Analysis of the Characteristics of Inertia-Gravity Waves during an Orographic Precipitation Event

NASA Astrophysics Data System (ADS)

Liu, Lu; Ran, Lingkun; Gao, Shouting

2018-05-01

A numerical experiment was performed using the Weather Research and Forecasting (WRF) model to analyze the generation and propagation of inertia-gravity waves during an orographic rainstorm that occurred in the Sichuan area on 17 August 2014. To examine the spatial and temporal structures of the inertia-gravity waves and identify the wave types, three wavenumber-frequency spectral analysis methods (Fourier analysis, cross-spectral analysis, and wavelet cross-spectrum analysis) were applied. During the storm, inertia-gravity waves appeared at heights of 10-14 km, with periods of 80-100 min and wavelengths of 40-50 km. These waves were generated over a mountain and propagated eastward at an average speed of 15-20 m s-1. Meanwhile, comparison between the reconstructed inertia-gravity waves and accumulated precipitation showed there was a mutual promotion process between them. The Richardson number and Scorer parameter were used to demonstrate that the eastward-moving inertia-gravity waves were trapped in an effective atmospheric ducting zone with favorable reflector and critical level conditions, which were the primary causes of the long lives of the waves. Finally, numerical experiments to test the sensitivity to terrain and diabatic heating were conducted, and the results suggested a cooperative effect of terrain and diabatic heating contributed to the propagation and enhancement of the waves.

First tomographic observations of gravity waves by the infrared limb imager GLORIA

NASA Astrophysics Data System (ADS)

Krisch, Isabell; Preusse, Peter; Ungermann, Jörn; Dörnbrack, Andreas; Eckermann, Stephen D.; Ern, Manfred; Friedl-Vallon, Felix; Kaufmann, Martin; Oelhaf, Hermann; Rapp, Markus; Strube, Cornelia; Riese, Martin

2017-12-01

Atmospheric gravity waves are a major cause of uncertainty in atmosphere general circulation models. This uncertainty affects regional climate projections and seasonal weather predictions. Improving the representation of gravity waves in general circulation models is therefore of primary interest. In this regard, measurements providing an accurate 3-D characterization of gravity waves are needed. Using the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA), the first airborne implementation of a novel infrared limb imaging technique, a gravity wave event over Iceland was observed. An air volume disturbed by this gravity wave was investigated from different angles by encircling the volume with a closed flight pattern. Using a tomographic retrieval approach, the measurements of this air mass at different angles allowed for a 3-D reconstruction of the temperature and trace gas structure. The temperature measurements were used to derive gravity wave amplitudes, 3-D wave vectors, and direction-resolved momentum fluxes. These parameters facilitated the backtracing of the waves to their sources on the southern coast of Iceland. Two wave packets are distinguished, one stemming from the main mountain ridge in the south of Iceland and the other from the smaller mountains in the north. The total area-integrated fluxes of these two wave packets are determined. Forward ray tracing reveals that the waves propagate laterally more than 2000 km away from their source region. A comparison of a 3-D ray-tracing version to solely column-based propagation showed that lateral propagation can help the waves to avoid critical layers and propagate to higher altitudes. Thus, the implementation of oblique gravity wave propagation into general circulation models may improve their predictive skills.

Role of Gravity Waves in Determining Cirrus Cloud Properties

NASA Technical Reports Server (NTRS)

OCStarr, David; Singleton, Tamara; Lin, Ruei-Fong

2008-01-01

Cirrus clouds are important in the Earth's radiation budget. They typically exhibit variable physical properties within a given cloud system and from system to system. Ambient vertical motion is a key factor in determining the cloud properties in most cases. The obvious exception is convectively generated cirrus (anvils), but even in this case, the subsequent cloud evolution is strongly influenced by the ambient vertical motion field. It is well know that gravity waves are ubiquitous in the atmosphere and occur over a wide range of scales and amplitudes. Moreover, researchers have found that inclusion of statistical account of gravity wave effects can markedly improve the realism of simulations of persisting large-scale cirrus cloud features. Here, we use a 1 -dimensional (z) cirrus cloud model, to systematically examine the effects of gravity waves on cirrus cloud properties. The model includes a detailed representation of cloud microphysical processes (bin microphysics and aerosols) and is run at relatively fine vertical resolution so as to adequately resolve nucleation events, and over an extended time span so as to incorporate the passage of multiple gravity waves. The prescribed gravity waves "propagate" at 15 m s (sup -1), with wavelengths from 5 to 100 km, amplitudes range up to 1 m s (sup -1)'. Despite the fact that the net gravity wave vertical motion forcing is zero, it will be shown that the bulk cloud properties, e.g., vertically-integrated ice water path, can differ quite significantly from simulations without gravity waves and that the effects do depend on the wave characteristics. We conclude that account of gravity wave effects is important if large-scale models are to generate realistic cirrus cloud property climatology (statistics).

Relationship between ionospheric plasma bubble occurrence and lightning strikes over the Amazon region

NASA Astrophysics Data System (ADS)

Sousasantos, Jonas; Sobral, José Humberto Andrade; Alam Kherani, Esfhan; Magalhães Fares Saba, Marcelo; Rodolfo de Campos, Diovane

2018-03-01

The vertical coupling between the troposphere and the ionosphere presents some remarkable features. Under intense tropospheric convection, gravity waves may be generated, and once they reach the ionosphere, these waves may seed instabilities and spread F and equatorial plasma bubble events may take place. Additionally, there is a close association between severe tropospheric convection and lightning strikes. In this work an investigation covering an equinox period (September-October) during the deep solar minimum (2009) presents the relation between lightning strike activity and spread F (equatorial plasma bubble) detected over a low-latitude Brazilian region. The results show a considerable correlation between these two phenomena. The common element in the center of this conformity seems to be the gravity waves. Once gravity waves and lightning strikes share the same source (intense tropospheric convection) and the effects of such gravity waves in the ionosphere include the seeding of instabilities according to the gravity waves magnitude, the monitoring of the lightning strike activity seems to offer some information about the subsequent development of spread F over the equatorial region.

Causal properties of nonlinear gravitational waves in modified gravity

NASA Astrophysics Data System (ADS)

Suvorov, Arthur George; Melatos, Andrew

2017-09-01

Some exact, nonlinear, vacuum gravitational wave solutions are derived for certain polynomial f (R ) gravities. We show that the boundaries of the gravitational domain of dependence, associated with events in polynomial f (R ) gravity, are not null as they are in general relativity. The implication is that electromagnetic and gravitational causality separate into distinct notions in modified gravity, which may have observable astrophysical consequences. The linear theory predicts that tachyonic instabilities occur, when the quadratic coefficient a2 of the Taylor expansion of f (R ) is negative, while the exact, nonlinear, cylindrical wave solutions presented here can be superluminal for all values of a2. Anisotropic solutions are found, whose wave fronts trace out time- or spacelike hypersurfaces with complicated geometric properties. We show that the solutions exist in f (R ) theories that are consistent with Solar System and pulsar timing experiments.

Rayleigh lidar observations of gravity wave activity in the stratosphere and lower mesosphere

NASA Technical Reports Server (NTRS)

Miller, M. S.; Gardner, C. S.; Liu, C. H.

1987-01-01

Forty-two monochromatic gravity wave events were observed in the 25 to 55 km altitude region during 16 nights of Rayleigh lidar measurements at Poker Flat, Alaska and Urbana, Illinois. The measured wave parameters were compared to previous radar and lidar measurements of gravity wave activity. Vertical wavelengths, lambda(z), between 2 and 11.5 km with vertical phase velocities, c(z), between 0.1 and 1 m/s were observed. Measured values of lambda(z) and c(z) were used to infer observed wave periods, T(ob), between 50 and 1000 minutes and horizontal wavelengths, lambda(x), from 25 to 2000 km. Dominant wave activity was found at vertical wavelengths between 2 to 4 km and 7 to 10 km. No seasonal variations were evident in the observed wave parameters. Vertical and horizontal wavelengths showed a clear tendency to increase with T(ob), which is consistent with recent sodium lidar studies of monochromatic wave events near the mesopause. Measured power law relationships between the wave parameters were lambda(z) varies as T(ob) sup 0.96, lambda(x) varies as T(ob) sup 1.8, and c(z) varies as T(ob) sup -0.85. The kinetic energy calculated for the monochromatic wave events varied as k(z) sup -2, k(x) sup -1, and f(ob) sup -1.7. The atmospheric scale heights calculated for each observation date range from 6.5 to 7.6 km with a mean value of 7 km. The increase of rms wind perturbations with altitude indicated an amplitude growth length of 20.9 km. The altitude profile of kinetic energy density decreased with height, suggesting that waves in this altitude region were subject to dissipation or saturation effects.

First 3D measurements of temperature fluctuations induced by gravity wave with the infrared limb imager GLORIA

NASA Astrophysics Data System (ADS)

Krisch, Isabell; Preusse, Peter; Ungermann, Jörn; Friedl-Vallon, Felix; Riese, Martin

2017-04-01

Gravity waves (GWs) are one of the most important coupling mechanisms in the atmosphere. They couple different compartments of the atmosphere. The GW-LCYCLE (Gravity Wave Life Cycle) project aims on studying the excitation, propagation, and dissipation of gravity waves. An aircraft campaign has been performed in winter 2015/2016, during which the first 3D tomographic measurements of GWs were performed with the infrared limb imager GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere). GLORIA combines a classical Fourier Transform Spectrometer with a 2D detector array. The capability to image the atmosphere and thereby take several thousand spectra simultaneously improves the spatial sampling compared to conventional limb sounders by an order of magnitude. Furthermore GLORIA is able to pan the horizontal viewing direction and therefore measure the same volume of air under different angles. Due to these properties tomographic methods can be used to derive 3D temperature and tracer fields with spatial resolutions of better than 30km x 30km x 250m from measurements taken during circular flight patterns. Temperature distributions measured during a strong GW event on the 25.01.2016 during the GW-LCycle campaign over Iceland will be presented and analyzed for gravity waves. The three dimensional nature of the GLORIA measurements allows for the determination of the gravity wave momentum flux, including its horizontal direction. The calculated momentum fluxes rank this event under one of the strongest 1% observed in that latitude range in January 2016. The three dimensional wave vectors determined from the GLORIA measurements can be used for a ray tracing study with the Gravity wave Regional Or Global RAy Tracer (GROGRAT). Here 1D ray tracing, meaning solely vertical column propagation, as used by standard parameterizations in numerical weather prediction and climate models is compared to 4D ray tracing (spatially three dimensional with time varying background) for the presented event on the 25.01.2016. Here it is shown, that in the 1D case the GWs are filtered at lower altitudes, whereas in the 4D case the rays were able to propagate to altitudes of above 30km. Besides the forward propagation up to higher altitudes, also the backward propagation to the source region can be study with GROGRAT. Here the mountains of Iceland could be clearly identified as the source region of the measured GWs.

Gravity Wave Detection through All-sky Imaging of Airglow

NASA Astrophysics Data System (ADS)

Nguyen, T. V.; Martinez, A.; Porat, I.; Hampton, D. L.; Bering, E., III; Wood, L.

2017-12-01

Airglow, the faint glow of the atmosphere, is caused by the interaction of air molecules with radiation from the sun. Similarly, the aurora is created by interactions of air molecules with the solar wind. It has been shown that airglow emissions are altered by gravity waves passing through airglow source region (100-110km), making it possible to study gravity waves and their sources through airglow imaging. University of Houston's USIP - Airglow team designed a compact, inexpensive all-sky imager capable of detecting airglow and auroral emissions using a fisheye lens, a simple optical train, a filter wheel with 4 specific filters, and a CMOS camera. This instrument has been used in USIP's scientific campaign in Alaska throughout March 2017. During this period, the imager captured auroral activity in the Fairbanks region. Due to lunar conditions and auroral activity images from the campaign did not yield visible signs of airglow. Currently, the team is trying to detect gravity wave patterns present in the images through numerical analysis. Detected gravity wave patterns will be compared to local weather data, and may be used to make correlations between gravity waves and weather events. Such correlations could provide more data on the relationship between the mesosphere and lower layers of the atmosphere. Practical applications of this research include weather prediction and detection of air turbulence.

Gravity Waves in the Presence of Shear during DEEPWAVE

NASA Astrophysics Data System (ADS)

Doyle, J. D.; Jiang, Q.; Reinecke, P. A.; Reynolds, C. A.; Eckermann, S. D.; Fritts, D. C.; Smith, R. B.; Taylor, M. J.; Dörnbrack, A.

2016-12-01

The DEEP propagating gravity WAVE program (DEEPWAVE) is a comprehensive, airborne and ground-based measurement and modeling program centered on New Zealand and focused on providing a new understanding of gravity wave dynamics and impacts from the troposphere through the mesosphere and lower thermosphere. This program employed the NSF/NCAR GV (NGV) research aircraft from a base in New Zealand in a 6-week field measurement campaign in June-July 2014. During the field phase, the NGV was equipped with new Rayleigh and sodium resonance lidars and an advanced mesospheric temperature mapper (AMTM), a microwave temperature profiler (MTP), as well as dropwindsondes and flight level instruments providing measurements spanning altitudes from immediately above the NGV flight altitude ( 13 km) to 100 km. In this study, we utilize the DEEPWAVE observations and the nonhydrostatic COAMPS configured at high resolution (2 km) with a deep domain (60-80 km) to explore the effects of horizontal wind shear on gravity wave propagation and wave characteristics. Real-data simulations have been conducted for several DEEPWAVE cases. The results suggest that horizontal shear associated with the stratospheric polar night jet refracts the gravity waves and leads to propagation of waves significantly downwind of the South Island. These waves have been referred to as "trailing gravity waves", since they are found predominantly downwind of the orography of the South Island and the wave crests rotate nearly normal to the mountain crest. Observations from the G-V, remote sensing instruments, and the AIRS satellite confirm the presence of gravity waves downwind of the orography in numerous events. The horizontal propagation in the stratosphere can be explained by group velocity arguments for gravity waves in which the wave energy is advected downwind by the component of the flow normal to the horizontal wavevector. We explore the impact of the shear on gravity wave propagation in COAMPS configured in an idealized mode initialized with a zonally balanced stratospheric jet. The idealized results confirm the importance of horizontal wind shear for the refraction of the waves. The zonal momentum flux minimum is shown to bend or refract into the jet in the stratosphere as a consequence of the wind shear.

Extreme gravity tests with gravitational waves from compact binary coalescences: (II) ringdown

NASA Astrophysics Data System (ADS)

Berti, Emanuele; Yagi, Kent; Yang, Huan; Yunes, Nicolás

2018-05-01

The LIGO/Virgo detections of binary black hole mergers marked a watershed moment in astronomy, ushering in the era of precision tests of Kerr dynamics. We review theoretical and experimental challenges that must be overcome to carry out black hole spectroscopy with present and future gravitational wave detectors. Among other topics, we discuss quasinormal mode excitation in binary mergers, astrophysical event rates, tests of black hole dynamics in modified theories of gravity, parameterized "post-Kerr" ringdown tests, exotic compact objects, and proposed data analysis methods to improve spectroscopic tests of Kerr dynamics by stacking multiple events.

Optical Dark Rogue Wave

NASA Astrophysics Data System (ADS)

Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan

2016-02-01

Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system.

Optical Dark Rogue Wave.

PubMed

Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan

2016-02-11

Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system.

Optical Dark Rogue Wave

PubMed Central

Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan

2016-01-01

Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system. PMID:26864099

High-Resolution Observations of a Meteo-Tsunami

NASA Astrophysics Data System (ADS)

Assink, J. D.; Evers, L. G.; Smink, M.; Apituley, A.

2017-12-01

In the early morning of 29 May 2017, unusually large waves of over 2 m height hit the west coast of the Netherlands, leading to some property damage. The waves were due to a meteo-tsunami, which is a tsunami of meteorological origin, unlike seismogenic tsunamis. This particular event was caused by a rapidly moving cold front which featured a sharp squall line that moved towards the coast. Associated was a large perturbation in air pressure of 5 hPa which, along with Proudman resonance effects and the upsloping seabottom lead to the tidal surge. While the meteorological conditions leading up to such an event are relatively common, the more extreme events appear to happen under specific conditions only. As a result of the meteo-tsunami, gravity waves were observed all over the Netherlands with a variety of meteorlogical instruments, including weather radar, ceilometers and a network of microbarometers that are typically used for the detection of infrasound. In this presentation, these high-resolution observations of gravity waves are compared with mesoscale weather models.

Stratospheric mountain wave attenuation in positive and negative ambient wind shear

NASA Astrophysics Data System (ADS)

Kruse, C. G.; Smith, R. B.

2016-12-01

Recently, much has been learned about the vertical propagation and attenuation of mountain waves launched by the Southern Alps of New Zealand (NZ) from the Deep Propagating Gravity Wave Experiment (DEEPWAVE) field campaign. Over NZ, approximately half of mountain wave events are strongly attenuated in a lower-stratospheric "valve layer," defined as a layer of reduced wind with no critical levels. Within a valve layer, negative wind shear causes mountain waves steepen and attenuate, with the amount of transmitted momentum flux controlled by the minimum wind speed within the layer. The other half of wave events are deep (propagating to 35+ km), usually with positive wind shear. Within these deep events, increasing amplitude with decreasing density causes mountain waves to attenuate gradually (after spatial/temporal averaging). Global reanalyses indicate that this valve layer is a climatological feature in the wintertime mid-latitudes above the subtropical jet, while deep events and gradual attenuation occur over higher latitudes below the polar stratospheric jet. The local physics of mountain wave attenuation in positive and negative ambient wind shear are investigated using realistic winter-long (JJA) 6-km resolution Weather Research and Forecasting (WRF) model simulations over the Andes. Attention is given to the spatiotemporal variability of wave attenuation and the various factors driving this variability (e.g. variability in wave generation, ambient conditions at attenuation level, inherent wave-induced instabilities). Mesoscale potential vorticity generation is used as an indicator of wave attenuation. Additionally, regionally integrated wave momentum flux and gravity wave drag (GWD) within WRF are quantified and compared with parameterized quantities in the MERRA1 and 2 reanalyses.

The response of plasma density to breaking inertial gravity wave in the lower regions of ionosphere

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

Tang, Wenbo, E-mail: Wenbo.Tang@asu.edu; Mahalov, Alex, E-mail: Alex.Mahalov@asu.edu

2014-04-15

We present a three-dimensional numerical study for the E and lower F region ionosphere coupled with the neutral atmosphere dynamics. This model is developed based on a previous ionospheric model that examines the transport patterns of plasma density given a prescribed neutral atmospheric flow. Inclusion of neutral dynamics in the model allows us to examine the charge-neutral interactions over the full evolution cycle of an inertial gravity wave when the background flow spins up from rest, saturates and eventually breaks. Using Lagrangian analyses, we show the mixing patterns of the ionospheric responses and the formation of ionospheric layers. The correspondingmore » plasma density in this flow develops complex wave structures and small-scale patches during the gravity wave breaking event.« less

Eruptive Source Parameters from Near-Source Gravity Waves Induced by Large Vulcanian eruptions

NASA Astrophysics Data System (ADS)

Barfucci, Giulia; Ripepe, Maurizio; De Angelis, Silvio; Lacanna, Giorgio; Marchetti, Emanuele

2016-04-01

The sudden ejection of hot material from volcanic vent perturbs the atmosphere generating a broad spectrum of pressure oscillations from acoustic infrasound (<10 Hz) to gravity waves (<0.03 Hz). However observations of gravity waves excited by volcanic eruptions are still rare, mostly limited to large sub-plinian eruptions and frequently at large distance from the source (>100 km). Atmospheric Gravity waves are induced by perturbations of the hydrostatic equilibrium of the atmosphere and propagate within a medium with internal density stratification. They are initiated by mechanisms that cause the atmosphere to be displaced as for the injection of volcanic ash plume during an eruption. We use gravity waves to infer eruptive source parameters, such as mass eruption rate (MER) and duration of the eruption, which may be used as inputs in the volcanic ash transport and dispersion models. We present the analysis of near-field observations (<7 km) of atmospheric gravity waves, with frequencies of 0.97 and 1.15 mHz, recorded by a pressure sensors network during two explosions in July and December 2008 at Soufrière Hills Volcano, Montserrat. We show that gravity waves at Soufrière Hills Volcano originate above the volcanic dome and propagate with an apparent horizontal velocities of 8-10 m/s. Assuming a single mass injection point source model, we constrain the source location at ~3.5 km a.s.l., above the vent, duration of the gas thrust < 140 s and MERs of 2.6 and 5.4 x10E7 kg/s, for the two eruptive events. Source duration and MER derived by modeling Gravity Waves are fully compatible with others independent estimates from field observations. Our work strongly supports the use of gravity waves to model eruption source parameters and can have a strong impact on our ability to monitor volcanic eruption at a large distance and may have future application in assessing the relative magnitude of volcanic explosions.

Ocean Wave-to-Ice Energy Transfer Determined from Seafloor Pressure and Ice Shelf Seismic Observations

NASA Astrophysics Data System (ADS)

Chen, Z.; Bromirski, P. D.; Gerstoft, P.; Stephen, R. A.; Wiens, D.; Aster, R. C.; Nyblade, A.

2017-12-01

Ice shelves play an important role in buttressing land ice from reaching the sea, thus restraining the rate of sea level rise. Long-period gravity wave impacts excite vibrations in ice shelves that may trigger tabular iceberg calving and/or ice shelf collapse events. Three kinds of seismic plate waves were continuously observed by broadband seismic arrays on the Ross Ice Shelf (RIS) and on the Pine Island Glacier (PIG) ice shelf: (1) flexural-gravity waves, (2) flexural waves, and (3) extensional Lamb waves, suggesting that all West Antarctic ice shelves are subjected to similar gravity wave excitation. Ocean gravity wave heights were estimated from pressure perturbations recorded by an ocean bottom differential pressure gauge at the RIS front, water depth 741 m, about 8 km north of an on-ice seismic station that is 2 km from the shelf front. Combining the plate wave spectrum, the frequency-dependent energy transmission and reflection at the ice-water interface were determined. In addition, Young's modulus and Poisson's ratio of the RIS are estimated from the plate wave motions, and compared with the widely used values. Quantifying these ice shelf parameters from observations will improve modeling of ice shelf response to ocean forcing, and ice shelf evolution.

Experimentally Modeling Black and White Hole Event Horizons via Fluid Flow

NASA Astrophysics Data System (ADS)

Manheim, Marc E.; Lindner, John F.; Manz, Niklas

We will present a scaled down experiment that hydrodynamically models the interaction between electromagnetic waves and black/white holes. It has been mathematically proven that gravity waves in water can behave analogously to electromagnetic waves traveling through spacetime. In this experiment, gravity waves will be generated in a water tank and propagate in a direction opposed to a flow of varying rate. We observe a noticeable change in the wave's spreading behavior as it travels through the simulated horizon with decreased wave speeds up to standing waves, depending on the opposite flow rate. Such an experiment has already been performed in a 97.2 cubic meter tank. We reduced the size significantly to be able to perform the experiment under normal lab conditions.

Deep Orographic Gravity Wave Dynamics over Subantarctic Islands as Observed and Modeled during the Deep Propagating Gravity Wave Experiment (DEEPWAVE)

NASA Astrophysics Data System (ADS)

Eckermann, S. D.; Broutman, D.; Ma, J.; Doyle, J. D.; Pautet, P. D.; Taylor, M. J.; Bossert, K.; Williams, B. P.; Fritts, D. C.; Smith, R. B.; Kuhl, D.; Hoppel, K.; McCormack, J. P.; Ruston, B. C.; Baker, N. L.; Viner, K.; Whitcomb, T.; Hogan, T. F.; Peng, M.

2016-12-01

The Deep Propagating Gravity Wave Experiment (DEEPWAVE) was an international aircraft-based field program to observe and study the end-to-end dynamics of atmospheric gravity waves from 0-100 km altitude and the effects on atmospheric circulations. On 14 July 2014, aircraft remote-sensing instruments detected large-amplitude gravity-wave oscillations within mesospheric airglow and sodium layers downstream of the Auckland Islands, located 1000 km south of Christchurch, New Zealand. A high-altitude reanalysis and a three-dimensional Fourier gravity wave model are used to investigate the dynamics of this event from the surface to the mesosphere. At 0700 UTC when first observations were made, surface flow across the islands' terrain generated linear three-dimensional wavefields that propagated rapidly to ˜78 km altitude, where intense breaking occurred in a narrow layer beneath a zero-wind region at ˜83 km altitude. In the following hours, the altitude of weak winds descended under the influence of a large-amplitude migrating semidiurnal tide, leading to intense breaking of these wavefields in subsequent observations starting at 1000 UTC. The linear Fourier model constrained by upstream reanalysis reproduces the salient aspects of observed wavefields, including horizontal wavelengths, phase orientations, temperature and vertical displacement amplitudes, heights and locations of incipient wave breaking, and momentum fluxes. Wave breaking has huge effects on local circulations, with inferred layer-averaged westward mean-flow accelerations of ˜350 m s-1 hour-1 and dynamical heating rates of ˜8 K hour-1, supporting recent speculation of important impacts of orographic gravity waves from subantarctic islands on the mean circulation and climate of the middle atmosphere during austral winter. We also study deep orographic gravity waves from islands during DEEPWAVE more widely using observations from the Atmospheric Infrared Sounder (AIRS) and high-resolution high-altitude numerical weather prediction models.

Analysis of a jet stream induced gravity wave associated with an observed ice cloud over Greenland

NASA Astrophysics Data System (ADS)

Buss, S.; Hertzog, A.; Hostettler, C.; Bui, T. P.; Lüthi, T.; Wernli, H.

2003-11-01

A polar stratospheric ice cloud (PSC type II) was observed by airborne lidar above Greenland on 14 January 2000. Is was the unique observation of an ice cloud over Greenland during the SOLVE/THESEO 2000 campaign. Mesoscale simulations with the hydrostatic HRM model are presented which, in contrast to global analyses, are capable to produce a vertically propagating gravity wave that induces the low temperatures at the level of the PSC afforded for the ice formation. The simulated minimum temperature is ~8 K below the driving analyses and ~3 K below the frost point, exactly coinciding with the location of the observed ice cloud. Despite the high elevations of the Greenland orography the simulated gravity wave is not a mountain wave. Analyses of the horizontal wind divergence, of the background wind profiles, of backward gravity wave ray-tracing trajectories, of HRM experiments with reduced Greenland topography and of several instability diagnostics near the tropopause level provide consistent evidence that the wave is emitted by the geostrophic adjustment of a jet instability associated with an intense, rapidly evolving, anticyclonically curved jet stream. In order to evaluate the potential frequency of such non-orographic polar stratospheric cloud events, an approximate jet instability diagnostic is performed for the winter 1999/2000. It indicates that ice-PSCs are only occasionally generated by gravity waves emanating from an unstable jet.

Observation of Kelvin-Helmholtz instabilities and gravity waves in the summer mesopause above Andenes in Northern Norway

NASA Astrophysics Data System (ADS)

Stober, Gunter; Sommer, Svenja; Schult, Carsten; Latteck, Ralph; Chau, Jorge L.

2018-05-01

We present observations obtained with the Middle Atmosphere Alomar Radar System (MAARSY) to investigate short-period wave-like features using polar mesospheric summer echoes (PMSEs) as a tracer for the neutral dynamics. We conducted a multibeam experiment including 67 different beam directions during a 9-day campaign in June 2013. We identified two Kelvin-Helmholtz instability (KHI) events from the signal morphology of PMSE. The MAARSY observations are complemented by collocated meteor radar wind data to determine the mesoscale gravity wave activity and the vertical structure of the wind field above the PMSE. The KHIs occurred in a strong shear flow with Richardson numbers Ri < 0.25. In addition, we observed 15 wave-like events in our MAARSY multibeam observations applying a sophisticated decomposition of the radial velocity measurements using volume velocity processing. We retrieved the horizontal wavelength, intrinsic frequency, propagation direction, and phase speed from the horizontally resolved wind variability for 15 events. These events showed horizontal wavelengths between 20 and 40 km, vertical wavelengths between 5 and 10 km, and rather high intrinsic phase speeds between 45 and 85 m s-1 with intrinsic periods of 5-10 min.

Analysis of a jet stream induced gravity wave associated with an observed stratospheric ice cloud over Greenland

NASA Astrophysics Data System (ADS)

Buss, S.; Hertzog, A.; Hostettler, C.; Bui, T. B.; Lüthi, D.; Wernli, H.

2004-08-01

A polar stratospheric ice cloud (PSC type II) was observed by airborne lidar above Greenland on 14 January 2000. It was the unique observation of an ice cloud over Greenland during the SOLVE/THESEO 2000 campaign. Mesoscale simulations with the hydrostatic HRM model are presented which, in contrast to global analyses, are capable to produce a vertically propagating gravity wave that induces the low temperatures at the level of the PSC afforded for the ice formation. The simulated minimum temperature is ~8 K below the driving analyses and ~4.5 K below the frost point, exactly coinciding with the location of the observed ice cloud. Despite the high elevations of the Greenland orography the simulated gravity wave is not a mountain wave. Analyses of the horizontal wind divergence, of the background wind profiles, of backward gravity wave ray-tracing trajectories, of HRM experiments with reduced Greenland topography and of several diagnostics near the tropopause level provide evidence that the wave is emitted from an intense, rapidly evolving, anticyclonically curved jet stream. The precise physical process responsible for the wave emission could not be identified definitely, but geostrophic adjustment and shear instability are likely candidates.

In order to evaluate the potential frequency of such non-orographic polar stratospheric cloud events, the non-linear balance equation diagnostic is performed for the winter 1999/2000. It indicates that ice-PSCs are only occasionally generated by gravity waves emanating from spontaneous adjustment.

Stratospheric gravity waves at southern hemisphere orographic hotspots: 2003-2014 AIRS/Aqua observations

NASA Astrophysics Data System (ADS)

Hoffmann, Lars; Grimsdell, Alison W.; Alexander, M. Joan

2017-04-01

Stratospheric gravity waves from small-scale orographic sources are currently not well-represented in general circulation models. This may be a reason why many simulations have difficulty reproducing the dynamical behaviour of the southern hemisphere polar vortex in a realistic manner. Here we discuss a 12-year record (2003 - 2014) of stratospheric gravity wave activity at southern hemisphere orographic hotspots as observed by the Atmospheric InfraRed Sounder (AIRS) aboard the National Aeronautics and Space Administration's (NASA's) Aqua satellite. We introduce a simple and effective approach, referred to as the 'two-box method', to detect gravity wave activity from infrared nadir sounder measurements and to discriminate between gravity waves from orographic and other sources. From austral mid fall to mid spring (April - October) the contributions of orographic sources to the observed gravity wave occurrence frequencies were found to be largest for the Andes (90%), followed by the Antarctic Peninsula (76%), Kerguelen Islands (73%), Tasmania (70%), New Zealand (67%), Heard Island (60%), and other hotspots (24 - 54%). Mountain wave activity was found to be closely correlated with peak terrain altitudes, and with zonal winds in the lower troposphere and mid stratosphere. We propose a simple model to predict the occurrence of mountain wave events in the AIRS observations using zonal wind thresholds at 3 hPa and 750 hPa. The model has significant predictive skill for hotspots where gravity wave activity is primarily due to orographic sources. It typically reproduces seasonal variations of the mountain wave occurrence frequencies at the Antarctic Peninsula and Kerguelen Islands from near zero to over 60% with mean absolute errors of 4 - 5 percentage points. The prediction model can be used to disentangle upper level wind effects on observed occurrence frequencies from low level source and other influences. The data and methods presented here can help to identify interesting case studies in the vast amount of AIRS data, which could then be further explored to study the specific characteristics of stratospheric gravity waves from orographic sources and to support model validation. Reference: Hoffmann, L., Grimsdell, A. W., and Alexander, M. J.: Stratospheric gravity waves at Southern Hemisphere orographic hotspots: 2003-2014 AIRS/Aqua observations, Atmos. Chem. Phys., 16, 9381-9397, doi:10.5194/acp-16-9381-2016, 2016.

Applications of acoustic-gravity waves numerical modeling to tsunami signals observed by gravimetry satellites in very low orbit

NASA Astrophysics Data System (ADS)

Brissaud, Q.; Garcia, R.; Sladen, A.; Martin, R.; Komatitsch, D.

2016-12-01

Acoustic and gravity waves propagating in planetary atmospheres have been studied intensively as markers of specific phenomena (tectonic events, explosions) or as contributors to atmosphere dynamics. To get a better understanding of the physics behind these dynamic processes, both acoustic and gravity waves propagation should be modeled in an attenuating and windy 3D atmosphere from the ground all the way to the upper thermosphere. Thus, in order to provide an efficient numerical tool at the regional or global scale we introduce a high-order finite-difference time domain (FDTD) approach that relies on the linearized compressible Navier-Stokes equations with spatially non constant physical parameters (density, viscosities and speed of sound) and background velocities (wind). We present applications of these simulations to the propagation of gravity waves generated by tsunamis for realistic cases for which atmospheric models are extracted from empirical models including variations with altitude of atmospheric parameters, and tsunami forcing at the ocean surface is extracted from shallow water simulations. We describe the specific difficulties induced by the size of the simulation, the boundary conditions and the spherical geometry and compare the simulation outputs to data gathered by gravimetric satellites crossing gravity waves generated by tsunamis.

Investigating Gravity Waves in Polar Mesospheric Clouds Using Tomographic Reconstructions of AIM Satellite Imagery

NASA Astrophysics Data System (ADS)

Hart, V. P.; Taylor, M. J.; Doyle, T. E.; Zhao, Y.; Pautet, P.-D.; Carruth, B. L.; Rusch, D. W.; Russell, J. M.

2018-01-01

This research presents the first application of tomographic techniques for investigating gravity wave structures in polar mesospheric clouds (PMCs) imaged by the Cloud Imaging and Particle Size instrument on the NASA AIM satellite. Albedo data comprising consecutive PMC scenes were used to tomographically reconstruct a 3-D layer using the Partially Constrained Algebraic Reconstruction Technique algorithm and a previously developed "fanning" technique. For this pilot study, a large region (760 × 148 km) of the PMC layer (altitude 83 km) was sampled with a 2 km horizontal resolution, and an intensity weighted centroid technique was developed to create novel 2-D surface maps, characterizing the individual gravity waves as well as their altitude variability. Spectral analysis of seven selected wave events observed during the Northern Hemisphere 2007 PMC season exhibited dominant horizontal wavelengths of 60-90 km, consistent with previous studies. These tomographic analyses have enabled a broad range of new investigations. For example, a clear spatial anticorrelation was observed between the PMC albedo and wave-induced altitude changes, with higher-albedo structures aligning well with wave troughs, while low-intensity regions aligned with wave crests. This result appears to be consistent with current theories of PMC development in the mesopause region. This new tomographic imaging technique also provides valuable wave amplitude information enabling further mesospheric gravity wave investigations, including quantitative analysis of their hemispheric and interannual characteristics and variations.

On the construction of a direct numerical simulation of a breaking inertia-gravity wave in the upper mesosphere

NASA Astrophysics Data System (ADS)

Fruman, Mark D.; Remmler, Sebastian; Achatz, Ulrich; Hickel, Stefan

2014-10-01

A systematic approach to the direct numerical simulation (DNS) of breaking upper mesospheric inertia-gravity waves of amplitude close to or above the threshold for static instability is presented. Normal mode or singular vector analysis applied in a frame of reference moving with the phase velocity of the wave (in which the wave is a steady solution) is used to determine the most likely scale and structure of the primary instability and to initialize nonlinear "2.5-D" simulations (with three-dimensional velocity and vorticity fields but depending only on two spatial coordinates). Singular vector analysis is then applied to the time-dependent 2.5-D solution to predict the transition of the breaking event to three-dimensional turbulence and to initialize three-dimensional DNS. The careful choice of the computational domain and the relatively low Reynolds numbers, on the order of 25,000, relevant to breaking waves in the upper mesosphere, makes the three-dimensional DNS tractable with present-day computing clusters. Three test cases are presented: a statically unstable low-frequency inertia-gravity wave, a statically and dynamically stable inertia-gravity wave, and a statically unstable high-frequency gravity wave. The three-dimensional DNS are compared to ensembles of 2.5-D simulations. In general, the decay of the wave and generation of turbulence is faster in three dimensions, but the results are otherwise qualitatively and quantitatively similar, suggesting that results of 2.5-D simulations are meaningful if the domain and initial condition are chosen properly.

Sediment gravity flows triggered by remotely generated earthquake waves

NASA Astrophysics Data System (ADS)

Johnson, H. Paul; Gomberg, Joan S.; Hautala, Susan L.; Salmi, Marie S.

2017-06-01

Recent great earthquakes and tsunamis around the world have heightened awareness of the inevitability of similar events occurring within the Cascadia Subduction Zone of the Pacific Northwest. We analyzed seafloor temperature, pressure, and seismic signals, and video stills of sediment-enveloped instruments recorded during the 2011-2015 Cascadia Initiative experiment, and seafloor morphology. Our results led us to suggest that thick accretionary prism sediments amplified and extended seismic wave durations from the 11 April 2012 Mw8.6 Indian Ocean earthquake, located more than 13,500 km away. These waves triggered a sequence of small slope failures on the Cascadia margin that led to sediment gravity flows culminating in turbidity currents. Previous studies have related the triggering of sediment-laden gravity flows and turbidite deposition to local earthquakes, but this is the first study in which the originating seismic event is extremely distant (> 10,000 km). The possibility of remotely triggered slope failures that generate sediment-laden gravity flows should be considered in inferences of recurrence intervals of past great Cascadia earthquakes from turbidite sequences. Future similar studies may provide new understanding of submarine slope failures and turbidity currents and the hazards they pose to seafloor infrastructure and tsunami generation in regions both with and without local earthquakes.

Sediment gravity flows triggered by remotely generated earthquake waves

USGS Publications Warehouse

Johnson, H. Paul; Gomberg, Joan S.; Hautala, Susan; Salmi, Marie

2017-01-01

Recent great earthquakes and tsunamis around the world have heightened awareness of the inevitability of similar events occurring within the Cascadia Subduction Zone of the Pacific Northwest. We analyzed seafloor temperature, pressure, and seismic signals, and video stills of sediment-enveloped instruments recorded during the 2011–2015 Cascadia Initiative experiment, and seafloor morphology. Our results led us to suggest that thick accretionary prism sediments amplified and extended seismic wave durations from the 11 April 2012 Mw8.6 Indian Ocean earthquake, located more than 13,500 km away. These waves triggered a sequence of small slope failures on the Cascadia margin that led to sediment gravity flows culminating in turbidity currents. Previous studies have related the triggering of sediment-laden gravity flows and turbidite deposition to local earthquakes, but this is the first study in which the originating seismic event is extremely distant (> 10,000 km). The possibility of remotely triggered slope failures that generate sediment-laden gravity flows should be considered in inferences of recurrence intervals of past great Cascadia earthquakes from turbidite sequences. Future similar studies may provide new understanding of submarine slope failures and turbidity currents and the hazards they pose to seafloor infrastructure and tsunami generation in regions both with and without local earthquakes.

Modified gravity (MOG), the speed of gravitational radiation and the event GW170817/GRB170817A

NASA Astrophysics Data System (ADS)

Green, M. A.; Moffat, J. W.; Toth, V. T.

2018-05-01

Modified gravity (MOG) is a covariant, relativistic, alternative gravitational theory whose field equations are derived from an action that supplements the spacetime metric tensor with vector and scalar fields. Both gravitational (spin 2) and electromagnetic waves travel on null geodesics of the theory's one metric. MOG satisfies the weak equivalence principle and is consistent with observations of the neutron star merger and gamma ray burster event GW170817/GRB170817A.

Effects of a Major Tsunami on the Energetics and Dynamics of the Thermosphere

NASA Astrophysics Data System (ADS)

Hickey, M. P.; Walterscheid, R. L.; Schubert, G.

2009-12-01

Using a spectral full-wave model we investigate how the energetics and dynamics of the thermosphere are influenced by the dissipation of a tsunami-driven gravity wave disturbance. Gravity waves are generated in the model by a surface displacement that mimics a tsunami having a characteristic horizontal wavelength of 400 km and a horizontal phase speed of 200 m/s. The gravity wave disturbance is fast with a large vertical wavelength and is able to reach F-region altitudes before significant viscous dissipation occurs. The gravity wave transports significant amounts of energy and momentum to this region of the atmosphere. The energy reaching the lower thermosphere could be ~ 1012 J for large tsunami events. The change in velocity associated with the wave momentum deposition in a region ~ 100 km deep centered on 250 km altitude could be 150 - 200 m/s. Thermal effects associated with the divergence of the sensible heat flux are modest (~ 20 K over the same region). The affected region could have a lateral extent of 1000 km or more, and an along-track extent of as much as 8000 km. The induced winds should be observable through a variety of methods but the thermal effects might be difficult to observe.

Constraints on Born-Infeld gravity from the speed of gravitational waves after GW170817 and GRB 170817A

NASA Astrophysics Data System (ADS)

Jana, Soumya; Chakravarty, Girish Kumar; Mohanty, Subhendra

2018-04-01

The observations of gravitational waves from the binary neutron star merger event GW170817 and the subsequent observation of its electromagnetic counterparts from the gamma-ray burst GRB 170817A provide us a significant opportunity to study theories of gravity beyond general relativity. An important outcome of these observations is that they constrain the difference between the speed of gravity and the speed of light to less than 10-15c . Also, the time delay between the arrivals of gravitational waves at different detectors constrains the speed of gravity at the Earth to be in the range 0.55 c

Tsunamigenic Gravity Waves in the Thermosphere-Ionosphere System: Challenges and Opportunities (Invited)

NASA Astrophysics Data System (ADS)

Hickey, M. P.

2010-12-01

There has been a recent resurgence of interest in the association between tsunamis and traveling ionospheric disturbances (TIDs), fueled in part by the use of GPS satellite technologies to remotely monitor the ionosphere. The TID observations have also triggered a renewed interest in the modeling of such events. Up to this point in time the various model simulations have incorporated various simplifications, some of which are briefly described. A future challenge is to bring together suites of models that each realistically describes one of the subsystems. In this talk I will describe the results of using a linear spectral full-wave model to simulate the propagation of a gravity wave disturbance from the sea surface to the thermosphere. In the model this disturbance is driven by a lower boundary perturbation that mimics a tsunami. A linear model describing the response of the ionosphere to neutral atmosphere perturbations, and airglow perturbations driven by ionosphere and neutral atmosphere fluctuations are also described. Additionally, the gravity wave disturbances carries wave momentum, which will be deposited in the thermosphere accompanying the viscous dissipation of wave energy and lead to accelerations of the mean state. In spite of the simplicity of these models, much can be learned from them. It is suggested that these rare events offer a fairly unique opportunity to test models describing such processes. Model predictions of total electron content (TEC) fluctuations are also briefly compared with TEC measurements obtained following some recent major tsunamis.

Observation of acoustic-gravity waves in the upper atmosphere during severe storm activity

NASA Technical Reports Server (NTRS)

Hung, R. J.

1975-01-01

A nine-element continuum wave spectrum, high-frequency, Doppler sounder array has been used to detect upper atmospheric wave-like disturbances during periods with severe weather activity, particularly severe thunderstorms and tornadoes. Five events of severe weather activity, including extreme tornado outbreak of April 3, 1974, were chosen for the present study. The analysis of Doppler records shows that both infrasonic waves and gravity waves were excited when severe storms appeared in the north Alabama area. Primarily, in the case of tornado activity, S-shaped Doppler fluctuations or Doppler fold-backs are observed, while quasi-sinusoidal fluctuations are more common in the case of thunderstorm activity. A criterion for the production of Doppler fold-backs is derived and compared with possible tornado conditions.

Flexural-gravity Wave Attenuation in a Thick Ice Shelf

NASA Astrophysics Data System (ADS)

Stephen, R. A.; Bromirski, P. D.; Gerstoft, P.; Chen, Z.; Wiens, D.; Aster, R. C.; Nyblade, A.

2016-12-01

A thirty-four station broadband seismic array was deployed on the Ross Ice Shelf, Antarctica from November 2014 to November 2017. Analyses indicate that phase speeds of infra-gravity wave and tsunami excitation in the 0.003 to 0.02 Hz band are 70 m/s, corresponding to the low frequency limit of flexural-gravity waves. Median spectral amplitudes in this band decay exponentially with distance from the shelf edge in a manner consistent with intrinsic attenuation. Seismic Q is typically 7-9, with an RMS amplitude decay of 0.04-0.05dB/km and an e-folding distance of 175-220 km. Amplitudes do not appear to drop crossing crevasse fields. Vertical and horizontal acceleration levels at stations on the floating ice shelf are 50 dB higher than those on grounded ice. Horizontal accelerations are about 15 dB higher than vertical accelerations. Median spectral levels at 0.003 Hz are within 6 dB for stations from 2 to 430 km from the shelf edge. In contrast, the levels drop by 90 dB at 0.02 Hz. Ocean gravity wave excitation has been proposed as a mechanism that can weaken ice shelves and potentially trigger disintegration events. These measurements indicate that the propensity for shelf weakening and disintegration decays exponentially with distance from the ice front for gravity waves in the 0.003 to 0.02Hz band.

Upper atmospheric gravity wave details revealed in nightglow satellite imagery

PubMed Central

Miller, Steven D.; Straka, William C.; Yue, Jia; Smith, Steven M.; Alexander, M. Joan; Hoffmann, Lars; Setvák, Martin; Partain, Philip T.

2015-01-01

Gravity waves (disturbances to the density structure of the atmosphere whose restoring forces are gravity and buoyancy) comprise the principal form of energy exchange between the lower and upper atmosphere. Wave breaking drives the mean upper atmospheric circulation, determining boundary conditions to stratospheric processes, which in turn influence tropospheric weather and climate patterns on various spatial and temporal scales. Despite their recognized importance, very little is known about upper-level gravity wave characteristics. The knowledge gap is mainly due to lack of global, high-resolution observations from currently available satellite observing systems. Consequently, representations of wave-related processes in global models are crude, highly parameterized, and poorly constrained, limiting the description of various processes influenced by them. Here we highlight, through a series of examples, the unanticipated ability of the Day/Night Band (DNB) on the NOAA/NASA Suomi National Polar-orbiting Partnership environmental satellite to resolve gravity structures near the mesopause via nightglow emissions at unprecedented subkilometric detail. On moonless nights, the Day/Night Band observations provide all-weather viewing of waves as they modulate the nightglow layer located near the mesopause (∼90 km above mean sea level). These waves are launched by a variety of physical mechanisms, ranging from orography to convection, intensifying fronts, and even seismic and volcanic events. Cross-referencing the Day/Night Band imagery with conventional thermal infrared imagery also available helps to discern nightglow structures and in some cases to attribute their sources. The capability stands to advance our basic understanding of a critical yet poorly constrained driver of the atmospheric circulation. PMID:26630004

Upper atmospheric gravity wave details revealed in nightglow satellite imagery.

PubMed

Miller, Steven D; Straka, William C; Yue, Jia; Smith, Steven M; Alexander, M Joan; Hoffmann, Lars; Setvák, Martin; Partain, Philip T

2015-12-08

Gravity waves (disturbances to the density structure of the atmosphere whose restoring forces are gravity and buoyancy) comprise the principal form of energy exchange between the lower and upper atmosphere. Wave breaking drives the mean upper atmospheric circulation, determining boundary conditions to stratospheric processes, which in turn influence tropospheric weather and climate patterns on various spatial and temporal scales. Despite their recognized importance, very little is known about upper-level gravity wave characteristics. The knowledge gap is mainly due to lack of global, high-resolution observations from currently available satellite observing systems. Consequently, representations of wave-related processes in global models are crude, highly parameterized, and poorly constrained, limiting the description of various processes influenced by them. Here we highlight, through a series of examples, the unanticipated ability of the Day/Night Band (DNB) on the NOAA/NASA Suomi National Polar-orbiting Partnership environmental satellite to resolve gravity structures near the mesopause via nightglow emissions at unprecedented subkilometric detail. On moonless nights, the Day/Night Band observations provide all-weather viewing of waves as they modulate the nightglow layer located near the mesopause (∼ 90 km above mean sea level). These waves are launched by a variety of physical mechanisms, ranging from orography to convection, intensifying fronts, and even seismic and volcanic events. Cross-referencing the Day/Night Band imagery with conventional thermal infrared imagery also available helps to discern nightglow structures and in some cases to attribute their sources. The capability stands to advance our basic understanding of a critical yet poorly constrained driver of the atmospheric circulation.

A new physics-based modeling approach for tsunami-ionosphere coupling

NASA Astrophysics Data System (ADS)

Meng, X.; Komjathy, A.; Verkhoglyadova, O. P.; Yang, Y.-M.; Deng, Y.; Mannucci, A. J.

2015-06-01

Tsunamis can generate gravity waves propagating upward through the atmosphere, inducing total electron content (TEC) disturbances in the ionosphere. To capture this process, we have implemented tsunami-generated gravity waves into the Global Ionosphere-Thermosphere Model (GITM) to construct a three-dimensional physics-based model WP (Wave Perturbation)-GITM. WP-GITM takes tsunami wave properties, including the wave height, wave period, wavelength, and propagation direction, as inputs and time-dependently characterizes the responses of the upper atmosphere between 100 km and 600 km altitudes. We apply WP-GITM to simulate the ionosphere above the West Coast of the United States around the time when the tsunami associated with the March 2011 Tohuku-Oki earthquke arrived. The simulated TEC perturbations agree with Global Positioning System observations reasonably well. For the first time, a fully self-consistent and physics-based model has reproduced the GPS-observed traveling ionospheric signatures of an actual tsunami event.

Detection of large-scale concentric gravity waves from a Chinese airglow imager network

NASA Astrophysics Data System (ADS)

Lai, Chang; Yue, Jia; Xu, Jiyao; Yuan, Wei; Li, Qinzeng; Liu, Xiao

2018-06-01

Concentric gravity waves (CGWs) contain a broad spectrum of horizontal wavelengths and periods due to their instantaneous localized sources (e.g., deep convection, volcanic eruptions, or earthquake, etc.). However, it is difficult to observe large-scale gravity waves of >100 km wavelength from the ground for the limited field of view of a single camera and local bad weather. Previously, complete large-scale CGW imagery could only be captured by satellite observations. In the present study, we developed a novel method that uses assembling separate images and applying low-pass filtering to obtain temporal and spatial information about complete large-scale CGWs from a network of all-sky airglow imagers. Coordinated observations from five all-sky airglow imagers in Northern China were assembled and processed to study large-scale CGWs over a wide area (1800 km × 1 400 km), focusing on the same two CGW events as Xu et al. (2015). Our algorithms yielded images of large-scale CGWs by filtering out the small-scale CGWs. The wavelengths, wave speeds, and periods of CGWs were measured from a sequence of consecutive assembled images. Overall, the assembling and low-pass filtering algorithms can expand the airglow imager network to its full capacity regarding the detection of large-scale gravity waves.

On the Importance of High Frequency Gravity Waves for Ice Nucleation in the Tropical Tropopause Layer

NASA Technical Reports Server (NTRS)

Jensen, Eric J.

2016-01-01

Recent investigations of the influence of atmospheric waves on ice nucleation in cirrus have identified a number of key processes and sensitivities: (1) ice concentrations produced by homogeneous freezing are strongly dependent on cooling rates, with gravity waves dominating upper tropospheric cooling rates; (2) rapid cooling driven by high-frequency waves are likely responsible for the rare occurrences of very high ice concentrations in cirrus; (3) sedimentation and entrainment tend to decrease ice concentrations as cirrus age; and (4) in some situations, changes in temperature tendency driven by high-frequency waves can quench ice nucleation events and limit ice concentrations. Here we use parcel-model simulations of ice nucleation driven by long-duration, constant-pressure balloon temperature time series, along with an extensive dataset of cold cirrus microphysical properties from the recent ATTREX high-altitude aircraft campaign, to statistically examine the importance of high-frequency waves as well as the consistency between our theoretical understanding of ice nucleation and observed ice concentrations. The parcel-model simulations indicate common occurrence of peak ice concentrations exceeding several hundred per liter. Sedimentation and entrainment would reduce ice concentrations as clouds age, but 1-D simulations using a wave parameterization (which underestimates rapid cooling events) still produce ice concentrations higher than indicated by observations. We find that quenching of nucleation events by high-frequency waves occurs infrequently and does not prevent occurrences of large ice concentrations in parcel simulations of homogeneous freezing. In fact, the high-frequency variability in the balloon temperature data is entirely responsible for production of these high ice concentrations in the simulations.

Temporal variability of gravity wave drag - vertical coupling and possible climate links

NASA Astrophysics Data System (ADS)

Miksovsky, Jiri; Sacha, Petr; Kuchar, Ales; Pisoft, Petr

2017-04-01

In the atmosphere, the internal gravity waves (IGW) are one of the fastest ways of natural information transfer in the vertical direction. Tropospheric changes that result in modification of sourcing, propagation or breaking conditions for IGWs almost immediately influence the distribution of gravity wave drag in the stratosphere. So far most of the related studies deal with IGW impacts higher in the upper stratospheric/mesospheric region and with the modulation of IGWs by planetary waves. This is most likely due to the fact that IGWs induce highest accelerations in the mesosphere and lower thermosphere region. However, the imposed drag force is much bigger in the stratosphere. In the presented analysis, we have assessed the relationship between the gravity wave activity in the stratosphere and other climatic phenomena through statistical techniques. Multivariable regression has been applied to investigate the IGW-related eastward and northward wind tendencies in the CMAM30-SD data, subject to the explanatory variables involving local circulation characteristics (derived from regional configuration of the thermobaric field) as well as the phases of the large-scale internal climate variability modes (ENSO, NAO, QBO). Our tests have highlighted several geographical areas with statistically significant responses of the orographic gravity waves effect to each of the variability modes under investigation; additional experiments have also indicated distinct signs of nonlinearity in some of the links uncovered. Furthermore, we have also applied composite analysis of displaced and split stratospheric polar vortex events (SPV) from CMAM30-SD to focus on how the strength and occurrence of the IGW hotspots can play a role in SPV occurrence and frequency.

Investigating mesospheric mountain wave characteristics over New Zealand during DEEPWAVE

NASA Astrophysics Data System (ADS)

McLaughlin, P.; Taylor, M. J.; Pautet, P. D.; Kaifler, B.; Smith, S. M.

2017-12-01

The Deep Propagating Gravity Wave Experiment, "DEEPWAVE" was an international measurement and modelling program designed to characterize and predict the generation and propagation of a broad range of atmospheric gravity waves (GWs) with measurements extending from the ground to 100 km altitude. An analysis of 2 months of GW image data obtained during 2014 in New Zealand by a ground-based Advanced Mesospheric Temperature Mapper (AMTM) identified 19 events with clear signatures of orographic forcing. This is by far the largest occurrence of MW activity ever recorded at MLT heights. The observed events were quasi-stationary, exhibited a variety of horizontal wavelengths and lasted for > 1 hour. One prior study has reported such waves in the mesosphere over the Andes Mountain Range. We utilize data obtained by a collection of ground-based instrumentation operated at NIWA Lauder Station, NZ [45.0°S] to perform a detailed investigation of the generation and propagation of mountain waves into the upper mesosphere and to quantify their impact on this region using their measured momentum fluxes (MF). Instruments included an AMTM, a Rayleigh Lidar and an all-sky imager. The results focus on the derived MFs, comparing and contrasting their magnitudes and variability under different forcing conditions.

A Maxwell-vector p-wave holographic superconductor in a particular background AdS black hole metric

NASA Astrophysics Data System (ADS)

Wen, Dan; Yu, Hongwei; Pan, Qiyuan; Lin, Kai; Qian, Wei-Liang

2018-05-01

We study the p-wave holographic superconductor for AdS black holes with planar event horizon topology for a particular Lovelock gravity, in which the action is characterized by a self-interacting scalar field nonminimally coupled to the gravity theory which is labeled by an integer k. As the Lovelock theory of gravity is the most general metric theory of gravity based on the fundamental assumptions of general relativity, it is a desirable theory to describe the higher dimensional spacetime geometry. The present work is devoted to studying the properties of the p-wave holographic superconductor by including a Maxwell field which nonminimally couples to a complex vector field in a higher dimensional background metric. In the probe limit, we find that the critical temperature decreases with the increase of the index k of the background black hole metric, which shows that a larger k makes it harder for the condensation to form. We also observe that the index k affects the conductivity and the gap frequency of the holographic superconductors.

Wave-induced boundary-layer separation: A case study comparing airborne observations and results from a mesoscale model

NASA Astrophysics Data System (ADS)

Strauss, L.; Serafin, S.; Grubišić, V.

2012-04-01

Wave-induced boundary-layer separation (BLS) results from the adverse-pressure gradient forces that are exerted on the atmospheric boundary-layer by internal gravity waves in flow over orography. BLS has received significant attention in recent years, particularly so, because it is a key ingredient in the formation of atmospheric rotors. Traditionally depicted as horizontal eddies in the lee of mountain ranges, rotors originate from the interaction between internal gravity waves and the atmospheric boundary-layer. Our study focuses on the first observationally documented case of wave-induced BLS, which occurred on 26 Jan 2006 in the lee of the Medicine Bow Mountains in SE Wyoming (USA). Observations from the University of Wyoming King Air (UWKA) aircraft, in particular, the remote sensing measurements with the Wyoming Cloud Radar (WCR), reveal strong wave activity, downslope winds in excess of 30 m/s, and near-surface flow reversal in the lee of the mountain range. The fine resolution of WCR data (on the order of 40x40 m2 for two-dimensional velocity fields) exhibits fine-scale vortical structures ("subrotors") which are embedded within the main rotor zone. Our case study intends to complete the characterisation of the observed boundary-layer separation event. Modelling of the event with the mesoscale Weather Research and Forecast Model (WRF) provides insight into the mesoscale triggers of wave-induced BLS and turbulence generation. Indeed, the mesoscale model underpins the expected concurrence of the essential processes (gravity waves, wave breaking, downslope windstorms, etc.) leading to BLS. To exploit the recorded in situ and radar data to their full extent, a quantitative evaluation of the structure and intensity of turbulence is conducted by means of a power spectral analysis of the vertical wind component, measured along the flight track. An intercomparison of observational and modelling results serves the purpose of model verification and can shed some more light onto the limits of validity of airborne observations and mesoscale modelling. For example, the exact timing, magnitude, and evolution of the internal gravity waves present in the mesoscale model are carefully analysed. As for the observations, measures of turbulence gained from in situ and radar data, collected over complex topography within a limited period of time, must be interpreted with caution. Approaches to tackling these challenges are a matter of ongoing research and will be discussed in concluding.

Probing gravitational parity violation with gravitational waves from stellar-mass black hole binaries

NASA Astrophysics Data System (ADS)

Yagi, Kent; Yang, Huan

2018-05-01

The recent discovery of gravitational-wave events has offered us unique test beds of gravity in the strong and dynamical field regime. One possible modification to General Relativity is the gravitational parity violation that arises naturally from quantum gravity. Such parity violation gives rise to the so-called amplitude birefringence in gravitational waves, in which one of the circularly polarized modes is amplified while the other one is suppressed during their propagation. In this paper, we study how well one can measure gravitational parity violation via the amplitude birefringence effect of gravitational waves sourced by stellar-mass black hole binaries. We choose Chern-Simons gravity as an example and work within an effective field theory formalism to ensure that the approximate theory is well posed. We consider gravitational waves from both individual sources and stochastic gravitational-wave backgrounds. Regarding bounds from individual sources, we estimate such bounds using a Fisher analysis and carry out Monte Carlo simulations by randomly distributing sources over their sky location and binary orientation. We find that the bounds on the scalar field evolution in Chern-Simons gravity from the recently discovered gravitational-wave events are too weak to satisfy the weak Chern-Simons approximation, while aLIGO with its design sensitivity can place meaningful bounds. Regarding bounds from stochastic gravitational-wave backgrounds, we set the threshold signal-to-noise ratio for detection of the parity-violation mode as 5 and estimate projected bounds with future detectors assuming that signals are consistent with no parity violation. In an ideal situation in which all the source parameters and binary black hole merger-rate history are known a priori, we find that a network of two third-generation detectors is able to place bounds that are comparable to or slightly stronger than binary pulsar bounds. In a more realistic situation in which one does not have such information beforehand, approximate bounds can be derived if the regular parity-insensitive mode is detected and the peak redshift of the merger-rate history is known theoretically. Since gravitational-wave observations probe either the difference in parity violation between the source and the detector (with individual sources) or the line-of-sight cosmological integration of the scalar field (with gravitational-wave backgrounds), such bounds are complementary to local measurements from solar system experiments and binary pulsar observations.

The ionospheric disturbances caused by the explosion of the Mount Tongariro volcano in 2012

NASA Astrophysics Data System (ADS)

Po Cheng, C.; Lin, C.; Chang, L. C.; Chen, C.

2013-12-01

Volcanic explosions are known to trigger acoustic waves that propagate in the atmosphere at infrasonic speeds. At ionospheric heights, coupling between neutral particles and free electrons induces variations of electron density detectable by dual-frequency Global Positioning System (GPS) measurements. In November 21 2012, the explosion of the Mount Tongariro volcano in New Zealand occurred at UT 0:20, when there were active synoptic waves passing over north New Zealand. The New Zealand dense array of Global Positioning System recorded ionospheric disturbances reflected in total electron content (TEC) ~10 minutes after the eruption, and the concentric spread of disturbances also can be observed this day. The velocity of disturbances varies from 130m/s to 700m/s. A spectral analysis of the rTEC time series shows two peaks. The larger amplitudes are centered at 800 and 1500 seconds, in the frequency range of acoustic waves and gravity waves. On the other hand, to model the rTEC perturbation created by the acoustic wave caused by the explosive eruption of the Mount Tongariro, we perform acoustic ray tracing and obtain sound speed at subionospheric height in a horizontally stratified atmosphere model (MSIS-E-90). The result show that the velocity of the disturbances is slower than sound speed range. Through using the MSIS-E-90 Atmosphere Model and Horizontal Wind Model(HWM), we obtain the vertical wave number and indicate that the gravity waves could propagate at subionospheric height for this event, suggesting that the ionospheric disturbances caused by the explosive eruption is gravity-wave type. This work demonstrates that GPS are useful for near real-time ionospheric disturbances monitoring, and help to understand the mechanism of the gravity wave caused by volcano eruption in the future.

Longitudinal Variations of Low-Latitude Gravity Waves and Their Impacts on the Ionosphere

NASA Astrophysics Data System (ADS)

Cullens, C. Y.; England, S.; Immel, T. J.

2014-12-01

The lower atmospheric forcing has important roles in the ionospheric variability. However, influences of lower atmospheric gravity waves on the ionospheric variability are still not clear due to the simplified gravity wave parameterizations and the limited knowledge of gravity wave distributions. In this study, we aim to study the longitudinal variations of gravity waves and their impacts of longitudinal variations of low-latitude gravity waves on the ionospheric variability. Our SABER results show that longitudinal variations of gravity waves at the lower boundary of TIME-GCM are the largest in June-August and January-February. We have implemented these low-latitude gravity wave variations from SABER instrument into TIME-GCM model. TIME-GCM simulation results of ionospheric responses to longitudinal variations of gravity waves and physical mechanisms will be discussed.

Atmospheric Gravity Waves and Turbulent Processes in the Mesopause Region Based on PMSE MAARSY Observations

NASA Astrophysics Data System (ADS)

Gudadze, N.; Chau, J. L.; Stober, G.; Latteck, R.

2016-12-01

Mesosphere-lower-thermosphere (MLT) polar dynamics are interesting and important subject for study in atmospheric physic. It is considered that mesopause region is where the main part of the Atmospheric gravity waves breaks and/or dissipates. However this region is difficult to observe. Continuous Observations of the polar summer mesosphere with the Middle Atmosphere Alomar Radar System (MAARSY) and its predecessor the ALOMAR-Wind-Radar (ALWIN) (before 2010), have been used to investigate dynamical structures of well-known phenomenon - Polar Mesosphere Summer Echoes (PMSE) which is an important tracer in the summer polar mesopause region. Signal to Noise Ratio (SNR) and Doppler radial velocity from the PMSE are used to investigate the wave-like motions with periods larger than 5 minutes. Such oscillations are studied in terms of atmospheric gravity waves (AGWs). Processes also connected with AGWs as PMSE layering, are studied in connection with the background conditions of the neutral atmosphere as well. Background winds are obtained from collocated meteor radar (MR). We used local enhancement method for the processing of altitude-time SNR images to detect layers in the PMSEs and characterised them. Our preliminary results indicate that PMSE strength and behaviour is correlated with the meridional wind. Furthermore we found that the spectral width (SW), which is a proxy of turbulence, is most of the time weakly dependent on SNR strength. However, there are some events where SW is highly dependent on SNR intensity indicating that they could be associated to turbulent-dominated events.

Acoustic Gravity Waves in the Ionosphere and Thermosphere During the 2017 Solar Eclipse

NASA Astrophysics Data System (ADS)

Lin, C. Y. T.; Deng, Y.

2017-12-01

During the 2017 solar eclipse, as the sudden cavity of solar radiation created by the lunar shadow moves across the United States on August 21, 2017, decreases in local IT temperature and density are expected. The average velocity of the total solar eclipse across the United States is 700 m/s. The forefront and wake of the lunar shadow are expected to induce acoustic gravity waves according to previous studies of atmosphere waves induced by traveling wave packets moving at different velocities. Meanwhile, moving toward the cross-track direction of the obscuration footprint, weaker transitions will likely create mesoscale to large-scale traveling disturbances. We will use the Global Ionosphere Thermosphere Model, a global circulation model solving for non-hydrostatic equations, with high-resolution settings to investigate the IT responses related to the acoustic-gravity wave perturbations during the 2017 solar eclipse. The simulation will be performed with a sub-degree resolution in longitude and latitude for 3 hours when the atmosphere of the North America sector is mostly obscured. The observable differences between the eclipsed and non-eclipsed scenarios will be examined in detail and be interpreted as consequences from the solar eclipse. We will investigate the evolution of waves during the event and establish a theoretical baseline for further comparisons with observations.

Wave Dynamics and Transport in the Stratosphere

NASA Technical Reports Server (NTRS)

Holton, James R.; Alexander, M. Joan

1999-01-01

The report discusses: (1) Gravity waves generated by tropical convection: A study in which a two-dimensional cloud-resolving model was used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation was completed. (2) Gravity wave ray tracing studies:It was developed a linear ray tracing model of gravity wave propagation to extend the nonlinear storm model results into the mesosphere and thermosphere. (3) tracer filamentation: Vertical soundings of stratospheric ozone often exhibit laminated tracer structures characterized by strong vertical tracer gradients. (4) Mesospheric gravity wave modeling studies: Although our emphasis in numerical simulation of gravity waves generated by convection has shifted from simulation of idealized two-dimensional squall lines to the most realistic (and complex) study of wave generation by three-dimensional storms. (5) Gravity wave climatology studies: Mr. Alexander applied a linear gravity wave propagation model together with observations of the background wind and stability fields to compute climatologies of gravity wave activity for comparison to observations. (6) Convective forcing of gravity waves: Theoretical study of gravity wave forcing by convective heat sources has completed. (7) Gravity waves observation from UARS: The objective of this work is to apply ray tracing, and other model technique, in order to determine to what extend the horizontal and vertical variation in satellite observed distribution of small-scale temperature variance can be attributed to gravity waves from particular sources. (8) The annual and interannual variations in temperature and mass flux near the tropical tropopause. and (9) Three dimensional cloud model.

A Multiscale Nested Modeling Framework to Simulate the Interaction of Surface Gravity Waves with Nonlinear Internal Gravity Waves

DTIC Science & Technology

2015-09-30

We aim at understanding the impact of tidal , seasonal, and mesoscale variability of the internal wave field and how it influences the surface waves ...Interaction of Surface Gravity Waves with Nonlinear Internal Gravity Waves Lian Shen St. Anthony Falls Laboratory and Department of Mechanical...on studying surface gravity wave evolution and spectrum in the presence of surface currents caused by strongly nonlinear internal solitary waves

First results of warm mesospheric temperature over Gadanki (13.5°N, 79.2°E) during the sudden stratospheric warming of 2009

NASA Astrophysics Data System (ADS)

Sridharan, S.; Raghunath, K.; Sathishkumar, S.; Nath, D.

2010-09-01

Rayleigh lidar observations at Gadanki (13.5°N, 79.2°E) show an enhancement of the nightly mean temperature by 10-15 K at altitudes 70-80 km and of gravity wave potential energy at 60-70 km during the 2009 major stratospheric warming event. An enhanced quasi-16-day wave activity is observed at 50-70 km in the wavelet spectrum of TIMED-SABER temperatures, possibly due to the absence of a critical level in the low-latitude stratosphere because of less westward winds caused by this warming event. The observed low-latitude mesospheric warming could be due to wave breaking, as waves are damped at 80 km.

Numerical modeling of a multiscale gravity wave event and its airglow signatures over Mount Cook, New Zealand, during the DEEPWAVE campaign

NASA Astrophysics Data System (ADS)

Heale, C. J.; Bossert, K.; Snively, J. B.; Fritts, D. C.; Pautet, P.-D.; Taylor, M. J.

2017-01-01

A 2-D nonlinear compressible model is used to simulate a large-amplitude, multiscale mountain wave event over Mount Cook, NZ, observed as part of the Deep Propagating Gravity Wave Experiment (DEEPWAVE) campaign and to investigate its observable signatures in the hydroxyl (OH) layer. The campaign observed the presence of a λx=200 km mountain wave as part of the 22nd research flight with amplitudes of >20 K in the upper stratosphere that decayed rapidly at airglow heights. Advanced Mesospheric Temperature Mapper (AMTM) showed the presence of small-scale (25-28 km) waves within the warm phase of the large mountain wave. The simulation results show rapid breaking above 70 km altitude, with the preferential formation of almost-stationary vortical instabilities within the warm phase front of the mountain wave. An OH airglow model is used to identify the presence of small-scale wave-like structures generated in situ by the breaking of the mountain wave that are consistent with those seen in the observations. While it is easy to interpret these feature as waves in OH airglow data, a considerable fraction of the features are in fact instabilities and vortex structures. Simulations suggest that a combination of a large westward perturbation velocity and shear, in combination with strong perturbation temperature gradients, causes both dynamic and convective instability conditions to be met particularly where the wave wind is maximized and the temperature gradient is simultaneously minimized. This leads to the inevitable breaking and subsequent generation of smaller-scale waves and instabilities which appear most prominent within the warm phase front of the mountain wave.

Internal Gravity Wave Induced by the Queen Charlotte Event (27 October 2012, Mw 7.8): Airglow Observation and Modeling.

NASA Astrophysics Data System (ADS)

Occhipinti, G.; Bablet, A.; Makela, J. J.

2015-12-01

The detection of the tsunami related internal gravity waves (IGWtsuna) by airglow camera has been recently validated by observation (Makela et al., 2011) and modeling (Occhipinti et al., 2011) in the case of the Tohoku event (11 March 2011, Mw 9.0). The airglow is measuring the photon emission at 630 nm, indirectly linked to the plasma density of O2+ (Link & Cogger, 1988) and it is commonly used to detect transient event in the ionosphere (Kelley et al., 2002, Makela et al., 2009, Miller et al., 2009). The modeling of the IGWtsuna clearly reproduced the pattern of the airglow measurement observed over Hawaii and the comparison between the observation and the modeling allows to recognize the wave form and allow to explain the IGWtsuna arriving before the tsunami wavefront at the sea level (Occhipinti et al., 2011). Approaching the Hawaiian archipelagos the tsunami propagation is slowed down (reduction of the sea depth), instead, the IGWtsuna, propagating in the atmosphere/ionosphere, conserves its speed. In this work, we present the modeling of the new airglow observation following the Queen Charlotte event (27 October 2012, Mw 7.8) that has been recently detected, proving that the technique can be generalized for smaller events. Additionally, the effect of the wind on the IGWtsuna, already evocated in the past, is included in the modeling to better reproduce the airglow observations. All ref. here @ www.ipgp.fr/~ninto

Small-Scale Gravity Waves in ER-2 MMS/MTP Wind and Temperature Measurements during CRYSTAL-FACE

NASA Technical Reports Server (NTRS)

Wang, L.; Alexander, M. J.; Bui, T. P.; Mahoney, M. J.

2006-01-01

Lower stratospheric wind and temperature measurements made from NASA's high-altitude ER-2 research aircraft during the CRYSTAL-FACE campaign in July 2002 were analyzed to retrieve information on small scale gravity waves (GWs) at the aircraft's flight level (typically approximately 20 km altitude). For a given flight segment, the S-transform (a Gaussian wavelet transform) was used to search for and identify small horizontal scale GW events, and to estimate their apparent horizontal wavelengths. The horizontal propagation directions of the events were determined using the Stokes parameter method combined with the cross S-transform analysis. The vertical temperature gradient was used to determine the vertical wavelengths of the events. GW momentum fluxes were calculated from the cross S-transform. Other wave parameters such as intrinsic frequencies were calculated using the GW dispersion relation. More than 100GW events were identified. They were generally high frequency waves with vertical wavelength of approximately 5 km and horizontal wavelength generally shorter than 20 km. Their intrinsic propagation directions were predominantly toward the east, whereas their ground-based propagation directions were primarily toward the west. Among the events, approximately 20% of them had very short horizontal wavelength, very high intrinsic frequency, and relatively small momentum fluxes, and thus they were likely trapped in the lower stratosphere. Using the estimated GW parameters and the background winds and stabilities from the NCAR/NCEP reanalysis data, we were able to trace the sources of the events using a simple reverse ray-tracing. More than 70% of the events were traced back to convective sources in the troposphere, and the sources were generally located upstream of the locations of the events observed at the aircraft level. Finally, a probability density function of the reversible cooling rate due to GWs was obtained in this study, which may be useful for cirrus cloud models.

On resonant coupling of acoustic waves and gravity waves

NASA Astrophysics Data System (ADS)

Millet, Christophe

2017-11-01

Acoustic propagation in the atmosphere is often modeled using modes that are confined within waveguides causing the sound to propagate through multiple paths to the receiver. On the other hand, direct observations in the lower stratosphere show that the gravity wave field is intermittent, and is often dominated by rather well defined large-amplitude wave packets. In the present work, we use normal modes to describe both the gravity wave field and the acoustic field. The gravity wave spectrum is obtained by launching few monochromatic waves whose properties are chosen stochastically to mimic the intermittency. Owing to the disparity of the gravity and acoustic length scales, the interactions between the gravity wave field and each of the acoustic modes can be described using a multiple-scale analysis. The appropriate amplitude evolution equation for the acoustic field involves certain random terms that can be directly related to the gravity wave sources. We will show that the cumulative effect of gravity wave breakings makes the sensitivity of ground-based acoustic signals large, in that small changes in the gravity wave parameterization can create or destroy specific acoustic features.

The Origins of Air Parcels Uplifted in a Two Dimensional Gravity Wave in the Tropical Upper Troposphere During the NASA Stratosphere Troposphere Exchange Project (STEP)

NASA Technical Reports Server (NTRS)

Selkirk, Henry B.; Pfister, Leonhard; Chan, K. Roland; Kritz, Mark; Kelly, Ken

1989-01-01

During January and February 1987, as part of the Stratosphere-Troposphere Exchange Project, the NASA ER-2 made 11 flights from Darwin, Australia to investigate dehydration mechanisms in the vicinity of the tropical tropopause. After the monsoon onset in the second week of January, steady easterly flow of 15-25 ms (exp -1) was established in the upper troposphere and lower stratosphere over northern Australia and adjacent seas. Penetrating into this regime were elements of the monsoon convection such as overshooting convective turrets and extensive anvils including cyclone cloud shields. In cases of the latter, the resulting flow obstructions tended to produce mesoscale gravity waves. In several instances the ER- 2 meteorological and trace constituent measurements provide a detailed description of the structure of these gravity waves. Among these was STEP Flight 6, 22-23 January. It is of particular interest to STEP because of the close proximity of ice-laden and dehydrated air on the same isentropic surfaces. Convective events inject large amounts of ice into the upper troposphere and lower stratosphere which may not be completely removed by local precipitation processes. In the present instance, a gravity wave for removed from the source region appears to induce relativity rapid upward motion in the ice-laden air and subsequent dessication. Potential mechanisms for such a localized removal process are under investigation.

A reinterpretation of the data from the NASA Stratosphere-Troposphere Exchange Project

NASA Astrophysics Data System (ADS)

Newman, Paul A.; Schoeberl, Mark R.

Data obtained during the NASA Stratosphere Troposphere Exchange Project (STEP) Mid-Latitude Field Experiment displayed laminae of ozone, water, and condensation nuclei in the stratosphere in association with a mid-latitude stratosphere-troposphere folding event. Danielsen et al. (1991) constructed cross sections of these observations, and interpreted these quasi-horizontal laminae as evidence of ultra-low frequency gravity waves. We use a new technique to show that these laminae could have resulted from differential advection, rather than transport by ultra-low frequency gravity waves. This new technique uses reverse domain filling back trajectories on multiple isentropic surfaces in conjunction with modified potential vorticity to reveal the qualitative details of the constituent laminae.

Widespread tsunami-like waves of 23-27 June in the Mediterranean and Black Seas generated by high-altitude atmospheric forcing.

PubMed

Šepić, Jadranka; Vilibić, Ivica; Rabinovich, Alexander B; Monserrat, Sebastian

2015-06-29

A series of tsunami-like waves of non-seismic origin struck several southern European countries during the period of 23 to 27 June 2014. The event caused considerable damage from Spain to Ukraine. Here, we show that these waves were long-period ocean oscillations known as meteorological tsunamis which are generated by intense small-scale air pressure disturbances. An unique atmospheric synoptic pattern was tracked propagating eastward over the Mediterranean and the Black seas in synchrony with onset times of observed tsunami waves. This pattern favoured generation and propagation of atmospheric gravity waves that induced pronounced tsunami-like waves through the Proudman resonance mechanism. This is the first documented case of a chain of destructive meteorological tsunamis occurring over a distance of thousands of kilometres. Our findings further demonstrate that these events represent potentially dangerous regional phenomena and should be included in tsunami warning systems.

Widespread tsunami-like waves of 23-27 June in the Mediterranean and Black Seas generated by high-altitude atmospheric forcing

PubMed Central

Šepić, Jadranka; Vilibić, Ivica; Rabinovich, Alexander B.; Monserrat, Sebastian

2015-01-01

A series of tsunami-like waves of non-seismic origin struck several southern European countries during the period of 23 to 27 June 2014. The event caused considerable damage from Spain to Ukraine. Here, we show that these waves were long-period ocean oscillations known as meteorological tsunamis which are generated by intense small-scale air pressure disturbances. An unique atmospheric synoptic pattern was tracked propagating eastward over the Mediterranean and the Black seas in synchrony with onset times of observed tsunami waves. This pattern favoured generation and propagation of atmospheric gravity waves that induced pronounced tsunami-like waves through the Proudman resonance mechanism. This is the first documented case of a chain of destructive meteorological tsunamis occurring over a distance of thousands of kilometres. Our findings further demonstrate that these events represent potentially dangerous regional phenomena and should be included in tsunami warning systems. PMID:26119833

Gravity Waves Generated by Convection: A New Idealized Model Tool and Direct Validation with Satellite Observations

NASA Astrophysics Data System (ADS)

Alexander, M. Joan; Stephan, Claudia

2015-04-01

In climate models, gravity waves remain too poorly resolved to be directly modelled. Instead, simplified parameterizations are used to include gravity wave effects on model winds. A few climate models link some of the parameterized waves to convective sources, providing a mechanism for feedback between changes in convection and gravity wave-driven changes in circulation in the tropics and above high-latitude storms. These convective wave parameterizations are based on limited case studies with cloud-resolving models, but they are poorly constrained by observational validation, and tuning parameters have large uncertainties. Our new work distills results from complex, full-physics cloud-resolving model studies to essential variables for gravity wave generation. We use the Weather Research Forecast (WRF) model to study relationships between precipitation, latent heating/cooling and other cloud properties to the spectrum of gravity wave momentum flux above midlatitude storm systems. Results show the gravity wave spectrum is surprisingly insensitive to the representation of microphysics in WRF. This is good news for use of these models for gravity wave parameterization development since microphysical properties are a key uncertainty. We further use the full-physics cloud-resolving model as a tool to directly link observed precipitation variability to gravity wave generation. We show that waves in an idealized model forced with radar-observed precipitation can quantitatively reproduce instantaneous satellite-observed features of the gravity wave field above storms, which is a powerful validation of our understanding of waves generated by convection. The idealized model directly links observations of surface precipitation to observed waves in the stratosphere, and the simplicity of the model permits deep/large-area domains for studies of wave-mean flow interactions. This unique validated model tool permits quantitative studies of gravity wave driving of regional circulation and provides a new method for future development of realistic convective gravity wave parameterizations.

The Effect of the Leeuwin Current on Offshore Surface Gravity Waves in Southwest Western Australia

NASA Astrophysics Data System (ADS)

Wandres, Moritz; Wijeratne, E. M. S.; Cosoli, Simone; Pattiaratchi, Charitha

2017-11-01

The knowledge of regional wave regimes is critical for coastal zone planning, protection, and management. In this study, the influence of the offshore current regime on surface gravity waves on the southwest Western Australian (SWWA) continental shelf was examined. This was achieved by coupling the three dimensional, free surface, terrain-following hydrodynamic Regional Ocean Modelling System (ROMS) and the third generation wave model Simulating WAves Nearshore (SWAN) using the Coupled Ocean-Atmosphere-WaveSediment Transport (COAWST) model. Different representative states of the Leeuwin Current (LC), a strong pole-ward flowing boundary current with a persistent eddy field along the SWWA shelf edge were simulated and used to investigate their influence on different large wave events. The coupled wave-current simulations were compared to wave only simulations, which represented scenarios in the absence of a background current field. Results showed that the LC and the eddy field significantly impact SWWA waves. Significant wave heights increased (decreased) when currents were opposing (aligning with) the incoming wave directions. During a fully developed LC system significant wave heights were altered by up to ±25% and wave directions by up to ±20°. The change in wave direction indicates that the LC may modify nearshore wave dynamics and consequently alter sediment patterns. Operational regional wave forecasts and hindcasts may give flawed predictions if wave-current interaction is not properly accounted for.

A climatology of gravity wave parameters based on satellite limb soundings

NASA Astrophysics Data System (ADS)

Ern, Manfred; Trinh, Quang Thai; Preusse, Peter; Riese, Martin

2017-04-01

Gravity waves are one of the main drivers of atmospheric dynamics. The resolution of most global circulation models (GCMs) and chemistry climate models (CCMs), however, is too coarse to properly resolve the small scales of gravity waves. Horizontal scales of gravity waves are in the range of tens to a few thousand kilometers. Gravity wave source processes involve even smaller scales. Therefore GCMs/CCMs usually parametrize the effect of gravity waves on the global circulation. These parametrizations are very simplified, and comparisons with global observations of gravity waves are needed for an improvement of parametrizations and an alleviation of model biases. In our study, we present a global data set of gravity wave distributions observed in the stratosphere and the mesosphere by the infrared limb sounding satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). We provide various gravity wave parameters (for example, gravity variances, potential energies and absolute momentum fluxes). This comprehensive climatological data set can serve for comparison with other instruments (ground based, airborne, or other satellite instruments), as well as for comparison with gravity wave distributions, both resolved and parametrized, in GCMs and CCMs. The purpose of providing various different parameters is to make our data set useful for a large number of potential users and to overcome limitations of other observation techniques, or of models, that may be able to provide only one of those parameters. We present a climatology of typical average global distributions and of zonal averages, as well as their natural range of variations. In addition, we discuss seasonal variations of the global distribution of gravity waves, as well as limitations of our method of deriving gravity wave parameters from satellite data.

Sensitivity of Gravity Wave Fluxes to Interannual Variations in Tropical Convection and Zonal Wind.

PubMed

Alexander, M Joan; Ortland, David A; Grimsdell, Alison W; Kim, Ji-Eun

2017-09-01

Using an idealized model framework with high-frequency tropical latent heating variability derived from global satellite observations of precipitation and clouds, the authors examine the properties and effects of gravity waves in the lower stratosphere, contrasting conditions in an El Niño year and a La Niña year. The model generates a broad spectrum of tropical waves including planetary-scale waves through mesoscale gravity waves. The authors compare modeled monthly mean regional variations in wind and temperature with reanalyses and validate the modeled gravity waves using satellite- and balloon-based estimates of gravity wave momentum flux. Some interesting changes in the gravity spectrum of momentum flux are found in the model, which are discussed in terms of the interannual variations in clouds, precipitation, and large-scale winds. While regional variations in clouds, precipitation, and winds are dramatic, the mean gravity wave zonal momentum fluxes entering the stratosphere differ by only 11%. The modeled intermittency in gravity wave momentum flux is shown to be very realistic compared to observations, and the largest-amplitude waves are related to significant gravity wave drag forces in the lowermost stratosphere. This strong intermittency is generally absent or weak in climate models because of deficiencies in parameterizations of gravity wave intermittency. These results suggest a way forward to improve model representations of the lowermost stratospheric quasi-biennial oscillation winds and teleconnections.

Characteristics of atmospheric gravity waves observed using the MU (Middle and Upper atmosphere) radar and GPS (Global Positioning System) radio occultation.

PubMed

Tsuda, Toshitaka

2014-01-01

The wind velocity and temperature profiles observed in the middle atmosphere (altitude: 10-100 km) show perturbations resulting from superposition of various atmospheric waves, including atmospheric gravity waves. Atmospheric gravity waves are known to play an important role in determining the general circulation in the middle atmosphere by dynamical stresses caused by gravity wave breaking. In this paper, we summarize the characteristics of atmospheric gravity waves observed using the middle and upper atmosphere (MU) radar in Japan, as well as novel satellite data obtained from global positioning system radio occultation (GPS RO) measurements. In particular, we focus on the behavior of gravity waves in the mesosphere (50-90 km), where considerable gravity wave attenuation occurs. We also report on the global distribution of gravity wave activity in the stratosphere (10-50 km), highlighting various excitation mechanisms such as orographic effects, convection in the tropics, meteorological disturbances, the subtropical jet and the polar night jet.

Characteristics of atmospheric gravity waves observed using the MU (Middle and Upper atmosphere) radar and GPS (Global Positioning System) radio occultation

PubMed Central

TSUDA, Toshitaka

2014-01-01

The wind velocity and temperature profiles observed in the middle atmosphere (altitude: 10–100 km) show perturbations resulting from superposition of various atmospheric waves, including atmospheric gravity waves. Atmospheric gravity waves are known to play an important role in determining the general circulation in the middle atmosphere by dynamical stresses caused by gravity wave breaking. In this paper, we summarize the characteristics of atmospheric gravity waves observed using the middle and upper atmosphere (MU) radar in Japan, as well as novel satellite data obtained from global positioning system radio occultation (GPS RO) measurements. In particular, we focus on the behavior of gravity waves in the mesosphere (50–90 km), where considerable gravity wave attenuation occurs. We also report on the global distribution of gravity wave activity in the stratosphere (10–50 km), highlighting various excitation mechanisms such as orographic effects, convection in the tropics, meteorological disturbances, the subtropical jet and the polar night jet. PMID:24492645

Speed of Gravitational Waves from Strongly Lensed Gravitational Waves and Electromagnetic Signals.

PubMed

Fan, Xi-Long; Liao, Kai; Biesiada, Marek; Piórkowska-Kurpas, Aleksandra; Zhu, Zong-Hong

2017-03-03

We propose a new model-independent measurement strategy for the propagation speed of gravitational waves (GWs) based on strongly lensed GWs and their electromagnetic (EM) counterparts. This can be done in two ways: by comparing arrival times of GWs and their EM counterparts and by comparing the time delays between images seen in GWs and their EM counterparts. The lensed GW-EM event is perhaps the best way to identify an EM counterpart. Conceptually, this method does not rely on any specific theory of massive gravitons or modified gravity. Its differential setting (i.e., measuring the difference between time delays in GW and EM domains) makes it robust against lens modeling details (photons and GWs travel in the same lensing potential) and against internal time delays between GW and EM emission acts. It requires, however, that the theory of gravity is metric and predicts gravitational lensing similar to general relativity. We expect that such a test will become possible in the era of third-generation gravitational-wave detectors, when about 10 lensed GW events would be observed each year. The power of this method is mainly limited by the timing accuracy of the EM counterpart, which for kilonovae is around 10^{4}  s. This uncertainty can be suppressed by a factor of ∼10^{10}, if strongly lensed transients of much shorter duration associated with the GW event can be identified. Candidates for such short transients include short γ-ray bursts and fast radio bursts.

Long-Term Global Morphology of Gravity Wave Activity Using UARS Data

NASA Technical Reports Server (NTRS)

Eckermann, Stephen D.; Bacmeister, Julio T.; Wu, Dong L.

1998-01-01

This is the first quarter's report on research to extract global gravity-wave data from satellite data and to model those observations synoptically. Preliminary analysis of global maps of extracted middle atmospheric temperature variance from the CRISTA instrument is presented, which appear to contain gravity-wave information. Corresponding simulations of global gravity-wave and mountain-wave activity during this mission period are described using global ray-tracing and mountain-wave models, and interesting similarities among simulated data and CRISTA data are noted. Climatological simulations of mesospheric gravity-wave activity using the HWM-03 wind-temperature climatology are also reported, for comparison with UARS MLS data. Preparatory work on modeling of gravity wave observations from space-based platforms and subsequent interpretation of the MLS gravity-wave product are also described. Preliminary interpretation and relation to the research objectives are provided, and further action for the next quarter's research is recommended.

Recent Advances in Remote Sensing of Natural Hazards-Induced Atmospheric and Ionospheric Perturbations

NASA Astrophysics Data System (ADS)

Yang, Y. M.; Komjathy, A.; Meng, X.; Verkhoglyadova, O. P.; Langley, R. B.; Mannucci, A. J.

2015-12-01

Traveling ionospheric disturbances (TIDs) induced by acoustic-gravity waves in the neutral atmosphere have significant impact on trans-ionospheric radio waves such as Global Navigation Satellite System (GNSS, including Global Position System (GPS)) measurements. Natural hazards and solid Earth events, such as earthquakes, tsunamis and volcanic eruptions are actual sources that may trigger acoustic and gravity waves resulting in traveling ionospheric disturbances (TIDs) in the upper atmosphere. Trans-ionospheric radio wave measurements sense the total electron content (TEC) along the signal propagation path. In this research, we introduce a novel GPS-based detection and estimation technique for remote sensing of atmospheric wave-induced TIDs including space weather phenomena induced by major natural hazard events, using TEC time series collected from worldwide ground-based dual-frequency GNSS (including GPS) receiver networks. We demonstrate the ability of using ground- and space-based dual-frequency GPS measurements to detect and monitor tsunami wave propagation from the 2011 Tohoku-Oki earthquake and tsunami. Major wave trains with different propagation speeds and wavelengths were identified through analysis of the GPS remote sensing observations. Dominant physical characteristics of atmospheric wave-induced TIDs are found to be associated with specific tsunami propagations and oceanic Rayleigh waves. In this research, we compared GPS-based observations, corresponding model simulations and tsunami wave propagation. Results are shown to lead to a better understanding of the tsunami-induced ionosphere responses. Based on current distribution of Plate Boundary Observatory GPS stations, the results indicate that tsunami-induced TIDs may be detected about 60 minutes prior to tsunamis arriving at the U.S. west coast. It is expected that this GNSS-based technology will become an integral part of future early-warning systems.

A Case Study of the Mechanisms Modulating the Evolution of Valley Fog

NASA Astrophysics Data System (ADS)

Hang, C.; Nadeau, D. F.; Gultepe, I.; Hoch, S. W.; Román-Cascón, C.; Pryor, K.; Fernando, H. J. S.; Creegan, E. D.; Leo, L. S.; Silver, Z.; Pardyjak, E. R.

2016-09-01

We present a valley fog case study in which radiation fog is modulated by topographic effects using data obtained from a field campaign conducted in Heber Valley, Utah from January 7-February 1, 2015, as part of the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) program. We use data collected on January 9, 2015 to gain insight into relationships between typical shallow radiation fog, turbulence, and gravity waves associated with the surrounding topography. A ≈ 10-30 m fog layer formed by radiative cooling was observed from 0720 to 0900 MST under cold air temperatures (≈-9 °C), near-saturated (relative humidity with respect to water ≈95 %), and calm wind (mostly <0.5 m s-1) conditions. Drainage flows were observed occasionally prior to fog formation, which modulated heat exchanges between air masses through the action of internal gravity waves and cold-air pool sloshing. The fog appeared to be triggered by cold-air advection from the south (≈200°) at 0700 MST. Quasi-periodic oscillations were observed before and during the fog event with a time period of about 15 min. These oscillations were detected in surface pressure, temperature, sensible heat flux, incoming longwave radiation, and turbulent kinetic energy measurements. We hypothesize that the quasi-periodic oscillations were caused by atmospheric gravity waves with a time period of about 10-20 min based on wavelet analysis. During the fog event, internal gravity waves led to about 1 °C fluctuations in air temperatures. After 0835 MST when net radiation became positive, fog started to dissipate due to the surface heating and heat absorption by the fog particles. Overall, this case study provides a concrete example of how fog evolution is modulated by very weak thermal circulations in mountainous terrain and illustrates the need for high density vertical and horizontal measurements to ensure that the highly spatially varying physics in complex terrain are sufficient for hypothesis testing.

Tsunami mitigation - redistribution of energy

NASA Astrophysics Data System (ADS)

Kadri, Usama

2017-04-01

Tsunamis are water waves caused by the displacement of a large volume of water, in the deep ocean or a large lake, following an earthquake, landslide, underwater explosion, meteorite impacts, or other violent geological events. On the coastline, the resulting waves evolve from unnoticeable to devastating, reaching heights of tens of meters and causing destruction of property and loss of life. Over 225,000 people were killed in the 2004 Indian Ocean tsunami alone. For many decades, scientists have been studying tsunami, and progress has been widely reported in connection with the causes (1), forecasting (2), and recovery (3). However, none of the studies ratifies the approach of a direct mitigation of tsunamis, with the exception of mitigation using submarine barriers (e.g. see Ref. (4)). In an attempt to open a discussion on direct mitigation, I examine the feasibility of redistributing the total energy of a very long surface ocean (gravity) wave over a larger space through nonlinear resonant interaction with two finely tuned acoustic-gravity waves (see Refs. (5-8)). Theoretically, while the energy input in the acoustic-gravity waves required for an effective interaction is comparable to that in a tsunami (i.e. impractically large), employing the proposed mitigation technique the initial tsunami amplitude could be reduced substantially resulting in a much milder impact at the coastline. Moreover, such a technique would allow for the harnessing of the tsunami's own energy. Practically, this mitigation technique requires the design of highly accurate acoustic-gravity wave frequency transmitters or modulators, which is a rather challenging ongoing engineering problem. References 1. E. Bryant, 2014. Tsunami: the underrated hazard. Springer, doi:10.1007/978-3-319- 06133-7. 2. V. V. Titov, F. I. Gonza`lez, E. N. Bernard, M. C. Eble, H. O. Mofjeld, J. C. Newman, A. J. Venturato, 2005. Real-Time Tsunami Forecasting: Challenges and Solutions. Nat. Hazards 35:41-58, doi:10.1007/1-4020-3607-8 3 3. E. Check, 2005. Natural disasters: Roots of recovery. Nature 438, 910-911, doi:10.1038/438910a. 4. A. M. Fridman, L. S. Alperovich, L. Shemer, L. Pustil'nik, D. Shtivelman, A. G. Marchuk, D. Liberzon, 2010. Tsunami wave suppression using submarine barriers. Phys. Usp. 53 809-816, doi:10.3367/UFNe.0180.201008d.0843. 5. U. Kadri, M. Stiassnie, 2013. Generation of an acoustic-gravity wave by two gravity waves, and their mutual interaction. J. Fluid Mech. 735, R6, doi:10.1017/jfm.2013.539. 6. U. Kadri, 2015. Wave motion in a heavy compressible fluid: revisited. European Journal of Mechanics - B/Fluids, 49(A), 50-57, doi:10.1016/j.euromechflu.2014.07.008 7. U. Kadri, T.R. Akylas, 2016. On resonant triad interactions of acoustic-gravity waves. J. Fluid Mech., 788, R1(12 pages), doi:10.1017/jfm.2015.721. 8. U. Kadri, 2016. Triad resonance between a surface-gravity wave and two high frequency hydro-acoustic waves. Eur. J. Mech. B/Fluid, 55(1), 157-161, doi:10.1016/j.euromechflu.2015.09.008.

Meso-beta scale numerical simulation studies of terrain-induced jet streak mass/momentum perturbations

NASA Technical Reports Server (NTRS)

Lin, Yuh-Lang; Kaplan, Michael L.

1995-01-01

Mesoscale model simulations provide insight into the complex jet streak adjustments on 11-12 July 1981 that preceded the first of two significant gravity wave events to have been generated over the Rocky Mountains in Montana. Simulations employing a variety of terrain treatments indicate that prior to wave formation, geostrophic adjustment processes modified the structure of the mid-upper tropospheric jet streak by creating secondary jetlets to the southeast of the polar jet streak in proximity to the gravity wave generation region. This simulated restructuring of the mid-upper tropospheric jet streak is the result of a four stage process. During stage 1, the wind adjusts to the mass field as the jet streak exit region propagates into the inflection point between the upstream trough and downstream ridge in the height field. Stage 2 is initiated as the mass field is forced to adjust to the new ageostrophic wind field created during stage 1. Stage 3 is defined by a second geostrophic adjustment process occurring in a similar manner but to the south and east of the adjustment which occurs during stage 1. A low-level mesoscale jetlet is formed during stage 4 in response to the low-level pressure falls that are established during stage 3. The perturbation of this jetlet, caused by orographically-induced adiabatic and diabatic physical processes, is the likely mechanism responsible for the generation of the first and second episode of observed gravity waves. The dynamics responsible for this wave episode are discussed as differential surface sensible heating inducing an orographically-forced mountain-plains solenoid, resulting in the formation of additional mesoscale jetlets and internal gravity waves. Also discussed is how convective latent heating modifies the numerically simulated terrain-induced internal gravity waves, especially their amplitude and phase velocities, which provide better agreement with those wave characteristics observed in nature. Finally, the three-dimensional linear response of a zonally uniform barotropic flow in a vertically unbounded, continuously stratified, Boussinesq atmosphere which is perturbed from geostrophic equilibrium is investigated.

Tropospheric weather influenced by solar wind through atmospheric vertical coupling downward control

NASA Astrophysics Data System (ADS)

Prikryl, Paul; Bruntz, Robert; Tsukijihara, Takumi; Iwao, Koki; Muldrew, Donald B.; Rušin, Vojto; Rybanský, Milan; Turňa, Maroš; Šťastný, Pavel

2018-06-01

Occurrence of severe weather in the context of solar wind coupling to the magnetosphere-ionosphere-atmosphere (MIA) system is investigated. It is observed that significant snowfall, wind and heavy rain, particularly if caused by low pressure systems in winter, tend to follow arrivals of high-speed solar wind. Previously published statistical evidence that explosive extratropical cyclones in the northern hemisphere tend to occur within a few days after arrivals of high-speed solar wind streams from coronal holes (Prikryl et al., 2009, 2016) is corroborated for the southern hemisphere. Cases of severe weather events are examined in the context of the magnetosphere-ionosphere-atmosphere (MIA) coupling. Physical mechanism to explain these observations is proposed. The leading edge of high-speed solar wind streams is a locus of large-amplitude magneto-hydrodynamic waves that modulate Joule heating and/or Lorentz forcing of the high-latitude lower thermosphere generating medium-scale atmospheric gravity waves that propagate upward and downward through the atmosphere. Simulations of gravity wave propagation in a model atmosphere using the Transfer Function Model (Mayr et al., 1990) reveal that propagating waves originating in the lower thermosphere can excite a spectrum of gravity waves in the lower atmosphere. In spite of significantly reduced amplitudes but subject to amplification upon reflection in the upper troposphere, these gravity waves can provide a lift of unstable air to release instabilities in the troposphere and initiate convection to form cloud/precipitation bands. It is primarily the energy provided by release of latent heat that leads to intensification of storms. These results indicate that vertical coupling in the atmosphere exerts downward control from solar wind to the lower atmospheric levels influencing tropospheric weather development.

New Gravity Wave Treatments for GISS Climate Models

NASA Technical Reports Server (NTRS)

Geller, Marvin A.; Zhou, Tiehan; Ruedy, Reto; Aleinov, Igor; Nazarenko, Larissa; Tausnev, Nikolai L.; Sun, Shan; Kelley, Maxwell; Cheng, Ye

2011-01-01

Previous versions of GISS climate models have either used formulations of Rayleigh drag to represent unresolved gravity wave interactions with the model-resolved flow or have included a rather complicated treatment of unresolved gravity waves that, while being climate interactive, involved the specification of a relatively large number of parameters that were not well constrained by observations and also was computationally very expensive. Here, the authors introduce a relatively simple and computationally efficient specification of unresolved orographic and nonorographic gravity waves and their interaction with the resolved flow. Comparisons of the GISS model winds and temperatures with no gravity wave parameterization; with only orographic gravity wave parameterization; and with both orographic and nonorographic gravity wave parameterizations are shown to illustrate how the zonal mean winds and temperatures converge toward observations. The authors also show that the specifications of orographic and nonorographic gravity waves must be different in the Northern and Southern Hemispheres. Then results are presented where the nonorographic gravity wave sources are specified to represent sources from convection in the intertropical convergence zone and spontaneous emission from jet imbalances. Finally, a strategy to include these effects in a climate-dependent manner is suggested.

New Gravity Wave Treatments for GISS Climate Models

NASA Technical Reports Server (NTRS)

Geller, Marvin A.; Zhou, Tiehan; Ruedy, Reto; Aleinov, Igor; Nazarenko, Larissa; Tausnev, Nikolai L.; Sun, Shan; Kelley, Maxwell; Cheng, Ye

2010-01-01

Previous versions of GISS climate models have either used formulations of Rayleigh drag to represent unresolved gravity wave interactions with the model resolved flow or have included a rather complicated treatment of unresolved gravity waves that, while being climate interactive, involved the specification of a relatively large number of parameters that were not well constrained by observations and also was computationally very expensive. Here, we introduce a relatively simple and computationally efficient specification of unresolved orographic and non-orographic gravity waves and their interaction with the resolved flow. We show comparisons of the GISS model winds and temperatures with no gravity wave parametrization; with only orographic gravity wave parameterization; and with both orographic and non-orographic gravity wave parameterizations to illustrate how the zonal mean winds and temperatures converge toward observations. We also show that the specifications of orographic and nonorographic gravity waves must be different in the Northern and Southern Hemispheres. We then show results where the non-orographic gravity wave sources are specified to represent sources from convection in the Intertropical Convergence Zone and spontaneous emission from jet imbalances. Finally, we suggest a strategy to include these effects in a climate dependent manner.

Influence of Internal Waves on Transport by a Gravity Current

NASA Astrophysics Data System (ADS)

Koseff, Jeffrey; Hogg, Charlie; Ouillon, Raphael; Ouellette, Nicholas; Meiburg, Eckart

2017-11-01

Gravity currents moving along the continental slope can be influenced by internal waves shoaling on the slope resulting in mixing between the gravity current and the ambient fluid. Whilst some observations of the potential influence of internal waves on gravity currents have been made, the process has not been studied systematically. We present laboratory experiments, and some initial numerical simulations, in which a gravity current descends down a sloped boundary through a pycnocline at the same time as an internal wave at the pycnocline shoals on the slope. Measurements of the downslope mass flux of the gravity current fluid in cases with different amplitudes of the incident internal wave will be discussed. For the parameter regime considered, the mass flux in the head of the gravity current was found to reduce with increasingly larger incident amplitude waves. This reduction was effectively caused by a ``decapitation'' process whereby the breaking internal wave captures and moves fluid from the head of the gravity current back up the slope. The significance of the impact of the internal waves on gravity current transport, strongly suggests that the local internal wave climate may need to be considered when calculating gravity current transport. The Bob and Norma Street Environmental Fluid Mechanics Laboratory.

Synoptic-scale variability of arctic gravity wave activity during summer and potential impacts on the high latitude middle atmosphere

NASA Astrophysics Data System (ADS)

Gerrard, Andrew John

Although the role of gravity waves in the global atmospheric circulation is generally understood, discussion of synoptic gravity wave activity, especially pertaining to high latitude summer environments, is lacking in the literature. Tropospherically generated gravity waves greatly contribute to the zonal drag necessary to induce meridional outflow and subsequent upwelling observed in the adiabatically cooled summer mesosphere, ultimately resulting in an environment conducive to mesospheric cloud formation. However, the very gravity wave activity responsible for this induced cooling is also believed to be a major source of variability on mesospheric clouds over shorter time scales, and this topic should be of considerable interest if such clouds are to be used as tracers of the global climate. It is therefore the purpose of this thesis to explore high latitude synoptic gravity wave activity and ultimately seek an understanding of the associated influence on overlaying summer mesospheric clouds. Another goal is to better understand and account for potential variability in high latitude middle and upper atmospheric measurements that can be directly associated with "weather conditions" at lower altitudes. These endeavors are addressed through Rayleigh/aerosol lidar data obtained from the ARCtic LIdar TEchnology (ARCLITE) facility located at Sondrestrom, Greenland (67°N, 310°E), global tropospheric and stratospheric analyses and forecasts, and the Gravity-wave Regional Or Global RAy Tracer (GROGRAT) model. In this study we are able to show that (a) the upper stratospheric gravity wave strength and the brightness of overlaying mesospheric clouds, as measured by representative field proxies, are negatively correlated over time scales of less than a day, (b) such upper stratospheric gravity wave variability is inversely related to mesospheric cloud variability on time scales of ˜1 to 4 hours, (c) gravity wave hindcasts faithfully reproduce experimental lidar observations taken over the month of August 1996, (d) the observed upper stratospheric gravity wave activity is shown to originate from regionalized, non-orographic sources in the troposphere, (e) such gravity wave activity can propagate through the middle atmosphere, potentially impacting overlaying mesospheric clouds, and (f) the forecasting of such upper stratospheric gravity wave activity, and therefore the corresponding mesospheric cloud activity, is feasible. In conclusion, the results herein provide additional evidence of gravity wave influence on mesospheric clouds, a step towards the forecasting of regional gravity wave activity, and ultimately a better understanding of synoptic gravity wave activity at high latitudes.

1974: the discovery of the first binary pulsar

NASA Astrophysics Data System (ADS)

Damour, Thibault

2015-06-01

The 1974 discovery, by Russell A Hulse and Joseph H Taylor, of the first binary pulsar, PSR B1913+16, opened up new possibilities for the study of relativistic gravity. PSR B1913+16, as well as several other binary pulsars, provided direct observational proof that gravity propagates at the velocity of light and has a quadrupolar structure. Binary pulsars also provided accurate tests of the strong-field regime of relativistic gravity. General relativity has passed all of the binary pulsar tests with flying colors. The discovery of binary pulsars also had very important consequences for astrophysics, leading to accurate measurement of neutron star masses, improved understanding of the possible evolution scenarios for the co-evolution of binary stars, and proof of the existence of binary neutron stars emitting gravitational waves for hundreds of millions of years, before coalescing in catastrophic events radiating intense gravitational wave signals, and probably also leading to important emissions of electromagnetic radiation and neutrinos. This article reviews the history of the discovery of the first binary pulsar, and describes both its immediate impact and its longer-term effect on theoretical and experimental studies of relativistic gravity.

Background Lamb waves in the Earth's atmosphere

NASA Astrophysics Data System (ADS)

Nishida, Kiwamu; Kobayashi, Naoki; Fukao, Yoshio

2014-01-01

Lamb waves of the Earth's atmosphere in the millihertz band have been considered as transient phenomena excited only by large events. Here, we show the first evidence of background Lamb waves in the Earth's atmosphere from 0.2 to 10 mHz, based on the array analysis of microbarometer data from the USArray in 2012. The observations suggest that the probable excitation source is atmospheric turbulence in the troposphere. Theoretically, their energy in the troposphere tunnels into the thermosphere at a resonant frequency via thermospheric gravity wave, where the observed amplitudes indeed take a local minimum. The energy leak through the frequency window could partly contribute to thermospheric wave activity.

Quadratic curvature terms and deformed Schwarzschild-de Sitter black hole analogues in the laboratory

NASA Astrophysics Data System (ADS)

da Rocha, R.; Sobreiro, R. F.; Tomaz, A. A.

2017-12-01

Sound waves on a fluid stream, in a de Laval nozzle, are shown to correspond to quasinormal modes emitted by black holes that are physical solutions in a quadratic curvature gravity with cosmological constant. Sound waves patterns in transsonic regimes at a laboratory are employed here to provide experimental data regarding generalized theories of gravity, comprised by the exact de Sitter-like solution and a perturbative solution around the Schwarzschild-de Sitter standard solution as well. Using the classical tests of General Relativity to bound free parameters in these solutions, acoustic perturbations on fluid flows in nozzles are then regarded, to study quasinormal modes of these black holes solutions, providing deviations of the de Laval nozzle cross-sectional area, when compared to the Schwarzschild solution. The fluid sonic point in the nozzle, for sound waves in the fluid, is shown to implement the acoustic event horizon corresponding to quasinormal modes.

Modeling magnetic field and TEC signatures of large-amplitude acoustic and gravity waves generated by natural hazard events

NASA Astrophysics Data System (ADS)

Zettergren, M. D.; Snively, J. B.; Inchin, P.; Komjathy, A.; Verkhoglyadova, O. P.

2017-12-01

Ocean and solid earth responses during earthquakes are a significant source of large amplitude acoustic and gravity waves (AGWs) that perturb the overlying ionosphere-thermosphere (IT) system. IT disturbances are routinely detected following large earthquakes (M > 7.0) via GPS total electron content (TEC) observations, which often show acoustic wave ( 3-4 min periods) and gravity wave ( 10-15 min) signatures with amplitudes of 0.05-2 TECU. In cases of very large earthquakes (M > 8.0) the persisting acoustic waves are estimated to have 100-200 m/s compressional velocities in the conducting ionospheric E and F-regions and should generate significant dynamo currents and magnetic field signatures. Indeed, some recent reports (e.g. Hao et al, 2013, JGR, 118, 6) show evidence for magnetic fluctuations, which appear to be related to AGWs, following recent large earthquakes. However, very little quantitative information is available on: (1) the detailed spatial and temporal dependence of these magnetic fluctuations, which are usually observed at a small number of irregularly arranged stations, and (2) the relation of these signatures to TEC perturbations in terms of relative amplitudes, frequency, and timing for different events. This work investigates space- and time-dependent behavior of both TEC and magnetic fluctuations following recent large earthquakes, with the aim to improve physical understanding of these perturbations via detailed, high-resolution, two- and three-dimensional modeling case studies with a coupled neutral atmospheric and ionospheric model, MAGIC-GEMINI (Zettergren and Snively, 2015, JGR, 120, 9). We focus on cases inspired by the large Chilean earthquakes from the past decade (viz., the M > 8.0 earthquakes from 2010 and 2015) to constrain the sources for the model, i.e. size, frequency, amplitude, and timing, based on available information from ocean buoy and seismometer data. TEC data are used to validate source amplitudes and to constrain background ionospheric conditions. Preliminary comparisons against available magnetic field and TEC data from these events provide evidence, albeit limited and localized, that support the validity of the spatially-resolved simulation results.

Rayleigh lidar observations of gravity wave characteristics in the middle atmosphere at Gadanki, India (13.5 degrees N, 79.2 degreesE.)

NASA Astrophysics Data System (ADS)

Parameswaran, K.; Rajeev, K.; Sasi, M. N.; Ramkumar, Geetha; Krishna Murthy, B. V.; Satheesan, K.; Jain, A. R.; Bhavanikumar, Y.; Raghunath, Kalavai J.; Krishnaiah, M.

2002-01-01

Rayleigh lidar observations of temperature in the stratosphere and mesosphere are carried out an Gadanki from February 29 to March 31, 2000, which provided a powerful means of studying the gravity wave characteristics over the tropical atmosphere during winter. The potential energy per unit mass associated with the gravity wave activity in the upper stratosphere and mesosphere is found to undergo periodic fluctuations, which are closely correlated with the zonal wind fluctuations in the stratosphere produced by the equatorial waves. This provides the first observational evidence for the modulation of the gravity wave activity by the long period equatorial waves over the tropical middle atmosphere. The vertical wave number spectra of gravity waves shows that power spectral density decease with increasing wave number with a slope less than that expected for the saturated gravity wave spectrum in the stratosphere and mesosphere. PSD decreases for vertical wavelengths smaller than about 10 km in the stratosphere while the decrease is observed for the complete range of observed gravity wave spectrum in the mesosphere. A monochromatic upward propagating gravity wave with periodicity of 6 hour, amplitude of about 1 K to 3 K and vertical wavelength of 11 km was observed on 22 March, 2000.

Observational signatures of unusual outgoing longwave radiation (OLR) and atmospheric gravity waves (AGW) as precursory effects of May 2015 Nepal earthquakes

NASA Astrophysics Data System (ADS)

Chakraborty, Suman; Sasmal, Sudipta; Chakrabarti, Sandip K.; Bhattacharya, Arnab

2018-01-01

Earthquake preparation processes may start 1-30 days before its actual occurrence. Measurements of outgoing longwave radiation (OLR) and detection of the presence of atmospheric gravity waves (AGW) in very low frequency (VLF) radio signals can be used as tools to identify such processes. We studied these signals monitored prior to a recent major earthquake that occurred in Nepal at southeast of Kodari on May 12, 2015 at 12:50 pm local time (07:05 UTC) with Richter scale magnitude of M = 7.3 and depth 10 km (6.21 miles). It was preceded by another major earthquake on April 25, 2015 with magnitude M = 7.9. First, to study the effects of seismic events on OLR, we used NOAA/IR daily (two degree gridded) data from April 16 to May 30, 2015 and followed the method of Eddy field calculation mean to find pre-seismic anomalies. We found singularities in Eddy field OLR curves around the earthquake epicenter starting 3 days prior to the earthquake days and disappearance of such singularities after the events. Such singularities can be associated with a large amount of energy released by the earthquakes. Second, we analyzed very low frequency (VLF) data recorded at Ionospheric and Earthquake Research Centre (IERC) of Indian Centre for Space Physics transmitted from JJI (22.2 kHz) station of Japan. We looked for the presence of atmospheric gravity waves in the ionosphere which can be considered as an important factor in finding seismo-ionospheric correlations. We performed both fast Fourier transform (FFT) and wavelet analysis on the signal and found significant presence of such waves (periods of almost 1 h) four days before the earthquake.

Testing the Speed of Gravitational Waves over Cosmological Distances with Strong Gravitational Lensing.

PubMed

Collett, Thomas E; Bacon, David

2017-03-03

Probing the relative speeds of gravitational waves and light acts as an important test of general relativity and alternative theories of gravity. Measuring the arrival time of gravitational waves (GWs) and electromagnetic (EM) counterparts can be used to measure the relative speeds, but only if the intrinsic time lag between emission of the photons and gravitational waves is well understood. Here we suggest a method that does not make such an assumption, using future strongly lensed GW events and EM counterparts; Biesiada et al. [J. Cosmol. Astropart. Phys.10 (2014) 080JCAPBP1475-751610.1088/1475-7516/2014/10/080] forecast that 50-100 strongly lensed GW events will be observed each year with the Einstein Telescope. A single strongly lensed GW event would produce robust constraints on c_{GW}/c_{γ} at the 10^{-7} level, if a high-energy EM counterpart is observed within the field of view of an observing γ-ray burst monitor.

The mean zonal flow response to Rossby wave and gravity wave forcing in the equatorial lower stratosphere - Relationship to the QBO

NASA Technical Reports Server (NTRS)

Takahashi, Masaaki; Holton, James R.

1991-01-01

Observations show that the westerly acceleration of the equatorial quasi-biennial oscillation (QBO) can be accounted for by Kelvin waves, but that there is a deficiency in the easterly acceleration due to Rossby-gravity waves. Rossby waves and westward propagating gravity waves have been suggested as alternative sources for the easterly acceleration. The possible role of these two wave modes has been tested in a two-dimensional model of the QBO. When the easterly acceleration is due to Rossby waves, the zonal-mean response is steady; when it is due to gravity waves, an oscillation with some features similar to the QBO occurs, but it is of short period and weak amplitude. A similar result occurs when a standing-wave forcing pattern is imposed. These results suggest that Rossby waves play only a minor role in the QBO, and that while the Rossby-gravity mode is essential, other gravity modes may also be important for the easterly phase.

Dense Gravity Currents with Breaking Internal Waves

NASA Astrophysics Data System (ADS)

Tanimoto, Yukinobu; Hogg, Charlie; Ouellette, Nicholas; Koseff, Jeffrey

2017-11-01

Shoaling and breaking internal waves along a pycnocline may lead to mixing and dilution of dense gravity currents, such as cold river inflows into lakes or brine effluent from desalination plants in near-coastal environments. In order to explore the interaction between gravity currents and breaking interfacial waves a series of laboratory experiments was performed in which a sequence of internal waves impinge upon a shelf-slope gravity current. The waves are generated in a two-layer thin-interface ambient water column under a variety of conditions characterizing both the waves and the gravity currents. The mixing of the gravity current is measured through both intrusive (CTD probe) and nonintrusive (Planar-laser inducted fluorescence) techniques. We will present results over a full range of Froude number (characterizing the waves) and Richardson number (characterizing the gravity current) conditions, and will discuss the mechanisms by which the gravity current is mixed into the ambient environment including the role of turbulence in the process. National Science Foundation.

A numerical model of gravity wave breaking and stress in the mesosphere

NASA Technical Reports Server (NTRS)

Schoeberl, M. R.; Strobel, D. F.; Apruzese, J. P.

1983-01-01

The goal of the study is to calculate numerically the deceleration and heating caused by breaking gravity waves. The effect of the radiative dissipation of the wave is included as vertical-wavelength-dependent Newtonian cooling. The parameterization for zonal deceleration is extended by breaking gravity waves (Lindzen, 1981) to include the turbulent diffusion of heat and momentum. After describing the numerical model, the numerical results are presented and compared with the parameterizations in a noninteractive model of the mean zonal wind. Attention is then given to the transport of constituents by gravity waves and the attendant turbulent zone. It is noted that if gravity wave breaking were not an intermittent process, gravity wave stresses would produce an adiabatic mesosphere with a zonal mean velocity close to the phase speed of the breaking wave.

Strong lensing of gravitational waves as seen by LISA.

PubMed

Sereno, M; Sesana, A; Bleuler, A; Jetzer, Ph; Volonteri, M; Begelman, M C

2010-12-17

We discuss strong gravitational lensing of gravitational waves from the merging of massive black hole binaries in the context of the LISA mission. Detection of multiple events would provide invaluable information on competing theories of gravity, evolution and formation of structures and, possibly, constraints on H0 and other cosmological parameters. Most of the optical depth for lensing is provided by intervening massive galactic halos, for which wave optics effects are negligible. Probabilities to observe multiple events are sizable for a broad range of formation histories. For the most optimistic models, up to ≲ 4 multiple events with a signal to noise ratio ≳ 8 are expected in a 5-year mission. Chances are significant even for conservative models with either light (≲ 60%) or heavy (≲ 40%) seeds. Because of lensing amplification, some intrinsically too faint signals are brought over threshold (≲ 2 per year).

A coordinated study of 1 h mesoscale gravity waves propagating from Logan to Boulder with CRRL Na Doppler lidars and temperature mapper

NASA Astrophysics Data System (ADS)

Lu, Xian; Chen, Cao; Huang, Wentao; Smith, John A.; Chu, Xinzhao; Yuan, Tao; Pautet, Pierre-Dominique; Taylor, Mike J.; Gong, Jie; Cullens, Chihoko Y.

2015-10-01

We present the first coordinated study using two lidars at two separate locations to characterize a 1 h mesoscale gravity wave event in the mesopause region. The simultaneous observations were made with the Student Training and Atmospheric Research (STAR) Na Doppler lidar at Boulder, CO, and the Utah State University Na Doppler lidar and temperature mapper at Logan, UT, on 27 November 2013. The high precision possessed by the STAR lidar enabled these waves to be detected in vertical wind. The mean wave amplitudes are ~0.44 m/s in vertical wind and ~1% in relative temperature at altitudes of 82-107 km. Those in the zonal and meridional winds are 6.1 and 5.2 m/s averaged from 84 to 99 km. The horizontal and vertical wavelengths inferred from the mapper and lidars are ~219 ± 4 and 16.0 ± 0.3 km, respectively. The intrinsic period is ~1.3 h for the airglow layer, Doppler shifted by a mean wind of ~17 m/s. The wave packet propagates from Logan to Boulder with an azimuth angle of ~135° clockwise from north and an elevation angle of ~ 3° from the horizon. The observed phase difference between the two locations can be explained by the traveling time of the 1 h wave from Logan to Boulder, which is about ~2.4 h. The wave polarization relations are examined through the simultaneous quantifications of the three wind components and temperature. This study has developed a systematic methodology for fully characterizing mesoscale gravity waves, inspecting their intrinsic properties and validating the derivation of horizontal wave structures by applying multiple instruments from coordinated stations.

GRACILE: a comprehensive climatology of atmospheric gravity wave parameters based on satellite limb soundings

NASA Astrophysics Data System (ADS)

Ern, Manfred; Trinh, Quang Thai; Preusse, Peter; Gille, John C.; Mlynczak, Martin G.; Russell, James M., III; Riese, Martin

2018-04-01

Gravity waves are one of the main drivers of atmospheric dynamics. The spatial resolution of most global atmospheric models, however, is too coarse to properly resolve the small scales of gravity waves, which range from tens to a few thousand kilometers horizontally, and from below 1 km to tens of kilometers vertically. Gravity wave source processes involve even smaller scales. Therefore, general circulation models (GCMs) and chemistry climate models (CCMs) usually parametrize the effect of gravity waves on the global circulation. These parametrizations are very simplified. For this reason, comparisons with global observations of gravity waves are needed for an improvement of parametrizations and an alleviation of model biases. We present a gravity wave climatology based on atmospheric infrared limb emissions observed by satellite (GRACILE). GRACILE is a global data set of gravity wave distributions observed in the stratosphere and the mesosphere by the infrared limb sounding satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Typical distributions (zonal averages and global maps) of gravity wave vertical wavelengths and along-track horizontal wavenumbers are provided, as well as gravity wave temperature variances, potential energies and absolute momentum fluxes. This global data set captures the typical seasonal variations of these parameters, as well as their spatial variations. The GRACILE data set is suitable for scientific studies, and it can serve for comparison with other instruments (ground-based, airborne, or other satellite instruments) and for comparison with gravity wave distributions, both resolved and parametrized, in GCMs and CCMs. The GRACILE data set is available as supplementary data at https://doi.org/10.1594/PANGAEA.879658.

Seasonal and height variation of gravity wave activities observed by a meteor radar at King Sejong Station (62°S, 57°W), Antarctica

NASA Astrophysics Data System (ADS)

Kim, Y.; Lee, C.; Kim, J.; Choi, J.; Jee, G.

2010-12-01

We have analyzed wind data from individual meteor echoes detected by a meteor radar at King Sejong Station, Antarctica to measure gravity wave activity in the mesopause region. Wind data in the meteor altitudes has been obtained routinely by the meteor radar since its installation in March 2007. The mean variances in the wind data that were filtered for large scale motions (mean winds and tides) can be regarded as the gravity wave activity. Monthly mean gravity wave activities show strong seasonal and height dependences in the altitude range of 80 to 100 km. The gravity wave activities except summer monotonically increase with altitude, which is expected since decreasing atmospheric densities cause wave amplitudes to increase. During summer (Dec. - Feb.) the height profiles of gravity wave activities show a minimum near 90 - 95 km, which may be due to different zonal wind and strong wind shear near 80 - 95 km. Our gravity wave activities are generally stronger than those of the Rothera station, implying sensitive dependency on location. The difference may be related to gravity wave sources in the lower atmosphere near Antarctic vortex.

Investigating gravity waves evidences in the Venus upper atmosphere

NASA Astrophysics Data System (ADS)

Migliorini, Alessandra; Altieri, Francesca; Shakun, Alexey; Zasova, Ludmila; Piccioni, Giuseppe; Bellucci, Giancarlo; Grassi, Davide

2014-05-01

We present a method to investigate gravity waves properties in the upper mesosphere of Venus, through the O2 nightglow observations acquired with the imaging spectrometer VIRTIS on board Venus Express. Gravity waves are important dynamical features that transport energy and momentum. They are related to the buoyancy force, which lifts air particles. Then, the vertical displacement of air particles produces density changes that cause gravity to act as restoring force. Gravity waves can manifest through fluctuations on temperature and density fields, and hence on airglow intensities. We use the O2 nightglow profiles showing double peaked structures to study the influence of gravity waves in shaping the O2 vertical profiles and infer the waves properties. In analogy to the Earth's and Mars cases, we use a well-known theory to model the O2 nightglow emissions affected by gravity waves propagation. Here we propose a statistical discussion of the gravity waves characteristics, namely vertical wavelength and wave amplitude, with respect to local time and latitude. The method is applied to about 30 profiles showing double peaked structures, and acquired with the VIRTIS/Venus Express spectrometer, during the mission period from 2006-07-05 to 2008-08-15.

Altimeter Observations of Baroclinic Oceanic Inertia-Gravity Wave Turbulence

NASA Technical Reports Server (NTRS)

Glazman, R. E.; Cheng, B.

1996-01-01

For a wide range of nonlinear wave processes - from capillary to planetary waves - theory predicts the existence of Kolmogorov-type spectral cascades of energy and other conserved quantities occuring via nonlinear resonant wave-wave interactions. So far, observations of wave turbulence (WT) have been limited to small-scale processes such as surface gravity and capillary-gravity waves.

Secondary Gravity Waves in the Winter Mesosphere: Results From a High-Resolution Global Circulation Model

NASA Astrophysics Data System (ADS)

Becker, Erich; Vadas, Sharon L.

2018-03-01

This study analyzes a new high-resolution general circulation model with regard to secondary gravity waves in the mesosphere during austral winter. The model resolves gravity waves down to horizontal and vertical wavelengths of 165 and 1.5 km, respectively. The resolved mean wave drag agrees well with that from a conventional model with parameterized gravity waves up to the midmesosphere in winter and up to the upper mesosphere in summer. About half of the zonal-mean vertical flux of westward momentum in the southern winter stratosphere is due to orographic gravity waves. The high intermittency of the primary orographic gravity waves gives rise to secondary waves that result in a substantial eastward drag in the winter mesopause region. This induces an additional eastward maximum of the mean zonal wind at z ˜ 100 km. Radar and lidar measurements at polar latitudes and results from other high-resolution global models are consistent with this finding. Hence, secondary gravity waves may play a significant role in the general circulation of the winter mesopause region.

Ionospheric acoustic and gravity waves associated with midlatitude thunderstorms

DOE PAGES

Lay, Erin H.; Shao, Xuan -Min; Kendrick, Alexander K.; ...

2015-07-30

Acoustic waves with periods of 2 - 4 minutes and gravity waves with periods of 6 - 16 minutes have been detected at ionospheric heights (250-350 km) using GPS Total Electron Content (TEC) measurements. The area disturbed by these waves and the wave amplitudes have been associated with underlying thunderstorm activity. A statistical study comparing NEXRAD radar thunderstorm measurements with ionospheric acoustic and gravity waves in the mid-latitude U.S. Great Plains region was performed for the time period of May - July 2005. An increase of ionospheric acoustic wave disturbed area and amplitude is primarily associated with large thunderstorms (mesoscalemore » convective systems). Ionospheric gravity wave disturbed area and amplitude scale with thunderstorm activity, with even small storms (i.e. individual storm cells) producing an increase of gravity waves.« less

When Black Holes Collide

NASA Technical Reports Server (NTRS)

Baker, John

2010-01-01

Among the fascinating phenomena predicted by General Relativity, Einstein's theory of gravity, black holes and gravitational waves, are particularly important in astronomy. Though once viewed as a mathematical oddity, black holes are now recognized as the central engines of many of astronomy's most energetic cataclysms. Gravitational waves, though weakly interacting with ordinary matter, may be observed with new gravitational wave telescopes, opening a new window to the universe. These observations promise a direct view of the strong gravitational dynamics involving dense, often dark objects, such as black holes. The most powerful of these events may be merger of two colliding black holes. Though dark, these mergers may briefly release more energy that all the stars in the visible universe, in gravitational waves. General relativity makes precise predictions for the gravitational-wave signatures of these events, predictions which we can now calculate with the aid of supercomputer simulations. These results provide a foundation for interpreting expect observations in the emerging field of gravitational wave astronomy.

GPS-TEC of the Ionospheric Disturbances as a Tool for Early Tsunami Warning

NASA Astrophysics Data System (ADS)

Kunitsyn, Viacheslav E.; Nesterov, Ivan A.; Shalimov, Sergey L.; Krysanov, Boris Yu.; Padokhin, Artem M.; Rekenthaler, Douglas

2013-04-01

Recently, the GPS measurements were used for retrieving the information on the various types of ionospheric responses to seismic events (earthquakes, seismic Rayleigh waves, and tsunami) which generate atmospheric waves propagating up to the ionospheric altitudes where the collisions between the neutrals and charge particles give rise to the motion of the ionospheric plasma. These experimental results can well be used in architecture of the future tsunami warning system. The point is an earlier (in comparison with seismological methods) detection of the ionospheric signal that can indicate the moment of tsunami generation. As an example we consider the two-dimensional distributions of the vertical total electron content (TEC) variations in the ionosphere both close to and far from the epicenter of the Japan undersea earthquake of March 11, 2011 using radio tomographic (RT) reconstruction of high-temporal-resolution (2-minute) data from the Japan and the US GPS networks. Near-zone TEC variations shows a diverging ionospheric perturbation with multi-component spectral composition emerging after the main shock. The initial phase of the disturbance can be used as an indicator of the tsunami generation and subsequently for the tsunami early warning. Far-zone TEC variations reveals distinct wave train associated with gravity waves generated by tsunami. According to observations tsunami arrives at Hawaii and further at the coast of Southern California with delay relative to the gravity waves. Therefore the gravity wave pattern can be used in the early tsunami warning. We support this scenario by the results of modeling with the parameters of the ocean surface perturbation corresponding to the considered earthquake. In addition it was observed in the modeling that at long distance from the source the gravity wave can pass ahead of the tsunami. The work was supported by the Russian Foundation for Basic Research (grants 11-05-01157 and 12-05-33065).

Nonstationary Gravity Wave Forcing of the Stratospheric Zonal Mean Wind

NASA Technical Reports Server (NTRS)

Alexander, M. J.; Rosenlof, K. H.

1996-01-01

The role of gravity wave forcing in the zonal mean circulation of the stratosphere is discussed. Starting from some very simple assumptions about the momentum flux spectrum of nonstationary (non-zero phase speed) waves at forcing levels in the troposphere, a linear model is used to calculate wave propagation through climatological zonal mean winds at solstice seasons. As the wave amplitudes exceed their stable limits, a saturation criterion is imposed to account for nonlinear wave breakdown effects, and the resulting vertical gradient in the wave momentum flux is then used to estimate the mean flow forcing per unit mass. Evidence from global, assimilated data sets are used to constrain these forcing estimates. The results suggest the gravity-wave-driven force is accelerative (has the same sign as the mean wind) throughout most of the stratosphere above 20 km. The sense of the gravity wave forcing in the stratosphere is thus opposite to that in the mesosphere, where gravity wave drag is widely believed to play a principal role in decelerating the mesospheric jets. The forcing estimates are further compared to existing gravity wave parameterizations for the same climatological zonal mean conditions. Substantial disagreement is evident in the stratosphere, and we discuss the reasons for the disagreement. The results suggest limits on typical gravity wave amplitudes near source levels in the troposphere at solstice seasons. The gravity wave forcing in the stratosphere appears to have a substantial effect on lower stratospheric temperatures during southern hemisphere summer and thus may be relevant to climate.

Selective excitation of tropical atmospheric waves in wave-CISK: The effect of vertical wind shear

NASA Technical Reports Server (NTRS)

Zhang, Minghua; Geller, Marvin A.

1994-01-01

The growth of waves and the generation of potential energy in wave-CISK require unstable waves to tilt with height oppositely to their direction of propagation. This makes the structures and instability properties of these waves very sensitive to the presence of vertical shear in the basic flow. Equatorial Kelvin and Rossby-gravity waves have opposite phase tilt with height to what they have in the stratosphere, and their growth is selectively favored by basic flows with westward vertical shear and eastward vertical shear, respectively. Similar calculations are also made for gravity waves and Rossby waves. It is shown that eastward vertical shear of the basic flow promotes CISK for westward propagating Rossby-gravity, Rossby, and gravity waves and suppresses CISK for eastward propagating Kelvin and gravity waves, while westward shear of the basic flow has the reverse effects.

Triad Resonance in the Gravity-Acoustic Family

NASA Astrophysics Data System (ADS)

Kadri, U.

2015-12-01

Resonance interactions of waves play a prominent role in energy share among the different wave types involved. Such interactions may significantly contribute, among others, to the evolution of the ocean energy spectrum by exchanging energy between surface-gravity waves; surface and internal gravity waves; or even surface and compression-type waves, that can transfer energy from the upper ocean through the whole water column reaching down to the seafloor. A resonant triad occurs among a triplet of waves, usually involving interaction of nonlinear terms of second order perturbed equations. Until recently, it has been believed that in a homogeneous fluid a resonant triad is possible only when tension forces are included, or at the limit of a shallow water, and that when the compressibility of water is considered, no resonant triads can occur within the family of gravity-acoustic waves. However, more recently it has been proved that, under some circumstances, resonant triads comprising two opposing surface-gravity waves of similar periods (though not identical) and a much longer acoustic-gravity wave, of almost double the frequency, exist [Kadri and Stiassnie 2013, J. Fluid Mech.735 R6]. Here, I report on a new resonant triad involving a gravity wave and two acoustic waves of almost double the length. Interestingly, the two acoustic waves propagate in the same direction with similar wavelengths, that are almost double of that of the gravity wave. The evolution of the wave triad amplitudes is periodic and it is derived analytically, in terms of Jacobian elliptic functions and elliptic integrals. The physical importance of this type of triad interactions is the modulation of pertinent acoustic signals, leading to inaccurate signal perceptions. Enclosed figure: presents an example spatio-temporal evolution of the wave triad amplitudes. The gravity wave (top) remains almost unaltered, while the envelope slowly displaces to the left. However, the prescribed acoustic envelope (middle) travels relatively fast to the right minimising the interaction time. Consequently, the resultant acoustic wave envelope (bottom) might be significantly smaller. As the two acoustic beams concurrently move away from the gravity wave, with disparate group velocities, the resonant interaction gradually vanishes.

The mean zonal flow response to Rossby wave and gravity wave forcing in the equatorial lower stratosphere: Relationship to the QBO. [QBO (quasi-biennial oscillation)

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

Takahashi, M.; Holton, J.R.

1991-09-15

Observations show that the westerly acceleration of the equatorial quasi-biennial oscillation (QBO) can be accounted for by Kelvin waves, but that there is a deficiency in the easterly acceleration due to Rossby-gravity waves. Rossby waves and westward propagating gravity waves have been suggested as alternative sources for the easterly acceleration. We have tested the possible role of these two wave modes in a two-dimensional model of the QBO. When the easterly acceleration is due to Rossby waves, the zonal-mean response is steady; when it is due to gravity waves, an oscillation with some features similar to the QBO occurs, butmore » it is of short period and weak amplitude. A similar result occurs when a standing-wave forcing pattern is imposed. These results suggest that Rossby waves play only a minor role in the QBO, and that while the Rossby-gravity mode is essential, other gravity modes may also be important for the easterly phase. 12 refs., 22 figs.« less

Middle Atmosphere Program. Handbook for MAP, volume 20

NASA Technical Reports Server (NTRS)

Bowhill, S. A. (Editor); Edwards, B. (Editor)

1986-01-01

Various topics related to investigations of the middle atmosphere are discussed. Numerical weather prediction, performance characteristics of weather profiling radars, determination of gravity wave and turbulence parameters, case studies of gravity-wave propagation, turbulence and diffusion due to gravity waves, the climatology of gravity waves, mesosphere-stratosphere-troposphere radar, antenna arrays, and data management techniques are among the topics discussed.

Constraining alternative theories of gravity using GW150914 and GW151226

NASA Astrophysics Data System (ADS)

De Laurentis, Mariafelicia; Porth, Oliver; Bovard, Luke; Ahmedov, Bobomurat; Abdujabbarov, Ahmadjon

2016-12-01

The recently reported gravitational wave events GW150914 and GW151226 caused by the mergers of binary black holes [Abbott et al., Phys. Rev. Lett. 116, 221101 (2016); Phys. Rev. Lett. 116, 241103 (2016); Phys. Rev. X 6, 041015] provide a formidable way to set constraints on alternative metric theories of gravity in the strong field regime. In this paper, we develop an approach where an arbitrary theory of gravity can be parametrized by an effective coupling Geff and an effective gravitational potential Φ (r ). The standard Newtonian limit of general relativity is recovered as soon as Geff→GN and Φ (r )→ΦN. The upper bound on the graviton mass and the gravitational interaction length, reported by the LIGO-VIRGO Collaboration, can be directly recast in terms of the parameters of the theory that allows an analysis where the gravitational wave frequency modulation sets constraints on the range of possible alternative models of gravity. Numerical results based on published parameters for the binary black hole mergers are also reported. The comparison of the observed phases of GW150914 and GW151226 with the modulated phase in alternative theories of gravity does not give reasonable constraints due to the large uncertainties in the estimated parameters for the coalescing black holes. In addition to these general considerations, we obtain limits for the frequency dependence of the α parameter in scalar tensor theories of gravity.

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.

Upper atmospheric planetary-wave and gravity-wave observations

NASA Technical Reports Server (NTRS)

Justus, C. G.; Woodrum, A.

1973-01-01

Previously collected data on atmospheric pressure, density, temperature and winds between 25 and 200 km from sources including Meteorological Rocket Network data, ROBIN falling sphere data, grenade release and pitot tube data, meteor winds, chemical release winds, satellite data, and others were analyzed by a daily-difference method, and results on the magnitude of atmospheric perturbations interpreted as gravity waves and planetary waves are presented. Traveling planetary-wave contributions in the 25-85 km range were found to have significant height and latitudinal variation. It was found that observed gravity-wave density perturbations and wind are related to one another in the manner predicted by gravity-wave theory. It was determined that, on the average, gravity-wave energy deposition or reflection occurs at all altitudes except the 55-75 km region of the mesosphere.

Shear waves in inhomogeneous, compressible fluids in a gravity field.

PubMed

Godin, Oleg A

2014-03-01

While elastic solids support compressional and shear waves, waves in ideal compressible fluids are usually thought of as compressional waves. Here, a class of acoustic-gravity waves is studied in which the dilatation is identically zero, and the pressure and density remain constant in each fluid particle. These shear waves are described by an exact analytic solution of linearized hydrodynamics equations in inhomogeneous, quiescent, inviscid, compressible fluids with piecewise continuous parameters in a uniform gravity field. It is demonstrated that the shear acoustic-gravity waves also can be supported by moving fluids as well as quiescent, viscous fluids with and without thermal conductivity. Excitation of a shear-wave normal mode by a point source and the normal mode distortion in realistic environmental models are considered. The shear acoustic-gravity waves are likely to play a significant role in coupling wave processes in the ocean and atmosphere.

Spectral evolution and extreme value analysis of non-linear numerical simulations of narrow band random surface gravity waves.

NASA Astrophysics Data System (ADS)

Socquet-Juglard, H.; Dysthe, K. B.; Trulsen, K.; Liu, J.; Krogstad, H. E.

2003-04-01

Numerical simulations of a narrow band gaussian spectrum of random surface gravity waves have been carried out in two and three spatial dimensions [7]. Different types of non-linear Schr&{uml;o}dinger equations, [1] and [4], have been used in these simulations. Simulations have now been carried with a JONSWAP spectrum associated with a spreading function of the type cosine-squared [5]. The evolution of the spectrum, skewness, kurtosis, ... will be presented. In addition, some results about stochastic properties of the surface will be shown. Based on the approach found in [2], [3] and [6], the results are presented in terms of deviations from linear Gaussian theory and the standard second order small slope perturbation theory. begin{thebibliography}{9} bibitem{kk96} Trulsen, K. &Dysthe, K. B. (1996). A modified nonlinear Schr&{uml;o}dinger equation for broader bandwidth gravity waves on deep water. Wave Motion, 24, pp. 281-289. bibitem{BK2000} Krogstad, H.E. and S.F. Barstow (2000). A uniform approach to extreme value analysis of ocean waves, Proc. ISOPE'2000, Seattle, USA, 3, pp. 103-108. bibitem{PRK} Prevosto, M., H. E. Krogstad and A. Robin (2000). Probability distributions for maximum wave and crest heights, Coast. Eng., 40, 329-360. bibitem{ketal} Trulsen, K., Kliakhandler, I., Dysthe, K. B. &Velarde, M. G. (2000) On weakly nonlinear modulation of waves on deep water, Phys. Fluids, 12, pp. L25-L28. bibitem{onorato} Onorato, M., Osborne, A.R. and Serio, M. (2002) Extreme wave events in directional, random oceanic sea states, Phys. Fluids, 14, pp. 2432-2437. bibitem{BK2002} Krogstad, H.E. and S.F. Barstow (2002). Analysis and Applications of Second Order Models for the Maximum Crest height, % Proc. 21nd Int. Conf. Offshore Mechanics and Arctic Engineering, Oslo. Paper no. OMAE2002-28479. bibitem{JFMP} Dysthe, K. B., Trulsen, K., Krogstad, H. E. and Socquet-Juglard, H. (2002, in press) Evolution of a narrow band spectrum of random surface gravity waves, J. Fluid Mech.

Role of Compressibility on Tsunami Propagation

NASA Astrophysics Data System (ADS)

Abdolali, Ali; Kirby, James T.

2017-12-01

In the present paper, we aim to reduce the discrepancies between tsunami arrival times evaluated from tsunami models and real measurements considering the role of ocean compressibility. We perform qualitative studies to reveal the phase speed reduction rate via a modified version of the Mild Slope Equation for Weakly Compressible fluid (MSEWC) proposed by Sammarco et al. (2013). The model is validated against a 3-D computational model. Physical properties of surface gravity waves are studied and compared with those for waves evaluated from an incompressible flow solver over realistic geometry for 2011 Tohoku-oki event, revealing reduction in phase speed.