewes, Delaware). Thus, dominant wet precipitation of Saharan dust in the Intertropical Convergence Zone (ITCZ) areas of the equatorial Atlantic appears to be a large potential source of micronutrients (i.e., Fe) to surface seawater.

Origins of Eddy Kinetic Energy in the Bay of Bengal

NASA Astrophysics Data System (ADS)

Chen, Gengxin; Li, Yuanlong; Xie, Qiang; Wang, Dongxiao

2018-03-01

By analyzing satellite observational data and ocean general circulation model experiments, this study investigates the key processes that determine the spatial distribution and seasonality of intraseasonal eddy kinetic energy (EKE) within the Bay of Bengal (BOB). It is revealed that a complicated mechanism involving both local and remote wind forcing and ocean internal instability is responsible for the generation and modulation of EKE in this region. High-level EKE mainly resides in four regions: east of Sri Lanka (Region 1), the western BOB (Region 2), northwest of Sumatra (Region 3), and the coastal rim of the BOB (Region 4). The high EKE levels in Regions 1 and 2 are predominantly produced by ocean internal instability, which contributes 90% and 79%, respectively. Prominent seasonality is also observed in these two regions, with higher EKE levels in boreal spring and fall due to enhanced instability of the East Indian Coast Current and the Southwest Monsoon Current, respectively. In contrast, ocean internal instability contributes 49% and 52% of the total EKE in Regions 3 and 4, respectively, whereas the atmospheric forcing of intraseasonal oscillations (ISOs) also plays an important role. ISOs produce EKE mainly through wind stress, involving both the remote effect of equatorial winds and the local effect of monsoonal winds. Equatorial-origin wave signals significantly enhance the EKE levels in Regions 3 and 4, in the form of reflected Rossby waves and coastal Kelvin waves, respectively. The local wind forcing effect through Ekman pumping also has a significant contribution in Regions 3 and 4 (24% and 22%, respectively).

Attribution of ionospheric vertical plasma drift perturbations to large-scale waves and the dependence on solar activity (Invited)

NASA Astrophysics Data System (ADS)

Liu, H.; Richmond, A. D.

2013-12-01

In this study we quantify the contribution of individual large-scale waves to ionospheric electrodynamics, and examine the dependence of the ionospheric perturbations on solar activity. We focus on migrating diurnal tide (DW1) plus mean winds, migrating semidiurnal tide (SW2), quasi-stationary planetary wave 1 (QSPW1), and nonmigrating semidiurnal westward wave 1 (SW1) under northern winter conditions, when QSPW1 and SW1 are climatologically strong. From TIME-GCM simulations under solar minimum conditions, we calculate equatorial vertical ExB drifts due to mean winds and DW1, SW2, SW1 and QSPW1. In particular, wind components of both SW2 and SW1 become large at mid to high latitudes in the E-region, and kernel functions obtained from numerical experiments reveal that they can significantly affect the equatorial ion drift, likely through modulating the E-region wind dynamo. The most evident changes of total ionospheric vertical drift when solar activity is increased are seen around dawn and dusk, reflecting the more dominant role of large F-region Pedersen conductivity and of the F-region dynamo under high solar activity. Therefore, the lower atmosphere driving of the ionospheric variability is more evident under solar minimum conditions, not only because variability is more identifiable in a quieter background, but also because the E-region wind dynamo is more significant. These numerical experiments also demonstrate that the amplitudes, phases and latitudinal and vertical structures of large-scale waves are important in quantifying the ionospheric responses.

Coronal Hole Facing Earth

NASA Image and Video Library

2018-05-15

An extensive equatorial coronal hole has rotated so that it is now facing Earth (May 2-4, 2018). The dark coronal hole extends about halfway across the solar disk. It was observed in a wavelength of extreme ultraviolet light. This magnetically open area is streaming solar wind (i.e., a stream of charged particles released from the sun) into space. When Earth enters a solar wind stream and the stream interacts with our magnetosphere, we often experience nice displays of aurora. https://photojournal.jpl.nasa.gov/catalog/PIA00577

Global modeling of storm-time thermospheric dynamics and electrodynamics

NASA Astrophysics Data System (ADS)

Fuller-Rowell, T. J.; Richmond, A. D.; Maruyama, N.

Understanding the neutral dynamic and electrodynamic response of the upper atmosphere to geomagnetic storms, and quantifying the balance between prompt penetration and disturbance dynamo effects, are two of the significant challenges facing us today. This paper reviews our understanding of the dynamical and electrodynamic response of the upper atmosphere to storms from a modeling perspective. After injection of momentum and energy at high latitude during a geomagnetic storm, the neutral winds begin to respond almost immediately. The high-latitude wind system evolves quickly by the action of ion drag and the injection of kinetic energy; however, Joule dissipation provides the bulk of the energy source to change the dynamics and electrodynamics globally. Impulsive energy injection at high latitudes drives large-scale gravity waves that propagate globally. The waves transmit pressure gradients initiating a change in the global circulation. Numerical simulations of the coupled thermosphere, ionosphere, plasmasphere, and electrodynamic response to storms indicate that although the wind and waves are dynamic, with significant apparent "sloshing" between the hemispheres, the net effect is for an increased equatorward wind. The dynamic changes during a storm provide the conduit for many of the physical processes that ensue in the upper atmosphere. For instance, the increased meridional winds at mid latitudes push plasma parallel to the magnetic field to regions of different composition. The global circulation carries molecular rich air from the lower thermosphere upward and equatorward, changing the ratio of atomic and molecular neutral species, and changing loss rates for the ionosphere. The storm wind system also drives the disturbance dynamo, which through plasma transport modifies the strength and location of the equatorial ionization anomaly peaks. On a global scale, the increased equatorward meridional winds, and the generation of zonal winds at mid latitudes via the Coriolis effects, produce a current system opposing the normal quiet-time Sq current system. At the equator, the storm-time zonal electric fields reduce or reverse the normal upward and downward plasma drift on the dayside and nightside, respectively. In the numerical simulations, on the dayside, the disturbance dynamo appears fairly uniform, whereas at night a stronger local time dependence is apparent with increased upward drift between midnight and dawn. The simulations also indicate the possibility for a rapid dynamo response at the equator, within 2 h of storm onset, before the arrival of the large-scale gravity waves. All these wind-driven processes can result in dramatic ionospheric changes during storms. The disturbance dynamo can combine and interact with the prompt penetration of magnetospheric electric fields to the equator.

Solar Wind Helium Abundance as a Function of Speed and Heliographic Latitude: Variation through a Solar Cycle

NASA Technical Reports Server (NTRS)

Kasper, J. C.; Stenens, M. L.; Stevens, M. L.; Lazarus, A. J.; Steinberg, J. T.; Ogilvie, Keith W.

2006-01-01

We present a study of the variation of the relative abundance of helium to hydrogen in the solar wind as a function of solar wind speed and heliographic latitude over the previous solar cycle. The average values of A(sub He), the ratio of helium to hydrogen number densities, are calculated in 25 speed intervals over 27-day Carrington rotations using Faraday Cup observations from the Wind spacecraft between 1995 and 2005. The higher speed and time resolution of this study compared to an earlier work with the Wind observations has led to the discovery of three new aspects of A(sub He), modulation during solar minimum from mid-1995 to mid-1997. First, we find that for solar wind speeds between 350 and 415 km/s, A(sub He), varies with a clear six-month periodicity, with a minimum value at the heliographic equatorial plane and a typical gradient of 0.01 per degree in latitude. For the slow wind this is a 30% effect. We suggest that the latitudinal gradient may be due to an additional dependence of coronal proton flux on coronal field strength or the stability of coronal loops. Second, once the gradient is subtracted, we find that A(sub He), is a remarkably linear function of solar wind speed. Finally, we identify a vanishing speed, at which A(sub He), is zero, is 259 km/s and note that this speed corresponds to the minimum solar wind speed observed at one AU. The vanishing speed may be related to previous theoretical work in which enhancements of coronal helium lead to stagnation of the escaping proton flux. During solar maximum the A(sub He), dependences on speed and latitude disappear, and we interpret this as evidence of two source regions for slow solar wind in the ecliptic plane, one being the solar minimum streamer belt and the other likely being active regions.

Determining the Ocean's Role on the Variable Gravity Field and Earth Rotation

NASA Technical Reports Server (NTRS)

Ponte, Rui M.; Frey, H. (Technical Monitor)

2000-01-01

A number of ocean models of different complexity have been used to study changes in the oceanic angular momentum (OAM) and mass fields and their relation to the variable Earth rotation and gravity field. Time scales examined range from seasonal to a few days. Results point to the importance of oceanic signals in driving polar motion, in particular the Chandler and annual wobbles. Results also show that oceanic signals have a measurable impact on length-of-day variations. Various circulation features and associated mass signals, including the North Pacific subtropical gyre, the equatorial currents, and the Antarctic Circumpolar Current play a significant role in oceanic angular momentum variability. The impact on OAM values of an optimization procedure that uses available data to constrain ocean model results was also tested for the first time. The optimization procedure yielded substantial changes, in OAM, related to adjustments in both motion and mass fields,as well as in the wind stress torques acting on the ocean. Constrained OAM values were found to yield noticeable improvements in the agreement with the observed Earth rotation parameters, particularly at the seasonal timescale.

TIME-DEPENDENT TURBULENT HEATING OF OPEN FLUX TUBES IN THE CHROMOSPHERE, CORONA, AND SOLAR WIND

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woolsey, L. N.; Cranmer, S. R., E-mail: lwoolsey@cfa.harvard.edu

We investigate several key questions of plasma heating in open-field regions of the corona that connect to the solar wind. We present results for a model of Alfvén-wave-driven turbulence for three typical open magnetic field structures: a polar coronal hole, an open flux tube neighboring an equatorial streamer, and an open flux tube near a strong-field active region. We compare time-steady, one-dimensional turbulent heating models against fully time-dependent three-dimensional reduced-magnetohydrodynamic modeling of BRAID. We find that the time-steady results agree well with time-averaged results from BRAID. The time dependence allows us to investigate the variability of the magnetic fluctuations andmore » of the heating in the corona. The high-frequency tail of the power spectrum of fluctuations forms a power law whose exponent varies with height, and we discuss the possible physical explanation for this behavior. The variability in the heating rate is bursty and nanoflare-like in nature, and we analyze the amount of energy lost via dissipative heating in transient events throughout the simulation. The average energy in these events is 10{sup 21.91} erg, within the “picoflare” range, and many events reach classical “nanoflare” energies. We also estimated the multithermal distribution of temperatures that would result from the heating-rate variability, and found good agreement with observed widths of coronal differential emission measure distributions. The results of the modeling presented in this paper provide compelling evidence that turbulent heating in the solar atmosphere by Alfvén waves accelerates the solar wind in open flux tubes.« less

Warm Pacific Water Wave Heads East, But No El Niño Yet

NASA Image and Video Library

2004-08-04

Sea-level height data from NASA U.S./France Jason altimetric satellite during a 10-day cycle ending July 27, 2004, show weaker than normal trade winds in the western and central equatorial Pacific have triggered an eastward moving, warm Kelvin wave.

Temporal change of EIA asymmetry revealed by a beacon receiver network in Southeast Asia

NASA Astrophysics Data System (ADS)

Watthanasangmechai, Kornyanat; Yamamoto, Mamoru; Saito, Akinori; Maruyama, Takashi; Yokoyama, Tatsuhiro; Nishioka, Michi; Ishii, Mamoru

2015-05-01

To reveal the temporal change of the equatorial ionization anomaly (EIA) asymmetry, a multipoint satellite-ground beacon experiment was conducted along the meridional plane of the Thailand-Indonesia sector. The observation includes one station near the magnetic equator and four stations at off-equator latitudes. This is the first EIA asymmetry study with high spatial resolution using GNU Radio Beacon Receiver (GRBR) observations in Southeast Asia. GRBR-total electron contents (TECs) from 97 polar-orbit satellite passes in March 2012 were analyzed in this study. Successive passes captured rapid evolution of EIA asymmetry, especially during geomagnetic disturbances. The penetrating electric fields that occur during geomagnetic disturbed days are not the cause of the asymmetry. Instead, high background TEC associated with an intense electric field empowers the neutral wind to produce severe asymmetry of the EIA. Such rapid evolution of EIA asymmetry was not seen during nighttime, when meridional wind mainly controlled the asymmetric structures. Additional data are necessary to identify the source of the variations, i.e., atmospheric waves. Precisely capturing the locations of the crests and the evolution of the asymmetry enhances understanding of the temporal change of EIA asymmetry at the local scale and leads to a future local modeling for TEC prediction in Southeast Asia.

Transmission of the electric fields to the low latitude ionosphere in the magnetosphere-ionosphere current circuit

NASA Astrophysics Data System (ADS)

Kikuchi, Takashi; Hashimoto, Kumiko K.

2016-12-01

The solar wind energy is transmitted to low latitude ionosphere in a current circuit from a dynamo in the magnetosphere to the equatorial ionosphere via the polar ionosphere. During the substorm growth phase and storm main phase, the dawn-to-dusk convection electric field is intensified by the southward interplanetary magnetic field (IMF), driving the ionospheric DP2 currents composed of two-cell Hall current vortices in high latitudes and Pedersen currents amplified at the dayside equator (EEJ). The EEJ-Region-1 field-aligned current (R1 FAC) circuit is completed via the Pedersen currents in midlatitude. On the other hand, the shielding electric field and the Region-2 FACs develop in the inner magnetosphere, tending to cancel the convection electric field at the mid-equatorial latitudes. The shielding often causes overshielding when the convection electric field reduces substantially and the EEJ is overcome by the counter electrojet (CEJ), leading to that even the quasi-periodic DP2 fluctuations are contributed by the overshielding as being composed of the EEJ and CEJ. The overshielding develop significantly during substorms and storms, leading to that the mid and low latitude ionosphere is under strong influence of the overshielding as well as the convection electric fields. The electric fields on the day- and night sides are in opposite direction to each other, but the electric fields in the evening are anomalously enhanced in the same direction as in the day. The evening anomaly is a unique feature of the electric potential distribution in the global ionosphere. DP2-type electric field and currents develop during the transient/short-term geomagnetic disturbances like the geomagnetic sudden commencements (SC), which appear simultaneously at high latitude and equator within the temporal resolution of 10 s. Using the SC, we can confirm that the electric potential and currents are transmitted near-instantaneously to low latitude ionosphere on both day- and night sides, which is explained by means of the light speed propagation of the TM0 mode waves in the Earth-ionosphere waveguide.

Transmission of the Magnetospheric Electric Fields to the Low Latitude Ionosphere during Storm and Substorms

NASA Astrophysics Data System (ADS)

Kikuchi, T.; Hashimoto, K. K.; Ebihara, Y.; Tanaka, T.; Tomizawa, I.; Nagatsuma, T.

2016-12-01

The solar wind energy is transmitted to the low latitude ionosphere in a current circuit from a dynamo in the magnetosphere to the equatorial ionosphere via the polar ionosphere. During the substorm growth phase and storm main phase, the dawn-to-dusk convection electric field is intensified by the southward interplanetary magnetic field (IMF), driving the ionospheric DP2 currents composed of two-cell Hall current vortices in high latitudes and Pedersen currents amplified at the dayside equator (EEJ). The EEJ-Region-1 field-aligned current (R1 FAC) circuit is completed via the Pedersen currents in midlatitude. On the other hand, the shielding electric field and the Region-2 FACs develop in the inner magnetosphere, tending to cancel the convection electric field at the mid-equatorial latitudes. The shielding often causes overshielding when the convection electric field reduces substantially and the EEJ is overcome by the counter-electrojet (CEJ), leading to that even the quasi-periodic DP2 fluctuations are contributed by the overshielding. The overshielding develop significantly during substorms and storms, leading to that the mid and low latitude ionosphere is under strong influence of the overshielding as well as the convection electric fields. The electric fields on the day- and night-sides are in opposite direction to each other, but the electric fields in the evening are anomalously enhanced in the same direction as in the day. The evening anomaly is a unique feature of the electric potential distribution in the global ionosphere. DP2-type electric field and currents also develop during the transient/short-term geomagnetic disturbances like the geomagnetic sudden commencements (SC) and ULF pulsations, which appear simultaneously at high latitude and equator within the temporal resolution of 10 sec. Using the SC, we can confirm that the electric potential and currents are transmitted near-instantaneously to low latitude ionosphere on both the day- and night-sides, which is explained by means of the light speed propagation of the TM0 mode waves in the Earth-ionosphere waveguide.

Low-latitude Temperatures, Pressures, and Winds on Saturn from Cassini Radio Occultations

NASA Astrophysics Data System (ADS)

Flasar, F. M.; Schinder, P. J.; Kliore, A. J.; French, R. G.; Marouf, E. A.; Nagy, A.; Rappaport, N. J.; Anabtawi, A.; Asmar, S.; Barbinis, E.; Fleischman, D. U.; Goltz, G. L.; Johnston, D. V.; Rochblatt, D.; McGhee, C. A.

2005-12-01

We present results from 12 ingress and egress soundings done within 10 degrees of Saturn's equator. Above the 100-mbar level, near the tropopause, the vertical profiles of temperature are marked by undulatory structure that may be associated with vertically propagating waves. Below the 200-mbar level, in the upper troposphere, the vertical profiles are smoother, and the overall trend of temperatures is to increase away from the equator. This implies a decay of the zonal winds with altitude. The zonal winds can actually be inferred directly from the meridional gradient in pressure, without the need of a boundary condition on the winds. We summarize results of these calculations. This is of interest because recent cloud tracking studies have indicated lower equatorial winds than found earlier, but whether this indicates a real change in the winds at a given altitude or a change in the altitudes of the features tracked is controversial.

Spatio-Temporal Evolutions of Non-Orthogonal Equatorial Wave Modes Derived from Observations

NASA Astrophysics Data System (ADS)

Barton, C.; Cai, M.

2015-12-01

Equatorial waves have been studied extensively due to their importance to the tropical climate and weather systems. Historically, their activity is diagnosed mainly in the wavenumber-frequency domain. Recently, many studies have projected observational data onto parabolic cylinder functions (PCF), which represent the meridional structure of individual wave modes, to attain time-dependent spatial wave structures. In this study, we propose a methodology that seeks to identify individual wave modes in instantaneous fields of observations by determining their projections on PCF modes according to the equatorial wave theory. The new method has the benefit of yielding a closed system with a unique solution for all waves' spatial structures, including IG waves, for a given instantaneous observed field. We have applied our method to the ERA-Interim reanalysis dataset in the tropical stratosphere where the wave-mean flow interaction mechanism for the quasi-biennial oscillation (QBO) is well-understood. We have confirmed the continuous evolution of the selection mechanism for equatorial waves in the stratosphere from observations as predicted by the theory for the QBO. This also validates the proposed method for decomposition of observed tropical wave fields into non-orthogonal equatorial wave modes.

An investigation of a super-Earth exoplanet with a greenhouse-gas atmosphere using a general circulation model

NASA Astrophysics Data System (ADS)

Zalucha, Angela M.; Michaels, Timothy I.; Madhusudhan, Nikku

2013-11-01

We use the Massachusetts Institute of Technology general circulation model (GCM) dynamical core, in conjunction with a Newtonian relaxation scheme that relaxes to a gray, analytical solution of the radiative transfer equation, to simulate a tidally locked, synchronously orbiting super-Earth exoplanet. This hypothetical exoplanet is simulated under the following main assumptions: (1) the size, mass, and orbital characteristics of GJ 1214b (Charbonneau, D. [2009]. Nature 462, 891-894), (2) a greenhouse-gas dominated atmosphere, (3), the gas properties of water vapor, and (4) a surface. We have performed a parameter sweep over global mean surface pressure (0.1, 1, 10, and 100 bar) and global mean surface albedo (0.1, 0.4, and 0.7). Given assumption (1) above, the period of rotation of this exoplanet is 1.58 Earth-days, which we classify as the rapidly rotating regime. Our parameter sweep differs from Heng and Vogt (Heng, K., Vogt, S.S. [2011]. Mon. Not. R. Astron. Soc. 415, 2145-2157), who performed their study in the slowly rotating regime and using Held and Suarez (Held, I.M., Suarez, M.J. [1994]. Bull. Am. Meteorol. Soc. 75 (10), 1825-1830) thermal forcing. This type of thermal forcing is a prescribed function, not related to any radiative transfer, used to benchmark Earth’s atmosphere. An equatorial, westerly, superrotating jet is a robust feature in our GCM results. This equatorial jet is westerly at all longitudes. At high latitudes, the flow is easterly. The zonal winds do show a change with global mean surface pressure. As global mean surface pressure increases, the speed of the equatorial jet decreases between 9 and 15 h local time (substellar point is located at 12 h local time). The latitudinal extent of the equatorial jet increases on the nightside. For the two greatest initial surface pressure cases, an increasingly westerly component of flow develops at middle to high latitudes between 11 and 18 h local time. On the nightside, the easterly flow in the midlatitudes also increases in speed as global mean surface pressure increases. Furthermore, the zonal wind speed in the equatorial and midlatitude jets decreases with increasing surface albedo. Also, the latitudinal width of the equatorial jet decreases as surface albedo increases.

Observations of the interplanetary magnetic field between 0.46 and 1 A.U. by the Mariner 10 spacecraft. Ph.D. Thesis - Catholic Univ. of Am.

NASA Technical Reports Server (NTRS)

Behannon, K. W.

1976-01-01

Almost continuous measurement of the interplanetary magnetic field (IMF) at a sampling rate of 25 vectors/sec was performed by the magnetic field experiment onboard the Mariner 10 spacecraft during the period November 3, 1973 to April 14, 1974, comprising approximately 5-2/3 solar rotations and extending in radial distance from the sun from 1 to 0.46 AU. A clearly discernible two-sector pattern of field polarity was observed during the last 3-1/2 months of the period, with the dominant polarity toward the sun below the solar equatorial plane. Two compound high-speed solar wind streams were also present during this period, one in each magnetic field sector. Relative fluctuations of the field in magnitude and direction were found to have large time variations, but on average the relative magnitude fluctuations were approximately constant over the range of heliocentric distance covered while the relative directional fluctuations showed a slight decrease on average with increasing distance. The occurrence rate of directional discontinuities was also found to decrease with increasing radial distance from the sun.

The monsoon imprint during the `atypical' MIS 13 as seen through north and equatorial Indian Ocean records

NASA Astrophysics Data System (ADS)

Caley, Thibaut; Malaizé, Bruno; Bassinot, Franck; Clemens, Steven C.; Caillon, Nicolas; Linda, Rossignol; Charlier, Karine; Rebaubier, Helene

2011-09-01

Previous studies have suggested that Marine Isotope Stage (MIS) 13, recognized as atypical in many paleoclimate records, is marked by the development of anomalously strong summer monsoons in the northern tropical areas. To test this hypothesis, we performed a multi-proxy study on three marine records from the tropical Indian Ocean in order to reconstruct and analyse changes in the summer Indian monsoon winds and precipitations during MIS 13. Our data confirm the existence of a low-salinity event during MIS 13 in the equatorial Indian Ocean but we argue that this event should not be considered as "atypical". Taking only into account a smaller precession does not make it possible to explain such precipitation episode. However, when considering also the larger obliquity in a more complete orbitally driven monsoon "model," one can successfully explain this event. In addition, our data suggest that intense summer monsoon winds, although not atypical in strength, prevailed during MIS 13 in the western Arabian Sea. These strong monsoon winds, transporting important moisture, together with the effect of insolation and Eurasian ice sheet, are likely one of the factors responsible for the intense monsoon precipitation signal recorded in China loess, as suggested by model simulations.

Forecasting of Radiation Belts: Results From the PROGRESS Project.

NASA Astrophysics Data System (ADS)

Balikhin, M. A.; Arber, T. D.; Ganushkina, N. Y.; Walker, S. N.

2017-12-01

Forecasting of Radiation Belts: Results from the PROGRESS Project. The overall goal of the PROGRESS project, funded in frame of EU Horizon2020 programme, is to combine first principles based models with the systems science methodologies to achieve reliable forecasts of the geo-space particle radiation environment.The PROGRESS incorporates three themes : The propagation of the solar wind to L1, Forecast of geomagnetic indices, and forecast of fluxes of energetic electrons within the magnetosphere. One of the important aspects of the PROGRESS project is the development of statistical wave models for magnetospheric waves that affect the dynamics of energetic electrons such as lower band chorus, hiss and equatorial noise. The error reduction ratio (ERR) concept has been used to optimise the set of solar wind and geomagnetic parameters for organisation of statistical wave models for these emissions. The resulting sets of parameters and statistical wave models will be presented and discussed. However the ERR analysis also indicates that the combination of solar wind and geomagnetic parameters accounts for only part of the variance of the emissions under investigation (lower band chorus, hiss and equatorial noise). In addition, advances in the forecast of fluxes of energetic electrons, exploiting empirical models and the first principles IMPTAM model achieved by the PROGRESS project is presented.

Studies on the latitudinal distribution of ground-based geomagnetic pulsations and fluctuations in the interplanetary medium using discrete mathematical analysis methods

NASA Astrophysics Data System (ADS)

Zelinsky, N. R.; Kleimenova, N. G.; Malysheva, L. M.

2014-07-01

Ground-based geomagnetic Pc5 (2-7 mHz) pulsations, caused by the passage of dense transients (density disturbances) in the solar wind, were analyzed. It was shown that intensive bursts can appear in the density of the solar wind and its fluctuations, up to Np ˜ 30-50 cm3, even during the most magnetically calm year in the past decades (2009). The analysis, performed using one of the latest methods of discrete mathematical analysis (DMA), is presented. The energy functional of a time-series fragment (called "anomaly rectification" in DMA terms) of two such events was calculated. It was established that fluctuations in the dynamic pressure (density) of the solar wind (SW) cause the global excitation of Pc5 geomagnetic pulsations in the daytime sector of the Earth's magnetosphere, i.e., from polar to equatorial latitudes. Such pulsations started and ended suddenly and simultaneously at all latitudes. Fluctuations in the interplanetary magnetic field (IMF) have turned up to be less geoeffective in exciting geomagnetic pulsations than fluctuations in the SW density. The pulsation generation mechanisms in various structural regions of the magnetosphere were probably different. It was therefore concluded that the most probable source of ground-based pulsations are fluctuations of the corresponding periods in the SW density.

Magnetosphere and ionosphere response to a positive-negative pulse pair of solar wind dynamic pressure

NASA Astrophysics Data System (ADS)

Tian, A.; Degeling, A. W.

2017-12-01

Simulations and observations had shown that single positive/negative solar wind dynamic pressure pulse would excite geomagnetic impulsive events along with ionosphere and/or magnetosphere vortices which are connected by field aligned currents(FACs). In this work, a large scale ( 9min) magnetic hole event in solar wind provided us with the opportunity to study the effects of positive-negative pulse pair (△p/p 1) on the magnetosphere and ionosphere. During the magnetic hole event, two traveling convection vortices (TCVs, anti-sunward) first in anticlockwise then in clockwise rotation were detected by geomagnetic stations located along the 10:30MLT meridian. At the same time, another pair of ionospheric vortices azimuthally seen up to 3 MLT first in clockwise then in counter-clockwise rotation were also appeared in the afternoon sector( 14MLT) and centered at 75 MLAT without obvious tailward propagation feature. The duskside vortices were also confirmed in SuperDARN radar data. We simulated the process of magnetosphere struck by a positive-negative pulse pair and it shows that a pair of reversed flow vortices in the magnetosphere equatorial plane appeared which may provide FACs for the vortices observed in ionosphere. Dawn dusk asymmetry of the vortices as well as the global geomagnetism perturbation characteristics were also discussed.

On the wind production from hot accretion flows with different accretion rates

NASA Astrophysics Data System (ADS)

Bu, De-Fu; Gan, Zhao-Ming

2018-02-01

We perform two-dimensional simulations to study how the wind strength changes with accretion rate. We take into account bremsstrahlung, synchrotron radiation and the Comptonization. We find that when the accretion rate is low, radiative cooling is not important, and the accretion flow is hot. For the hot accretion flow, wind is very strong. The mass flux of wind can be ˜ 50 per cent of the mass inflow rate. When the accretion rate increases to a value at which radiative cooling rate is roughly equal to or slightly larger than viscous heating rate, cold clumps can form around the equatorial plane. In this case, the gas pressure gradient force is small and wind is very weak. Our results may be useful for the sub-grid model of active galactic nuclear feedback study.

Wind Variability of B Supergiants. No. 2; The Two-component Stellar Wind of gamma Arae

NASA Technical Reports Server (NTRS)

Prinja, R. K.; Massa, D.; Fullerton, A. W.; Howarth, I. D.; Pontefract, M.

1996-01-01

The stellar wind of the rapidly rotating early-B supergiant, gamma Ara, is studied using time series, high-resolution IUE spectroscopy secured over approx. 6 days in 1993 March. Results are presented based on an analysis of several line species, including N(N), C(IV), Si(IV), Si(III), C(II), and Al(III). The wind of this star is grossly structured, with evidence for latitude-dependent mass loss which reflects the role of rapid rotation. Independent, co-existing time variable features are identified at low-velocity (redward of approx. -750 km/s) and at higher-speeds extending to approx. -1500 km/s. The interface between these structures is 'defined' by the appearance of a discrete absorption component which is extremely sharp (in velocity space). The central velocity of this 'Super DAC' changes only gradually, over several days, between approx. -400 and -750 km/s in most of the ions. However, its location is shifted redward by almost 400 km/s in Al(III) and C(II), indicating that the physical structure giving rise to this feature has a substantial velocity and ionization jump. Constraints on the relative ionization properties of the wind structures are discussed, together with results based on SEI line-profile-fitting methods. The overall wind activity in gamma Ara exhibits a clear ion dependence, such that low-speed features are promoted in low-ionization species, including Al(III), C(II), and Si(III). We also highlight that - in contrast to most OB stars - there are substantial differences in the epoch-to-epoch time-averaged wind profiles of gamma Ara. We interpret the results in terms of a two-component wind model for gamma Ara, with an equatorially compressed low ionization region, and a high speed, higher-ionization polar outflow. This picture is discussed in the context of the predicted bi-stability mechanism for line-driven winds in rapidly rotating early-B type stars, and the formation of compressed wind regions in rapidly rotating hot stars. The apparent absence of a substantial shift in the wind ionization mixture of gamma Ara, and the normal nature of its photospheric spectrum, suggests wind-compression as the likely dominant cause for the observed equatorial density enhancements.

On the presence of equatorial waves in the lower stratosphere of a general circulation model

NASA Astrophysics Data System (ADS)

Maury, P.; Lott, F.

2014-02-01

To challenge the hypothesis that equatorial waves in the lower stratosphere are essentially forced by convection, we use the LMDz atmospheric model extended to the stratosphere and compare two versions having very different convection schemes but no quasi-biennial oscillation (QBO). The two versions have realistic time mean precipitation climatologies but very different precipitation variabilities. Despite these differences, the equatorial stratospheric Kelvin waves at 50 hPa are almost identical in the two versions and quite realistic. The Rossby gravity waves are also very similar but significantly weaker than in observations. We demonstrate that this bias on the Rossby gravity waves is essentially due to a dynamical filtering occurring because the model zonal wind is systematically westward. During a westward phase of the QBO, the ERA-Interim Rossby gravity waves compare well with those in the model. These results suggest that (i) in the model the effect of the convection scheme on the waves is in part hidden by the dynamical filtering, and (ii) the waves are produced by other sources than equatorial convection. For the Kelvin waves, this last point is illustrated by an Eliassen and Palm flux analysis, showing that in the model they come more from the subtropics and mid-latitude regions, whereas in the ERA-Interim reanalysis the sources are more equatorial. We show that non-equatorial sources are also significant in reanalysis data sets as they explain the presence of the Rossby gravity waves in the stratosphere. To illustrate this point, we identify situations with large Rossby gravity waves in the reanalysis middle stratosphere for dates selected when the stratosphere is dynamically separated from the equatorial troposphere. We refer to this process as a stratospheric reloading.

On the presence of equatorial waves in the lower stratosphere of a general circulation model

NASA Astrophysics Data System (ADS)

Maury, P.; Lott, F.

2013-08-01

To challenge the hypothesis that equatorial waves in the lower stratosphere are essentially forced by convection, we use the LMDz atmospheric model extended to the stratosphere and compare two versions having very different convection schemes but no quasi biennial oscillation (QBO). The two versions have realistic time mean precipitation climatologies but very different precipitation variabilities. Despite these differences, the equatorial stratospheric Kelvin waves at 50 hPa are almost identical in the two versions and quite realistic. The Rossby-gravity waves are also very close but significantly weaker than in observations. We demonstrate that this bias on the Rossby-gravity waves is essentially due to a dynamical filtering occurring because the model zonal wind is systematically westward: during a westward phase of the QBO, the Rossby-gravity waves in ERA-Interim compare well with those in the model. These results suggest that in the model the effect of the convection scheme on the waves is in part hidden by the dynamical filtering and the waves are produced by other sources than equatorial convection. For the Kelvin waves, this last point is illustrated by an Eliassen and Palm flux analysis, showing that in the model they come more from the subtropics and mid-latitude regions whereas in the ERA-Interim reanalysis the sources are more equatorial. We also show that non-equatorial sources are significant in reanalysis data, and we consider the case of the Rossby-gravity waves. We identify situations in the reanalysis where here are large Rossby-gravity waves in the middle stratosphere, and for dates when the stratosphere is dynamically separated from the equatorial troposphere. We refer to this process as a "stratospheric reloading".

Solar Wind Prediction at Pluto During the New Horizons Flyby: Results From a Two-Dimensional Multi-fluid MHD Model of the Outer Heliosphere

NASA Astrophysics Data System (ADS)

Zieger, B.; Toth, G.; Opher, M.; Gombosi, T. I.

2015-12-01

We adapted the outer heliosphere (OH) component of the Space Weather Modeling Framework, which is a 3-D global multi-fluid MHD model of the outer heliosphere with one ion fluid and four neutral populations, for time-dependent 2-D multi-fluid MHD simulations of solar wind propagation from a heliocentric distance of 1 AU up to 50 AU. We used this model to predict the solar wind plasma parameters as well as the interplanetary magnetic field components at Pluto and along the New Horizons trajectory during the whole calendar year of 2015 including the closest approach on July 14. The simulation is run in the solar equatorial plane in the heliographic inertial frame (HGI). The inner boundary conditions along a circle of 1 AU radius are set by near-Earth solar wind observations (hourly OMNI data), assuming that the global solar wind distribution does not change much during a Carrington rotation (27.2753 days). Our 2-D multi-fluid MHD code evolves one ion fluid and two neutral fluids, which are the primary interstellar neutral atoms and the interstellar neutral atoms deflected in the outer heliosheath between the slow bow shock and the heliopause. Spherical expansion effects are properly taken into account for the ions and the solar magnetic field. The inflow parameters of the two neutral fluids (density, temperature, and velocity components) are set at the negative X (HGI) boundary at 50 AU distance, which are taken from previous 3-D global multi-fluid MHD simulations of the heliospheric interface in a much larger simulation box (1500x1500x1500 AU). The inflow velocity vectors of the two neutral fluids define the so-called hydrogen deflection plane. The solar wind ions and the interstellar neutrals interact through charge exchange source terms included in the multi-fluid MHD equations, so the two neutral populations are evolved self-consistently. We validate our model with the available plasma data from New Horizons as well as with Voyager 2 plasma and magnetic field observations within the heliocentric distance of 50 AU. Our new time-dependent 2-D multi-fluid MHD model is generally applicable for solar wind predictions at any outer planet (Jupiter, Saturn, Uranus, Neptune) or spacecraft in the outer heliosphere where charge exchange between solar wind ions and interstellar neutrals play an important role.

Tropical Atlantic Impacts on the Decadal Climate Variability of the Tropical Ocean and Atmosphere.

NASA Astrophysics Data System (ADS)

Li, X.; Xie, S. P.; Gille, S. T.; Yoo, C.

2015-12-01

Previous studies revealed atmospheric bridges between the tropical Pacific, Atlantic, and Indian Ocean. In particular, several recent works indicate that the Atlantic sea surface temperature (SST) may contribute to the climate variability over the equatorial Pacific. Inspired by these studies, our work aims at investigating the impact of the tropical Atlantic on the entire tropical climate system, and uncovering the physical dynamics under these tropical teleconnections. We first performed a 'pacemaker' simulation by restoring the satellite era tropical Atlantic SST changes in a fully coupled model - the CESM1. Results reveal that the Atlantic warming heats the Indo-Western Pacific and cools the Eastern Pacific, enhances the Walker circulation and drives the subsurface Pacific to a La Niña mode, contributing to 60-70% of the above tropical changes in the past 30 years. The same pan-tropical teleconnections have been validated by the statistics of observations and 106 CMIP5 control simulations. We then used a hierarchy of atmospheric and oceanic models with different complexities, to single out the roles of atmospheric dynamics, atmosphere-ocean fluxes, and oceanic dynamics in these teleconnections. With these simulations we established a two-step mechanism as shown in the schematic figure: 1) Atlantic warming generates an atmospheric deep convection and induces easterly wind anomalies over the Indo-Western Pacific in the form of Kelvin waves, and westerly wind anomalies over the eastern equatorial Pacific as Rossby waves, in line with Gill's solution. This circulation changes warms the Indo-Western Pacific and cools the Eastern Pacific with the wind-evaporation-SST effect, forming a temperature gradient over the Indo-Pacific basins. 2) The temperature gradient further generates a secondary atmospheric deep convection, which reinforces the easterly wind anomalies over the equatorial Pacific and enhances the Walker circulation, triggering the Pacific to a La Niña mode with Bjerknes ocean dynamical feedback. This mechanism contributes to the understanding of the global decadal climate variability and predictability. In particular, Atlantic contributes to the Eastern Pacific cooling, which is considered as an important source of the recent global warming hiatus.

Hubble’s Global View of Jupiter During the Juno Mission

NASA Astrophysics Data System (ADS)

Simon, Amy A.; Wong, Michael H.; Orton, Glenn S.; Cosentino, Richard; Tollefson, Joshua; Johnson, Perianne

2017-10-01

With two observing programs designed for mapping clouds and hazes in Jupiter's atmosphere during the Juno mission, the Hubble Space Telescope is acquiring an unprecedented set of global maps for study. The Outer Planet Atmospheres Legacy program (OPAL, PI: Simon) and the Wide Field Coverage for Juno program (WFCJ, PI: Wong) are designed to enable frequent multi-wavelength global mapping of Jupiter, with many maps timed specifically for Juno’s perijove passes. Filters span wavelengths from 212 to 894 nm. Besides offering global views for Juno observation context, they also reveal a wealth of information about interesting atmospheric dynamical features. We will summarize the latest findings from these global mapping programs, including changes in the Great Red Spot, zonal wind profile analysis, and persistent cyclone-generated waves in the North Equatorial Belt.

Aurora on Uranus - A Faraday disc dynamo mechanism

NASA Technical Reports Server (NTRS)

Hill, T. W.; Rassbach, M. E.; Dessler, A. J.

1983-01-01

A mechanism is proposed whereby the solar wind flowing past the magnetosphere of Uranus causes a Faraday disk dynamo topology to be established and power to be extracted from the kinetic energy of rotation of Uranus. An immediate consequence of this dynamo is the generation of Birkeland currents that flow in and out of the sunlit polar cap with the accompanying production of polar aurora. The power extracted from planetary rotation is calculated as a function of planetary dipole magnetic moment and the ionospheric conductivity of Uranus. For plausible values of ionospheric conductivity, the observed auroral power requires a magnetic moment corresponding to a surface equatorial field of the order of 4 Gauss, slightly larger than the value 1.8 Gauss given by the empirical 'magnetic Bodes law'.

Modelling soil dust aerosol in the Bodélé depression during the BoDEx campaign

NASA Astrophysics Data System (ADS)

Tegen, I.; Heinold, B.; Todd, M.; Helmert, J.; Washington, R.; Dubovik, O.

2006-05-01

We present regional model simulations of the dust emission events during the Bodélé Dust Experiment (BoDEx) that was carried out in February and March 2005 in Chad. A box model version of the dust emission model is used to test different input parameters for the emission model, and to compare the dust emissions computed with observed wind speeds to those calculated with wind speeds from the regional model simulation. While field observations indicate that dust production occurs via self-abrasion of saltating diatomite flakes in the Bodélé, the emission model based on the assumption of dust production by saltation and using observed surface wind speeds as input parameters reproduces observed dust optical thicknesses well. Although the peak wind speeds in the regional model underestimate the highest wind speeds occurring on 10-12 March 2005, the spatio-temporal evolution of the dust cloud can be reasonably well reproduced by this model. Dust aerosol interacts with solar and thermal radiation in the regional model; it is responsible for a decrease in maximum daytime temperatures by about 5 K at the beginning the dust storm on 10 March 2005. This direct radiative effect of dust aerosol accounts for about half of the measured temperature decrease compared to conditions on 8 March. Results from a global dust model suggest that the dust from the Bodélé is an important contributor to dust crossing the African Savannah region towards the Gulf of Guinea and the equatorial Atlantic, where it can contribute up to 40% to the dust optical thickness.

Modelling soil dust aerosol in the Bodélé depression during the BoDEx campaign

NASA Astrophysics Data System (ADS)

Tegen, I.; Heinold, B.; Todd, M.; Helmert, J.; Washington, R.; Dubovik, O.

2006-09-01

We present regional model simulations of the dust emission events during the Bodélé Dust Experiment (BoDEx) that was carried out in February and March 2005 in Chad. A box model version of the dust emission model is used to test different input parameters for the emission model, and to compare the dust emissions computed with observed wind speeds to those calculated with wind speeds from the regional model simulation. While field observations indicate that dust production occurs via self-abrasion of saltating diatomite flakes in the Bodélé, the emission model based on the assumption of dust production by saltation and using observed surface wind speeds as input parameters reproduces observed dust optical thicknesses well. Although the peak wind speeds in the regional model underestimate the highest wind speeds occurring on 10-12 March 2005, the spatio-temporal evolution of the dust cloud can be reasonably well reproduced by this model. Dust aerosol interacts with solar and thermal radiation in the regional model; it is responsible for a decrease in maximum daytime temperatures by about 5 K at the beginning the dust storm on 10 March 2005. This direct radiative effect of dust aerosol accounts for about half of the measured temperature decrease compared to conditions on 8 March. Results from a global dust model suggest that the dust from the Bodélé is an important contributor to dust crossing the African Savannah region towards the Gulf of Guinea and the equatorial Atlantic, where it can contribute up to 40% to the dust optical thickness.

Modulation of ENSO evolution by strong tropical volcanic eruptions

NASA Astrophysics Data System (ADS)

Wang, Tao; Guo, Dong; Gao, Yongqi; Wang, Huijun; Zheng, Fei; Zhu, Yali; Miao, Jiapeng; Hu, Yongyun

2017-11-01

The simulated responses of the El Niño-Southern Oscillation (ENSO) to volcanic forcings are controversial, and some mechanisms of these responses are not clear. We investigate the impacts of volcanic forcing on the ENSO using a long-term simulation covering 1400-1999 as simulated by the Bergen Climate Model (BCM) and a group of simulations performed with the Community Atmosphere Model version 4.0 (CAM4) and the BCM's ocean component Miami Isopycanic Coordinated Ocean Model (MICOM). The analysis of the long-term BCM simulation indicates that ENSO has a negative-positive-negative response to strong tropical volcanic eruptions (SVEs), which corresponds to the different stages of volcanic forcing. In the initial forcing stage, a brief and weak La Niña-like response is caused by the cooling along the west coast of the South American continent and associated enhancement of the trade winds. In the peak forcing stage, westerly wind anomalies are excited by both reduced east-west sea level pressure gradients and weakened and equatorward shifted tropical convergence zones. These westerly wind anomalies extend to the equatorial eastern Pacific, leading to an El Niño-like response. At the same time, easterly wind anomalies west of 120°E and strong cooling effects can promote a discharged thermocline state and excite an upwelling Kelvin wave in the western Pacific. In the declining forcing stage, forced by the recovered trade winds, the upwelling Kelvin wave propagates eastward and reaches the equatorial eastern Pacific. Through the Bjerknes feedback, a strong and temporally extended La Niña-like response forms. Additional CAM4 simulations suggest a more important role of the surface cooling over the Maritime Continent and surrounding ocean in shaping the westerly wind anomalies over the equatorial central-eastern Pacific and the easterly wind anomalies west of 120° E, which are key to causing the El Niño-like responses and subsequent La Niña-like responses, respectively. The MICOM sensitivity simulations confirm that SVE-induced tropical atmospheric circulation anomalies play a dominant role in regulating post-eruption ENSO evolution in the observation, while the influences of anomalous buoyance forcing (heat and freshwater fluxes) are secondary. Therefore, SVEs play an important role in modulating the ENSO evolution. Compared with proxy data, the simulated El Niño-like responses and subsequent La Niña-like responses are consistent with the reconstructed ENSO responses to SVEs. However, the simulated initial brief La Niña-like response, which is reproduced by most models, is seen in only one proxy dataset and is absent in most of the reconstructed ENSOs and those observed. The reason for this model-data mismatch will require further investigation.

Equatorial electrojet and its response to external electromagnetic effects

NASA Astrophysics Data System (ADS)

Bespalov, P. A.; Savina, O. N.

2012-09-01

In the quiet low-latitude Earth's ionosphere, a sufficiently developed current system that is responsible for the Sq magnetic-field variations is formed in quiet Sun days under the action of tidal streams. The density of the corresponding currents is maximum in the midday hours at the equatorial latitudes, where the so-called equatorial electrojet is formed. In this work, we discuss the nature of the equatorial electrojet. This paper studies the value of its response to external effects. First of all, it is concerned with estimating the possibility of using the equatorial electrojet for generating low-frequency electromagnetic signals during periodic heating of the ionosphere by the heating-facility radiation. The equatorial electrojet can also produce electrodynamic response to the natural atmospheric processes, e.g., an acoustic-gravity wave.

Continuous day-time time series of E-region equatorial electric fields derived from ground magnetic observatory data

NASA Astrophysics Data System (ADS)

Alken, P.; Chulliat, A.; Maus, S.

2012-12-01

The day-time eastward equatorial electric field (EEF) in the ionospheric E-region plays an important role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly (EIA). Due to its importance, there is much interest in accurately measuring and modeling the EEF. However, there are limited sources of direct EEF measurements with full temporal and spatial coverage of the equatorial ionosphere. In this work, we propose a method of estimating a continuous day-time time series of the EEF at any longitude, provided there is a pair of ground magnetic observatories in the region which can accurately track changes in the strength of the EEJ. First, we derive a climatological unit latitudinal current profile from direct overflights of the CHAMP satellite and use delta H measurements from the ground observatory pair to determine the magnitude of the current. The time series of current profiles is then inverted for the EEF by solving the governing electrodynamic equations. While this method has previously been applied and validated in the Peruvian sector, in this work we demonstrate the method using a pair of magnetometers in Africa (Samogossoni, SAM, 0.18 degrees magnetic latitude and Tamanrasset, TAM, 11.5 degrees magnetic latitude) and validate the resulting EEF values against the CINDI ion velocity meter (IVM) instrument on the C/NOFS satellite. We find a very good 80% correlation with C/NOFS IVM measurements and a root-mean-square difference of 9 m/s in vertical drift velocity. This technique can be extended to any pair of ground observatories which can capture the day-time strength of the EEJ. We plan to apply this work to more observatory pairs around the globe and distribute real-time equatorial electric field values to the community.

Coronal Hole Facing Earth

NASA Image and Video Library

2018-05-08

An extensive equatorial coronal hole has rotated so that it is now facing Earth (May 2-4, 2018). The dark coronal hole extends about halfway across the solar disk. It was observed in a wavelength of extreme ultraviolet light. This magnetically open area is streaming solar wind (i.e., a stream of charged particles released from the sun) into space. When Earth enters a solar wind stream and the stream interacts with our magnetosphere, we often experience nice displays of aurora. Videos are available at https://photojournal.jpl.nasa.gov/catalog/PIA00624

Calculation of wind-driven surface currents in the North Atlantic Ocean

NASA Technical Reports Server (NTRS)

Rees, T. H.; Turner, R. E.

1976-01-01

Calculations to simulate the wind driven near surface currents of the North Atlantic Ocean are described. The primitive equations were integrated on a finite difference grid with a horizontal resolution of 2.5 deg in longitude and latitude. The model ocean was homogeneous with a uniform depth of 100 m and with five levels in the vertical direction. A form of the rigid-lid approximation was applied. Generally, the computed surface current patterns agreed with observed currents. The development of a subsurface equatorial countercurrent was observed.

Equatorial Magnetohydrodynamic Shallow Water Waves in the Solar Tachocline

NASA Astrophysics Data System (ADS)

Zaqarashvili, Teimuraz

2018-03-01

The influence of a toroidal magnetic field on the dynamics of shallow water waves in the solar tachocline is studied. A sub-adiabatic temperature gradient in the upper overshoot layer of the tachocline causes significant reduction of surface gravity speed, which leads to trapping of the waves near the equator and to an increase of the Rossby wave period up to the timescale of solar cycles. Dispersion relations of all equatorial magnetohydrodynamic (MHD) shallow water waves are obtained in the upper tachocline conditions and solved analytically and numerically. It is found that the toroidal magnetic field splits equatorial Rossby and Rossby-gravity waves into fast and slow modes. For a reasonable value of reduced gravity, global equatorial fast magneto-Rossby waves (with the spatial scale of equatorial extent) have a periodicity of 11 years, matching the timescale of activity cycles. The solutions are confined around the equator between latitudes ±20°–40°, coinciding with sunspot activity belts. Equatorial slow magneto-Rossby waves have a periodicity of 90–100 yr, resembling the observed long-term modulation of cycle strength, i.e., the Gleissberg cycle. Equatorial magneto-Kelvin and slow magneto-Rossby-gravity waves have the periodicity of 1–2 years and may correspond to observed annual and quasi-biennial oscillations. Equatorial fast magneto-Rossby-gravity and magneto-inertia-gravity waves have periods of hundreds of days and might be responsible for observed Rieger-type periodicity. Consequently, the equatorial MHD shallow water waves in the upper overshoot tachocline may capture all timescales of observed variations in solar activity, but detailed analytical and numerical studies are necessary to make a firm conclusion toward the connection of the waves to the solar dynamo.

On the Long-Term Variability of Jupiter's Winds and Brightness as Observed from Hubble

NASA Technical Reports Server (NTRS)

Simon-Miller, Amy A.; Gierasch, Peter J.

2010-01-01

Hubble Space Telescope Wide Field Planetary Camera 2 imaging data of Jupiter were combined with wind profiles from Voyager and Cassini data to study long-term variability in Jupiter's winds and cloud brightness. Searches for evidence of wind velocity periodicity yielded a few latitudes with potential variability; the most significant periods were found nearly symmetrically about the equator at 0 deg., 10-12 deg. N, and 14-18 deg. S planetographic latitude. The low to mid-latitude signals have components consistent with the measured stratospheric temperature Quasi-Quadrennial Oscillation (QQO) period of-5 years, while the equatorial signal is approximately seasonal and could be tied to mesoscale wave formation, robustness tests indicate that a constant or continuously varying periodic signal near 4.5 years would appear with high significance in the data periodograms as long as uncertainties or noise in the data are not of greater magnitude. However, the lack of a consistent signal over many latitudes makes it difficult to interpret as a QQO-related change. In addition, further analyses of calibrated 410-nm and 953-nm brightness scans found few corresponding changes in troposphere haze and cloud structure on QQO timescales. However, stratospheric haze reflectance at 255-nm did appear to vary on seasonal timescales, though the data do not have enough temporal coverage or photometric accuracy to be conclusive. Sufficient temporal coverage and spacing, as well as data quality, are critical to this type of search.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Opher, M.; Drake, J. F.; Zieger, B.

The classic accepted view of the heliosphere is a quiescent, comet-like shape aligned in the direction of the Sun’s travel through the interstellar medium (ISM) extending for thousands of astronomical units (AUs). Here, we show, based on magnetohydrodynamic (MHD) simulations, that the tension (hoop) force of the twisted magnetic field of the Sun confines the solar wind plasma beyond the termination shock and drives jets to the north and south very much like astrophysical jets. These jets are deflected into the tail region by the motion of the Sun through the ISM similar to bent galactic jets moving through themore » intergalactic medium. The interstellar wind blows the two jets into the tail but is not strong enough to force the lobes into a single comet-like tail, as happens to some astrophysical jets. Instead, the interstellar wind flows around the heliosphere and into the equatorial region between the two jets. As in some astrophysical jets that are kink unstable, we show here that the heliospheric jets are turbulent (due to large-scale MHD instabilities and reconnection) and strongly mix the solar wind with the ISM beyond 400 AU. The resulting turbulence has important implications for particle acceleration in the heliosphere. The two-lobe structure is consistent with the energetic neutral atom (ENA) images of the heliotail from IBEX where two lobes are visible in the north and south and the suggestion from the Cassini ENAs that the heliosphere is “tailless.”.« less

On the relation among the solar activity, the quasi-biennial oscillation in the equatorial stratosphere and El Nino.

NASA Astrophysics Data System (ADS)

Gul, Zhennian

The possibility of a relation among Quasi-Biennial Oscillation (QBO) of zonal winds in the equatorial stratosphere, sunspot Wolf number and SST's in the eastern Pacific during the same interval are analyzed. The band filter and the wavelet method which are capable of finding local periods and amplitudes are used in the data processing. It is shown that the coherence estimates between the series of QBO in Wolf and in lower tropical stratosphere are of order of -0.6. A possible dynamical explanation for skip a beat of QBO linked El Nino suggested by Angel and Gray is presented. Solar activity is a hypothetical mechanism of this skip.

Off-equatorial circular orbits in magnetic fields of compact objects

NASA Astrophysics Data System (ADS)

Stuchlík, Zdeněk; Kovář, Jiří; Karas, Vladimír

2009-04-01

We present results of investigation of the off-equatorial circular orbits existence in the vicinity of neutron stars, Schwarzschild black holes with plasma ring, and near Kerr-Newman black holes and naked singularities.

Response of equatorial and low latitude mesosphere lower thermospheric dynamics to the northern hemispheric sudden stratospheric warming events

NASA Astrophysics Data System (ADS)

Koushik, N.; Kumar, Karanam Kishore; Ramkumar, Geetha; Subrahmanyam, K. V.

2018-04-01

The changes in zonal mean circulation and meridional temperature gradient brought about by Sudden Stratospheric Warming (SSW) events in polar middle atmosphere are found to significantly affect the low latitude counterparts. Several studies have revealed the signatures of SSW events in the low latitude Mesosphere- Lower Thermosphere (MLT) region. Using meteor wind radar observations, the present study investigates the response of semidiurnal oscillations and quasi 2-day waves in the MLT region, simultaneously over low latitude and equatorial stations Thumba (8.5oN, 76.5oE) and Kototabang (0.2oS, 100oE). Unlike many case studies, the present analysis examines the response of low and equatorial latitude MLT region to typical polar stratospheric conditions viz., Quiet winter, Major SSW winter and Minor SSW winter. The present results show that (i) the amplitudes of semidiurnal oscillations and quasi 2-day waves in the equatorial and low latitude MLT region enhance in association with major SSW events, (ii) the semidiurnal oscillations show significant enhancement selectively in the zonal and meridional components over the Northern Hemispheric low latitude and the equatorial stations, respectively (iii) The minor SSW event of January 2012 resulted in anomalously large amplitudes of quasi 2- day waves without any notable increase in the amplitude of semidiurnal oscillations. The significance of the present study lies in comprehensively bringing out the signatures of SSW events in the semidiurnal oscillations and quasi 2-day waves in low latitude and equatorial MLT region, simultaneously for the first time over these latitudes.

Dynamics in the Modern Upper Atmosphere of Venus: Zonal Wind Transition to Subsolar-to-Antisolar Flow

NASA Astrophysics Data System (ADS)

Livengood, T. A.; Kostiuk, T.; Hewagama, T.; Fast, K. E.

2017-12-01

We observed Venus on 19-23 Aug 2010 (UT) to investigate equatorial wind velocities from above the cloud tops through the lower thermosphere. Measurements were made from the NASA Infrared Telescope Facility using the NASA Goddard Space Flight Center Heterodyne Instrument for Planetary Winds and Composition. High-resolution spectra were acquired on a CO2 pressure-broadened absorption feature that probes the lower mesosphere ( 70 km altitude) with a non-LTE core emission of the same transition that probes the lower thermosphere ( 110 km). The resolving power of λ/Δλ≈3×107 determines line-of-sight velocity from Doppler shifts to high precision. The altitude differential between the features enables investigating the transition from zonal wind flow near the cloud tops to subsolar-to-antisolar flow in the thermosphere. The fully-resolved carbon dioxide transition was measured near 952.8808 cm-1 (10.494 µm) rest frequency at the equator with 1 arcsec field-of-view on Venus (24 arcsec diameter) distributed about the central meridian and across the terminator at ±15° intervals in longitude. The non-LTE emission is solar-pumped and appears only on the daylight side, probing subsolar-to-antisolar wind velocity vector flowing radially from the subsolar point through the terminator, which was near the central meridian in these observations and had zero line-of-sight wind projection at the terminator. The velocity of the zonal flow is approximately uniform, with maximum line-of-sight projection at the limb, and can be measured by the frequency of the absorption line on both the daylight and dark side. Variations in Doppler shift between the observable features and the differing angular dependence of the contributing wind phenomena thus provide independent mechanisms to distinguish the dynamical processes at the altitude of each observed spectral feature. Winds up to >100 m/s were determined in previous investigations with uncertainties of order 10 m/s or less.

The relationship between African easterly waves and equatorial waves and the influence from the Southern Hemisphere

NASA Astrophysics Data System (ADS)

Methven, John; Guiying, Yang; Hodges, Kevin; Woolnough, Steve

2017-04-01

There is strong intraseasonal and interannual variability in African easterly waves (AEWs). AEWs are crucial to precipitation across West Africa, but also generate positive vorticity centres that sometimes develop into tropical storms which can in turn spin-up into hurricanes in the easterlies across the North Atlantic. In this paper we show that there are connections between African easterly waves (AEWs), equatorial Rossby (R1 and R2) waves and westward-moving mixed Rossby gravity (WMRG) waves and that the conditions for propagation of equatorial waves may have a major influence on AEW and hence tropical cyclone variability. Two analysis approaches are taken using ERA-Interim data from 1979-2010: i) positive vorticity centres within AEWs are tracked at 600 hPa over West Africa to the Atlantic region and ii) the re-analysis data is filtered using a broad frequency and zonal wavenumber band and the filtered meridional wind is projected onto the horizontal structure functions derived from equatorial wave theory. The tracked vorticity centres are part of AEWs and are found to move along with features in the meridional wind projecting onto R1 and R2 waves. In contrast, the structures projecting onto WMRG waves move westwards at a faster rate. The projection is calculated independently on each pressure level to create composite cross-sections of each wave mode in the zonal-height plane, shown relative to the 600 hPa vorticity centres. The R2 waves tilt in the sense necessary for baroclinic growth and amplify from east to west, indicating that R2 horizontal structure captures the baroclinic wave component of AEWs. The composites show that the R2 structures have a wavelength matching the spacing between vorticity centres, while R1 and WMRG waves are longer. Intriguingly, the WMRG component has very strong cross-equatorial flow immediately to the east of positive vorticity centres developing on the AEJ. Although the WMRG propagates faster to the west and gets ahead of the original vorticity centre, the next AEW vorticity centre to the east develops with cross-equatorial flow in the same phase. This flow brings moist air from the southern hemisphere at low levels on the eastern flank of the vorticity centre, while there is an upper tropospheric "return flow" into the southern hemisphere above. Thus, there is a strong cross-equatorial component to the developing tropical storm outflow. WMRG waves may aid the initiation and development of AEW vorticity centres. Over West Africa, regressions show that the eastward group propagation of a WMRG packet precedes the genesis of vorticity centres on the AEJ. In years with stronger AEW activity, the upper tropospheric easterlies are stronger at the equator and extend further into the southern hemisphere. It is shown that stronger easterlies provide a waveguide for SH westward-moving Rossby waves in the upper troposphere to penetrate into the tropics, exciting equatorial WMRG waves and hence stronger AEW activity via the lower tropospheric cross-equatorial flow associated with WMRG waves.

Nonlinear Equatorial Spread F: The Effect of Neutral Winds and Background Pedersen Conductivity.

DTIC Science & Technology

1981-07-29

course of our simulation. This is tantamount to neglecting compressibility (Pedersen mobility ) effects in the E region plasma. Thus, we are utilizing...Neier - Code 4141 Or. C. Szszczowlcz - Code 4187 Utah State Universityr. j. Goodn - code 4180 4th N. and 8th Streets Science Aplications . Inc. Loan

Revisiting the false alarm in the 2014 El Niño prediction

NASA Astrophysics Data System (ADS)

Shin, C. S.; Huang, B.

2016-12-01

In early 2014, most dynamic forecast models predicted a developing strong El Niño in the following winter. However, this forecast turned out to be a representative case of the false alarms since 2000. In this study, a set of CFSv2 ensemble seasonal reforecast is conducted to examine some possible causes of the unrealistic El Niño prediction in 2014. Zooming in on the NINO3.4 index, the ensemble-mean reforecast initialized in April 2014 predicted a very strong El Niño as the 1997-98 one with most ensemble members warmer than the observations. In contrast, the ensemble-mean reforecast initialized in January (July) 2014 predicted a slower growth (a decline) of the NINO3.4 index for 12-month lead (from November to the spring in 2015), with the spreads of the ensemble members enveloping the observations. Since the observed SST anomalies in equatorial eastern Pacific changed its polarity in late March from the coldest SST anomalies in February accompanied by strong easterly wind to warmer SST in mid April, the atmospheric and oceanic instantaneous initial states in early April 2014 may misrepresent these intra-seasonal variations, possibly resulting in warm bias in equatorial Pacific even at 0-month lead. Our experiments show that colder ocean surface initial conditions in tropical eastern Pacific tend to hinder developing warm SST anomalies in equatorial eastern Pacific and weaken the Bjerknes-type air-sea feedback in the summer of 2014, which reduce excessive westerly wind (warm SST anomalies) in equatorial western Pacific (near the Dateline) and decrease the air-sea feedback. As a result, the predicted amplitude of NINO3.4 at the peak phase is comparable to the observed one, suggesting that the initial condition errors are partially responsible for the false alarm in the 2014 El Niño prediction issued in the spring. Nonetheless, the initial condition errors could not account for easterly wind burst observed in mid June associated with enhanced extratropical anti-cyclonic atmospheric circulation anomalies in the Southern Hemisphere, which is regarded as another major factor to stall the El Niño occurrence in 2014. What drives this anomalous atmospheric forcing in mid June and how much it contributes to a more realistic prediction of the 2014 El Niño will also be discussed.

Indian Ocean warming during 1958-2004 simulated by a climate system model and its mechanism

NASA Astrophysics Data System (ADS)

Dong, Lu; Zhou, Tianjun; Wu, Bo

2014-01-01

The mechanism responsible for Indian Ocean Sea surface temperature (SST) basin-wide warming trend during 1958-2004 is studied based on both observational data analysis and numerical experiments with a climate system model FGOALS-gl. To quantitatively estimate the relative contributions of external forcing (anthropogenic and natural forcing) and internal variability, three sets of numerical experiments are conducted, viz. an all forcing run forced by both anthropogenic forcing (greenhouse gases and sulfate aerosols) and natural forcing (solar constant and volcanic aerosols), a natural forcing run driven by only natural forcing, and a pre-industrial control run. The model results are compared to the observations. The results show that the observed warming trend during 1958-2004 (0.5 K (47-year)-1) is largely attributed to the external forcing (more than 90 % of the total trend), while the residual is attributed to the internal variability. Model results indicate that the anthropogenic forcing accounts for approximately 98.8 % contribution of the external forcing trend. Heat budget analysis shows that the surface latent heat flux due to atmosphere and surface longwave radiation, which are mainly associated with anthropogenic forcing, are in favor of the basin-wide warming trend. The basin-wide warming is not spatially uniform, but with an equatorial IOD-like pattern in climate model. The atmospheric processes, oceanic processes and climatological latent heat flux together form an equatorial IOD-like warming pattern, and the oceanic process is the most important in forming the zonal dipole pattern. Both the anthropogenic forcing and natural forcing result in easterly wind anomalies over the equator, which reduce the wind speed, thereby lead to less evaporation and warmer SST in the equatorial western basin. Based on Bjerknes feedback, the easterly wind anomalies uplift the thermocline, which is unfavorable to SST warming in the eastern basin, and contribute to SST warming via deeper thermocline in the western basin. The easterly anomalies also drive westward anomalous equatorial currents, against the eastward climatology currents, which is in favor of the SST warming in the western basin via anomalous warm advection. Therefore, both the atmospheric and oceanic processes are in favor of the IOD-like warming pattern formation over the equator.

Westerly wind bursts simulated in CAM4 and CCSM4

NASA Astrophysics Data System (ADS)

Lian, Tao; Tang, Youmin; Zhou, Lei; Islam, Siraj Ul; Zhang, Chan; Li, Xiaojing; Ling, Zheng

2018-02-01

The equatorial westerly wind bursts (WWBs) play an important role in modulating and predicting the El Niño-Southern Oscillation (ENSO). In this study, the ability of the Community Atmospheric Model version 4 (CAM4) and the Community Climate System Model version 4 (CCSM4) in simulating WWBs is systematically evaluated. Many characteristics of WWBs, including their longitude distributions, durations, zonal extensions, variabilities at seasonal, intraseasonal, and interannual timescales, as well as their relations with the Madden-Julian Oscillation (MJO) and ENSO, are discussed. Generally speaking, these characteristics of WWBs can be successfully reproduced by CAM4, owning to the improvement of the deep convection in the model. In CCSM4, significant bias such as the lack of the equatorial Pacific WWBs in boreal spring season and the weak modulation by a strong MJO are found. Our findings confirm the fact that the WWBs are greatly modulated by the surface temperature. It's also suggested that improving the air-sea coupling in CCSM4 may improve model performance in simulating WWBs, and may further improve the predictability of ENSO in the coupled model.

Quasi-biennial modulation of planetary-wave fluxes in the Northern Hemisphere winter

NASA Technical Reports Server (NTRS)

Dunkerton, Timothy J.; Baldwin, Mark P.

1991-01-01

Using 25 years of National Meteorological Center (NMC) data for 1964-88 the relation between tropical and extratropical quasi-biennial oscillations (QBOs) was examined for zonally averaged quantities and planetary-wave Eliassen-Palm fluxes in the Northern Hemisphere winter. The extratropical QBO discussed by Holton and Tan (1980) existed in both temporal halves of the dataset. Autocorrelation analysis demonstrated that it was an important mode of interannual variability in the extratropical winter stratosphere. Correlation with the tropics was strongest when 40-mb equatorial winds were used to define the tropical QBO. Easterly phase at 40 mb implied a weaker than normal polar night jet and warmer than normal polar temperature and vice versa. An opposite relationship was obtained using 10-mb equatorial winds. The association between tropical and extratropical QBOs was observed in about 90 percent of the winters and was statistically significant. It is shown that planetary-wave Eliassen-Palm fluxes were generally consistent with the extratropical QBO. These fluxes were more (less) convergent in the midlatitude (subtropical) upper stratosphere in the 40-mb east (= easterly) phase category relative to the west category.

Plasma observations near Saturn - Initial results from Voyager 2

NASA Technical Reports Server (NTRS)

Bridge, H. S.; Bagenal, F.; Belcher, J. W.; Lazarus, A. J.; Mcnutt, R. L.; Sullivan, J. D.; Gazis, P. R.; Hartle, R. E.; Ogilvie, K. W.; Scudder, J. D.

1982-01-01

Results of plasma measurements made by Voyager 2 in the vicinity of Saturn are discussed and compared with those made by Pioneer 11 and Voyager 1 in a more limited range of latitudes. The initial bow shock crossing on the inbound trajectory closely agreed with the shock position inferred from the external ram pressure in the solar wind, although boundaries on the outbound pass were much further out than expected. Magnetospheric plasma observations reveal the presence of (1) shocked solar wind plasma in the magnetosheath between 30 and 22 Saturn radii; (2) a variable density region between 17 Saturn radii and the magnetopause; (3) an extended thick plasma sheet between 17 and 7 Saturn radii; and (4) an inner plasma torus probably originating from local sources. The ratio of heavy to light ions was observed to vary with distance to the equatorial plane in the dayside magnetosphere, with the heavy ions, probably O(+), more closely confined to the equatorial plane. The plasma data also account for the observed inner boundary of the neutral hydrogen torus discovered by Voyager 1.

An analysis of the Venus measurements

NASA Technical Reports Server (NTRS)

Ainsworth, J. E.; Herman, J. R.

1972-01-01

Plots of the Mariner 5 and Venera 4, 5, and 6 pressure vs temperature show that the Venera profiles are essentially congruent with the Mariner 5 day and night profiles, but are displaced 28 percent higher in pressure. Data suggest a variability in the atmospheric water vapor content in the region from 30 to 50 km. The Venera 7 measurements are interpreted as evidence for updrafts, down-drafts, horizontal wind layers, and nonaqueous precipitation. The previously observed band of retrograde winds which circle the equator with an average speed of 110 m/s is found to extend downward to the one atmosphere level at the equatorial morning terminator. The possibility of a low altitude equator-to-pole circulation with warm gas rising at the poles is inferred. Venera 7 temperature data used with radar topography and microwaves interferometer measurements suggest that the variation of surface temperature with altitude in a band about the equator is less than 5 K/km. The available data are used to calculate a model of the structure of the Venus atmosphere for the first 75 km above the equatorial region.

Tropical Meridional Overturning Circulation Observed by Subsurface Moorings in the Western Pacific.

PubMed

Song, Lina; Li, Yuanlong; Wang, Jianing; Wang, Fan; Hu, Shijian; Liu, Chuanyu; Diao, Xinyuan; Guan, Cong

2018-05-16

Meridional ocean current in the northwestern Pacific was documented by seven subsurface moorings deployed at 142°E during August 2014-October 2015. A sandwich structure of the tropical meridional overturning circulation (TMOC) was revealed between 0-6°N that consists of a surface northward flow (0-80 m), a thermocline southward flow (80-260 m; 22.6-26.5 σ θ ), and a subthermocline northward flow (260-500 m; 26.5-26.9 σ θ ). Based on mooring data, along with satellite and reanalysis data, prominent seasonal-to-interannual variations were observed in all three layers, and the equatorial zonal winds were found to be a dominant cause of the variations. The TMOC is generally stronger in boreal winter and weaker in summer. During 2014-2015, the TMOC was greatly weakened by westerly wind anomalies associated with the El Niño condition. Further analysis suggests that the TMOC can affect equatorial surface temperature in the western Pacific through anomalous upwelling/downwelling and likely plays a vital role in the El Niño-Southern Oscillation (ENSO).

Equatorial All Sky Imager Images from the Seychelles during the March 17th, 2015 geomagnetic storm.

NASA Astrophysics Data System (ADS)

Curtis, B.

2015-12-01

An all sky imager was installed in the Seychelles earlier this year. The Seychelles islands are located northeast of Madagascar and east of Somalia in the equatorial Indian Ocean. The all sky imager is located on the island of Mahe (4.6667°S, 55.4667°E geographic), (10.55°S, 127.07°E geomagnetic), with filters of 557.7, 620.0, 630.0, 765.0 and 777.4 nm. Images with a 90 second exposure from Seychelles in 777.4nm and 630.0nm from the night before and night of the March 17th geomagnetic storm are discussed in comparison to solar wind measurements at ACE and the disturbance storm time (Dst) index. These images show line-of-sight intensities of photons received dependent on each filters wavelength. A time series of these images sometimes will show the movement of relatively dark areas, or depletions, in each emission. The depletion regions are known to cause scintillation in GPS signals. The direction and speed of movement of these depletions are related to changes observed in the solar wind.

Spatial organization and time dependence of Jupiter's tropospheric temperatures, 1980-1993

NASA Technical Reports Server (NTRS)

Orton, Glenn S.; Friedson, A. James; Yanamandra-Fisher, Padmavati A.; Caldwell, John; Hammel, Heidi B.; Baines, Kevin H.; Bergstralh, Jay T.; Martin, Terry Z.; West, Robert A.; Veeder, Glenn J., Jr.

1994-01-01

The spatial organization and time dependence of Jupiter's temperature near 250-millibar pressure were measured through a jovian year by imaging thermal emission at 18 micrometers. The temperature field is influenced by seasonal radiative forcing, and its banded organization is closely correlated with the visible cloud field. Evidence was found for a quasi-periodic oscillation of temperatures in the Equatorial Zone, a correlation between tropospheric and stratospheric waves in the North Equatorial Belt, and slowly moving thermal features in the North and South Equatorial Belts. There appears to be no common relation between temporal changes of temperature and changes in the visual albedo of the various axisymmetric bands.

Penetration of ELF currents and electromagnetic fields into the Earth's equatorial ionosphere

NASA Astrophysics Data System (ADS)

Eliasson, B.; Papadopoulos, K.

2009-10-01

The penetration of extremely low frequency (ELF) transient electromagnetic fields and associated currents in the Earth's equatorial E-region plasma is studied theoretically and numerically. In the low-frequency regime, the plasma dynamics of the E-region is characterized by helicon waves since the ions are viscously coupled to neutrals while the electrons remain mobile. For typical equatorial E-region parameters, the plasma is magnetically insulated from penetration of very long timescale magnetic fields by a thin diffusive sheath. Wave penetration driven by a vertically incident pulse localized in space and time leads to both vertical penetration and the triggering of ELF helicon/whistler waves that carry currents obliquely to the magnetic field lines. The study presented here may have relevance for ELF wave generation by lightning discharges and seismic activity and can lead to new concepts in ELF/ULF injection in the earth-ionosphere waveguide.

Improved spatial and temporal characteristics of ionospheric irregularities and polar mesospheric summer echoes using coherent MIMO and aperture synthesis radar imaging

NASA Astrophysics Data System (ADS)

Chau, J. L.; Urco, J. M.; Milla, M. A.; Vierinen, J.

2017-12-01

We have recently implemented Multiple-input multiple-output (MIMO) radar techniques to resolve temporal and spatial ambiguities of ionospheric and atmospheric irregularities, with improve capabilities than previously experiments using single-input multi-output (SIMO) techniques. SIMO techniques in the atmospheric and ionospheric coherent scatter radar field are usually called aperture synthesis radar imaging. Our implementations have done at the Jicamarca Radio Observatory (JRO) in Lima, Peru, and at the Middle Atmosphere Alomar Radar System (MAARSY) in Andenes, Norway, to study equatorial electrojet (EEJ) field-aligned irregularities and polar mesospheric summer echoes (PMSE), respectively. Figure 1 shows an example of a configuration used at MAARSY and the comparison between the SIMO and MIMO resulting antenna point spread functions, respectively. Although in this work we present the details of the implementations at each facility, we will focus on the observed peculiarities of each phenomenon, making emphasis in the underlying physical mechanisms that govern their existence and their spatial and temporal modulation. For example, what are the typical horizontal scales of PMSE variability in both intensity and wind field?

Evolution of Tropical and Extratropical Precipitation Anomalies During the 1997 to 1999 ENSO Cycle

NASA Technical Reports Server (NTRS)

Curtis, Scott; Adler, Robert; Huffman, George; Nelkin, Eric; Bolvin, David; Einaudi, Franco (Technical Monitor)

2000-01-01

The 1997-1999 ENSO period was very powerful, but also well observed. Multiple satellite rainfall estimates combined with gauge observations allow for a quantitative analysis of precipitation anomalies in the tropics and elsewhere accompanying the 1997-99 ENSO cycle. An examination of the evolution of the El Nino and accompanying precipitation anomalies revealed that a dry Maritime Continent preceded the formation of positive SST anomalies in the eastern Pacific Ocean. 30-60 day oscillations in the winter of 1996/97 may have contributed to this lag relationship. Furthermore, westerly wind burst events may have maintained the drought over the Maritime Continent. The warming of the equatorial Pacific was then followed by an increase in convection. A rapid transition from El Nino to La Nina occurred in May 1998, but as early as October-November 1997 precipitation indices captured substantial changes in Pacific rainfall anomalies. The global precipitation patterns for this event were in good agreement with the strong consistent ENSO-related precipitation signals identified in earlier studies. Differences included a shift in precipitation anomalies over Africa during the 1997-98 El Nino and unusually wet conditions over northeast Australia during the later stages of the El Nino. Also, the typically wet region in the north tropical Pacific was mostly dry during the 1998-99 La Nina. Reanalysis precipitation was compared to observations during this time period and substantial differences were noted. In particular, the model had a bias towards positive precipitation anomalies and the magnitudes of the anomalies in the equatorial Pacific were small compared to the observations. Also, the evolution of the precipitation field, including the drying of the Maritime Continent and eastward progression of rainfall in the equatorial Pacific was less pronounced for the model compared to the observations.

Modeling of O+ ions in the plasmasphere

NASA Astrophysics Data System (ADS)

Guiter, S. M.; Moore, T. E.; Khazanov, G. V.

1995-11-01

Heavy ion (O+, O++, and N+) density enhancements in the outer plasmasphere have been observed using the retarding ion mass spectrometer instrument on the DE 1 satellite. These are seen at L shells from 2 to 5, with most occurrences in the L=3 to 4 region; the maximum L shell at which these enhancements occur varies inversely with Dst. It is also known that enhancements of O+ and O++ overlie ionospheric electron temperature peaks. It is thought that these enhancements are related to heating of plasmaspheric particles through interactions with ring current ions. This was investigated using a time-dependent one-stream hydrodynamic model for plasmaspheric flows, in which the model flux tube is connected to the ionosphere. The model simultaneously solves the coupled continuity, momentum, and energy equations of a two-ion (H+ and O+) quasi-neutral, currentless plasma. This model is fully interhemispheric and diffusive equilibrium is not assumed; it includes a corotating tilted dipole magnetic field and neutral winds. First, diurnally reproducible results were found assuming only photoelectron heating of thermal electrons. For this case the modeled equatorial O+ density was below 1 cm-3 throughout the day. The O+ results also show significant diurnal variability, with standing shocks developing when production stops and O+ flows downward under the influence of gravity. Numerical tests were done with different levels of electron heating in the plasmasphere; these show that the equatorial O+ density is highly dependent on the assumed electron heating rates. Over the range of integrated plasmaspheric electron heating (along the flux tube) from 8.7 to 280×109 eV/s, the equatorial O+ density goes like the heating raised to the power 2.3.

Transverse Aeolian Ridges on Mars: Sediment sources, volumes, and ages.

NASA Astrophysics Data System (ADS)

Berman, D. C.; Balme, M. R.

2014-12-01

Transverse Aeolian Ridges (TARs) are aeolian bedforms that are morphologically and dimensionally distinct from Large Dark Dune (LDD) fields, being generally brighter than, or of similar albedo to, the surrounding terrain. These features are significantly smaller than the LDDs, appear to form normal to local winds, and tend to have simple, transverse, ripple-like morphologies. Whether these small martian bedforms represent large granule ripples, small transverse dunes, or something else entirely is currently under debate. The spatial distribution of TARs provides important information about where on Mars aeolian sediments are concentrated, and determining their volume can help us constrain the sediment transport regime on Mars. Also, if we can determine if TARs were active only in the past, or whether TARs are mobile under today's wind conditions, then we can begin to assess when and where TARs are/were active over Mars' recent geological history. Thus TARs have the potential for being indicators/records of climate change on Mars. In this work we build on previous work [1,2] and focus on the local/regional scale. We have identified six regional study areas, each 5° by 5°, to investigate the behavior of TARs in detail; one in the northern hemisphere, three in the equatorial band, and two in the southern hemisphere. We have systematically mapped TAR and LDD deposits in each study area to constrain sediment transport pathways and identify sediment sources. In general, TAR sediments appear to be tied to local sources such as LDDs or layered terrains. HiRISE DTMs were utilized to measure TAR heights, widths, wavelengths, and lengths to calculate sediment volumes and estimate volumes over entire study areas based on mapping. Crater count analyses on contiguous TAR fields in the equatorial regions, where the bedforms appear more lithified, reveal ages of several million years. Mid-latitude TAR fields do not show any superposed craters, suggesting much younger deposits. References: [1] Balme, M.R., D.C. Berman, M.C. Bourke, and J.R. Zimbelman, Transverse Aeolian Ridges (TARs) on Mars, Geomorphology, 101, 703-720, 2008. [2] Berman, D.C., M.R. Balme, S. Rafkin, and J.R. Zimbelman, Transverse Aeolian Ridges (TARs) on Mars II: Distributions, orientations, and ages, Icarus 213, 116-130, 2011

EEJ and EIA variations during modeling substorms with different onset moments

NASA Astrophysics Data System (ADS)

Klimenko, V. V.; Klimenko, M. V.

2015-11-01

This paper presents the simulations of four modeling substorms with different moment of substorm onset at 00:00 UT, 06:00 UT, 12:00 UT, and 18:00 UT for spring equinoctial conditions in solar activity minimum. Such investigation provides opportunity to examine the longitudinal dependence of ionospheric response to geomagnetic substorms. Model runs were performed using modified Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP). We analyzed GSM TIP simulated global distributions of foF2, low latitude electric field and ionospheric currents at geomagnetic equator and their disturbances at different UT moments substorms. We considered in more detail the variations in equatorial ionization anomaly, equatorial electrojet and counter equatorial electrojet during substorms. It is shown that: (1) the effects in EIA, EEJ and CEJ strongly depend on the substorm onset moment; (2) disturbances in equatorial zonal current density during substorm has significant longitudinal dependence; (3) the observed controversy on the equatorial ionospheric electric field signature of substorms can depend on the substorm onset moments, i.e., on the longitudinal variability in parameters of the thermosphere-ionosphere system.

First plasma wave observations at neptune.

PubMed

Gurnett, D A; Kurth, W S; Poynter, R L; Granroth, L J; Cairns, I H; Macek, W M; Moses, S L; Coroniti, F V; Kennel, C F; Barbosa, D D

1989-12-15

The Voyager 2 plasma wave instrument detected many familiar plasma waves during the encounter with Neptune, including electron plasma oscillations in the solar wind upstream of the bow shock, electrostatic turbulence at the bow shock, and chorus, hiss, electron cyclotron waves, and upper hybrid resonance waves in the inner magnetosphere. Low-frequency radio emissions, believed to be generated by mode conversion from the upper hybrid resonance emissions, were also observed propagating outward in a disklike beam along the magnetic equatorial plane. At the two ring plane crossings many small micrometer-sized dust particles were detected striking the spacecraft. The maximum impact rates were about 280 impacts per second at the inbound ring plane crossing, and about 110 impacts per second at the outbound ring plane crossing. Most of the particles are concentrated in a dense disk, about 1000 kilometers thick, centered on the equatorial plane. However, a broader, more tenuous distribution also extends many tens of thousands of kilometers from the equatorial plane, including over the northern polar region.

Estimates of upwelling rates in the Arabian Sea and the equatorial Indian Ocean based on bomb radiocarbon.

PubMed

Bhushan, R; Dutta, K; Somayajulu, B L K

2008-10-01

Radiocarbon measurements were made in the water column of the Arabian Sea and the equatorial Indian Ocean during 1994, 1995 and 1997 to assess the temporal variations in bomb 14C distribution and its inventory in the region with respect to GEOSECS measurements made during 1977-1978. Four GEOSECS stations were reoccupied (three in the Arabian Sea and one in the equatorial Indian Ocean) during this study, with all of them showing increased penetration of bomb 14C along with decrease in its surface water activity. The upwelling rates derived by model simulation of bomb 14C depth profile using the calculated exchange rates ranged from 3 to 9 m a(-1). The western region of the Arabian Sea experiencing high wind-induced upwelling has higher estimated upwelling rates. However, lower upwelling rates obtained for the stations occupied during this study could be due to reduced 14C gradient compared to that during GEOSECS.

Seasonal Variability of Saturn's Tropospheric Temperatures, Winds and Para-H2 from Cassini Far-IR Spectroscopy

NASA Technical Reports Server (NTRS)

Fletcher, Leigh N.; Irwin, P. G. J; Achterberg, R. K.; Orton, G. S.; Flasar, F. M.

2015-01-01

Far-IR 16-1000 micrometer spectra of Saturn's hydrogen-helium continuum measured by Cassini's Composite Infrared Spectrometer (CIRS) are inverted to construct a near-continuous record of upper tropospheric (70-700 mbar) temperatures and para-H2 fraction as a function of latitude, pressure and time for a third of a saturnian year (2004-2014, from northern winter to northern spring). The thermal field reveals evidence of reversing summertime asymmetries superimposed onto the belt/zone structure. The temperature structure is almost symmetric about the equator by 2014, with seasonal lag times that increase with depth and are qualitatively consistent with radiative climate models. Localised heating of the tropospheric hazes (100-250 mbar) create a distinct perturbation to the temperature profile that shifts in magnitude and location, declining in the autumn hemisphere and growing in the spring. Changes in the para-H2 (f(sub p)) distribution are subtle, with a 0.02-0.03 rise over the spring hemisphere (200-500 mbar) perturbed by (i) low-f(sub p) air advected by both the springtime storm of 2010 and equatorial upwelling; and (ii) subsidence of high-f(sub p) air at northern high latitudes, responsible for a developing north-south asymmetry in f(sub p). Conversely, the shifting asymmetry in the para-H2 disequilibrium primarily reflects the changing temperature structure (and hence the equilibrium distribution of f(sub p)), rather than actual changes in f(sub p) induced by chemical conversion or transport. CIRS results interpolated to the same point in the seasonal cycle as re-analysed Voyager-1 observations (early northern spring) show qualitative consistency from year to year (i.e., the same tropospheric asymmetries in temperature and f(sub p)), with the exception of the tropical tropopause near the equatorial zones and belts, where downward propagation of a cool temperature anomaly associated with Saturn's stratospheric oscillation could potentially perturb tropopause temperatures, para-H2 and winds. Quantitative differences between the Cassini and Voyager epochs suggest that the oscillation is not in phase with the seasonal cycle at these tropospheric depths (i.e., it should be described as quasi-periodic rather than 'semi annual'). Variability in the zonal wind field derived from latitudinal thermal gradients is small (less than 10 m/s per scale height near the tropopause) and mostly affects the broad retrograde jets, with the notable exception of large variability on the northern flank of the equatorial jet. The meridional potential vorticity (PV) gradient, and hence the 'staircase of PV' associated with spatial variations in the vigour of vertical mixing, has varied over the course of the mission but maintained its overall shape. PV gradients in latitude and altitude are used to estimate the atmospheric refractive index for the propagation of stationary planetary (Rossby) waves, predicting that such wave activity would be confined to regions of real refractivity (tropical regions plus bands at 35-45 in both hemispheres). The penetration depth of these regions into the upper troposphere is temporally variable (potentially associated with stratification changes), whereas the latitudinal structure is largely unchanged over time (associated with the zonal jet system).

Sub-seasonal prediction of significant wave heights over the Western Pacific and Indian Oceans, part II: The impact of ENSO and MJO

NASA Astrophysics Data System (ADS)

Shukla, Ravi P.; Kinter, James L.; Shin, Chul-Su

2018-03-01

This study evaluates the effect of El Niño and the Southern Oscillation (ENSO) and Madden Julian Oscillation (MJO) events on 14-day mean significant wave height (SWH) at 3 weeks lead time (Wk34) over the Western Pacific and Indian Oceans using the National Centers for Environmental Prediction (NCEP) Climate Forecast System, version 2 (CFSv2). The WAVEWATCH-3 (WW3) model is forced with daily 10m-winds predicted by a modified version of CFSv2 that is initialized with multiple ocean analyses in both January and May for 1979-2008. A significant anomaly correlation of predicted and observed SWH anomalies (SWHA) at Wk34 lead-time is found over portions of the domain, including the central western Pacific, South China Sea (SCS), Bay of Bengal (BOB) and southern Indian Ocean (IO) in January cases, and over BOB, equatorial western Pacific, the Maritime Continent and southern IO in May cases. The model successfully predicts almost all the important features of the observed composite SWHA during El Niño events in January, including negative SWHA in the central IO where westerly wind anomalies act on an easterly mean state, and positive SWHA over the southern Ocean (SO) where westerly wind anomalies act on a westerly mean state. The model successfully predicts the sign and magnitude of SWHA at Wk34 lead-time in May over the BOB and SCS in composites of combined phases-2-3 and phases-6-7 of MJO. The observed leading mode of SWHA in May and the third mode of SWHA in January are influenced by the combined effects of ENSO and MJO. Based on spatial and temporal correlations, the spatial patterns of SWHA in the model at Wk34 in both January and May are in good agreement with the observations over the equatorial western Pacific, equatorial and southern IO, and SO.

Properties of QBO and SAO Generated by Gravity Waves

NASA Technical Reports Server (NTRS)

Mayr, H. G.; Mengel, J. G.; Reddy, C. A.; Chan, K. L.; Porter, H. S.

1999-01-01

We present an extension for the 2D (zonal mean) version of our Numerical Spectral Mode (NSM) that incorporates Hines' Doppler spread parameterization (DSP) for small scale gravity waves (GW). This model is applied to describe the seasonal variations and the semi-annual and quasi-biennial oscillations (SAO and QBO). Our earlier model reproduced the salient features of the mean zonal circulation in the middle atmosphere, including the QBO extension into the upper mesosphere inferred from UARS measurements. In the present model we incorporate also tropospheric heating to reproduce the upwelling at equatorial latitudes associated with the Brewer-Dobson circulation that affects significantly the dynamics of the stratosphere as Dunkerton had pointed out. Upward vertical winds increase the period of the QBO observed from the ground. To compensate for that, one needs to increase the eddy diffusivity and the GW momentum flux, bringing the latter closer to values recommended in the DSP. The QBO period in the model is 30 months (mo), which is conducive to synchronize this oscillation with the seasonal cycle of solar forcing. Multi-year interannual oscillations are generated through wave filtering by the solar driven annual oscillation in the zonal circulation. Quadratic non-linearities generate interseasonal variations to produce a complicated pattern of variability associated with the QBO. The computed temperature amplitudes for the SAO and QBO are in substantial agreement with observations at equatorial and extratropical latitudes. At high latitudes, however, the observed QBO amplitudes are significantly larger, which may be a signature of propagating planetary waves not included in the present model. The assumption of hydrostatic equilibrium not being imposed, we find that the effects from the vertical Coriolis force associated with the equatorial oscillations are large for the vertical winds and significant for the temperature variations even outside the tropics but are relatively small for the zonal winds.

Experiments on tropical stratospheric mean-wind variations in a spectral general circulation model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamilton, K.; Yuan, L.

1992-12-15

A 30-level version of the rhomboidal-15 GFDL spectral climate model was constructed with roughly 2-km vertical resolution. This model fails to produce a realistic quasi-biennial oscillation (QBO) in the tropical stratosphere. Several simulations were conducted in which the zonal-mean winds and temperatures in the equatorial lower and middle stratosphere were instantaneously perturbed and the model was integrated while the mean state relaxed toward its equilibrium. The time scale for the mean wind relaxation varied from over one month at 40 km to a few months in the lower stratosphere. The wind relaxations in the model also displayed the downward phasemore » propagation characteristic of QBO wind reversals, and mean wind anomalies of opposite sign to the imposed perturbation appear at higher levels. In the GCM the downward propagation is clear only above about 20 mb. Detailed investigations were made of the zonal-mean zonal momentum budget in the equatorial stratosphere. The mean flow relaxations above 20 mb were mostly driven by the vertical Eliassen-Palm flux convergence. The anomalies in the horizontal Eliassen-Palm fluxes from extratropical planetary waves were found to be the dominant effect forcing the mean flow to its equilibrium at altitudes below 20 mb. The vertical eddy momentum fluxes near the equator in the model were decomposed using space-time Fourier analysis. While total fluxes associated with easterly and westerly waves are comparable to those used in simple mechanistic models of the QBO, the GCM has its flux spread over a broad range of wavenumbers and phase speeds. The effects of vertical resolution were studied by repeating part of the control integration with a 69-level version of the model with greatly enhance vertical resolution in the lower and middle stratosphere. The results showed that there is almost no sensitivity of the simulation in the tropical stratosphere to the increased vertical resolution. 34 refs., 16 figs., 3 tabs.« less

Eastern equatorial Pacific sea surface temperature annual cycle in the Kiel climate model: simulation benefits from enhancing atmospheric resolution

NASA Astrophysics Data System (ADS)

Wengel, C.; Latif, M.; Park, W.; Harlaß, J.; Bayr, T.

2018-05-01

A long-standing difficulty of climate models is to capture the annual cycle (AC) of eastern equatorial Pacific (EEP) sea surface temperature (SST). In this study, we first examine the EEP SST AC in a set of integrations of the coupled Kiel Climate Model, in which only atmosphere model resolution differs. When employing coarse horizontal and vertical atmospheric resolution, significant biases in the EEP SST AC are observed. These are reflected in an erroneous timing of the cold tongue's onset and termination as well as in an underestimation of the boreal spring warming amplitude. A large portion of these biases are linked to a wrong simulation of zonal surface winds, which can be traced back to precipitation biases on both sides of the equator and an erroneous low-level atmospheric circulation over land. Part of the SST biases also is related to shortwave radiation biases related to cloud cover biases. Both wind and cloud cover biases are inherent to the atmospheric component, as shown by companion uncoupled atmosphere model integrations forced by observed SSTs. Enhancing atmosphere model resolution, horizontal and vertical, markedly reduces zonal wind and cloud cover biases in coupled as well as uncoupled mode and generally improves simulation of the EEP SST AC. Enhanced atmospheric resolution reduces convection biases and improves simulation of surface winds over land. Analysis of a subset of models from the Coupled Model Intercomparison Project phase 5 (CMIP5) reveals that in these models, very similar mechanisms are at work in driving EEP SST AC biases.

On the dynamic forcing of short-term climate fluctuations by feedback mechanisms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reiter, E.R.

1979-09-01

The energies involved in the general circulation of the atmosphere, especially the zonal available potential energy, show considerable interannual variability, suggesting the presence of various internal feedback mechanisms in the ocean-atmosphere system. Sea-surface temperature (SST) variations appear to have some effect on the hydrological cycle. The possible existence of feedback mechanisms between ocean and atmosphere seem to be evident in some of the data from the North Pacific and North Atlantic. One of these proposed mechanisms involves the variation in the convergence between the North and South Pacific trade-wind systems and is strongly reflected in rainfall variability within the drymore » region of the equatorial Pacific. Similar variations appear in low-latitude SST anomalies. The convergence between the two trade-wind systems in the Atlantic region also undergoes marked interannual variations. This quasi-biennial oscillation (QBO) in trade-wind convergence over the Atlantic appears to be tied to the global QBO of equatorial stratospheric winds and to regional rainfall regimes in the dry region of northeastern Brazil. A variability pattern of SST's with a QBO has been detected off the coast of Senegal, in the Gulf of Guinea and even in the Gulf Stream as it leaves the North American continental shelf. Possible physical connections between some of these QBO's are pointed out by a hypothetical feedback model. It is also suggested that interaction of a QBO with the annual cycle may lead to beating frequencies resembling climatic trends of a duration of several years.« less

Multiple Magnetic Storm Study of the High-Altitude Redistribution of Equatorial Plasma

NASA Astrophysics Data System (ADS)

Bust, G. S.; Crowley, G.; Curtis, N.; Anderson, D.

2008-12-01

During geomagnetic storms, particularly when prompt penetration electric fields (PPE) occur, the equatorial plasma can be lifted to very high altitudes and then diffuse along magnetic field lines to higher than normal latitudes. During these cases very high plasma density (total electron content (TEC) greater than 200 TECU) can be found at these higher latitudes. Shortly after the PPE lifts the equatorial plasma to higher altitudes, at least in the US sector, phenomena known as storm-enhanced density (SED) can occur. SEDs occur in the post-noon time frame and consist of a very high density bulge that seems to occur in the southern USA and Caribbean region, followed by a narrow plume of high density plasma that flows into the high-latitude throat near local noon, and across the polar cap. An outstanding research question is: Exactly how is the high density SED plasma, particularly in the bulge related to the PPE and lifting of the equatorial plasma? Ionospheric imaging of electron density and TEC seem to show a gap in density between the poleward extent of the equatorial plasma and the equatorial extent of the SED plasma. Further, there are magnetic storm events where SEDs do not form (November 2004 as a good example). This paper will investigate the relationship between the equatorial high altitude plasma distribution during magnetic storms, and the initiation and evolution of the SED feature. We will examine eight separate storms from 2003-2006 using the ionospheric data assimilation algorithm IDA4D. In particular we will focus on time periods when LEO satellite GPS TEC data is available from CHAMP, SACC, GRACE and the COSMIC constellation (2006 and beyond). These data sets directly measure the TEC above the satellites, and therefore are good tracers of the high altitude plasma distribution. IDA4D ingests these data sets and uses them to get an improved image of the plasma density for the topside ionosphere and plasmasphere. The resulting 4D images of high altitude densities will be cross compared for the various storms and the similarities and differences will be studied and correlated with various geophysical parameters such as the interplanetary magnetic field (Bz), Dst, hemispheric power, cross cap potential, PPE, equatorial vertical drifts, and the interplanetary electric field. The overall objective is to elucidate the physical relationships that govern the redistribution of equatorial plasma during storms, and the generation and evolution of SEDs.

Constraints on Wave Drag Parameterization Schemes for Simulating the Quasi-Biennial Oscillation. Part II: Combined Effects of Gravity Waves and Equatorial Planetary Waves.

NASA Astrophysics Data System (ADS)

Campbell, Lucy J.; Shepherd, Theodore G.

2005-12-01

This study examines the effect of combining equatorial planetary wave drag and gravity wave drag in a one-dimensional zonal mean model of the quasi-biennial oscillation (QBO). Several different combinations of planetary wave and gravity wave drag schemes are considered in the investigations, with the aim being to assess which aspects of the different schemes affect the nature of the modeled QBO. Results show that it is possible to generate a realistic-looking QBO with various combinations of drag from the two types of waves, but there are some constraints on the wave input spectra and amplitudes. For example, if the phase speeds of the gravity waves in the input spectrum are large relative to those of the equatorial planetary waves, critical level absorption of the equatorial planetary waves may occur. The resulting mean-wind oscillation, in that case, is driven almost exclusively by the gravity wave drag, with only a small contribution from the planetary waves at low levels. With an appropriate choice of wave input parameters, it is possible to obtain a QBO with a realistic period and to which both types of waves contribute. This is the regime in which the terrestrial QBO appears to reside. There may also be constraints on the initial strength of the wind shear, and these are similar to the constraints that apply when gravity wave drag is used without any planetary wave drag.In recent years, it has been observed that, in order to simulate the QBO accurately, general circulation models require parameterized gravity wave drag, in addition to the drag from resolved planetary-scale waves, and that even if the planetary wave amplitudes are incorrect, the gravity wave drag can be adjusted to compensate. This study provides a basis for knowing that such a compensation is possible.

Manifestation of remote response over the equatorial Pacific in a climate model

NASA Astrophysics Data System (ADS)

Misra, Vasubandhu; Marx, L.

2007-10-01

In this paper we examine the simulations over the tropical Pacific Ocean from long-term simulations of two different versions of the Center for Ocean-Land-Atmosphere Studies (COLA) coupled climate model that have a different global distribution of the inversion clouds. We find that subtle changes made to the numerics of an empirical parameterization of the inversion clouds can result in a significant change in the coupled climate of the equatorial Pacific Ocean. In one coupled simulation of this study we enforce a simple linear spatial filtering of the diagnostic inversion clouds to ameliorate its spatial incoherency (as a result of the Gibbs effect) while in the other we conduct no such filtering. It is found from the comparison of these two simulations that changing the distribution of the shallow inversion clouds prevalent in the subsidence region of the subtropical high over the eastern oceans in this manner has a direct bearing on the surface wind stress through surface pressure modifications. The SST in the warm pool region responds to this modulation of the wind stress, thus affecting the convective activity over the warm pool region and also the large-scale Walker and Hadley circulation. The interannual variability of SST in the eastern equatorial Pacific Ocean is also modulated by this change to the inversion clouds. Consequently, this sensitivity has a bearing on the midlatitude height response. The same set of two experiments were conducted with the respective versions of the atmosphere general circulation model uncoupled to the ocean general circulation model but forced with observed SST to demonstrate that this sensitivity of the mean climate of the equatorial Pacific Ocean is unique to the coupled climate model where atmosphere, ocean and land interact. Therefore a strong case is made for adopting coupled ocean-land-atmosphere framework to develop climate models as against the usual practice of developing component models independent of each other.

ULYSSES comes full circle, before revisiting the Sun's poles

NASA Astrophysics Data System (ADS)

1998-04-01

From its unique perspective, Ulysses has provided scientists with the very first all-round map of the heliosphere, the huge bubble in space filled by the Sun's wind. The Earth swims deep inside the heliosphere, and gusts and shocks in the solar wind can harm satellites, power supplies and ommunications. They may also affect our planet's weather. A better grasp of the solar weather in the heliosphere is therefore one of the major aims of ESA's science programme. In a project of international cooperation between ESA and NASA, Ulysses was launched towards Jupiter in October 1990 by the US space shuttle Discovery. Arriving in February 1992, Ulysses stole energy from the giant planet in a slingshot manoeuvre and was propelled back towards the Sun in an elongated orbit almost at right angles to the ecliptic plane, where the Earth and other planets circle the Sun. "This month Ulysses returns to the point in space where its out-of-ecliptic journey began, but Jupiter isn't there," explains Richard Marsden, ESA's project scientist for Ulysses. "Following its own inexorable path around the Sun, Jupiter is far away on the opposite side of the Solar System. So Ulysses' course will not be changed a second time. The spacecraft is now in effect a man-made comet, forever bound into a 6-year polar orbit around the Sun." Ulysses now starts its second orbit. It will travel over the poles of the Sun in 2000-2001 just as the count of dark sunspots is expected to reach a maximum. With its operational life extended for the Ulysses Solar Maximum Mission, the spacecraft will find the heliosphere much stormier than during its first orbit. Discoveries so far Like its mythical namesake, Ulysses has already had an eventful voyage of discovery. Its unique trajectory has provided the scientific teams with a new perspective, from far out in space and especially in the previously unknown regions of the heliosphere over the Sun's poles. Passing within 9.8 degrees of the polar axis, the highly slanted orbit took Ulysses to solar latitudes greater than 70 degrees for a total of 234 days -- first in the southern hemisphere and then in the north. Also of great interest was the rapid passage from the south to the north, via the Sun's equatorial region, during which Ulysses covered 160 degrees in solar latitude in less than a year. Nine onboard experiments have gathered data continuously since launch, for international teams totalling 150 scientists. Some instruments detect the outward-blowing solar wind and its magnetic field, which create the heliosphere. Others record cosmic rays coming in from the Galaxy, which are strongly influenced by the solar wind. Ulysses picks up natural radio signals emitted by the Sun, the planets and the heliosphere itself. Innovative techniques identify alien atoms and dust particles infiltrating the heliosphere from interstellar space. Ulysses is also a key member of a network of interplanetary spacecraft making observations of enigmatic bursts of gamma rays originating in the far reaches of the Universe. New facts about the fast solar wind were among Ulysses' most fundamental discoveries. The typical solar wind emerging from the Sun's equatorial zone is variable but relatively slow, at 350-400 kilometres per second. The fast wind blows at a steady 750 kilometres per second. It comes from cool regions of the solar atmosphere called coronal holes which (when the Sun is quiet) are close to the poles and fairly small. Yet Ulysses found the fast wind fanning out to fill two-thirds of the volume of the heliosphere. The boundary between the two windstreams is unexpectedly sharp. The magnetic field of the Sun turns out to be strangely uniform at all latitudes in the heliosphere. Close to the visible surface of the Sun, the magnetic field is strongest over the poles, but this intensification disappears at Ulysses' distance. Apparently magnetic pressure in the solar wind averages out the differences in field strength. On the other hand Ulysses discovered unusually strong magnetic waves in the polar regions. Another surprise concerns unexpected connections between the polar and equatorial regions. Rhythmic variations in the intensity of energetic particles and cosmic rays, recorded by Ulysses at high latitudes, originate in effects of the Sun's rotation much closer to the equator. Scientists are debating how their picture of the magnetic field in the heliosphere must change, to make sense of the Ulysses observations. Without this new knowledge of the solar wind's behaviour, and its widespread effects, shocks felt in the Earth's vicinity would remain incomprehensible. For two centuries, sketchy links between sunspots, auroras and magnetic storms have puzzled scientists. Results from Ulysses and other solar spacecraft, including ESA's SOHO and Cluster II, are expected to transform human understanding of solar-terrestrial events. The task is urgent because astronauts and technological systems are becoming ever more vulnerable to the stormy Sun. After the quiet Sun, a peak of activity When Ulysses conducted the first-ever investigation of the high-latitude heliosphere, the Sun was quiet, being near the minimum of solar activity. As scientists expected, the circumstances were ideal for revealing the underlying structure of the Sun's atmosphere and the solar wind, in their simplest form. With the first phase of the voyage safely and very productively completed, Ulysses faces a new challenge, as it continues along its unique path. Obeying a cycle of roughly eleven years, the Sun is once again becoming restless as sunspot activity builds towards the next peak around 2000. When Ulysses revisits the polar regions at that time it will encounter conditions vastly different from those of 1994-95. The international mission of exploration has already given a new and thought-provoking view of the heliosphere. Its findings at solar maximum are guaranteed to do the same, and to give new insights into the gusts and shocks in the solar wind that affect the Earth most severely. "Gone will be the stable picture dominated by the fast solar wind," Richard Marsden predicts. "Most likely this will have been replaced by variability at all latitudes, with slow and fast wind streams jostling one another for prime position. But what exactly awaits Ulysses remains to be seen. Just like the first orbit, the second is truly a voyage into the unknown." Illustrations accompanying this release can be found at the following World Wide Web address: http://helio.estec.esa.nl/ulysses/artwork.html For more information, please contact : ESA Public Relations Division Tel : +33(0)1.53.69.71.55 Fax : +33(0)1.53.69.76.90 Richard Marsden Ulysses Project Scientist, ESTEC Tel : +31.(0)71.565.3583 Fax: +31(0)71.565.4697

CEP populations observed by ISEE 1

NASA Astrophysics Data System (ADS)

Whitaker, Katherine E.; Chen, Jiasheng; Fritz, Theodore A.

2006-12-01

Observations on October 30, 1978 show the ISEE 1 spacecraft passing though the high-altitude dayside northern cusp region from roughly 16:00 to 18:30 UT, during a slow solar wind period (~380 km/s). More than two orders of magnitude enhancements of the cusp energetic particle (CEP) fluxes are observed along with a depressed and turbulent local magnetic field and both ionospheric and solar wind plasma. The clock angle of the local magnetic field is different from that of the IMF, implying that the spacecraft was indeed inside the magnetosphere. The observed variations of the pitch angle distributions provide a unique opportunity to determine the structure of the cusp. The CEP fluxes were measured at about 8.5 hours MLT when the IMF had both an 8-10 nT duskward and southward component. The dawnside location of the cusp under these IMF conditions is unexpected by the existing models. No obvious time-energy dispersion is measured for the CEP fluxes. The time evolution of the phase space density as the spacecraft crossed the cusp boundary layer exhibits a positive gradient pointed to the high-altitude cusp, indicating a probable cusp source of the energetic particles. Through a careful analysis of the data available, we report the first detailed study of the equatorial orbiting ISEE 1 spacecraft passing through the high altitude cusp region.

Consequences of systematic model drift in DYNAMO MJO hindcasts with SP-CAM and CAM5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hannah, Walter M.; Maloney, Eric D.; Pritchard, Michael S.

Hindcast simulations of MJO events during the dynamics of the MJO (DYNAMO) field campaign are conducted with two models, one with conventional parameterization (CAM5) and a comparable model that utilizes superparameterization (SP–CAM). SP–CAM is shown to produce a qualitatively better reproduction of the fluctuations of precipitation and low–level zonal wind associated with the first two DYNAMO MJO events compared to CAM5. Interestingly, skill metrics using the real–time multivariate MJO index (RMM) suggest the opposite conclusion that CAM5 has more skill than SP–CAM. This inconsistency can be explained by a systematic increase of RMM amplitude with lead time, which results frommore » a drift of the large–scale wind field in SP–CAM that projects strongly onto the RMM index. CAM5 hindcasts exhibit a contraction of the moisture distribution, in which extreme wet and dry conditions become less frequent with lead time. SP–CAM hindcasts better reproduce the observed moisture distribution, but also have stronger drift patterns of moisture budget terms, such as an increase in drying by meridional advection in SP–CAM. This advection tendency in SP–CAM appears to be associated with enhanced off–equatorial synoptic eddy activity with lead time. In conclusion, systematic drift moisture tendencies in SP–CAM are of similar magnitude to intraseasonal moisture tendencies, and therefore are important for understanding MJO prediction skill.« less

Comparative In Situ Measurements of Plasma Instabilities in the Equatorial and Auroral Electrojets

NASA Technical Reports Server (NTRS)

Pfaff, Robert F.

2008-01-01

This presentation provides a comparison of in situ measurements of plasma instabilities gathered by rocket-borne probes in the equatorial and auroral electrojets. Specifically, using detailed measurements of the DC electric fields, current density, and plasma number density within the unstable daytime equatorial electrojet from Brazil (Guara Campaign) and in the auroral electrojet from Sweden (ERRIS Campaign), we present comparative observations and general conclusions regarding the observed physical properties of Farley-Buneman two-stream waves and large scale, gradient drift waves. The two stream observations reveal coherent-like waves propagating near the E x B direction but at reduced speeds (nearer to the presumed acoustic velocity) with wavelengths of approximately 5-10m in both the equatorial and auroral electrojet, as measured using the spaced-receiver technique. The auroral electrojet data generally shows extensions to shorter wavelengths, in concert with the fact that these waves are driven harder. With respect to gradient-drift driven waves, observations of this instability are much more pronounced in the equatorial electrojet, given the more favorable geometry for growth provided by the vertical gradient and horizontal magnetic field lines. We present new analysis of Guara rocket observations of electric field and plasma density data that reveal considerable structuring in the middle and lower portion of the electrojet (90-105 km) where the ambient plasma density gradient is unstable. Although the electric field amplitudes are largest (approximately 10-15 mV/m) in the zonal direction, considerable structure (approximately 5-10 mV/m) is also observed in the vertical electric field component as well, implying that the dominant large scale waves involve significant vertical interaction and coupling within the narrow altitude range where they are observed. Furthermore, a detailed examination of the phase of the waveforms show that on some, but not all occasions, locally enhanced eastward fields are associated with locally enhanced upwards (polarization) electric fields. The measurements are discussed in terms of theories involving the non-linear evolution and structuring of plasma waves.

The storm-time equatorial electrojet

NASA Technical Reports Server (NTRS)

Burrows, K.; Sastry, T. S. G.; Sampath, S.; Stolarik, J. D.; Usher, M. J.

1977-01-01

A Petrel rocket carrying a double cell rubidium magnetometer was launched from the Thumba Equatorial Rocket Launching Station during the early main phase of a magnetic storm. No ionospheric currents associated with the storm were observed, and the large field depression at the flight time must therefore be attributed to currents at higher altitudes. The equatorial enhancement of ionospheric magnetic storm currents, predicted on the basis of theory and earlier ground data, was not observed.

The storm-time equatorial electrojet

NASA Technical Reports Server (NTRS)

Burrows, K.; Sastry, T. S. G.; Sampath, S.; Stolarik, J. D.; Usher, M. J.

1976-01-01

A Petrel rocket carrying a double cell rubidium magnetometer was launched from the Thumba Equatorial Rocket Launching Station during the early main phase of a magnetic storm. No ionospheric currents associated with the storm were observed and the large field depression, at the flight time, must therefore be attributed to currents at higher altitudes. The equatorial enhancement of ionospheric magnetic storm currents, predicted on the basis of theory and earlier ground data, was not observed.

Effects of convection electric field on the distribution of ring current type protons

NASA Technical Reports Server (NTRS)

Grebowsky, J. M.; Chen, A. J.

1975-01-01

The topology of the boundaries of penetration (or, inversely, the boundaries of the forbidden regions) of 90-deg pitch-angle equatorial protons with energies less than 100 keV are explored for an equatorial convection E-field which is directed in general from dawn to dusk. Due to the dependence of drift path on energy (or magnetic moment), complex structural features are expected in the proton energy spectra detected by satellites since the penetration distance of a proton is not a monotonically increasing or decreasing function of energy. During a storm when the convection E is enhanced, model calculations predict elongations of the forbidden regions analogous to tail extensions of the plasmasphere. Following a reduction in the convection field, spiral-structured forbidden regions can occur. Structural features inherent to large-scale convection field changes may be seen in the nose-like proton spectrograms observed near dusk by instrumentation on Explorer 45. These nose events are modelled by using an electric field model developed originally by Volland (1973). The strength of the field is related to the Kp index through night-time equatorial plasmapause measurements.

Effects of subsurface ocean dynamics on instability waves in the tropical Pacific

NASA Astrophysics Data System (ADS)

Lawrence, Sean P.; Allen, Myles R.; Anderson, David L. T.; Llewellyn-Jones, David T.

1998-08-01

Tropical instability waves in a primitive equation model of the tropical Pacific Ocean, forced with analyzed wind stresses updated daily, show unexpectedly close phase correspondence with observation through the latter half of 1992. This suggests that these waves are not pure instabilities developing from infinitesimal disturbances, but that their phases and phase speeds are at least partially determined by the wind stress forcing. To quantify and explain this observation, we perfomed several numerical experiments, which indicate that remotely forced Rossby waves can influence both the phase and phase speed of tropical instability waves. We suggest that a remote wind forcing determines the high model/observation phase correspondence of tropical instability waves through a relatively realistic simulation of equatorial Kelvin and Rossby wave activity.

How does an asymmetric magnetic field change the vertical structure of a hot accretion flow?

NASA Astrophysics Data System (ADS)

Samadi, M.; Abbassi, S.; Lovelace, R. V. E.

2017-09-01

This paper explores the effects of large-scale magnetic fields in hot accretion flows for asymmetric configurations with respect to the equatorial plane. The solutions that we have found show that the large-scale asymmetric magnetic field can significantly affect the dynamics of the flow and also cause notable outflows in the outer parts. Previously, we treated a viscous resistive accreting disc in the presence of an odd symmetric B-field about the equatorial plane. Now, we extend our earlier work by taking into account another configuration of large-scale magnetic field that is no longer symmetric. We provide asymmetric field structures with small deviations from even and odd symmetric B-field. Our results show that the disc's dynamics and appearance become different above and below the equatorial plane. The set of solutions also predicts that even a small deviation in a symmetric field causes the disc to compress on one side and expand on the other. In some cases, our solution represents a very strong outflow from just one side of the disc. Therefore, the solution may potentially explain the origin of one-sided jets in radio galaxies.

A Strong High Altitude Narrow Jet At Saturn'S Equator From Cassini/ISS Images

NASA Astrophysics Data System (ADS)

Garcia-Melendo, Enrique; Sánchez-Lavega, A.; Legarreta, J.; Pérez-Hoyos, S.; Hueso, R.

2010-10-01

The intense equatorial eastward jets observed at cloud level in Jupiter and Saturn, represent a major challenge for geophysical fluid dynamics. Saturn's equatorial jet is of particular interest in view of its three dimensional structure, suspected large temporal variability, and related stratospheric semiannual oscillation. Here we report the discovery at the upper cloud level of an extremely narrow and strong jet centered in the middle of the broad equatorial jet. Previously published works on Saturn's equatorial winds at cloud level provided only a partial coverage. Automatic correlation of brightness scans and manually tracked cloud features, retrieved from images obtained by the Cassini Imaging Science Subsystem (ISS), show that the jet reaches 430 ms-1 with a peak speed difference of 180 ms-1 relative to nearby latitudes at 60 mbar and 390 ms-1 at depths > 500 mbar. Images were obtained in two filters: MT3, centred at the 889nm strong methane absorption band, and CB3 centred at the near infrared 939nm continuum, which are sensitive to different altitude levels at the upper clouds and hazes. Contrarily to what is observed in other latitudes, its velocity increases with altitude. Our findings helps to extend the view we have of the equatorial stratospheric dynamics of fast rotating planets beyond the best known terrestrial environment, and extract more general consequences of the interaction between waves and mean flow. It remains to be known if this equatorial jet structure, now determined in detail in three dimensions, is permanent or variable with the seasonal solar insolation cycle, including the variable shadow cast by the rings. EGM, ASL, JL, SPH, and RH have been funded by the Spanish MICIIN AYA2009-10701 with FEDER support and ASL, JL, SPH, and RH by Grupos Gobierno Vasco IT-464-07

Anomalous behaviors of Wyrtki Jets in the equatorial Indian Ocean during 2013

PubMed Central

Duan, Yongliang; Liu, Lin; Han, Guoqing; Liu, Hongwei; Yu, Weidong; Yang, Guang; Wang, Huiwu; Wang, Haiyuan; Liu, Yanliang; Zahid; Waheed, Hussain

2016-01-01

In-situ measurement of the upper ocean velocity discloses significant abnormal behaviors of two Wyrtki Jets (WJs) respectively in boreal spring and fall, over the tropical Indian Ocean in 2013. The two WJs both occurred within upper 130 m depth and persisted more than one month. The exceptional spring jet in May was unusually stronger than its counterpart in fall, which is clearly against the previous understanding. Furthermore, the fall WJ in 2013 unexpectedly peaked in December, one month later than its climatology. Data analysis and numerical experiments illustrate that the anomalous changes in the equatorial zonal wind, associated with the strong intra-seasonal oscillation events, are most likely the primary reason for such anomalous WJs activities. PMID:27436723

Stationary equatorial MHD flows in general relativity

NASA Astrophysics Data System (ADS)

Daigne, F.; Drenkhahn, G.

2002-01-01

We derive a new formulation of the fully general relativistic equations describing a stationary equatorial MHD outflow from a rotating central object. The wind solution appears as a level contour of a ``Bernoulli'' function fixed by the requirements that it must pass through the slow and fast critical points. This approach is the general relativistic extension to the classical treatment of Sakurai (\\cite{sakurai:85}). We discuss in details how the efficiency of the magnetic to kinetic energy conversion depends mainly on the geometry of the flux tubes and show that the magnetic acceleration can work very well under some conditions. We show how this tool can be used for the study of several astrophysical phenomena, among which gamma-ray bursts.

A new data-based model of the global magnetospheric B-field: Modular structure, parameterization, first results.

NASA Astrophysics Data System (ADS)

Tsyganenko, Nikolai

2013-04-01

A new advanced model of the dynamical geomagnetosphere is presented, based on a large set of data from Geotail, Cluster, Polar, and Themis missions, taken during 138 storm events with SYM-H from -40 to -487nT over the period from 1996 through 2012 in the range of geocentric distances from ~3Re to ~60Re. The model magnetic field is confined within a realistic magnetopause, based on Lin et al. [JGRA, v.115, A04207, 2010] empirical boundary, driven by the dipole tilt angle, solar wind pressure, and IMF Bz. The magnetic field is modeled as a flexible combination of several modules, representing contributions from principal magnetospheric current systems such as the symmetric and partial ring currents (SRC/PRC), Region 1 and 2 field-aligned currents (FAC), and the equatorial tail current sheet (TCS). In the inner magnetosphere the model field is dominated by contributions from the SRC and PRC, derived from realistic particle pressure models and represented by four modules, providing variable degree of dawn-dusk and noon-midnight asymmetry. The TCS field is comprised of several independent modules, ensuring sufficient flexibility of the model field and correct asymptotic values in the distant tail. The Region 2 FAC is an inherent part of the PRC, derived from the continuity of the azimuthal current. The Region 1 FAC is modulated by the diurnal and seasonal variations of the dipole tilt angle, in agreement with earlier statistical studies [Ohtani et al., JGRA, v.110, A09230, 2005]. Following the approach introduced in our earlier TS05 model [Tsyganenko and Sitnov, JGRA, v.110, A03208, 2005], contributions from all individual field sources are parameterized by the external driving functions, derived from the solar wind/IMF OMNI database as solutions of dynamic equations with source and loss terms in the right-hand side. Global magnetic configurations and their evolution during magnetospheric storms are analyzed and discussed in context of the model results.

Anomalous meridional thermospheric neutral winds in the AE-E NATE data: Effects of the equatorial nighttime pressure bulge

NASA Technical Reports Server (NTRS)

Goembel, L.; Herrero, F. A.

1995-01-01

The work described here makes it possible to identify anomalous wind behavior such as the nighttime meridional wind abatements that occur at F-region heights. A new analysis technique uses a simple empirical wind model to simulate measurements of 'normal' winds (as measured by the Neutral Atmosphere and Temperature Experiment (NATE) that flew on the Atmosphere Explorer-E (AE-E)) to highlight anomalous wind measurements made by the satellite while in circular orbits at 270-290 km altitude. Our approach is based on the recognition that the 'in orbit' wind variation must show the combined effects of the diurnal wind variation as seen from the ground with the latitude variation of the satellite orbit. For the data period 77250-78035 examined thus far, the wind abatement always occurred with a corresponding pressure or temperature maximum, and was detected on 12 out of the 36 nights with data. This study has revealed that the wind abatement occur only during or shortly after increases in solar extreme ultraviolet (EUV) flux, as indicated by daily radio flux measurements. In the past, nighttime wind reversals at mid-latitudes have been associated with increased geomagnetic activity. This study indicates that intensified solar EUV heating may be responsible for anomalous thermospheric nighttime winds at mid-latitudes.

ROCSAT and HF Doppler sounder observations of the DP2-type electric field during the global Pc5 magnetic pulsation event

NASA Astrophysics Data System (ADS)

Hashimoto, K. K.; Kikuchi, T.; Nagatsuma, T.; Tomizawa, I.

2016-12-01

During the stormtime Pc5 magnetic pulsations on 31 October 2003, we detected large amplitude oscillations in the ionospheric electric field with the HF Doppler sounders at midlatitude for 10 hours from 11 to 21 LT. Similar oscillations were recorded on the magnetometer data at high-to-equatorial latitudes with significant amplitude enhancement at the dayside equator. We deduced the equatorial electrojet (EEJ) by subtracting the low latitude Pc5 from the equatorial Pc5 and found that the midlatitude electric field (EF) is well correlated with the EEJ with correlation coefficients (0.80-0.95) and that the EEJ to EF ratio reached maximum at 11 LT and dramatically decreased until 18 LT in a function of cos0.6(solar zenith angle). With these observations, we suggest that the midlatitude electric field (EF) is associated with the DP2 type ionospheric currents transmitted from high latitude to the equator. It is to be noted that the EF is well correlated with the EEJ during the night after 18 LT, indicating that the Pc5 electric field is so strong as to drive equatorial electrojet in the nighttime ionosphere. Using the electric field measured by ROCSAT-1/IPEI, we confirmed that the Pc5 electric field in the mid- and low-latitude ionosphere is comparable to or even stronger than those observed by the HF Doppler sounders. High correlations between the ground- and satellite-based observations over 15 minutes indicate that the Pc5 electric field distribute uniform over 6500 km along the ROCSAT orbit which is consistent with the large-scale DP2 electric field.

On the vertical wind shear of Saturn's Equatorial Jet at cloud level

NASA Astrophysics Data System (ADS)

Sánchez-Lavega, A.; Pérez-Hoyos, S.

2005-08-01

With the aim of retrieving the altitude of cloud features used as zonal wind tracers in Saturn's atmosphere, we have reanalyzed three different sets of photometric and calibrated data corresponding to the Voyager epoch 1979-1981 (ground-based in 1979, Voyager 2 PPS and ISS observations in 1981), and we have analyze a new set of Hubble Space Telescope images for 2004. This analysis is put in the perspective of our previous HST study for 1994-2003 (Pérez-Hoyos et al., Icarus, 176, 155. 2005). A common result is found that the individual cloud tracers are embedded within a variable tropospheric haze. According to our models, the Voyager 2 ISS images locate the cloud tracers moving with zonal velocities of 455 to 465 (± 2) m/s at a pressure level of 360 ± 140 mbar. For HST observations, the cloud tracers moving with zonal wind speeds of 280 ± 10 m/s, locate at a pressure level of about 50 ± 10 mbar. All these values are calculated in the latitude 3 deg North. The speed difference, if interpreted as a vertical wind shear (Porco et al., Science, 307, 1226. 2005), requires a change of 90 m/s per scale height, two times greater than that estimated from Cassini CIRS data (Flasar et al., Science, 307, 1247, 2005). We also perform an initial guess on Cassini ISS vertical sounding levels, retrieving values compatible with the HST ones but not with Voyager wind measurements. We conclude that the wind speed velocity differences measured between 1979-81 and 2004 in the upper troposphere cannot be solely explained as a wind shear effect and demand dynamical processes. We discuss the possible action of Rossby waves or an intrinsic circulation change in the ammonia cloud layer and above, following a large period of equatorial storm activity. Acknowledgments: This work was supported by MCYT AYA2003-03216, FEDER, and Grupos UPV 15946/2004. S.P.-H. acknowledges a PhD fellowship from the Spanish MEC and R. H. a post-doc contract from Gobierno Vasco.

Equatorial Annual Oscillation with QBO-driven 5-year Modulation in NCEP Data

NASA Technical Reports Server (NTRS)

Mayr, H. G.; Mengel, J. G.; Huang, F. T.; Nash, E. R.

2007-01-01

An analysis is presented of the zonal wind and temperature variations supplied by the National Center for Environmental Prediction (NCEP), which have been assimilated in the Reanalysis and the Climate Prediction Center (CCP) data sets. The derived zonal-mean variations are employed. Stimulated by modeling studies, the data are separated into the hemispherically symmetric and anti-symmetric components, and spectral analysis is applied to study the annual 12-month oscillation and Quasi-biennial Oscillation (QBO). For data samples that cover as much as 40 years, the results reveal a pronounced 5-year modulation of the symmetric AO in the lower stratosphere, which is confined to equatorial latitudes. This modulation is also inferred for the temperature variations but extends to high latitudes, qualitatively consistent with published model results. A comparison between different data samples indicates that the signature of the 5-year oscillation is larger when the QBO of 30 months is more pronounced. Thus there is circumstantial evidence that this periodicity of the QBO is involved in generating the oscillation. The spectral analysis shows that there is a weak anti-symmetric 5-year oscillation in the zonal winds, which could interact with the large antisymmetric A0 to produce the modulation of the symmetric AO as was shown in earlier modeling studies. According to these studies, the 30-month QBO tends to be synchronized by the equatorial Semi-annual Oscillation (SAO), and this would explain why the inferred 5-year modulation is observed to persist and is phase locked over several cycles.

The Role of Solar Wind Structures in the Generation of ULF Waves in the Inner Magnetosphere

NASA Astrophysics Data System (ADS)

Alves, L. R.; Souza, V. M.; Jauer, P. R.; da Silva, L. A.; Medeiros, C.; Braga, C. R.; Alves, M. V.; Koga, D.; Marchezi, J. P.; de Mendonça, R. R. S.; Dallaqua, R. S.; Barbosa, M. V. G.; Rockenbach, M.; Dal Lago, A.; Mendes, O.; Vieira, L. E. A.; Banik, M.; Sibeck, D. G.; Kanekal, S. G.; Baker, D. N.; Wygant, J. R.; Kletzing, C. A.

2017-07-01

The plasma of the solar wind incident upon the Earth's magnetosphere can produce several types of geoeffective events. Among them, an important phenomenon consists of the interrelation of the magnetospheric-ionospheric current systems and the charged-particle population of the Earth's Van Allen radiation belts. Ultra-low-frequency (ULF) waves resonantly interacting with such particles have been claimed to play a major role in the energetic particle flux changes, particularly at the outer radiation belt, which is mainly composed of electrons at relativistic energies. In this article, we use global magnetohydrodynamic simulations along with in situ and ground-based observations to evaluate the ability of two different solar wind transient (SWT) events to generate ULF (few to tens of mHz) waves in the equatorial region of the inner magnetosphere. Magnetic field and plasma data from the Advanced Composition Explorer (ACE) satellite were used to characterize these two SWT events as being a sector boundary crossing (SBC) on 24 September 2013, and an interplanetary coronal mass ejection (ICME) in conjunction with a shock on 2 October 2013. Associated with these events, the twin Van Allen Probes measured a depletion of the outer belt relativistic electron flux concurrent with magnetic and electric field power spectra consistent with ULF waves. Two ground-based observatories apart in 90°C longitude also showed evidence of ULF-wave activity for the two SWT events. Magnetohydrodynamic (MHD) simulation results show that the ULF-like oscillations in the modeled electric and magnetic fields observed during both events are a result from the SWT coupling to the magnetosphere. The analysis of the MHD simulation results together with the observations leads to the conclusion that the two SWT structures analyzed in this article can be geoeffective on different levels, with each one leading to distinct ring current intensities, but both SWTs are related to the same disturbance in the outer radiation belt, i.e. a dropout in the relativistic electron fluxes. Therefore, minor disturbances in the solar wind parameters, such as those related to an SBC, may initiate physical processes that are able to be geoeffective for the outer radiation belt.

Dual-band beacon experiment over Southeast Asia for ionospheric irregularity analysis

NASA Astrophysics Data System (ADS)

Watthanasangmechai, K.; Yamamoto, M.; Saito, A.; Saito, S.; Maruyama, T.; Tsugawa, T.; Nishioka, M.

2013-12-01

An experiment of dual-band beacon over Southeast Asia was started in March 2012 in order to capture and analyze ionospheric irregularities in equatorial region. Five GNU Radio Beacon Receivers (GRBRs) were aligned along 100 degree geographic longitude. The distances between the stations reach more than 500 km. The field of view of this observational network covers +/- 20 degree geomagnetic latitude including the geomagnetic equator. To capture ionospheric irregularities, the absolute TEC estimation technique was developed. The two-station method (Leitinger et al., 1975) is generally accepted as a suitable method to estimate TEC offsets of dual-band beacon experiment. However, the distances between the stations directly affect on the robustness of the technique. In Southeast Asia, the observational network is too sparse to attain a benefit of the classic two-station method. Moreover, the least-squares approch used in the two-station method tries too much to adjust the small scales of the TEC distribution which are the local minima. We thus propose a new technique to estimate the TEC offsets with the supporting data from absolute GPS-TEC from local GPS receivers and the ionospheric height from local ionosondes. The key of the proposed technique is to utilize the brute-force technique with weighting function to find the TEC offset set that yields a global minimum of RMSE in whole parameter space. The weight is not necessary when the TEC distribution is smooth, while it significantly improves the TEC estimation during the ESF events. As a result, the latitudinal TEC shows double-hump distribution because of the Equatorial Ionization Anomaly (EIA). In additions, the 100km-scale fluctuations from an Equatorial Spread F (ESF) are captured at night time in equinox seasons. The plausible linkage of the meridional wind with triggering of ESF is under invatigating and will be presented. The proposed method is successful to estimate the latitudinal TEC distribution from dual-band frequency beacon data for the sparse observational network in Southeast Asia which may be useful for other equatorial sectors like Affrican region as well.

Jet formation and equatorial superrotation in Jupiter's atmosphere: Numerical modelling using a new efficient parallel code

NASA Astrophysics Data System (ADS)

Rivier, Leonard Gilles

Using an efficient parallel code solving the primitive equations of atmospheric dynamics, the jet structure of a Jupiter like atmosphere is modeled. In the first part of this thesis, a parallel spectral code solving both the shallow water equations and the multi-level primitive equations of atmospheric dynamics is built. The implementation of this code called BOB is done so that it runs effectively on an inexpensive cluster of workstations. A one dimensional decomposition and transposition method insuring load balancing among processes is used. The Legendre transform is cache-blocked. A "compute on the fly" of the Legendre polynomials used in the spectral method produces a lower memory footprint and enables high resolution runs on relatively small memory machines. Performance studies are done using a cluster of workstations located at the National Center for Atmospheric Research (NCAR). BOB performances are compared to the parallel benchmark code PSTSWM and the dynamical core of NCAR's CCM3.6.6. In both cases, the comparison favors BOB. In the second part of this thesis, the primitive equation version of the code described in part I is used to study the formation of organized zonal jets and equatorial superrotation in a planetary atmosphere where the parameters are chosen to best model the upper atmosphere of Jupiter. Two levels are used in the vertical and only large scale forcing is present. The model is forced towards a baroclinically unstable flow, so that eddies are generated by baroclinic instability. We consider several types of forcing, acting on either the temperature or the momentum field. We show that only under very specific parametric conditions, zonally elongated structures form and persist resembling the jet structure observed near the cloud level top (1 bar) on Jupiter. We also study the effect of an equatorial heat source, meant to be a crude representation of the effect of the deep convective planetary interior onto the outer atmospheric layer. We show that such heat forcing is able to produce strong equatorial superrotating winds, one of the most striking feature of the Jovian circulation.

Plasma pressure distribution in the surrounding the Earth plasma ring and its role in the magnetospheric dynamics

NASA Astrophysics Data System (ADS)

Antonova, E. E.; Kirpichev, I. P.; Stepanova, M. V.

2014-08-01

We analyzed the characteristics of the plasma region surrounding the Earth at the geocentric distances between 6 and 15RE using the data of THEMIS mission from April 2007 to September 2012. The obtained averaged distributions of plasma pressure, of pressure anisotropy, and of magnetic field near the equatorial plane showed the presence of a ring-shaped structure surrounding the Earth. It was found that for quiet geomagnetic conditions the plasma pressure is nearly isotropic for all magnetic local times at geocentric distances >6RE. Taking into consideration that the minimal values of the magnetic field at the field lines near noon are shifted from the equatorial plane, we estimate the value of plasma beta parameter in the region of minimal values of the magnetic field using the Tsyganenko-2001 magnetic field model. It was found that the values of plasma beta parameter are of the order of unity for the nightside part of the ring-shaped structure in the equatorial plane and for the region of minimal values of the magnetic field in the dayside, indicating that the ring-shaped structure should play an active role in the magnetic field distortion. Comparison of obtained distribution of plasma pressure at the equatorial plane with the values of plasma pressure at low altitudes, showed that the considerable part of the auroral oval can be mapped into the analyzed plasma ring. The role of the high-beta plasma ring surrounding the Earth for Earth-Sun System disturbances is discussed.

Structure and sources of solar wind in the growing phase of 24th solar cycle

NASA Astrophysics Data System (ADS)

Slemzin, Vladimir; Goryaev, Farid; Shugay, Julia; Rodkin, Denis; Veselovsky, Igor

2015-04-01

We present analysis of the solar wind (SW) structure and its association with coronal sources during the minimum and rising phase of 24th solar cycle (2009-2011). The coronal sources prominent in this period - coronal holes, small areas of open magnetic fields near active regions and transient sources associated with small-scale solar activity have been investigated using EUV solar images and soft X-ray fluxes obtained by the CORONAS-Photon/TESIS/Sphinx, PROBA2/SWAP, Hinode/EIS and AIA/SDO instruments as well as the magnetograms obtained by HMI/SDO. It was found that at solar minimum (2009) velocity and magnetic field strength of high speed wind (HSW) and transient SW from small-scale flares did not differ significantly from those of the background slow speed wind (SSW). The major difference between parameters of different SW components was seen in the ion composition represented by the C6/C5, O7/O6, Fe/O ratios and the mean charge of Fe ions. With growing solar activity, the speed of HSW increased due to transformation of its sources - small-size low-latitude coronal holes into equatorial extensions of large polar holes. At that period, the ion composition of transient SW changed from low-temperature to high-temperature values, which was caused by variation of the source conditions and change of the recombination/ionization rates during passage of the plasma flow through the low corona. However, we conclude that criteria of separation of the SW components based on the ion ratios established earlier by Zhao&Fisk (2009) for higher solar activity are not applicable to the extremely weak beginning of 24th cycle. The research leading to these results has received funding from the European Commission's Seventh Framework Programme (FP7/2007-2013) under the grant agreement eHeroes (project n° 284461, www.eheroes.eu).

The Angola Current and its seasonal variability as observed at 11°S

NASA Astrophysics Data System (ADS)

Kopte, Robert; Brandt, Peter; Dengler, Marcus; Claus, Martin; Greatbatch, Richard J.

2016-04-01

The eastern boundary circulation off the coast of Angola has been described only sparsely to date. The region off Angola, which connects the equatorial Atlantic and the Angola-Benguela upwelling regime, is of particular interest to understand the relative importance of transient equatorial versus local forcing of the observed variability in the coastal upwelling region. For the first time multi-year velocity observations of the Angola Current at 11°S are available. From July 2013 to November 2015 a bottom shield equipped with an ADCP had been deployed at 500m water depth, accompanied by a mooring sitting on the 1200m-isobath with an ADCP being installed at 500m depth. Both upward-looking instruments measured the current speed up to about 50m below the sea surface. During the deployment period the Angola Current was characterized by a weak southward mean flow of 5-8 cm/s at 50m depth (slightly stronger at the in-shore mooring position), with the southward current penetrating down to about 200m depth. The alongshore velocity component reveals a pronounced seasonal variability. It is dominated by 120-day, semi-annual, and annual oscillations with distinct baroclinic structures. Here we apply a reduced gravity model of the tropical Atlantic for the first five baroclinic modes forced with interannually varying wind stress to investigate the seasonal variability along the equatorial and coastal waveguides. In the equatorial Atlantic the 120-day, semi-annual, and annual oscillations are associated with resonant basin modes of the 1st, 2nd, and 4th baroclinic mode, respectively. These basin modes are composed of equatorial Kelvin and Rossby waves as well as coastally trapped waves. The reduced gravity model is further used to study the respective role of the remote equatorial forcing, more specifically the influence of equatorial basin modes via coastally trapped waves, and the local forcing for the observed seasonal variability and associated baroclinic structure of the Angola Current at 11°S.

Methane at Ascension Island, southern tropical Atlantic Ocean: continuous ground measurement and vertical profiling above the Trade-Wind Inversion

NASA Astrophysics Data System (ADS)

Lowry, David; Brownlow, Rebecca; Fisher, Rebecca; Nisbet, Euan; Lanoisellé, Mathias; France, James; Thomas, Rick; Mackenzie, Rob; Richardson, Tom; Greatwood, Colin; Freer, Jim; Cain, Michelle; Warwick, Nicola; Pyle, John

2015-04-01

Methane mixing ratios have been rising rapidly worldwide since 2007. At Ascension Island (8oS in the equatorial Atlantic), a sustained rise has occurred. Prior to 2010, growth was comparable to other regions, but in 2010-11, during a strong la Nina event, the increase was 10ppb year-on-year. Reduced growth followed in 2011-12, but in 2012-13 strong growth resumed and continues. This rise has been accompanied by a shift to lighter δ13CCH4 values in 2010-11 in the equatorial tropics. The most likely cause of this shift is emissions from isotopically 'light' biological sources in the equatorial and savanna tropics. Ascension Island is in the Trade Wind belt of the tropical Atlantic, perfectly located to measure the South Atlantic marine boundary layer. The SE Trade Winds are almost invariant, derived from the deep South Atlantic and with little contact with Africa. However, above the Trade Wind Inversion (TWI) at about 1200-2000m asl, the air masses are very different, coming dominantly from tropical Africa and occasionally S. America. Depending on season, air above the TWI is sourced from the African southern savanna grasslands or the equatorial wetlands of Congo and Uganda, with inputs of air also from southern tropical S. America (Brazil, Paraguay, Bolivia). African methane sources are a major contributor to the global methane budget, but although local campaign studies have been made, African emissions are not well studied in bulk. In September 2014, an octocopter was used to retrieve air samples from heights up to 2700m asl on Ascension (see Thomas, R. et al, this volume). This allowed sampling through the marine boundary layer, across the TWI cloud layer, and into the mid-troposphere. Samples were collected in part-filled 5L Tedlar bags, which were analysed for CH4 concentration using Royal Holloway's Picarro 1301 CRDS system at the Met Office, Ascension. This has high precision and accuracy, with a 6-gas calibration suite. Bags were then analysed in the UK for δ13CCH4. The marine boundary layer at the surface has CH4 mixing ratios below 1800ppb. In the mixing layer of the TWI, values increase, and above 2000m, methane is above 1820ppb. Back trajectory analysis shows that these inputs are from African savanna and wetland emissions. After vertical mixing events the difference across the TWI reduces to less than 10ppb. The experiment has demonstrated the feasibility of UAV work to observe methane at Ascension. In effect, Ascension becomes a 'virtual mountain observatory' - measurements here can both use the Trade Winds to monitor the wide South Atlantic and Southern Ocean, and also the air above the TWI to assess inputs from tropical Africa and S. America. Comparison of continuous ground measurements, vertical UAV profiles and data from the Ascension TCCON site, potentially allows observation of a complete atmospheric profile. Acknowledgement This work is supported by the Natural Environment Research Council Grant NE/K005979/1

3D ELECTRON DENSITY DISTRIBUTIONS IN THE SOLAR CORONA DURING SOLAR MINIMA: ASSESSMENT FOR MORE REALISTIC SOLAR WIND MODELING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patoul, Judith de; Foullon, Claire; Riley, Pete, E-mail: j.depatoul@exeter.ac.uk, E-mail: c.foullon@exeter.ac.uk, E-mail: rileype@saic.com

Knowledge of the electron density distribution in the solar corona put constraints on the magnetic field configurations for coronal modeling and on initial conditions for solar wind modeling. We work with polarized SOHO/LASCO-C2 images from the last two recent minima of solar activity (1996–1997 and 2008–2010), devoid of coronal mass ejections. The goals are to derive the 4D electron density distributions in the corona by applying a newly developed time-dependent tomographic reconstruction method and to compare the results between the two solar minima and with two magnetohydrodynamic models. First, we confirm that the values of the density distribution in thermodynamic models aremore » more realistic than in polytropic ones. The tomography provides more accurate distributions in the polar regions, and we find that the density in tomographic and thermodynamic solutions varies with the solar cycle in both polar and equatorial regions. Second, we find that the highest-density structures do not always correspond to the predicted large-scale heliospheric current sheet or its helmet streamer but can follow the locations of pseudo-streamers. We deduce that tomography offers reliable density distributions in the corona, reproducing the slow time evolution of coronal structures, without prior knowledge of the coronal magnetic field over a full rotation. Finally, we suggest that the highest-density structures show a differential rotation well above the surface depending on how they are magnetically connected to the surface. Such valuable information on the rotation of large-scale structures could help to connect the sources of the solar wind to their in situ counterparts in future missions such as Solar Orbiter and Solar Probe Plus.« less

HUBBLE VIEWS THE GALILEO PROBE ENTRY SITE ON JUPITER

NASA Technical Reports Server (NTRS)

2002-01-01

[left] - This Hubble Space Telescope image of Jupiter was taken on Oct. 5, 1995, when the giant planet was at a distance of 534 million miles (854 million kilometers) from Earth. The arrow points to the predicted site at which the Galileo Probe will enter Jupiter's atmosphere on December 7, 1995. At this latitude, the eastward winds have speeds of about 250 miles per hour (110 meters per second). The white oval to the north of the probe site drifts westward at 13 miles per hour (6 meters per second), rolling in the winds which increase sharply toward the equator. The Jupiter image was obtained with the high resolution mode of Hubble's Wide Field Planetary Camera 2 (WFPC2). Because the disk of the planet is larger than the field of view of the camera, image processing was used to combine overlapping images from three consecutive orbits to produce this full disk view of the planet. [right] - These four enlarged Hubble images of Jupiter's equatorial region show clouds sweeping across the predicted Galileo probe entry site, which is at the exact center of each frame (a small white dot has been inserted at the centered at the predicted entry site). The first image (upper left quadrant) was obtained with the WFPC2 on Oct. 4, 1995 at (18 hours UT). The second, third and fourth images (from upper right to lower right) were obtained 10, 20 and 60 hours later, respectively. The maps extend +/- 15 degrees in latitude and longitude. The distance across one of the images is about three Earth diameters (37,433 kilometers). During the intervening time between the first and fourth maps, the winds have swept the clouds 15,000 miles (24,000 kilometers) eastward. Credit: Reta Beebe (New Mexico State University), and NASA

3D electron density distributions in the solar corona during solar minima: assessment for more realistic solar wind modeling

NASA Astrophysics Data System (ADS)

de Patoul, J.; Foullon, C.; Riley, P.

2015-12-01

Knowledge of the electron density distribution in the solar corona put constraints on the magnetic field configurations for coronal modeling, and on initial conditions for solar wind modeling. We work with polarized SOHO/LASCO-C2 images from the last two recent minima of solar activity (1996-1997 and 2008-2010), devoid of coronal mass ejections. We derive the 4D electron density distributions in the corona by applying a newly developed time-dependent tomographic reconstruction method. First we compare the density distributions obtained from tomography with magnetohydrodynamic (MHD) solutions. The tomography provides more accurate distributions of electron densities in the polar regions, and we find that the observed density varies with the solar cycle in both polar and equatorial regions. Second, we find that the highest-density structures do not always correspond to the predicted large-scale heliospheric current sheet or its helmet streamer but can follow the locations of pseudo-streamers. We conclude that tomography offers reliable density distribution in the corona, reproducing the slow time evolution of coronal structures, without prior knowledge of the coronal magnetic field over a full rotation. Finally, we suggest that the highest-density structures show a differential rotation well above the surface depending on how it is magnetically connected to the surface. Such valuable information on the rotation of large-scale structures could help to connect the sources of the solar wind to their in-situ counterparts in future missions such as Solar Orbiter and Solar Probe Plus. This research combined with the MHD coronal modeling efforts has the potential to increase the reliability for future space weather forecasting.

Control of tropical instability waves in the Pacific

NASA Astrophysics Data System (ADS)

Allen, M. R.; Lawrence, S. P.; Murray, M. J.; Mutlow, C. T.; Stockdale, T. N.; Llewellyn-Jones, D. T.; Anderson, D. L. T.

Westward-propagating waves with periods of 20-30 days and wavelengths of ˜ 1,100km are a prominent feature of sea-surface temperatures (SSTs) in the equatorial Pacific and Atlantic Oceans. They have been attributed to instabilities due to current shear. We compare SST observations from the spaceborne Along Track Scanning Radiometer (ATSR) and TOGA-TAO moored buoys with SSTs from a model of the tropical Pacific forced with observed daily windstress data. The phases of the strongest “Tropical Instability Waves” (TIWs) in the model are in closer correspondence with those observed than we would expect if these waves simply developed from infinitesimal disturbances (in which case their phases would be arbitrary). If we filter out the intraseasonal component of the windstress, all phase-correspondence is lost. We conclude that the phases of these waves are not arbitrary, but partially determined by the intraseasonal winds. The subsurface evolution of the model suggests a possible control mechanism is through interaction with remotely-forced subsurface Kelvin and Rossby waves. This is supported by an experiment which shows how zonal wind bursts in the west Pacific can modify the TIW field, but other mechanisms, such as local feedbacks, are also possible.

Electron Injections Caused by a Dipolarization Flux Bundle

NASA Astrophysics Data System (ADS)

Kabin, K.; Kalugin, G. A.; Donovan, E.; Spanswick, E.

2017-12-01

We study electron injections caused by an earthward propagating electromagnetic pulse. The background magnetic field model is fully three-dimensional and includes the day-night asymmetry, however, the field lines are contained in the meridional planes. The transient pulse fields, which are prescribed analytically, are also three-dimensional. We study electron energization as a function of the initial radial position and the initial energy. We present results for equatorially-mirroring particles as well as for particles with several other values of the initial pitch angles. The pitch-angle dependence of the energization rates is relatively weak for the equatorial pitch angles greater than about 60o, but particles with smaller pitch angles gain significantly less energy than the equatorial ones. Energy gain factors of 3 to 10 are easily achievable in our model which is sufficient to produce observable features in ground based observations, such as those done by riometers.

Multi-year predictability in a coupled general circulation model

NASA Astrophysics Data System (ADS)

Power, Scott; Colman, Rob

2006-02-01

Multi-year to decadal variability in a 100-year integration of a BMRC coupled atmosphere-ocean general circulation model (CGCM) is examined. The fractional contribution made by the decadal component generally increases with depth and latitude away from surface waters in the equatorial Indo-Pacific Ocean. The relative importance of decadal variability is enhanced in off-equatorial “ wings” in the subtropical eastern Pacific. The model and observations exhibit “ENSO-like” decadal patterns. Analytic results are derived, which show that the patterns can, in theory, occur in the absence of any predictability beyond ENSO time-scales. In practice, however, modification to this stochastic view is needed to account for robust differences between ENSO-like decadal patterns and their interannual counterparts. An analysis of variability in the CGCM, a wind-forced shallow water model, and a simple mixed layer model together with existing and new theoretical results are used to improve upon this stochastic paradigm and to provide a new theory for the origin of decadal ENSO-like patterns like the Interdecadal Pacific Oscillation and Pacific Decadal Oscillation. In this theory, ENSO-driven wind-stress variability forces internal equatorially-trapped Kelvin waves that propagate towards the eastern boundary. Kelvin waves can excite reflected internal westward propagating equatorially-trapped Rossby waves (RWs) and coastally-trapped waves (CTWs). CTWs have no impact on the off-equatorial sub-surface ocean outside the coastal wave guide, whereas the RWs do. If the frequency of the incident wave is too high, then only CTWs are excited. At lower frequencies, both CTWs and RWs can be excited. The lower the frequency, the greater the fraction of energy transmitted to RWs. This lowers the characteristic frequency (reddens the spectrum) of variability off the equator relative to its equatorial counterpart. At low frequencies, dissipation acts as an additional low pass filter that becomes more effective, as latitude increases. At the same time, ENSO-driven off-equatorial surface heating anomalies drive mixed layer temperature responses in both hemispheres. Both the eastern boundary interactions and the accumulation of surface heat fluxes by the surface mixed layer act to low pass filter the ENSO-forcing. The resulting off-equatorial variability is therefore more coherent with low pass filtered (decadal) ENSO indices [e.g. NINO3 sea-surface temperature (SST)] than with unfiltered ENSO indices. Consequently large correlations between variability and NINO3 extend further poleward on decadal time-scales than they do on interannual time-scales. This explains why decadal ENSO-like patterns have a broader meridional structure than their interannual counterparts. This difference in appearance can occur even if ENSO indices do not have any predictability beyond interannual time-scales. The wings around 15-20°S, and sub-surface variability at many other locations are predictable on interannual and multi-year time-scales. This includes westward propagating internal RWs within about 25° of the equator. The slowest of these take up to 4 years to reach the western boundary. This sub-surface predictability has significant oceanographic interest. However, it is linked to only low levels of SST variability. Consequently, extrapolation of delayed action oscillator theory to decadal time-scales might not be justified.

Impact of resolving the diurnal cycle in an ocean-atmosphere GCM. Part 2: A diurnally coupled CGCM

NASA Astrophysics Data System (ADS)

Bernie, D. J.; Guilyardi, E.; Madec, G.; Slingo, J. M.; Woolnough, S. J.; Cole, J.

2008-12-01

Coupled ocean atmosphere general circulation models (GCM) are typically coupled once every 24 h, excluding the diurnal cycle from the upper ocean. Previous studies attempting to examine the role of the diurnal cycle of the upper ocean and particularly of diurnal SST variability have used models unable to resolve the processes of interest. In part 1 of this study a high vertical resolution ocean GCM configuration with modified physics was developed that could resolve the diurnal cycle in the upper ocean. In this study it is coupled every 3 h to atmospheric GCM to examine the sensitivity of the mean climate simulation and aspects of its variability to the inclusion of diurnal ocean-atmosphere coupling. The inclusion of the diurnal cycle leads to a tropics wide increase in mean sea surface temperature (SST), with the strongest signal being across the equatorial Pacific where the warming increases from 0.2°C in the central and western Pacific to over 0.3°C in the eastern equatorial Pacific. Much of this warming is shown to be a direct consequence of the rectification of daily mean SST by the diurnal variability of SST. The warming of the equatorial Pacific leads to a redistribution of precipitation from the Inter tropical convergence zone (ITCZ) toward the equator. In the western Pacific there is an increase in precipitation between Papa new guinea and 170°E of up to 1.2 mm/day, improving the simulation compared to climatology. Pacific sub tropical cells are increased in strength by about 10%, in line with results of part 1 of this study, due to the modification of the exchange of momentum between the equatorially divergent Ekman currents and the geostropic convergence at depth, effectively increasing the dynamical response of the tropical Pacific to zonal wind stresses. During the spring relaxation of the Pacific trade winds, a large diurnal cycle of SST increases the seasonal warming of the equatorial Pacific. When the trade winds then re-intensify, the increase in the dynamical response of the ocean leads to a stronger equatorial upwelling. These two processes both lead to stronger seasonal basin scale feedbacks in the coupled system, increasing the strength of the seasonal cycle of the tropical Pacific sector by around 10%. This means that the diurnal cycle in the upper ocean plays a part in the coupled feedbacks between ocean and atmosphere that maintain the basic state and the timing of the seasonal cycle of SST and trade winds in the tropical Pacific. The Madden-Julian Oscillation (MJO) is examined by use of a large scale MJO index, lag correlations and composites of events. The inclusion of the diurnal cycle leads to a reduction in overall MJO activity. Precipitation composites show that the MJO is stronger and more coherent when the diurnal cycle of coupling is resolved, with the propagation and different phases being far more distinct both locally and to larger lead times across the tropical Indo-Pacific. Part one of this study showed that that diurnal variability of SST is modulated by the MJO and therefore increases the intraseasonal SST response to the different phases of the MJO. Precipitation-based composites of SST variability confirm this increase in the coupled simulations. It is argued that including this has increased the thermodynamical coupling of the ocean and atmosphere on the timescale of the MJO (20-100 days), accounting for the improvement in the MJO strength and coherency seen in composites of precipitation and SST. These results show that the diurnal cycle of ocean-atmosphere interaction has profound impact on a range of up-scale variability in the tropical climate and as such, it is an important feature of the modelled climate system which is currently either neglected or poorly resolved in state of the art coupled models.

Participation in the Mars Data Analysis Program: Analysis of cloud forms in Viking and Mariner 9 images

NASA Technical Reports Server (NTRS)

Gierasch, P.; Kahn, R. A.

1985-01-01

The first systematic account of the climate of Mars, based upon observations was produced. Cloud data were used to determine spatially and temporally varying near-surface wind direction, relative wind speed, static stability, and humidity conditions on a global scale. Existing models of meteorological processes were critically reexamined in light of the data, and more stringent constraints were set on global processes. Several discoveries were made, including the large extent and seasonal variability of the Mars equatorial Hadley cell, the failure of high latitude winds to reverse direction in early northern spring, the change in meridional wind component in southern midautum, and the almost constant cloud cover in the northern hemisphere, during spring and summer primarily by condensate clouds and in fall and winter by condensates and dust. The implications of these observations are discussed.

Modeling the quasi-biennial oscillation's effect on the winter stratospheric circulation

NASA Technical Reports Server (NTRS)

O'Sullivan, Donal; Young, Richard E.

1992-01-01

The influence of the equatorial quasi-biennial oscillation (QBO) on the winter middle atmosphere is modeled with a mechanistic global primitive equation model. The model's polar vortex evolution is sensitive to the lower stratosphere's tropical winds, with the polar vortex becoming more (less) disturbed as the lower stratospheric winds are more easterly (westerly). This agrees with the observed relationship between wintertime polar circulation strength and the phase of the QBO in the lower stratosphere. In these experiments it is the extratropical planetary Rossby waves that provide the tropical-extratropical coupling mechanism. More easterly tropical winds in the lower stratosphere act to confine the extratropical Rossby waves farther north and closer to the vortex at the QBO altitudes, weakening the vortex relative to the case of westerly QBO phase. While the QBO winds occur in the lower stratosphere, the anomaly in the polar vortex strength is strongest at higher levels.

Magnetic Dipole Inflation with Cascaded ARC and Applications to Mini-Magnetospheric Plasma Propulsion

NASA Technical Reports Server (NTRS)

Giersch, L.; Winglee, R.; Slough, J.; Ziemba, T.; Euripides, P.

2003-01-01

Mini-Magnetospheric Plasma Propulsion (M2P2) seeks to create a plasma-inflated magnetic bubble capable of intercepting significant thrust from the solar wind for the purposes of high speed, high efficiency spacecraft propulsion. Previous laboratory experiments into the M2P2 concept have primarily used helicon plasma sources to inflate the dipole magnetic field. The work presented here uses an alternative plasma source, the cascaded arc, in a geometry similar to that used in previous helicon experiments. Time resolved measurements of the equatorial plasma density have been conducted and the results are discussed. The equatorial plasma density transitions from an initially asymmetric configuration early in the shot to a quasisymmetric configuration during plasma production, and then returns to an asymmetric configuration when the source is shut off. The exact reasons for these changes in configuration are unknown, but convection of the loaded flux tube is suspected. The diffusion time was found to be an order of magnitude longer than the Bohm diffusion time for the period of time after the plasma source was shut off. The data collected indicate the plasma has an electron temperature of approximately 11 eV, an order of magnitude hotter than plasmas generated by cascaded arcs operating under different conditions. In addition, indirect evidence suggests that the plasma has a beta of order unity in the source region.

An Ionosphere/Magnetosphere Coupling Current System Located in the Gap Between Saturn and its Rings

NASA Astrophysics Data System (ADS)

Khurana, K. K.; Dougherty, M. K.; Cao, H.; Hunt, G. J.; Provan, G.

2017-12-01

The Grand Finale Orbits of the Cassini spacecraft traversed through Saturn's D ring and brought the spacecraft to within 3000 km of Saturn's cloud tops. The closest approaches (CA) were near the equatorial plane of Saturn and were distributed narrowly around the local noon. The difference field (observations - internal field - magnetospheric ring current field) obtained from the Grand Finale orbits show persistent residual fields centered around the CA which diminish at higher latitudes on field lines that connect to the ring. Modeling of this perturbation in terms of internal harmonics shows that the perturbation is not of internal origin but is produced by external currents that couple the ionosphere to the magnetosphere. The sense of the current system suggests that the southern feet of the field lines in the ionosphere lead their northern footprints. We show that the observed field perturbations are consistent with a meridional Pedersen current whose strength is 1 MA/radian, i.e. comparable in strength to the Planetary-period-oscillation related current systems observed in the auroral zone. We show that the implied Lorentz force in the ionosphere extracts momentum from the faster moving southern ionosphere and passes it on to the northern ionosphere. We discuss several ideas for generating this current system. In particular, we highlight a mechanism that involves shears in the neutral winds in the thermospheric region to generate the observed magnetic field.

Survey of Magnetosheath Plasma Properties at Saturn and Inference of Upstream Flow Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomsen, M. F.; Coates, A. J.; Jackman, C. M.

A new Cassini magnetosheath data set is introduced that is based on a comprehensive survey of intervals in which the observed magnetosheath flow was encompassed within the plasma analyzer field of view and for which the computed numerical moments are therefore expected to be accurate. The data extend from 2004 day 299 to 2012 day 151 and comprise 19,155 416-s measurements. In addition to the plasma ion moments (density, temperature, and flow velocity), merged values of the plasma electron density and temperature, the energetic particle pressure, and the magnetic field vector are included in the data set. Statistical properties ofmore » various magnetosheath parameters, including dependence on local time, are presented. The magnetosheath field and flow are found to be only weakly aligned, primarily because of a relatively large z-component of the magnetic field, attributable to the field being pulled out of the equatorial orientation by flows at higher latitudes. A new procedure for using magnetosheath properties to estimate the upstream solar wind speed is proposed and used to determine that the amount of electron heating at Saturn's high Mach-number bow shock is ~4% of the dissipated flow energy. The data set is available as an electronic supplement to this paper.« less

Survey of Magnetosheath Plasma Properties at Saturn and Inference of Upstream Flow Conditions

DOE PAGES

Thomsen, M. F.; Coates, A. J.; Jackman, C. M.; ...

2018-03-01

A new Cassini magnetosheath data set is introduced that is based on a comprehensive survey of intervals in which the observed magnetosheath flow was encompassed within the plasma analyzer field of view and for which the computed numerical moments are therefore expected to be accurate. The data extend from 2004 day 299 to 2012 day 151 and comprise 19,155 416-s measurements. In addition to the plasma ion moments (density, temperature, and flow velocity), merged values of the plasma electron density and temperature, the energetic particle pressure, and the magnetic field vector are included in the data set. Statistical properties ofmore » various magnetosheath parameters, including dependence on local time, are presented. The magnetosheath field and flow are found to be only weakly aligned, primarily because of a relatively large z-component of the magnetic field, attributable to the field being pulled out of the equatorial orientation by flows at higher latitudes. A new procedure for using magnetosheath properties to estimate the upstream solar wind speed is proposed and used to determine that the amount of electron heating at Saturn's high Mach-number bow shock is ~4% of the dissipated flow energy. The data set is available as an electronic supplement to this paper.« less

Middle atmosphere simulated with high vertical and horizontal resolution versions of a GCM: Improvements in the cold pole bias and generation of a QBO-like oscillation in the tropics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamilton, K.; Wilson, R.J.; Hemler, R.S.

1999-11-15

The large-scale circulation in the Geophysical Fluid Dynamics Laboratory SKYHI troposphere-stratosphere-mesosphere finite-difference general circulation model is examined as a function of vertical and horizontal resolution. The experiments examined include one with horizontal grid spacing of {approximately}35 km and another with {approximately}100 km horizontal grid spacing but very high vertical resolution (160 levels between the ground and about 85 km). The simulation of the middle-atmospheric zonal-mean winds and temperatures in the extratropics is found to be very sensitive to horizontal resolution. For example, in the early Southern Hemisphere winter the South Pole near 1 mb in the model is colder thanmore » observed, but the bias is reduced with improved horizontal resolution (from {approximately}70 C in a version with {approximately}300 km grid spacing to less than 10 C in the {approximately}35 km version). The extratropical simulation is found to be only slightly affected by enhancements of the vertical resolution. By contrast, the tropical middle-atmospheric simulation is extremely dependent on the vertical resolution employed. With level spacing in the lower stratosphere {approximately}1.5 km, the lower stratospheric zonal-mean zonal winds in the equatorial region are nearly constant in time. When the vertical resolution is doubled, the simulated stratospheric zonal winds exhibit a strong equatorially centered oscillation with downward propagation of the wind reversals and with formation of strong vertical shear layers. This appears to be a spontaneous internally generated oscillation and closely resembles the observed QBO in many respects, although the simulated oscillation has a period less than half that of the real QBO.« less

Jupiter cloud morphology and zonal winds from ground-based observations before and during Juno's first perijove

NASA Astrophysics Data System (ADS)

Hueso, R.; Sánchez-Lavega, A.; Iñurrigarro, P.; Rojas, J. F.; Pérez-Hoyos, S.; Mendikoa, I.; Gómez-Forrellad, J. M.; Go, C.; Peach, D.; Colas, F.; Vedovato, M.

2017-05-01

We analyze Jupiter observations between December 2015 and August 2016 in the 0.38-1.7 μm wavelength range from the PlanetCam instrument at the 2.2 m telescope at Calar Alto Observatory and in the optical range by amateur observers contributing to the Planetary Virtual Observatory Laboratory. Over this time Jupiter was in a quiescent state without notable disturbances. Analysis of ground-based images and Hubble Space Telescope observations in February 2016 allowed the retrieval of mean zonal winds from -74.5° to +73.2°. These winds did not change over 2016 or when compared with winds from previous years with the sole exception of intense zonal winds at the North Temperate Belt. We also present results concerning the major wave systems in the North Equatorial Belt and in the upper polar hazes visible in methane absorption bands, a description of the planet's overall cloud morphology and observations of Jupiter hours before Juno's orbit insertion.

Projected changes of the low-latitude north-western Pacific wind-driven circulation under global warming

NASA Astrophysics Data System (ADS)

Duan, Jing; Chen, Zhaohui; Wu, Lixin

2017-05-01

Based on the outputs of 25 models participating in the Coupled Model Intercomparison Project Phase 5, the projected changes of the wind-driven circulation in the low-latitude north-western Pacific are evaluated. Results demonstrate that there will be a decrease in the mean transport of the North Equatorial Current (NEC), Mindanao Current, and Kuroshio Current in the east of the Philippines, accompanied by a northward shift of the NEC bifurcation Latitude (NBL) off the Philippine coast with over 30% increase in its seasonal south-north migration amplitude. Numerical simulations using a 1.5-layer nonlinear reduced-gravity ocean model show that the projected changes of the upper ocean circulation are predominantly determined by the robust weakening of the north-easterly trade winds and the associated wind stress curl under the El Niño-like warming pattern. The changes in the wind forcing and intensified upper ocean stratification are found equally important in amplifying the seasonal migration of the NBL.

Indo-Pacific sea level variability at multidecadal time scales

NASA Astrophysics Data System (ADS)

Merrifield, M. A.; Thompson, P. R.

2016-12-01

Long tide gauge and atmospheric pressure measurements are used to infer multidecadal fluctuations in trade wind forcing and the associated Indo-Pacific sea level response along coastal and equatorial waveguides. The trade wind variations are marked by a weakening beginning with the late 1970s climate shift and a subsequent return to mean conditions since the early 1990s. These fluctuations covary with multidecadal wind changes at mid-latitudes, as measured by the Pacific Decadal Oscillation or the North Pacific indices; however, the mid-latitude multidecadal variations prior to 1970 or noticeably absent in the inferred trade wind record. The different behavior of tropical and mid-latitude winds support the notion that multidecadal climate variations in the Pacific result from a combination of processes and not a single coherent mode spanning the basin. In particular, the two-decade long satellite altimeter record represents a period of apparent connection between the two regions that was not exhibited earlier in the century.

New Approaches to the Parameterization of Gravity-Wave and Flow-Blocking Drag due to Unresolved Mesoscale Orography Guided by Mesoscale Model Predictability Research

DTIC Science & Technology

2012-09-30

oscillation (SAO) and quasi-biennial oscillation ( QBO ) of stratospheric equatorial winds in long-term (10-year) nature runs. The ability of these new schemes...to generate and maintain tropical SAO and QBO circulations in Navy models for the first time is an important breakthrough, since these circulations

Solar radiation, phytoplankton pigments and the radiant heating of the equatorial Pacific warm pool

NASA Technical Reports Server (NTRS)

Siegel, David A.; Ohlmann, J. Carter; Washburn, Libe; Bidigare, Robert R.; Nosse, Craig T.; Fields, Erik; Zhou, Yimei

1995-01-01

Recent optical, physical, and biological oceanographic observations are used to assess the magnitude and variability of the penetrating flux of solar radiation through the mixed layer of the warm water pool (WWP) of the western equatorial Pacific Ocean. Typical values for the penetrative solar flux at the climatological mean mixed layer depth for the WWP (30 m) are approx. 23 W/sq m and are a large fraction of the climatological mean net air-sea heat flux (approx. 40 W/sq m). The penetrating solar flux can vary significantly on synoptic timescales. Following a sustained westerly wind burst in situ solar fluxes were reduced in response to a near tripling of mixed layer phytoplankton pigment concentrations. This results in a reduction in the penetrative flux at depth (5.6 W/sq m at 30 m) and corresponds to a biogeochemically mediated increase in the mixed layer radiant heating rate of 0.13 C per month. These observations demonstrate a significant role of biogeochemical processes on WWP thermal climate. We speculate that this biogeochemically mediated feedback process may play an important role in enhancing the rate at which the WWP climate system returns to normal conditions following a westerly wind burst event.

Monthly mean global climatology of temperature, wind, geopotential height, and pressure for 0 - 120 km

NASA Technical Reports Server (NTRS)

Fleming, Eric L.; Chandra, Sushil; Schoeberl, Mark R.; Barnett, John J.

1988-01-01

A monthly mean climatology is presented of temperature, wind, and geopotential height with nearly pole-to-pole coverage (80 S to 80 N) for 0 to 210 km, which can be used as a function of altitude and pressure. The purpose is to provide a reference for various atmospheric research and analysis activities. Data sources and methods of computation are described; in general, hydrostatic and thermal wind balance are maintained at all levels and latitudes. As observed in a series of cross-sectional plots, this climatology accurately reproduces most of the characteristic features of the atmosphere such as equatorial wind and the general structure of the tropopause, stratopause, and mesopause. A series of zonal wind profiles is also represented comparing this climatological wind with monthly mean climatological direct wind measurements in the upper mesosphere and lower thermosphere. The temperature and zonal wind climatology at stratospheric levels is compared with corresponding data from the National Meteorological Center, and general agreement is observed between the two data sets. Tables of the climatological values as a function of latitude and height for each month are contained in Appendix B, and are also available in floppy disk.

Aeolian Landscapes of Titan from Cassini RADAR Reveal Winds, Elevation Constraints and Sediment Characteristics

NASA Astrophysics Data System (ADS)

Radebaugh, J.; Lewis, R. C.; Bishop, B.; Christiansen, E. H.; Kerber, L.; Rodriguez, S.; Narteau, C.; Le Gall, A. A.; Lucas, A.; Malaska, M.

2017-12-01

Similar to terrestrial bodies with atmospheres, a significant portion of the surface of Titan is covered in aeolian landscapes, now imaged by Cassini RADAR at close to 50% coverage. While the compositions of the wind-carried and wind-carved sediments are under discussion, their characteristics, such as being rounded, loose and capable of being saltated, or being fine, soft and forming easily erodible deposits, can be discerned from the geomorphology. Large duneforms are similar to those in Earth's big deserts, formed by particles in strict size and shape limits, and steep, badlands-like morphologies of yardang regions indicate soft rocks with armored features. Shapes and orientations of dunes and yardangs can also reveal wind directions and effects of elevation and topographic obstacles. Recent studies of dunes in the Belet Sand Sea of Titan's equatorial trailing hemisphere reveal dunes are generally wider and with greater spacing near the center, similar to dunes in the Namib Sand Sea of Earth. Dune-to-interdune ratios decrease toward higher latitudes, as was previously observed, and are slightly higher in regions of low elevation, which may relate to elevation affecting winds and sand transport capacity. However, this relationship is not as strong for the Namib. Furthermore, the effects of the location of dunes with respect to sand sea margins on dune parameter values has only begun to be explored. The European ERA-Interim (observations plus model) wind results for the Namib reveal vector sum winds are several degrees away from down the dune long axis, consistent with the fingering mode of dune growth, and allowing for down-axis sand transport. We assume similar model winds for the dunes of Titan. Model winds for the yardangs of the Lut desert of Earth are directly down axis, which means wind directions should be able to be determined in the isolated yardang fields of Titan's northern midlatitudes. Further studies of dune parameters on Titan from Cassini can help reveal the reasons for the extent of the sand seas and how (and whether) sands are transported across them. Further studies of winds and sediment properties of yardangs on Earth will reveal expected winds, material requirements and relative ages of the yardangs with respect to other landforms of Titan.

Mean motions and tidal and two-day structure and variability in the mesosphere and lower thermosphere over Hawaii

NASA Technical Reports Server (NTRS)

Fritts, David C.; Isler, Joseph R.

1994-01-01

An overview of the motion field and an analysis of the tidal and 2-day wave motions observed in the mesosphere and lower thermosphere over the central Pacific from 1 October 1990 through 19 August 1992 is presented. Characteristics and interactions of motions at lower and higher frequencies will be addressed elsewhere. Wind measurements were obtained with an MF radar operating on Kauai, Hawaii (22 deg N, 160 deg W), using the partial reflection drift technique. Results presented in this paper reveal a zonal mean motion reflecting the mesopause semiannual oscillation (MSAO) observed at more equatorial latitudes from approximately January to July, coinciding with the period during which the MSAO and the annual cycle of the zonal mean wind at higher latitudes are in phase. Eastward and westward maxima are 55 m/s below 80 km and 45 m/s near 85 km during the first year, with maxima of 57 and 53 m/s during the second year and evidence of substantial interannual variability. The second MSAO cycle is greatly suppressed in the Hawaiian data due to the reversal of the correlation between this and the annual cycle at higher latitudes from approximately July to December and because the second cycle is weaker climatologically at equatorial latitudes. Significant planetary wave activity is observed during periods of mean eastward motions, and tidal and 2-day motions are found to be large and variable. The maximum diurnal tides were observed during October and November 1990, and February, March, April, July, and August of 1991 and 1992. Maximum 2-day amplitudes occurred during February, July, and August of 1991 and 1992. Significantly, the large diurnal amplitude maximum noted during November 1990 failed to appear the following year, while the February 2-day amplitude maximum declined somewhat in 1992.

Influence of coronal mass ejections on parameters of high-speed solar wind: a case study

NASA Astrophysics Data System (ADS)

Shugay, Yulia; Slemzin, Vladimir; Rodkin, Denis; Yermolaev, Yuri; Veselovsky, Igor

2018-05-01

We investigate the case of disagreement between predicted and observed in-situ parameters of the recurrent high-speed solar wind streams (HSSs) existing for Carrington rotation (CR) 2118 (December 2011) in comparison with CRs 2117 and 2119. The HSSs originated at the Sun from a recurrent polar coronal hole (CH) expanding to mid-latitudes, and its area in the central part of the solar disk increased with the rotation number. This part of the CH was responsible for the equatorial flank of the HSS directed to the Earth. The time and speed of arrival for this part of the HSS to the Earth were predicted by the hierarchical empirical model based on EUV-imaging and the Wang-Sheeley-Arge ENLIL semi-empirical replace model and compared with the parameters measured in-situ by model. The predicted parameters were compared with those measured in-situ. It was found, that for CR 2117 and CR 2119, the predicted HSS speed values agreed with the measured ones within the typical accuracy of ±100 km s-1. During CR 2118, the measured speed was on 217 km s-1 less than the value predicted in accordance with the increased area of the CH. We suppose that at CR 2118, the HSS overtook and interacted with complex ejecta formed from three merged coronal mass ejections (CMEs) with a mean speed about 400 km s-1. According to simulations of the Drag-based model, this complex ejecta might be created by several CMEs starting from the Sun in the period between 25 and 27 December 2011 and arriving to the Earth simultaneously with the HSS. Due to its higher density and magnetic field strength, the complex ejecta became an obstacle for the equatorial flank of the HSS and slowed it down. During CR 2117 and CR 2119, the CMEs appeared before the arrival of the HSSs, so the CMEs did not influence on the HSSs kinematics.

Equatorial E region electric fields at the dip equator: 2. Seasonal variabilities and effects over Brazil due to the secular variation of the magnetic equator

NASA Astrophysics Data System (ADS)

Moro, J.; Denardini, C. M.; Resende, L. C. A.; Chen, S. S.; Schuch, N. J.

2016-10-01

In this work, the seasonal dependency of the E region electric field (EEF) at the dip equator is examined. The eastward zonal (Ey) and the daytime vertical (Ez) electric fields are responsible for the overall phenomenology of the equatorial and low-latitude ionosphere, including the equatorial electrojet (EEJ) and its plasma instability. The electric field components are studied based on long-term backscatter radars soundings (348 days for both systems) collected during geomagnetic quiet days (Kp ≤ 3+), from 2001 to 2010, at the São Luís Space Observatory (SLZ), Brazil (2.33°S, 44.20°W), and at the Jicamarca Radio Observatory (JRO), Peru (11.95°S, 76.87°W). Among the results, we observe, for the first time, a seasonal difference between the EEF in these two sectors in South America based on coherent radar measurements. The EEF is more intense in summer at SLZ, in equinox at JRO, and has been highly variable with season in the Brazilian sector compared to the Peruvian sector. In addition, the secular variation on the geomagnetic field and its effect on the EEJ over Brazil resulted that as much farther away is the magnetic equator from SLZ, later more the EEJ is observed (10 h LT) and sooner it ends (16 h LT). Moreover, the time interval of type II occurrence decreased significantly after the year 2004, which is a clear indication that SLZ is no longer an equatorial station due to the secular variation of the geomagnetic field.

Quasi-biennial variation of equatorial waves as seen in satellite remote sensing data

NASA Astrophysics Data System (ADS)

Chen, Zeyu

The quasi-biennial oscillation (QBO) in zonal winds in the lower stratosphere at the Equator is the most prominent inter-annual variation signal in the middle atmosphere. Theoretically, it is driven by the drag from the damping of equatorial waves including the equatorially trapped planetary scale waves, such as Kelvin waves propagating eastward and Rossby-gravity waves propagating westward, inertio-gravity waves and gravity waves. In current research, the tem-perature data collected by the SABER/TIMED mission in 2002-2009 are used to investigate the equatorial waves activities. The Fast Fourier Synoptic Mapping (FFSM) method is applied to delineate planetary wave components with the zonal wavenumber spanning over -6 to +6, hereby, positive (negative) wavenumber is assigned to westward (eastward) propagating waves. Limited by the SABER/TIMED sampling scheme, only the waves with periods longer than one day can be resolved. Focusing on the height region 70-10 hPa where the QBO signal is most significant, it is clearly observed that the composite activity of all the eastward waves exhibit QBO like variation. Specifically, for each QBO cycle, the activity at 50 hPa level is characterized by the occurrence of a substantially clear minimum that coincides to the fast downward propagation of the westerly phase, the typical pattern of the QBO phenomenon. Phase speed spectra are derived by using the FFSM analysis results. And vertical shear of the zonal wind is derived by using the rawinsonde data at Singapore. Comparison of the phase speed spectra and the wind shear indicates that the minimum is due to the westerly shear below 30 hPa. Between the minimum, significant wave activities emerge, thus the property for the components are investigated. Results show that in height range 70-10 hPa, both wave 1 to wave 3 are prominent during the inter-minimum period for each QBO cycle. At 50 hPa level, wave 1 component exhibits amplitude spectral peak at three kinds of period, 8, 11 and 20 day. Meanwhile, shifting to shorter period is seen as wave number increases, for example, the 20-day period spectrum is attenuated substantially for wave 2 and wave 3 components. Moreover, results also show that although with small amplitude, wave 4 and wave 5 with shorter periods of 4-7 days are discernable in particular in the inter-minimum period. Further details will be presented in the talk.

Intraseasonal-to-semiannual variability of sea-surface height in the eastern, equatorial Indian Ocean and southern Bay of Bengal

NASA Astrophysics Data System (ADS)

Cheng, X.; McCreary, J. P., Jr.; Qiu, B.; Yu, Z.; DU, Y.

2016-12-01

Intraseasonal-to-semiannual variability of sea-surface height (SSH) in the eastern, equatorial Indian Ocean (EEIO) and southern Bay of Bengal (BoB) is investigated using altimetric data, and solutions to 1½-layer (first-baroclinic-mode) and linear, continuously stratified (LCS; multi-baroclinic-mode) models. The amplitude and dominant period of SSH variability differ regionally. Large-amplitude variability is found along the west coast of Sumatra, in a zonal band across the BoB centered along 5°N, east of Sri Lanka, and in the northwestern BoB. Along the Sumatran west coast, SSH variability peaks at 30-60 days, 90 days, and 180 days. Along 5°N and east of Sri Lanka, 30-60-day variability is dominant. Sensitivity experiments using a nonlinear version of the 1½-layer model forced by realistic winds reproduce the observed patterns of intraseasonal variability in the southern BoB. At 30-60 days, the solutions show that eddies (nonlinear Rossby waves) propagating from the east, rather than local wind forcing, account for most of the variance east of Sri Lanka; furthermore, they demonstrate that the variance is significantly enhance by the nonlinear transfer of 90-120-day energy into the intraseasonal band. The LCS solutions show that the first two baroclinic modes explain most of the SSH variance at 90-180 days. The second-baroclinic-mode dominates the SSH variance at 180 days, a consequence of basin resonance and strong wind forcing.

Use of the 4D-Global Reference Atmosphere Model (GRAM) for space shuttle descent design

NASA Technical Reports Server (NTRS)

Mccarty, S. M.

1987-01-01

The method of using the Global Reference Atmosphere Model (GRAM) mean and dispersed atmospheres to study skipout/overshoot requirements, to characterize mean and worst case vehicle temperatures, study control requirements, and verify design was discussed. Landing sites in these analyses range from 65 N to 30 S, while orbit inclinations vary from 20 deg to 98 deg. The primary concern was that they cannot use as small vertical steps in the reentry calculation as desired because the model predicts anomalously large density shear rates for very small vertical step sizes. The winds predicted by the model are not satisfactory. This is probably because they are geostrophic winds and because the model has an error in the computation of winds in the equatorial regions.

Evaporation/SST Sensitivity Over the Tropical Oceans During ENSO Events as Estimated from the da Silva, Young, Levitus Surface Marine Data Set

NASA Technical Reports Server (NTRS)

Robertson, F. R.; Fitzjarrald, D. E.; Sohn, B.-J.; Arnold, James E. (Technical Monitor)

2001-01-01

The da Silva, Young and Levitus Surface Marine Atlas, based on observations from the Comprehensive Ocean Atmosphere Data Set (COADS) Release 1, has been used to investigate the relationship between evaporation and sea-surface temperature (SST) over the global oceans. For the period 1950 to 1987 SST, surface latent heat flux, and other related variables have been filtered to minimize data uncertainties and to focus upon interannual variations associated with warm (El Nino) and cold (La Nina) ENSO events. Compositing procedures have enabled identification of systematic variations in latent heat fluxes accompanying these events and the relationship to spatial anomalies in ocean surface wind speed and humidity. The evaporation response associated with ENSO sea surface temperature (SST) variability is systematic in nature and composed of offsetting contributions from the surface wind and humidity variations. During warm events exceeding 1.0 S.D. delta SST, increases in the surface humidity deficit, delta(qs-qa), between the surface and 2m height dominate regions of positive SST anomalies and lead to increases in evaporation of almost 2 Wm (exp -2) at deltaSST = 0.23 K. Despite the increases in specific humidity, relative humidity decreases slightly in regions of elevated SSTs. For the most part, variations in wind speed are consistent with previous investigations. Weakening of the equatorial easterlies (and generation of westerlies) between 160 degrees E and 140 degrees W dominates during the early phases of warm events. Elevated wind speeds in adjacent subtropical regions and in the eastern equatorial Pacific subsequently develop too. The net contribution of these winds, which reflect adjustments in Hadley and Walker circulation components is toward reduced evaporation. Results for cold periods are approximately similar, but opposite in sign to warm events, though evidence of different temporal evolution is noted.

Dynamical diagnostics of the SST annual cycle in the eastern equatorial Pacific: Part II analysis of CMIP5 simulations

NASA Astrophysics Data System (ADS)

Chen, Ying-Ying; Jin, Fei-Fei

2017-12-01

In this study, a simple coupled framework established in Part I is utilized to investigate inter-model diversity in simulating the equatorial Pacific SST annual cycle (SSTAC). It demonstrates that the simulated amplitude and phase characteristics of SSTAC in models are controlled by two internal dynamical factors (the damping rate and phase speed) and two external forcing factors (the strength of the annual and semi-annual harmonic forcing). These four diagnostic factors are further condensed into a dynamical response factor and a forcing factor to derive theoretical solutions of amplitude and phase of SSTAC. The theoretical solutions are in remarkable agreement with observations and CMIP5 simulations. The great diversity in the simulated SSTACs is related to the spreads in these dynamic and forcing factors. Most models tend to simulate a weak SSTAC, due to their weak damping rate and annual harmonic forcing. The latter is due to bias in the meridional asymmetry of the annual mean state of the tropical Pacific, represented by the weak cross-equatorial winds in the cold tongue region.

Reorientation Timescales and Pattern Dynamics for Titan's Dunes: Does the Tail Wag the Dog or the Dragon?

NASA Astrophysics Data System (ADS)

Hayes, A. G.; Ewing, R. C.; Cassini Radar Science Team, T.

2011-12-01

Fields of bedform patterns persist across many orders of magnitude, from cm-scale sub-aqueous current ripples to km-scale aeolian dunes, and form with surprisingly little difference in expression despite a range of formative environments. Because of the remarkable similarity between and among patterns, extracting information about climate and environment from these patterns is a challenge. For example, crest orientation is not diagnostic of a particular flow regime; similar patterns form under many different flow configurations. On Titan, these challenges have played out with many attempts to reconcile dune-field patterns with modeled and expected wind regimes. We propose that thinking about the change in dune orientation, rather than the orientation itself, can provide new insights on the long-term stability of the dune-field patterns and the formative wind regime. In this work, we apply the re-orientation model presented by Werner and Kocurek [Geology, 1997] to the equatorial dune fields of Titan. We measure variations in pattern parameters (crest spacing, crest length and defect density, which is the number of defect pairs per total crest length) both within and between Titan's dune fields to describe pattern maturity and identify areas where changes in dune orientation are likely to occur (or may already be occurring). Measured defect densities are similar to Earth's largest linear dune fields, such as the Namib Sand Sea and the Simpson Desert. We use measured defect densities in the Werner and Kocurek model to estimate crestline reorientation rates. We find reorientation timescales varying from ten to a hundred thousand times the average migration timescale (time to migrate a bedform one meter, ~1 Titan year according to Tokano (Aeolian Research, 2010)). Well organized patterns have the longest reorientation time scales (~10^5 migration timescales), while the topographically or spatially isolated patches of dunes show the shortest reorientation times (~10^3 migration timescales). In addition, comparisons between spacing and defect density of Titan's dunes and some of the largest fields observed on Earth and Mars reveal that dune patterns on all three planets are geometrically similar, suggesting that growth and organization share common pattern dynamics. Our results suggest that Titan's dunes may react to gross bedform transport averaged over orbital timescales, relaxing the requirement that a single modern wind regime is required to produce the observed pattern.

Unusual subauroral neutral wind disturbances during geomagnetic storms

NASA Astrophysics Data System (ADS)

Zhang, S.; Erickson, P. J.; Holt, J. M.

2016-12-01

Under the influence of geomagnetic storms, general circulation of the global thermosphere undergoes substantial changes that vary with latitudes. High latitude heating processes establish pressure gradients both vertically and horizontally. The equatorward wind surge and the associated westward wind enhancement are a typical disturbance wind characteristic that affacts ionosphere and thermosphere dynamics at mid-, low, and equatorial latitudes. At subauroral latitudes, however, new observations of neutral wind disturbances show some "abnormal" (unusual) behaviors in responding to complicated ion-neutral coupling processes. During the 2015 St. Patrick's Day great geomagnetic storm, incoherent scatter radar measurements at Millstone Hill show the following salient variations: (1) oscillating meridional wind disturbances with the Traveling Atmosphere Disturbance (TAD) feature; (2) vertical wind signature; (3) pre-mindnight poleward wind surges. The latter two variations appear to be associated with strong ion-neutral interaction developed during the subauroral polarization streams (SAPS) presence. Strong frictional heating caused by the relative velocity between the ions with SAPS speed and the neutrals leads to appreciable thermospheric upperwelling. Strong westward ion drifts shown as SAPS also enhance the wseward neutral flow, which subsequently causes a poleward component of the meridional wind due to the Coriolis force. This paper will present these observations of the wind and discuss ion-neutral coupling effects associated with SAPS.

Equatorial sandhoppers use body scans to detect the earth's magnetic field.

PubMed

Ugolini, A

2006-01-01

Adults of Talorchestia martensii were individually released in a confined environment, with and without the natural magnetic field, under the sun and in a dark room. The sandhoppers scanned the horizontal component of the magnetic field by left and right oscillations of the entire major body axis. The frequency of this behaviour increased in a zeroed magnetic field, as did the frequencies of other behavioural indicators that reflect the difficulty in identifying the ecologically efficient orientation direction (sea-land axis). Therefore, like head scans in birds, body scans seem to be used by equatorial sandhoppers to detect the magnetic symmetry plane.

Dunes on Titan observed by Cassini Radar

USGS Publications Warehouse

Radebaugh, J.; Lorenz, R.D.; Lunine, J.I.; Wall, S.D.; Boubin, G.; Reffet, E.; Kirk, R.L.; Lopes, R.M.; Stofan, E.R.; Soderblom, L.; Allison, M.; Janssen, M.; Paillou, P.; Callahan, P.; Spencer, C.; ,

2008-01-01

Thousands of longitudinal dunes have recently been discovered by the Titan Radar Mapper on the surface of Titan. These are found mainly within ??30?? of the equator in optically-, near-infrared-, and radar-dark regions, indicating a strong proportion of organics, and cover well over 5% of Titan's surface. Their longitudinal duneform, interactions with topography, and correlation with other aeolian forms indicate a single, dominant wind direction aligned with the dune axis plus lesser, off-axis or seasonally alternating winds. Global compilations of dune orientations reveal the mean wind direction is dominantly eastwards, with regional and local variations where winds are diverted around topographically high features, such as mountain blocks or broad landforms. Global winds may carry sediments from high latitude regions to equatorial regions, where relatively drier conditions prevail, and the particles are reworked into dunes, perhaps on timescales of thousands to tens of thousands of years. On Titan, adequate sediment supply, sufficient wind, and the absence of sediment carriage and trapping by fluids are the dominant factors in the presence of dunes. ?? 2007 Elsevier Inc. All rights reserved.

Climate variability and predictability associated with the Indo-Pacific Oceanic Channel Dynamics in the CCSM4 Coupled System Model

NASA Astrophysics Data System (ADS)

Yuan, Dongliang; Xu, Peng; Xu, Tengfei

2017-01-01

An experiment using the Community Climate System Model (CCSM4), a participant of the Coupled Model Intercomparison Project phase-5 (CMIP5), is analyzed to assess the skills of this model in simulating and predicting the climate variabilities associated with the oceanic channel dynamics across the Indo-Pacific Oceans. The results of these analyses suggest that the model is able to reproduce the observed lag correlation between the oceanic anomalies in the southeastern tropical Indian Ocean and those in the cold tongue in the eastern equatorial Pacific Ocean at a time lag of 1 year. This success may be largely attributed to the successful simulation of the interannual variations of the Indonesian Throughflow, which carries the anomalies of the Indian Ocean Dipole (IOD) into the western equatorial Pacific Ocean to produce subsurface temperature anomalies, which in turn propagate to the eastern equatorial Pacific to generate ENSO. This connection is termed the "oceanic channel dynamics" and is shown to be consistent with the observational analyses. However, the model simulates a weaker connection between the IOD and the interannual variability of the Indonesian Throughflow transport than found in the observations. In addition, the model overestimates the westerly wind anomalies in the western-central equatorial Pacific in the year following the IOD, which forces unrealistic upwelling Rossby waves in the western equatorial Pacific and downwelling Kelvin waves in the east. This assessment suggests that the CCSM4 coupled climate system has underestimated the oceanic channel dynamics and overestimated the atmospheric bridge processes.

Oxygen Pathways and Budget for the Eastern South Pacific Oxygen Minimum Zone

NASA Astrophysics Data System (ADS)

Llanillo, P. J.; Pelegrí, J. L.; Talley, L. D.; Peña-Izquierdo, J.; Cordero, R. R.

2018-03-01

Ventilation of the eastern South Pacific Oxygen Minimum Zone (ESP-OMZ) is quantified using climatological Argo and dissolved oxygen data, combined with reanalysis wind stress data. We (1) estimate all oxygen fluxes (advection and turbulent diffusion) ventilating this OMZ, (2) quantify for the first time the oxygen contribution from the subtropical versus the traditionally studied tropical-equatorial pathway, and (3) derive a refined annual-mean oxygen budget for the ESP-OMZ. In the upper OMZ layer, net oxygen supply is dominated by tropical-equatorial advection, with more than one-third of this supply upwelling into the Ekman layer through previously unevaluated vertical advection, within the overturning component of the regional Subtropical Cell (STC). Below the STC, at the OMZ's core, advection is weak and turbulent diffusion (isoneutral and dianeutral) accounts for 89% of the net oxygen supply, most of it coming from the oxygen-rich subtropical gyre. In the deep OMZ layer, net oxygen supply occurs only through turbulent diffusion and is dominated by the tropical-equatorial pathway. Considering the entire OMZ, net oxygen supply (3.84 ± 0.42 µmol kg-1 yr-1) is dominated by isoneutral turbulent diffusion (56.5%, split into 32.3% of tropical-equatorial origin and 24.2% of subtropical origin), followed by isoneutral advection (32.0%, split into 27.6% of tropical-equatorial origin and 4.4% of subtropical origin) and dianeutral diffusion (11.5%). One-quarter (25.8%) of the net oxygen input escapes through dianeutral advection (most of it upwelling) and, assuming steady state, biological consumption is responsible for most of the oxygen loss (74.2%).

High Speed Stream as driver of low latitude ionosphere variability: A study case in Brazilian sector

NASA Astrophysics Data System (ADS)

Nicoli Candido, C. M.; Batista, I. S.; Becker-Guedes, F.; Klausner, V.; da Silva, R.

2016-12-01

The solar activity period of solar cycle 23 was unusually long and quiet in comparison to other solar minima in last century. Several reports have analyzed its features and its impact under diverse points-of-view. In this work, we analyze the low latitude ionosphere behavior in Brazil and its response during this peculiar period. The ionospheric variation is analyzed through typical parameters such as vertical total electron content (VTEC), the peak height of F2 layer and its critical frequency, hmF2 and foF2, in 2008, around the southern crest of the Equatorial Ionization Anomaly (EIA), in Cachoeira Paulista (22.5º S, 45.0 ºW, mag. lat: 16 º S, dip angle: -32.3º) and at an equatorial station, São Luís (2.33º S, 44.2º W, dip angle: -6.7º). VTEC values present a semiannual variation pattern and two well-defined peaks in March and October. It was observed periodicities observed of 9, 13.5 and 27 days in VTEC and hmF2, mainly at the first and the second half of 2008. These periods match with the observed periods in solar and geomagnetic indexes such as Vsw, Kp and AE and are associated with occurrence of high speed streams (HSS) coming from solar coronal holes. A complex response of the low latitude ionosphere is observed, with prominent increases and decreases of VTEC at daytime during the interval of occurrence of HSSs. It is suggested that a combination of several factors such as prompt penetration of electric field, disturbed dynamo electric field, meridional winds, thermal expansion of thermosphere and composition changes of neutral atmosphere are responsible for the high day-to-day variability of the ionosphere.

Dst Index in the 2008 GEM Modeling Challenge - Model Performance for Moderate and Strong Magnetic Storms

NASA Technical Reports Server (NTRS)

Rastaetter, Lutz; Kuznetsova, Maria; Hesse, Michael; Chulaki, Anna; Pulkkinen, Antti; Ridley, Aaron J.; Gombosi, Tamas; Vapirev, Alexander; Raeder, Joachim; Wiltberger, Michael James;

ON THE RETRIEVAL OF MESOSPHERIC WINDS ON MARS AND VENUS FROM GROUND-BASED OBSERVATIONS AT 10 μm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lopez-Valverde, M. A.; Montabone, L.; Sornig, M.

A detailed analysis is presented of ground-based observations of atmospheric emissions on Mars and Venus under non-local thermodynamic equilibrium (non-LTE) conditions at high spectral resolution. Our first goal is to comprehend the difficulties behind the derivation of wind speeds from ground-based observations. A second goal is to set a framework to permit comparisons with other observations and with atmospheric models. A forward model including non-LTE radiative transfer is used to evaluate the information content within the telescopic beam, and is later convolved with the beam function and a typical wind field to discern the major contributions to the measured radiance,more » including limb and nadir views. The emission mostly arises from the non-LTE limb around altitudes of 75 km on Mars and 110 km on Venus. We propose a parameterization of the limb emission using few geophysical parameters which can be extended to other hypothetical CO{sub 2} planetary atmospheres. The tropospheric or LTE component of the emission varies with the temperature and is important at low solar illumination but only for the emerging radiance, not for the wind determinations since these are derived from the Doppler shift at the non-LTE line cores. We evaluated the sources of uncertainty and found that the forward model errors amount to approximately 12% of the measured winds, which is normally smaller than the instrumental errors. We applied this study to revise a set of measurements extending for three Martian years and confirmed previous results suggesting winds that are too large simulated by current Martian circulation models at equatorial latitudes during solstice. We encourage new observational campaigns, particularly for the strong jet at mid–high latitudes on Mars, and propose general guidelines and recommendations for future observations.« less

Are we near the predictability limit of tropical Indo-Pacific sea surface temperatures?

NASA Astrophysics Data System (ADS)

Newman, Matthew; Sardeshmukh, Prashant D.

2017-08-01

The predictability of seasonal anomalies worldwide rests largely on the predictability of tropical sea surface temperature (SST) anomalies. Tropical forecast skill is also a key metric of climate models. We find, however, that despite extensive model development, the tropical SST forecast skill of the operational North American Multi-Model Ensemble (NMME) of eight coupled atmosphere-ocean models remains close both regionally and temporally to that of a vastly simpler linear inverse model (LIM) derived from observed covariances of SST, sea surface height, and wind fields. The LIM clearly captures the essence of the predictable SST dynamics. The NMME and LIM skills also closely track and are only slightly lower than the potential skill estimated using the LIM's forecast signal-to-noise ratios. This suggests that the scope for further skill improvement is small in most regions, except in the western equatorial Pacific where the NMME skill is currently much lower than the LIM skill.

Studies of dynamo field structure and related effects: DE satellite project guest investigator program

NASA Technical Reports Server (NTRS)

Coley, W. R.

1986-01-01

The establishment of the latitudinal and longitudinal structure of the low latitude dynamo electric (DE) field was initiated using data primarily from the Unified Abstract (UA) files of the Atmosphere Explorer E (AE-E) satellite. Mass plots of the vertical ion drift values were made for 1977, 1978, and 1979. The average diurnal variation of V sub v within 20 degrees of the dip equator is remarkably similar to that obtained at Jicamarca in the same years. The average meridional ion drift velocity vectors, obtained as a function of latitude by combining the average vertical and horizontal (nearly north-south) ion drift values from the AE-E, showed the expected variations with local time and season based on the well known equatorial fountain effect theory. The average diurnal variation of the vertical drift was found for four different ranges of dip latitude for a northern solstice season. The effect of the transequatorial neutral winds was as evident in this plotting format as in the meridional or fountain effect format. Finally, the average vertical drift velocity V sub v, not the east-west electric field E sub ew, was found to be approximately independent of longitude, as expected from the dynamo theory.

Nonlinear simulations of Jupiter's 5-micron hot spots

NASA Technical Reports Server (NTRS)

Showman, A. P.; Dowling, T. E.

2000-01-01

Large-scale nonlinear simulations of Jupiter's 5-micron hot spots produce long-lived coherent structures that cause subsidence in local regions, explaining the low cloudiness and the dryness measured by the Galileo probe inside a hot spot. Like observed hot spots, the simulated coherent structures are equatorially confined, have periodic spacing, propagate west relative to the flow, are generally confined to one hemisphere, and have an anticyclonic gyre on their equatorward side. The southern edge of the simulated hot spots develops vertical shear of up to 70 meters per second in the eastward wind, which can explain the results of the Galileo probe Doppler wind experiment.

Local time asymmetries and toroidal field line resonances: Global magnetospheric modeling in SWMF

NASA Astrophysics Data System (ADS)

Ellington, S. M.; Moldwin, M. B.; Liemohn, M. W.

2016-03-01

We present evidence of resonant wave-wave coupling via toroidal field line resonance (FLR) signatures in the Space Weather Modeling Framework's (SWMF) global, terrestrial magnetospheric model in one simulation driven by a synthetic upstream solar wind with embedded broadband dynamic pressure fluctuations. Using in situ, stationary point measurements of the radial electric field along the 1500 LT meridian, we show that SWMF reproduces a multiharmonic, continuous distribution of FLRs exemplified by 180° phase reversals and amplitude peaks across the resonant L shells. By linearly increasing the amplitude of the dynamic pressure fluctuations in time, we observe a commensurate increase in the amplitude of the radial electric and azimuthal magnetic field fluctuations, which is consistent with the solar wind driver being the dominant source of the fast mode energy. While we find no discernible local time changes in the FLR frequencies despite large-scale, monotonic variations in the dayside equatorial mass density, in selectively sampling resonant points and examining spectral resonance widths, we observe significant radial, harmonic, and time-dependent local time asymmetries in the radial electric field amplitudes. A weak but persistent local time asymmetry exists in measures of the estimated coupling efficiency between the fast mode and toroidal wave fields, which exhibits a radial dependence consistent with the coupling strength examined by Mann et al. (1999) and Zhu and Kivelson (1988). We discuss internal structural mechanisms and additional external energy sources that may account for these asymmetries as we find that local time variations in the strength of the compressional driver are not the predominant source of the FLR amplitude asymmetries. These include resonant mode coupling of observed Kelvin-Helmholtz surface wave generated Pc5 band ultralow frequency pulsations, local time differences in local ionospheric dampening rates, and variations in azimuthal mode number, which may impact the partitioning of spectral energy between the toroidal and poloidal wave modes.

Cluster and THEMIS observations of the magnetosphere dayside boundaries in preparation for the SMILE mission

NASA Astrophysics Data System (ADS)

Escoubet, C. P.; Dimmock, A. P.; Walsh, B.; Sibeck, D. G.; Berchem, J.; Nykyri, K.; Turc, L.; Read, A.; Branduardi-Raymont, G.; Wang, C.; Sembay, S.; Kuntz, K. D.; Dai, L.; Li, L.; Donovan, E.; Spanswick, E.; Laakso, H. E.; Zheng, J.; Rebuffat, D.

2016-12-01

Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) is a novel self-standing mission, in collaboration between ESA and Chinese Academy of Science. Its objective is to observe the solar wind-magnetosphere coupling via simultaneous in situ solar wind/magnetosheath plasma and magnetic field measurements, soft X-Ray images of the magnetosheath and polar cusps, and UV images of global auroral distributions. The observations of the cusps and magnetosheath with the X-ray imager are possible through the relatively recent discovery of solar wind charge exchange (SWCX) X-ray emission, first observed at comets, and subsequently found to occur in the vicinity of the Earth's magnetosphere. In preparation for the mission, we need to determine the cusp's morphology, motion and in situ properties (density, velocity, temperature) that are expected to be observed by the spacecraft. To do so, we have selected a series of cusp crossings by the Cluster spacecraft that can be used to simulate X-ray emissions across the width of the cusp for different IMF orientations. In view of the well-known cusp ion dispersions, we expect that X ray emissions peak near the equatorial boundary of the cusp for southward IMF Bz, but near the poleward boundary of the cusp for northward IMF Bz. We also employ Cluster cusp observations during storms to predict X-ray emissions to be expected for periods of high solar wind fluxes. In addition, we use THEMIS observations from January 2008 to July 2015 for moderate (nsw*vsw < 4.9x10^8 /cm^2s) and high (nsw*vsw > 4.9x10^8 /cm^2s) solar wind fluxes to investigate X-rays emitted by the magnetosheath and to determine their variation as a function of distance from the subsolar point along the Sun-Earth line and along the flanks of the magnetosphere. We will show that high solar wind fluxes greatly enhance soft X-ray emissions, not only because solar wind fluxes increases but also because the emission region moves deeper within the Earth's exosphere.

Typical values of the electric drift E × B/B2 in the inner radiation belt and slot region as determined from Van Allen Probe measurements

NASA Astrophysics Data System (ADS)

Lejosne, Solène; Mozer, F. S.

2016-12-01

The electric drift E × B/B2 plays a fundamental role for the description of plasma flow and particle acceleration. Yet it is not well-known in the inner belt and slot region because of a lack of reliable in situ measurements. In this article, we present an analysis of the electric drifts measured below L 3 by both Van Allen Probes A and B from September 2012 to December 2014. The objective is to determine the typical components of the equatorial electric drift in both radial and azimuthal directions. The dependences of the components on radial distance, magnetic local time, and geographic longitude are examined. The results from Van Allen Probe A agree with Van Allen Probe B. They show, among other things, a typical corotation lag of the order of 5 to 10% below L 2.6, as well as a slight radial transport of the order of 20 m s-1. The magnetic local time dependence of the electric drift is consistent with that of the ionosphere wind dynamo below L 2 and with that of a solar wind-driven convection electric field above L 2. A secondary longitudinal dependence of the electric field is also found. Therefore, this work also demonstrates that the instruments on board Van Allen Probes are able to perform accurate measurements of the electric drift below L 3.

Potential Impact of North Atlantic Climate Variability on Ocean Biogeochemical Processes

NASA Astrophysics Data System (ADS)

Liu, Y.; Muhling, B.; Lee, S. K.; Muller-Karger, F. E.; Enfield, D. B.; Lamkin, J. T.; Roffer, M. A.

2016-02-01

Previous studies have shown that upper ocean circulations largely determine primary production in the euphotic layers, here the global ocean model with biogeochemistry (GFDL's Modular Ocean Model with TOPAZ biogeochemistry) forced with the ERA-Interim is used to simulate the natural variability of biogeochemical processes in global ocean during 1979-present. Preliminary results show that the surface chlorophyll is overall underestimated in MOM-TOPAZ, but its spatial pattern is fairly realistic. Relatively high chlorophyll variability is shown in the subpolar North Atlantic, northeastern tropical Atlantic, and equatorial Atlantic. Further analysis suggests that the chlorophyll variability in the North Atlantic Ocean is affected by long-term climate variability. For the subpolar North Atlantic region, the chlorophyll variability is light-limited and is significantly correlated with North Atlantic Oscillation. A dipole pattern of chlorophyll variability is found between the northeastern tropical Atlantic and equatorial Atlantic. For the northeastern North Atlantic, the chlorophyll variability is significantly correlated with Atlantic Meridional Mode (AMM) and Atlantic Multidecadal Oscillation (AMO). During the negative phase of AMM and AMO, the increased trade wind in the northeast North Atlantic can lead to increased upwelling of nutrients. In the equatorial Atlantic region, the chlorophyll variability is largely link to Atlantic-Niño and associated equatorial upwelling of nutrients. The potential impact of climate variability on the distribution of pelagic fishes (i.e. yellowfin tuna) are discussed.

Primary productivity and its variability in the equatorial South China Sea during the northeast monsoon

NASA Astrophysics Data System (ADS)

Ooi, S. H.; Samah, A. A.; Braesicke, P.

2013-08-01

Near coastal areas of the equatorial South China Sea (SCS) are one of the world's regions with highest primary productivity (phytoplankton growth). Concentrations of phytoplankton in the SCS depend significantly on atmospheric forcings and the oceanic state, in particular during the northeast (winter) monsoon season from November to March. Aided by new ocean-observing satellite data, we present a climatological overview of recent surface atmospheric and oceanic features in the equatorial SCS during the northeast monsoon to identify the dominant air-sea processes influencing and modulating the primary productivity of the region. Measured chlorophyll a concentrations are used as a proxy for phytoplankton amounts and the spatial and temporal variations are characterized according to meteorological conditions. Converging northeasterly surface winds support high chlorophyll a concentrations along East Malaysia's coastline in conjunction with a continual nutrient supply from the bottom of the continental shelf by vertical mixing. The mixing can be enhanced due to increased turbulence by wind-generated high waves when they approach shallow water from the deep basin during strong cold surges and monsoon disturbances. Intraseasonal variability during the winter monsoon is characterized by a coastal increase of chlorophyll a starting in November and peaking in January. A general decrease is observed in March. Interannual variability of chlorophyll a concentrations is influenced by ENSO (due to the known modulation of cold surge occurrences), with decreases during El Niño and increases during La Niña in early winter along the shore of East Malaysia. As an example, we discuss an enhanced phytoplankton growth event that occurred due to a typical cold surge-induced Borneo vortex event in January 2010.

Was the nineteenth century giant eruption of Eta Carinae a merger event in a triple system?

NASA Astrophysics Data System (ADS)

Portegies Zwart, S. F.; van den Heuvel, E. P. J.

2016-03-01

We discuss the events that led to the giant eruption of Eta Carinae, and find that the mid-nineteenth century (in 1838-1843) giant mass-loss outburst has the characteristics of being produced by the merger event of a massive close binary, triggered by the gravitational interaction with a massive third companion star, which is the current binary companion in the Eta Carinae system. We come to this conclusion by a combination of theoretical arguments supported by computer simulations using the Astrophysical Multipurpose Software Environment. According to this model the ˜90 M⊙ present primary star of the highly eccentric Eta Carinae binary system is the product of this merger, and its ˜30 M⊙ companion originally was the third star in the system. In our model, the Homunculus nebula was produced by an extremely enhanced stellar wind, energized by tidal energy dissipation prior to the merger, which enormously boosted the radiation-driven wind mass-loss. The current orbital plane is then aligned with the equatorial plane of the Homunculus, and the symmetric lobes are roughly aligned with the argument of periastron of the current Eta Carina binary. The merger itself then occurred in 1838, which resulted in a massive asymmetric outflow in the equatorial plane of the Homunculus. The 1843 outburst can in our model be attributed to the subsequent encounter when the companion star (once the outermost star in the triple system) plunges through the bloated envelope of the merger product, once when it passed periastron again. We predict that the system has an excess space velocity of order 50 km s-1 in the equatorial plane of the Homunculus. Our triple model gives a viable explanation for the high runaway velocities typically observed in LBVs.

The Pacific SST response to volcanic eruptions over the past millennium based on the CESM-LME

NASA Astrophysics Data System (ADS)

Man, W.; Zuo, M.

2017-12-01

The impact of the northern hemispheric, tropical and southern hemispheric volcanic eruptions on the Pacific sea surface temperature (SST) and its mechanism are investigated using the Community Earth System Model Last Millennium Ensemble. Analysis of the simulations indicates that the Pacific SST features a significant El Niño-like pattern a few months after the northern hemispheric and tropical eruptions, and with a weaker such tendency after the southern hemispheric eruptions. Furthermore, the Niño3 index peaks lagging one and a half years after the northern hemispheric and tropical eruptions. Two years after all three types of volcanic eruptions, a La Niña-like pattern over the equatorial Pacific is observed, which seems to form an El Niño-Southern Oscillation (ENSO) cycle. In addition, the westerly anomalies at 850 hPa over the western-to-central Pacific appear ahead of the warm SST; hence, the El Niño-like warming over the eastern Pacific can be attributed to the weakening of the trade winds. We further examined the causes of westerly anomalies and find that a shift of the intertropical convergence zone (ITCZ) can explain the El Niño-like response to the northern hemispheric eruptions, which is not applicable for tropical or southern hemispheric eruptions. Instead, the reduction in the zonal equatorial SST gradient through the ocean dynamical thermostat mechanism, combined with the land-sea thermal contrast between the Maritime Continent (MC) and the surrounding ocean and the divergent wind induced by the decreased precipitation over the MC, can trigger the westerly anomalies over the equatorial Pacific, which is applicable for all three types of eruptions.

Interhemispheric currents in the ring current region as seen by the Cluster spacecraft

NASA Astrophysics Data System (ADS)

Tenfjord, P.; Ostgaard, N.; Haaland, S.; Laundal, K.; Reistad, J. P.

2013-12-01

The existence of interhemispheric currents has been predicted by several authors, but their extent in the ring current has to our knowledge never been studied systematically by using in-situ measurements. These currents have been suggested to be associated with observed asymmetries of the aurora. We perform a statistical study of current density and direction during ring current crossings using the Cluster spacecraft. We analyse the extent of the interhemispheric field aligned currents for a wide range of solar wind conditions. Direct estimations of equatorial current direction and density are achieved through the curlometer technique. The curlometer technique is based on Ampere's law and requires magnetic field measurements from all four spacecrafts. The use of this method requires careful study of factors that limit the accuracy, such as tetrahedron shape and configuration. This significantly limits our dataset, but is a necessity for accurate current calculations. Our goal is to statistically investigate the occurrence of interhemispheric currents, and determine if there are parameters or magnetospheric states on which the current magnitude and directions depend upon.

Magnetic field studies at jupiter by voyager 2: preliminary results.

PubMed

Ness, N F; Acuna, M H; Lepping, R P; Burlaga, L F; Behannon, K W; Neubauer, F M

1979-11-23

Data from the Goddard Space Flight Center magnetometers on Voyager 2 have yielded on inbound trajectory observations of multiple crossings of the bow shock and magnetosphere near the Jupiter-sun line at radial distances of 99 to 66 Jupiter radii (RJ) and 72 to 62 RJ, respectively. While outbound at a local hour angle of 0300, these distances increase appreciably so that at the time of writing only the magnetopause has been observed between 160 and 185 RJ. These results and the magnetic field geometry confirm the earlier conclusion from Voyager I studies that Jupiter has an enormous magnetic tail, approximately 300 to 400 RJ in diameter, trailing behind the planet with respect to the supersonic flow of the solar wind. Addi- tional observations of the distortion of the inner magnetosphere by a concentrated plasma show a spatial merging of the equatorial magnetodisk current with the cur- rent sheet in the magnetic tail. The spacecraft passed within 62,000 kilometers of Ganymede (radius = 2,635 kilometers) and observed characteristic fluctuations in- terpreted tentatively as being due to disturbances arising from the interaction of the Jovian magnetosphere with Ganymede.

CPC - Climate Weather Linkage: El Niño Southern Oscillation

Science.gov Websites

Equatorial Pacific Temperature Depth Anomalies Animation Time longitude section of Anomalous OLR 850 hecto Temperatures anomalies Time series of weekly sea surface temperatures anomalies for the 4 Niño regions Time (OLR) Pentad mean and anomalous OLR Time-longitude section of anomalous OLR 850-hPa Zonal Wind Time

Effects of the seasonal cycle on superrotation in planetary atmospheres

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitchell, Jonathan L.; Vallis, Geoffrey K.; Potter, Samuel F.

2014-05-20

The dynamics of dry atmospheric general circulation model simulations forced by seasonally varying Newtonian relaxation are explored over a wide range of two control parameters and are compared with the large-scale circulation of Earth, Mars, and Titan in their relevant parameter regimes. Of the parameters that govern the behavior of the system, the thermal Rossby number (Ro) has previously been found to be important in governing the spontaneous transition from an Earth-like climatology of winds to a superrotating one with prograde equatorial winds, in the absence of a seasonal cycle. This case is somewhat unrealistic as it applies only ifmore » the planet has zero obliquity or if surface thermal inertia is very large. While Venus has nearly vanishing obliquity, Earth, Mars, and Titan (Saturn) all have obliquities of ∼25° and varying degrees of seasonality due to their differing thermal inertias and orbital periods. Motivated by this, we introduce a time-dependent Newtonian cooling to drive a seasonal cycle using idealized model forcing, and we define a second control parameter that mimics non-dimensional thermal inertia of planetary surfaces. We then perform and analyze simulations across the parameter range bracketed by Earth-like and Titan-like regimes, assess the impact on the spontaneous transition to superrotation, and compare Earth, Mars, and Titan to the model simulations in the relevant parameter regime. We find that a large seasonal cycle (small thermal inertia) prevents model atmospheres with large thermal Rossby numbers from developing superrotation by the influences of (1) cross-equatorial momentum advection by the Hadley circulation and (2) hemispherically asymmetric zonal-mean zonal winds that suppress instabilities leading to equatorial momentum convergence. We also demonstrate that baroclinic instabilities must be sufficiently weak to allow superrotation to develop. In the relevant parameter regimes, our seasonal model simulations compare favorably to large-scale, seasonal phenomena observed on Earth and Mars. In the Titan-like regime the seasonal cycle in our model acts to prevent superrotation from developing, and it is necessary to increase the value of a third parameter—the atmospheric Newtonian cooling time—to achieve a superrotating climatology.« less

Contribution of storm time substorms to the prompt electric field disturbances in the equatorial ionosphere

DOE PAGES

Hui, Debrup; Chakrabarty, D.; Sekar, R.; ...

2017-05-08

This study tries to bring out the fact that storm time substorms can compete and at times significantly contribute to the geomagnetically disturbed time prompt penetration electric field effects on low and equatorial latitudes. Observations of unusual equatorial plasma drift data from Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere during two space weather events show that substorms can induce both eastward and westward penetration electric fields under steady southward interplanetary magnetic field (IMF B z) conditions. During the first event on 2 January 2005, the enhancement of the daytime eastward electric field over Jicamarca due to substorm ismore » found to be comparable with the Sq and interplanetary electric field (IEFy) generated electric fields combined. During the second event on 19 August 2006, the substorm is seen to weaken the daytime eastward field thereby inducing a westward field in spite of the absence of northward turning of IMF B z (overshielding). The westward electric field perturbation in the absence of any overshielding events is observationally sparse and contrary to the earlier results. Further, the substorm-induced field is found to be strong enough to compete or almost nullify the effects of storm time IEFy fields. This study also shows quantitatively that at times substorm contribution to the disturbed time prompt electric fields can be significant and thus should be taken into consideration in evaluating penetration events over low latitudes.« less

Contribution of storm time substorms to the prompt electric field disturbances in the equatorial ionosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hui, Debrup; Chakrabarty, D.; Sekar, R.

This study tries to bring out the fact that storm time substorms can compete and at times significantly contribute to the geomagnetically disturbed time prompt penetration electric field effects on low and equatorial latitudes. Observations of unusual equatorial plasma drift data from Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere during two space weather events show that substorms can induce both eastward and westward penetration electric fields under steady southward interplanetary magnetic field (IMF B z) conditions. During the first event on 2 January 2005, the enhancement of the daytime eastward electric field over Jicamarca due to substorm ismore » found to be comparable with the Sq and interplanetary electric field (IEFy) generated electric fields combined. During the second event on 19 August 2006, the substorm is seen to weaken the daytime eastward field thereby inducing a westward field in spite of the absence of northward turning of IMF B z (overshielding). The westward electric field perturbation in the absence of any overshielding events is observationally sparse and contrary to the earlier results. Further, the substorm-induced field is found to be strong enough to compete or almost nullify the effects of storm time IEFy fields. This study also shows quantitatively that at times substorm contribution to the disturbed time prompt electric fields can be significant and thus should be taken into consideration in evaluating penetration events over low latitudes.« less

Spectral characteristics of geomagnetic field variations at low and equatorial latitudes

USGS Publications Warehouse

Campbell, W.H.

1977-01-01

Geomagnetic field spectra from eight standard observations at geomagnetic latitudes below 30?? were studied to determine the field characteristics unique to the equatorial region. Emphasis was placed upon those variations having periods between 5 min and 4 hr for a selection of magnetically quiet, average, and active days in 1965. The power spectral density at the equator was about ten times that the near 30?? latitude. The initial manifestation of the equatorial electrojet as evidenced by the east-west alignment of the horizontal field or the change in vertical amplitudes occurred below about 20?? latitude. Induced current effects upon the vertical component from which the Earth conductivity might be inferred could best be obtained at times and latitudes unaffected by the electrojet current. Values of about 1.6 ?? 103 mhos/m for an effective skin depth of 500-600 km were determined. The spectral amplitudes increased linearly with geomagnetic activity index, Ap. The spectral slope had a similar behavior at all latitudes. The slope changed systematically with Ap-index and showed a diurnal variation, centered on local noon, that changed form with geomagnetic activity.

Isotope and methane dynamics above and below the Trade Wind Inversion at Ascension Island using UAVs

NASA Astrophysics Data System (ADS)

Brownlow, R.; Lowry, D.; Nisbet, E. G.; Fisher, R. E.; France, J.; Lanoisellé, M.; Thomas, R.; Richardson, T.; Greatwood, C.; Freer, J. E.; MacKenzie, A. R.

2015-12-01

Ascension Island (8oS, 14 oW) is a South Atlantic background site for atmospheric measurement. Royal Holloway, in collaboration with the UK Met Office, installed a Picarro 1301 CRDS in 2010 for continuous methane monitoring. This has high precision and accuracy, with a 6-gas calibration and target suite, to measure long term methane mole fraction. Regular flask sampling is also carried out for NOAA and RHUL (co-located), to measure δ13CCH4 isotopic trends.Ascension Island experiences near-constant SE Trade winds below the Trade Wind Inversion (TWI), with air from the remote S. Atlantic. In flask samples and in continuous monitoring at the Airhead location, atmospheric methane mole fraction has been increasing since 2007 whilst the δ13CCH4 isotope record has shifted to more depleted values. Above the normally well-defined TWI (1200 - 1800m altitude), variable tropical air masses pass over Ascension. This air last mixed with the boundary layer over Africa or South America. Field work undertaken in September 2014 and July 2015, in collaboration with U. Bristol and U. Birmingham, using UAVs (octocopters) collected samples with Tedlar bags or aluminium flasks from different heights above and below the TWI. The maximum altitude reached was 2700masl. Sample bags were immediately analysed on Ascension for CH4 mole fraction using the Picarro CRDS and subsequently analysed at RHUL for δ13CCH4 using continuous-flow gas chromatography/isotope-ratio mass spectrometry (CF-GC/IRMS). The TWI was clearly identified by an increase in CH4 mole fraction above the TWI. Back trajectory analysis was used to distinguish the origins of the air masses, with air above showing inputs from the land surfaces of equatorial and southern Africa, and from southern S. America.The campaigns have extended the envelope of altitudes accessed by micro-UAVs for atmospheric science, demonstrating their utility for probing the remote free troposphere and for penetrating the TWI. Sampling at Ascension is able to measure both the deep S. Atlantic air and also the air that has been mixed by convective systems in the equatorial and southern savannah tropics. Biomass burning plumes in southern hemisphere winter may also be accessible. Ascension is thus potentially a measurement site of global significance.

Investigating the effect of geomagnetic storm and equatorial electrojet on equatorial ionospheric irregularity over East African sector

NASA Astrophysics Data System (ADS)

Seba, Ephrem Beshir; Nigussie, Melessew

2016-11-01

The variability of the equatorial ionosphere is still a big challenge for ionospheric dependent radio wave technology users. To mitigate the effect of equatorial ionospheric irregularity on trans-ionospheric radio waves considerable efforts are being done to understand and model the equatorial electrodynamics and its connection to the creation of ionospheric irregularity. However, the effect of the East-African ionospheric electrodynamics on ionospheric irregularity is not yet well studied due to lack of multiple ground based instruments. But, as a result of International Heliophysical Year (IHY) initiative, which was launched in 2007, some facilities are being deployed in Africa since then. Therefore, recently deployed instruments, in the Ethiopian sector, such as SCINDA-GPS receiver (2.64°N dip angle) for TEC and amplitude scintillation index (S4) data and two magnetometers, which are deployed on and off the magnetic equator, data collected in the March equinoctial months of the years 2011, 2012, and 2015 have been used for this study in conjunction with geomagnetic storm data obtained from high resolution OMNI WEB data center. We have investigated the triggering and inhibition mechanisms for ionospheric irregularities using, scintillation index (S4), equatorial electrojet (EEJ), interplanetary electric field (IEFy), symH index, AE index and interplanetary magnetic field (IMF) Bz on five selected storm and two storm free days. We have found that when the eastward EEJ fluctuates in magnitude due to storm time induced electric fields at around noontime, the post-sunset scintillation is inhibited. All observed post-sunset scintillations in equinox season are resulted when the daytime EEJ is non fluctuating. The strength of noontime EEJ magnitude has shown direct relation with the strength of the post-sunset scintillations. This indicates that non-fluctuating EEJ stronger than 20 nT, can be precursor for the occurrence of the evening time ionospheric irregularities. It is also found that prolonged eastward undershielding electric field during the daytime intensified the daytime EEJ magnitude and resulted in strong post-sunset scintillations. We have also observed that the rate of change of BZ (i.e. electric field produced by Faraday's Induction law) and eastward IEFy around the PRE hour is nicely correlated with strong post-sunset scintillations. Moreover, discussions about the causes for the appearance and disappearance of ionospheric scintillation are presented in this paper.

Diversity of moderate El Niño events evolution: role of air-sea interactions in the eastern tropical Pacific

NASA Astrophysics Data System (ADS)

Dewitte, Boris; Takahashi, Ken

2017-12-01

In this paper we investigate the evolution of moderate El Niño events during their developing phase with the objective to understand why some of them did not evolve as extreme events despite favourable conditions for the non-linear amplification of the Bjerknes feedback (i.e. warm SST in Austral winter in the eastern equatorial Pacific). Among the moderate events, two classes are considered consisting in the Eastern Pacific (EP) El Niño events and Central Pacific (CP) events. We first show that the observed SST variability across moderate El Niño events (i.e. inter-event variability) is largest in the far eastern Pacific (east of 130°W) in the Austral winter prior to their peak, which is associated to either significant warm anomaly (moderate EP El Niño) or an anomaly between weak warm and cold (moderate CP El Niño) as reveals by the EOF analysis of the SST anomaly evolution during the development phase of El Niño across the El Niño years. Singular value decomposition (SVD) analysis of SST and wind stress anomalies across the El Niño years further indicates that the inter-event SST variability is associated with an air-sea mode explaining 31% of the covariance between SST and wind stress. The associated SST pattern consists in SST anomalies developing along the coast of Ecuador in Austral fall and expanding westward as far as 130°W in Austral winter. The associated wind stress pattern features westerlies (easterlies) west of 130°W along the equator peaking around June-August for EP (CP) El Niño events. This air-sea mode is interpreted as resulting from a developing seasonal Bjerknes feedback for EP El Niño events since it is shown to be associated to a Kelvin wave response at its peak phase. However equatorial easterlies east of 130°W emerge in September that counters the growing SST anomalies associated to the air-sea mode. These have been particularly active during both the 1972 and the 2015 El Niño events. It is shown that the easterlies are connected to an off-equatorial southerly wind off the coast of Peru and Ecuador. The southerly wind is a response to the coastal SST anomalies off Peru developing from Austral fall. Implications of our results for the understanding of the seasonal ENSO dynamics and diversity are discussed in the light of the analysis of two global climate models simulating realistically ENSO diversity (GFDL_CM2.1 and CESM).

Dayside Magnetosphere-Ionosphere Coupling and Prompt Response of Low-Latitude/Equatorial Ionosphere

NASA Astrophysics Data System (ADS)

Tu, J.; Song, P.

2017-12-01

We use a newly developed numerical simulation model of the ionosphere/thermosphere to investigate magnetosphere-ionosphere coupling and response of the low-latitude/equatorial ionosphere. The simulation model adapts an inductive-dynamic approach (including self-consistent solutions of Faraday's law and retaining inertia terms in ion momentum equations), that is, based on magnetic field B and plasma velocity v (B-v paradigm), in contrast to the conventional modeling based on electric field E and current j (E-j paradigm). The most distinct feature of this model is that the magnetic field in the ionosphere is not constant but self-consistently varies, e.g., with currents, in time. The model solves self-consistently time-dependent continuity, momentum, and energy equations for multiple species of ions and neutrals including photochemistry, and Maxwell's equations. The governing equations solved in the model are a set of multifluid-collisional-Hall MHD equations which are one of unique features of our ionosphere/thermosphere model. With such an inductive-dynamic approach, all possible MHD wave modes, each of which may refract and reflect depending on the local conditions, are retained in the solutions so that the dynamic coupling between the magnetosphere and ionosphere and among different regions of the ionosphere can be self-consistently investigated. In this presentation, we show that the disturbances propagate in the Alfven speed from the magnetosphere along the magnetic field lines down to the ionosphere/thermosphere and that they experience a mode conversion to compressional mode MHD waves (particularly fast mode) in the ionosphere. Because the fast modes can propagate perpendicular to the field, they propagate from the dayside high-latitude to the nightside as compressional waves and to the dayside low-latitude/equatorial ionosphere as rarefaction waves. The apparent prompt response of the low-latitude/equatorial ionosphere, manifesting as the sudden increase of the upward flow around the equator and global antisunward convection, is the result of such coupling of the high-latitude and the low-latitude/equatorial ionosphere, and the requirement of the flow continuity, instead of mechanisms such as the penetration electric field.

Centennial changes in North Pacific anoxia linked to tropical trade winds

USGS Publications Warehouse

Deutsch, Curtis; Berelson, William; Thunell, Robert; Weber, Thomas; Tems, Caitlin; McManus, James; Crusius, John; Ito, Taka; Baumgartner, Timothy; Ferreira, Vicente; Mey, Jacob; van Geen, Alexander

2014-01-01

Climate warming is expected to reduce oxygen (O2) supply to the ocean and expand its oxygen minimum zones (OMZs). We reconstructed variations in the extent of North Pacific anoxia since 1850 using a geochemical proxy for denitrification (δ15N) from multiple sediment cores. Increasing δ15N since ~1990 records an expansion of anoxia, consistent with observed O2 trends. However, this was preceded by a longer declining δ15N trend that implies that the anoxic zone was shrinking for most of the 20th century. Both periods can be explained by changes in winds over the tropical Pacific that drive upwelling, biological productivity, and O2 demand within the OMZ. If equatorial Pacific winds resume their predicted weakening trend, the ocean’s largest anoxic zone will contract despite a global O2 decline.

Obtaining Networked Scintillation and Total Electron Content Data Across Africa and Asia: Partnering with the IHY/UNBSSI Developing Nations Program

NASA Astrophysics Data System (ADS)

Groves, K. M.; Basu, S.; Erickson, T.; Sunanda, B.; David, B.

2005-12-01

Under the Scintillation Network Decision Aid (SCINDA) project, scientists at the Air Force Research Laboratory (AFRL) have developed a sensor network for the purpose of monitoring low-latitude ionospheric total electron content (TEC) and scintillations associated with equatorial Spread F. In addition to monitoring GPS scintillations, TEC and VHF scintillations, the sensor package measures ionospheric drifts when irregularities are present providing important data on vertical electric fields in the F-region .The network currently consists of twelve stations distributed around the globe and the data have been used to conduct numerous studies on the characteristics and climatology of equatorial scintillation, including the impacts of magnetic storms on the equatorial ionosphere. Notably absent from the existing network are observing sites in Africa where both satellite observations and limited historical data sets suggest significant scintillation activity, though the detailed behavior and longitudinal variations across the continent are largely unknown. The latter aspect, in particular, is of great interest because of substantial changes in the orientation of the geomagnetic field in extreme West Africa that transition to a more uniform field geometry spanning the rest of the continent. Understanding the effects of these changes on scintillation climatology will provide new insights into the processes that trigger equatorial Spread F and assist researchers in developing improved forecasts of such activity. AFRL aims to establish 5-8 monitoring sites across equatorial Africa in collaboration with host nations participating in the United Nations Basic Space Science Initiative during the IHY period. In addition to expanding scientific opportunities, it is hoped that these sites will lead to greater awareness of the significant space weather issues impacting Africa and result in enhanced international collaboration between both African and non-African scientists interested in constructing an improved description of the equatorial ionosphere.

Simulations of Atmospheric Neutral Wave Coupling to the Ionosphere

NASA Astrophysics Data System (ADS)

Siefring, C. L.; Bernhardt, P. A.

2005-12-01

The densities in the E- and F-layer plasmas are much less than the density of background neutral atmosphere. Atmospheric neutral waves are primary sources of plasma density fluctuations and are the sources for triggering plasma instabilities. The neutral atmosphere supports acoustic waves, acoustic gravity waves, and Kelvin Helmholtz waves from wind shears. These waves help determine the structure of the ionosphere by changes in neutral density that affect ion-electron recombination and by neutral velocities that couple to the plasma via ion-neutral collisions. Neutral acoustic disturbances can arise from thunderstorms, chemical factory explosions and intentional high-explosive tests. Based on conservation of energy, acoustic waves grow in amplitude as they propagate upwards to lower atmospheric densities. Shock waves can form in an acoustic pulse that is eventually damped by viscosity. Ionospheric effects from acoustic waves include transient perturbations of E- and F-Regions and triggering of E-Region instabilities. Acoustic-gravity waves affect the ionosphere over large distances. Gravity wave sources include thunderstorms, auroral region disturbances, Space Shuttle launches and possibly solar eclipses. Low frequency acoustic-gravity waves propagate to yield traveling ionospheric disturbances (TID's), triggering of Equatorial bubbles, and possible periodic structuring of the E-Region. Gravity wave triggering of equatorial bubbles is studied numerically by solving the equations for plasma continuity and ion velocity along with Ohms law to provide an equation for the induced electric potential. Slow moving gravity waves provide density depressions on bottom of ionosphere and a gravitational Rayleigh-Taylor instability is initiated. Radar scatter detects field aligned irregularities in the resulting plasma bubble. Neutral Kelvin-Helmholtz waves are produced by strong mesospheric wind shears that are also coincident with the formation of intense E-layers. An atmospheric model for periodic structures with Kelvin-Helmholtz (KH) wavelengths is used to show the development of quasi-periodic structures in the E-layer. For the model, a background atmosphere near 100 km altitude with a scale height of 12.2 km is subjected to a wind shear profile varying by 100 m/s over a distance of 1.7 km. This neutral speed shear drives the KH instability with a growth time of about 100 seconds. The neutral KH wave is a source of plasma turbulence. The E-layer responds to the KH-Wave structure in the neutral atmosphere as an electrodynamic tracer. The plasma flow leads to small scale plasma field aligned irregularities from a gradient drift, plasma interchange instability (GDI) or a Farley-Buneman, two-stream instability (FBI). These irregularities are detected by radar scatter as quasi-periodic structures. All of these plasma phenomena would not occur without the initiation by neutral atmospheric waves.

A study on ionospheric scintillation near the EIA crest in relation to equatorial electrodynamics

NASA Astrophysics Data System (ADS)

Chatterjee, S.; Chakraborty, S. K.; Veenadhari, B.; Banola, S.

2014-02-01

Equatorial electrojet (EEJ) data, which are considered as a proxy index of equatorial electric field, are analyzed in conjunction with equatorial ionosonde, total electron content (TEC) and scintillation data near the equatorial ionization anomaly (EIA) crest for the equinoctial months of high solar activity years (2011-2012) to identify any precursor index of postsunset evolution of equatorial electron density irregularities and subsequent occurrence of scintillation near the northern EIA crest. Only geomagnetically quiet and normal electrojet days are considered. The diurnal profiles of EEJ on the scintillation days exhibit a secondary enhancement in the afternoon to presunset hours following diurnal peaks. A series of electrodynamical processes conducive for generation of irregularities emerge following secondary enhancement of EEJ. Latitudinal profile of TEC exhibits resurgence in EIA structure around the postsunset period. Diurnal TEC profile near the EIA crest resembles postsunset secondary enhancement on the days with afternoon enhancement in EEJ. Occurrence of equatorial spread F and postsunset scintillation near the EIA crest seems to follow the secondary enhancement events in EEJ. Both the magnitude and duration of enhanced EEJ are found to be important for postsunset intensification of EIA structure and subsequent occurrence of equatorial irregularities. A critical value combining the two may be considered an important precursor for postsunset occurrence of scintillation near the EIA crest. The results are validated using archived data for the years 1989-1990 and explained in terms of modulation effects of enhanced equatorial fountain.

Ocean Surface Winds Drive Dynamics of Transoceanic Aerial Movements

PubMed Central

Felicísimo, Ángel M.; Muñoz, Jesús; González-Solis, Jacob

2008-01-01

Global wind patterns influence dispersal and migration processes of aerial organisms, propagules and particles, which ultimately could determine the dynamics of colonizations, invasions or spread of pathogens. However, studying how wind-mediated movements actually happen has been hampered so far by the lack of high resolution global wind data as well as the impossibility to track aerial movements. Using concurrent data on winds and actual pathways of a tracked seabird, here we show that oceanic winds define spatiotemporal pathways and barriers for large-scale aerial movements. We obtained wind data from NASA SeaWinds scatterometer to calculate wind cost (impedance) models reflecting the resistance to the aerial movement near the ocean surface. We also tracked the movements of a model organism, the Cory's shearwater (Calonectris diomedea), a pelagic bird known to perform long distance migrations. Cost models revealed that distant areas can be connected through “wind highways” that do not match the shortest great circle routes. Bird routes closely followed the low-cost “wind-highways” linking breeding and wintering areas. In addition, we found that a potential barrier, the near surface westerlies in the Atlantic sector of the Intertropical Convergence Zone (ITCZ), temporally hindered meridional trans-equatorial movements. Once the westerlies vanished, birds crossed the ITCZ to their winter quarters. This study provides a novel approach to investigate wind-mediated movements in oceanic environments and shows that large-scale migration and dispersal processes over the oceans can be largely driven by spatiotemporal wind patterns. PMID:18698354

Ocean surface winds drive dynamics of transoceanic aerial movements.

PubMed

Felicísimo, Angel M; Muñoz, Jesús; González-Solis, Jacob

2008-08-13

Global wind patterns influence dispersal and migration processes of aerial organisms, propagules and particles, which ultimately could determine the dynamics of colonizations, invasions or spread of pathogens. However, studying how wind-mediated movements actually happen has been hampered so far by the lack of high resolution global wind data as well as the impossibility to track aerial movements. Using concurrent data on winds and actual pathways of a tracked seabird, here we show that oceanic winds define spatiotemporal pathways and barriers for large-scale aerial movements. We obtained wind data from NASA SeaWinds scatterometer to calculate wind cost (impedance) models reflecting the resistance to the aerial movement near the ocean surface. We also tracked the movements of a model organism, the Cory's shearwater (Calonectris diomedea), a pelagic bird known to perform long distance migrations. Cost models revealed that distant areas can be connected through "wind highways" that do not match the shortest great circle routes. Bird routes closely followed the low-cost "wind-highways" linking breeding and wintering areas. In addition, we found that a potential barrier, the near surface westerlies in the Atlantic sector of the Intertropical Convergence Zone (ITCZ), temporally hindered meridional trans-equatorial movements. Once the westerlies vanished, birds crossed the ITCZ to their winter quarters. This study provides a novel approach to investigate wind-mediated movements in oceanic environments and shows that large-scale migration and dispersal processes over the oceans can be largely driven by spatiotemporal wind patterns.

Impact of disturbance electric fields in the evening on prereversal vertical drift and spread F developments in the equatorial ionosphere

NASA Astrophysics Data System (ADS)

Abdu, Mangalathayil A.; Nogueira, Paulo A. B.; Santos, Angela M.; de Souza, Jonas R.; Batista, Inez S.; Sobral, Jose H. A.

2018-04-01

Equatorial plasma bubble/spread F irregularity occurrence can present large variability depending upon the intensity of the evening prereversal enhancement in the zonal electric field (PRE), that is, the F region vertical plasma drift, which basically drives the post-sunset irregularity development. Forcing from magnetospheric disturbances is an important source of modification and variability in the PRE vertical drift and of the associated bubble development. Although the roles of magnetospheric disturbance time penetration electric fields in the bubble irregularity development have been studied in the literature, many details regarding the nature of the interaction between the penetration electric fields and the PRE vertical drift still lack our understanding. In this paper we have analyzed data on F layer heights and vertical drifts obtained from digisondes operated in Brazil to investigate the connection between magnetic disturbances occurring during and preceding sunset and the consequent variabilities in the PRE vertical drift and associated equatorial spread F (ESF) development. The impact of the prompt penetration under-shielding eastward electric field and that of the over-shielding, and disturbance dynamo, westward electric field on the evolution of the evening PRE vertical drift and thereby on the ESF development are briefly examined.

Ulysses breaks latitude record

NASA Astrophysics Data System (ADS)

1993-06-01

Ulysses is gathering important new information concerning the Sun and its environment. Its prime mission objective is to carry out the first systematic exploration of the inner part of the heliosphere - the region of space carved out of the interstellar medium by the solar wind - at all latitudes from the solar equator to the poles. The spacecraft, launched by the space shuttle Discovery on 6 October 1990 in the framework of an ESA-NASA collaborative venture, underwent a gravity assist manoeuvre at Jupiter in February 1992 and is now in a highly inclined solar orbit that will bring it over the south pole of the Sun in September 1994. At that time, Ulysses will establish a new record as it climbs to its maximum latitude of just over 80 degrees. The spacecraft and its scientific instruments are in excellent condition and the data coverage since launch has been consistently close to 100% thanks to the dedicated efforts of the joint ESA-NASA Mission Operations Team and NASA's Deep Space Network. Although the most exciting phase of the mission - the study of the Sun's polar regions - will only begin in mid-1994, Ulysses has already produced a wealth of new scientific results. These include : * - The first direct detection of neutral helium atoms arriving from interstellar space. * - The measurement of micron-sized dust grains arriving from interstellar space. * - The first measurement of singly-charged H, N, O and Ne ions which entered the heliosphere as interstellar neutral atoms and were then ionised. * - The highest-resolution measurements to date of the isotopic composition of cosmic ray nuclei (e.g. C, N, O, Ne, Si and Mg). In addition to the above, the traversal of Jupiter's magnetosphere at the time of the fly-by enabled the Ulysses investigators to acquire new and highly valuable data concerning this very complex and dynamic plasma environment. Among the more exciting results to emerge are the possible entry into the polar cap of Jupiter's magnetosphere near the time of closest approach, and the unexpectedly strong influence of the solar wind deep in the magnetosphere during the outbound passage. With the Jupiter fly-by safely accomplished, the scientific focus is now directed towards phenomena related to the increasing latitute of the spacecraft. Already, there is strong evidence that Ulysses is now in the domain of the southern polar magnetic field. By a fortunate coincidence, just as Ulysses was reaching 32 degrees South, the magnetic field and plasma analyser scientific teams were seeing the first evidence of the effect of increasing latitude on the magnetised solar wind. The two complementary sets of observations reveal the passage of Ulysses into a magnetic unipolar regime corresponding to latitudes above the sunspot belt, having permanently crossed the boundary separating northern and southern magnetic fields. Following the flight over the Sun's southern pole, Ulysses' orbit will bring the spaceprobe swinging back towards the equatorial regions, heading for its second high-latitude excursion in mid-1995, this time above the North polar regions. "By the end of September 1995, Ulysses will have put our knowledge of the Sun and its environment in a completely new perspective", says Dr. Marsden, ESA's Project Scientist for Ulysses. "Only by studying the way the Sun influences the space around it in a global manner can we hope to understand its influence on our local interplanetary environment". An example of this "local" influence is the disturbance experienced by technical systems in Earth orbit and on the ground (e.g., telecommunications systems) at the time of major solar flares. Note to the Editors: Near the Sun's equatorial regions, the interplanetary magnetic field alternately points toward and away from the Sun during a single solar rotation which gives rise to so-called magnetic sectors. The existence of these sectors is interpreted as the effect of a vast current sheet, tilted with respect to the Sun's rotation axis, which separates oppositely-directed magnetic fields from the North and South polar caps. The recent Ulysses magnetic field observations reveal a single polarity, i.e. the disappearance of magnetic sectors. This implies that Ulysses is now above the current sheet. The polarity of the observed fields corresponds to that of the Sun's south polar cap as would be expected. Concurrent with the magnetic sector disappearance, the Ulysses solar wind plasma instrument, which detects solar wind ions and electrons, shows a persistently fast solar wind flow. High speed solar wind is thought to issue from coronal holes (regions of reduced X-ray brightness and density in the Sun's corona), and it is known that extended coronal holes cover each of the polar caps at this phase of the solar cycle. The Ulysses observations are interpreted as indicating that the spacecraft has now entered the region above the southern polar coronal hole.

Application of a Reduced Order Kalman Filter to Initialize a Coupled Atmosphere-Ocean Model: Impact on the Prediction of El Nino

NASA Technical Reports Server (NTRS)

Ballabrera-Poy, J.; Busalacchi, A.; Murtugudde, R.

2000-01-01

A reduced order Kalman Filter, based on a simplification of the Singular Evolutive Extended Kalman (SEEK) filter equations, is used to assimilate observed fields of the surface wind stress, sea surface temperature and sea level into the nonlinear coupled ocean-atmosphere model of Zebiak and Cane. The SEEK filter projects the Kalman Filter equations onto a subspace defined by the eigenvalue decomposition of the error forecast matrix, allowing its application to high dimensional systems. The Zebiak and Cane model couples a linear reduced gravity ocean model with a single vertical mode atmospheric model of Zebiak. The compatibility between the simplified physics of the model and each observed variable is studied separately and together. The results show the ability of the model to represent the simultaneous value of the wind stress, SST and sea level, when the fields are limited to the latitude band 10 deg S - 10 deg N In this first application of the Kalman Filter to a coupled ocean-atmosphere prediction model, the sea level fields are assimilated in terms of the Kelvin and Rossby modes of the thermocline depth anomaly. An estimation of the error of these modes is derived from the projection of an estimation of the sea level error over such modes. This method gives a value of 12 for the error of the Kelvin amplitude, and 6 m of error for the Rossby component of the thermocline depth. The ability of the method to reconstruct the state of the equatorial Pacific and predict its time evolution is demonstrated. The method is shown to be quite robust for predictions up to six months, and able to predict the onset of the 1997 warm event fifteen months before its occurrence.

Application of a Reduced Order Kalman Filter to Initialize a Coupled Atmosphere-Ocean Model: Impact on the Prediction of El Nino

NASA Technical Reports Server (NTRS)

Ballabrera-Poy, Joaquim; Busalacchi, Antonio J.; Murtugudde, Ragu

2000-01-01

A reduced order Kalman Filter, based on a simplification of the Singular Evolutive Extended Kalman (SEEK) filter equations, is used to assimilate observed fields of the surface wind stress, sea surface temperature and sea level into the nonlinear coupled ocean-atmosphere model. The SEEK filter projects the Kalman Filter equations onto a subspace defined by the eigenvalue decomposition of the error forecast matrix, allowing its application to high dimensional systems. The Zebiak and Cane model couples a linear reduced gravity ocean model with a single vertical mode atmospheric model of Zebiak. The compatibility between the simplified physics of the model and each observed variable is studied separately and together. The results show the ability of the model to represent the simultaneous value of the wind stress, SST and sea level, when the fields are limited to the latitude band 10 deg S - 10 deg N. In this first application of the Kalman Filter to a coupled ocean-atmosphere prediction model, the sea level fields are assimilated in terms of the Kelvin and Rossby modes of the thermocline depth anomaly. An estimation of the error of these modes is derived from the projection of an estimation of the sea level error over such modes. This method gives a value of 12 for the error of the Kelvin amplitude, and 6 m of error for the Rossby component of the thermocline depth. The ability of the method to reconstruct the state of the equatorial Pacific and predict its time evolution is demonstrated. The method is shown to be quite robust for predictions I up to six months, and able to predict the onset of the 1997 warm event fifteen months before its occurrence.

The Role of Ocean Dynamical Thermostat in Delaying the El Niño–Like Response over the Equatorial Pacific to Climate Warming

DOE PAGES

Luo, Yiyong; Lu, Jian; Liu, Fukai; ...

2017-03-27

The role of the ocean dynamics in the response of the equatorial Pacific Ocean to climate warming is investigated using both an atmosphere-ocean coupled climate system and its ocean component. Results show that the initial response (fast pattern) to an uniform heating imposed on to the ocean is a warming centered to the west of the dateline owing to the conventional ocean dynamical thermostat (ODT) mechanism in the eastern equatorial Pacific-a cooling effect arising from the up-gradient upwelling. In time, the warming pattern gradually propagates eastward, becoming more El Niño-like (slow pattern). The transition from the fast to the slowmore » patterns is likely resulted from i) the gradual warming of the equatorial thermocline temperature, which is associated with the arrival of the relatively warmer extratropical waters advected along the subsurface branch of the subtropical cells (STC) and ii) the reduction of the STC strength itself. A mixed layer heat budget analysis finds that it is the total ocean dynamical effect rather than the conventional ODT that holds the key for understanding the pattern of the SST in the equatorial Pacific and that the surface heat flux works mainly to compensate the ocean dynamics. Further passive tracer experiments with the ocean component of the coupled system verify the role of the ocean dynamical processes in initiating a La Niña-like SST warming and in setting the pace of the transition to an El Niño-like warming and identify an oceanic origin for the slow eastern Pacific warming independent of the weakening trade wind.« less

ENSO-driven nutrient variability recorded by central equatorial Pacific corals

NASA Astrophysics Data System (ADS)

LaVigne, M.; Nurhati, I. S.; Cobb, K. M.; McGregor, H. V.; Sinclair, D. J.; Sherrell, R. M.

2012-12-01

Recent evidence for shifts in global ocean primary productivity suggests that surface ocean nutrient availability is a key link between global climate and ocean carbon cycling. Time-series records from satellite, in situ buoy sensors, and bottle sampling have documented the impact of the El Niño Southern Oscillation (ENSO) on equatorial Pacific hydrography and broad changes in biogeochemistry since the late 1990's, however, data are sparse prior to this. Here we use a new paleoceanographic nutrient proxy, coral P/Ca, to explore the impact of ENSO on nutrient availability in the central equatorial Pacific at higher-resolution than available from in situ nutrient data. Corals from Christmas (157°W 2°N) and Fanning (159°W 4°N) Islands recorded a well-documented decrease in equatorial upwelling as a ~40% decrease in P/Ca during the 1997-98 ENSO cycle, validating the application of this proxy to Pacific Porites corals. We compare the biogeochemical shifts observed through the 1997-98 event with two pre-TOGA-TAO ENSO cycles (1982-83 and 1986-87) reconstructed from a longer Christmas Island core. All three corals revealed ~30-40% P/Ca depletions during ENSO warming as a result of decreased regional wind stress, thermocline depth, and equatorial upwelling velocity. However, at the termination of each El Niño event, surface nutrients did not return to pre-ENSO levels for ~4-12 months after, SST as a result of increased biological draw down of surface nutrients. These records demonstrate the utility of high-resolution coral nutrient archives for understanding the impact of tropical Pacific climate on the nutrient and carbon cycling of this key region.

Meteorology of Jupiter's Equatorial Hot Spots and Plumes from Cassini

NASA Technical Reports Server (NTRS)

Choi, David Sanghun; Showman, Adam P.; Vasavada, Ashwin R.; Simon-Miller, Amy A.

2013-01-01

We present an updated analysis of Jupiter's equatorial meteorology from Cassini observations. For two months preceding the spacecraft's closest approach, the Imaging Science Subsystem (ISS) onboard regularly imaged the atmosphere. We created time-lapse movies from this period in order to analyze the dynamics of equatorial hot spots and their interactions with adjacent latitudes. Hot spots are relatively cloud-free regions that emit strongly at 5 lm; improved knowledge of these features is crucial for fully understanding Galileo probe measurements taken during its descent through one. Hot spots are quasistable, rectangular dark areas on visible-wavelength images, with defined eastern edges that sharply contrast with surrounding clouds, but diffuse western edges serving as nebulous boundaries with adjacent equatorial plumes. Hot spots exhibit significant variations in size and shape over timescales of days and weeks. Some of these changes correspond with passing vortex systems from adjacent latitudes interacting with hot spots. Strong anticyclonic gyres present to the south and southeast of the dark areas appear to circulate into hot spots. Impressive, bright white plumes occupy spaces in between hot spots. Compact cirrus-like 'scooter' clouds flow rapidly through the plumes before disappearing within the dark areas. These clouds travel at 150-200 m/s, much faster than the 100 m/s hot spot and plume drift speed. This raises the possibility that the scooter clouds may be more illustrative of the actual jet stream speed at these latitudes. Most previously published zonal wind profiles represent the drift speed of the hot spots at their latitude from pattern matching of the entire longitudinal image strip. If a downward branch of an equatorially-trapped Rossby wave controls the overall appearance of hot spots, however, the westward phase velocity of the wave leads to underestimates of the true jet stream speed.

The Role of Ocean Dynamical Thermostat in Delaying the El Niño–Like Response over the Equatorial Pacific to Climate Warming

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Yiyong; Lu, Jian; Liu, Fukai

The role of the ocean dynamics in the response of the equatorial Pacific Ocean to climate warming is investigated using both an atmosphere-ocean coupled climate system and its ocean component. Results show that the initial response (fast pattern) to an uniform heating imposed on to the ocean is a warming centered to the west of the dateline owing to the conventional ocean dynamical thermostat (ODT) mechanism in the eastern equatorial Pacific-a cooling effect arising from the up-gradient upwelling. In time, the warming pattern gradually propagates eastward, becoming more El Niño-like (slow pattern). The transition from the fast to the slowmore » patterns is likely resulted from i) the gradual warming of the equatorial thermocline temperature, which is associated with the arrival of the relatively warmer extratropical waters advected along the subsurface branch of the subtropical cells (STC) and ii) the reduction of the STC strength itself. A mixed layer heat budget analysis finds that it is the total ocean dynamical effect rather than the conventional ODT that holds the key for understanding the pattern of the SST in the equatorial Pacific and that the surface heat flux works mainly to compensate the ocean dynamics. Further passive tracer experiments with the ocean component of the coupled system verify the role of the ocean dynamical processes in initiating a La Niña-like SST warming and in setting the pace of the transition to an El Niño-like warming and identify an oceanic origin for the slow eastern Pacific warming independent of the weakening trade wind.« less

Investigation of Jupiter's Equatorial Hotspots and Plumes Using Cassini ISS Observations

NASA Technical Reports Server (NTRS)

Choi, David S.; Showman, A. P.; Vasavada, A. R.; Simon-Miller, A. A.

2012-01-01

We present updated analysis of Jupiter's equatorial meteorology from Cassini observations. For two months preceding the spacecraft's closest approach, the ISS onboard regularly imaged the atmosphere. We created time-lapse movies from this period in order to analyze the dynamics of equatorial 5-micron hot spots and their interactions with adjacent latitudes. Hot spots are quasi-stable, rectangular dark areas on visible-wavelength images, with defined eastern edges that sharply contrast with surrounding clouds, but a diffuse western edge serving as a nebulous boundary with adjacent equatorial plumes. Hot spots exhibit significant variations in size and shape over timescales of days and weeks. Some of these changes correspond with passing vortex systems from adjacent latitudes interacting with hot spots. Strong anticyclonic gyres present to the south and southeast of the dark areas appear to circulate into hot spots. Impressive, bright white plumes occupy spaces in between hot spots. Compact cirrus-iike 'scooter' clouds flow rapidly through the plumes before disappearing within the dark areas. This raises the possibility that the plumes and fast-moving clouds are at higher altitudes, because their speed does not match previously published zonal wind profiles. Most profiles represent the drift speed of the hot spots at their latitude from pattern matching of the entire longitudinal image strip. If a downward branch of an equatorially-trapped Rossby waves controls the overall appearance of hot spots, however, the westward phase velocity of the wave leads to underestimates of the true jet stream speed. Instead, our expanded data set demonstrating the rapid flow of these scooter clouds may be more illustrative of the actual jet stream speed at these latitudes. This research was supported by a NASA JDAP grant and the NASA Postdoctoral Program.

Assessment of the simulation of Indian Ocean Dipole in the CESM—Impacts of atmospheric physics and model resolution

NASA Astrophysics Data System (ADS)

Yao, Zhixiong; Tang, Youmin; Chen, Dake; Zhou, Lei; Li, Xiaojing; Lian, Tao; Ul Islam, Siraj

2016-12-01

This study examines the possible impacts of coupling processes on simulations of the Indian Ocean Dipole (IOD). Emphasis is placed on the atmospheric model resolution and physics. Five experiments were conducted for this purpose, including one control run of the ocean-only model, four coupled experiments using two different versions of the Community Atmosphere Model (CAM4 and CAM5) and two different resolutions. The results show that the control run could effectively simulate various features of the IOD. The coupled experiments run at the higher resolution yielded more realistic IOD period and intensity than their counterparts at the low resolution. The coupled experiments using CAM5 generally showed a better simulation skill in the tropical Indian SST climatology and phase-locking than those using CAM4, but the wind anomalies were stronger and the IOD period were longer in the former experiments than in the latter. In all coupled experiments, the IOD intensity was much stronger than the observed intensity, which is attributable to wind-thermocline depth feedback and thermocline depth-subsurface temperature feedback. The CAM5 physics seems beneficial for the simulation of summer rainfall over the eastern equatorial Indian Ocean and the CAM4 physics tends to produce less biases over the western equatorial Indian Ocean, whereas the higher resolution tends to generate unrealistically strong meridional winds. The IOD-ENSO relationship was captured reasonably well in coupled experiments, with improvements in CAM5 relative to CAM4. However, the teleconnection of the IOD-Indian summer monsoon and ENSO-Indian summer monsoon was not realistically simulated in all experiments.

Intraseasonal-to-semiannual variability of sea-surface height in the astern, equatorial Indian Ocean and southern Bay of Bengal

NASA Astrophysics Data System (ADS)

Cheng, Xuhua; McCreary, Julian P.; Qiu, Bo; Qi, Yiquan; Du, Yan

2017-05-01

Intraseasonal-to-semiannual variability of sea-surface height (SSH) in the eastern, equatorial Indian Ocean (EEIO) and southern Bay of Bengal (BoB) is investigated using altimetric data, and solutions to 1½ layer (first baroclinic mode) and linear, continuously stratified (LCS; multibaroclinic-mode) models. The amplitude and dominant periods of SSH variability differ regionally. Large-amplitude variability is found along the west coast of Sumatra, in a zonal band across the BoB centered along 5°N, east of Sri Lanka, and in the northwestern BoB, respectively. Along the Sumatran west coast, SSH variability peaks at 30-60, 90, and 180 days. Along 5°N and east of Sri Lanka, the 30-60 day variability is dominant. Sensitivity experiments using a nonlinear version of the 1½ layer model forced by realistic winds reproduce the observed patterns of intraseasonal variability in the southern BoB. At 30-60 days, the solutions show that eddies (nonlinear Rossby waves) propagating from the east, rather than local wind forcing, account for most of the variance east of Sri Lanka; furthermore, they demonstrate that the variance is significantly enhanced by the nonlinear transfer of 90-120 day energy into the intraseasonal band of 30-60 days. The LCS solutions show that the first two baroclinic modes explain most of the SSH variance at 90-180 days. The second baroclinic mode dominates the SSH variance at 180 days, a consequence of basin resonance and strong wind forcing.

Temperatures and Composition in the Saturn System from Cassini CIRS

NASA Technical Reports Server (NTRS)

Flasar, F. Michael

2008-01-01

We summarize recent observations by the Composite Infrared Spectrometer of Saturn, its rings, Titan, and the icy satellites. Limb observations of Saturn show vertical oscillations of temperatures and zonal-wind shears in the equatorial region that may be related to a temporal oscillation similar to the terrestrial QBO and Jupiter's QQO. There is also evidence of subsidence at mid-northern latitudes driven by the equatorial activity. Nadir-viewing observations show compact warm spots in the troposphere and stratosphere at both (summer and winter) poles, likely associated with subsidence. Observations of Titan have defined better the characteristics of the northern winter polar vortex, with 190 m/s winds surrounding a cold atmosphere at 1 microbar. The very warm polar stratopause at 10 microbar and the enhanced abundances of organic compounds suggest subsidence within the vortex. Analysis of the zonal structure in temperature indicates that the stratospheric zonal winds rotate about an axis that is displaced approximately 4.1 deg from the IAU pole. Additional flybys, including a close one in March 2008, continue to characterize the endogenic activity in Enceladus s south polar region. Temperature maps of bright and dark terrains on Iapetus indicate that its ice is approximately stable to sublimation in the bright regions and highly unstable in the dark regions. Thermal mapping of Saturn s rings continues to constrain their composition, and observations at different solar phase angles, spacecraft elevations, solar elevations, and local hour angles have elucidated the effects of ring-particle shadowing and vertical motions on the thermal structure, and revealed the presence of small-scale structure associated with self-gravity wakes.