Simulations of Atmospheric Neutral Wave Coupling to the Ionosphere

NASA Astrophysics Data System (ADS)

Siefring, C. L.; Bernhardt, P. A.

2005-12-01

The densities in the E- and F-layer plasmas are much less than the density of background neutral atmosphere. Atmospheric neutral waves are primary sources of plasma density fluctuations and are the sources for triggering plasma instabilities. The neutral atmosphere supports acoustic waves, acoustic gravity waves, and Kelvin Helmholtz waves from wind shears. These waves help determine the structure of the ionosphere by changes in neutral density that affect ion-electron recombination and by neutral velocities that couple to the plasma via ion-neutral collisions. Neutral acoustic disturbances can arise from thunderstorms, chemical factory explosions and intentional high-explosive tests. Based on conservation of energy, acoustic waves grow in amplitude as they propagate upwards to lower atmospheric densities. Shock waves can form in an acoustic pulse that is eventually damped by viscosity. Ionospheric effects from acoustic waves include transient perturbations of E- and F-Regions and triggering of E-Region instabilities. Acoustic-gravity waves affect the ionosphere over large distances. Gravity wave sources include thunderstorms, auroral region disturbances, Space Shuttle launches and possibly solar eclipses. Low frequency acoustic-gravity waves propagate to yield traveling ionospheric disturbances (TID's), triggering of Equatorial bubbles, and possible periodic structuring of the E-Region. Gravity wave triggering of equatorial bubbles is studied numerically by solving the equations for plasma continuity and ion velocity along with Ohms law to provide an equation for the induced electric potential. Slow moving gravity waves provide density depressions on bottom of ionosphere and a gravitational Rayleigh-Taylor instability is initiated. Radar scatter detects field aligned irregularities in the resulting plasma bubble. Neutral Kelvin-Helmholtz waves are produced by strong mesospheric wind shears that are also coincident with the formation of intense E-layers. An atmospheric model for periodic structures with Kelvin-Helmholtz (KH) wavelengths is used to show the development of quasi-periodic structures in the E-layer. For the model, a background atmosphere near 100 km altitude with a scale height of 12.2 km is subjected to a wind shear profile varying by 100 m/s over a distance of 1.7 km. This neutral speed shear drives the KH instability with a growth time of about 100 seconds. The neutral KH wave is a source of plasma turbulence. The E-layer responds to the KH-Wave structure in the neutral atmosphere as an electrodynamic tracer. The plasma flow leads to small scale plasma field aligned irregularities from a gradient drift, plasma interchange instability (GDI) or a Farley-Buneman, two-stream instability (FBI). These irregularities are detected by radar scatter as quasi-periodic structures. All of these plasma phenomena would not occur without the initiation by neutral atmospheric waves.

Observations of height-dependent pressure-perturbation structure of a strong mesoscale gravity wave

NASA Technical Reports Server (NTRS)

Starr, David O'C.; Korb, C. L.; Schwemmer, Geary K.; Weng, Chi Y.

1992-01-01

Airborne observations using a downward-looking, dual-frequency, near-infrared, differential absorption lidar system provide the first measurements of the height-dependent pressure-perturbation field associated with a strong mesoscale gravity wave. A pressure-perturbation amplitude of 3.5 mb was measured within the lowest 1.6 km of the atmosphere over a 52-km flight line. Corresponding vertical displacements of 250-500 m were inferred from lidar-observed displacement of aerosol layers. Accounting for probable wave orientation, a horizontal wavelength of about 40 km was estimated. Satellite observations reveal wave structure of a comparable scale in concurrent cirrus cloud fields over an extended area. Smaller-scale waves were also observed. Local meteorological soundings are analyzed to confirm the existence of a suitable wave duct. Potential wave-generation mechanisms are examined and discussed. The large pressure-perturbation wave is attributed to rapid amplification or possible wave breaking of a gravity wave as it propagated offshore and interacted with a very stable marine boundary layer capped by a strong shear layer.

Synthesis of regional crust and upper-mantle structure from seismic and gravity data

NASA Technical Reports Server (NTRS)

Alexander, S. S.; Lavin, P. M.

1979-01-01

Available seismic and ground based gravity data are combined to infer the three dimensional crust and upper mantle structure in selected regions. This synthesis and interpretation proceeds from large-scale average models suitable for early comparison with high-altitude satellite potential field data to more detailed delineation of structural boundaries and other variations that may be significant in natural resource assessment. Seismic and ground based gravity data are the primary focal point, but other relevant information (e.g. magnetic field, heat flow, Landsat imagery, geodetic leveling, and natural resources maps) is used to constrain the structure inferred and to assist in defining structural domains and boundaries. The seismic data consists of regional refraction lines, limited reflection coverage, surface wave dispersion, teleseismic P and S wave delay times, anelastic absorption, and regional seismicity patterns. The gravity data base consists of available point gravity determinations for the areas considered.

Vertical temperature and density patterns in the Arctic mesosphere analyzed as gravity waves

NASA Technical Reports Server (NTRS)

Eberstein, I. J.; Theon, J. S.

1975-01-01

Rocket soundings conducted from high latitude sites in the Arctic mesosphere are described. Temperature and wind profiles and one density profile were observed independently to obtain the thermodynamic structure, the wind structure, and their interdependence in the mesosphere. Temperature profiles from all soundings were averaged, and a smooth curve (or series of smooth curves) drawn through the points. A hydrostatic atmosphere based on the average, measured temperature profile was computed, and deviations from the mean atmosphere were analyzed in terms of gravity wave theory. The vertical wavelengths of the deviations were 10-20 km, and the wave amplitudes slowly increased with height. The experimental data were matched by calculated gravity waves having a period of 15-20 minutes and a horizontal wavelength of 60-80 km. The wind measurements are consistent with the thermodynamic measurements. The results also suggest that gravity waves travel from East to West with a horizontal phase velocity of approximately 60 m sec-1.

Some classes of gravitational shock waves from higher order theories of gravity

NASA Astrophysics Data System (ADS)

Oikonomou, V. K.

2017-02-01

We study the gravitational shock wave generated by a massless high energy particle in the context of higher order gravities of the form F(R,R_{μν}R^{μν},R_{μναβ}R^{μν αβ}). In the case of F(R) gravity, we investigate the gravitational shock wave solutions corresponding to various cosmologically viable gravities, and as we demonstrate the solutions are rescaled versions of the Einstein-Hilbert gravity solution. Interestingly enough, other higher order gravities result to the general relativistic solution, except for some specific gravities of the form F(R_{μν}R^{μν}) and F(R,R_{μν}R^{μν}), which we study in detail. In addition, when realistic Gauss-Bonnet gravities of the form R+F(G) are considered, the gravitational shock wave solutions are identical to the general relativistic solution. Finally, the singularity structure of the gravitational shock waves solutions is studied, and it is shown that the effect of higher order gravities makes the singularities milder in comparison to the general relativistic solutions, and in some particular cases the singularities seem to be absent.

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.

Long-term variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric gravity waves by using airglow images obtained at Shigarkai, Japan

NASA Astrophysics Data System (ADS)

Takeo, D.; Kazuo, S.; Hujinami, H.; Otsuka, Y.; Matsuda, T. S.; Ejiri, M. K.; Yamamoto, M.; Nakamura, T.

2016-12-01

Atmospheric gravity waves generated in the lower atmosphere transport momentum into the upper atmosphere and release it when they break. The released momentum drives the global-scale pole-to-pole circulation and causes global mass transport. Vertical propagation of the gravity waves and transportation of momentum depend on horizontal phase velocity of gravity waves according to equation about dispersion relation of waves. Horizontal structure of gravity waves including horizontal phase velocity can be seen in the airglow images, and there have been many studies about gravity waves by using airglow images. However, long-term variation of horizontal phase velocity spectrum of gravity waves have not been studied yet. In this study, we used 3-D FFT method developed by Matsuda et al., (2014) to analyze the horizontal phase velocity spectrum of gravity waves by using 557.7-nm (altitude of 90-100 km) and 630.0-nm (altitude of 200-300 km) airglow images obtained at Shigaraki MU Observatory (34.8 deg N, 136.1 deg E) over 16 years from October 1, 1998 to July 26, 2015. Results about 557.7-nm shows clear seasonal variation of propagation direction of gravity waves in the mesopause region. Between summer and winter, there are propagation direction anisotropies which probably caused by filtering due to zonal mesospheric jet and by difference of latitudinal location of wave sources relative to Shigaraki. Results about 630.0-nm shows clear negative correlation between the yearly power spectrum density of horizontal phase velocity and sunspot number. This negative correlation with solar activity is consistent with growth rate of the Perkins instability, which may play an important role in generating the nighttime medium-scale traveling ionospheric disturbances at middle latitudes.

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.

Two- and Three-Dimensional Probes of Parity in Primordial Gravity Waves.

PubMed

Masui, Kiyoshi Wesley; Pen, Ue-Li; Turok, Neil

2017-06-02

We show that three-dimensional information is critical to discerning the effects of parity violation in the primordial gravity-wave background. If present, helical gravity waves induce parity-violating correlations in the cosmic microwave background (CMB) between parity-odd polarization B modes and parity-even temperature anisotropies (T) or polarization E modes. Unfortunately, EB correlations are much weaker than would be naively expected, which we show is due to an approximate symmetry resulting from the two-dimensional nature of the CMB. The detectability of parity-violating correlations is exacerbated by the fact that the handedness of individual modes cannot be discerned in the two-dimensional CMB, leading to a noise contribution from scalar matter perturbations. In contrast, the tidal imprints of primordial gravity waves fossilized into the large-scale structure of the Universe are a three-dimensional probe of parity violation. Using such fossils the handedness of gravity waves may be determined on a mode-by-mode basis, permitting future surveys to probe helicity at the percent level if the amplitude of primordial gravity waves is near current observational upper limits.

Investigation of fog structure affected by gravity waves and turbulence in the mountainous region of Pyeongchang, Korea, the place for the 2018 Winter Olympics and Paralympics

NASA Astrophysics Data System (ADS)

La, I.; Yum, S. S.; Yeom, J. M.; Gultepe, I.

2017-12-01

Since microphysical and dynamical processes of fog are not well-known and have non-linear relationships among processes that are related to fog formation, improving the accuracy of the fog forecasting/nowcasting system is challenging. For these reasons, understanding the fog mechanism is needed to develop the fog forecasting system. So, we focus on understanding fog-turbulence interactions and fog-gravity wave interactions. Many studies noted that turbulence plays important roles in fog. However, a discrepancy between arguments for the effect of turbulent mixing on fog formation exists. Several studies suggested that turbulent mixing suppresses fog formation. Some other studies reported that turbulent mixing contributes to fog formation. On the other hand, several quasi-periodic oscillations of temperature, visibility, and vertical velocity, which have period of 10-20 minutes, were observed to be related to gravity waves in fog; because gravity waves play significant dynamic roles in the atmosphere. Furthermore, a numerical study suggested that gravity waves, simulated near the top of the fog layer, may affect fog microphysics. Thus, we investigate the effects of turbulent mixing on fog formation and the influences of gravity waves on fog microphysics to understand fog structure in Pyeongchang. In these studies, we analyze the data that are obtained from doppler lidar and 3.5 m meteorological observation tower including 3D-ultrasonic anemometer, IR sensor, and fog monitor during ICE-POP (International Collaborative Experiments for Pyeongchang 2018 Olympic and Paralympic winter games) campaign. In these instruments, doppler lidar is a good instrument to observe the gravity waves near the fog top, while in situ measurements have small spatial coverage. The instruments are installed at the mountainous terrain of Pyeongchang, Korea. More details will be presented at the conference.

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.

The Formation and Fate of Internal Waves in the South China Sea

DTIC Science & Technology

2015-11-05

FOf’miiiiiiM and Fate at Internal Waves In the South •C:hln;~t Sea --- --------· . _.,.. --- -------Author(s) Name{s) (Firsi,MI,La$t), Code, Atfi(iation...Tswen-Yung (David) Tang7 Internal gravity waves , the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in...for man-made structures in the ocean4. Generated primarily by the wind and the tides, internal waves can travel thousands of kilometres from their

Gravity Wave Seeding of Equatorial Plasma Bubbles

NASA Technical Reports Server (NTRS)

Singh, Sardul; Johnson, F. S.; Power, R. A.

1997-01-01

Some examples from the Atmosphere Explorer E data showing plasma bubble development from wavy ion density structures in the bottomside F layer are described. The wavy structures mostly had east-west wavelengths of 150-800 km, in one example it was about 3000 km. The ionization troughs in the wavy structures later broke up into either a multiple-bubble patch or a single bubble, depending upon whether, in the precursor wavy structure, shorter wavelengths were superimposed on the larger scale wavelengths. In the multiple bubble patches, intrabubble spacings vaned from 55 km to 140 km. In a fully developed equatorial spread F case, east-west wavelengths from 690 km down to about 0.5 km were present simultaneously. The spacings between bubble patches or between bubbles in a patch appear to be determined by the wavelengths present in the precursor wave structure. In some cases, deeper bubbles developed on the western edge of a bubble patch, suggesting an east-west asymmetry. Simultaneous horizontal neutral wind measurements showed wavelike perturbations that were closely associated with perturbations in the plasma horizontal drift velocity. We argue that the wave structures observed here that served as the initial seed ion density perturbations were caused by gravity waves, strengthening the view that gravity waves seed equatorial spread F irregularities.

Temporal variability of tidal and gravity waves during a record long 10-day continuous lidar sounding

NASA Astrophysics Data System (ADS)

Baumgarten, Kathrin; Gerding, Michael; Baumgarten, Gerd; Lübken, Franz-Josef

2018-01-01

Gravity waves (GWs) as well as solar tides are a key driving mechanism for the circulation in the Earth's atmosphere. The propagation of gravity waves is strongly affected by tidal waves as they modulate the mean background wind field and vice versa, which is not yet fully understood and not adequately implemented in many circulation models. The daylight-capable Rayleigh-Mie-Raman (RMR) lidar at Kühlungsborn (54° N, 12° E) typically provides temperature data to investigate both wave phenomena during one full day or several consecutive days in the middle atmosphere between 30 and 75 km altitude. Outstanding weather conditions in May 2016 allowed for an unprecedented 10-day continuous lidar measurement, which shows a large variability of gravity waves and tides on timescales of days. Using a one-dimensional spectral filtering technique, gravity and tidal waves are separated according to their specific periods or vertical wavelengths, and their temporal evolution is studied. During the measurement period a strong 24 h wave occurs only between 40 and 60 km and vanishes after a few days. The disappearance is related to an enhancement of gravity waves with periods of 4-8 h. Wind data provided by ECMWF are used to analyze the meteorological situation at our site. The local wind structure changes during the observation period, which leads to different propagation conditions for gravity waves in the last days of the measurement period and therefore a strong GW activity. The analysis indicates a further change in wave-wave interaction resulting in a minimum of the 24 h tide. The observed variability of tides and gravity waves on timescales of a few days clearly demonstrates the importance of continuous measurements with high temporal and spatial resolution to detect interaction phenomena, which can help to improve parametrization schemes of GWs in general circulation models.

Tropical waves and the quasi-biennial oscillation in the lower stratosphere

NASA Technical Reports Server (NTRS)

Miller, A. J.; Angell, J. K.; Korshover, J.

1976-01-01

By means of spectrum analysis of 11 years of lower stratospheric daily winds and temperatures at Balboa, Ascension and Canton-Singapore, evidence is presented supporting the existence of two principal wave modes with periods of about 11-17 days (Kelvin waves) and about 4-5 days (mixed Rossby-gravity waves). The structure of the two wave modes, as well as the vertical eddy momentum flux by the waves, is shown to be related to the quasi-biennial cycle, although for the mixed Rossby-gravity waves this is obvious only at Ascension. In addition, the Coriolis term, suggested as a source of vertical easterly momentum flux for the mixed Rossby-gravity waves, is investigated and found to be of the same magnitude as the vertical eddy flux term. Finally, we have examined the mean meridional motion and the meridional eddy momentum flux for its possible association with the quasi- biennial variation.

Picture of the global field of quasi-monochromatic gravity waves observed by stratospheric balloons and MST radars

NASA Technical Reports Server (NTRS)

Yamanaka, M. D.

1989-01-01

In MAP observations, it was found that: (1) gravity waves in selected or filtered portions of data are fit for monochromatic structures, whereas (2) those in fully continuous and resolved observations take universal continuous spectra. It is possible to explain (2) by dispersion of quasi-monochromatic (or slowly varying) wave packets observed locally as (1), since the medium atmosphere is unsteady and nonuniform. Complete verification of the wave-mean flow interactions by tracking individual wave packets seems hopeless, because the wave induced flow cannot be distinguished from the basic flow independent of the waves. Instead, the primitive picture is looked at before MAP, that is, the atmosphere is just like an entertainment stage illuminated by cocktail lights of quasi-monochromatic gravity waves. The wave parameters are regarded as functions of time and spatial coordinates. The observational evidences (1) and (2) suggest that the wave parameter field is rather homogeneous, which can be explained by interference of quasi-monochromatic wave packets.

Small-Scale Dynamical Structures Using OH Airglow From Astronomical Observations

NASA Astrophysics Data System (ADS)

Franzen, C.; Espy, P. J.; Hibbins, R. E.; Djupvik, A. A.

2017-12-01

Remote sensing of perturbations in the hydroxyl (OH) Meinel airglow has often been used to observe gravity, tidal and planetary waves travelling through the 80-90 km region. While large scale (>1 km) gravity waves and the winds caused by their breaking are widely documented, information on the highest frequency waves and instabilities occurring during the breaking process is often limited by the temporal and spatial resolution of the available observations. In an effort to better quantify the full range of wave scales present near the mesopause, we present a series of observations of the OH Meinel (9,7) transition that were executed with the Nordic Optical Telescope on La Palma (18°W, 29°N). These measurements have a 24 s repetition rate and horizontal spatial resolutions at 87 km as small as 10 cm, allowing us to quantify the transition in the mesospheric wave domains as the gravity waves break. Temporal scales from hours to minutes, as well as sub-100 m coherent structures in the OH airglow have been observed and will be presented.

No slip gravity

NASA Astrophysics Data System (ADS)

Linder, Eric V.

2018-03-01

A subclass of the Horndeski modified gravity theory we call No Slip Gravity has particularly interesting properties: 1) a speed of gravitational wave propagation equal to the speed of light, 2) equality between the effective gravitational coupling strengths to matter and light, Gmatter and Glight, hence no slip between the metric potentials, yet difference from Newton's constant, and 3) suppressed growth to give better agreement with galaxy clustering observations. We explore the characteristics and implications of this theory, and project observational constraints. We also give a simple expression for the ratio of the gravitational wave standard siren distance to the photon standard candle distance, in this theory and others, and enable a direct comparison of modified gravity in structure growth and in gravitational waves, an important crosscheck.

Gravity wave and tidal structures between 60 and 140 km inferred from space shuttle reentry data

NASA Technical Reports Server (NTRS)

Fritts, David C.; Wang, Ding-Yi; Blanchard, Robert C.

1993-01-01

This study presents an analysis of density measurements made using high-resolution accelerometers aboard several space shuttles at altitudes from 60 to 140 km during reentry into the earth's atmosphere. The observed density fluctuations are interpreted in terms of gravity waves and tides and provide evidence of the importance of such motions well into the thermosphere. Height profiles of fractional density variance reveal that wave amplitudes increase at a rate consistent with observations at lower levels up to about 90 km. The rate of amplitude growth decreases at greater heights, however, and appears to cease above about 110 km. Wave amplitudes are nevertheless large at these heights and suggest that gravity waves may play an important role in forcing of the lower thermosphere.

The effect of breaking gravity waves on the dynamics and chemistry of the mesosphere and lower thermosphere (invited review)

NASA Technical Reports Server (NTRS)

Garcia, R. R.

1986-01-01

The influence of breaking gravity waves on the dynamics and chemical composition of the 60 to 110 km region is investigated with a two dimensional model that includes a parameterization of gravity wave momentum deposition and diffusion. The dynamical model is described by Garcia and Solomon (1983) and Solomon and Garcia (1983) and includes a complete chemical scheme for the mesosphere and lower thermosphere. The parameterization of Lindzen (1981) is used to calculate the momentum deposited and the turbulent diffusion produced by the gravity waves. It is found that wave momentum deposition drives a very vigorous mean meridional circulation, produces a very cold summer mesopause and reverse the zonal wind jets above about 85 km. The seasonal variation of the turbulent diffusion coefficient is consistent with the behavior of mesospheric turbulences inferred from MST radar echoes. The large degree of consistency between model results and various types of dynamical and chemical data supports very strongly the hypothesis that breaking gravity waves play a major role in determining the zonally-averaged dynamical and chemical structure of the 60 to 110 km region of the atmosphere.

Waiting for 21-Lutetia "Rosetta" images as a final proof of structurizing force of inertia-gravity waves

NASA Astrophysics Data System (ADS)

Kochemasov, Gennady G.

2010-05-01

The 100 km long flattened asteroid 21-Lutetia will be imaged by the "Rosetta' spacecraft in July 2010. Knowing that heavenly bodies are effectively structurized by warping inertia-gravity waves one might expect that Lutetia will not be an exclusion out of a row of bodies subjected to an action of these waves [1-9]. The elliptical keplerian orbits with periodically changing bodies' accelerations imply inertia-gravity forces applied to any body notwithstanding its size, mass, density, chemical composition, and physical state. These forces produce inertia-gravity waves having in rotating bodied standing character and four directions of propagation (orthogonal and diagonal). Interfering these waves produce in bodies three (five) kinds of tectonic blocks: uprising strongly and moderately (++, +), subsiding deeply and moderately (--, -), and neutral (0) where + and - are compensated. Lengths and amplitudes of warping waves form the harmonic sequence. The fundamental wave1 (long 2πR) makes ubiquitous tectonic dichotomy (two antipodean segments or hemispheres: one risen, another fallen). In small bodies this structurization is expressed in their convexo-concave shape: one hemisphere is bulged, another one pressed in. Bulging hemisphere is extended, pressed in hemisphere contracted. This wave shaping tends to transform a globular body into a tetrahedron - the essentially dichotomous simplest Plato's figure. In this polyhedron always there is an opposition of extension (a face) to contraction (a vertex). The first overtone wave2 (long πR) makes tectonic sectors, also risen and fallen, and regularly disposed on (and in) a globe. This regularity is expressed in an octahedron form. The octahedron (diamond) or its parts are often observed in shapes of small bodies with small gravities. Larger bodies with rather strong gravity tend to smooth polyhedron vertices and edges but a polyhedron structurization is always present inside their globes and is shown in their tectonics, geomorphology and geophysical fields. The shorter warping waves are also present but because of their comparatively small lengths and amplitudes they are not so important in distorting globes. The presented main harmonic row is complicated by superimposed individual waves lengths of which are inversely proportional to orbital frequencies: higher frequency - smaller wave, and, vice versa, lower frequency - larger wave. In the main asteroid belt the fundamental wave of the main sequence and the individual wave (also long 2πR) are in the strongest 1:1 resonance what prohibits an accretion of a real planet because of prevailing debris scattering. Thus, the Lutetia shape can support the main point of the wave planetology - «orbits make structures». [1] Kochemasov G.G. (1999) "Diamond" and "dumb-bells"-like shapes of celestial bodies induced by inertia-gravity waves // 30th Vernadsky-Brown microsymposium on comparative planetology, Abstracts, Moscow, Vernadsky Inst., 49-50. [2] -"- (1999) On convexo-concave shape of small celestial bodies // Asteroids, Comets, Meteors. Cornell Univ., July 26-30, 1999, Abstr. # 24.22. [3] -"- (2006) The wave planetology illustrated - I: dichotomy, sectoring // 44th Vernadsky-Brown microsymposium "Topics in Comparative Planetology", Oct. 9-11, 2006, Moscow, Vernadsky Inst., Abstr. m44_39, CD-ROM; [4] -"- (2006) Theorems of the wave planetology imprinted in small bodies // Geophys. Res. Abstracts, Vol. 8, EGU06-A-01098, CD-ROM. [5] -"- (2007) Plato's polyhedra in space // EPSC Abstracts, Vol. 2, EPSC2007-A-00014, 2007. [6] -"-(2007) Wave shaping of small saturnian satellites and wavy granulation of saturnian rings // Geophys. Res. Abstracts, Vol. 9, EGU2007-A-01594, CD-ROM. [7] -"- (2007) Plato's polyhedra as shapes of small satellites in the outer Solar system // New Concepts in Global Tectonics Newsletter, # 44, 43-45. [8] -"- (2008) Plato' polyhedra as shapes of small icy satellites // Geophys. Res. Abstracts, Vol. 10, EGU2008-A-01271, CD-ROM. [9] -"- (2008) A wave geometrization of small heavenly bodies // GRA, Vol. 10, EGU2008-A-01275, CD-ROM.

Study of atmospheric gravity waves and infrasonic sources using the USArray Transportable Array pressure data

NASA Astrophysics Data System (ADS)

Hedlin, Michael; de Groot-Hedlin, Catherine; Hoffmann, Lars; Alexander, M. Joan; Stephan, Claudia

2016-04-01

The upgrade of the USArray Transportable Array (TA) with microbarometers and infrasound microphones has created an opportunity for a broad range of new studies of atmospheric sources and the large- and small-scale atmospheric structure through which signals from these events propagate. These studies are akin to early studies of seismic events and the Earth's interior structure that were made possible by the first seismic networks. In one early study with the new dataset we use the method of de Groot-Hedlin and Hedlin (2015) to recast the TA as a massive collection of 3-element arrays to detect and locate large infrasonic events. Over 2,000 events have been detected in 2013. The events cluster in highly active regions on land and offshore. Stratospherically ducted signals from some of these events have been recorded more than 2,000 km from the source and clearly show dispersion due to propagation through atmospheric gravity waves. Modeling of these signals has been used to test statistical models of atmospheric gravity waves. The network is also useful for making direct observations of gravity waves. We are currently studying TA and satellite observations of gravity waves from singular events to better understand how the waves near ground level relate to those observed aloft. We are also studying the long-term statistics of these waves from the beginning of 2010 through 2014. Early work using data bandpass filtered from 1-6 hr shows that both the TA and satellite data reveal highly active source regions, such as near the Great Lakes. de Groot-Hedlin and Hedlin, 2015, A method for detecting and locating geophysical events using clusters of arrays, Geophysical Journal International, v203, p960-971, doi: 10.1093/gji/ggv345.

Integration of P- and SH-wave high-resolution seismic reflection and micro-gravity techniques to improve interpretation of shallow subsurface structure: New Madrid seismic zone

USGS Publications Warehouse

Bexfield, C.E.; McBride, J.H.; Pugin, Andre J.M.; Ravat, D.; Biswas, S.; Nelson, W.J.; Larson, T.H.; Sargent, S.L.; Fillerup, M.A.; Tingey, B.E.; Wald, L.; Northcott, M.L.; South, J.V.; Okure, M.S.; Chandler, M.R.

2006-01-01

Shallow high-resolution seismic reflection surveys have traditionally been restricted to either compressional (P) or horizontally polarized shear (SH) waves in order to produce 2-D images of subsurface structure. The northernmost Mississippi embayment and coincident New Madrid seismic zone (NMSZ) provide an ideal laboratory to study the experimental use of integrating P- and SH-wave seismic profiles, integrated, where practicable, with micro-gravity data. In this area, the relation between "deeper" deformation of Paleozoic bedrock associated with the formation of the Reelfoot rift and NMSZ seismicity and "shallower" deformation of overlying sediments has remained elusive, but could be revealed using integrated P- and SH-wave reflection. Surface expressions of deformation are almost non-existent in this region, which makes seismic reflection surveying the only means of detecting structures that are possibly pertinent to seismic hazard assessment. Since P- and SH-waves respond differently to the rock and fluid properties and travel at dissimilar speeds, the resulting seismic profiles provide complementary views of the subsurface based on different levels of resolution and imaging capability. P-wave profiles acquired in southwestern Illinois and western Kentucky (USA) detect faulting of deep, Paleozoic bedrock and Cretaceous reflectors while coincident SH-wave surveys show that this deformation propagates higher into overlying Tertiary and Quaternary strata. Forward modeling of micro-gravity data acquired along one of the seismic profiles further supports an interpretation of faulting of bedrock and Cretaceous strata. The integration of the two seismic and the micro-gravity methods therefore increases the scope for investigating the relation between the older and younger deformation in an area of critical seismic hazard. ?? 2006 Elsevier B.V. All rights reserved.

Wave Structures in Thermospheric Density from Satellite Electrostatic Triaxial Accelerometer Measurements.

DTIC Science & Technology

1987-06-04

Testud , J. (1970) Gravity waves generated diring magnetic substorms, .1. Atmos. Terr. Phys., 32:1793. .6 t9, "-€ according to their horizontal...auroral oval during polar substorms, J. Geophys. Res., 74:5721. 7. Testud , J. P., Amayenc, P., and Blanc, M. (1975) Middle and low latitude effects of...1730. 13. Bertin, F.J., Testud , J., Kersley, L., and Rees, P. R. (1978) The meteorological jet stream as a source of medium scale gravity waves in

A case study of A mesoscale gravity wave in the MLT region using simultaneous multi-instruments in Beijing

NASA Astrophysics Data System (ADS)

Jia, Mingjiao; Xue, Xianghui; Dou, Xiankang; Tang, Yihuan; Yu, Chao; Wu, Jianfei; Xu, Jiyao; Yang, Guotao; Ning, Baiqi; Hoffmann, Lars

2016-03-01

In this work, we used observational data from an all-sky airglow imager at Xinglong (40.2 °N, 117.4 °E), a sodium lidar at Yanqing (40.4 °N, 116.0 °E) and a meteor radar at Shisanling (40.3 °N, 116.2 °E) to study the propagation of a mesoscale gravity wave. During the night of March 1, 2011, the imager identified a mesoscale gravity wave structure in the OH airglow that had a wave period of 2 hours, propagated along an azimuthal direction (clockwise) with an angle of 163°, a phase speed of 73 m/s, and a horizontal wavelength of 566 km. Simultaneous measurements provided by the sodium lidar also showed a perturbation in the sodium layer with a 2-hour period. Based on the SABER/TIMED and radar data, we estimated that the momentum flux and the energy flux of the gravity wave were approximately 0.59 m2/s2 and 0.22 mW/m2, respectively. Ray-tracing analysis showed that the gravity wave was likely generated in the center of Lake Baikal owing to the existence of a jet- front system in the upper troposphere at that time.

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

An integrated geophysical study of north African and Mediterranean lithospheric structure

NASA Astrophysics Data System (ADS)

Dial, Paul Joseph

1998-07-01

This dissertation utilizes gravity and seismic waveform modeling techniques to: (1) determine models of lithospheric structure across northern African through gravity modeling and (2) determine lithospheric and crustal structure and seismic wave propagation characteristics across northern Africa and the Mediterranean region. The purpose of the gravity investigation was to construct models of lithospheric structure across northern Africa through the analysis of gravity data constrained by previous geological and geophysical studies. Three lithospheric models were constructed from Bouguer gravity data using computer modeling, and the gravity data was wavelength-filtered to investigate the relative depth and extent of the structures associated with the major anomalies. In the Atlas Mountains area, the resulting earth models showed slightly greater crustal thickness than those of previous studies if a low density mantle region is not included in the models. However, if a low density mantle region (density = 3.25 g/cm3) was included beneath the Atlas, the earth models showed little crustal thickening (38 km), in accord with previous seismic studies. The second portion of the research consisted of seismic waveform modeling of regional and teleseismic events to determine crustal and lithospheric structure across northern Africa and the Mediterranean. A total of 174 seismograms (145 at regional distances (200--1400 km) and 29 with epicentral distances exceeding 1900 km) were modeled using 1-D velocity models and a reflectivity code. At regional distances from four stations surrounding the western Mediterranean basin (MAL, TOL, PTO and AQU) and one station near the Red Sea (HLW), 1-D velocity models can satisfactorily model the relative amplitudes of both the Pnl and surface wave portions of the seismograms. Modeling of propagation paths greater than 1900 km was also conducted across northern Africa and the Mediterranean. The results indicate that the S-wave velocity model of Corchete et al. (1995) is more appropriate for the Iberian Peninsula, southwestern Mediterranean basin and northwest African coast than the other models tested. This model was better able to predict both the timing and amplitudes of the observed Sn and surface wave components on the observed seismograms. (Abstract shortened by UMI.)

Velocity Structure of the Iran Region Using Seismic and Gravity Observations

NASA Astrophysics Data System (ADS)

Syracuse, E. M.; Maceira, M.; Phillips, W. S.; Begnaud, M. L.; Nippress, S. E. J.; Bergman, E.; Zhang, H.

2015-12-01

We present a 3D Vp and Vs model of Iran generated using a joint inversion of body wave travel times, Rayleigh wave dispersion curves, and high-wavenumber filtered Bouguer gravity observations. Our work has two main goals: 1) To better understand the tectonics of a prominent example of continental collision, and 2) To assess the improvements in earthquake location possible as a result of joint inversion. The body wave dataset is mainly derived from previous work on location calibration and includes the first-arrival P and S phases of 2500 earthquakes whose initial locations qualify as GT25 or better. The surface wave dataset consists of Rayleigh wave group velocity measurements for regional earthquakes, which are inverted for a suite of period-dependent Rayleigh wave velocity maps prior to inclusion in the joint inversion for body wave velocities. We use gravity anomalies derived from the global gravity model EGM2008. To avoid mapping broad, possibly dynamic features in the gravity field intovariations in density and body wave velocity, we apply a high-pass wavenumber filter to the gravity measurements. We use a simple, approximate relationship between density and velocity so that the three datasets may be combined in a single inversion. The final optimized 3D Vp and Vs model allows us to explore how multi-parameter tomography addresses crustal heterogeneities in areas of limited coverage and improves travel time predictions. We compare earthquake locations from our models to independent locations obtained from InSAR analysis to assess the improvement in locations derived in a joint-inversion model in comparison to those derived in a more traditional body-wave-only velocity model.

Dynamics of Nearshore Sand Bars and Infra-gravity Waves: The Optimal Theory Point of View

NASA Astrophysics Data System (ADS)

Bouchette, F.; Mohammadi, B.

2016-12-01

It is well known that the dynamics of near-shore sand bars are partly controlled by the features (location of nodes, amplitude, length, period) of the so-called infra-gravity waves. Reciprocally, changes in the location, size and shape of near-shore sand bars can control wave/wave interactions which in their turn alter the infra-gravity content of the near-shore wave energy spectrum. The coupling infra-gravity / near-shore bar is thus definitely two ways. Regarding numerical modelling, several approaches have already been considered to analyze such coupled dynamics. Most of them are based on the following strategy: 1) define an energy spectrum including infra-gravity, 2) tentatively compute the radiation stresses driven by this energy spectrum, 3) compute sediment transport and changes in the seabottom elevation including sand bars, 4) loop on the computation of infra-gravity taking into account the morphological changes. In this work, we consider an alternative approach named Nearshore Optimal Theory, which is a kind of breakdown point of view for the modeling of near-shore hydro-morphodynamics and wave/ wave/ seabottom interactions. Optimal theory applied to near-shore hydro-morphodynamics arose with the design of solid coastal defense structures by shape optimization methods, and is being now extended in order to model dynamics of any near-shore system combining waves and sand. The basics are the following: the near-shore system state is through a functional J representative of the energy of the system in some way. This J is computed from a model embedding the physics to be studied only (here hydrodynamics forced by simple infra-gravity). Then the paradigm is to say that the system will evolve so that the energy J tends to minimize. No really matter the complexity of wave propagation nor wave/bottom interactions. As soon as J embeds the physics to be explored, the method does not require a comprehensive modeling. Near-shore Optimal Theory has already given promising results for the generation of near-shore sand bar from scratch and their growth when forced by fair-weather waves. Here, we use it to explore the coupling between a very simple infra-gravity content and the nucleation of near-shore sand-bars. It is shown that even a very poor infra-gravity content strongly improves the generation of sand bars.

Simultaneous, Joint Inversion of Seismic Body Wave Travel Times and Satellite Gravity Data for Three-Dimensional Tomographic Imaging of Western Colombia

NASA Astrophysics Data System (ADS)

Dionicio, V.; Rowe, C. A.; Maceira, M.; Zhang, H.; Londoño, J.

2009-12-01

We report on the three-dimensional seismic structure of western Colombia determined through the use of a new, simultaneous, joint inversion tomography algorithm. Using data recorded by the national Seismological Network of Colombia (RSNC), we have selected 3,609 earthquakes recorded at 33 sensors distributed throughout the country, with additional data from stations in neighboring countries. 20,338 P-wave arrivals and 17,041 S-wave arrivals are used to invert for structure within a region extending approximately 72.5 to 77.5 degrees West and 2 to 7.5 degrees North. Our algorithm is a modification of the Maceira and Ammon joint inversion code, in combination with the Zhang and Thurber TomoDD (double-difference tomography) program, with a fast LSQR solver operating on the gridded values jointly. The inversion uses gravity anomalies obtained during the GRACE2 satellite mission, and solves using these values with the seismic travel-times through application of an empirical relationship first proposed by Harkrider, mapping densities to Vp and Vs within earth materials. In previous work, Maceira and Ammon demonstrated that incorporation of gravity data predicts shear wave velocities more accurately than the inversion of surface waves alone, particularly in regions where the crust exhibits abrupt and significant lateral variations in lithology, such as the Tarim Basin. The significant complexity of crustal structure in Colombia, due to its active tectonic environment, makes it a good candidate for the application with gravity and body waves. We present the results of this joint inversion and compare it to results obtained using travel times alone

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.

3D Structure of Iran and Surrounding Areas From The Simultaneous Inversion of Complementary Geophysical Observations

NASA Astrophysics Data System (ADS)

Ammon, C. J.; Maceira, M.; Cleveland, M.

2010-12-01

We present a three-dimensional seismic-structure model of the Arabian-Eurasian collision zone obtained via simultaneous, joint inversion of surface-wave dispersion measurements, teleseismic P-wave receiver functions, and gravity observations. We use a simple, approximate relationship between density and seismic velocities so that the three data sets may be combined in a single inversion. The sensitivity of the different data sets are well known: surface waves provide information on the smooth variations in elastic properties, receiver functions provide information on abrupt velocity contrasts, and gravity measurements provide information on broad-wavenumber shallow density variations and long-wavenumber components of deeper density structures. The combination of the data provides improved resolution of shallow-structure variations, which in turn help produce the smooth features at depth with less contamination from the strong heterogeneity often observed in the upper crust. We also explore geologically based smoothness constraints to help resolve sharp features in the underlying shallow 3D structure. Our focus is on the region surrounding Iran from east Turkey and Iraq in the west, to Pakistan and Afghanistan in the east. We use Bouguer gravity anomalies derived from the global gravity model extracted from the GRACE satellite mission. Surface-wave dispersion velocities in the period range between 7 and 150 s are taken from previously published tomographic maps for the region. Preliminary results show expected strong variations in the Caspian region as well as the deep sediment regions of the Persian Gulf. Regions constrained with receiver-function information generally show sharper crust-mantle boundary structure than that obtained by inversion of the surface waves alone (with thin layers and smoothing constraints). Final results of the simultaneous inversion will help us to better understand one of the most prominent examples of continental collision. Such models also provide an important starting model for time-consuming and fully 3D inversions.

Initial Results of the Spread F Experiment (SpreadFEx): Overview and Evidence of Possible Gravity Wave Excitation of Equatorial Plasma Bubbles

NASA Astrophysics Data System (ADS)

Fritts, D. C.

2007-05-01

The Spread F Experiment (SpreadFEx) was performed in Brazil by Brazilian and U.S. researchers during two ~20- day periods extending from September to November 2005. We employed extensive ground-based and space- based observations of gravity waves, plasma structures, electron densities, and mean atmospheric and ionospheric conditions using airglow, digisonde, VHF and meteor radar, balloon, GPS and satellite instrumentation at multiple sites in Brazil and with GUVI aboard the TIMED satellite. These measurements focused on deep convection, gravity waves, and plasma bubble structures. This comprehensive data set has provided the first promising indications of the specific roles of gravity waves arising from deep convection and other sources in contributing to the seeding of equatorial spread F and plasma bubbles extending to high altitudes. This talk will summarize the campaign results related to possible neutral atmosphere seeding of spread F and plasma bubbles during these observations. Specifically, our measurements have revealed significant neutral density (and related wind and temperature) perturbations extending from ~80 km well into the thermosphere and ionosphere. Many of these appear to arise from deep convection over the Amazon basin. Others occurring at larger scales under magnetically-disturbed conditions may have auroral or other higher-latitude sources. Both appear to lead, on occasion, to sufficiently large perturbations of the bottomside F layer to trigger plasma bubbles extending to much higher altitudes thereafter. Upon completion of our analyses, we believe that these observations will yield the first persuasive evidence of the role of neutral atmosphere gravity waves in the seeding of equatorial plasma bubbles.

First tsunami gravity wave detection in ionospheric radio occultation data

DOE PAGES

Coïsson, Pierdavide; Lognonné, Philippe; Walwer, Damian; ...

2015-05-09

After the 11 March 2011 earthquake and tsunami off the coast of Tohoku, the ionospheric signature of the displacements induced in the overlying atmosphere has been observed by ground stations in various regions of the Pacific Ocean. We analyze here the data of radio occultation satellites, detecting the tsunami-driven gravity wave for the first time using a fully space-based ionospheric observation system. One satellite of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) recorded an occultation in the region above the tsunami 2.5 h after the earthquake. The ionosphere was sounded from top to bottom, thus providing themore » vertical structure of the gravity wave excited by the tsunami propagation, observed as oscillations of the ionospheric Total Electron Content (TEC). The observed vertical wavelength was about 50 km, with maximum amplitude exceeding 1 total electron content unit when the occultation reached 200 km height. We compared the observations with synthetic data obtained by summation of the tsunami-coupled gravity normal modes of the Earth/Ocean/atmosphere system, which models the associated motion of the ionosphere plasma. These results provide experimental constraints on the attenuation of the gravity wave with altitude due to atmosphere viscosity, improving the understanding of the propagation of tsunami-driven gravity waves in the upper atmosphere. They demonstrate that the amplitude of the tsunami can be estimated to within 20% by the recorded ionospheric data.« less

14 CFR 29.563 - Structural ditching provisions.

Code of Federal Regulations, 2011 CFR

2011-01-01

... speed landing conditions. The rotorcraft must initially contact the most critical wave for reasonably... the mean water surface. Rotor lift may be used to act through the center of gravity throughout the..., unsymmetrical rotorcraft loading, water wave action, rotorcraft inertia, and probable structural damage and...

14 CFR 27.563 - Structural ditching provisions.

Code of Federal Regulations, 2014 CFR

2014-01-01

... speed landing conditions. The rotorcraft must initially contact the most critical wave for reasonably... the mean water surface. Rotor lift may be used to act through the center of gravity throughout the..., unsymmetrical rotorcraft loading, water wave action, rotorcraft inertia, and probable structural damage and...

14 CFR 27.563 - Structural ditching provisions.

Code of Federal Regulations, 2013 CFR

2013-01-01

... speed landing conditions. The rotorcraft must initially contact the most critical wave for reasonably... the mean water surface. Rotor lift may be used to act through the center of gravity throughout the..., unsymmetrical rotorcraft loading, water wave action, rotorcraft inertia, and probable structural damage and...

14 CFR 27.563 - Structural ditching provisions.

Code of Federal Regulations, 2011 CFR

2011-01-01

... speed landing conditions. The rotorcraft must initially contact the most critical wave for reasonably... the mean water surface. Rotor lift may be used to act through the center of gravity throughout the..., unsymmetrical rotorcraft loading, water wave action, rotorcraft inertia, and probable structural damage and...

14 CFR 27.563 - Structural ditching provisions.

Code of Federal Regulations, 2010 CFR

2010-01-01

... speed landing conditions. The rotorcraft must initially contact the most critical wave for reasonably... the mean water surface. Rotor lift may be used to act through the center of gravity throughout the..., unsymmetrical rotorcraft loading, water wave action, rotorcraft inertia, and probable structural damage and...

14 CFR 29.563 - Structural ditching provisions.

Code of Federal Regulations, 2012 CFR

2012-01-01

... speed landing conditions. The rotorcraft must initially contact the most critical wave for reasonably... the mean water surface. Rotor lift may be used to act through the center of gravity throughout the..., unsymmetrical rotorcraft loading, water wave action, rotorcraft inertia, and probable structural damage and...

14 CFR 29.563 - Structural ditching provisions.

Code of Federal Regulations, 2010 CFR

2010-01-01

... speed landing conditions. The rotorcraft must initially contact the most critical wave for reasonably... the mean water surface. Rotor lift may be used to act through the center of gravity throughout the..., unsymmetrical rotorcraft loading, water wave action, rotorcraft inertia, and probable structural damage and...

14 CFR 29.563 - Structural ditching provisions.

Code of Federal Regulations, 2014 CFR

2014-01-01

... speed landing conditions. The rotorcraft must initially contact the most critical wave for reasonably... the mean water surface. Rotor lift may be used to act through the center of gravity throughout the..., unsymmetrical rotorcraft loading, water wave action, rotorcraft inertia, and probable structural damage and...

14 CFR 29.563 - Structural ditching provisions.

Code of Federal Regulations, 2013 CFR

2013-01-01

... speed landing conditions. The rotorcraft must initially contact the most critical wave for reasonably... the mean water surface. Rotor lift may be used to act through the center of gravity throughout the..., unsymmetrical rotorcraft loading, water wave action, rotorcraft inertia, and probable structural damage and...

14 CFR 27.563 - Structural ditching provisions.

Code of Federal Regulations, 2012 CFR

2012-01-01

... speed landing conditions. The rotorcraft must initially contact the most critical wave for reasonably... the mean water surface. Rotor lift may be used to act through the center of gravity throughout the..., unsymmetrical rotorcraft loading, water wave action, rotorcraft inertia, and probable structural damage and...

Gravity Waves in the Southern Hemisphere Extratropical Winter in the 7-km GEOS-5 Nature Run

NASA Astrophysics Data System (ADS)

Holt, L. A.; Alexander, M. J.; Coy, L.; Putman, W.; Molod, A.; Pawson, S.

2016-12-01

This study investigates winter Southern Hemisphere extratropical gravity waves and their sources in a 7-km horizontal resolution global climate simulation, the GEOS-5 Nature Run (NR). Gravity waves are evaluated by comparing brightness temperature anomalies to those from the Atmospheric Infrared Sounder (AIRS). Gravity wave amplitudes, wavelengths, and propagation directions are also computed in the NR and AIRS. The NR shows good agreement with AIRS in terms of spatial patterns of gravity wave activity and propagation directions, but the NR amplitudes are smaller by about a factor of 5 and the wavelengths are about a factor of 2 longer than in AIRS. In addition to evaluating gravity wave characteristics, gravity wave sources in the NR are also investigated by relating diagnostics of tropospheric sources of gravity waves, such as precipitation, frontogenesis, and potential vorticity anomalies to absolute gravity wave momentum fluxes in the lower stratosphere. Strong precipitation events are the most strongly correlated with absolute momentum flux, supporting previous studies highlighting the importance of moist processes in the generation of Southern Hemisphere extratropical gravity waves. Additionally, gravity wave absolute momentum fluxes over land are compared to those over ocean, and the contribution of orographic and nonorographic gravity waves to the total absolute momentum flux is examined.

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.

The Influence of Surface Gravity Waves on Marine Current Turbine Performance

NASA Astrophysics Data System (ADS)

Lust, E.; Luznik, L.; Flack, K. A.; Walker, J.; Van Benthem, M.

2013-12-01

Surface gravity waves can significantly impact operating conditions for a marine current turbine, imparting unsteady velocities several orders of magnitude larger than the ambient turbulence. The influence of surface waves on the performance characteristics of a two-bladed horizontal axis marine current turbine was investigated experimentally in a large towing tank facility at the United States Naval Academy. The turbine model had a 0.8 m diameter (D) rotor with a NACA 63-618 cross section, which is Reynolds number independent with respect to lift coefficient in the operating range of Rec ≈ 4 x 105. The torque, thrust and rotational speed were measured at a range of tip speed ratios (TSR) from 5 < TSR < 11. Tests were performed at two rotor depths (1.3D and 2.25D) with and without waves. The average turbine performance characteristics were largely unchanged by depth or the presence of waves. However, tests with waves indicate large variations in thrust, rotational speed, and torque occurred with the passage of the wave. These results demonstrate the impact of surface gravity waves on power production and structural loading and suggest that turbines should be positioned vertically within the water column at a depth which maximizes power output while minimizing material fatigue. Keywords-- marine current turbine, tidal turbine, towing-tank experiments, surface gravity waves, fatigue loading, phase averaging

Stability characteristics of the mesopause region above the Andes

NASA Astrophysics Data System (ADS)

Yang, F.; Liu, A. Z.

2017-12-01

The structure and seasonal variations of static and dynamic (shear) instabilities in the upper atmosphere (80 to 110 km) are examined using 3-year high-resolution wind and temperature data obtained with the Na Lidar at Andes Lidar Observatory (30S,71W). The stabilities are primarily determined by background temperature and wind, but strongly affected by tidal and gravity wave variations. Gravity waves perturb the atmosphere, causing intermittent unstable layers. The stabilities are characterized by their vertical and seasonal distributions of probability of instabilities. As have been found in previous studies, there is a correlation between high static stability (large N2) and strong vertical wind shear. The mechanism for this relationship is investigated in the context of gravity waves interacting with varying background.

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

Gravity waves in Titan's atmosphere

NASA Technical Reports Server (NTRS)

Friedson, A. James

1994-01-01

Scintillations (high frequency variations) observed in the radio signal during the occultation of Voyager 1 by Titan (Hinson and Tyler, 1983) provide information concerning neutral atmospheric density fluctuations on scales on hundreds of meters to a few kilometers. Those seen at altitudes higher than 25 km above the surface were interpreted by Hinson and Tyler as being caused by linear, freely propagating (energy-conserving) gravity waves, but this interpretation was found to be inconsistent with the scintillation data below the 25-km altitude level. Here an attempt is made to interpret the entire scintillation profile between the surface and the 90-km altitude level in terms of gravity waves generated at the surface. Numerical calculations of the density fluctuations caused by two-dimensional, nonhydrostatic, finite-amplitude gravity waves propagating vertically through Titan's atmosphere are performed to produce synthetic scintillation profiles for comparison with the observations. The numerical model accurately treats the effects of wave transience, nonlinearity, and breakdown due to convective instability in the overturned part of the wave. The high-altitude scintillation data were accurately recovered with a freely propagating wave solution, confirming the analytic model of Hinson and Tyler. It is found that the low-altitude scintillation data can be fit by a model where a component of the gravity waves becomes convectively unstable and breaks near the 15 km level. The large-scale structure of the observed scintillation profile in the entire altitude range between 5 and 85 km can be simulated by a model where the freely propagating and breaking waves are forced at the surface simultaneously. Further analysis of the Voyager 1 Titan low-altitude scintillation data, using inversion theory appropriate for strong scattering, could potentially remove some of the ambiguities remaining in this analysis and allow a better determination of the strength and source of the waves.

Performance evaluation of low-cost airglow cameras for mesospheric gravity wave measurements

NASA Astrophysics Data System (ADS)

Suzuki, S.; Shiokawa, K.

2016-12-01

Atmospheric gravity waves significantly contribute to the wind/thermal balances in the mesosphere and lower thermosphere (MLT) through their vertical transport of horizontal momentum. It has been reported that the gravity wave momentum flux preferentially associated with the scale of the waves; the momentum fluxes of the waves with a horizontal scale of 10-100 km are particularly significant. Airglow imaging is a useful technique to observe two-dimensional structure of small-scale (<100 km) gravity waves in the MLT region and has been used to investigate global behaviour of the waves. Recent studies with simultaneous/multiple airglow cameras have derived spatial extent of the MLT waves. Such network imaging observations are advantageous to ever better understanding of coupling between the lower and upper atmosphere via gravity waves. In this study, we newly developed low-cost airglow cameras to enlarge the airglow imaging network. Each of the cameras has a fish-eye lens with a 185-deg field-of-view and equipped with a CCD video camera (WATEC WAT-910HX) ; the camera is small (W35.5 x H36.0 x D63.5 mm) and inexpensive, much more than the airglow camera used for the existing ground-based network (Optical Mesosphere Thermosphere Imagers (OMTI) operated by Solar-Terrestrial Environmental Laboratory, Nagoya University), and has a CCD sensor with 768 x 494 pixels that is highly sensitive enough to detect the mesospheric OH airglow emission perturbations. In this presentation, we will report some results of performance evaluation of this camera made at Shigaraki (35-deg N, 136-deg E), Japan, where is one of the OMTI station. By summing 15-images (i.e., 1-min composition of the images) we recognised clear gravity wave patterns in the images with comparable quality to the OMTI's image. Outreach and educational activities based on this research will be also reported.

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.

Ground testing of bioconvective variables such as morphological characterizations and mechanisms which regulate macroscopic patterns

NASA Technical Reports Server (NTRS)

Johnson, Adriel D.

1992-01-01

Conditions simulating low- and high-gravity, reveal changes in macroscopic pattern formation in selected microorganisms, but whether these structures are gravity dependent is not clear. Two theories have been identified in the fluid dynamics community which support macroscopic pattern formation. The first one is gravity dependent (fluid density models) where small concentrated regions of organisms sink unstably, and the second is gravity independent (wave reinforcement theory) where organisms align their movements in concert, such that either their swimming strokes beat in phase or their vortices entrain neighbors to follow parallel paths. Studies have shown that macroscopic pattern formation is consistent with the fluid density models for protozoa and algae and wave reinforcement hypothesis for caprine spermatozoa.

Small-scale structure and turbulence observed in MAP/WINE)

NASA Technical Reports Server (NTRS)

Blix, T. A.

1989-01-01

During MAP/WINE small scale structure and turbulence in the mesosphere and lower thermosphere was studied in situ by rocket-borne instruments as well as from the ground by remote sensing techniques. The eight salvoes launched during the campaign resulted in a wealth of information on the dynamical structure of these regions. The experimental results are reviewed and their interpretation is discussed in terms of gravity waves and turbulence. It is shown that eddy diffusion coefficients and turbulent energy dissipation rates may be derived from the in situ measurements in a consistent manner. The observations are also shown to be consistent with the hypothesis that turbulence can be created by a process of gravity wave saturation.

Gravity

NASA Astrophysics Data System (ADS)

Poisson, Eric; Will, Clifford M.

2014-05-01

Preface; 1. Foundations of Newtonian gravity; 2. Structure of self-gravitating bodies; 3. Newtonian orbital dynamics; 4. Minkowski spacetime; 5. Curved spacetime; 6. Post-Minkowskian theory: formulation; 7. Post-Minkowskian theory: implementation; 8. Post-Newtonian theory: fundamentals; 9. Post-Newtonian theory: system of isolated bodies; 10. Post-Newtonian celestial mechanics, astrometry and navigation; 11. Gravitational waves; 12. Radiative losses and radiation reaction; 13. Alternative theories of gravity; References; Index.

Using ion flows parallel and perpendicular to gravity to modify dust acoustic waves

NASA Astrophysics Data System (ADS)

Thomas, E.; Fisher, R.

2008-11-01

Recent studies of dust acoustic waves have shown that the dust kinetic temperature can play an important role in determining the resulting dispersion relation [M. Rosenberg, et al., Phys. Plasmas, 15, 073701 (2008)]. In these studies, it is believed that ion flows play a dominant role in determining both the kinetic temperature of the charged microparticles as well as providing the source of energy for triggering the waves. In this presentation, results will be presented on the effects of ion flow on spatial structure and velocity distribution of dust acoustic waves. Here, the waves will be formed in dusty plasmas consisting of 3 ± 1 micron diameter silica microspheres. Two separate electrodes will be used to modify the ion flow in the plasma -- one parallel to the direction of gravity and one perpendicular to the direction of gravity. Particle image velocimetry (PIV) techniques will be used to observe the particles and to measure their velocity distributions.

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.

Momentum flux measurements: Techniques and needs, part 4.5A

NASA Technical Reports Server (NTRS)

Fritts, D. C.

1984-01-01

The vertical flux of horizontal momentum by internal gravity waves is now recognized to play a significant role in the large-scale circulation and thermal structure of the middle atmosphere. This is because a divergence of momentum flux due to wave dissipation results in an acceleration of the local mean flow towards the phase speed of the gravity wave. Such mean flow acceleration are required to offset the large zonal accelerations driven by Coriolis torques acting on the diabatic meridional circulation. Techniques and observations regarding the momentum flux distribution in the middle atmosphere are discussed.

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

Dynamics of the middle atmosphere as observed by the ARISE project

NASA Astrophysics Data System (ADS)

Blanc, Elisabeth

2015-04-01

The atmosphere is a complex system submitted to disturbances in a wide range of scales, including high frequency sources as volcanoes, thunderstorms, tornadoes and at larger scales, gravity waves from deep convection or wind over mountains, atmospheric tides and planetary waves. These waves affect the different atmospheric layers submitted to different temperature and wind systems which strongly control the general atmospheric circulation. The full description of gravity and planetary waves constitutes a challenge for the development of future models of atmosphere and climate. The objective of this paper is to present a review of recent advances obtained in this topic, especially in the framework of the ARISE (Atmospheric dynamics Research InfraStructure in Europe) project

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.

Some characteristics of the three-dimensional structure of Santa Ana winds

Treesearch

Michael A. Fosberg; Clyde A. O' Dell; Mark J. Schroeder

1966-01-01

The three-dimensional structure of the Santa Ana was investigated in two case studies. Incorporated into a descriptive model of the Santa Ana were: (a) a bispectral gravity wave flow with a lee trough, produced by conservation of potential vorticity having a wave length of the order of 300 km. and short waves 6 to 10 km. long; (b) intensity of the foehn related to the...

Transition wave in the collapse of the San Saba bridge

NASA Astrophysics Data System (ADS)

Brun, Michele; Giaccu, Gian Felice; Movchan, Alexander; Slepyan, Leonid

2014-09-01

A domino wave is a well-known illustration of a transition wave, which appears to reach a stable regime of propagation. Nature also provides spectacular cases of gravity driven transition waves at large scale, observed in snow avalanches and landslides. On a different scale, the micro-structure level interaction between different constituents of the macro-system may influence critical regimes leading to instabilities in avalanche-like flow systems. Most transition waves observed in systems such as bulletproof vests, racing helmets under impact, shock-wave driven fracture in solids, are transient. For some structured waveguides a transition wave may stabilize to achieve a steady regime. Here we show that the failure of a long bridge is also driven by a transition wave that may allow for steady-state regimes. The recent observation of a failure of the San Saba Bridge in Texas provides experimental evidence supporting an elegant theory based on the notion of transition failure wave. No one would think of an analogy between a snow avalanche and a collapsing bridge. Despite an apparent controversy of such a comparison, these two phenomena can both be described in the framework of a model of the dynamic gravity driven transition fault.

Forced Gravity Waves and the Tropospheric Response to Convection

NASA Astrophysics Data System (ADS)

Halliday, O. J.; Griffiths, S. D.; Parker, D. J.; Stirling, A.

2017-12-01

It has been known for some time that gravity waves facilitate atmospheric adjustment to convective heating. Further, convectively forced gravity waves condition the neighboring atmosphere for the initiation and / or suppression of convection. Despite this, the radiation of gravity waves in macro-scale models (which are typically forced at the grid-scale, by existing parameterization schemes) is not well understood. We present here theoretical and numerical work directed toward improving our understanding of convectively forced gravity wave effects at the mesoscale. Using the linear hydrostatic equations of motion for an incompressible (but non-Boussinesq) fluid with vertically varying buoyancy frequency, we find a radiating solution to prescribed sensible heating. We then interrogate the spatial and temporal sensitivity of the vertical velocity and potential temperature response to different heating functions, considering the remote and near-field forced response both to steady and pulsed heating. We find that the meso-scale tropospheric response to convection is significantly dependent on the upward radiation characteristics of the gravity waves, which are in turn dependent upon the temporal and spatial structure of the source, and stratification of the domain. Moving from a trapped to upwardly-radiating solution there is a 50% reduction in tropospherically averaged vertical velocity, but significant perturbations persist for up to 4 hours in the far-field. We find the tropospheric adjustment to be sensitive to the horizontal length scale which characterizes the heating, observing a 20% reduction in vertical velocity when comparing the response from a 10 km to a 100 km heat source. We assess the implications for parameterization of convection in coarse-grained models in the light of these findings. We show that an idealized `full-physics' nonlinear simulation of deep convection in the UK Met Office Unified Model is qualitatively described by the linear solution: departures are quantified and explored.

A ground-base Radar network to access the 3D structure of MLT winds

NASA Astrophysics Data System (ADS)

Stober, G.; Chau, J. L.; Wilhelm, S.; Jacobi, C.

2016-12-01

The mesosphere/lower thermosphere (MLT) is a highly variable atmospheric region driven by wave dynamics at various scales including planetary waves, tides and gravity waves. Some of these propagate through the MLT into the thermosphere/ionosphere carrying energy and momentum from the middle atmosphere into the upper atmosphere. To improve our understanding of the wave energetics and momentum transfer during their dissipation it is essential to characterize their space time properties. During the last two years we developed a new experimental approach to access the horizontal structure of wind fields at the MLT using a meteor radar network in Germany, which we called MMARIA - Multi-static Multi-frequency Agile Radar for Investigation of the Atmosphere. The network combines classical backscatter meteor radars and passive forward scatter radio links. We present our preliminary results using up to 7 different active and passive radio links to obtain horizontally resolved wind fields applying a statistical inverse method. The wind fields are retrieved with 15-30 minutes temporal resolution on a grid with 30x30 km horizontal spacing. Depending on the number of observed meteors, we are able to apply the wind field inversion at heights between 84-94 km. The horizontally resolved wind fields provide insights of the typical horizontal gravity wave length and the energy cascade from large scales to small scales. We present first power spectra indicating the transition from the synoptic wave scale to the gravity wave scale.

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.

Observations of planetary mixed Rossby-gravity waves in the upper stratosphere

NASA Technical Reports Server (NTRS)

Randel, William J.; Boville, Byron A.; Gille, John C.

1990-01-01

Observational evidence is presented for planetary scale (zonal wave number 1-2) mixed Rossby-gravity (MRG) waves in the equatorial upper stratosphere (35-50 km). These waves are detected in LIMS measurements as coherently propagating temperature maxima of amplitude 0.1-0.3 K, which are antisymmetric (out of phase) about the equator, centered near 10-15 deg north and south latitude. These features have vertical wavelengths of order 10-15 km, periods near 2-3 days, and zonal phase velocities close to 200 m/s. Both eastward and westward propagating waves are found, and the observed vertical wavelengths and meridional structures are in good agreement with the MRG dispersion relation. Theoretical estimates of the zonal accelerations attributable to these waves suggest they do not contribute substantially to the zonal momentum balance in the middle atmosphere.

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.

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.

Crustal and mantle structure of the greater Jan Mayen-East Greenland region (NE Atlantic) from combined 3D structural, S-wave velocity, and gravity modeling

NASA Astrophysics Data System (ADS)

Tan, P.; Sippel, J.; Scheck-Wenderoth, M.; Meeßen, C.; Breivik, A. J.

2016-12-01

The study area is located between the Jan Mayen Ridge and the east coast of Greenland. It has a complex geological setting with the ultraslow Kolbeinsey and Mohn's spreading ridges, the anomalously shallow Eggvin Bank, the Jan Mayen Microcontinent (JMMC), and the tectonically active West Jan Mayen Fracture Zone (WJMFZ). In this study, we present the results of forward 3D structural, S-wave velocity, and gravity modeling which provide new insights into the deep crust and mantle structure and the wide-ranging influence of the Iceland Plume. The crustal parts of the presented 3D structural model are mainly constrained by local seismic refraction and reflection data. Accordingly, greatest crustal thicknesses (24 km) are observed on the northern boundary of the JMMC, while the average crustal thickness is 8.5 km and 4 km in the Kolbeinsey and Mohn's Ridge, respectively. The densities of the crustal parts are from previous studies. Additionally, the mantle density is derived from S-wave velocity data (between 50 and 250 km depth), while densities of the lithospheric mantle between the Moho and 50 km are calculated assuming isostatic equilibrium at 250 km depth. This is used as a starting density model which is further developed to obtain a reasonable fit between the calculated and measured (free-air) gravity fields. The observed S-wave tomographic data and the gravity modeling prove that the Iceland plume anomaly in the asthenosphere affects the lithospheric thickness and temperature, from the strongly influenced Middle Kolbeinsey Ridge, to the less affected North Kolbeinsey Ridge (Eggvin Bank), and to the little impacted Mohn's Ridge. Thus, the age-temperature relations of the different mid-ocean ridges of the study area are perturbed to different degrees controlled by the distance from the Iceland Plume. Furthermore, we find that the upper 50 km of lithospheric mantle are thermally affected by the plume only in the southwestern parts of the study area.

The Effects of Gravity on Combustion and Structure Formation During Combustion Synthesis in Gasless Systems

NASA Technical Reports Server (NTRS)

Varma, Arvind; Mukasyan, Alexander; Pelekh, Aleksey

1997-01-01

There have been relatively few publications examining the role of gravity during combustion synthesis (CS), mostly involving thermite systems. The main goal of this research was to study the influence of gravity on the combustion characteristics of heterogeneous gasless systems. In addition, some aspects of microstructure formation processes which occur during gasless CS were also studied. Four directions for experimental investigation have been explored: (1) the influence of gravity force on the characteristic features of heterogeneous combustion wave propagation (average velocity, instantaneous velocities, shape of combustion front); (2) the combustion of highly porous mixtures (with porosity greater than that for loose powders), which cannot be obtained in normal gravity; (3) the effect of gravity on sample expansion during combustion, in order to produce highly porous materials under microgravity conditions; and (4) the effect of gravity on the structure formation mechanism during the combustion synthesis of poreless composite materials.

The PMC-Turbo Balloon Mission to Study Gravity Waves and Turbulence through High-Resolution Imaging of Polar Mesospheric Clouds

NASA Astrophysics Data System (ADS)

Williams, B. P.; Kjellstrand, B.; Jones, G.; Reimuller, J. D.; Fritts, D. C.; Miller, A.; Geach, C.; Limon, M.; Hanany, S.; Kaifler, B.; Wang, L.; Taylor, M. J.

2017-12-01

PMC-Turbo is a NASA long-duration, high-altitude balloon mission that will deploy 7 high-resolution cameras to image polar mesospheric clouds (PMC) and measure gravity wave breakdown and turbulence. The mission has been enhanced by the addition of the DLR Balloon Lidar Experiment (BOLIDE) and an OH imager from Utah State University. This instrument suite will provide high horizontal and vertical resolution of the wave-modified PMC structure along a several thousand kilometer flight track. We have requested a flight from Kiruna, Sweden to Canada in June 2017 or McMurdo Base, Antarctica in Dec 2017. Three of the PMC camera systems were deployed on an aircraft and two tomographic ground sites for the High Level campaign in Canada in June/July 2017. On several nights the cameras observed PMC's with strong gravity wave breaking signatures. One PMC camera will piggyback on the Super Tiger mission scheduled to be launched in Dec 2017 from McMurdo, so we will obtain PMC images and wave/turbulence data from both the northern and southern hemispheres.

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.

Rayleigh lidar observations of enhanced stratopause temperature over Gadanki (13.5° N, 79.2° E) during major stratospheric warming in 2006

NASA Astrophysics Data System (ADS)

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

2009-01-01

Rayleigh lidar observations of temperature structure and gravity wave activity were carried out at Gadanki (13.5° N, 79.2° E) during January-February 2006. A major stratospheric warming event occurred at high latitude during the end of January and early February. There was a sudden enhancement in the stratopause temperature over Gadanki coinciding with the date of onset of the major stratospheric warming event which occurred at high latitudes. The temperature enhancement persisted even after the end of the high latitude major warming event. During the same time, the UKMO (United Kingdom Meteorological Office) zonal mean temperature showed a similar warming episode at 10° N and cooling episode at 60° N around the region of stratopause. This could be due to ascending (descending) motions at high (low) latitudes above the critical level of planetary waves, where there was no planetary wave flux. The time variation of the gravity wave potential energy computed from the temperature perturbations over Gadanki shows variabilities at planetary wave periods, suggesting a non-linear interaction between gravity waves and planetary waves. The space-time analysis of UKMO temperature data at high and low latitudes shows the presence of similar periodicities of planetary wave of zonal wavenumber 1.

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.

Lutetia: an example of prediction of polyhedra in shapes of small cosmic bodies

NASA Astrophysics Data System (ADS)

Kochemasov, G. G.

2011-10-01

The following prediction based on rules of the wave planetology [1-12] was published before the Rosetta spacecraft imaged asteroid Lutetia [13]. "A 100 km long flattened asteroid 21-Lutetia will be imaged by the "Ros etta' s pacecraft in July 2010. Knowing that heavenly bodies are effectively structurized by warping inertia -gravity waves one might expect that Lutetia will not be an exclusion out of a row of bodies subjected to an action of these waves [1-9]. The elliptical keplerian orbits with periodically changing bodies 'accelerations imply inertia -gravity forces applied to any body notwithstanding its size, mass, density, chemical composition, and physical state. These forces produce inertia-gravity waves having in rotating bodied standing character and four direct ions of propagation (orthogonal and diagonal). Interfering these waves produce in bodies three (five) kinds of tectonic blocks: uprising s trongly and moderately (++, +), subsiding deeply and moderately (--, -), and neutral (0) where + and - are compensated. Lengths and amplitudes of warping waves form the harmonic sequence. The fundamental wave1 (long 2πR) ma kes ubiquitous tectonic dichotomy (two antipodean segments or hemispheres: one risen, another fallen). In small bodies this structurization is expressed in their convexo-concave shape: one hemisphere is bulged, another one pressed in. Bulging hemisphere is extended, pressed in hemisphere contracted. This wave shaping tends to transform a globular body into a tetrahedron - the ess entially dichotomous s imp les t Plato's figure. In this polyhedron always there is an oppos ition of extension (a face) to contraction (a vertex). The firs t overtone wave2 (long πR) ma kes tectonic s ectors , als o ris en and fallen, and regularly disposed on (and in) a globe. This regularity is expressed in an octahedron form. The octahedron (diamond) or its parts are often observed in shapes of small bodies with small gravities. Larger bodies with rather strong gravity tend to smooth polyhedron vertices and edges but a polyhedron structurization is always present inside their globes a nd is shown in their tectonics, geomorphology and geophysical fields. The shorter warping waves are also present but because of their comparatively small lengths and amplitudes they are not so important in distorting globes. The presented main harmonic row is complicated by superimposed individual waves lengths of which are inversely proportional to orbital frequencies: higher frequency - smaller wave, and, vice versa, lower frequency - larger wave. In the main asteroid belt the fundamental wave of the ma in s equence and the individual wave (a ls o long 2π R) a re in the s tron gest 1:1 resonance what prohibits an accretion of a real planet because of prevailing debris scattering. Thus, the Lutetia shape can support the main point of the wave planetology - "orbits make s tructures ." [13]. Below are some examples of cosmic polyhedra belonging to small bodies of various classes (asteroids, satellites, comets), s izes and compos itions . Thus , the prediction of Lutetia' s hape (s trengthened by the later Tempel's images ) was bas ed on rathe r representative observations.

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.

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.

An estimate of equatorial wave energy flux at 9- to 90-day periods in the Central Pacific

NASA Technical Reports Server (NTRS)

Eriksen, Charles C.; Richman, James G.

1988-01-01

Deep fluctuations in current along the equator in the Central Pacific are dominated by coherent structures which correspond closely to narrow-band propagating equatorial waves. Currents were measured roughly at 1500 and 3000 m depths at five moorings between 144 and 148 deg W from January 1981 to March 1983, as part of the Pacific Equatorial Ocean Dynamics program. In each frequency band resolved, a single complex empirical orthogonal function accounts for half to three quarters of the observed variance in either zonal or meridional current. Dispersion for equatorial first meridional Rossby and Rossby gravity waves is consistent with the observed vertical-zonal coherence structure. The observations indicate that energy flux is westward and downward in long first meridional mode Rossby waves at periods 45 days and longer, and eastward and downward in short first meridional mode Rossby waves and Rossby-gravity waves at periods 30 days and shorter. A local minimum in energy flux occurs at periods corresponding to a maximum in upper-ocean meridional current energy contributed by tropical instability waves. Total vertical flux across the 9- to 90-day period range is 2.5 kW/m.

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

Peralta, J.; López-Valverde, M. A.; Imamura, T.

This paper is the first of a two-part study devoted to developing tools for a systematic classification of the wide variety of atmospheric waves expected on slowly rotating planets with atmospheric superrotation. Starting with the primitive equations for a cyclostrophic regime, we have deduced the analytical solution for the possible waves, simultaneously including the effect of the metric terms for the centrifugal force and the meridional shear of the background wind. In those cases when the conditions for the method of the multiple scales in height are met, these wave solutions are also valid when vertical shear of the backgroundmore » wind is present. A total of six types of waves have been found and their properties were characterized in terms of the corresponding dispersion relations and wave structures. In this first part, only waves that are direct solutions of the generic dispersion relation are studied—acoustic and inertia-gravity waves. Concerning inertia-gravity waves, we found that in the cases of short horizontal wavelengths, null background wind, or propagation in the equatorial region, only pure gravity waves are possible, while for the limit of large horizontal wavelengths and/or null static stability, the waves are inertial. The correspondence between classical atmospheric approximations and wave filtering has been examined too, and we carried out a classification of the mesoscale waves found in the clouds of Venus at different vertical levels of its atmosphere. Finally, the classification of waves in exoplanets is discussed and we provide a list of possible candidates with cyclostrophic regimes.« less

Midlatitude sporadic-E layers

NASA Technical Reports Server (NTRS)

Miller, K. L.; Smith, L. G.

1976-01-01

The partially transparent echo from midlatitude sporadic E layers was recorded by ionosondes between the blanketing frequency and the maximum frequency. The theory that the midlatitude sporadic E layers are not uniform in the horizontal plane but contain localized regions of high electron density was evaluated using data obtained by incoherent scatter radar and found to provide a satisfactory explanation. The main features of midlatitude sporadic E layers are consistent with the convergence of metallic ions as described by the wind shear theory applied to gravity waves and tides. The interference of gravity waves with other gravity waves and tides can be recognized in the altitudes of occurrence and the structure of the layers. Small scale horizontal irregularities are attributed in some cases to critical level effects and in others to fluid instabilities. The convergence of a meteor trail can, under some circumstances, account for localized enhancement of the electron density in the layer.

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.

Crust and Upper Mantle Structure from Joint Inversion of Body Wave and Gravity Data (Postprint). Annual Report 1

DTIC Science & Technology

2012-05-10

Basin, China , the crust and subduction zone beneath western Colombia, and a thermally active region within Utah in the central United States...Burlacu, R., Rowe, C., and Y. Yang (2009). Joint geophysical imaging of the geothermal sites in the Utah area using seismic body waves, surface waves and

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

Dynamics of the Venus upper atmosphere: Outstanding problems and new constraints expected from Venus Express

NASA Astrophysics Data System (ADS)

Bougher, S. W.; Rafkin, S.; Drossart, P.

2006-11-01

A consistent picture of the dynamics of the Venus upper atmosphere from ˜90 to 200 km has begun to emerge [e.g., Bougher, S.W., Alexander, M.J., Mayr, H.G., 1997. Upper Atmosphere Dynamics: Global Circulation and Gravity Waves. Venus II, CH. 2.4. University of Arizona Press, Tucson, pp. 259-292; Lellouch, E., Clancy, T., Crisp, D., Kliore, A., Titov, D., Bougher, S.W., 1997. Monitoring of Mesospheric Structure and Dynamics. Venus II, CH. 3.1. University of Arizona Press, Tucson, pp. 295-324]. The large-scale circulation of the Venus upper atmosphere (upper mesosphere and thermosphere) can be decomposed into two distinct flow patterns: (1) a relatively stable subsolar-to-antisolar (SS-AS) circulation cell driven by solar heating, and (2) a highly variable retrograde superrotating zonal (RSZ) flow. Wave-like perturbations have also been observed. However, the processes responsible for maintaining (and driving variations in) these SS-AS and RSZ winds are not well understood. Variations in winds are thought to result from gravity wave breaking and subsequent momentum and energy deposition in the upper atmosphere [Alexander, M.J., 1992. A mechanism for the Venus thermospheric superrotation. Geophys. Res. Lett. 19, 2207-2210; Zhang, S., Bougher, S.W., Alexander, M.J., 1996. The impact of gravity waves on the Venus thermosphere and O2 IR nightglow. J. Geophys. Res. 101, 23195-23205]. However, existing data sets are limited in their spatial and temporal coverage, thereby restricting our understanding of these changing circulation patterns. One of the major goals of the Venus Express (VEX) mission is focused upon increasing our understanding of the circulation and dynamical processes of the Venus atmosphere up to the exobase [Titov, D.V., Lellouch, E., Taylor, F.W., 2001. Venus Express: Response to ESA's call for ideas for the re-use of the Mars Express platform. Proposal to European Space Agency, 1-74]. Several VEX instruments are slated to obtain remote measurements (2006-2008) that will complement those obtained earlier by the Pioneer Venus Orbiter (PVO) between 1978 and 1992. These VEX measurements will provide a more comprehensive investigation of the Venus upper atmosphere (90-200 km) structure and dynamics over another period in the solar cycle and for variable lower atmosphere conditions. An expanded climatology of Venus upper atmosphere structure and wind components will be developed. In addition, gravity wave parameters above the cloud tops will be measured (or inferred), and used to constrain gravity wave breaking models. In this manner, the gravity wave breaking mechanism (thought to regulate highly variable RSZ winds) can be tested using Venus general circulation models (GCMs).

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.

Case Study Investigations of Large-Amplitude Inertia-Gravity Wave Environments and Mesoscale Structures

NASA Technical Reports Server (NTRS)

Bosart, Lance F.

2001-01-01

The research effort supported by NASA Grant NAG5-7469, awarded to the University at Albany, State University of New York (UA/SUNY), comprises the following two projects: (1) the observational study of large-amplitude inertia-gravity wave environments over the continental United States; and (2) the definition of opportunities and issues in extratropical cyclone dynamics and related phenomenological studies that may be addressed using high-resolution global datasets produced by the Data Assimilation Office (DAO) at the NASA/Goddard Space Flight Center.

Current Scientific Issues in Large Scale Atmospheric Dynamics

NASA Technical Reports Server (NTRS)

Miller, T. L. (Compiler)

1986-01-01

Topics in large scale atmospheric dynamics are discussed. Aspects of atmospheric blocking, the influence of transient baroclinic eddies on planetary-scale waves, cyclogenesis, the effects of orography on planetary scale flow, small scale frontal structure, and simulations of gravity waves in frontal zones are discussed.

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.

Planetary wave-gravity wave interactions during mesospheric inversion layer events

NASA Astrophysics Data System (ADS)

Ramesh, K.; Sridharan, S.; Raghunath, K.; Vijaya Bhaskara Rao, S.; Bhavani Kumar, Y.

2013-07-01

lidar temperature observations over Gadanki (13.5°N, 79.2°E) show a few mesospheric inversion layer (MIL) events during 20-25 January 2007. The zonal mean removed SABER temperature shows warm anomalies around 50°E and 275°E indicating the presence of planetary wave of zonal wave number 2. The MIL amplitudes in SABER temperature averaged for 10°N-15°N and 70°E-90°E show a clear 2 day wave modulation during 20-28 January 2007. Prior to 20 January 2007, a strong 2day wave (zonal wave number 2) is observed in the height region of 80-90 km and it gets largely suppressed during 20-26 January 2007 as the condition for vertical propagation is not favorable, though it prevails at lower heights. The 10 day mean zonal wind over Tirunelveli (8.7°N, 77.8°E) shows deceleration of eastward winds indicating the westward drag due to wave dissipation. The nightly mean MF radar observed zonal winds show the presence of alternating eastward and westward winds during the period of 20-26 January 2007. The two dimensional spectrum of Rayleigh lidar temperature observations available for the nights of 20, 22, and 24 January 2007 shows the presence of gravity wave activity with periods 18 min, 38 min, 38 min, and vertical wavelengths 6.4 km, 4.0 km, 6.4 km respectively. From the dispersion relation of gravity waves, it is inferred that these waves are internal gravity waves rather than inertia gravity waves with the horizontal phase speeds of ~40 m/s, ~37 m/s, and ~50 m/s respectively. Assuming the gravity waves are eastward propagating waves, they get absorbed only in the eastward local wind fields of the planetary wave thereby causing turbulence and eddy diffusion which can be inferred from the estimation of large drag force due to the breaking of gravity wave leading to the formation of large amplitude inversion events in alternate nights. The present study shows that, the mesospheric temperature inversion is caused mainly due to the gravity wave breaking and the inversion amplitude may get modulated by the interaction between gravity waves and planetary waves. The eddy diffusion associated with gravity wave drag may also cause suppression in the planetary wave activity.

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.

Detection of traveling ionospheric disturbances induced by atmospheric gravity waves using the global positioning system

NASA Technical Reports Server (NTRS)

Bassiri, Sassan; Hajj, George A.

1993-01-01

Natural and man-made events like earthquakes and nuclear explosions launch atmospheric gravity waves (AGW) into the atmosphere. Since the particle density decreases exponentially with height, the gravity waves increase exponentially in amplitude as they propagate toward the upper atmosphere and ionosphere. As atmospheric gravity waves approach the ionospheric heights, the neutral particles carried by gravity waves collide with electrons and ions, setting these particles in motion. This motion of charged particles manifests itself by wave-like fluctuations and disturbances that are known as traveling ionospheric disturbances (TID). The perturbation in the total electron content due to TID's is derived analytically from first principles. Using the tilted dipole magnetic field approximation and a Chapman layer distribution for the electron density, the variations of the total electron content versus the line-of-sight direction are numerically analyzed. The temporal variation associated with the total electron content measurements due to AGW's can be used as a means of detecting characteristics of the gravity waves. As an example, detection of tsunami generated earthquakes from their associated atmospheric gravity waves using the Global Positioning System is simulated.

Can inertia-gravity waves persistently alter the tropopause inversion layer?

NASA Astrophysics Data System (ADS)

Kunkel, Daniel; Hoor, Peter; Wirth, Volkmar

2014-11-01

Previous simulations of baroclinic life cycles have shown, among many other features, the evolution of a tropopause inversion layer (TIL) as well as the spontaneous emission of inertia-gravity waves (IGWs). This study suggests that the latter two are related to each other, i.e., that IGWs may affect the TIL in a persistent manner. The IGWs are emitted along the jet and grow to large amplitudes, leading to the appearance of low-gradient Richardson numbers that indicate Kelvin-Helmholtz instability. Ensuing energy dissipation, local heating, and turbulence may persistently alter the thermodynamical structure of the tropopause region and, therefore, contribute to TIL formation or alter an existing TIL. Moreover, the flow in the region of the IGW favors the occurrence of wave capture, which may enhance the effect of wave breaking.

Middle Atmosphere Dynamics with Gravity Wave Interactions in the Numerical Spectral Model: Tides and Planetary Waves

NASA Technical Reports Server (NTRS)

Mayr, Hans G.; Mengel, J. G.; Chan, K. L.; Huang, F. T.

2010-01-01

As Lindzen (1981) had shown, small-scale gravity waves (GW) produce the observed reversals of the zonal-mean circulation and temperature variations in the upper mesosphere. The waves also play a major role in modulating and amplifying the diurnal tides (DT) (e.g., Waltersheid, 1981; Fritts and Vincent, 1987; Fritts, 1995a). We summarize here the modeling studies with the mechanistic numerical spectral model (NSM) with Doppler spread parameterization for GW (Hines, 1997a, b), which describes in the middle atmosphere: (a) migrating and non-migrating DT, (b) planetary waves (PW), and (c) global-scale inertio gravity waves. Numerical experiments are discussed that illuminate the influence of GW filtering and nonlinear interactions between DT, PW, and zonal mean variations. Keywords: Theoretical modeling, Middle atmosphere dynamics, Gravity wave interactions, Migrating and non-migrating tides, Planetary waves, Global-scale inertio gravity waves.

On the three dimensional structure of stratospheric material transport associated with various types of waves

NASA Astrophysics Data System (ADS)

Kinoshita, T.; Sato, K.

2016-12-01

The Transformed Eulerian-Mean (TEM) equations were derived by Andrews and McIntyre (1976, 1978) and have been widely used to examine wave-mean flow interaction in the meridional cross section. According to previous studies, the Brewer-Dobson circulation in the stratosphere is driven by planetary waves, baroclinic waves, and inertia-gravity waves, and that the meridional circulation from the summer hemisphere to the winter hemisphere in the mesosphere is mainly driven by gravity waves (e.g., Garcia and Boville 1994; Plumb and Semeniuk 2003; Watanabe et al. 2008; Okamoto et al. 2011). However, the TEM equations do not provide the three-dimensional view of the transport, so that the three dimensional TEM equations have been formulated (Hoskins et al. 1983, Trenberth 1986, Plumb 1985, 1986, Takaya and Nakamura 1997, 2001, Miyahara 2006, Kinoshita et al. 2010, Noda 2010, Kinoshita and Sato 2013a, b, and Noda 2014). On the other hand, the TEM equations cannot properly treat the lower boundary and unstable waves. The Mass-weighted Isentropic Mean (MIM) equations derived by Iwasaki (1989, 1990) are the equations that overcome those problems and the formulation of three-dimensional MIM equations have been studied. The present study applies the three-dimensional TEM and MIM equations to the ERA-Interim reanalysis data and examines the climatological character of three-dimensional structure of Stratospheric Brewer-Dobson circulation. Next, we will discuss how to treat the flow associated with spatial structure of stationary waves.

Atmospheric gravity waves with small vertical-to-horizotal wavelength ratios

NASA Astrophysics Data System (ADS)

Song, I. S.; Jee, G.; Kim, Y. H.; Chun, H. Y.

2017-12-01

Gravity wave modes with small vertical-to-horizontal wavelength ratios of an order of 10-3 are investigated through the systematic scale analysis of governing equations for gravity wave perturbations embedded in the quasi-geostrophic large-scale flow. These waves can be categorized as acoustic gravity wave modes because their total energy is given by the sum of kinetic, potential, and elastic parts. It is found that these waves can be forced by density fluctuations multiplied by the horizontal gradients of the large-scale pressure (geopotential) fields. These theoretical findings are evaluated using the results of a high-resolution global model (Specified Chemistry WACCM with horizontal resolution of 25 km and vertical resolution of 600 m) by computing the density-related gravity-wave forcing terms from the modeling results.

Atmospheric Gravity Waves (AGWs) as the driver of seismo-ionospheric coupling: recent major earthquakes of Nepal and Imphal - case study

NASA Astrophysics Data System (ADS)

Chakraborty, Suman; Chakrabarti, Sandip Kumar; Sasmal, Sudipta

2016-07-01

An important channel of the lithosphere-atmosphere-ionosphere coupling (LAIC) is the acoustic and gravity wave channel where the atmospheric gravity waves (AGW) play the most important part. Atmospheric waves are excited due to seismic gravitational vibrations before earthquakes and their effects on the atmosphere are the sources for seismo-ionospheric coupling which are manifested as perturbations in Very Low Frequency (VLF)/Low Frequency (LF) signal (amplitude/phase). For our study, we chose the recent major earthquakes that took place in Nepal and Imphal. The Nepal earthquake occurred on 12th May, 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) at southeast of Kodari. The Imphal earthquake occurred on 4th January, 2016 at 4:35 am local time (23:05 UTC , 3rd January, UTC) with Richter scale magnitude of M = 6.7 and depth 55 km (34.2 miles). The data has been collected from Ionospheric and Earthquake Research Centre (IERC) of Indian Centre for Space Physics (ICSP) transmitted from JJI station of Japan. We performed both Fast Fourier Transform (FFT) and wavelet analysis on the VLF data for a couple of days before and after the major earthquakes. For both earthquakes, we observed wave like structures with periods of almost an hour before and after the earthquake day. The wave like oscillations after the earthquake may be due to the aftershock effects. We also observed that the amplitude of the wave like structures depends on the location of the epicenter between the transmitting and the receiving points and also on the depth of the earthquake.

Satellite Observations of Stratospheric Gravity Waves Associated With the Intensification of Tropical Cyclones

NASA Astrophysics Data System (ADS)

Hoffmann, Lars; Wu, Xue; Alexander, M. Joan

2018-02-01

Forecasting the intensity of tropical cyclones is a challenging problem. Rapid intensification is often preceded by the formation of "hot towers" near the eyewall. Driven by strong release of latent heat, hot towers are high-reaching tropical cumulonimbus clouds that penetrate the tropopause. Hot towers are a potentially important source of stratospheric gravity waves. Using 13.5 years (2002-2016) of Atmospheric Infrared Sounder observations of stratospheric gravity waves and tropical cyclone data from the International Best Track Archive for Climate Stewardship, we found empirical evidence that stratospheric gravity wave activity is associated with the intensification of tropical cyclones. The Atmospheric Infrared Sounder and International Best Track Archive for Climate Stewardship data showed that strong gravity wave events occurred about twice as often for tropical cyclone intensification compared to storm weakening. Observations of stratospheric gravity waves, which are not affected by obscuring tropospheric clouds, may become an important future indicator of storm intensification.

Gravitation: Foundations and Frontiers

NASA Astrophysics Data System (ADS)

Padmanabhan, T.

2010-01-01

1. Special relativity; 2. Scalar and electromagnetic fields in special relativity; 3. Gravity and spacetime geometry: the inescapable connection; 4. Metric tensor, geodesics and covariant derivative; 5. Curvature of spacetime; 6. Einstein's field equations and gravitational dynamics; 7. Spherically symmetric geometry; 8. Black holes; 9. Gravitational waves; 10. Relativistic cosmology; 11. Differential forms and exterior calculus; 12. Hamiltonian structure of general relativity; 13. Evolution of cosmological perturbations; 14. Quantum field theory in curved spacetime; 15. Gravity in higher and lower dimensions; 16. Gravity as an emergent phenomenon; Notes; Index.

Thermal infrared sounding observations of lower atmospheric variances at Mars and their implications for gravity wave activity: a preliminary examination

NASA Astrophysics Data System (ADS)

Heavens, N. G.

2017-12-01

It has been recognized for over two decades that the mesoscale statistical variance observed by Earth-observing satellites at temperature-sensitive frequencies above the instrumental noise floor is a measure of gravity wave activity. These types of observation have been made by a variety of satellite instruments have been an important validation tool for gravity wave parameterizations in global and mesoscale models. At Mars, the importance of topographic and non-topographic sources of gravity waves for the general circulation is now widely recognized and the target of recent modeling efforts. However, despite several ingenious studies, gravity wave activity near hypothetical lower atmospheric sources has been poorly and unsystematically characterized, partly because of the difficulty of separating the gravity wave activity from baroclinic wave activity and the thermal tides. Here will be presented a preliminary analysis of calibrated radiance variance at 15.4 microns (635-665 cm-1) from nadir, off-nadir, and limb observations by the Mars Climate Sounder on board Mars Reconnaissance Orbiter. The overarching methodology follows Wu and Waters (1996, 1997). Nadir, off-nadir, and lowest detector limb observations should sample variability with vertical weighting functions centered high in the lower atmosphere (20-30 km altitude) and full width half maximum (FWHM) 20 km but be sensitive to gravity waves with different horizontal wavelengths and slightly different vertical wavelengths. This work is supported by NASA's Mars Data Analysis Program (NNX14AM32G). References Wu, D.L. and J.W. Waters, 1996, Satellite observations of atmospheric variances: A possible indication of gravity waves, GRL, 23, 3631-3634. Wu D.L. and J.W. Waters, 1997, Observations of Gravity Waves with the UARS Microwave Limb Sounder. In: Hamilton K. (eds) Gravity Wave Processes. NATO ASI Series (Series I: Environmental Change), vol 50. Springer, Berlin, Heidelberg.

Tsunami-driven gravity waves in the presence of vertically varying background and tidal wind structures

NASA Astrophysics Data System (ADS)

Laughman, B.; Fritts, D. C.; Lund, T. S.

2017-05-01

Many characteristics of tsunami-driven gravity waves (TDGWs) enable them to easily propagate into the thermosphere and ionosphere with appreciable amplitudes capable of producing detectable perturbations in electron densities and total electron content. The impact of vertically varying background and tidal wind structures on TDGW propagation is investigated with a series of idealized background wind profiles to assess the relative importance of wave reflection, critical-level approach, and dissipation. These numerical simulations employ a 2-D nonlinear anelastic finite-volume neutral atmosphere model which accounts for effects accompanying vertical gravity wave (GW) propagation such as amplitude growth with altitude. The GWs are excited by an idealized tsunami forcing with a 50 cm sea surface displacement, a 400 km horizontal wavelength, and a phase speed of 200 ms-1 consistent with previous studies of the tsunami generated by the 26 December 2004 Sumatra earthquake. Results indicate that rather than partial reflection and trapping, the dominant process governing TDGW propagation to thermospheric altitudes is refraction to larger and smaller vertical scales, resulting in respectively larger and smaller vertical group velocities and respectively reduced and increased viscous dissipation. Under all considered background wind profiles, TDGWs were able to attain ionospheric altitudes with appreciable amplitudes. Finally, evidence of nonlinear effects is observed and the conditions leading to their formation is discussed.

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.

Tsunami-Generated Atmospheric Gravity Waves and Their Atmospheric and Ionospheric Effects: a Review and Some Recent Modeling Results

NASA Astrophysics Data System (ADS)

Hickey, M. P.

2017-12-01

Tsunamis propagate on the ocean surface at the shallow water phase speed which coincides with the phase speed of fast atmospheric gravity waves. The forcing frequency also corresponds with those of internal atmospheric gravity waves. Hence, the coupling and effective forcing of gravity waves due to tsunamis is particularly effective. The fast horizontal phase speeds of the resulting gravity waves allows them to propagate well into the thermosphere before viscous dissipation becomes strong, and the waves can achieve nonlinear amplitudes at these heights resulting in large amplitude traveling ionospheric disturbances (TIDs). Additionally, because the tsunami represents a moving source able to traverse large distances across the globe, the gravity waves and associated TIDs can be detected at large distances from the original tsunami (earthquake) source. Although it was during the mid 1970s when the tsunami source of gravity waves was first postulated, only relatively recently (over the last ten to fifteen years) has there has been a surge of interest in this research arena, driven largely by significant improvements in measurement technologies and computational capabilities. For example, the use of GPS measurements to derive total electron content has been a particularly powerful technique used to monitor the propagation and evolution of TIDs. Monitoring airglow variations driven by atmospheric gravity waves has also been a useful technique. The modeling of specific events and comparison with the observed gravity waves and/or TIDs has been quite revealing. In this talk I will review some of the most interesting aspects of this research and also discuss some interesting and outstanding issues that need to be addressed. New modeling results relevant to the Tohoku tsunami event will also be presented.

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).

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

NASA Technical Reports Server (NTRS)

Eckermann, Stephen D.; Jackman, C. (Technical Monitor)

2000-01-01

An extensive body of research this quarter is documented. Further methodical analysis of temperature residuals in Cryogenic Limb Array Etalon Spectrometer (CLAES) Version 8 level 3AT data show signatures during December 1992 at middle and high northern latitudes that, when compared to Naval Research Laboratory/Mountain Wave Forecast Model (NRL)/(MWFM) mountain wave hindcasts, reveal evidence of long mountain waves in these data over Eurasia, Greenland, Scandinavia and North America. The explicit detection of gravity waves in limb-scanned Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) temperatures is modeled at length, to derive visibility functions. These insights are used to convert CRISTA gravity wave temperature residuals into data that more closely resemble gravity wave fluctuations detected in data from other satellite instruments, such as Microwave Limb Sounder (MLS), Limb Infrared Monitor of the Stratosphere (LIMS) and Global Positioning System/Meteorology (GPS)/(MET). Finally, newly issued mesospheric temperatures from inversion of CRISTA 15gin emissions are analyzed using a new method that uses separate Kalman fits to the ascending and descending node data. This allows us to study global gravity wave amplitudes at two local times, 12 hours apart. In the equatorial mesosphere, where a large diurnal tidal temperature signal exists, we see modulations of gravity wave activity that are consistent with gravity wave-tidal interactions produced by tidal temperature variability.

A new two-metric theory of gravity with prior geometry

NASA Technical Reports Server (NTRS)

Lightman, A. P.; Lee, D. L.

1972-01-01

A theory is presented of gravity which has the same post-Newtonian (PN) as that of general relativity. The field equations, and a calculation of the PN limit of the theory are discussed along with the equations of stellar structure for static spherically symmetric stars. A special exterior spherically symmetric solution, time dependent solutions, conservations, and gravitational waves are analyzed.

A high-order 3-D spectral-element method for the forward modelling and inversion of gravimetric data—Application to the western Pyrenees

NASA Astrophysics Data System (ADS)

Martin, Roland; Chevrot, Sébastien; Komatitsch, Dimitri; Seoane, Lucia; Spangenberg, Hannah; Wang, Yi; Dufréchou, Grégory; Bonvalot, Sylvain; Bruinsma, Sean

2017-04-01

We image the internal density structure of the Pyrenees by inverting gravity data using an a priori density model derived by scaling a Vp model obtained by full waveform inversion of teleseismic P-waves. Gravity anomalies are computed via a 3-D high-order finite-element integration in the same high-order spectral-element grid as the one used to solve the wave equation and thus to obtain the velocity model. The curvature of the Earth and surface topography are taken into account in order to obtain a density model as accurate as possible. The method is validated through comparisons with exact semi-analytical solutions. We show that the spectral-element method drastically accelerates the computations when compared to other more classical methods. Different scaling relations between compressional velocity and density are tested, and the Nafe-Drake relation is the one that leads to the best agreement between computed and observed gravity anomalies. Gravity data inversion is then performed and the results allow us to put more constraints on the density structure of the shallow crust and on the deep architecture of the mountain range.

Acoustic-gravity waves, theory and application

NASA Astrophysics Data System (ADS)

Kadri, Usama; Farrell, William E.; Munk, Walter

2015-04-01

Acoustic-gravity waves (AGW) propagate in the ocean under the influence of both the compressibility of sea water and the restoring force of gravity. The gravity dependence vanishes if the wave vector is normal to the ocean surface, but becomes increasingly important as the wave vector acquires a horizontal tilt. They are excited by many sources, including non-linear surface wave interactions, disturbances of the ocean bottom (submarine earthquakes and landslides) and underwater explosions. In this introductory lecture on acoustic-gravity waves, we describe their properties, and their relation to organ pipe modes, to microseisms, and to deep ocean signatures by short surface waves. We discuss the generation of AGW by underwater earthquakes; knowledge of their behaviour with water depth can be applied for the early detection of tsunamis. We also discuss their generation by the non-linear interaction of surface gravity waves, which explains the major role they play in transforming energy from the ocean surface to the crust, as part of the microseisms phenomenon. Finally, they contribute to horizontal water transport at depth, which might affect benthic life.

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

Progress in research into the global morphology of gravity wave activity using UARS data is described for the period March-June, 1998. Highlights this quarter include further progress in the analysis and interpretation of CRISTA temperature variances; model-generated climatologies of mesospheric gravity wave activity using the HWM-93 wind and temperature model; and modeling of gravity wave detection from space-based platforms. Preliminary interpretations and recommended avenues for further analysis are also described.

The accretion and spreading of matter on white dwarfs

NASA Astrophysics Data System (ADS)

Fisker, Jacob Lund; Balsara, Dinshaw S.; Burger, Tom

2006-10-01

For a slowly rotating non-magnetized white dwarf the accretion disk extends all the way to the star. At the interface between the accretion disk and the star, the matter moves through a boundary layer (BL) and then spreads toward the poles as new matter continuously piles up behind it. We have solved the 3d compressible Navier-Stokes equations on an axisymmetric grid to determine the structure of this BL for different accretion rates (states). The high states show a spreading BL which sets off a gravity wave in the surface matter. The accretion flow moves supersonically over the cusp making it susceptible to the rapid development of gravity wave and/or Kelvin-Helmholtz instabilities. This BL is optically thick and extends more than 30° to either side of the disk plane after 3/4 of a Keplerian rotation period (tK = 19 s). The low states also show a spreading BL, but here the accretion flow does not set off gravity waves and it is optically thin.

Dynamics of severe storms through the study of thermospheric-tropospheric coupling

NASA Technical Reports Server (NTRS)

Hung, R. J.; Smith, R. E.

1979-01-01

Atmospheric acoustic-gravity waves associated with severe local thunderstorms, tornadoes, and hurricanes can be studied through the coupling between the thermosphere and the troposphere. Reverse group ray tracing computations of acoustic-gravity waves, observed by an ionospheric Doppler sounder array, show that the wave sources are in the neighborhood of storm systems and the waves are excited prior to the storms. It is suggested that the overshooting and ensuing collapse of convective turrets may be responsible for generating the acoustic-gravity waves observed. The results of this study also show that the study of wave-wave resonant interactions may be a potential tool for investigating the dynamical behavior of severe storm systems using ionospheric observations of atmospheric acoustic-gravity waves associated with severe storms.

Gravity Wave Predictability and Dynamics in Deepwave

NASA Astrophysics Data System (ADS)

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

2015-12-01

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 (MLT). 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 lidar and airglow instruments, as well as dropwindsondes and a full suite of flight level instruments including the microwave temperature profiler (MTP), providing temperatures and vertical winds spanning altitudes from immediately above the NGV flight altitude (~13 km) to ~100 km. The region near New Zealand was chosen since all the relevant GW sources (e.g., mountains, cyclones, jet streams) occur strongly here, and upper-level winds in austral winter permit gravity waves to propagate to very high altitudes. The COAMPS adjoint modeling system provided forecast sensitivity in real time during the six-week DEEPWAVE field phase. Five missions were conducted using the NGV to observe regions of high forecast sensitivity, as diagnosed using the COAMPS adjoint model. In this presentation, we provide a summary of the sensitivity characteristics and explore the implications for predictability of low-level winds crucial for gravity wave launching, as well as predictability of gravity wave characteristics in the stratosphere. In general, the sensitive regions were characterized by localized strong dynamics, often involving intense baroclinic systems with deep convection. The results of the adjoint modeling system suggest that gravity wave launching and the characteristics of the gravity waves can be linked to these sensitive regions near frontal zones within baroclinic systems. The predictability links between the tropospheric fronts, cyclones, jet regions, and gravity waves that vertically propagate upward through the stratosphere will be addressed further in the presentation. We examine RF23 during DEEPWAVE, which sampled deep propagating gravity waves over Auckland and Macquarie Islands. We provide insight into the gravity wave dynamics through applying the COAMPS and its adjoint at high resolution.

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.

Interhemispheric Asymmetry in the Mesosphere and Lower Thermosphere Observed by SABER/TIMED

NASA Astrophysics Data System (ADS)

Yee, J. H.

2017-12-01

In this paper we analyze nearly 15 years of satellite observations of temperature, airglow, and composition in the Mesosphere and Lower Thermosphere (MLT) to quantify their interhemispheric asymmetries ao one can provide quantitative links between observed asymmetries and the spatial and temporal variations of the gravity wave activity. Two processes are believed to be responsible for observed interhemispheric differences in the MLT. The first is the direct radiation effect from the eccentricity of the Earth orbit amd the other is the difference in gravity wave source distribution and filtering due to asymmetries in mean winds of the lower atmosphere. Both processes have been theoretically investigated to explain the observed asymmetry in some of the atmospheric parameters, but not self-consistently in all observed parameters together. In this paper we will show the asymmetry in the time-varying zonal-mean latitudinal structures of temperature, airglow emission rate, and composition observed by TIMED/SABER. We will quantify their interhemispheric asymmetries for different seasons under different solar activity conditions. In addition, temperature measurements will also be used to obtain temporal and spatial morphology of gravity wave potential energies. We will interpret the asymmetry in the observed fields and examine qualitatively their consistency with the two responsible processes, especially the one due to gravity wave filtering process. Our goal is to introduce and to share the spatial and temporal morphologies of all the observed fields to the modeling community so, together self-consistently, they be can be used to gain physical insights into the relative importance of various drivers responsible for the observed asymmetry, especially the role of gravity wave induced eddy drag and mixing, a critical, but least quantitatively understood process.

Modeling the Diurnal Tides in the MLT Region with the Doppler Spread Parameterization of Gravity Waves

NASA Technical Reports Server (NTRS)

Mayr, H. G.; Mengel, J. G.; Chan, K. L.; Trob, D.; Porter, H. C.; Einaudi, Franco (Technical Monitor)

2000-01-01

Special Session: SA03 The mesosphere/lower thermosphere region: Structure, dynamics, composition, and emission. Ground based and satellite observations in the upper mesosphere and lower thermosphere (MLT) reveal large seasonal variations in the horizontal wind fields of the diurnal and semidiurnal tides. To provide an understanding of the observations, we discuss results obtained with our Numerical Spectral Model (NMS) that incorporates the gravity wave Doppler Spread Parameterization (DSP) of Hines. Our model reproduces many of the salient features observed, and we discuss numerical experiments that delineate the important processes involved. Gravity wave momentum deposition and the seasonal variations in the tidal excitation contribute primarily to produce the large equinoctial amplitude maxima in the diurnal tide. Gravity wave induced variations in eddy viscosity, not accounted for in the model, have been shown by Akmaev to be important too. For the semidiurnal tide, with amplitude maximum observed during winter solstice, these processes also contribute, but filtering by the mean zonal circulation is more important. A deficiency of our model is that it cannot reproduce the observed seasonal variations in the phase of the semidiurnal tide, and numerical experiments are being carried out to diagnose the cause and to alleviate this problem. The dynamical components of the upper mesosphere are tightly coupled through non-linear processes and wave filtering, and this may constrain the model and require it to reproduce in detail the observed phenomenology.

A ray tracing model of gravity wave propagation and breakdown in the middle atmosphere

NASA Technical Reports Server (NTRS)

Schoeberl, M. R.

1985-01-01

Gravity wave ray tracing and wave packet theory is used to parameterize wave breaking in the mesosphere. Rays are tracked by solving the group velocity equations, and the interaction with the basic state is determined by considering the evolution of the packet wave action density. The ray tracing approach has a number of advantages over the steady state parameterization as the effects of gravity wave focussing and refraction, local dissipation, and wave response to rapid changes in the mean flow are more realistically considered; however, if steady state conditions prevail, the method gives identical results. The ray tracing algorithm is tested using both interactive and noninteractive models of the basic state. In the interactive model, gravity wave interaction with the polar night jet on a beta-plane is considered. The algorithm produces realistic polar night jet closure for weak topographic forcing of gravity waves. Planetary scale waves forced by local transfer of wave action into the basic flow in turn transfer their wave action into the zonal mean flow. Highly refracted rays are also found not to contribute greatly to the climatology of the mesosphere, as their wave action is severely reduced by dissipation during their lateral travel.

Experimental observation of negative effective gravity in water waves.

PubMed

Hu, Xinhua; Yang, Jiong; Zi, Jian; Chan, C T; Ho, Kai-Ming

2013-01-01

The gravity of Earth is responsible for the formation of water waves and usually difficult to change. Although negative effective gravity was recently predicted theoretically in water waves, it has not yet been observed in experiments and remains a mathematical curiosity which is difficult to understand. Here we experimentally demonstrate that close to the resonant frequency of purposely-designed resonating units, negative effective gravity can occur for water waves passing through an array of resonators composing of bottom-mounted split tubes, resulting in the prohibition of water wave propagation. It is found that when negative gravity occurs, the averaged displacement of water surface in a unit cell of the array has a phase difference of π to that along the boundary of the unit cell, consistent with theoretical predictions. Our results provide a mechanism to block water waves and may find applications in wave energy conversion and coastal protection.

Experimental Observation of Negative Effective Gravity in Water Waves

PubMed Central

Hu, Xinhua; Yang, Jiong; Zi, Jian; Chan, C. T.; Ho, Kai-Ming

2013-01-01

The gravity of Earth is responsible for the formation of water waves and usually difficult to change. Although negative effective gravity was recently predicted theoretically in water waves, it has not yet been observed in experiments and remains a mathematical curiosity which is difficult to understand. Here we experimentally demonstrate that close to the resonant frequency of purposely-designed resonating units, negative effective gravity can occur for water waves passing through an array of resonators composing of bottom-mounted split tubes, resulting in the prohibition of water wave propagation. It is found that when negative gravity occurs, the averaged displacement of water surface in a unit cell of the array has a phase difference of π to that along the boundary of the unit cell, consistent with theoretical predictions. Our results provide a mechanism to block water waves and may find applications in wave energy conversion and coastal protection. PMID:23715132

Study of gravity waves propagation in the thermosphere of Mars based on MAVEN/NGIMS density measurements

NASA Astrophysics Data System (ADS)

Vals, M.

2017-09-01

We use MAVEN/NGIMS CO2 density measurements to analyse gravity waves in the thermosphere of Mars. In particular the seasonal/latitudinal variability of their amplitude is studied and interpreted. Key background parameters controlling the activity of gravity waves are analysed with the help of the Mars Climate Database (MCD). Gravity waves activity presents a good anti-correlation to the temperature variability retrieved from the MCD. An analysis at pressure levels is ongoing.

Dark- and bright-rogue-wave solutions for media with long-wave-short-wave resonance.

PubMed

Chen, Shihua; Grelu, Philippe; Soto-Crespo, J M

2014-01-01

Exact explicit rogue-wave solutions of intricate structures are presented for the long-wave-short-wave resonance equation. These vector parametric solutions feature coupled dark- and bright-field counterparts of the Peregrine soliton. Numerical simulations show the robustness of dark and bright rogue waves in spite of the onset of modulational instability. Dark fields originate from the complex interplay between anomalous dispersion and the nonlinearity driven by the coupled long wave. This unusual mechanism, not available in scalar nonlinear wave equation models, can provide a route to the experimental realization of dark rogue waves in, for instance, negative index media or with capillary-gravity waves.

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

NASA Astrophysics Data System (ADS)

Campbell, Lucy J.; Shepherd, Theodore G.

2005-12-01

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

A Comparison Between Gravity Wave Momentum Fluxes in Observations and Climate Models

NASA Technical Reports Server (NTRS)

Geller, Marvin A.; Alexadner, M. Joan; Love, Peter T.; Bacmeister, Julio; Ern, Manfred; Hertzog, Albert; Manzini, Elisa; Preusse, Peter; Sato, Kaoru; Scaife, Adam A.;

Long-Term Observation of Small and Medium-Scale Gravity Waves over the Brazilian Equatorial Region

NASA Astrophysics Data System (ADS)

Essien, Patrick; Buriti, Ricardo; Wrasse, Cristiano M.; Medeiros, Amauri; Paulino, Igo; Takahashi, Hisao; Campos, Jose Andre

2016-07-01

This paper reports the long term observations of small and medium-scale gravity waves over Brazilian equatorial region. Coordinated optical and radio measurements were made from OLAP at Sao Joao do Cariri (7.400S, 36.500W) to investigate the occurrences and properties and to characterize the regional mesospheric gravity wave field. All-sky imager measurements were made from the site. for almost 11 consecutive years (September 2000 to November 2010). Most of the waves propagated were characterized as small-scale gravity. The characteristics of the two waves events agreed well with previous gravity wave studies from Brazil and other sites. However, significant differences in the wave propagation headings indicate dissimilar source regions. The observed medium-scale gravity wave events constitute an important new dataset to study their mesospheric properties at equatorial latitudes. These data exhibited similar propagation headings to the short period events, suggesting they originated from the same source regions. It was also observed that some of the medium-scale were capable of propagating into the lower thermosphere where they may have acted directly as seeds for the Rayleigh-Taylor instability development. The wave events were primarily generated by meteorological processes since there was no correlation between the evolution of the wave events and solar cycle F10.7.

Southern Argentina Agile Meteor Radar: Initial assessment of gravity wave momentum fluxes

NASA Astrophysics Data System (ADS)

Fritts, D. C.; Janches, D.; Hocking, W. K.

2010-10-01

The Southern Argentina Agile Meteor Radar (SAAMER) was installed on Tierra del Fuego (53.8°S) in May 2008 and has been operational since that time. This paper describes tests of the SAAMER ability to measure gravity wave momentum fluxes and applications of this capability during different seasons. Test results for specified mean, tidal, and gravity wavefields, including tidal amplitudes and gravity wave momentum fluxes varying strongly with altitude and/or time, suggest that the distribution of meteors throughout the diurnal cycle and averaged over a month allows characterization of both monthly mean profiles and diurnal variations of the gravity wave momentum fluxes. Applications of the same methods for real data suggest confidence in the monthly mean profiles and the composite day diurnal variations of gravity wave momentum fluxes at altitudes where meteor counts are sufficient to yield good statistical fits to the data. Monthly mean zonal winds and gravity wave momentum fluxes exhibit anticorrelations consistent with those seen at other midlatitude and high-latitude radars during austral spring and summer, when no strong local gravity wave sources are apparent. When stratospheric variances are significantly enhanced over the Drake Passage “hot spot” during austral winter, however, MLT winds and momentum fluxes over SAAMER exhibit very different correlations that suggest that MLT dynamics are strongly influenced by strong local gravity wave sources within this “hot spot.” SAAMER measurements of mean zonal and meridional winds at these times and their differences from measurements at a conjugate site provide further support for the unusual momentum flux measurements.

W-waves Explain Gravitropism, Phototropism, Sap Flow, Plant Structure, and other Plant Processes

NASA Astrophysics Data System (ADS)

Wagner, Raymond E.; Wagner, Orvin E.

1996-11-01

Eight years of research here confirm that plants act as wave guides for W-waves: The wavelengths of these longitudinal plant waves depend on the angle with which they are traveling with respect to the gravitational field. A structure grows tuned to a particular angle under the influence of genetics. If a structure is displaced from this angle plant action produces a correction. (2) Light waves produce certain W-wave modes in the W-wave medium and a plant's response to light results. (3) Wave action produces forces in the plant (that cancel gravity in the vertical case), combined with other affects, and sap flow results. (4) Plant structures are determined by genetics and environment from a set of quantized wavelengths available to all plants. The quantized values available to plants and all life provide templates for life to develop. Compare with quantum mechanics as a template for the structure of matter. Life processes suggest that templates also influence the development and stability of all structures in the universe (see www.chatlink.com/ oedphd/ for references).

Effect of Gravity Waves from Small Islands in the Southern Ocean on the Southern Hemisphere Atmospheric Circulation

NASA Technical Reports Server (NTRS)

Garfinkel, C. I.; Oman, L. D.

2018-01-01

The effect of small islands in the Southern Ocean on the atmospheric circulation in the Southern Hemisphere is considered with a series of simulations using the NASA Goddard Earth Observing System Chemistry-Climate Model in which the gravity wave stress generated by these islands is increased to resemble observed values. The enhanced gravity wave drag leads to a 2 K warming of the springtime polar stratosphere, partially ameliorating biases in this region. Resolved wave drag declines in the stratospheric region in which the added orographic gravity waves deposit their momentum, such that changes in gravity waves are partially compensated by changes in resolved waves, though resolved wave drag increases further poleward. The orographic drag from these islands has impacts for surface climate, as biases in tropospheric jet position are also partially ameliorated. These results suggest that these small islands are likely contributing to the missing drag near 60 degrees S in the upper stratosphere evident in many data assimilation products.

Ionospheric effects of magneto-acoustic-gravity waves: Dispersion relation

NASA Astrophysics Data System (ADS)

Jones, R. Michael; Ostrovsky, Lev A.; Bedard, Alfred J.

2017-06-01

There is extensive evidence for ionospheric effects associated with earthquake-related atmospheric disturbances. Although the existence of earthquake precursors is controversial, one suggested method of detecting possible earthquake precursors and tsunamis is by observing possible ionospheric effects of atmospheric waves generated by such events. To study magneto-acoustic-gravity waves in the atmosphere, we have derived a general dispersion relation including the effects of the Earth's magnetic field. This dispersion relation can be used in a general atmospheric ray tracing program to calculate the propagation of magneto-acoustic-gravity waves from the ground to the ionosphere. The presence of the Earth's magnetic field in the ionosphere can radically change the dispersion properties of the wave. The general dispersion relation obtained here reduces to the known dispersion relations for magnetoacoustic waves and acoustic-gravity waves in the corresponding particular cases. The work described here is the first step in achieving a generalized ray tracing program permitting propagation studies of magneto-acoustic-gravity waves.

Relationship between Ripples and Gravity Waves Observed in OH Airglow over the Andes Lidar Observatory

NASA Astrophysics Data System (ADS)

Cao, B.; Gelinas, L. J.; Liu, A. Z.; Hecht, J. H.

2016-12-01

Instabilities generated by large amplitude gravity waves are ubiquitous in the mesopause region, and contribute to the strong forcing on the background atmosphere. Gravity waves and ripples generated by instability are commonly detected by high resolution airglow imagers that measure the hydroxyl emissions near the mesopause ( 87 km). Recently, a method based on 2D wavelet is developed by Gelinas et al. to characterize the statistics of ripple parameters from the Aerospace Infrared Camera at Andes Lidar Observatory located at Cerro Pachón, Chile (70.74°W, 30.25°S). In the meantime, data from a collocated all-sky imager is used to derive gravity wave parameters and their statistics. In this study, the relationship between the ripples and gravity waves that appeared at the same time and location are investigated in terms of their orientations, magnitudes and scales, to examine the statistical properties of the gravity wave induced instabilities and the ripples they generate.

Complexity-action duality of the shock wave geometry in a massive gravity theory

NASA Astrophysics Data System (ADS)

Miao, Yan-Gang; Zhao, Long

2018-01-01

On the holographic complexity dual to the bulk action, we investigate the action growth for a shock wave geometry in a massive gravity theory within the Wheeler-DeWitt (WDW) patch at the late time limit. For a global shock wave, the graviton mass does not affect the action growth in the bulk, i.e., the complexity on the boundary, showing that the action growth (complexity) is the same for both the Einstein gravity and the massive gravity. Nevertheless, for a local shock wave that depends on transverse coordinates, the action growth (complexity) caused by the boundary disturbance (perturbation) is proportional to the butterfly velocity for the two gravity theories, but the butterfly velocity of the massive gravity theory is smaller than that of the Einstein gravity theory, indicating that the action growth (complexity) of the massive gravity is depressed by the graviton mass. In addition, we extend the black hole thermodynamics of the massive gravity and obtain the right Smarr formula.

On the use of infrasound for constraining global climate models

NASA Astrophysics Data System (ADS)

Millet, Christophe; Ribstein, Bruno; Lott, Francois; Cugnet, David

2017-11-01

Numerical prediction of infrasound is a complex issue due to constantly changing atmospheric conditions and to the random nature of small-scale flows. Although part of the upward propagating wave is refracted at stratospheric levels, where gravity waves significantly affect the temperature and the wind, yet the process by which the gravity wave field changes the infrasound arrivals remains poorly understood. In the present work, we use a stochastic parameterization to represent the subgrid scale gravity wave field from the atmospheric specifications provided by the European Centre for Medium-Range Weather Forecasts. It is shown that regardless of whether the gravity wave field possesses relatively small or large features, the sensitivity of acoustic waveforms to atmospheric disturbances can be extremely different. Using infrasound signals recorded during campaigns of ammunition destruction explosions, a new set of tunable parameters is proposed which more accurately predicts the small-scale content of gravity wave fields in the middle atmosphere. Climate simulations are performed using the updated parameterization. Numerical results demonstrate that a network of ground-based infrasound stations is a promising technology for dynamically tuning the gravity wave parameterization.

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.

Internal Gravity Waves in the Magnetized Solar Atmosphere. I. Magnetic Field Effects

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

Vigeesh, G.; Steiner, O.; Jackiewicz, J., E-mail: vigeesh@leibniz-kis.de

Observations of the solar atmosphere show that internal gravity waves are generated by overshooting convection, but are suppressed at locations of magnetic flux, which is thought to be the result of mode conversion into magnetoacoustic waves. Here, we present a study of the acoustic-gravity wave spectrum emerging from a realistic, self-consistent simulation of solar (magneto)convection. A magnetic field free, hydrodynamic simulation and a magnetohydrodynamic (MHD) simulation with an initial, vertical, homogeneous field of 50 G flux density were carried out and compared with each other to highlight the effect of magnetic fields on the internal gravity wave propagation in themore » Sun’s atmosphere. We find that the internal gravity waves are absent or partially reflected back into the lower layers in the presence of magnetic fields and argue that the suppression is due to the coupling of internal gravity waves to slow magnetoacoustic waves still within the high- β region of the upper photosphere. The conversion to Alfvén waves is highly unlikely in our model because there is no strongly inclined magnetic field present. We argue that the suppression of internal waves observed within magnetic flux concentrations may also be due to nonlinear breaking of internal waves due to vortex flows that are ubiquitously present in the upper photosphere and the chromosphere.« less

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

NASA Technical Reports Server (NTRS)

Lin, Yuh-Lang; Kaplan, Michael L.

1994-01-01

An in-depth analysis of observed gravity waves and their relationship to precipitation bands over the Montana mesonetwork during the 11-12 July 1981 CCOPE case study indicated two episodes of coherent waves. While geostrophic adjustment, shearing instability, and terrain were all implicated separately or in combination as possible wave generation mechanisms, the lack of upper-air data within the wave genesis region made it difficult to define the genesis processes from observations alone. The first part of this paper, 3D Numerical Modeling Studies of Terrain-Induced Mass/Momentum Perturbations, employs a mesoscale numerical model to help diagnose the intricate early wave generation mechanisms during the first observed gravity wave episode. The meso-beta scale numerical model is used to study various simulations of the role of multiple geostrophic adjustment processes in focusing a region for gravity wave genesis. The second part of this paper, Linear Theory and Theoretical Modeling, investigates the response of non-resting rotating homogeneous and continuously stratified Boussinesq models of the terrestrial atmosphere to temporally impulsive and uniformly propagating three-dimensional localized zonal momentum sources representative of midlatitude jet streaks. The methods of linear perturbation theory applied to the potential vorticity (PV) and wave field equations are used to study the geostrophic adjustment dynamics. The total zonal and meridional wind perturbations are separated into geostrophic and ageostrophic components in order to define and follow the evolution of both the primary and secondary mesocirculations accompanying midlatitude jetogenesis forced by geostrophic adjustment processes. This problem is addressed to help fill the gap in understanding the dynamics and structure of mesoscale inertia-gravity waves forced by geostrophic adjustment processes in simple two-dimensional quiescent current systems and those produced by mesoscale numerical models simulating the orographic and diabatic perturbation of three-dimensional quasi-geostrophically balanced synoptic scale jet streaks associated with complex baroclinic severe storm producing environments.

Occurrence characteristics of medium-scale gravity waves observed in OH and OI nightglow over Adelaide (34.5°S, 138.5°E)

NASA Astrophysics Data System (ADS)

Ding, F.; Yuan, H.; Wan, W.; Reid, I. M.; Woithe, J. M.

2004-07-01

This paper presents a 7 year climatology describing medium-scale gravity waves observed in the menopause region covering the years from 1995 to 2001. The data comes from the OI and OH airglow observations of the three-field photometer employed at the University of Adelaide's Buckland Park, Australia (34.5°S, 138.5°E). About 1300 gravity wave events (AGW) are identified during the years 1995-2001. These AGW events usually persist for between 40 min and 4 hours. The magnitudes range from 1% to 14% of the background intensities and peak at 2% for OI observations and at 3% for OH observations. The observed periods range from 10 to 30 min, and the horizontal phase speeds range from 20 to 250 m s-1, with dominant wave scales of 17 min, 70 m s-1 for OI observations and 20 min, 40 m s-1 for OH observations. The intrinsic parameters are obtained by using medium-frequency (MF) wind data observed at the same place. The occurrence frequency of AGW events peaks at 13 min, 40 m s-1 for both OI and OH observations. The occurrence rate of gravity waves has a major peak in summer and a minor peak in winter. There is an obvious dominating southeastward direction for gravity waves, with azimuths of 160° in summer and 130° in winter. Studies for gravity waves observed in various locations show a similar tendency of propagating meridionally toward the summer pole. This implies that the tendency of propagating toward the summer pole may be a global trend for medium-scale gravity waves observed in the mesopause region. During summer, gravity waves propagate against winds measured by MF radar in their dominating direction. Using the ray tracing method, we found that the seasonal variation of winds limits the access of gravity waves to the observation height through reflection and critical coupling, which is one of the causes leading to the seasonal behavior of gravity waves observed over Adelaide.

Equatorial waves in the NCAR stratospheric general circulation model

NASA Technical Reports Server (NTRS)

Boville, B. A.

1985-01-01

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

Demystifying the Complexities of Gravity Wave Dynamics in the Middle Atmosphere: a Roadmap to Improved Weather Forecasts through High-Fidelity Modeling

NASA Astrophysics Data System (ADS)

Mixa, T.; Fritts, D. C.; Bossert, K.; Laughman, B.; Wang, L.; Lund, T.; Kantha, L. H.

2017-12-01

Gravity waves play a profound role in the mixing of the atmosphere, transporting vast amounts of momentum and energy among different altitudes as they propagate vertically. Above 60km in the middle atmosphere, high wave amplitudes enable a series of complex, nonlinear interactions with the background environment that produce highly-localized wind and temperature variations which alter the layering structure of the atmosphere. These small-scale interactions account for a significant portion of energy transport in the middle atmosphere, but they are difficult to characterize, occurring at spatial scales that are both challenging to observe with ground instruments and prohibitively small to include in weather forecasting models. Using high fidelity numerical simulations, these nuanced wave interactions are analyzed to better our understanding of these dynamics and improve the accuracy of long-term weather forecasting.

Popsicle-Stick Cobra Wave

NASA Astrophysics Data System (ADS)

Boucher, Jean-Philippe; Clanet, Christophe; Quéré, David; Chevy, Frédéric

2017-08-01

The cobra wave is a popular physical phenomenon arising from the explosion of a metastable grillage made of popsicle sticks. The sticks are expelled from the mesh by releasing the elastic energy stored during the weaving of the structure. Here we analyze both experimentally and theoretically the propagation of the wave front depending on the properties of the sticks and the pattern of the mesh. We show that its velocity and its shape are directly related to the recoil imparted to the structure by the expelled sticks. Finally, we show that the cobra wave can only exist for a narrow range of parameters constrained by gravity and rupture of the sticks.

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.

The southern stratospheric gravity wave hot spot: individual waves and their momentum fluxes measured by COSMIC GPS-RO

NASA Astrophysics Data System (ADS)

Hindley, N. P.; Wright, C. J.; Smith, N. D.; Mitchell, N. J.

2015-07-01

Nearly all general circulation models significantly fail to reproduce the observed behaviour of the southern wintertime polar vortex. It has been suggested that these biases result from an underestimation of gravity wave drag on the atmosphere at latitudes near 60° S, especially around the "hot spot" of intense gravity wave fluxes above the mountainous Southern Andes and Antarctic peninsula. Here, we use Global Positioning System radio occultation (GPS-RO) data from the COSMIC satellite constellation to determine the properties of gravity waves in the hot spot and beyond. We show considerable southward propagation to latitudes near 60° S of waves apparently generated over the southern Andes. We propose that this propagation may account for much of the wave drag missing from the models. Furthermore, there is a long leeward region of increased gravity wave energy that sweeps eastwards from the mountains over the Southern Ocean. Despite its striking nature, the source of this region has historically proved difficult to determine. Our observations suggest that this region includes both waves generated locally and orographic waves advected downwind from the hot spot. We describe and use a new wavelet-based analysis technique for the quantitative identification of individual waves from COSMIC temperature profiles. This analysis reveals different geographical regimes of wave amplitude and short-timescale variability in the wave field over the Southern Ocean. Finally, we use the increased numbers of closely spaced pairs of profiles from the deployment phase of the COSMIC constellation in 2006 to make estimates of gravity wave horizontal wavelengths. We show that, given sufficient observations, GPS-RO can produce physically reasonable estimates of stratospheric gravity wave momentum flux in the hot spot that are consistent with measurements made by other techniques. We discuss our results in the context of previous satellite and modelling studies and explain how they advance our understanding of the nature and origins of waves in the southern stratosphere.

Generation of intermittent gravitocapillary waves via parametric forcing

NASA Astrophysics Data System (ADS)

Castillo, Gustavo; Falcón, Claudio

2018-04-01

We report on the generation of an intermittent wave field driven by a horizontally moving wave maker interacting with Faraday waves. The spectrum of the local gravitocapillary surface wave fluctuations displays a power law in frequency for a wide range of forcing parameters. We compute the probability density function of the local surface height increments, which show that they change strongly across time scales. The structure functions of these increments are shown to display power laws as a function of the time lag, with exponents that are nonlinear functions of the order of the structure function. We argue that the origin of this scale-invariant intermittent spectrum is the Faraday wave pattern breakup due to its advection by the propagating gravity waves. Finally, some interpretations are proposed to explain the appearance of this intermittent spectrum.

Sodium Lidar-observed Strong Inertia-gravity Wave Activities in the Mesopause Region over Fort Collins, Colorado (41 deg N, 105 deg W)

NASA Technical Reports Server (NTRS)

Li, Tao; She, C. -Y.; Liu, Han-Li; Leblanc, Thierry; McDermid, I. Stuart

2007-01-01

In December 2004, the Colorado State University sodium lidar system at Fort Collins, Colorado (41 deg N, 105 deg W), conducted an approximately 80-hour continuous campaign for the simultaneous observations of mesopause region sodium density, temperature, and zonal and meridional winds. This data set reveals the significant inertia-gravity wave activities with a period of approximately 18 hours, which are strong in both wind components since UT day 338 (second day of the campaign), and weak in temperature and sodium density. The considerable variability of wave activities was observed with both wind amplitudes growing up to approximately 40 m/s at 95-100 km in day 339 and then decreasing dramatically in day 340. We also found that the sodium density wave perturbation is correlated in phase with temperature perturbation below 90 km, and approximately 180 deg out of phase above. Applying the linear wave theory, we estimated the wave horizontal propagation direction, horizontal wavelength, and apparent horizontal phase speed to be approximately 25 deg south of west, approximately 1800 +/- 150 km, and approximately 28 +/- 2 m/s, respectively of wave intrinsic period, intrinsic phase speed, and vertical wavelength were also estimated. While the onset of enhanced inertia-gravity wave amplitude in the night of 338 was observed to be in coincidence with short-period gravity wave breaking via convective instability, the decrease of inertia-gravity wave amplitude after noon of day 339 was also observed to coincide with the development of atmospheric dynamical instability layers with downward phase progression clearly correlated with the 18-hour inertia-gravity wave, suggesting likely breaking of this inertia-gravity wave via dynamical (shear) instability.

How tides get dissipated in Saturn? A question probably answerable by Cassni

NASA Astrophysics Data System (ADS)

Luan, Jing

2017-06-01

Tidal dissipation inside a giant planet is important in understanding the orbital evolutions of its natural satellites and perhaps some of the extrasolar giant planets. The tidal dissipation is conventionally parameterized by the tidal quality factor, Q. The corresponding tidal torque declines rapidly with distance adopting constant Q. However, the current fast migration rates of some Saturnian satellites reported by Lainey et al. (2015) conflict this conventional conceptual belief. Alternatively, resonance lock between a satellite and an internal oscillation mode or wave of Saturn, proposed by Fuller et al. (2016), could naturally match the observational migration rates. However, the question still remains to be answered what type of mode or wave is locked with each satellite. There are two candidates for resonance lock, one is gravity mode, and the other is inertial wave attractor. They generate very different gravity acceleration anomaly near the surface of Saturn, which may be distinguishable by the data to be collected by Cassini during its proximal orbits between April and September, 2017. Indicative information about the interior of Saturn may be extracted since the existence of both gravity mode and inertial wave attractor depends on the internal structure of Saturn.

Internal gravity waves in the upper atmosphere, generated by tropospheric jet streams

NASA Technical Reports Server (NTRS)

Chunchuzov, Y. P.; Torgashin, Y. M.

1979-01-01

A mechanism of internal gravity wave generation by jet streams in the troposphere is considered. Evaluations of the energy and pulse of internal gravity waves emitted into the upper atmosphere are given. The obtained values of flows can influence the thermal and dynamic regime of these layers.

Gravity waves and instabilities in the lower and middle atmosphere

NASA Technical Reports Server (NTRS)

Klostermeyer, Juergen

1989-01-01

Some basic aspects of mesoscale and small-scale gravity waves and instability mechanisms are discussed. Internal gravity waves with wavelengths between ten and less than one kilometer and periods between several hours and several minutes appear to play a central role in atmospheric wavenumber and frequency spectra. Therefore, the author discusses the propagation of gravity waves in simplified atmospheric models. Their interaction with the wind as well as their mutual interaction and stability mechanisms based on these processes are discussed. Mesosphere stratosphere troposphere radar observations showing the relevant hydrodynamic processes are stressed.

Inertia-gravity wave radiation from the merging of two co-rotating vortices in the f-plane shallow water system

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

Sugimoto, Norihiko, E-mail: nori@phys-h.keio.ac.jp

Inertia-gravity wave radiation from the merging of two co-rotating vortices is investigated numerically in a rotating shallow water system in order to focus on cyclone–anticyclone asymmetry at different values of the Rossby number (Ro). A numerical study is conducted on a model using a spectral method in an unbounded domain to estimate the gravity wave flux with high accuracy. Continuous gravity wave radiation is observed in three stages of vortical flows: co-rotating of the vortices, merging of the vortices, and unsteady motion of the merged vortex. A cyclone–anticyclone asymmetry appears at all stages at smaller Ro (≤20). Gravity waves frommore » anticyclones are always larger than those from cyclones and have a local maximum at smaller Ro (∼2) compared with that for an idealized case of a co-rotating vortex pair with a constant rotation rate. The source originating in the Coriolis acceleration has a key role in cyclone–anticyclone asymmetry in gravity waves. An additional important factor is that at later stages, the merged axisymmetric anticyclone rotates faster than the elliptical cyclone due to the effect of the Rossby deformation radius, since a rotation rate higher than the inertial cutoff frequency is required to radiate gravity waves.« less

Gravity waves in the thermosphere observed by the AE satellites

NASA Technical Reports Server (NTRS)

Gross, S. H.; Reber, C. A.; Huang, F. T.

1983-01-01

Atmospheric Explorer (AE) satellite data were used to investigate the spectra characteristics of wave-like structure observed in the neutral and ionized components of the thermosphere. Power spectral analysis derived by the maximum entropy method indicate the existence of a broad spectrum of scale sizes for the fluctuations ranging from tens to thousands of kilometers.

Tropical Cumulus Convection and Upward Propagating Waves in Middle Atmospheric GCMs

NASA Technical Reports Server (NTRS)

Horinouchi, T.; Pawson, S.; Shibata, K.; Langematz, U.; Manzini, E.; Giorgetta, M. A.; Sassi, F.; Wilson, R. J.; Hamilton, K. P.; deGranpre, J.;

Advancement of Techniques for Modeling the Effects of Atmospheric Gravity-Wave-Induced Inhomogeneities on Infrasound Propagation

DTIC Science & Technology

2010-09-01

ADVANCEMENT OF TECHNIQUES FOR MODELING THE EFFECTS OF ATMOSPHERIC GRAVITY-WAVE-INDUCED INHOMOGENEITIES ON INFRASOUND PROPAGATION Robert G...number of infrasound observations indicate that fine-scale atmospheric inhomogeneities contribute to infrasonic arrivals that are not predicted by...standard modeling techniques. In particular, gravity waves, or buoyancy waves, are believed to contribute to the multipath nature of infrasound

Ionospsheric observation of enhanced convection-initiated gravity waves during tornadic storms

NASA Technical Reports Server (NTRS)

Hung, R. J.

1981-01-01

Atmospheric gravity waves associated with tornadoes, with locally severe storms occuring with tornadoes, and with hurricanes were studied through the coupling between the ionosphere and the troposphere. Reverse group ray tracing computations of gravity waves observed by an ionospheric Doppler sounder array were analyzed. The results of ray tracing computations and comparisons between the computed location of the wave sources and with conventional meteorological data indicate that the computed sources of the waves were near the touchdown of the tornadoes, near the eye of the hurricanes, and directly on the squall line of the severe thunderstorms. The signals excited occurred one hour in advance of the tornadoes and three hours in advance of the hurricanes. Satellite photographs show convective overshooting turrets occurring at the same locations and times the gravity waves were being excited. It is suggested that gravity wave observations, conventional meteorological data, and satellite photographs be combined to develop a remote sensing technique for detecting severe storms.

The non-Gaussian joint probability density function of slope and elevation for a nonlinear gravity wave field. [in ocean surface

NASA Technical Reports Server (NTRS)

Huang, N. E.; Long, S. R.; Bliven, L. F.; Tung, C.-C.

1984-01-01

On the basis of the mapping method developed by Huang et al. (1983), an analytic expression for the non-Gaussian joint probability density function of slope and elevation for nonlinear gravity waves is derived. Various conditional and marginal density functions are also obtained through the joint density function. The analytic results are compared with a series of carefully controlled laboratory observations, and good agreement is noted. Furthermore, the laboratory wind wave field observations indicate that the capillary or capillary-gravity waves may not be the dominant components in determining the total roughness of the wave field. Thus, the analytic results, though derived specifically for the gravity waves, may have more general applications.

The Effect of Internal Gravity Waves on Fluctuations in Meteorological Parameters of the Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Zaitseva, D. V.; Kallistratova, M. A.; Lyulyukin, V. S.; Kouznetsov, R. D.; Kuznetsov, D. D.

2018-03-01

Variations in the intensity of turbulence during wave activity in the stable atmospheric boundary layer over a homogeneous steppe surface have been analyzed. Eight wave activity episodes recorded with a Doppler sodar in August 2015 at the Tsimlyansk Scientific Station of the Obukhov Institute of Atmospheric Physics have been studied. These episodes include seven trains of Kelvin-Helmholtz waves and one train of buoyancy waves. Variations in the rms deviation of the vertical wind-velocity component, the temperature structure parameter, and vertical heat and momentum fluxes have been estimated for each episode of wave activity. It has been found that Kelvin-Helmholtz waves slightly affect the intensity of turbulence, while buoyancy waves cause the temperature structure parameter and the vertical fluxes to increase by more than an order of magnitude.

3D DNS and LES of Breaking Inertia-Gravity Waves

NASA Astrophysics Data System (ADS)

Remmler, S.; Fruman, M. D.; Hickel, S.; Achatz, U.

2012-04-01

As inertia-gravity waves we refer to gravity waves that have a sufficiently low frequency and correspondingly large horizontal wavelength to be strongly influenced by the Coriolis force. Inertia-gravity waves are very active in the middle atmosphere and their breaking is potentially an important influence on the circulation in this region. The parametrization of this process requires a good theoretical understanding, which we want to enhance with the present study. Primary linear instabilities of an inertia-gravity wave and "2.5-dimensional" nonlinear simulations (where the spatial dependence is two dimensional but the velocity and vorticity fields are three-dimensional) with the wave perturbed by its leading primary instabilities by Achatz [1] have shown that the breaking differs significantly from that of high-frequency gravity waves due to the strongly sheared component of velocity perpendicular to the plane of wave-propagation. Fruman & Achatz [2] investigated the three-dimensionalization of the breaking by computing the secondary linear instabilities of the same waves using singular vector analysis. These secondary instabilities are variations perpendicular to the direction of the primary perturbation and the wave itself, and their wavelengths are an order of magnitude shorter than both. In continuation of this work, we carried out fully three-dimensional nonlinear simulations of inertia-gravity waves perturbed by their leading primary and secondary instabilities. The direct numerical simulation (DNS) was made tractable by restricting the domain size to the dominant scales selected by the linear analyses. The study includes both convectively stable and unstable waves. To the best of our knowledge, this is the first fully three-dimensional nonlinear direct numerical simulation of inertia-gravity waves at realistic Reynolds numbers with complete resolution of the smallest turbulence scales. Previous simulations either were restricted to high frequency gravity waves (e. g. Fritts et al. [3]), or the ratio N/f was artificially reduced (e. g. Lelong & Dunkerton [4]). The present simulations give us insight into the three-dimensional breaking process as well as the emerging turbulence. We assess the possibility of reducing the computational costs of three-dimensional simulations by using an implicit turbulence subgrid-scale parametrization based on the Adaptive Local Deconvolution Method (ALDM) for stratified turbulence [5]. In addition, we have performed ensembles of nonlinear 2.5-dimensional DNS, like those in Achatz [1] but with a small amount of noise superposed to the initial state, and compared the results with coarse-resolution simulations using either ALDM as well as with standard LES schemes. We found that the results of the models with parametrized turbulence, which are orders of magnitude more computationally economical than the DNS, compare favorably with the DNS in terms of the decay of the wave amplitude with time (the quantity most important for application to gravity-wave drag parametrization) suggesting that they may be trusted in future simulations of gravity wave breaking.

Geophysical Analysis of Major Geothermal Anomalies in Romania

NASA Astrophysics Data System (ADS)

Panea, Ionelia; Mocanu, Victor

2017-11-01

The Romanian segment of the Eastern Pannonian Basin and the Moesian Platform are known for their geothermal and hydrocarbon-bearing structures. We used seismic, gravity, and geothermal data to analyze the geothermal behavior in the Oradea and Timisoara areas, from the Romanian segment of Eastern Pannonian Basin, and the Craiova-Bals-Optasi area, from the Moesian Platform. We processed 22 seismic reflection data sets recorded in the Oradea and Timisoara areas to obtain P-wave velocity distributions and time seismic sections. The P-wave velocity distributions correlate well with the structural trends observed along the seismic lines. We observed a good correlation between the high areas of crystalline basement seen on the time seismic sections and the high heat flow and gravity-anomaly values. For the Craiova-Bals-Optasi area, we computed a three-dimensional (3D) temperature model using calculated and measured temperature and geothermal gradient values in wells with an irregular distribution on the territory. The high temperatures from the Craiova-Bals-Optasi area correlate very well with the uplifted basement blocks seen on the time seismic sections and high gravity-anomaly values.

Status of MTP Data Analysis for TCSP

NASA Technical Reports Server (NTRS)

Mahoney, Michael J.

2006-01-01

Topics covered include: a) MTP temperature calibration and data analysis; b) Background for interpreting MTP data; c) Large amplitude temperature structure; d) Gravity waves (GWs) in MTP data; and e) Subsidence over hurricanes.

A thermosphere-ionosphere-mesosphere-electrodynamic general circulation model (time-GCM): Equinox solar cycle minimum simulations (30-500 km)

NASA Technical Reports Server (NTRS)

Roble, R. G.; Ridley, E. C.

1994-01-01

A new simulation model of the mesosphere, thermosphere, and ionosphere with coupled electrodynamics has been developed and used to calculate the global circulation, temperature and compositional structure between 30-500 km for equinox, solar cycle minimum, geomagnetic quiet conditions. The model incorporates all of the features of the National Center for Atmospheric Research (NCAR) thermosphere-ionosphere- electrodynamics general circulation model (TIE-GCM) but the lower boundary has been extended downward from 97 to 30 km (10 mb) and it includes the physical and chemical processes appropriate for the mesosphere and upper stratosphere. The first simulation used Rayleigh friction to represent gravity wave drag in the middle atmosphere and although it was able to close the mesospheric jets it severely damped the diurnal tide. Reduced Rayleigh friction allowed the tide to penetrate to thermospheric heights but did not close the jets. A gravity wave parameterization developed by Fritts and Lu (1993) allows both features to exist simultaneously with the structure of tides and mean flow dependent upon the strength of the gravity wave source. The model calculates a changing dynamic structure with the mean flow and diurnal tide dominant in the mesosphere, the in-situ generated semi-diurnal tide dominating the lower thermosphere and an in-situ generated diurnal tide in the upper thermosphere. The results also show considerable interaction between dynamics and composition, especially atomic oxygen between 85 and 120 km.

Ionospheric acoustic and gravity wave activity above low-latitude thunderstorms

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

Lay, Erin Hoffmann

In this report, we study the correlation between thunderstorm activity and ionospheric gravity and acoustic waves in the low-latitude ionosphere. We use ionospheric total electron content (TEC) measurements from the Low Latitude Ionospheric Sensor Network (LISN) and lightning measurements from the World- Wide Lightning Location Network (WWLLN). We find that ionospheric acoustic waves show a strong diurnal pattern in summer, peaking in the pre-midnight time period. However, the peak magnitude does not correspond to thunderstorm area, and the peak time is significantly after the peak in thunderstorm activity. Wintertime acoustic wave activity has no discernable pattern in these data. Themore » coverage area of ionospheric gravity waves in the summer was found to increase with increasing thunderstorm activity. Wintertime gravity wave activity has an observable diurnal pattern unrelated to thunderstorm activity. These findings show that while thunderstorms are not the only, or dominant source of ionospheric perturbations at low-latitudes, they do have an observable effect on gravity wave activity and could be influential in acoustic wave activity.« less

On the detection and attribution of gravity waves generated by the 20 March 2015 solar eclipse

PubMed Central

2016-01-01

Internal gravity waves are generated as adjustment radiation whenever a sudden change in forcing causes the atmosphere to depart from its large-scale balanced state. Such a forcing anomaly occurs during a solar eclipse, when the Moon’s shadow cools part of the Earth’s surface. The resulting atmospheric gravity waves are associated with pressure and temperature perturbations, which in principle are detectable both at the surface and aloft. In this study, surface pressure and temperature data from two UK sites at Reading and Lerwick are examined for eclipse-driven gravity wave perturbations during the 20 March 2015 solar eclipse over northwest Europe. Radiosonde wind data from the same two sites are also analysed using a moving parcel analysis method, to determine the periodicities of the waves aloft. On this occasion, the perturbations both at the surface and aloft are found not to be confidently attributable to eclipse-driven gravity waves. We conclude that the complex synoptic weather conditions over the UK at the time of this particular eclipse helped to mask any eclipse-driven gravity waves. This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’. PMID:27550763

On the detection and attribution of gravity waves generated by the 20 March 2015 solar eclipse.

PubMed

Marlton, G J; Williams, P D; Nicoll, K A

2016-09-28

Internal gravity waves are generated as adjustment radiation whenever a sudden change in forcing causes the atmosphere to depart from its large-scale balanced state. Such a forcing anomaly occurs during a solar eclipse, when the Moon's shadow cools part of the Earth's surface. The resulting atmospheric gravity waves are associated with pressure and temperature perturbations, which in principle are detectable both at the surface and aloft. In this study, surface pressure and temperature data from two UK sites at Reading and Lerwick are examined for eclipse-driven gravity wave perturbations during the 20 March 2015 solar eclipse over northwest Europe. Radiosonde wind data from the same two sites are also analysed using a moving parcel analysis method, to determine the periodicities of the waves aloft. On this occasion, the perturbations both at the surface and aloft are found not to be confidently attributable to eclipse-driven gravity waves. We conclude that the complex synoptic weather conditions over the UK at the time of this particular eclipse helped to mask any eclipse-driven gravity waves.This article is part of the themed issue 'Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse'. © 2016 The Authors.

Planetesimal formation in self-gravitating discs - the effects of particle self-gravity and back-reaction

NASA Astrophysics Data System (ADS)

Gibbons, P. G.; Mamatsashvili, G. R.; Rice, W. K. M.

2014-07-01

We study particle dynamics in self-gravitating gaseous discs with a simple cooling law prescription via two-dimensional simulations in the shearing sheet approximation. It is well known that structures arising in the gaseous component of the disc due to a gravitational instability can have a significant effect on the evolution of dust particles. Previous results have shown that spiral density waves can be highly efficient at collecting dust particles, creating significant local overdensities of particles. The degree of such concentrations has been shown to be dependent on two parameters: the size of the dust particles and the rate of gas cooling. We expand on these findings, including the self-gravity of dust particles, to see how these particle overdensities evolve. We use the PENCIL code to solve the local shearing sheet equations for gas on a fixed grid together with the equations of motion for solids coupled to the gas through an aerodynamic drag force. We find that the enhancements in the surface density of particles in spiral density wave crests can reach levels high enough to allow the solid component of the disc to collapse under its own self-gravity. This produces many gravitationally bound collections of particles within the spiral structure. The total mass contained in bound structures appears nearly independent of the cooling time, suggesting that the formation of planetesimals through dust particle trapping by self-gravitating density waves may be possible at a larger range of radii within a disc than previously thought. So, density waves due to gravitational instabilities in the early stages of star formation may provide excellent sites for the rapid formation of many large, planetesimal-sized objects.

Density response of the mesospheric sodium layer to gravity wave perturbations

NASA Technical Reports Server (NTRS)

Shelton, J. D.; Gardner, C. S.; Sechrist, C. F., Jr.

1980-01-01

Lidar observations of the mesospheric sodium layer often reveal wavelike features moving through the layer. It is often assumed that these features are a layer density response to gravity waves. Chiu and Ching (1978) described the approximate form of the linear response of atmospheric layers to gravity waves. In this paper, their results are used to predict the response of the sodium layer to gravity waves. These simulations are compared with experimental observations and a good correlation is found between the two. Because of the thickness of the sodium layer and the density gradients found in it, a linear model of the layer response is not always adequate to describe gravity wave-sodium layer interactions. Inclusion of nonlinearities in the layer response is briefly discussed. Experimental data is seen to contain features consistent with the predicted nonlinearities.

A Simple Theory of Capillary-Gravity Wave Turbulence

NASA Technical Reports Server (NTRS)

Glazman, Roman E.

1995-01-01

Employing a recently proposed 'multi-wave interaction' theory, inertial spectra of capillary gravity waves are derived. This case is characterized by a rather high degree of nonlinearity and a complicated dispersion law. The absence of scale invariance makes this and some other problems of wave turbulence (e.g., nonlinear inertia gravity waves) intractable by small-perturbation techniques, even in the weak-turbulence limit. The analytical solution obtained in the present work for an arbitrary degree of nonlinearity is shown to be in reasonable agreement with experimental data. The theory explains the dependence of the wave spectrum on wind input and describes the accelerated roll-off of the spectral density function in the narrow sub-range separating scale-invariant regimes of purely gravity and capillary waves, while the appropriate (long- and short-wave) limits yield power laws corresponding to the Zakharov-Filonenko and Phillips spectra.

Geophysical Exploration Technologies for the Deep Lithosphere Research: An Education Materials for High School Students

NASA Astrophysics Data System (ADS)

Xu, H.; Xu, C.; Luo, S.; Chen, H.; Qin, R.

2012-12-01

The science of Geophysics applies the principles of physics to study of the earth. Geophysical exploration technologies include the earthquake seismology, the seismic reflection and refraction methods, the gravity method, the magnetic method and the magnetotelluric method, which are used to measure the interior material distribution, their structure and the tectonics in the lithosphere of the earth. Part of the research project in SinoProbe-02-06 is to develop suitable education materials for carton movies targeting the high school students and public. The carton movies include five parts. The first part includes the structures of the earth's interior and variation in their physical properties that include density, p-wave, s-wave and so on, which are the fundamentals of the geophysical exploration technologies. The second part includes the seismology that uses the propagation of elastic waves through the earth to study the structure and the material distribution of the earth interior. It can be divided into earthquake seismology and artifice seismics commonly using reflection and refraction. The third part includes the magnetic method. Earth's magnetic field (also known as the geomagnetic field)extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun. The aim of magnetic survey is to investigate subsurface geology on the basis of anomalies in the Earth's magnetic field resulting from the magnetic properties of the underlying rocks. The magnetic method in the lithosphere attempts to use magnetic disturbance to analyse the regional geological structure and the magnetic boundaries of the crust. The fourth part includes the gravity method. A gravity anomaly results from the inhomogeneous distribution of density of the Earth. Usually gravity anomalies contain superposed anomalies from several sources. The long wave length anomalies due to deep density contrasts are called regional anomalies. They are important for understanding the large-scale structure of the earth's crust under major geographic features, such as mountain ranges, oceanic ridges and subduction zones. Short wave length residual anomalies are due to shallow anomalous masses that may be of interest for commercial exploitation. The last part is the magnetotellurics (MT), which is an electromagnetic geophysical method of imaging the earth's subsurface by measuring natural variations of electrical and magnetic fields at the Earth's surface. The long-period MT technique is used to exploration deep crustal. MT has been used to investigate the distribution of silicate melts in the Earth's mantle and crust and to better understand the plate-tectonic processes.

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.

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.

Observations and a model of undertow over the inner continental shelf

USGS Publications Warehouse

Lentz, Steven J.; Fewings, Melanie; Howd, Peter; Fredericks, Janet; Hathaway, Kent

2008-01-01

Onshore volume transport (Stokes drift) due to surface gravity waves propagating toward the beach can result in a compensating Eulerian offshore flow in the surf zone referred to as undertow. Observed offshore flows indicate that wave-driven undertow extends well offshore of the surf zone, over the inner shelves of Martha’s Vineyard, Massachusetts, and North Carolina. Theoretical estimates of the wave-driven offshore transport from linear wave theory and observed wave characteristics account for 50% or more of the observed offshore transport variance in water depths between 5 and 12 m, and reproduce the observed dependence on wave height and water depth.During weak winds, wave-driven cross-shelf velocity profiles over the inner shelf have maximum offshore flow (1–6 cm s−1) and vertical shear near the surface and weak flow and shear in the lower half of the water column. The observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the surf zone. Instead, the vertical structure is similar to the Stokes drift velocity profile but with the opposite direction. This vertical structure is consistent with a dynamical balance between the Coriolis force associated with the offshore flow and an along-shelf “Hasselmann wave stress” due to the influence of the earth’s rotation on surface gravity waves. The close agreement between the observed and modeled profiles provides compelling evidence for the importance of the Hasselmann wave stress in forcing oceanic flows. Summer profiles are more vertically sheared than either winter profiles or model profiles, for reasons that remain unclear.

Studies of high latitude mesospheric turbulence by radar and rocket. I - Energy deposition and wave structure

NASA Technical Reports Server (NTRS)

Goldberg, R. A.; Fritts, D. C.; Chou, H.-G.; Schmidlin, F. J.; Barcus, J. R.

1988-01-01

The origin of wintertime mesospheric echoes observed with the mesosphere-stratosphere-troposphere radar at Poker Flat, Alaska, was studied by probing the mesosphere with in situ rocket measurements during echo occurrences in the early spring, 1985. Within the height range 65-75 km, the structure of the large scale wave field was identified. In this region, a gravity wave with a vertical wavelength of about 2 km was found superimposed on a wave with a larger amplitude and a vertical wavelength of about 6.6 km. Because of the close correlation between the smaller amplitude wave and the modulation observed in the S/N profiles, it is concluded that the smaller wave was dominant in generating turbulence within the middle atmosphere.

Experimental investigation of gravity wave turbulence and of non-linear four wave interactions..

NASA Astrophysics Data System (ADS)

Berhanu, Michael

2017-04-01

Using the large basins of the Ecole Centrale de Nantes (France), non-linear interactions of gravity surface waves are experimentally investigated. In a first part we study statistical properties of a random wave field regarding the insights from the Wave Turbulence Theory. In particular freely decaying gravity wave turbulence is generated in a closed basin. No self-similar decay of the spectrum is observed, whereas its Fourier modes decay first as a time power law due to nonl-inear mechanisms, and then exponentially due to linear viscous damping. We estimate the linear, non-linear and dissipative time scales to test the time scale separation. By estimation of the mean energy flux from the initial decay of wave energy, the Kolmogorov-Zakharov constant of the weak turbulence theory is evaluated. In a second part, resonant interactions of oblique surface gravity waves in a large basin are studied. We generate two oblique waves crossing at an acute angle. These mother waves mutually interact and give birth to a resonant wave whose properties (growth rate, resonant response curve and phase locking) are fully characterized. All our experimental results are found in good quantitative agreement with four-wave interaction theory. L. Deike, B. Miquel, P. Gutiérrez, T. Jamin, B. Semin, M. Berhanu, E. Falcon and F. Bonnefoy, Role of the basin boundary conditions in gravity wave turbulence, Journal of Fluid Mechanics 781, 196 (2015) F. Bonnefoy, F. Haudin, G. Michel, B. Semin, T. Humbert, S. Aumaître, M. Berhanu and E. Falcon, Observation of resonant interactions among surface gravity waves, Journal of Fluid Mechanics (Rapids) 805, R3 (2016)

Tsunami and infragravity waves impacting Antarctic ice shelves

NASA Astrophysics Data System (ADS)

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

2017-07-01

The responses of the Ross Ice Shelf (RIS) to the 16 September 2015 8.3 (Mw) Chilean earthquake tsunami (>75 s period) and to oceanic infragravity (IG) waves (50-300 s period) were recorded by a broadband seismic array deployed on the RIS from November 2014 to November 2016. Here we show that tsunami and IG-generated signals within the RIS propagate at gravity wave speeds (˜70 m/s) as water-ice coupled flexural-gravity waves. IG band signals show measureable attenuation away from the shelf front. The response of the RIS to Chilean tsunami arrivals is compared with modeled tsunami forcing to assess ice shelf flexural-gravity wave excitation by very long period (VLP; >300 s) gravity waves. Displacements across the RIS are affected by gravity wave incident direction, bathymetry under and north of the shelf, and water layer and ice shelf thicknesses. Horizontal displacements are typically about 10 times larger than vertical displacements, producing dynamical extensional motions that may facilitate expansion of existing fractures. VLP excitation is continuously observed throughout the year, with horizontal displacements highest during the austral winter with amplitudes exceeding 20 cm. Because VLP flexural-gravity waves exhibit no discernable attenuation, this energy must propagate to the grounding zone. Both IG and VLP band flexural-gravity waves excite mechanical perturbations of the RIS that likely promote tabular iceberg calving, consequently affecting ice shelf evolution. Understanding these ocean-excited mechanical interactions is important to determine their effect on ice shelf stability to reduce uncertainty in the magnitude and rate of global sea level rise.

Wave theory in rotating systems: Schrödinger equations bridge the gaps between the equatorial β-plane and the spherical earth

NASA Astrophysics Data System (ADS)

Paldor, N.

2017-12-01

The concise and elegant wave theory developed on the equatorial β-plane by Matsuno (1966, M66 hereafter) is based on the formulation of a Schrödinger equation associated with the governing Linear Rotating Shallow Water Equations (LRSWE). The theory yields explicit expressions for the dispersion relations and meridional amplitude structures of all zonally propagating waves - Rossby, Inertia-Gravity, Kelvin and Yanai. In contrast, the spherical wave theory of Longuet-Higgins (1968) is a collection of asymptotic expansions in many sub-ranges e.g. large, small (and even negative) Lamb Number; high and low frequency; low-latitudes, etc. that rests upon extensive numerical solutions of several Ordinary Differential Equations. The difference between the two theories is highlighted by their lengths. The essential elements of the former planar study are completely revealed in just 3-4 pages including the derivation of explicit formulae for the phase speeds and amplitude meridional structures. In comtrast, the latter spherical theory contains 97 pages and the results of the numerical calculations are summarized in 30 pages of tables filled with numerical values and about 31 figures, each of which containing many separate curves! In my talk I will re-visit the wave problem on a sphere by developing several Schrödinger equations that approximate the governing eigenvalue equation associated with zonally propagating waves. Each of the Schrödinger equations approximates the original second order Ordinary Differential Equation in a different range of the 3 parameters: Lamb-Number, frequency and zonal wavenumber. As in M66, each of the Schrödinger equations yields explicit expressions for the dispersion relations and meridional amplitude structure of Rossby and Inertia-Gravity waves. In addition, the analysis shows that Yanai wave exists on a sphere even tough the zonal velocity is regular everywhere there (in contrast to the β-plane where the zonal velocity is singular everywhere) and that Kelvin waves do not exist as a separate mode (but the eastward propagating n=0 Inertia-Gravity is nearly non-dispersive). References Longuet-Higgins, M. S. Phil. Trans. Roy. Soc. London; 262, 511-607; 1968 Matsuno, T.; J. Met. Soc. Japan. 44(1), 25-43; 1966

Advanced Multivariate Inversion Techniques for High Resolution 3D Geophysical Modeling (Invited)

NASA Astrophysics Data System (ADS)

Maceira, M.; Zhang, H.; Rowe, C. A.

2009-12-01

We focus on the development and application of advanced multivariate inversion techniques to generate a realistic, comprehensive, and high-resolution 3D model of the seismic structure of the crust and upper mantle that satisfies several independent geophysical datasets. Building on previous efforts of joint invesion using surface wave dispersion measurements, gravity data, and receiver functions, we have added a fourth dataset, seismic body wave P and S travel times, to the simultaneous joint inversion method. We present a 3D seismic velocity model of the crust and upper mantle of northwest China resulting from the simultaneous, joint inversion of these four data types. Surface wave dispersion measurements are primarily sensitive to seismic shear-wave velocities, but at shallow depths it is difficult to obtain high-resolution velocities and to constrain the structure due to the depth-averaging of the more easily-modeled, longer-period surface waves. Gravity inversions have the greatest resolving power at shallow depths, and they provide constraints on rock density variations. Moreover, while surface wave dispersion measurements are primarily sensitive to vertical shear-wave velocity averages, body wave receiver functions are sensitive to shear-wave velocity contrasts and vertical travel-times. Addition of the fourth dataset, consisting of seismic travel-time data, helps to constrain the shear wave velocities both vertically and horizontally in the model cells crossed by the ray paths. Incorporation of both P and S body wave travel times allows us to invert for both P and S velocity structure, capitalizing on empirical relationships between both wave types’ seismic velocities with rock densities, thus eliminating the need for ad hoc assumptions regarding the Poisson ratios. Our new tomography algorithm is a modification of the Maceira and Ammon joint inversion code, in combination with the Zhang and Thurber TomoDD (double-difference tomography) program.

Gravity Waves and Mesospheric Clouds in the Summer Middle Atmosphere: A Comparison of Lidar Measurements and Ray Modeling of Gravity Waves Over Sondrestrom, Greenland

NASA Technical Reports Server (NTRS)

Gerrard, Andrew J.; Kane, Timothy J.; Eckermann, Stephen D.; Thayer, Jeffrey P.

2004-01-01

We conducted gravity wave ray-tracing experiments within an atmospheric region centered near the ARCLITE lidar system at Sondrestrom, Greenland (67N, 310 deg E), in efforts to understand lidar observations of both upper stratospheric gravity wave activity and mesospheric clouds during August 1996 and the summer of 2001. The ray model was used to trace gravity waves through realistic three-dimensional daily-varying background atmospheres in the region, based on forecasts and analyses in the troposphere and stratosphere and climatologies higher up. Reverse ray tracing based on upper stratospheric lidar observations at Sondrestrom was also used to try to objectively identify wave source regions in the troposphere. A source spectrum specified by reverse ray tracing experiments in early August 1996 (when atmospheric flow patterns produced enhanced transmission of waves into the upper stratosphere) yielded model results throughout the remainder of August 1996 that agreed best with the lidar observations. The model also simulated increased vertical group propagation of waves between 40 km and 80 km due to intensifying mean easterlies, which allowed many of the gravity waves observed at 40 km over Sondrestrom to propagate quasi-vertically from 40-80 km and then interact with any mesospheric clouds at 80 km near Sondrestrom, supporting earlier experimentally-inferred correlations between upper stratospheric gravity wave activity and mesospheric cloud backscatter from Sondrestrom lidar observations. A pilot experiment of real-time runs with the model in 2001 using weather forecast data as a low-level background produced less agreement with lidar observations. We believe this is due to limitations in our specified tropospheric source spectrum, the use of climatological winds and temperatures in the upper stratosphere and mesosphere, and missing lidar data from important time periods.

Initial results from SKiYMET meteor radar at Thumba (8.5°N, 77°E): 2. Gravity wave observations in the MLT region

NASA Astrophysics Data System (ADS)

Kumar, Karanam Kishore; Antonita, T. Maria; Shelbi, S. T.

2007-12-01

In the present communication, allSKy interferometric METeor (SKiYMET) radar observations of gravity wave activity in the mesosphere lower thermosphere (MLT) region over Thumba (8.5°N, 77°E) are presented. The present meteor radar system provides hourly zonal and meridional winds in the MLT region, which can be readily used for studying the tides, planetary waves, gravity waves of periods 2-6 hours, and other long period oscillations in this region. However, these hourly winds are not sufficient for studying short period gravity waves having periods less than an hour, which demand high temporal resolution measurements. Even though the winds are estimated on an hourly basis, information such as zenith angle, azimuth angle, and radial velocity of each detected meteor are archived. Using these details of the meteor, an algorithm is developed to obtain the 15-min temporal resolution wind data. The output of the algorithm is compared with hourly wind data, and it showed a good agreement during the high meteor shower periods. Most of the times high meteor counts are observed during late night and early morning hours (local) over this latitude. Continuous wind measurements during the high meteor shower periods are used for studying the gravity wave activity in the MLT region. As the wave activity is intermittent and nonstationary, wavelet analysis has been used for delineating the wave features. The results showed the upward propagating intermittent gravity waves with periods 1-2 and 4-5 hours. The new aspect of the present communication is the usage of meteor radar for gravity wave studies for the first time over this latitude and studying their seasonal variability.

Lunar gravity pattern: two modes of granulation

NASA Astrophysics Data System (ADS)

Kochemasov, G.

The Lunar Prospector's lunar gravity map [1] clearly shows two prevailing modes of granulation. Most abundant one evenly covering the whole surface is represented by even-sized shoulder-to-shoulder grains about 100 km in diameter (πR/60 -πR/48). This background is interrupted by a few much greater grains with a characteristic diameter about or less than πR/4 (hundreds to thousand km). Haw to explain this pattern? We now know that "orbits make structures"[2 & others]. This follows from the facts that all celestial bodies move in non-round (elliptical, parabolic) orbits and rotate. Cyclic movements in non-round orbits with periodically changing accelerations arouse inertia-gravity forces exiting warping waves of stationary character and 4 ortho- and diagonal directions. Interferences of these waves produce tectonic blocks of various sizes depending on wavelengths. Along with the fundamental wave1making ubiquitous dichotomy and its overtones (mainly the first one wave2) making tectonic sectors, every body is subjected to a warping action of waves whose lengths are strictly proportional to bodies orbital periods or inversely proportional to their orbital frequencies. These individual waves are responsible for ubiquitous tectonic granulation. Most known from the thirties of the 20th century is the solar supergranulation with the characteristic granule size about 30000 km (πR/60) corresponding to its orbital frequency around the center of the solar system about 1/1 month. But the same orbital frequency has the Moon around Earth. So, one might expect to find similar granulation in the lunar crust. This theoretical assumption was perfectly confirmed when a lunar gravity map was created [1]. Thus, the Sun's 30000 km supergranules are the same as the Moon's 100 km granules. Farther from Sun, the terrestrial planets orbital frequencies diminish and concordantly granule sizes increase: Mercury πR/16, Venus πR/6, Earth πR/4, Mars πR/2, asteroids πR/1. This sizes are found on available images of the planets and asteroids [3]. On the Mercury's surface they are best exposed by radar from Earth as the shoulder-to-shoulder grains about 500 km across. On Venus as "blobs" about 3000 km in diameter. On Earth as well known superstructures of the AR cratons about 5000 km in diameter and similarly sized ring structures on other terrains. Recently, in August 2005 the spacecraft Mars Reconnaissance Orbiter took an Earth's picture from a distance of 1170000 km (PIA04159) where are well visible round spots exactly πR/4 in diameter (4 spots in an arc long πR of the lighted-up crescent). The martian 4 granules in the equator produced by 2 waves explain its oblong shape known long ago but not explained. And finally, one wave long 2πR inscribed in an asteroid's outline makes it oblong and convexo-concave in shape. This particular shape of asteroids was not formerly explained. Now, back to the Moon. As a satellite it has two 1 orbits in our solar system. One with the frequency 1/1month and another with 1/1year. If the first one produces granules πR/60 (πR/48), then the second one should has granules πR/4 similar to Earth. And they or their cores are visible on the gravity map of the Moon. By this way based on the comparative wave planetology we can explain similar structurization patterns of two discs reduced to the same size: the lunar and solar discs. Moreover, the comparative wave planetology for the first time arranges structures from Sun to asteroids showing that one type of wave structurization can be applied to a huge plasma star (aster) and to a small asteroid using two fundamental properties of all celestial bodies notwithstanding their sizes, masses, densities, chemical compositions, physical states: namely, movements in non-round keplerian orbits and rotations. References: [1] Konopliv A.S. et al. (1998) Improved gravity field of the Moon from Lunar Prospector // Science, v.281, # 5382, 1476-1480; [2] Kochemasov G.G. (2000) Orbiting frequency modulation in Solar system and its imprint in shapes and structures of celestial bodies // Vernadsky-Brown microsymposium 32 on Comparative planetology, Oct. 9-11, 2000, Moscow, Russia, Abstracs, 88-89; [3] Kochemasov G.G.(1992) Concerted wave supergranulation of the solar system bodies // 16th Russian-American microsymposium on planetology, Abstracts, Moscow, Vernadsky Inst. (GEOKHI), 36- 37. 2

Recent Developments in Gravity-Wave Effects in Climate Models and the Global Distribution of Gravity-Wave Momentum Flux from Observations and Models

DTIC Science & Technology

2010-07-01

by changes in wind and stability to a vertical wavelength lying outside the observable range. Gravity-wave parametrizations also represent intermit ...tropopause variability. J. Atmos. Sci. 65: 1817–1837. Salby ML. 1982. Sampling theory for asynoptic satellite observations. Part II: Fast Fourier synoptic

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.

The Role of Gravity Waves in the Formation and Organization of Clouds during TWPICE

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

Reeder, Michael J.; Lane, Todd P.; Hankinson, Mai Chi Nguyen

2013-09-27

All convective clouds emit gravity waves. While it is certain that convectively-generated waves play important parts in determining the climate, their precise roles remain uncertain and their effects are not (generally) represented in climate models. The work described here focuses mostly on observations and modeling of convectively-generated gravity waves, using the intensive observations from the DoE-sponsored Tropical Warm Pool International Cloud Experiment (TWP-ICE), which took place in Darwin, from 17 January to 13 February 2006. Among other things, the research has implications the part played by convectively-generated gravity waves in the formation of cirrus, in the initiation and organization ofmore » further convection, and in the subgrid-scale momentum transport and associated large-scale stresses imposed on the troposphere and stratosphere. The analysis shows two groups of inertia-gravity waves are detected: group L in the middle stratosphere during the suppressed monsoon period, and group S in the lower stratosphere during the monsoon break period. Waves belonging to group L propagate to the south-east with a mean intrinsic period of 35 h, and have vertical and horizontal wavelengths of about 5-6 km and 3000-6000 km, respectively. Ray tracing calculations indicate that these waves originate from a deep convective region near Indonesia. Waves belonging to group S propagate to the south-south-east with an intrinsic period, vertical wavelength and horizontal wavelength of about 45 h, 2 km and 2000-4000 km, respectively. These waves are shown to be associated with shallow convection in the oceanic area within about 1000 km of Darwin. The intrinsic periods of high-frequency waves are estimated to be between 20-40 minutes. The high-frequency wave activity in the stratosphere, defined by mass-weighted variance of the vertical motion of the sonde, has a maximum following the afternoon local convection indicating that these waves are generated by local convection. The wave activity is strongest in the lower stratosphere below 22 km and, during the suppressed monsoon period, is modulated with a 3-4-day period. The concentration of the wave activity in the lower stratosphere is consistent with the properties of the environment in which these waves propagate, whereas its 3-4-day modulation is explained by the variation of the convection activity in the TWP-ICE domain. At low rainfall intensity the wave activity increases as rainfall intensity increases. At high values of rainfall intensity, however, the wave activity associated with deep convective clouds is independent of the rainfall intensity. The convection and gravity waves observed during TWP-ICE are simulated with the Weather Research and Forecasting (WRF) Model. These simulations are compared with radiosonde observations described above and are used to determine some of the properties of convectively generated gravity waves. The gravity waves appear to be well simulated by the model. The model is used to explore the relationships between the convection, the gravity waves and cirrus.« less

Directional asymmetry of the nonlinear wave phenomena in a three-dimensional granular phononic crystal under gravity.

PubMed

Merkel, A; Tournat, V; Gusev, V

2014-08-01

We report the experimental observation of the gravity-induced asymmetry for the nonlinear transformation of acoustic waves in a noncohesive granular phononic crystal. Because of the gravity, the contact precompression increases with depth inducing space variations of not only the linear and nonlinear elastic moduli but also of the acoustic wave dissipation. We show experimentally and explain theoretically that, in contrast to symmetric propagation of linear waves, the amplitude of the nonlinearly self-demodulated wave depends on whether the propagation of the waves is in the direction of the gravity or in the opposite direction. Among the observed nonlinear processes, we report frequency mixing of the two transverse-rotational modes belonging to the optical band of vibrations and propagating with negative phase velocities, which results in the excitation of a longitudinal wave belonging to the acoustic band of vibrations and propagating with positive phase velocity. We show that the measurements of the gravity-induced asymmetry in the nonlinear acoustic phenomena can be used to compare the in-depth distributions of the contact nonlinearity and of acoustic absorption.

Imaging the Chicxulub central crater zone from large scale seismic acoustic wave propagation and gravity modeling

NASA Astrophysics Data System (ADS)

Fucugauchi, J. U.; Ortiz-Aleman, C.; Martin, R.

2017-12-01

Large complex craters are characterized by central uplifts that represent large-scale differential movement of deep basement from the transient cavity. Here we investigate the central sector of the large multiring Chicxulub crater, which has been surveyed by an array of marine, aerial and land-borne geophysical methods. Despite high contrasts in physical properties,contrasting results for the central uplift have been obtained, with seismic reflection surveys showing lack of resolution in the central zone. We develop an integrated seismic and gravity model for the main structural elements, imaging the central basement uplift and melt and breccia units. The 3-D velocity model built from interpolation of seismic data is validated using perfectly matched layer seismic acoustic wave propagation modeling, optimized at grazing incidence using shift in the frequency domain. Modeling shows significant lack of illumination in the central sector, masking presence of the central uplift. Seismic energy remains trapped in an upper low velocity zone corresponding to the sedimentary infill, melt/breccias and surrounding faulted blocks. After conversion of seismic velocities into a volume of density values, we use massive parallel forward gravity modeling to constrain the size and shape of the central uplift that lies at 4.5 km depth, providing a high-resolution image of crater structure.The Bouguer anomaly and gravity response of modeled units show asymmetries, corresponding to the crater structure and distribution of post-impact carbonates, breccias, melt and target sediments

No further gravitational wave modes in F(T) gravity

NASA Astrophysics Data System (ADS)

Bamba, Kazuharu; Capozziello, Salvatore; De Laurentis, Mariafelicia; Nojiri, Shin'ichi; Sáez-Gómez, Diego

2013-11-01

We explore the possibility of further gravitational wave modes in F(T) gravity, where T is the torsion scalar in teleparallelism. It is explicitly demonstrated that gravitational wave modes in F(T) gravity are equivalent to those in General Relativity. This result is achieved by calculating the Minkowskian limit for a class of analytic function of F(T). This consequence is also confirmed by the preservative analysis around the flat background in the weak field limit with the scalar-tensor representation of F(T) gravity.

Megaquakes, prograde surface waves and urban evolution

NASA Astrophysics Data System (ADS)

Lomnitz, C.; Castaños, H.

2013-05-01

Cities grow according to evolutionary principles. They move away from soft-ground conditions and avoid vulnerable types of structures. A megaquake generates prograde surface waves that produce unexpected damage in modern buildings. The examples (Figs. 1 and 2) were taken from the 1985 Mexico City and the 2010 Concepción, Chile megaquakes. About 400 structures built under supervision according to modern building codes were destroyed in the Mexican earthquake. All were sited on soft ground. A Rayleigh wave will cause surface particles to move as ellipses in a vertical plane. Building codes assume that this motion will be retrograde as on a homogeneous elastic halfspace, but soft soils are intermediate materials between a solid and a liquid. When Poisson's ratio tends to ν→0.5 the particle motion turns prograde as it would on a homogeneous fluid halfspace. Building codes assume that the tilt of the ground is not in phase with the acceleration but we show that structures on soft ground tilt into the direction of the horizontal ground acceleration. The combined effect of gravity and acceleration may destabilize a structure when it is in resonance with its eigenfrequency. Castaños, H. and C. Lomnitz, 2013. Charles Darwin and the 1835 Chile earthquake. Seismol. Res. Lett., 84, 19-23. Lomnitz, C., 1990. Mexico 1985: the case for gravity waves. Geophys. J. Int., 102, 569-572. Malischewsky, P.G. et al., 2008. The domain of existence of prograde Rayleigh-wave particle motion. Wave Motion 45, 556-564.; Figure 1 1985 Mexico megaquake--overturned 15-story apartment building in Mexico City ; Figure 2 2010 Chile megaquake Overturned 15-story R-C apartment building in Concepción

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.

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.

Can gravity waves significantly impact PSC occurrence in the Antarctic?

NASA Astrophysics Data System (ADS)

McDonald, A. J.; George, S. E.; Woollands, R. M.

2009-11-01

A combination of POAM III aerosol extinction and CHAMP RO temperature measurements are used to examine the role of atmospheric gravity waves in the formation of Antarctic Polar Stratospheric Clouds (PSCs). POAM III aerosol extinction observations and quality flag information are used to identify Polar Stratospheric Clouds using an unsupervised clustering algorithm. A PSC proxy, derived by thresholding Met Office temperature analyses with the PSC Type Ia formation temperature (TNAT), shows general agreement with the results of the POAM III analysis. However, in June the POAM III observations of PSC are more abundant than expected from temperature threshold crossings in five out of the eight years examined. In addition, September and October PSC identified using temperature thresholding is often significantly higher than that derived from POAM III; this observation probably being due to dehydration and denitrification. Comparison of the Met Office temperature analyses with corresponding CHAMP observations also suggests a small warm bias in the Met Office data in June. However, this bias cannot fully explain the differences observed. Analysis of CHAMP data indicates that temperature perturbations associated with gravity waves may partially explain the enhanced PSC incidence observed in June (relative to the Met Office analyses). For this month, approximately 40% of the temperature threshold crossings observed using CHAMP RO data are associated with small-scale perturbations. Examination of the distribution of temperatures relative to TNAT shows a large proportion of June data to be close to this threshold, potentially enhancing the importance of gravity wave induced temperature perturbations. Inspection of the longitudinal structure of PSC occurrence in June 2005 also shows that regions of enhancement are geographically associated with the Antarctic Peninsula; a known mountain wave "hotspot". The latitudinal variation of POAM III observations means that we only observe this region in June-July, and thus the true pattern of enhanced PSC production may continue operating into later months. The analysis has shown that early in the Antarctic winter stratospheric background temperatures are close to the TNAT threshold (and PSC formation), and are thus sensitive to temperature perturbations associated with mountain wave activity near the Antarctic peninsula (40% of PSC formation). Later in the season, and at latitudes away from the peninsula, temperature perturbations associated with gravity waves contribute to about 15% of the observed PSC (a value which corresponds well to several previous studies). This lower value is likely to be due to colder background temperatures already achieving the TNAT threshold unaided. Additionally, there is a reduction in the magnitude of gravity waves perturbations observed as POAM III samples poleward of the peninsula.

The ANGWIN Antarctic Research Program: First Results on Coordinated Trans-Antarctic Gravity Wave Measurements

NASA Astrophysics Data System (ADS)

Taylor, M. J.; Pautet, P. D.; Zhao, Y.; Nakamura, T.; Ejiri, M. K.; Murphy, D. J.; Moffat-Griffin, T.; Kavanagh, A. J.; Takahashi, H.; Wrasse, C. M.

2014-12-01

ANGWIN (ANrctic Gravity Wave Instrument Network) is a new "scientist driven" research program designed to develop and utilize a network of Antarctic atmospheric gravity wave observatories, operated by different nations working together in a spirit of close scientific collaboration. Our research plan has brought together colleagues from several international institutions, all with a common goal to better understand the large "continental-scale" characteristics and impacts of gravity waves on the Mesosphere and Lower Thermosphere (MLT) environment over Antarctica. ANGWIN combines complementary measurements obtained using new and existing aeronomy instrumentation with new modeling capabilities. To date, our activities have focused on developing coordinated airglow image data of gravity waves in the MLT region at the following sites: McMurdo (US), Syowa (Japan), Davis (Australia), Halley (UK), Rothera (UK), and Comandante Ferraz (Brazil). These are all well-established international research stations that are uniformly distributed around the continental perimeter, and together with ongoing measurements at South Pole Station they provide unprecedented coverage of the Antarctic gravity wave field and its variability during the extended polar winter season. This presentation introduces the ANGWIN program and research goals, and presents first results on trans-Antarctic wave propagation using coordinated measurements during the winter season 2011. We also discuss future plans for the development of this exciting program for Antarctic research.

Influence of internal waves on the dispersion and transport of inclined gravity currents

NASA Astrophysics Data System (ADS)

Hogg, C. A. R.; Pietrasz, V. B.; Ouellette, N. T.; Koseff, J. R.

2016-02-01

Brine discharge from desalination facilities presents environmental risks, particularly to benthic organisms. High concentrations of salt and chemical additives, which can be toxic to local ecosystems, are typically mitigated by dilution close to the source. Our laboratory experiments investigate how breaking internal tides can help to dilute gravity currents caused by desalination effluents and direct them away from the benthic layer. In laboratory experiments, internal waves at the pycnocline of an ambient stratification were directed towards a sloping shelf, down which ran a gravity current. The breaking internal waves were seen to increase the proportion of the fluid from the gravity current diverted away from the slope into an intrusion along the pycnocline. In a parametric study, increasing the amplitude of the internal wave was seen to increase the amount of dense fluid in the pycnocline intrusion. The amplitude required to divert the gravity current into the intrusion compares well with an analytical theory that equates the incident energy in the internal wave to the potential energy required to dilute the gravity current. These experimental results suggest that sites of breaking internal waves may be good sites for effluent disposal. Effluent diverted into the intrusion avoids the ecologically sensitive benthic layer.

The role of collective self-gravity in the nonlinear evolution of viscous overstability in Saturn's rings

NASA Astrophysics Data System (ADS)

Lehmann, M.; Schmidt, J.; Salo, H.

2017-09-01

Observational evidence for the presence of axisymmetric periodic micro-structure on length scales of 100m - 200m in Saturn's A and B rings was revealed by several instruments onboard the Cassini mission to Saturn. The structure was seen in radio occultations performed by the Radio Science Subsystem (RSS) (Thomson et al. (2007)) and stellar occultations carried out with the Ultraviolet Imaging Spectrograph (UVIS) (Colwell et al. (2007)), and the Visual and Infrared Mapping Spectrometer (VIMS) (Hedman et al. (2014)). Up to date, this micro-structure is best explained by the viscous overstability, which arises as a spontaneous oscillatory instability in a dense ring, if certain conditions are met, leading to the formation of axisymmetric density waves with wavelengths on the order of 100m. We investigate the influence of collective self-gravity forces on the nonlinear, large scale evolution of the viscous overstability in Saturn's rings. To this end we numerically solve the nonlinear hydrodynamic model equations for a dense ring, including radial self-gravity and employing values for the transport coefficients (such as the ring's viscosity and heat conductivity) derived by salo et al. (2001). We concentrate on ring optical depths of order unity, which are appropriate to model Saturn's dense rings. Furthermore, local N-body simulations, incorporating vertical and radial collective self-gravity forces are performed. Direct particle-particle forces are omitted, which prevents small scale gravitational instabilities (self-gravity wakes) from forming, an approximation that allows us to study long radial scales of some 10 kilometers and to compare directly the hydrodynamic model and the N-body simulations. Our hydrodynamic model results, in the limit of vanishing self-gravity, compare very well with the studies of Latter & Ogilvie (2010) and Rein & Latter (2013). In contrast, for rings with non-vanishing radial self-gravity we find that the wavelengths of saturated overstable wave trains tend to settle close to the frequency minimum of the nonlinear dispersion relation, i.e. the saturation wavelengths decrease with increasing surface mass density of the ring. Good agreement between hydrodynamics and N-body simulations is found for disks with strong radial self-gravity, while the largest deviations occur in the limit of weak self-gravity. The resulting saturation wavelengths of the viscous overstability for moderate and strong radial self-gravity (100m-300m) agree reasonably well with the length scale of the axisymmetric periodic micro structure in Saturn's inner A ring and the B ring, as found by Cassini.

A coupling modulation model of capillary waves from gravity waves: Theoretical analysis and experimental validation

NASA Astrophysics Data System (ADS)

Chen, Pengzhen; Wang, Xiaoqing; Liu, Li; Chong, Jinsong

2016-06-01

According to Bragg theory, capillary waves are the predominant scatterers of high-frequency band (such as Ka-band) microwave radiation from the surface of the ocean. Therefore, understanding the modulation mechanism of capillary waves is an important foundation for interpreting high-frequency microwave remote sensing images of the surface of the sea. In our experiments, we discovered that modulations of capillary waves are significantly larger than the values predicted by the classical theory. Further, analysis shows that the difference in restoring force results in an inflection point while the phase velocity changes from gravity waves region to capillary waves region, and this results in the capillary waves being able to resonate with gravity waves when the phase velocity of the gravity waves is equal to the group velocity of the capillary waves. Consequently, we propose a coupling modulation model in which the current modulates the capillary wave indirectly by modulating the resonant gravity waves, and the modulation of the former is approximated by that of the latter. This model very effectively explains the results discovered in our experiments. Further, based on Bragg scattering theory and this coupling modulation model, we simulate the modulation of normalized radar cross section (NRCS) of typical internal waves and show that the high-frequency bands are superior to the low-frequency bands because of their greater modulation of NRCS and better radiometric resolution. This result provides new support for choice of radar band for observation of wave-current modulation oceanic phenomena such as internal waves, fronts, and shears.

Equatorial Magnetohydrodynamic Shallow Water Waves in the Solar Tachocline

NASA Astrophysics Data System (ADS)

Zaqarashvili, Teimuraz

2018-03-01

The influence of a toroidal magnetic field on the dynamics of shallow water waves in the solar tachocline is studied. A sub-adiabatic temperature gradient in the upper overshoot layer of the tachocline causes significant reduction of surface gravity speed, which leads to trapping of the waves near the equator and to an increase of the Rossby wave period up to the timescale of solar cycles. Dispersion relations of all equatorial magnetohydrodynamic (MHD) shallow water waves are obtained in the upper tachocline conditions and solved analytically and numerically. It is found that the toroidal magnetic field splits equatorial Rossby and Rossby-gravity waves into fast and slow modes. For a reasonable value of reduced gravity, global equatorial fast magneto-Rossby waves (with the spatial scale of equatorial extent) have a periodicity of 11 years, matching the timescale of activity cycles. The solutions are confined around the equator between latitudes ±20°–40°, coinciding with sunspot activity belts. Equatorial slow magneto-Rossby waves have a periodicity of 90–100 yr, resembling the observed long-term modulation of cycle strength, i.e., the Gleissberg cycle. Equatorial magneto-Kelvin and slow magneto-Rossby-gravity waves have the periodicity of 1–2 years and may correspond to observed annual and quasi-biennial oscillations. Equatorial fast magneto-Rossby-gravity and magneto-inertia-gravity waves have periods of hundreds of days and might be responsible for observed Rieger-type periodicity. Consequently, the equatorial MHD shallow water waves in the upper overshoot tachocline may capture all timescales of observed variations in solar activity, but detailed analytical and numerical studies are necessary to make a firm conclusion toward the connection of the waves to the solar dynamo.

A novel method for the extraction of local gravity wave parameters from gridded three-dimensional data: description, validation, and application

NASA Astrophysics Data System (ADS)

Schoon, Lena; Zülicke, Christoph

2018-05-01

For the local diagnosis of wave properties, we develop, validate, and apply a novel method which is based on the Hilbert transform. It is called Unified Wave Diagnostics (UWaDi). It provides the wave amplitude and three-dimensional wave number at any grid point for gridded three-dimensional data. UWaDi is validated for a synthetic test case comprising two different wave packets. In comparison with other methods, the performance of UWaDi is very good with respect to wave properties and their location. For a first practical application of UWaDi, a minor sudden stratospheric warming on 30 January 2016 is chosen. Specifying the diagnostics for hydrostatic inertia-gravity waves in analyses from the European Centre for Medium-Range Weather Forecasts, we detect the local occurrence of gravity waves throughout the middle atmosphere. The local wave characteristics are discussed in terms of vertical propagation using the diagnosed local amplitudes and wave numbers. We also note some hints on local inertia-gravity wave generation by the stratospheric jet from the detection of shallow slow waves in the vicinity of its exit region.

Observations of the Breakdown of Mountain Waves Over the Andes Lidar Observatory at Cerro Pachon on 8/9 July 2012

NASA Astrophysics Data System (ADS)

Hecht, J. H.; Fritts, D. C.; Wang, L.; Gelinas, L. J.; Rudy, R. J.; Walterscheid, R. L.; Taylor, M. J.; Pautet, P. D.; Smith, S.; Franke, S. J.

2018-01-01

Although mountain waves (MWs) are thought to be a ubiquitous feature of the wintertime southern Andes stratosphere, it was not known whether these waves propagated up to the mesopause region until Smith et al. (2009) confirmed their presence via airglow observations. The new Andes Lidar Observatory at Cerro Pachon in Chile provided the opportunity for a further study of these waves. Since MWs have near-zero phase speed, and zero wind lines often occur in the winter upper mesosphere (80 to 100 km altitude) region due to the reversal of the zonal mean and tidal wind, MW breakdown may routinely occur at these altitudes. Here we report on very high spatial/temporal resolution observations of the initiation of MW breakdown in the mesopause region. Because the waves are nearly stationary, the breakdown process was observed over several hours; a much longer interval than has previously been observed for any gravity wave breakdown. During the breakdown process observations were made of initial horseshoe-shaped vortices, leading to successive vortex rings, as is also commonly seen in Direct Numerical Simulations (DNS) of idealized and multiscale gravity wave breaking. Kelvin-Helmholtz instability (KHI) structures were also observed to form. Comparing the structure of observed KHI with the results of existing DNS allowed an estimate of the turbulent kinematic viscosity. This viscosity was found to be around 25 m2/s, a value larger than the nominal viscosity that is used in models.

On the generation of internal wave modes by surface waves

NASA Astrophysics Data System (ADS)

Harlander, Uwe; Kirschner, Ian; Maas, Christian; Zaussinger, Florian

2016-04-01

Internal gravity waves play an important role in the ocean since they transport energy and momentum and the can lead to mixing when they break. Surface waves and internal gravity waves can interact. On the one hand, long internal waves imply a slow varying shear current that modifies the propagation of surface waves. Surface waves generated by the atmosphere can, on the other hand, excite internal waves by nonlinear interaction. Thereby a surface wave packet consisting of two close frequencies can resonate with a low frequency internal wave (Phillips, 1966). From a theoretical point of view, the latter has been studied intensively by using a 2-layer model, i.e. a surface layer with a strong density contrast and an internal layer with a comparable weak density contrast (Ball, 1964; Craig et al., 2010). In the present work we analyse the wave coupling for a continuously stratified fluid using a fully non-linear 2D numerical model (OpenFoam) and compare this with laboratory experiments (see Lewis et al. 1974). Surface wave modes are used as initial condition and the time development of the dominant surface and internal waves are studied by spectral and harmonic analysis. For the simple geometry of a box, the results are compared with analytical spectra of surface and gravity waves. Ball, F.K. 1964: Energy transfer between external and internal gravity waves. J. Fluid Mech. 19, 465. Craig, W., Guyenne, P., Sulem, C. 2010: Coupling between internal and surface waves. Natural Hazards 57, 617-642. Lewis, J.E., Lake, B.M., Ko, D.R.S 1974: On the interaction of internal waves and surfacr gravity waves, J. Fluid Mech. 63, 773-800. Phillips, O.M. 1966: The dynamics of the upper ocean, Cambridge University Press, 336pp.

Absorption of inertia-gravity waves in vertically sheared rotating stratified flows

NASA Astrophysics Data System (ADS)

Millet, C.; Lott, F.

2012-12-01

It is well established that gravity waves have a substantial role on the large-scale atmospheric circulation, particularly in the middle atmosphere. In the present work, we re-examine the reflection and transmission of gravity waves through a critical layer surrounded by two inertial levels for the case of a constant vertically sheared flow. In this configuration, the vertical structure of the disturbance can be described as quasi-geostrophic from the critical layer up to the inertial levels, at which the Doppler-shifted frequency is equal to the Coriolis parameter. Near and beyond these levels, the balanced approximations do not apply and there is a transition from the quasi-geostrophic solution to propagating gravity waves. The three-dimensional disturbance solution is obtained analytically using both an exact method, in terms of hypergeometric functions, and a WKB approximation valid for large Richardson numbers; the latter includes an exponentially small term which captures the radiation feedback in the region between the inertial levels. We first focused on the homogeneous part of the disturbance equations, under the assumption of an unbounded domain. In contrast with past studies which show that there is a finite reflection and did not analyze the transmission (Yamanaka and Tanaka, 1984), we find that the reflection coefficient is too small to be significant and that the transmission coefficient is exactly like in the much simpler non-rotating case analyzed by Booker and Bretherton (1966). Our theoretical predictions are found to be in very good agreement with those obtained by numerically integrating the complete hydrostatic-Boussinesq equations with a small Rayleigh damping. The discrepancies between our results and those in Yamanaka and Tanaka (1984) are related to the fact that the solutions are given in term of multivalued functions and the values of the reflection and transmission coefficients are exponentially small, e.g. quite difficult to cross check numerically. More specifically, we suspect that the differences come from their treatment of the analytic continuations in the matching regions (e.g. the inertial layers). Our results are useful to study the evolution of initial disturbances. As an illustration, we consider the problem of gravity waves generated by potential-vorticity anomalies, a problem that was recently studied in Lott et al. (2013) for an unbounded atmosphere. The vertical structure of the potential-vorticity anomaly is represented by a Dirac distribution localized at the critical level. The disturbance field can be deduced from the homogeneous solutions above and below the critical level, by using suitable jump conditions. It is shown how the inclusion of a boundary condition within the problem, below the potential-vorticity anomaly, changes the amplitude of the radiated gravity wave, especially when the Richardson number is not too large. This process may be related to the occurrence of radiative instability waves in sheared rotating stratified flows.

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.

Seismic Tomography of the Sacramento -- San Joaquin River Delta: Joint P-wave/Gravity and Ambient Noise Methods

NASA Astrophysics Data System (ADS)

Teel, Alexander C.

The Sacramento -- San Joaquin River Delta (SSJRD) is an area that has been identified as having high seismic hazard but has resolution gaps in the seismic velocity models of the area due to a scarcity of local seismic stations and earthquakes. I present new three-dimensional (3D) P-wave velocity (Vp) and S-wave velocity (Vs) models for the SSJRD which fill in the sampling gaps of previous studies. I have created a new 3D seismic velocity model for the SSJRD, addressing an identified need for higher resolution velocity models in the region, using a new joint gravity/body-wave tomography algorithm. I am able to fit gravity and arrival-time residuals jointly using an empirical density-velocity relationship to take advantage of existing gravity data in the region to help fill in the resolution gaps of previous velocity models in the area. I find that the method enhances the ability to resolve the relief of basin structure relative to seismic-only tomography at this location. I find the depth to the basement to be the greatest in the northwest portion of the SSJRD and that there is a plateau in the basement structure beneath the southeast portion of the SSJRD. From my findings I infer that the SSJRD may be prone to focusing effects and basin amplification of ground motion. A 3D, Vs model for the SSJRD and surrounding area was created using ambient noise tomography. The empirical Green's functions are in good agreement with published cross-correlations and match earthquake waveforms sharing similar paths. The group velocity and shear velocity maps are in good agreement with published regional scale models. The new model maps velocity values on a local scale and successfully recovers the basin structure beneath the Delta. From this Vs model I find the maximum depth of the basin to reach approximately 15 km with the Great Valley Ophiolite body rising to a depth of 10 km east of the SSJRD. We consider our basement-depth estimates from the Vp model to be more robust than from the Vs model.

Geometric controls of the flexural gravity waves on the Ross Ice Shelf

NASA Astrophysics Data System (ADS)

Sergienko, O. V.

2017-12-01

Long-period ocean waves, formed locally or at distant sources, can reach sub-ice-shelf cavities and excite coupled motion in the cavity and the ice shelf - flexural gravity waves. Three-dimensional numerical simulations of the flexural gravity waves on the Ross Ice Shelf show that propagation of these waves is strongly controlled by the geometry of the system - the cavity shape, its water-column thickness and the ice-shelf thickness. The results of numerical simulations demonstrate that propagation of the waves is spatially organized in beams, whose orientation is determined by the direction of the of the open ocean waves incident on the ice-shelf front. As a result, depending on the beams orientation, parts of the Ross Ice Shelf experience significantly larger flexural stresses compared to other parts where the flexural gravity beams do not propagate. Very long-period waves can propagate farther away from the ice-shelf front exciting flexural stresses in the vicinity of the grounding line.

Gravity Waves in the Atmosphere: Instability, Saturation, and Transport.

DTIC Science & Technology

1995-11-13

role of gravity wave drag in the extratropical QBO , destabilization of large-scale tropical waves by deep moist convection, and a general theory of equatorial inertial instability on a zonally nonuniform, nonparallel flow.

Analysis of spatial and temporal spectra of liquid film surface in annular gas-liquid flow

NASA Astrophysics Data System (ADS)

Alekseenko, Sergey; Cherdantsev, Andrey; Heinz, Oksana; Kharlamov, Sergey; Markovich, Dmitriy

2013-09-01

Wavy structure of liquid film in annular gas-liquid flow without liquid entrainment consists of fast long-living primary waves and slow short-living secondary waves. In present paper, results of spectral analysis of this wavy structure are presented. Application of high-speed LIF technique allowed us to perform such analysis in both spatial and temporal domains. Power spectra in both domains are characterized by one-humped shape with long exponential tail. Influence of gas velocity, liquid Reynolds number, liquid viscosity and pipe diameter on frequency of the waves is investigated. When gravity effect is much lesser than the shear stress, similarity of power spectra at different gas velocities is observed. Using combination of spectral analysis and identification of characteristic lines of primary waves, frequency of generation of secondary waves by primary waves is measured.

Structure of the Lithosphere and Asthenosphere beneath the Western US from Simultaneous Multi-Parameter Inversion

NASA Astrophysics Data System (ADS)

Steck, L.; Maceira, M.; Ammon, C. J.; Herrmann, R. B.

2013-12-01

Joint inversion of multiple datasets should produce more realistic images of Earth structure. Here we simultaneously invert surface wave dispersion, receiver functions, and gravity to determine structure of the crust and upper mantle of the western United States. Our target region is comprised of a one-degree grid that spans latitudes from 30 to 50 degrees North and longitudes from 95 to 125 degrees West. Receiver functions come from the Earthscope Automated Receiver system, and are stacked to produce an average model for each cell. Rayleigh and Love dispersion data come from multiple filter analysis of regional earthquakes, while the gravity observations are extracted from the EGM2008 model. Our starting model is comprised of an oceanic PREM model west of the Pacific coast, a western US model between that and the eastern front of the Rocky Mountains, and a continental PREM model east of the Rocky Mountain Front. Several different velocity/density relationships have been tested and all result in very similar models. Our inversion reduces RMS surface wave residuals by 58% and receiver function misfits by about 18%. Gravity residuals are reduced by more than 90%. While the reduction in residuals for receiver functions is not as profound as for surface waves or gravity, they are meaningful and produce sharper boundaries for the observed crustal anomalies. The addition of gravity produces subtle changes to the final model. Our final results are consistent with numerous previous studies in the region. In general, the craton exhibits higher velocities than the tectonically active regions to its west. We see high mid-crustal velocities under the Snake River Plain and the Colorado Plateau. In the lower crust we observe lowest velocities in the western Basin and Range and under the Colorado Mineral Belt. At 80km depth we see broad low velocities fanning out from the Snake River Plain associated with the mantle plume feeding Yellowstone Caldera. Additionally we see high and low velocity anomalies along the west coast that reflect ongoing subduction processes beneath the western US, including the subducting slab and slab window.

Investigation of the small-scale structure and dynamics of Uranus' atmosphere

NASA Technical Reports Server (NTRS)

Eshleman, Von R.; Hinson, David P.

1991-01-01

This document constitutes the final technical report of the Uranus Analysis Program. Papers and/or abstracts resulting from this research are presented. The following topics are covered: (1) past and future of radio occultation studies of planetary atmospheres; (2) equatorial waves in the stratosphere of Uranus; (3) the atmosphere of Uranus- results of radio occultation measurements with Voyager 2; (4) Uranus' atmospheric dynamics and circulation; (5) small-scale structure and dynamics in the atmosphere of Uranus; (6) evidence for inertia-gravity waves in the stratosphere of Uranus derived from Voyager 2 radio occultation data; and (7) planetary waves in the equatorial stratosphere of Uranus.

Density of the Human Body in Gravity Contrasting Tectonic Blocks of Earth

NASA Astrophysics Data System (ADS)

Kochemasov, G. G.

Short duration cosmic experiments with humans in reduced gravity might be compared with results of practically time unlimited (many thousand of years!) existence of man in conditions of planetary tectonic blocks with rather small gravity gradient. These blocks with differing planetary radii are formed in the terrestrial globe (as well as in other celestial bodies) as a result of its movement in an elliptical orbit inevitably causing inertia-gravity warping waves. Depending on the wavelengths, Earth is tectonically dichotomic (wave1, 2π R-structure), sectoral (wave2, π R-structure) and granular (wave4, π R/2-structure) [1]. Alternations of uplifts (+) and subsidences (-) in rotating Earth requires an equilibration of angular momenta of different levels blocks by differing densities of composing them objects. ``Objects'' are geological as well as biological ones. Oceans (-) are filled with dense basaltic rocks, continents (+) are built by less dense granites (andesites, on average). Homo sapiens, widely spread over Earth, equally accommodates himself to conditions of tectonic blocks with differing radii (densities). The most pronounced (amplitudinal) tectonic dichotomy is an opposition of the subsided (-) western pacific hemisphere to the uplifted (+) eastern continental hemisphere. Recently populated (12 to 3 thousand years ago) America and Pacific made migrating mongoloids denser (higher the Rohrer's index* of Indians and Polynesians) than inhabitants of native Asia. Asia itself is a sector of the planetary sectoral π R-structure of the eastern hemisphere with the center at the Pamirs-Hindukush. Around this center converge 2 uplifted sectors (Africa-Mediterranean ++, Asian +) separated by 2 subsided ones (Eurasian -, Indoceanic - -). The 4 great races developed on these sectors have their own ``body density'' characteristics. The uplifted Africa bears ``light'' negroids, subsided Eurasia ``heavy'' europeoids. In the former USSR population of the Asian sector (+) has less mineralized bones and less Fe/Mn in hairs (thus less dense hairs) than population of the Eurasian sector (-) [2]. The differentiation of the great races can be traced to the gene level: frequencies of their Rh-system genetic markers are clearly different. the ratio of man's weight to his height in the cube power (can be used also the simple ratio of man's weight to his height, that means the ``linear density'' of man). References : [1] Kochemasov G. G. Theorems of wave planetary tectonics // Geophys. Res. Abstr., V. 1, # 3, 1999,700; [2] Alexeeva T. I. Geographical environment and human biology // Moscow, Mysl, 1977, 302 pp. (in Russian).

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

NASA Technical Reports Server (NTRS)

Eckermann, Stephen D.; Jackman, C. (Technical Monitor)

2000-01-01

Gravity waves in satellite data from CRISTA and MLS are studied in depth this quarter. Results this quarter are somewhat limited due to the PI'S heavy involvement throughout this reporting period in on-site forecasting of mountain wave-induced turbulence for the NASA's ER-2 research aircraft at Kiruna, Sweden during the SAGE Ill Ozone Loss and Validation Experiment (SOLVE). Results reported concentrate on further mesoscale modeling studies of mountain waves over the southern Andes, evident in CRISTA and MLS data. Two-dimensional mesoscale model simulations are extended through generalization of model equations to include both rotation and a first-order turbulence closure scheme. Results of three experiments are analyzed in depth and submitted for publication. We also commence simulations with a three-dimensional mesoscale model (MM5) and present preliminary results for the CRISTA 1 period near southern South America. Combination of ground-based temperature data at 87 km from two sites with global HRDl data was continued this quarter, showing stationary planetary wave structures. This work was also submitted for publication.

Mesospheric heating due to intense tropospheric convection

NASA Technical Reports Server (NTRS)

Taylor, L. L.

1979-01-01

A series of rocket measurements made twice daily at Wallops Island, Va., revealed a rapid heating of the mesosphere on the order of 10 K on days when thunderstorms or squall lines were in the area. This heating is explained as the result of frictional dissipation of vertically propagating internal gravity waves generated by intense tropospheric convection. Ray-tracing theory is used to determine the spectrum of gravity wave groups that actually reach mesospheric heights. This knowledge is used in an equation describing the spectral energy density of a penetrative convective element to calculate the fraction of the total energy initially available to excite those waves that do reach the level of heating. This value, converted into a vertical velocity, is used as the lower boundary condition for a multilayer model used to determine the detailed structure of the vertically propagating waves. The amount of frictional dissipation produced by the waves is calculated from the solutions of the frictionless model by use of a vertically varying eddy viscosity coefficient. The heating produced by the dissipation is then calculated from the thermodynamic equation.

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

NASA Technical Reports Server (NTRS)

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

1997-01-01

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

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

NASA Astrophysics Data System (ADS)

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

1997-11-01

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

Surfing surface gravity waves

NASA Astrophysics Data System (ADS)

Pizzo, Nick

2017-11-01

A simple criterion for water particles to surf an underlying surface gravity wave is presented. It is found that particles travelling near the phase speed of the wave, in a geometrically confined region on the forward face of the crest, increase in speed. The criterion is derived using the equation of John (Commun. Pure Appl. Maths, vol. 6, 1953, pp. 497-503) for the motion of a zero-stress free surface under the action of gravity. As an example, a breaking water wave is theoretically and numerically examined. Implications for upper-ocean processes, for both shallow- and deep-water waves, are discussed.

Large Stationary Gravity Waves: A Game Changer for Venus' Science

NASA Astrophysics Data System (ADS)

Navarro, T.; Schubert, G.; Lebonnois, S.

2017-11-01

In 2015, the discovery by the Akatsuki spacecraft of an astonishing, unexpected, 10,000 km long meridional structure at the cloud top, stationary with respect to the surface, calls into question our very basic understanding of Venus.

Science Teaching to Fire the Imagination.

ERIC Educational Resources Information Center

Sandford, Diana; Fleetwood, Julie

1997-01-01

Presents a range of exciting ideas for encouraging active learning, for illuminating new concepts, and for making science lessons fun. Topics include modeling, matter, heat, diffusion, changes of state, heat transfer, energy changes, atomic structure, waves, gravity, enzymes, and habitats. (JRH)

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.

Radiating Instabilities of Internal Inertio-gravity Waves

NASA Astrophysics Data System (ADS)

Kwasniok, F.; Schmitz, G.

The vertical radiation of local convective and shear instabilities of internal inertio- gravity waves is examined within linear stability theory. A steady, plane-parallel Boussinesq flow with vertical profiles of horizontal velocity and static stability re- sembling an internal inertio-gravity wave packet without mean vertical shear is used as dynamical framework. The influence of primary-wave frequency and amplitude as well as orientation and horizontal wavenumber of the instability on vertical radi- ation is discussed. Considerable radiation occurs at small to intermediate instability wavenumbers for basic state gravity waves with high to intermediate frequencies and moderately convectively supercritical amplitudes. Radiation is then strongest when the horizontal wavevector of the instability is aligned parallel to the horizontal wavevector of the basic state gravity wave. These radiating modes are essentially formed by shear instability. Modes of convective instability, that occur at large instability wavenum- bers or strongly convectively supercritical amplitudes, as well as modes at convec- tively subcritical amplitudes are nonradiating, trapped in the region of instability. The radiation of an instability is found to be related to the existence of critical levels, a radiating mode being characterized by the absence of critical levels outside the region of instability of the primary wave.

Dynamics of flexural gravity waves: from sea ice to Hawking radiation and analogue gravity

NASA Astrophysics Data System (ADS)

Das, S.; Sahoo, T.; Meylan, M. H.

2018-01-01

The propagation of flexural gravity waves, routinely used to model wave interaction with sea ice, is studied, including the effect of compression and current. A number of significant and surprising properties are shown to exist. The occurrence of blocking above a critical value of compression is illustrated. This is analogous to propagation of surface gravity waves in the presence of opposing current and light wave propagation in the curved space-time near a black hole, therefore providing a novel system for studying analogue gravity. Between the blocking and buckling limit of the compressive force, the dispersion relation possesses three positive real roots, contrary to an earlier observation of having a single positive real root. Negative energy waves, in which the phase and group velocity point in opposite directions, are also shown to exist. In the presence of an opposing current and certain critical ranges of compressive force, the second blocking point shifts from the positive to the negative branch of the dispersion relation. Such a shift is known as the Hawking effect from the analogous behaviour in the theory of relativity which leads to Hawking radiation. The theory we develop is illustrated with simulations of linear waves in the time domain.

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

NASA Technical Reports Server (NTRS)

Eckermann, Stephen D.; Jackman, Charles H. (Technical Monitor)

2000-01-01

This report provides a broad outline of the total body of research conducted during the past three years. We report on detailed model studies of the precise way in which infrared limb scanning satellites explicitly detect gravity waves, and use these insights to resolve earlier discrepant zonal mean estimates of gravity wave variances from satellite limb scanners. Detailed analysis of CRISTA temperature fluctuations are outlined, which provide new global information on long-wavelength stratospheric gravity waves generated by mountains, tropical convection and the mid-latitude jet stream- vortex system, as well as interactions higher in the mesosphere with the diurnal tide. The detailed insights gained from analyzing CRISTA data are applied to provide a multi- year analysis of stratospheric mountain waves over the Andes evident in MLS limb-track data. We also demonstrate for the first time that stratospheric temperature data from the CLAES instrument on UARS resolved gravity waves, and we highlight mountain wave information in a subset of these data. Final conclusions and recommendations are set forth, and the present findings are directly related to the original goals of the research contract. A full list of publications that resulted from this research is provided.

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

NASA Technical Reports Server (NTRS)

Eckermann, Stephen D.

2000-01-01

This report provides a broad outline of the total body of research conducted during the past three years. We report on detailed model studies of the precise way in which infrared limb scanning satellites explicitly detect gravity waves, and use these insights to resolve earlier discrepant zonal mean estimates of gravity wave variances from satellite limb scanners. Detailed analysis of CRISTA temperature fluctuations are outlined, which provide new global information on long-wavelength stratospheric gravity waves generated by mountains, tropical convection and the mid-latitude jet stream-vortex system, as well as interactions higher in the mesosphere with the diurnal tide. The detailed insights gained from analyzing CRISTA data are applied to provide a multiyear analysis of stratospheric mountain waves over the Andes evident in MLS limb-track data. We also demonstrate for the first time that stratospheric temperature data from the CLAES instrument on UARS resolved gravity waves, and we highlight mountain wave information in a subset of these data. Final conclusions and recommendations are set forth, and the present findings are directly related to the original goals of the research contract. A full list of publications that resulted from this research is provided.

Dynamics of flexural gravity waves: from sea ice to Hawking radiation and analogue gravity.

PubMed

Das, S; Sahoo, T; Meylan, M H

2018-01-01

The propagation of flexural gravity waves, routinely used to model wave interaction with sea ice, is studied, including the effect of compression and current. A number of significant and surprising properties are shown to exist. The occurrence of blocking above a critical value of compression is illustrated. This is analogous to propagation of surface gravity waves in the presence of opposing current and light wave propagation in the curved space-time near a black hole, therefore providing a novel system for studying analogue gravity. Between the blocking and buckling limit of the compressive force, the dispersion relation possesses three positive real roots, contrary to an earlier observation of having a single positive real root. Negative energy waves, in which the phase and group velocity point in opposite directions, are also shown to exist. In the presence of an opposing current and certain critical ranges of compressive force, the second blocking point shifts from the positive to the negative branch of the dispersion relation. Such a shift is known as the Hawking effect from the analogous behaviour in the theory of relativity which leads to Hawking radiation. The theory we develop is illustrated with simulations of linear waves in the time domain.

The analysis of the wavefront aberration caused by the gravity of the tunable-focus liquid-filled membrane lens

NASA Astrophysics Data System (ADS)

Zhang, Wei; Liu, Pengfei; Wei, Xiaona; Zhuang, Songlin; Yang, Bo

2010-11-01

Liquid lens is a novel optical device which can implement active zooming. With liquid lens, zoom camera can be designed with more miniature size and simpler structure than before. It is thought that the micro zoom system with liquid lens has a very wide potential applications in many fields, in which the volume and weight of the system are critically limited, such as endoscope, mobile, PDA and so on. There are mainly three types of tunable-focus liquid lens: liquid crystal lens, electrowetting effect based liquid lens and liquid-filled membrane lens. Comparing with the other two kinds of liquid lens, the liquid-filled membrane lens has the advantages of simple structure, flexible aperture and high zooming efficiency. But its membrane surface will have an initial shape deformation caused by the gravity when the aperture of the lens is at large size, which will lead to the wave front aberration and the imaging quality impairing. In this paper, the initial deformation of the lens caused by the gravity was simulated based on the theory of Elastic Mechanics, which was calculated by the Finite Element Analysis method. The relationship between the diameter of the lens and the wave front aberration caused by the gravity was studied. And the Optical path difference produced by different liquid density was also analyzed.

Sea loads on ships and offshore structures

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

Faltinsen, O.

1990-01-01

The book introduces the theory of the structural loading on ships and offshore structures caused by wind, waves and currents, and goes on to describe the applications of this theory in terms of real structures. The main topics described are linear-wave induced motions, loads on floating structures, numerical methods for ascertaining wave induced motions and loads, viscous wave loads and damping, stationkeeping and water impact and entry. The applications of the theoretical principles are introduced with extensive use of exercises and examples. Applications covered include conventional ships, barges, high speed marine vehicles, semisubmersibles, tension leg platforms, moored or dynamic positionedmore » ships, risers, buoys, fishing nets, jacket structures and gravity platforms. One aim of the book is to provide a physical understanding through simplified mathematical models. In this way one can develop analytical tools to evaluate results from test models, full scale trials or computer simulation, and learns which parameters represent the major contributions and influences on sea loads.« less

On the mechanism of self gravitating Rossby interfacial waves in proto-stellar accretion discs

NASA Astrophysics Data System (ADS)

Yellin-Bergovoy, Ron; Heifetz, Eyal; Umurhan, Orkan M.

2016-05-01

The dynamical response of edge waves under the influence of self-gravity is examined in an idealised two-dimensional model of a proto-stellar disc, characterised in steady state as a rotating vertically infinite cylinder of fluid with constant density except for a single density interface at some radius ?. The fluid in basic state is prescribed to rotate with a Keplerian profile ? modified by some additional azimuthal sheared flow. A linear analysis shows that there are two azimuthally propagating edge waves, kin to the familiar Rossby waves and surface gravity waves in terrestrial studies, which move opposite to one another with respect to the local basic state rotation rate at the interface. Instability only occurs if the radial pressure gradient is opposite to that of the density jump (unstably stratified) where self-gravity acts as a wave stabiliser irrespective of the stratification of the system. The propagation properties of the waves are discussed in detail in the language of vorticity edge waves. The roles of both Boussinesq and non-Boussinesq effects upon the stability and propagation of these waves with and without the inclusion of self-gravity are then quantified. The dynamics involved with self-gravity non-Boussinesq effect is shown to be a source of vorticity production where there is a jump in the basic state density In addition, self-gravity also alters the dynamics via the radial main pressure gradient, which is a Boussinesq effect. Further applications of these mechanical insights are presented in the conclusion including the ways in which multiple density jumps or gaps may or may not be stable.

Seasonal Variation of Wave Activities near the Mesopause Region Observed at King Sejong Station (62.22°S, 58.78°W), Antarctica

NASA Astrophysics Data System (ADS)

Kim, Y.; Lee, C.; Kim, J.; Jee, G.; Won, Y.; Wu, D. L.

2012-12-01

We have analyzed neutral wind data obtained from a VHF meteor radar at King Sejong Station (KSS), Antarctica to investigate wave activities in the altitude region of 80 - 100 km over the Antarctic vortex boundary. The seasonal behavior of semidiurnal tides is generally consistent with the prediction of GSWM (Global Scale Wave Model) except for the altitude region above ~96 km. The gravity wave activities inferred from variances of neutral winds show very similar seasonal characteristics to the semidiurnal tides, implying that there is a close interaction between the gravity wave and tide. Although the seasonal behaviors of the wind variance as an indicator of the gravity wave activity are consistent with those observed at the adjacent Rothera station, the magnitude of the variances at KSS is much larger above the mesopause, especially from May through September, than those at Rothera. The Aura Microwave Limb Sounder (MLS) satellite observations also confirmed the enhancement of gravity wave activity during the same period near the tip of Antarctic Peninsula, where KSS is located. The observed large wind variances at KSS may imply that the atmospheric conditions near the Antarctic vortex are very effective for generation of the gravity waves that propagate to the upper atmosphere.

Using the IMS infrasound network for the identification of mountain-associated waves and gravity waves hotspots

NASA Astrophysics Data System (ADS)

Hupe, Patrick; Ceranna, Lars; Pilger, Christoph; Le Pichon, Alexis

2017-04-01

The infrasound network of the International Monitoring System (IMS) has been established for monitoring the atmosphere to detect violations of the Comprehensive nuclear-Test-Ban Treaty (CTBT). The IMS comprises 49 certified infrasound stations which are globally distributed. Each station provides data for up to 16 years. Due to the uniform distribution of the stations, the IMS infrasound network can be used to derive global information on atmospheric dynamics' features. This study focuses on mountain-associated waves (MAWs), i.e. acoustic waves in the frequency range between approximately 0.01 Hz and 0.05 Hz. MAWs can be detected in infrasound data by applying the Progressive Multi-Channel Correlation (PMCC) algorithm. As a result of triangulation, global hotspots of MAWs can be identified. Previous studies on gravity waves indicate that global hotspots of gravity waves are similar to those found for MAWs by using the PMCC algorithm. The objective of our study is an enhanced understanding of the excitation sources and of possible interactions between MAWs and gravity waves. Therefore, spatial and temporal correlation analyses will be performed. As a preceding step, we will present (seasonal) hotspots of MAWs as well as hotspots of gravity waves derived by the IMS infrasound network.

Impact location of objects hitting the water surface

NASA Astrophysics Data System (ADS)

Kadri, Usama

2017-04-01

Analysis of data, recorded on March 8th 2014 at the Comprehensive Test ban Treaty Organisation's hydroacoustic station off Cape Leeuwin Western Australia, reveal pressure signatures of objects impacting at the sea surface which could be associated with falling meteorites as well as the missing Malaysian MH370 airplane. The location of the sources are identified analytically by an inverse solution based on acoustic-gravity wave theory (e.g. see references below) which have been developed and validated experimentally. Apart from the direct contribution to the search efforts after the missing airplane, the method we describe here is very efficient for identifying the location of sources that result in a sudden change in the water pressure in general. References 1. T.Yamamoto,1982.Gravity waves and acoustic waves generated by submarine earthquakes, Soil Dyn. Earthquake Eng., 1, 75-82. 2. M. Stiassnie, 2010. Tsunamis and acoustic-gravity waves from underwater earthquakes, J. Eng. Math., 67, 23-32, doi:10.1007/s10665-009-9323-x. 3. U. Kadri and M. Staissnie, 2012. Acoustic-gravity waves interacting with the shelf break. J. Geophys. Res., 117, C03035, doi: 10.1029/2011JC007674. 4. E. Eyov, A. Klar, U. Kadri and M. Stiassnie, 2013. Progressive waves in a compressible ocean with elastic bottom, Wave Motion 50, 929-939. doi: 10.1016/j.wavemoti.2013.03.003 5. G. Hendin and M. Stiassnie, 2013. Tsunami and acoustic-gravity waves in water of constant depth, Phys. Fluids 25, 086103, doi: 10.1063/1.481799. 6. U. Kadri, 2016. Acoustic-gravity waves from an oscillating ice-block in arctic zones. Advances in Acoustics and Vibration, 8076108, http://dx.doi.org/10.1155/2016/8076108 7. T.C.A. Oliveira, U. Kadri, 2016. Acoustic-gravity waves from the 2004 Indian Ocean earthquake and tsunami. Journal of Geophysical Research: Oceans. doi: 10.1002/2016JC011742

Impact of infrasound atmospheric noise on gravity detectors used for astrophysical and geophysical applications

NASA Astrophysics Data System (ADS)

Fiorucci, Donatella; Harms, Jan; Barsuglia, Matteo; Fiori, Irene; Paoletti, Federico

2018-03-01

Density changes in the atmosphere produce a fluctuating gravity field that affects gravity strainmeters or gravity gradiometers used for the detection of gravitational waves and for geophysical applications. This work addresses the impact of the atmospheric local gravity noise on such detectors, extending previous analyses. In particular we present the effect introduced by the building housing the detectors, and we analyze local gravity-noise suppression by constructing the detector underground. We present also new sound spectra and correlation measurements. The results obtained are important for the design of future gravitational-wave detectors and gravity gradiometers used to detect prompt gravity perturbations from earthquakes.

Instabilities of Internal Gravity Wave Beams

NASA Astrophysics Data System (ADS)

Dauxois, Thierry; Joubaud, Sylvain; Odier, Philippe; Venaille, Antoine

2018-01-01

Internal gravity waves play a primary role in geophysical fluids: They contribute significantly to mixing in the ocean, and they redistribute energy and momentum in the middle atmosphere. Until recently, most studies were focused on plane wave solutions. However, these solutions are not a satisfactory description of most geophysical manifestations of internal gravity waves, and it is now recognized that internal wave beams with a confined profile are ubiquitous in the geophysical context. We discuss the reason for the ubiquity of wave beams in stratified fluids, which is related to the fact that they are solutions of the nonlinear governing equations. We focus more specifically on situations with a constant buoyancy frequency. Moreover, in light of recent experimental and analytical studies of internal gravity beams, it is timely to discuss the two main mechanisms of instability for those beams: (a) the triadic resonant instability generating two secondary wave beams and (b) the streaming instability corresponding to the spontaneous generation of a mean flow.

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.

Observation of Wood's anomalies on surface gravity waves propagating on a channel.

PubMed

Schmessane, Andrea

2016-09-01

I report on experiments demonstrating the appearance of Wood's anomalies in surface gravity waves propagating along a channel with a submerged obstacle. Space-time measurements of surface gravity waves allow one to compute the stationary complex field of the wave and the amplitude growth of localized and propagative modes over all the entire channel, including the scattering region. This allows one to access the near and far field dynamics, which constitute a new and complementary way of observation of mode resonances of the incoming wave displaying Wood's anomalies. Transmission coefficient, dispersion relations and normalized wave energy of the incoming wave and the excited mode are measured and found to be in good agreement with theoretical predictions.

Analysis of gravity wave propagation and properties, comparison between WRF model simulations and LIDAR data in Southern France

NASA Astrophysics Data System (ADS)

Costantino, Lorenzo; Heinrich, Philippe

2014-05-01

Small scale atmospheric waves, usually referred as internal of Gravity Waves (GW), represent an efficient transport mechanism of energy and momentum through the atmosphere. They propagate upward from their sources in the lower atmosphere (flow over topography, convection and jet adjustment) to the middle and upper atmosphere. Depending on the horizontal wind shear, they can dissipate at different altitudes and force the atmospheric circulation of the stratosphere and mesosphere. The deposition of momentum associated with the dissipation, or wave breaking, exerts an acceleration to the mean flow, that can significantly alter the thermal and dynamical structure of the atmosphere. GW may have spatial scales that range from few to hundreds of kilometers and range from minutes to hours. For that reason, General Circulation Model (GCM) used in climate studies have generally a coarse resolution, of approximately 2-5° horizontally and 3 km vertically, in the stratosphere. This resolution is fine enough to resolve Rossby-waves but not the small-scale GW activity. Hence, to calculate the momentum-forcing generated by the unresolved waves, they use a drag parametrization which mainly consists in some tuning parameters, constrained by observations of wind circulation and temperature in the upper troposphere and middle atmosphere (Alexander et al., 2010). Traditionally, the GW Drag (GWD) parametrization is used in climate and forecasting models to adjust the structure of winter jets and the horizontal temperature gradient. It was firstly based on the parametrization of orographic waves, which represent zero-phase-speed waves generated by sub-grid topography. Regional models, with horizontal resolutions that can reach few tens or hundreds of meters, are able to directly resolve small-scale GW and may represent a valuable addition to direct observations. In the framework of the ARISE (Atmospheric dynamics Research InfraStructure in Europe) project, this study tests the capability of the Weather Research and Forecasting (WRF) model to generate and propagate GW forced by convection and orography, without any GW parametrization. Results from model simulations are compared with in-situ observations of potential energy vertical profiles in the stratosphere, measured by a LIDAR located at the Observatoire de Haute Provence (Southern France). This comparison allows, to a certain extent, to validate WRF numerical results and quantify some of those wave parameters (e.g., GW drag force, intrinsic frequency, breaking level altitude, etc..) that are fundamental for a deeper understanding of GW role in atmospheric dynamics, but that are not easily measurable by ground- or space-based systems (limited to specific region or certain latitude band). Alexander, M. J., Geller, M., McLandress, C., Polavarapu, S., Preusse, P., Sassi, F., Sato, K., Eckermann, S., Ern, M., Hertzog, A., Kawatani, Y., Pulido, M., Shaw, T. A., Sigmond, M., Vincent, R. and Watanabe, S. (2010), Recent developments in gravity-wave effects in climate models and the global distribution of gravity-wave momentum flux from observations and models. Q.J.R. Meteorol. Soc., 136: 1103-1124. doi: 10.1002/qj.637

Spatially covariant theories of gravity: disformal transformation, cosmological perturbations and the Einstein frame

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

Fujita, Tomohiro; Gao, Xian; Yokoyama, Jun'ichi, E-mail: tomofuji@stanford.edu, E-mail: gao@th.phys.titech.ac.jp, E-mail: yokoyama@resceu.s.u-tokyo.ac.jp

We investigate the cosmological background evolution and perturbations in a general class of spatially covariant theories of gravity, which propagates two tensor modes and one scalar mode. We show that the structure of the theory is preserved under the disformal transformation. We also evaluate the primordial spectra for both the gravitational waves and the curvature perturbation, which are invariant under the disformal transformation. Due to the existence of higher spatial derivatives, the quadratic Lagrangian for the tensor modes itself cannot be transformed to the form in the Einstein frame. Nevertheless, there exists a one-parameter family of frames in which themore » spectrum of the gravitational waves takes the standard form in the Einstein frame.« less

Universal power law of the gravity wave manifestation in the AIM CIPS polar mesospheric cloud images

NASA Astrophysics Data System (ADS)

Rong, Pingping; Yue, Jia; Russell, James M., III; Siskind, David E.; Randall, Cora E.

2018-01-01

We aim to extract a universal law that governs the gravity wave manifestation in polar mesospheric clouds (PMCs). Gravity wave morphology and the clarity level of display vary throughout the wave population manifested by the PMC albedo data. Higher clarity refers to more distinct exhibition of the features, which often correspond to larger variances and a better-organized nature. A gravity wave tracking algorithm based on the continuous Morlet wavelet transform is applied to the PMC albedo data at 83 km altitude taken by the Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) instrument to obtain a large ensemble of the gravity wave detections. The horizontal wavelengths in the range of ˜ 20-60 km are the focus of the study. It shows that the albedo (wave) power statistically increases as the background gets brighter. We resample the wave detections to conform to a normal distribution to examine the wave morphology and display clarity beyond the cloud brightness impact. Sample cases are selected at the two tails and the peak of the normal distribution to represent the full set of wave detections. For these cases the albedo power spectra follow exponential decay toward smaller scales. The high-albedo-power category has the most rapid decay (i.e., exponent = -3.2) and corresponds to the most distinct wave display. The wave display becomes increasingly blurrier for the medium- and low-power categories, which hold the monotonically decreasing spectral exponents of -2.9 and -2.5, respectively. The majority of waves are straight waves whose clarity levels can collapse between the different brightness levels, but in the brighter background the wave signatures seem to exhibit mildly turbulent-like behavior.

Earthquake- and tsunami-induced ionospheric disturbances detected by GPS total electron content observation

NASA Astrophysics Data System (ADS)

Tsugawa, T.; Nishioka, M.; Matsumura, M.; Shinagawa, H.; Maruyama, T.; Ogawa, T.; Saito, A.; Otsuka, Y.; Nagatsuma, T.; Murata, T.

2012-12-01

Ionospheric disturbances induced by the 2011 Tohoku earthquake and tsunami were studied by the high-resolution GPS total electron content (TEC) observation in Japan and in the world. The initial ionospheric disturbance appeared as sudden depletions by about 6 TEC unit (20%) about seven minutes after the earthquake onset, near the epicenter. From 06:00UT to 06:15UT, circular waves with short propagation distance propagated in the radial direction in the propagation velocity of 3,457, 783, 423 m/s for the first, second, third peak, respectively. Following these waves, concentric waves with long propagation distance appeared to propagate at the velocity of 138-288 m/s. In the vicinity of the epicenter, shortperiod oscillations with period of about 4 minutes were observed after 06:00 UT for 3 hours or more. We focus on the the circular and concentric waves in this paper. The circular or concentric structures indicate that these ionospheric disturbances had a point source. The center of these structures, termed as "ionospheric epicenter", was located around 37.5 deg N of latitude and 144.0 deg E of longitude, 170 km far from the epicenter to the southeast direction, and corresponded to the tsunami source. Comparing to the results of a numerical simulation using non-hydrostatic compressible atmosphere-ionosphere model, the first peak of circular wave would be caused by the acoustic waves generated from the propagating Rayleigh wave. The second and third waves would be caused by atmospheric gravity waves excited in the lower ionosphere due to the acoustic wave propagations from the tsunami source. The fourth and following waves are considered to be caused by the atmospheric gravity waves induced by the wavefronts of traveling tsunami. Long-propagation of these TEC disturbances were studied also using high-resolution GPS-TEC data in North America and Europe. Medium-scale wave structures with wavelengths of several 100 km appeared in the west part of North America at the almost same time as the tsunami arrival. On the other hand, no remarkable wave structure was observed in Europe. We will introduce these observational results and discuss about the generation and propagation mechanisms of the ionospheric disturbances induced by the earthquake and tsunami.

Self-similar gravity wave spectra resulting from the modulation of bound waves

NASA Astrophysics Data System (ADS)

Michel, Guillaume; Semin, Benoît; Cazaubiel, Annette; Haudin, Florence; Humbert, Thomas; Lepot, Simon; Bonnefoy, Félicien; Berhanu, Michaël; Falcon, Éric

2018-05-01

We experimentally study the properties of nonlinear surface gravity waves in a large-scale basin. We consider two different configurations: a one-dimensional (1D) monochromatic wave forcing, and a two-dimensional (2D) forcing with bichromatic waves satisfying resonant-wave interaction conditions. For the 1D forcing, we find a discrete wave-energy spectrum dominated at high frequencies by bound waves whose amplitudes decrease as a power law of the frequency. Bound waves (e.g., to the carrier) are harmonics superimposed on the carrier wave propagating with the same phase velocity as the one of the carrier. When a narrow frequency random modulation is applied to this carrier, the high-frequency part of the wave-energy spectrum becomes continuous with the same frequency-power law. Similar results are found for the 2D forcing when a random modulation is also applied to both carrier waves. Our results thus show that all these nonlinear gravity wave spectra are dominated at high frequencies by the presence of bound waves, even in the configuration where resonant interactions occur. Moreover, in all these configurations, the power-law exponent of the spectrum is found to depend on the forcing amplitude with the same trend as the one found in previous gravity wave turbulence experiments. Such a set of bound waves may thus explain this dependence that was previously poorly understood.

Medium-scale gravity wave activity in the bottomside F region in tropical regions

NASA Astrophysics Data System (ADS)

Liu, Huixin; Pedatella, Nicholas; Hocke, Klemens

2017-07-01

Thermospheric gravity waves (GWs) in the bottomside F region have been proposed to play a key role in the generation of equatorial plasma bubbles (EPBs). However, direct observations of such waves are scarce. This study provides a systematic survey of medium-scale (<620 km) neutral atmosphere perturbations at this critical altitude in the tropics, using 4 years of in situ Gravity Field and Steady-State Ocean Circulation Explorer satellite measurements of thermospheric density and zonal wind. The analysis reveals pronounced features on their global distribution and seasonal variability: (1) A prominent three-peak longitudinal structure exists in all seasons, with stronger perturbations over continents than over oceans. (2) Their seasonal variation consists of a primary semiannual oscillations (SAO) and a secondary annual oscillation (AO). The SAO component maximizes around solstices and minimizes around equinoxes, while the AO component maximizes around June solstice. These GW features resemble those of EPBs in spatial distribution but show opposite trend in climatological variations. This may imply that stronger medium-scale GW activity does not always lead to more EPBs. Possible origins of the bottomside GWs are discussed, among which tropical deep convection appears to be most plausible.

Do gravity waves significantly impact PSC occurrence in the Antarctic?

NASA Astrophysics Data System (ADS)

McDonald, A. J.; George, S. E.; Woollands, R. M.

2009-02-01

This study uses a combination of POAM III aerosol extinction measurements and CHAMP GPS/RO temperature measurements to examine the role of atmospheric gravity waves in Polar Stratospheric Cloud (PSC) formation in the Antarctic. POAM III aerosol extinction observations are used to identify Type I Polar Stratospheric Clouds using an unsupervised clustering algorithm. The seasonal and spatial distribution of PSCs observed by POAM III is examined to determine whether there is a bias towards regions of high wave activity early in the Antarctic winter which may enhance PSC formation. Examination of the probability of temperatures below the Type Ia formation temperature threshold based on UKMO analyses displays a good correspondence to the PSC occurrence derived from POAM III extinction data in general. However, in June the POAM III observations of PSC are more abundant than expected from temperature thresholds. In addition the PSC occurrence based on temperature thresholds in September and October is often significantly higher than the PSC occurrence observed by POAM III, this observation probably being due to dehydration and denitrification. Use of high resolution temperatures from CHAMP GPS/RO observations provide a slightly improved relationship to the POAM III derived values. Analysis of the CHAMP temperature observations indicates that temperature perturbations associated with gravity waves may explain the enhanced PSC incidence observed in June compared to the UKMO analyses. Comparison of the UKMO analyses temperatures relative to corresponding CHAMP observations also suggests a small warm bias in the UKMO analyses during June. Examination of the longitudinal structure PSC occurrence in June 2005 also shows that regions of enhancement are associated with data near the Antarctic peninsula a known Mountain wave "hotspot". The impact of temperature perturbations causing enhanced temperature threshold crossings is shown to be particularly important early in the Antarctic winter while later in the season temperature perturbations associated with gravity waves could contribute to about 15% of the PSC observed, a value which corresponds well to several previous studies.

Beyond concordance cosmology with magnification of gravitational-wave standard sirens.

PubMed

Camera, Stefano; Nishizawa, Atsushi

2013-04-12

We show how future gravitational-wave detectors would be able to discriminate between the concordance Λ cold dark matter cosmological model and up-to-date competing alternatives, e.g., dynamical dark energy (DE) models or modified gravity (MG) theories. Our method consists of using the weak-lensing magnification effect that affects a standard-siren signal because of its traveling through the Universe's large scale structure. As a demonstration, we present constraints on DE and MG from proposed gravitational-wave detectors, namely Einstein Telescope and DECI-Hertz Interferometer Gravitational-Wave Observatory and Big-Bang Observer.

Sloshing dynamics modulated fluid angular momentum and moment fluctuations driven by orbital gravity gradient and jitter accelerations in microgravity

NASA Technical Reports Server (NTRS)

Hung, R. J.; Pan, H. L.

1995-01-01

The dynamical behavior of spacecraft propellant affected by the asymmetric combined gravity gradient and jitter accelerations, in particular the effect of surface tension on partially-filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank has been investigated. Three different cases of orbital accelerations: (1) gravity gradient-dominated, (2) equally weighted between gravity gradient and jitter, and (3) gravity jitter-dominated accelerations are studied. The results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient-dominated accelerations provide a torsional moment with tidal motion of bubble oscillations in the rotating dewar. The results are clearly seen from the twisting shape of the bubble oscillations driven by gravity gradient-dominated acceleration. The results of slosh wave excitation along the liquid-vapor interface induced by gravity jitter-dominated acceleration indicate the results of bubble motion in a manner of down-and-up and leftward-and-rightward movement of oscillation when the bubble is rotating with respect to rotating dewar axis. Fluctuations of angular momentum, fluid moment and bubble mass center caused by slosh wave excitations driven by gravity gradient acceleration or gravity jitter acceleration are also investigated.

Rogue waves: from nonlinear Schrödinger breather solutions to sea-keeping test.

PubMed

Onorato, Miguel; Proment, Davide; Clauss, Günther; Klein, Marco

2013-01-01

Under suitable assumptions, the nonlinear dynamics of surface gravity waves can be modeled by the one-dimensional nonlinear Schrödinger equation. Besides traveling wave solutions like solitons, this model admits also breather solutions that are now considered as prototypes of rogue waves in ocean. We propose a novel technique to study the interaction between waves and ships/structures during extreme ocean conditions using such breather solutions. In particular, we discuss a state of the art sea-keeping test in a 90-meter long wave tank by creating a Peregrine breather solution hitting a scaled chemical tanker and we discuss its potential devastating effects on the ship.

Rogue Waves: From Nonlinear Schrödinger Breather Solutions to Sea-Keeping Test

PubMed Central

Onorato, Miguel; Proment, Davide; Clauss, Günther; Klein, Marco

2013-01-01

Under suitable assumptions, the nonlinear dynamics of surface gravity waves can be modeled by the one-dimensional nonlinear Schrödinger equation. Besides traveling wave solutions like solitons, this model admits also breather solutions that are now considered as prototypes of rogue waves in ocean. We propose a novel technique to study the interaction between waves and ships/structures during extreme ocean conditions using such breather solutions. In particular, we discuss a state of the art sea-keeping test in a 90-meter long wave tank by creating a Peregrine breather solution hitting a scaled chemical tanker and we discuss its potential devastating effects on the ship. PMID:23405086

Atmospheric gravity wave detection following the 2011 Tohoku earthquakes combining COSMIC occultation and GPS observations

NASA Astrophysics Data System (ADS)

Yan, X.; Tao, Y.; Xia, C.; Qi, Y.; Zuo, X.

2017-12-01

Several studies have reported the earthquake-induced atmospheric gravity waves detected by some new technologies such as airglow (Makela et al., 2011), GOCE (Garcia et al., 2013), GRACE (Yang et al., 2014), F3/C radio occultation sounding (Coïsson et al., 2015). In this work, we collected all occultation events on 11 March, and selected four events to analyze at last. The original and filtered podTEC is represented as function of the altitude of the impact parameter and UT of the four events. Then, the travel time diagrams of filtered podTEC derived from the events were analyzed. The occultation signal from one event (marked as No.73) is consistent with the previous results reported by Coïsson. 2015, which is corresponds to the ionospheric signal induced from tsunami gravity wave. What is noticeable, in this work, is that three occultation events of No.403, 77 and 118 revealed a disturbance of atmospheric gravity wave with velocity 300m/s, preceding the tsunami. It would probably be correspond to the gravity waves caused by seismic rupture but not tsunami. In addition, it can be seen that the perturbation height of occultation observation TEC is concentrated at 200-400km, corresponding ionosphere F region. The signals detected above are compared with GPS measurements of TEC from GEONET and IGS. From GPS data, traveling ionospheric disturbances were observed spreading out from the epicenter as a quasi-circular propagation pattern with the time. Exactly, we observed an acoustic wave coupled with Rayleigh wave starting from the epicenter with a speed of 3.0km/s and a superimposed acoustic-gravity wave moving with a speed of 800m/s. The acoustic-gravity wave generated at the epicenter and gradually attenuated 800km away, then it is replaced by a gravity wave coupled with the tsunami that moves with a speed of between 100 and 300m/s. It is necessary to confirm the propagation process of the waves if we attempt to evaluate the use of ionospheric seismology as a potential support for future earthquake and tsunami warning systems. Acknowledgement: This work is supported by NSFC (41604135), China Postdoctoral Science Foundation funded project (1231703), State Key Laboratory of Earthquake Dynamics (LED2015B04), Key Laboratory of Earth and Planetary Physics, Hubei Subsurface Multi-scale Imaging Key Laboratory.

Inertia critical layers and their impacts on nongeostrophic baroclinic instability

NASA Astrophysics Data System (ADS)

Shen, Bo-Wen

We investigate the effects of critical levels (CLs) on a baroclinic flow over mountains, nongeostrophic (NG) inertia critical layer instability, and NG baroclinic instability (BI) in a three-layer atmosphere with a small Richardson number (Ri) in the middle layer. We develop a numerical wave decomposition method in Chapter 2, which is found to be useful in determining the reflection coefficient (Ref) numerically when the flow system is too complicated to obtain Ref analytically. Effects of CLs on flow over mountains are studied both analytically and numerically in Chapter 3. We define the effective inertia critical level (ICL) as the height above which inertia-gravity waves attenuate significantly. Based on numerical simulations with a broad range of Rossby number (Ro) and Ri, four wave regimes are found: (a) Regime I: inertia- gravity waves. The flow behaves like unsheared inertia- gravity waves and the effective lower ICL plays a similar role as the classical critical level (CCL) does in a nonrotating flow. (b) Regime II: combined inertia-gravity waves and baroclinic lee waves. These waves behave like those in Regime I below the lower effective ICL, and like baroclinic lee waves near the CCL. (c) Regime III: combined evanescent and baroclinic lee waves. These waves still behave like baroclinic lee waves near the CCL, but are trapped near the surface. (d) Regime IV: transient waves. NG baroclinic instability exists, as evidenced by the positive domain-averaged north-south heat flux. Wave regime IV is further investigated in Chapter 5. We identify the NG baroclinic instability in Chapter 3 as an inertia critical layer (ICLY) instability. The role of the upper inertia critical level in this instability has been studied by choosing a periodic mountain. When only the CCL and upper ICL are present in the domain, the mesoscale ICLY instability tends to occur. For a periodic mountain ridge, the ICLY instability selects the mountain's tvavelength as its wavelength of maximum growth. For an isolated mountain ridge, the NG baroclinic lee wave is established in the beginning for flows with small Ri, which then develops its own upper ICL. The stability of Lindzen and Tung's (1976, hereafter LT76) type of three-layer nonrotating/rotating atmosphere is discussed in Chapter 6. We first investigate the transient dynamics of wave ducting by a numerical model. The adjustment time for waves to be ducted depends on the atmospheric structure and horizontal wavelength. Second, we study the effects of Coriolis force on LT76's wave ducting mechanism, and show that a wave with wavelength on the order of 100 km is hardly ducted. (Abstract shortened by UMI.)

'Downward control' of the mean meridional circulation and temperature distribution of the polar winter stratosphere

NASA Technical Reports Server (NTRS)

Garcia, Rolando R.; Boville, Byron A.

1994-01-01

According to the 'downward control' principle, the extratropical mean vertical velocity on a given pressure level is approximately proportional to the meridional gradient of the vertically integrated zonal force per unit mass exerted by waves above that level. In this paper, a simple numerical model that includes parameterizations of both planetary and gravity wave breaking is used to explore the influence of gravity wave breaking in the mesosphere on the mean meridional circulation and temperature distribution at lower levels in the polar winter stratosphere. The results of these calculations suggest that gravity wave drag in the mesosphere can affect the state of the polar winter stratosphere down to altitudes below 30 km. The effect is most important when planetary wave driving is relatively weak: that is, during southern winter and in early northern winter. In southern winter, downwelling weakens by a factor of 2 near the stratospause and by 20% at 30 km when gravity wave drag is not included in the calculations. As a consequence, temperatures decrease considerably throughout the polar winter stratosphere (over 20 K above 40 km and as much as 8 K at 30 km, where the effect is enhanced by the long radiative relaxation timescale). The polar winter states obtained when gravity wave drag is omitted in this simple model resemble the results of simulations with some general circulation models and suggest that some of the shortcomings of the latter may be due to a deficit in mesospheric momentum deposition by small-scale gravity waves.

Evidence for a continuous spectrum of equatorial waves in the Indian Ocean

NASA Astrophysics Data System (ADS)

Eriksen, Charles C.

1980-06-01

Seven-month records of current and temperature measurements from a moored array centered at 53°E on the equator in the Indian Ocean are consistent with a continuous spectrum of equatorially trapped internal inertial-gravity, mixed Rossby-gravity, and Kelvin waves. A model spectrum of free linear waves analogous to those for mid-latitude internal gravity waves is used to compute spectra of observed quantities at depths greater than about 2000 m. Model parameters are adjusted to fit general patterns in the observed spectra over periods from roughly 2 days to 1 month. Measurements at shallower depths presumably include forced motions which we have not attempted to model. This `straw-person' spectrum is consistent with the limited data available. The model spectru Ē (n, m, ω) = K · B(m) · C(n, ω), where Ē is an average local energy density in the equatorial wave guide which has amplitude K, wave number shape B(m) ∝ (1 + m/m*)-3, where m is vertical mode number and the bandwidth parameter m* is between 4 and 8, and frequency shape C(n, ω) ∝ [(2n + 1 + s2)½ · σ3]-1 where n is meridional mode number, and s and σ are dimensionless zonal wave number and frequency related by the usual dispersion relation. The scales are (β/cm)½ and (β · cm)½ for horizontal wave number and frequency, where cm is the Kelvin wave speed of the vertical mode m. At each frequency and vertical wave number, energy is partitioned equally among the available inertial gravity modes so that the field tends toward horizontal isotropy at high frequency. The transition between Kelvin and mixed Rossby-gravity motion at low frequency and inertial-gravity motion at high frequency occurs at a period of roughly 1 week. At periods in the range 1-3 weeks, the model spectrum which fits the observations suggests that mixed Rossby-gravity motion dominates; at shorter periods gravity motion dominates. The model results are consistent with the low vertical coherence lengths observed (roughly 80 m). Horizontal coherence over 2 km is consistent with isotropic energy flux. Evidence for net zontal energy flux is not found in this data, and the presence of a red wave number shape suggests that net flux will be difficult to observe from modest moored arrays. The equatorial wave spectrum does not match across the diurnal and semidiurnal tides to the high-frequency internal wave spectrum (the latter is roughly 1 decade higher).

Investigation of Ionospheric Turbulence and Whistler Wave Interactions with Space Plasmas

DTIC Science & Technology

2012-11-21

an oscillating LOS velocity with the same periodicity as the heating modulation pattern. A set of Fourier periodogram from the MUIR LOS velocity...scale ionospheric turbulence are discussed separately, viz., (a) anomalous heat source-induced acoustic gravity waves (AGW), and (b) HF radio wave...ionospheric ducts, acoustic gravity waves (AGWs), anomalous heat sources, inner and outer radiation belts, L parameter, whistler wave interactions

Gravitational wave production by Hawking radiation from rotating primordial black holes

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

Dong, Ruifeng; Kinney, William H.; Stojkovic, Dejan, E-mail: ruifengd@buffalo.edu, E-mail: whkinney@buffalo.edu, E-mail: ds77@buffalo.edu

In this paper we analyze in detail a rarely discussed question of gravity wave production from evaporating primordial black holes. These black holes emit gravitons which are, at classical level, registered as gravity waves. We use the latest constraints on their abundance, and calculate the power emitted in gravitons at the time of their evaporation. We then solve the coupled system of equations that gives us the evolution of the frequency and amplitude of gravity waves during the expansion of the universe. The spectrum of gravitational waves that can be detected today depends on multiple factors: fraction of the totalmore » energy density which was occupied by primordial black holes, the epoch in which they were formed, and quantities like their mass and angular momentum. We conclude that very small primordial black holes which evaporate before the big-bang nucleosynthesis emit gravitons whose spectral energy fraction today can be as large as 10{sup −7.5}. On the other hand, those which are massive enough so that they still exist now can yield a signal as high as 10{sup −6.5}. However, typical frequencies of the gravity waves from primordial black holes are still too high to be observed with the current and near future gravity wave observations.« less

Planetary and Gravity Waves in the Mesosphere and Lower Thermosphere

NASA Technical Reports Server (NTRS)

Vincent, R. A.

1985-01-01

Rocket and ground based studies of the mesosphere and lower thermosphere show that waves play an important role in the dynamics of their region. The waves manifest themselves in wind, temperature, density, pressure, ionization and airglow fluctuations in the 80-120 km height range. Rockets have enabled the density and temperature structure to be measured with excellent height resolution, while long term studies of wind motions using MST, partial reflection and meteor radars and, more recently, lidar investigations of temperature and density, have enabled the temporal behaviour of the waves to be better understood. A composite of power spectra is shown of wind motions measured near the mesopause at widely separated locations and illustrates how wave energy is distributed as a function of frequency. The spectra show three distinct parts; (1) a long period section corresponding to periods longer than 24 h; (2) a section between 12 and 24 h priod where the spectra are dominated by narrow; peaks associated with the semidiurnal and diurnal tides and (3) a section at periods less than 12 h where the spectral density decreases montonically (except for the 8 h tidal peak). The long period section is associated with transient planetary scale waves while the short period motions are caused by gravity waves.

Experimental study of three-wave interactions among capillary-gravity surface waves

NASA Astrophysics Data System (ADS)

Haudin, Florence; Cazaubiel, Annette; Deike, Luc; Jamin, Timothée; Falcon, Eric; Berhanu, Michael

2016-04-01

In propagating wave systems, three- or four-wave resonant interactions constitute a classical nonlinear mechanism exchanging energy between the different scales. Here we investigate three-wave interactions for gravity-capillary surface waves in a closed laboratory tank. We generate two crossing wave trains and we study their interaction. Using two optical methods, a local one (laser doppler vibrometry) and a spatiotemporal one (diffusive light photography), a third wave of smaller amplitude is detected, verifying the three-wave resonance conditions in frequency and in wave number. Furthermore, by focusing on the stationary regime and by taking into account viscous dissipation, we directly estimate the growth rate of the resonant mode. The latter is then compared to the predictions of the weakly nonlinear triadic resonance interaction theory. The obtained results confirm qualitatively and extend previous experimental results obtained only for collinear wave trains. Finally, we discuss the relevance of three-wave interaction mechanisms in recent experiments studying gravity-capillary turbulence.

Experimental study of three-wave interactions among capillary-gravity surface waves.

PubMed

Haudin, Florence; Cazaubiel, Annette; Deike, Luc; Jamin, Timothée; Falcon, Eric; Berhanu, Michael

2016-04-01

In propagating wave systems, three- or four-wave resonant interactions constitute a classical nonlinear mechanism exchanging energy between the different scales. Here we investigate three-wave interactions for gravity-capillary surface waves in a closed laboratory tank. We generate two crossing wave trains and we study their interaction. Using two optical methods, a local one (laser doppler vibrometry) and a spatiotemporal one (diffusive light photography), a third wave of smaller amplitude is detected, verifying the three-wave resonance conditions in frequency and in wave number. Furthermore, by focusing on the stationary regime and by taking into account viscous dissipation, we directly estimate the growth rate of the resonant mode. The latter is then compared to the predictions of the weakly nonlinear triadic resonance interaction theory. The obtained results confirm qualitatively and extend previous experimental results obtained only for collinear wave trains. Finally, we discuss the relevance of three-wave interaction mechanisms in recent experiments studying gravity-capillary turbulence.

Comparison of Gravity Wave Temperature Variances from Ray-Based Spectral Parameterization of Convective Gravity Wave Drag with AIRS Observations

NASA Technical Reports Server (NTRS)

Choi, Hyun-Joo; Chun, Hye-Yeong; Gong, Jie; Wu, Dong L.

2012-01-01

The realism of ray-based spectral parameterization of convective gravity wave drag, which considers the updated moving speed of the convective source and multiple wave propagation directions, is tested against the Atmospheric Infrared Sounder (AIRS) onboard the Aqua satellite. Offline parameterization calculations are performed using the global reanalysis data for January and July 2005, and gravity wave temperature variances (GWTVs) are calculated at z = 2.5 hPa (unfiltered GWTV). AIRS-filtered GWTV, which is directly compared with AIRS, is calculated by applying the AIRS visibility function to the unfiltered GWTV. A comparison between the parameterization calculations and AIRS observations shows that the spatial distribution of the AIRS-filtered GWTV agrees well with that of the AIRS GWTV. However, the magnitude of the AIRS-filtered GWTV is smaller than that of the AIRS GWTV. When an additional cloud top gravity wave momentum flux spectrum with longer horizontal wavelength components that were obtained from the mesoscale simulations is included in the parameterization, both the magnitude and spatial distribution of the AIRS-filtered GWTVs from the parameterization are in good agreement with those of the AIRS GWTVs. The AIRS GWTV can be reproduced reasonably well by the parameterization not only with multiple wave propagation directions but also with two wave propagation directions of 45 degrees (northeast-southwest) and 135 degrees (northwest-southeast), which are optimally chosen for computational efficiency.

GPS Observations of Medium-Scale Traveling Ionospheric Disturbances over New Zealand

NASA Astrophysics Data System (ADS)

Otsuka, Y.; Lee, C.; Shiokawa, K.; Tsugawa, T.; Nishioka, M.

2014-12-01

Using the GPS data obtained from dual-frequency GPS receivers in New Zealand, we have made two-dimensional maps of total electron content (TEC) in 2012 in order to reveal statistical characteristics of MSTIDs at mid-latitudes in southern hemisphere. As of 2012, approximately 40 GPS receivers are in operation in New Zealand. We found that most of the MSITDs over New Zealand propagate northwestward during nighttime in summer and northeastward during daytime in winter. The propagation direction of the nighttime MSTIDs is consistent with the theory that polarization electric fields play an important role in the generating MSTIDs. Because the daytime MSTIDs propagate equatorward, we can speculate that they could be caused by atmospheric gravity waves in the thermosphere. The propagation direction of the daytime MSTIDs also has an eastward component in addition to the equatorward component. This feature is consistent with the daytime MSTIDs observed at mid-latitudes in both northern and southern hemispheres. By carrying out model calculations, we have shown that the eastward component of the MSTID propagation direction during daytime is attributed to an interaction of gravity waves to the background neutral winds. Because most of the daytime MSTIDs appear before 14 LT, the background neutral winds could blow westward. According to the dispersion relation for atmospheric gravity waves, vertical wavelength of the gravity waves becomes larger when the gravity wave propagates in the direction opposite to the background winds. Consequently, the gravity waves having an eastward component of the propagation direction could cause larger amplitude of TEC variations compared to the gravity waves propagating westward. This could be a reason why the propagation direction of the dime MSTIDs has an eastward component.

The Effect of Aerosol on Gravity Wave Characteristics above the Boundary Layer over a Tropical Location

NASA Astrophysics Data System (ADS)

Rakshit, G.; Jana, S.; Maitra, A.

2017-12-01

The perturbations of temperature profile over a location give an estimate of the potential energy of gravity waves propagating through the atmosphere. Disturbances in the lower atmosphere due to tropical deep convection, orographic effects and various atmospheric disturbances generates of gravity waves. The present study investigates the gravity wave energy estimated from fluctuations in temperature profiles over the tropical location Kolkata (22°34' N, 88°22' E). Gravity waves are most intense during the pre-monsoon period (March-June) at the present location, the potential energy having high values above the boundary layer (2-4 km) as observed from radiosonde profiles. An increase in temperature perturbation, due to high ambient temperature in the presence of heat absorbing aerosols, causes an enhancement in potential energy. As the present study location is an urban metropolitan city experiencing high level of pollution, pollutant aerosols can go much above the normal boundary layer during daytime due to convection causing an extended boundary layer. The Aerosol Index (AAI) obtained from Global Ozone Monitoring Experiment-2 (GOME-2) on MetOp-A platform at 340 nm and 380 nm confirms the presence of absorbing aerosol particles over the present location. The Hysplit back trajectory analysis shows that the aerosol particles at those heights are of local origin and are responsible for depleting liquid water content due to cloud burning. The aerosol extinction coefficient obtained from CALIPSO data exhibits an increasing trend during 2006-2016 accompanied by a similar pattern of gravity wave energy. Thus the absorbing aerosols have a significant role in increasing the potential energy of gravity wave at an urban location in the tropical region.

Convectively-generated gravity waves and clear-air turbulence (CAT)

NASA Astrophysics Data System (ADS)

Sharman, Robert; Lane, Todd; Trier, Stanley

2013-04-01

Upper-level turbulence is a well-known hazard to aviation that is responsible for numerous injuries each year, with occasional fatalities, and results in millions of dollars of operational costs to airlines each year. It has been widely accepted that aviation-scale turbulence that occurs in clear air (CAT) at upper levels (upper troposphere and lower stratosphere) has its origins in Kelvin-Helmholtz instabilities induced by enhanced shears and reduced Richardson numbers associated with the jet stream and upper level fronts. However, it is becoming increasingly apparent that gravity waves and gravity wave "breaking" also play a major role in instigating turbulence that affects aviation. Gravity waves and inertia-gravity waves may be produced by a variety of sources, but one major source that impacts aviation seems to be those produced by convection. The relation of convectively-induced gravity waves to turbulence outside the cloud (either above cloud or laterally away from cloud) is examined based on high resolution cloud-resolving simulations, both with and without cloud microphysics in the simulations. Results for both warm-season and cold-season cloud systems indicate that the turbulence in the clear air away from cloud is often caused by gravity wave production processes in or near the cloud which once initiated, are able to propagate away from the storm, and may eventually "break." Without microphysics of course this effect is absent and turbulence is not produced in the simulations. In some cases the convectively-induced turbulence may be many kilometers away from the active convection and can easily be misinterpreted as "clear-air turbulence" (CAT). This is a significant result, and may be cause for a reassessment of the working definition of CAT ("turbulence encountered outside of convective clouds", FAA Advisory Circular AC 00-30B, 1997).

A numerical model for ocean ultra-low frequency noise: wave-generated acoustic-gravity and Rayleigh modes.

PubMed

Ardhuin, Fabrice; Lavanant, Thibaut; Obrebski, Mathias; Marié, Louis; Royer, Jean-Yves; d'Eu, Jean-François; Howe, Bruce M; Lukas, Roger; Aucan, Jerome

2013-10-01

The generation of ultra-low frequency acoustic noise (0.1 to 1 Hz) by the nonlinear interaction of ocean surface gravity waves is well established. More controversial are the quantitative theories that attempt to predict the recorded noise levels and their variability. Here a single theoretical framework is used to predict the noise level associated with propagating pseudo-Rayleigh modes and evanescent acoustic-gravity modes. The latter are dominant only within 200 m from the sea surface, in shallow or deep water. At depths larger than 500 m, the comparison of a numerical noise model with hydrophone records from two open-ocean sites near Hawaii and the Kerguelen islands reveal: (a) Deep ocean acoustic noise at frequencies 0.1 to 1 Hz is consistent with the Rayleigh wave theory, in which the presence of the ocean bottom amplifies the noise by 10 to 20 dB; (b) in agreement with previous results, the local maxima in the noise spectrum support the theoretical prediction for the vertical structure of acoustic modes; and (c) noise level and variability are well predicted for frequencies up to 0.4 Hz. Above 0.6 Hz, the model results are less accurate, probably due to the poor estimation of the directional properties of wind-waves with frequencies higher than 0.3 Hz.

Modeling the QBO-Improvements resulting from higher-model vertical resolution.

PubMed

Geller, Marvin A; Zhou, Tiehan; Shindell, D; Ruedy, R; Aleinov, I; Nazarenko, L; Tausnev, N L; Kelley, M; Sun, S; Cheng, Y; Field, R D; Faluvegi, G

2016-09-01

Using the NASA Goddard Institute for Space Studies (GISS) climate model, it is shown that with proper choice of the gravity wave momentum flux entering the stratosphere and relatively fine vertical layering of at least 500 m in the upper troposphere-lower stratosphere (UTLS), a realistic stratospheric quasi-biennial oscillation (QBO) is modeled with the proper period, amplitude, and structure down to tropopause levels. It is furthermore shown that the specified gravity wave momentum flux controls the QBO period whereas the width of the gravity wave momentum flux phase speed spectrum controls the QBO amplitude. Fine vertical layering is required for the proper downward extension to tropopause levels as this permits wave-mean flow interactions in the UTLS region to be resolved in the model. When vertical resolution is increased from 1000 to 500 m, the modeled QBO modulation of the tropical tropopause temperatures increasingly approach that from observations, and the "tape recorder" of stratospheric water vapor also approaches the observed. The transport characteristics of our GISS models are assessed using age-of-air and N 2 O diagnostics, and it is shown that some of the deficiencies in model transport that have been noted in previous GISS models are greatly improved for all of our tested model vertical resolutions. More realistic tropical-extratropical transport isolation, commonly referred to as the "tropical pipe," results from the finer vertical model layering required to generate a realistic QBO.

Turbulence and stress owing to gravity wave and tidal breakdown

NASA Technical Reports Server (NTRS)

Lindzen, R. S.

1981-01-01

For some years it has been accepted that tides and gravity waves propagating into the upper mesosphere from below are the major source of turbulence in the upper mesosphere. The considered investigation has the objective to examine the implications of such a situation in some detail. The main propagating diurnal mode seems to be the primary contributor at tropical latitudes. Because of the high phase speed of this mode, it is only slightly affected by the mean zonal flow of the atmosphere. Wavebreaking appears to occur around 85 km, leading to a layer of enhanced eddy diffusion and wave induced acceleration extending between 85 km and about 108 km. Above 108 km molecular transport dominates. Gravity waves appear to be dominant at middle and high latitudes. The flow distribution will effectively determine which gravity waves (depending on phase speed) can reach the mesosphere.

Observation and Modeling of Tsunami-Generated Gravity Waves in the Earth’s Upper Atmosphere

DTIC Science & Technology

2015-10-08

Observation and modeling of tsunami -generated gravity waves in the earth’s upper atmosphere 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6...ABSTRACT Build a compatible set of models which 1) calculate the spectrum of atmospheric GWs excited by a tsunami (using ocean model data as input...for public release; distribution is unlimited. Observation and modeling of tsunami -generated gravity waves in the earth’s upper atmosphere Sharon

The impact of gravity waves and cloud nucleation threshold on stratospheric water and tropical tropospheric cloud fraction

NASA Astrophysics Data System (ADS)

Schoeberl, Mark; Dessler, Andrew; Ye, Hao; Wang, Tao; Avery, Melody; Jensen, Eric

2016-08-01

Using the Modern Era Retrospective-Analysis for Research and Applications (MERRA) and MERRA-2 reanalysis winds, temperatures, and anvil cloud ice, we explore the impact of varying the cloud nucleation threshold relative humidity (RH) and high-frequency gravity waves on stratospheric water vapor (H2O) and upper tropical tropopause cloud fraction (TCF). Our model results are compared to 2008/2009 winter TCF derived from Cloud-Aerosol Lidar with Orthogonal Polarization and H2O observations from the Microwave Limb Sounder (MLS). The RH threshold affects both model H2O and TCF, while high-frequency gravity waves mostly impact TCF. Adjusting the nucleation RH and the amplitude of high-frequency gravity waves allows us to tune the model to observations. Reasonable observational agreement is obtained with a nucleation threshold between 130% and 150% RH consistent with airborne observations. For the MERRA reanalysis, we lower the tropopause temperature by 0.5 K roughly consistent with GPS radio occultation measurements and include ~0.1 K high-frequency gravity wave temperature oscillations in order to match TCF and H2O observations. For MERRA-2 we do not need to adjust the tropopause temperature nor add gravity waves, because there are sufficient high-frequency temperature oscillations already present in the MERRA-2 reanalysis to reproduce the observed TCF.

Gravity Waves and Wind-Farm Efficiency in Neutral and Stable Conditions

NASA Astrophysics Data System (ADS)

Allaerts, Dries; Meyers, Johan

2018-02-01

We use large-eddy simulations (LES) to investigate the impact of stable stratification on gravity-wave excitation and energy extraction in a large wind farm. To this end, the development of an equilibrium conventionally neutral boundary layer into a stable boundary layer over a period of 8 h is considered, using two different cooling rates. We find that turbulence decay has considerable influence on the energy extraction at the beginning of the boundary-layer transition, but afterwards, energy extraction is dominated by geometrical and jet effects induced by an inertial oscillation. It is further shown that the inertial oscillation enhances gravity-wave excitation. By comparing LES results with a simple one-dimensional model, we show that this is related to an interplay between wind-farm drag, variations in the Froude number and the dispersive effects of vertically-propagating gravity waves. We further find that the pressure gradients induced by gravity waves lead to significant upstream flow deceleration, reducing the average turbine output compared to a turbine in isolated operation. This leads us to the definition of a non-local wind-farm efficiency, next to a more standard wind-farm wake efficiency, and we show that both can be of the same order of magnitude. Finally, an energy flux analysis is performed to further elucidate the effect of gravity waves on the flow in the wind farm.

Quasi-12 h inertia-gravity waves in the lower mesosphere observed by the PANSY radar at Syowa Station (39.6° E, 69.0° S)

NASA Astrophysics Data System (ADS)

Shibuya, Ryosuke; Sato, Kaoru; Tsutsumi, Masaki; Sato, Toru; Tomikawa, Yoshihiro; Nishimura, Koji; Kohma, Masashi

2017-05-01

The first observations made by a complete PANSY radar system (Program of the Antarctic Syowa MST/IS Radar) installed at Syowa Station (39.6° E, 69.0° S) were successfully performed from 16 to 24 March 2015. Over this period, quasi-half-day period (12 h) disturbances in the lower mesosphere at heights of 70 to 80 km were observed. Estimated vertical wavelengths, wave periods and vertical phase velocities of the disturbances were approximately 13.7 km, 12.3 h and -0.3 m s-1, respectively. Under the working hypothesis that such disturbances are attributable to inertia-gravity waves, wave parameters are estimated using a hodograph analysis. The estimated horizontal wavelengths are longer than 1100 km, and the wavenumber vectors tend to point northeastward or southwestward. Using the nonhydrostatic numerical model with a model top of 87 km, quasi-12 h disturbances in the mesosphere were successfully simulated. We show that quasi-12 h disturbances are due to wave-like disturbances with horizontal wavelengths longer than 1400 km and are not due to semidiurnal migrating tides. Wave parameters, such as horizontal wavelengths, vertical wavelengths and wave periods, simulated by the model agree well with those estimated by the PANSY radar observations under the abovementioned assumption. The parameters of the simulated waves are consistent with the dispersion relationship of the inertia-gravity wave. These results indicate that the quasi-12 h disturbances observed by the PANSY radar are attributable to large-scale inertia-gravity waves. By examining a residual of the nonlinear balance equation, it is inferred that the inertia-gravity waves are likely generated by the spontaneous radiation mechanism of two different jet streams. One is the midlatitude tropospheric jet around the tropopause while the other is the polar night jet. Large vertical fluxes of zonal and meridional momentum associated with large-scale inertia-gravity waves are distributed across a slanted region from the midlatitude lower stratosphere to the polar mesosphere in the meridional cross section. Moreover, the vertical flux of the zonal momentum has a strong negative peak in the mesosphere, suggesting that some large-scale inertia-gravity waves originate in the upper stratosphere.

Convectively Generated Gravity Waves In The Tropical Stratosphere: Case Studies And Importance For The Circulation Of The Middle Atmosphere

NASA Technical Reports Server (NTRS)

Pfister, Leonhard; Chan, Kwoklong R.; Gary, Bruce; Singh, Hanwant B. (Technical Monitor)

1995-01-01

The advent of high altitude aircraft measurements in the stratosphere over tropical convective systems has made it possible to observe the mesoscale disturbances in the temperature field that these systems excite. Such measurements show that these disturbances have horizontal scales comparable to those of the underlying anvils (about 50-100 km) with peak to peak theta surface variations of about 300-400 meters. Moreover, correlative wind measurements from the tropical phase of the Stratosphere-Troposphere Exchange Project (STEP) clearly show that these disturbances are gravity waves. We present two case studies of anvil-scale gravity waves over convective systems. Using steady and time-dependent linear models of gravity wave propagation in the stratosphere, we show: (1) that the underlying convective systems are indeed the source of the observed phenomena; and (2) that their generating mechanism can be crudely represented as flow over a time-dependent mountain. We will then discuss the effects gravity waves of the observed amplitudes have on the circulation of the middle atmosphere, particularly the quasi-biennial, and semiannual oscillations.

Radar studies of gravity waves and tides in the middle atmosphere - A review

NASA Technical Reports Server (NTRS)

Rastogi, P. K.

1981-01-01

A review is presented of recent radar studies of gravity waves and tides in the middle atmosphere (over regions of approximately 10-30 and 60-90 km). The techniques used for monitoring the motions are outlined and their limitations are pointed out. The radars provide observations of short-period (1 min-1 h) gravity waves and tides at selected height intervals, depending on the radar frequency and the observation technique. The following contributions to the study of the midatmosphere are included in the discussion: (1) buoyancy oscillations and short-period (less than 10 min) acoustic-gravity waves have been observed in the troposphere and stratosphere and, in several cases, their generation and propagation near critical levels has been reconciled with theoretical models; (2) excitation of stratospheric waves by penetrative convection associated with thunderstorms has been established; (3) stratospheric and mesospheric tides at diurnal and semidiurnal periods have been observed; and (4) long-period (approximately 2 to 5 days) waves have been observed in the mesosphere. It is noted that more comprehensive data bases need to be obtained for further tidal and wave studies.

Observation of infrasonic and gravity waves at Soufrière Hills Volcano, Montserrat

NASA Astrophysics Data System (ADS)

Ripepe, Maurizio; De Angelis, Silvio; Lacanna, Giorgio; Voight, Barry

2010-04-01

The sudden ejection of material during an explosive eruption generates a broad spectrum of pressure oscillations, from infrasonic to gravity waves. An infrasonic array, installed at 3.5 km from the Soufriere Hills Volcano has successfully detected and located, in real-time, the infrasound generated by several pyroclastic flows (PF) estimating mean flow speeds of 30-75 m/s. On July 29 and December 3, 2008, two differential pressure transducers, co-located with the array, recorded ultra long-period (ULP) oscillations at frequencies of 0.97 and 3.5 mHz, typical of atmospheric gravity waves, associated with explosive eruptions. The observation of gravity waves in the near-field (<6 km) at frequencies as low as about 1 mHz is unprecedented during volcanic eruptions.

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.

Turbulent structure of stably stratified inhomogeneous flow

NASA Astrophysics Data System (ADS)

Iida, Oaki

2018-04-01

Effects of buoyancy force stabilizing disturbances are investigated on the inhomogeneous flow where disturbances are dispersed from the turbulent to non-turbulent field in the direction perpendicular to the gravity force. Attaching the fringe region, where disturbances are excited by the artificial body force, a Fourier spectral method is used for the inhomogeneous flow stirred at one side of the cuboid computational box. As a result, it is found that the turbulent kinetic energy is dispersed as layered structures elongated in the streamwise direction through the vibrating motion. A close look at the layered structures shows that they are flanked by colder fluids at the top and hotter fluids at the bottom, and hence vertically compressed and horizontally expanded by the buoyancy related to the countergradient heat flux, though they are punctuated by the vertical expansion of fluids at the forefront of the layered structures, which is related to the downgradient heat flux, indicating that the layered structures are gravity currents. However, the phase between temperature fluctuations and vertical velocity is shifted by π/2 rad, indicating that temperature fluctuations are generated by the propagation of internal gravity waves.

A Simulated Spectrum of Convectively Generated Gravity Waves: Propagation from the Tropopause to the Mesopause and Effects on the Middle Atmosphere

NASA Technical Reports Server (NTRS)

Alexander, Joan

1996-01-01

This work evaluates the interaction of a simulated spectrum of convectively generated gravity waves with realistic middle atmosphere mean winds. The wave spectrum is derived from the nonlinear convection model described by Alexander et al. that simulated a two-dimensional midlatitude squall line. This spectrum becomes input to a linear ray tracing model for evaluation of wave propagation as a function of height through climatological background wind and buoyancy frequency profiles. The energy defined by the spectrum as a function of wavenumber and frequency is distributed spatially and temporally into wave packets for the purpose of estimating wave amplitudes at the lower boundary of the ray tracing model. A wavelet analysis provides an estimate of these wave packet widths in space and time. Without this redistribution of energies into wave packets the Fourier analysis alone inaccurately assumes the energy is evenly distributed throughout the storm model domain. The growth with height of wave amplitudes is derived from wave action flux conservation coupled to a convective instability saturation condition. Mean flow accelerations and wave energy dissipation profiles are derived from this analysis and compared to parameterized estimates of gravity wave forcing, providing a measure of the importance of the storm source to global gravity wave forcing. The results suggest that a single large convective storm system like the simulated squall line could provide a significant fraction of the zonal mean gravity wave forcing at some levels, particularly in the mesosphere. The vertical distributions of mean flow acceleration and energy dissipation do not much resemble the parameterized profiles in form because of the peculiarities of the spectral properties of the waves from the storm source. The ray tracing model developed herein provides a tool for examining the role of convectively generated waves in middle atmosphere physics.

A Simulated Spectrum of Convectively Generated Gravity Waves: Propagation from the Tropopause to the Mesopause and Effects on the Middle Atmosphere

NASA Technical Reports Server (NTRS)

Alexander, M. Joan

1996-01-01

This work evaluates the interaction of a simulated spectrum of convectively generated gravity waves with realistic middle atmosphere mean winds. The wave spectrum is derived from the nonlinear convection model described by Alexander et al. [1995] that simulated a two-dimensional midlatitude squall line. This spectrum becomes input to a linear ray tracing model for evaluation of wave propagation as a function of height through climatological background wind and buoyancy frequency profiles. The energy defined by the spectrum as a function of wavenumber and frequency is distributed spatially and temporally into wave packets for the purpose of estimating wave amplitudes at the lower boundary of the ray tracing model. A wavelet analysis provides an estimate of these wave packet widths in space and time. Without this redistribution of energies into wave packets the Fourier analysis alone inaccurately assumes the energy is evenly distributed throughout the storm model domain. The growth with height of wave amplitudes is derived from wave action flux conservation coupled to a convective instability saturation condition. Mean flow accelerations and wave energy dissipation profiles are derived from this analysis and compared to parameterized estimates of gravity wave forcing, providing a measure of the importance of the storm source to global gravity wave forcing. The results suggest that a single large convective storm system like the simulated squall line could provide a significant fraction of the zonal mean gravity wave forcing at some levels, particularly in the mesosphere. The vertical distributions of mean flow acceleration and energy dissipation do not much resemble the parameterized profiles in form because of the peculiarities of the spectral properties of the waves from the storm source. The ray tracing model developed herein provides a tool for examining the role of convectively generated waves in middle atmosphere physics.

Location and extent of Tertiary structures in Cook Inlet Basin, Alaska, and mantle dynamics that focus deformation and subsidence

USGS Publications Warehouse

Haeussler, Peter J.; Saltus, Richard W.

2011-01-01

Subduction of the buoyant Yakutat microplate likely caused deformation to be focused preferentially in upper Cook Inlet. The upper Cook Inlet region has both the highest degree of shortening and the deepest part of the Neogene basin. This forearc region has a long-wavelength magnetic high, a large isostatic gravity low, high conductivity in the lower mantle, low p-wave velocity (Vp), and a high p-wave to shear-wave velocity ratio (Vp/Vs). These data suggest that fluids in the mantle wedge caused serpentinization of mafic rocks, which may, at least in part, contribute to the long-wavelength magnetic anomaly. This area lies adjacent to the subducting and buoyant Yakutat microplate slab. We suggest the buoyant Yakutat slab acts much like a squeegee to focus mantle-wedge fluid flow at the margins of the buoyant slab. Such lateral flow is consistent with observed shear-wave splitting directions. The additional fluid in the adjacent mantle wedge reduces the wedge viscosity and allows greater corner flow. This results in focused subsidence, deformation, and gravity anomalies in the forearc region.

Stochastic Convection Parameterizations

NASA Technical Reports Server (NTRS)

Teixeira, Joao; Reynolds, Carolyn; Suselj, Kay; Matheou, Georgios

2012-01-01

computational fluid dynamics, radiation, clouds, turbulence, convection, gravity waves, surface interaction, radiation interaction, cloud and aerosol microphysics, complexity (vegetation, biogeochemistry, radiation versus turbulence/convection stochastic approach, non-linearities, Monte Carlo, high resolutions, large-Eddy Simulations, cloud structure, plumes, saturation in tropics, forecasting, parameterizations, stochastic, radiation-clod interaction, hurricane forecasts

Middle Atmosphere Program. Handbook for MAP, volume 4

NASA Technical Reports Server (NTRS)

Sechrist, C. F., Jr. (Editor)

1982-01-01

Topics include winter in the Northern Hemisphere, temperature measurement, geopotential heights, wind measurement, atmospheric motions, photochemical reactions, solar spectral irradiance, trace constituents, tides, gravity waves, and turbulence. Highlights from the Map Steering Committee and a Map Open Meeting including organizational structure are also given.

Three-wave and four-wave interactions in gravity wave turbulence

NASA Astrophysics Data System (ADS)

Aubourg, Quentin; Campagne, Antoine; Peureux, Charles; Ardhuin, Fabrice; Sommeria, Joel; Viboud, Samuel; Mordant, Nicolas

2017-11-01

Weak-turbulence theory is a statistical framework to describe a large ensemble of nonlinearly interacting waves. The archetypal example of such system is the ocean surface that is made of interacting surface gravity waves. Here we describe a laboratory experiment dedicated to probe the statistical properties of turbulent gravity waves. We set up an isotropic state of interacting gravity waves in the Coriolis facility (13-m-diam circular wave tank) by exciting waves at 1 Hz by wedge wave makers. We implement a stereoscopic technique to obtain a measurement of the surface elevation that is resolved in both space and time. Fourier analysis shows that the laboratory spectra are systematically steeper than the theoretical predictions and the field observations in the Black Sea by Leckler et al. [F. Leckler et al., J. Phys. Oceanogr. 45, 2484 (2015), 10.1175/JPO-D-14-0237.1]. We identify a strong impact of surface dissipation on the scaling of the Fourier spectrum at the scales that are accessible in the experiments. We use bicoherence and tricoherence statistical tools in frequency and/or wave-vector space to identify the active nonlinear coupling. These analyses are also performed on the field data by Leckler et al. for comparison with the laboratory data. Three-wave coupling is characterized by and shown to involve mostly quasiresonances of waves with second- or higher-order harmonics. Four-wave coupling is not observed in the laboratory but is evidenced in the field data. We discuss temporal scale separation to explain our observations.

Frozen-wave instability in near-critical hydrogen subjected to horizontal vibration under various gravity fields.

PubMed

Gandikota, G; Chatain, D; Amiroudine, S; Lyubimova, T; Beysens, D

2014-01-01

The frozen-wave instability which appears at a liquid-vapor interface when a harmonic vibration is applied in a direction tangential to it has been less studied until now. The present paper reports experiments on hydrogen (H2) in order to study this instability when the temperature is varied near its critical point for various gravity levels. Close to the critical point, a liquid-vapor density difference and surface tension can be continuously varied with temperature in a scaled, universal way. The effect of gravity on the height of the frozen waves at the interface is studied by performing the experiments in a magnetic facility where effective gravity that results from the coupling of the Earth's gravity and magnetic forces can be varied. The stability diagram of the instability is obtained. The experiments show a good agreement with an inviscid model [Fluid Dyn. 21 849 (1987)], irrespective of the gravity level. It is observed in the experiments that the height of the frozen waves varies weakly with temperature and increases with a decrease in the gravity level, according to a power law with an exponent of 0.7. It is concluded that the wave height becomes of the order of the cell size as the gravity level is asymptotically decreased to zero. The interface pattern thus appears as a bandlike pattern of alternate liquid and vapor phases, a puzzling phenomenon that was observed with CO2 and H2 near their critical point in weightlessness [Acta Astron. 61 1002 (2007); Europhys. Lett. 86 16003 (2009)].

An evaluation of gravity waves and gravity wave sources in the Southern Hemisphere in a 7 km global climate simulation.

PubMed

Holt, L A; Alexander, M J; Coy, L; Liu, C; Molod, A; Putman, W; Pawson, S

2017-07-01

In this study, gravity waves (GWs) in the high-resolution GEOS-5 Nature Run are first evaluated with respect to satellite and other model results. Southern Hemisphere winter sources of non-orographic GWs in the model are then investigated by linking measures of tropospheric non-orographic gravity wave generation tied to precipitation and frontogenesis with absolute gravity wave momentum flux in the lower stratosphere. Finally, non-orographic GW momentum flux is compared to orographic gravity wave momentum flux and compared to previous estimates. The results show that the global patterns in GW amplitude, horizontal wavelength, and propagation direction are realistic compared to observations. However, as in other global models, the amplitudes are weaker and horizontal wavelengths longer than observed. The global patterns in absolute GW momentum flux also agree well with previous model and observational estimates. The evaluation of model non-orographic GW sources in the Southern Hemisphere winter shows that strong intermittent precipitation (greater than 10 mm h -1 ) is associated with GW momentum flux over the South Pacific, whereas frontogenesis and less intermittent, lower precipitation rates (less than 10 mm h -1 ) are associated with GW momentum flux near 60°S. In the model, orographic GWs contribute almost exclusively to a peak in zonal mean momentum flux between 70 and 75°S, while non-orographic waves dominate at 60°S, and non-orographic GWs contribute a third to a peak in zonal mean momentum flux between 25 and 30°S.

On the presence of equatorial waves in the lower stratosphere of a general circulation model

NASA Astrophysics Data System (ADS)

Maury, P.; Lott, F.

2014-02-01

To challenge the hypothesis that equatorial waves in the lower stratosphere are essentially forced by convection, we use the LMDz atmospheric model extended to the stratosphere and compare two versions having very different convection schemes but no quasi-biennial oscillation (QBO). The two versions have realistic time mean precipitation climatologies but very different precipitation variabilities. Despite these differences, the equatorial stratospheric Kelvin waves at 50 hPa are almost identical in the two versions and quite realistic. The Rossby gravity waves are also very similar but significantly weaker than in observations. We demonstrate that this bias on the Rossby gravity waves is essentially due to a dynamical filtering occurring because the model zonal wind is systematically westward. During a westward phase of the QBO, the ERA-Interim Rossby gravity waves compare well with those in the model. These results suggest that (i) in the model the effect of the convection scheme on the waves is in part hidden by the dynamical filtering, and (ii) the waves are produced by other sources than equatorial convection. For the Kelvin waves, this last point is illustrated by an Eliassen and Palm flux analysis, showing that in the model they come more from the subtropics and mid-latitude regions, whereas in the ERA-Interim reanalysis the sources are more equatorial. We show that non-equatorial sources are also significant in reanalysis data sets as they explain the presence of the Rossby gravity waves in the stratosphere. To illustrate this point, we identify situations with large Rossby gravity waves in the reanalysis middle stratosphere for dates selected when the stratosphere is dynamically separated from the equatorial troposphere. We refer to this process as a stratospheric reloading.

On the presence of equatorial waves in the lower stratosphere of a general circulation model

NASA Astrophysics Data System (ADS)

Maury, P.; Lott, F.

2013-08-01

To challenge the hypothesis that equatorial waves in the lower stratosphere are essentially forced by convection, we use the LMDz atmospheric model extended to the stratosphere and compare two versions having very different convection schemes but no quasi biennial oscillation (QBO). The two versions have realistic time mean precipitation climatologies but very different precipitation variabilities. Despite these differences, the equatorial stratospheric Kelvin waves at 50 hPa are almost identical in the two versions and quite realistic. The Rossby-gravity waves are also very close but significantly weaker than in observations. We demonstrate that this bias on the Rossby-gravity waves is essentially due to a dynamical filtering occurring because the model zonal wind is systematically westward: during a westward phase of the QBO, the Rossby-gravity waves in ERA-Interim compare well with those in the model. These results suggest that in the model the effect of the convection scheme on the waves is in part hidden by the dynamical filtering and the waves are produced by other sources than equatorial convection. For the Kelvin waves, this last point is illustrated by an Eliassen and Palm flux analysis, showing that in the model they come more from the subtropics and mid-latitude regions whereas in the ERA-Interim reanalysis the sources are more equatorial. We also show that non-equatorial sources are significant in reanalysis data, and we consider the case of the Rossby-gravity waves. We identify situations in the reanalysis where here are large Rossby-gravity waves in the middle stratosphere, and for dates when the stratosphere is dynamically separated from the equatorial troposphere. We refer to this process as a "stratospheric reloading".

Chilean Tsunami Rocks the Ross Ice Shelf

NASA Astrophysics Data System (ADS)

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

2016-12-01

The response of the Ross Ice Shelf (RIS) to the September 16, 2015 9.3 Mb Chilean earthquake tsunami (> 75 s period) and infragravity (IG) waves (50 - 300 s period) were recorded by a broadband seismic array deployed on the RIS from November 2014 to November 2015. The array included two linear transects, one approximately orthogonal to the shelf front extending 430 km southward toward the grounding zone, and an east-west transect spanning the RIS roughly parallel to the front about 100 km south of the ice edge (https://scripps.ucsd.edu/centers/iceshelfvibes/). Signals generated by both the tsunami and IG waves were recorded at all stations on floating ice, with little ocean wave-induced energy reaching stations on grounded ice. Cross-correlation and dispersion curve analyses indicate that tsunami and IG wave-generated signals propagate across the RIS at gravity wave speeds (about 70 m/s), consistent with coupled water-ice flexural-gravity waves propagating through the ice shelf from the north. Gravity wave excitation at periods > 100 s is continuously observed during the austral winter, providing mechanical excitation of the RIS throughout the year. Horizontal displacements are typically about 3 times larger than vertical displacements, producing extensional motions that could facilitate expansion of existing fractures. The vertical and horizontal spectra in the IG band attenuate exponentially with distance from the front. Tsunami model data are used to assess variability of excitation of the RIS by long period gravity waves. Substantial variability across the RIS roughly parallel to the front is observed, likely resulting from a combination of gravity wave amplitude variability along the front, signal attenuation, incident angle of the wave forcing at the front that depends on wave generation location as well as bathymetry under and north of the shelf, and water layer and ice shelf thickness and properties.

Instability-induced ordering, universal unfolding and the role of gravity in granular Couette flow

NASA Astrophysics Data System (ADS)

Alam, Meheboob; Arakeri, V. H.; Nott, P. R.; Goddard, J. D.; Herrmann, H. J.

2005-01-01

Linear stability theory and bifurcation analysis are used to investigate the role of gravity in shear-band formation in granular Couette flow, considering a kinetic-theory rheological model. We show that the only possible state, at low shear rates, corresponds to a "plug" near the bottom wall, in which the particles are densely packed and the shear rate is close to zero, and a uniformly sheared dilute region above it. The origin of such plugged states is shown to be tied to the spontaneous symmetry-breaking instabilities of the gravity-free uniform shear flow, leading to the formation of ordered bands of alternating dilute and dense regions in the transverse direction, via an infinite hierarchy of pitchfork bifurcations. Gravity plays the role of an "imperfection", thus destroying the "perfect" bifurcation structure of uniform shear. The present bifurcation problem admits universal unfolding of pitchfork bifurcations which subsequently leads to the formation of a sequence of a countably infinite number of "isolas", with the solution structures being a modulated version of their gravity-free counterpart. While the solution with a plug near the bottom wall looks remarkably similar to the shear-banding phenomenon in dense slow granular Couette flows, a "floating" plug near the top wall is also a solution of these equations at high shear rates. A two-dimensional linear stability analysis suggests that these floating plugged states are unstable to long-wave travelling disturbances.The unique solution having a bottom plug can also be unstable to long waves, but remains stable at sufficiently low shear rates. The implications and realizability of the present results are discussed in the light of shear-cell experiments under "microgravity" conditions.

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.

Is the spiral morphology of the Elias 2-27 circumstellar disc due to gravitational instability?

NASA Astrophysics Data System (ADS)

Hall, Cassandra; Rice, Ken; Dipierro, Giovanni; Forgan, Duncan; Harries, Tim; Alexander, Richard

2018-06-01

A recent Atacama Large Millimeter/submillimeter Array (ALMA) observation of the Elias 2-27 system revealed a two-armed structure extending out to ˜300 au in radius. The protostellar disc surrounding the central star is unusually massive, raising the possibility that the system is gravitationally unstable. Recent work has shown that the observed morphology of the system can be explained by disc self-gravity, so we examine the physical properties of the disc necessary to detect self-gravitating spiral waves. Using three-dimensional smoothed particle hydrodynamics, coupled with radiative transfer and synthetic ALMA imaging, we find that observable spiral structure can only be explained by self-gravity if the disc has a low opacity (and therefore efficient cooling), and is minimally supported by external irradiation. This corresponds to a very narrow region of parameter space, suggesting that, although it is possible for the spiral structure to be due to disc self-gravity, other explanations, such as an external perturbation, may be preferred.

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.

22 July 2009 total solar eclipse induced gravity waves in ionosphere as inferred from GPS observations over EIA

NASA Astrophysics Data System (ADS)

Kumar, K. Vijay; Maurya, Ajeet K.; Kumar, Sanjay; Singh, Rajesh

2016-11-01

In the present contribution we investigate the variation in the Global Positioning System (GPS) derived ionospheric Total Electron Content (TEC) over Equatorial Ionization Anomaly (EIA) region on the rare occasional astronomical phenomenon of total solar eclipse of 22 July 2009. The aim is to study and identify the wave like structure enumerated due to solar eclipse induced gravity waves in the F-region ionosphere altitude. The work is aimed to understand features of horizontal and vertical variation of atmospheric gravity waves (AGWs) properties over the Equatorial Ionization Anomaly (EIA) region in Indian low latitude region. The ionospheric observations is from the site of Allahabad (lat 25.4° N; lon. 81.9° E; dip 38.6° N) located at the fringe of eclipse totality path. The estimated vertical electron density profile from FORMOSAT-3/COSMIC GPS-RO satellite, considering all the satellite line of sight around the time of eclipse totality shows maximum depletion of 43%. The fast fourier transform and wavelet transform of GPS DTEC data from Allahabad station (Allahabad: lat 25.4 N; lon. 81.9 E) shows the presence of periodic waves of ∼20 to 45 min and ∼70 to 90 min period at F-region altitude. The shorter period correspond to the sunrise time morning terminator and longer period can be associated with solar eclipse generated AGWs. The most important result obtained is that our results along with previous result for wave like signatures in D-region ionosphere from Allahabad station show that AGWs generated by sunrise time terminator have similarity in the D and F region of the ionosphere but solar eclipse induced AGWs show higher period in the F-region compared to D-region ionosphere.

Modulation of Precipitation in the Olympic Mountains by Trapped Gravity Waves

NASA Astrophysics Data System (ADS)

Heymsfield, G. M.; Tian, L.; Grecu, M.; McLinden, M.; Li, L.

2017-12-01

Precipitation over the Olympic Mountains was studied intensely with multiple aircraft and ground-based measurements during the Olympic Mountains Experiment (OLYMPEX) during the fall-winter season 2015-2016 as part of validation for the Global Precipitation Mission (GPM) (Houze et al. 2017) and the Radar Definition Experiment (RADEX) supported by the Aerosol Chemistry, Ecosystem (ACE) NASA Decadal Mission. This presentation focuses on observations of a broad frontal cloud system with strong flow over the mountains on 5 December 2015. Unique observations of trapped waves were obtained with in the three Goddard Space Flight Center nadir-looking, X- through W-band, Doppler radars on the NASA high-altitude ER-2: the High-altitude Wind and Rain Airborne Profiler (HIWRAP) at Ku and Ka-band, the W-band Cloud Radar System (CRS), and the ER-2 X-band Radar (EXRAD). Analysis of the aircraft measurements showed the presence of deep, trapped gravity waves on a scale ranging from 10-25 km in the nadir-looking Doppler and reflectivity observations. These waves cause localized vertical up/down motions on the order of 1-2 ms-1 and they are superimposed on the widespread south-southwest flow over the Olympic Mountains. While much of this widespread flow over the mountains produces copious amounts of snowfall, the gravity waves play an important role in modulating this precipitation indirectly through microphysical processes in the ice region. We will describe analyses of the interactions between the air motions and precipitation structure for this case and other cases we observed similar waves. We will present preliminary results from precipitation retrievals based on optimal estimation (Grecu et al. 2011).

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.

Gravitational waves in modified teleparallel theories of gravity.

PubMed

Abedi, Habib; Capozziello, Salvatore

2018-01-01

Teleparallel theory of gravity and its modifications have been studied extensively in literature. However, gravitational waves has not been studied enough in the framework of teleparallelism. In the present study, we discuss gravitational waves in general theories of teleparallel gravity containing the torsion scalar T , the boundary term B and a scalar field ϕ . The goal is to classify possible new polarizations generalizing results presented in Bamba et al. (Phys Lett B 727:194-198, arXiv:1309.2698, 2013). We show that, if the boundary term is minimally coupled to the torsion scalar and the scalar field, gravitational waves have the same polarization modes of General Relativity.

Gravitational waves in modified teleparallel theories of gravity

NASA Astrophysics Data System (ADS)

Abedi, Habib; Capozziello, Salvatore

2018-06-01

Teleparallel theory of gravity and its modifications have been studied extensively in literature. However, gravitational waves has not been studied enough in the framework of teleparallelism. In the present study, we discuss gravitational waves in general theories of teleparallel gravity containing the torsion scalar T, the boundary term B and a scalar field φ . The goal is to classify possible new polarizations generalizing results presented in Bamba et al. (Phys Lett B 727:194-198, arXiv:1309.2698, 2013). We show that, if the boundary term is minimally coupled to the torsion scalar and the scalar field, gravitational waves have the same polarization modes of General Relativity.

Quantum spreading of a self-gravitating wave-packet in singularity free gravity

NASA Astrophysics Data System (ADS)

Buoninfante, Luca; Lambiase, Gaetano; Mazumdar, Anupam

2018-01-01

In this paper we will study for the first time how the wave-packet of a self-gravitating meso-scopic system spreads in theories beyond Einstein's general relativity. In particular, we will consider a ghost-free infinite derivative gravity, which resolves the 1 / r singularity in the potential - such that the gradient of the potential vanishes within the scale of non-locality. We will show that a quantum wave-packet spreads faster for a ghost-free and singularity-free gravity as compared to the Newtonian case, therefore providing us a unique scenario for testing classical and quantum properties of short-distance gravity in a laboratory in the near future.

Mean winds and momemtum fluxes over Jicamarca, Peru, during June and August 1987

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

Hitchman, M.H.; Bywaters, K.W.; Fritts, D.C.

1992-12-15

Data from the mesophere-stratosphere-troposphere (MST) radar at Jicamarca, Peru, together with other available data, are used to diagnose the mean structure of winds and gravity-wave momentum fluxes from the surface to 90 km during two ten-day campaigns in June and August of 1987. In the stratosphere a layer of maximum eastward flow associated with the quasi-biennial oscillation (QBO) was seen to strengthen and descend rapidly from June to August, overlying persitent westward flow. A layer of enhanced signal return, suggestive of a turbulent layer, was observed just above the descending QBO eastward maximum. Notable zonal asymmetries were present during thismore » transition and the local meridional circulation departed form zonal-mean QBO theory. A substantial northeastward momentum flux was found below 25 km, which may be related to topographic gravity waves excited by southeastward flow across the Andes. In the lower mesosphere a relatively weak second mesopause semiannual oxcillation is confirmed. Gravity-wave zonal and meridional momentum fluxes usually opposed the flow, yielding body forces of [approximately]10-100 ms[sup [minus]1] day [sup [minus]1]. In both the lower stratosphere and mesosphere, body forces were comparable in magnitude to inferred Coriolis torques. 52 refs., 9 figs.« less

Observation of gravity waves during the extreme tornado outbreak of 3 April 1974

NASA Technical Reports Server (NTRS)

Hung, R. J.; Phan, T.; Smith, R. E.

1978-01-01

A continuous wave-spectrum high-frequency radiowave Doppler sounder array was used to observe upper-atmospheric disturbances during an extreme tornado outbreak. The observations indicated that gravity waves with two harmonic wave periods were detected at the F-region ionospheric height. Using a group ray path computational technique, the observed gravity waves were traced in order to locate potential sources. The signals were apparently excited 1-3 hours before tornado touchdown. Reverse ray tracing indicated that the wave source was located at the aurora zone with a Kp index of 6 at the time of wave excitation. The summation of the 24-hour Kp index for the day was 36. The results agree with existing theories (Testud, 1970; Titheridge, 1971; Kato, 1976) for the excitation of large-scale traveling ionospheric disturbances associated with geomagnetic activity in the aurora zone.

The GISS global climate-middle atmosphere model. II - Model variability due to interactions between planetary waves, the mean circulation and gravity wave drag

NASA Technical Reports Server (NTRS)

Rind, D.; Suozzo, R.; Balachandran, N. K.

1988-01-01

The variability which arises in the GISS Global Climate-Middle Atmosphere Model on two time scales is reviewed: interannual standard deviations, derived from the five-year control run, and intraseasonal variability as exemplified by statospheric warnings. The model's extratropical variability for both mean fields and eddy statistics appears reasonable when compared with observations, while the tropical wind variability near the stratopause may be excessive possibly, due to inertial oscillations. Both wave 1 and wave 2 warmings develop, with connections to tropospheric forcing. Variability on both time scales results from a complex set of interactions among planetary waves, the mean circulation, and gravity wave drag. Specific examples of these interactions are presented, which imply that variability in gravity wave forcing and drag may be an important component of the variability of the middle atmosphere.

WINDII atmospheric wave airglow imaging

NASA Technical Reports Server (NTRS)

Armstrong, W. T.; Hoppe, U.-P.; Solheim, B. H.; Shepherd, G. G.

1996-01-01

Preliminary WINDII nighttime airglow wave-imaging data in the UARS rolldown attitude has been analyzed with the goal to survey gravity waves near the upper boundary of the middle atmosphere. Wave analysis is performed on O[sub 2](0,0) emissions from a selected 1[sup 0] x 1[sup 0] oblique view of the airglow layer at approximately 95 km altitude, which has no direct earth background and only an atmospheric background which is optically thick for the 0[sub 2](0,0) emission. From a small data set, orbital imaging of atmospheric wave structures is demonstrated, with indication of large variations in wave activity across land and sea. Comparison ground-based imagery is discussed with respect to similarity of wave variations across land/sea boundaries and future orbital mosaic image construction.

Observations of low-frequency inertia-gravity waves in the lower stratosphere over Arecibo

NASA Technical Reports Server (NTRS)

Cornish, C. R.; Larsen, M. F.

1989-01-01

Results are presented of a detailed analysis of the horizontal wind data in the subtropical upper troposphere and lower stratosphere, obtained with the 430-MHz radar at Arecibo (Puerto Rico) in May 1982 and April 1983. Both sets of observations displayed a slowly varying anticyclonically rotating persistent structure in the wind field just above the tropopause, of the type that would be expected if the oscillations were associated with quasi-inertial period waves. The quasi-inertial period structure in the Arecibo observations appears to be typical of the results of a number of other studies, indicating that quasi-inertial period waves are a ubiquitous feature in the lower stratosphere, similar to what is observed in the oceans.

Gravity wave characteristics in the middle atmosphere during the CESAR campaign at Palma de Mallorca in 2011/2012: Impact of extratropical cyclones and cold fronts

NASA Astrophysics Data System (ADS)

Kramer, R.; Wüst, S.; Schmidt, C.; Bittner, M.

2015-06-01

Based on a measuring campaign which was carried out at Mallorca (39.6°N, 2.7°E) as cooperation between Agència Estatal de Meteorologia (AEMET) and Deutsches Zentrum für Luft- und Raumfahrt, engl. 'German Aerospace Center' (DLR) in 2011/2012 (September-January), 143 radiosondes (day and night) providing vertical temperature and wind profiles were released. Additionally, nocturnal mesopause temperature measurements with a temporal resolution of about 1 min were conducted by the infrared (IR) - Ground-based Infrared P-branch Spectrometer (GRIPS) during the campaign period. Strongly enhanced gravity wave activity in the lower stratosphere is observed which can be attributed to a hurricane-like storm (so-called Medicane) and to passing by cold fronts. Statistical features of gravity wave parameters including energy densitiy and momentum fluxes are calculated. Gravity wave momentum fluxes turned out being up to five times larger during severe weather. Moreover, gravity wave horizontal propagation characteristics are derived applying hodograph and Stokes parameter analysis. Preferred directions are of southeast and northwest due to prevailing wind directions at Mallorca.

Gravity-wave spectra in the atmosphere observed by MST radar, part 4.2B

NASA Technical Reports Server (NTRS)

Scheffler, A. O.; Liu, C. H.

1984-01-01

A universal spectrum of atmospheric buoyancy waves is proposed based on data from radiosonde, Doppler navigation, not-wire anemometer and Jimsphere balloon. The possible existence of such a universal spectrum clearly will have significant impact on several areas in the study of the middle atmosphere dynamics such as the parameterization of sub-grid scale gravity waves in global circulation models; the transport of trace constituents and heat in the middle atmosphere, etc. Therefore, it is important to examine more global wind data with temporal and spatial resolutions suitable for the investigation of the wave spectra. Mesosphere-stratosphere-troposphere (MST) radar observations offer an excellent opportunity for such studies. It is important to realize that radar measures the line-of-sight velocity which, in general, contains the combination of the vertical and horizontal components of the wave-associated particle velocity. Starting from a general oblique radar observation configuration, applying the dispersion relation for the gravity waves, the spectrum for the observed fluctuations in the line-of-sight gravity-wave spectrum is investigated through a filter function. The consequence of the filter function on data analysis is discussed.

Complete synthetic seismograms based on a spherical self-gravitating Earth model with an atmosphere-ocean-mantle-core structure

NASA Astrophysics Data System (ADS)

Wang, Rongjiang; Heimann, Sebastian; Zhang, Yong; Wang, Hansheng; Dahm, Torsten

2017-04-01

A hybrid method is proposed to calculate complete synthetic seismograms based on a spherically symmetric and self-gravitating Earth with a multi-layered structure of atmosphere, ocean, mantle, liquid core and solid core. For large wavelengths, a numerical scheme is used to solve the geodynamic boundary-value problem without any approximation on the deformation and gravity coupling. With the decreasing wavelength, the gravity effect on the deformation becomes negligible and the analytical propagator scheme can be used. Many useful approaches are used to overcome the numerical problems that may arise in both analytical and numerical schemes. Some of these approaches have been established in the seismological community and the others are developed for the first time. Based on the stable and efficient hybrid algorithm, an all-in-one code QSSP is implemented to cover the complete spectrum of seismological interests. The performance of the code is demonstrated by various tests including the curvature effect on teleseismic body and surface waves, the appearance of multiple reflected, teleseismic core phases, the gravity effect on long period surface waves and free oscillations, the simulation of near-field displacement seismograms with the static offset, the coupling of tsunami and infrasound waves, and free oscillations of the solid Earth, the atmosphere and the ocean. QSSP is open source software that can be used as a stand-alone FORTRAN code or may be applied in combination with a Python toolbox to calculate and handle Green's function databases for efficient coding of source inversion problems.

Complete synthetic seismograms based on a spherical self-gravitating Earth model with an atmosphere-ocean-mantle-core structure

NASA Astrophysics Data System (ADS)

Wang, Rongjiang; Heimann, Sebastian; Zhang, Yong; Wang, Hansheng; Dahm, Torsten

2017-09-01

A hybrid method is proposed to calculate complete synthetic seismograms based on a spherically symmetric and self-gravitating Earth with a multilayered structure of atmosphere, ocean, mantle, liquid core and solid core. For large wavelengths, a numerical scheme is used to solve the geodynamic boundary-value problem without any approximation on the deformation and gravity coupling. With decreasing wavelength, the gravity effect on the deformation becomes negligible and the analytical propagator scheme can be used. Many useful approaches are used to overcome the numerical problems that may arise in both analytical and numerical schemes. Some of these approaches have been established in the seismological community and the others are developed for the first time. Based on the stable and efficient hybrid algorithm, an all-in-one code QSSP is implemented to cover the complete spectrum of seismological interests. The performance of the code is demonstrated by various tests including the curvature effect on teleseismic body and surface waves, the appearance of multiple reflected, teleseismic core phases, the gravity effect on long period surface waves and free oscillations, the simulation of near-field displacement seismograms with the static offset, the coupling of tsunami and infrasound waves, and free oscillations of the solid Earth, the atmosphere and the ocean. QSSP is open source software that can be used as a stand-alone FORTRAN code or may be applied in combination with a Python toolbox to calculate and handle Green's function databases for efficient coding of source inversion problems.

Worlds and Anti-worlds Revisted

NASA Astrophysics Data System (ADS)

Wolff, Milo

1996-05-01

In =D2Worlds and Anti-worlds=D3 (1960) Hannes Alfven=20 described a universe symmetric in matter and anti-matter. Today we cannot decide if galaxies and anti-galaxies exist because radiation from both=20 is alike. If matter attracts anti-matter by gravity, intense annihilation= =20 radiation is expected. Since this is not observed, cosmologists concluded the universe is un-symmetrical and tailored the big-bang accordingly. But there is another possibility. The anti-symmetry of particles and anti-particles, suggests repulsive gravity. The rarity of anti-matter and the weakness of gravity makes tesing difficult. But indeed if it is repulsive, galaxies and anti-galaxies would separate and the annihilation radiation would be small as observed. A first guess is 50-50 that anti-gravity exists but there is other evidence: Gamma-ray bursts observed by NASA satellites, solar anti-neutrino flux, and a proposed wave-structure of the electron: =D2Exploring the Physics of the Unknown Universe=D3(1991), ISBN 0-9627787-0-2, suggest that anti-gravity may exist. If true, expect a rush back to the drawing board to revise the expansion and structure of the universe.

Strong anti-gravity Life in the shock wave

NASA Astrophysics Data System (ADS)

Fabbrichesi, Marco; Roland, Kaj

1992-12-01

Strong anti-gravity is the vanishing of the net force between two massive particles at rest, to all orders in Newton's constant. We study this phenomenon and show that it occurs in any effective theory of gravity which is obtained from a higher-dimensional model by compactification on a manifold with flat directions. We find the exact solution of the Einstein equations in the presence of a point-like source of strong anti-gravity by dimensional reduction of a shock-wave solution in the higher-dimensional model.

Further SEASAT SAR coastal ocean wave analysis

NASA Technical Reports Server (NTRS)

Kasischke, E. S.; Shuchman, R. A.; Meadows, G. A.; Jackson, P. L.; Tseng, Y.

1981-01-01

Analysis techniques used to exploit SEASAT synthetic aperture radar (SAR) data of gravity waves are discussed and the SEASAT SAR's ability to monitor large scale variations in gravity wave fields in both deep and shallow water is evaluated. The SAR analysis techniques investigated included motion compensation adjustments and the semicausal model for spectral analysis of SAR wave data. It was determined that spectra generated from fast Fourier transform analysis (FFT) of SAR wave data were not significantly altered when either range telerotation adjustments or azimuth focus shifts were used during processing of the SAR signal histories, indicating that SEASAT imagery of gravity waves is not significantly improved or degraded by motion compensation adjustments. Evaluation of the semicausal (SC) model using SEASAT SAR data from Rev. 974 indicates that the SC spectral estimates were not significantly better than the FFT results.

Turbulent structures in cylindrical density currents in a rotating frame of reference

NASA Astrophysics Data System (ADS)

Salinas, Jorge S.; Cantero, Mariano I.; Dari, Enzo A.; Bonometti, Thomas

2018-06-01

Gravity currents are flows generated by the action of gravity on fluids with different densities. In some geophysical applications, modeling such flows makes it necessary to account for rotating effects, modifying the dynamics of the flow. While previous works on rotating stratified flows focused on currents of large Coriolis number, the present work focuses on flows with small Coriolis numbers (i.e. moderate-to-large Rossby numbers). In this work, cylindrical rotating gravity currents are investigated by means of highly resolved simulations. A brief analysis of the mean flow evolution to the final state is presented to provide a complete picture of the flow dynamics. The numerical results, showing the well-known oscillatory behavior of the flow (inertial waves) and a final state lens shape (geostrophic adjustment), are in good agreement with experimental observations and theoretical models. The turbulent structures in the flow are visualized and described using, among others, a stereoscopic visualization and videos as supplementary material. In particular, the structure of the lobes and clefts at the front of the current is presented in association to local turbulent structures. In rotating gravity currents, the vortices observed at the lobes front are not of hairpin type but are rather of Kelvin-Helmholtz type.

Intraseasonal to interannual variations in the tropical wave activity revealed in reanalyses and their potential impact on the QBO

NASA Astrophysics Data System (ADS)

Kim, Young-Ha; Yoo, Changhyun

2017-04-01

We investigate activities of tropical waves represented in reanalysis products. The wave activities are quantified by the Eliassen-Palm (EP) flux at 100 hPa, after decomposed into the following four components: equatorially trapped Kelvin waves and mixed Rossby-gravity waves, gravity waves, and Rossby waves. Monthly EP fluxes of the four waves exhibit considerable temporal variations at intraseasonal and interannual, along with seasonal, time scales. These variations are discussed with the tropical large-scale variabilities, including the Madden-Julian Oscillation (MJO), the El Ninõ-Southern Oscillation, and the stratospheric quasi-biennial oscillation (QBO). We find that during boreal winter, the interannual variation of Kelvin wave activity is in phase with that of the MJO amplitude, while such a simultaneous variation cannot be seen in other seasons. The gravity wave is dominated by a semi-annual cycle, while the departure from its semi-annual cycle is largely correlated with the QBO phase in the stratosphere. Potential impacts of the variations in the wave activity upon the QBO properties will be assessed using a simple one-dimensional QBO model.

Gravity Waves in the Atmosphere of Mars as seen by the Radio Science Experiment MaRS on Mars Express

NASA Astrophysics Data System (ADS)

Tellmann, S.; Paetzold, M.; Häusler, B.; Bird, M. K.; Tyler, G. L.; Hinson, D. P.

2016-12-01

Gravity waves are atmospheric waves whose restoring force is the buoyancy. They are known to play an essential role in the redistribution of energy, momentum and atmospheric constituents in all stably stratified planetary atmospheres. Possible excitation mechanisms comprise convection in an adjacent atmospheric layer, other atmospheric instabilities like wind shear instabilities, or air flow over orographic obstacles especially in combination with the strong winter jets on Mars. Gravity waves on Mars were observed in the lower atmosphere [1,2] but are also expected to play a major role in the cooling of the thermosphere [3] and the polar warming [4]. A fundamental understanding of the possible source mechanisms is required to reveal the influence of small scale gravity waves on the global atmospheric circulation. Radio occultation profiles from the MaRS experiment on Mars Express [5] with their exceptionally high vertical resolution can be used to study small-scale vertical gravity waves and their global distribution in the lower atmosphere from the planetary boundary layer up to 40 km altitude. Atmospheric instabilities, which are clearly identified in the data, are used to gain further insight into possible atmospheric processes contributing to the excitation of gravity waves. [1] Creasey, J. E., et al.,(2006), Geophys. Res. Lett., 33, L01803, doi:10.1029/2005GL024037. [2]Tellmann, S., et al.(2013), J. Geophys. Res. Planets, 118, 306-320, doi:10.1002/jgre.20058. [3]Medvedev, A. S., et al.(2015), J. Geophys. Res. Planets, 120, 913-927. doi:10.1002/2015JE004802.[4] Barnes, J. R. (1990), J. Geophys. Res., 95, B2, 1401-1421. [5] Pätzold, M., et al. (2016), Planet. Space Sci., 127, 44 - 90.

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.

f (T ) gravity after GW170817 and GRB170817A

NASA Astrophysics Data System (ADS)

Cai, Yi-Fu; Li, Chunlong; Saridakis, Emmanuel N.; Xue, Ling-Qin

2018-05-01

The combined observation of GW170817 and its electromagnetic counterpart GRB170817A reveals that gravitational waves propagate at the speed of light in high precision. We apply the standard analysis of cosmological perturbations, as well as the effective field theory approach, to investigate the experimental consequences for the theory of f (T ) gravity. Our analysis verifies for the first time that the speed of gravitational waves within f (T ) gravity is equal to the light speed, and hence, the constraints from GW170817 and GRB170817A are trivially satisfied. Nevertheless, by examining the dispersion relation and the frequency of cosmological gravitational waves, we observe a deviation from the results of general relativity, quantified by a new parameter. Although its value is relatively small in viable f (T ) models, its possible future measurement in advancing gravitational-wave astronomy would be the smoking gun of testing this type of modified gravity.

Investigating the Climatology of Mesospheric and Thermospheric Gravity Waves at High Northern Latitudes

NASA Astrophysics Data System (ADS)

Negale, Michael Ray

An important property of the Earth's atmosphere is its ability to support wave motions, and indeed, waves exist throughout the Earth's atmosphere at all times and all locations. What is the importance of these waves? Imagine standing on the beach as water waves come crashing into you. In this case, the waves transport energy and momentum to you, knocking you off balance. Similarly, waves in the atmosphere crash, known as breaking, but what do they crash into? They crash into the atmosphere knocking the atmosphere off balance in terms of the winds and temperatures. Although the Earth's atmosphere is full of waves, they cannot be observed directly; however, their effects on the atmosphere can be observed. Waves can be detected in the winds and temperatures, as mentioned above, but also in pressure and density. In this dissertation, three different studies of waves, known as gravity waves, were performed at three different locations. For these studies, we investigate the size of the waves and in which direction they move. Using specialized cameras, gravity waves were observed in the middle atmosphere (50-70 miles up) over Alaska (for three winter times) and Norway (for one winter time). A third study investigated gravity waves at a much higher altitude (70 miles on up) using radar data from Alaska (for three years). These studies have provided important new information on these waves and how they move through the atmosphere. This in turn helps to understand in which direction these waves are crashing into the atmosphere and therefore, which direction the energy and momentum are going. Studies such as these help to better forecast weather and climate.

Gravity wave momentum flux estimation from CRISTA satellite data

NASA Astrophysics Data System (ADS)

Ern, M.; Preusse, P.; Alexander, M. J.; Offermann, D.

2003-04-01

Temperature altitude profiles measured by the CRISTA satellite were analyzed for gravity waves (GWs). Amplitudes, vertical and horizontal wavelengths of GWs are retrieved by applying a combination of maximum entropy method (MEM) and harmonic analysis (HA) to the temperature height profiles and subsequently comparing the so retrieved GW phases of adjacent altitude profiles. From these results global maps of the absolute value of the vertical flux of horizontal momentum have been estimated. Significant differences between distributions of the temperature variance and distributions of the momentum flux exist. For example, global maps of the momentum flux show a pronounced northward shift of the equatorial maximum whereas temperature variance maps of the tropics/subtropics are nearly symmetric with respect to the equator. This indicates the importance of the influence of horizontal and vertical wavelength distribution on global structures of the momentum flux.

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

DTIC Science & Technology

2015-09-30

Meneveau, C., and L. Shen (2014), Large-eddy simulation of offshore wind farm , Physics of Fluids, 26, 025101. Zhang, Z., Fringer, O.B., and S.R...being centimeter scale, surface mixed layer processes arising from the combined actions of tides, winds and mesoscale currents. Issues related to...the internal wave field and how it impacts the surface waves. APPROACH We are focusing on the problem of modification of the wind -wave field

Properties of the Average Distribution of Equatorial Kelvin Waves Investigated with the GROGRAT Ray Tracer

DTIC Science & Technology

2009-01-01

spheric quasi-biennial oscillation ( QBO ). In this paper we combine several measured data sets with the Gravity wave Regional Or Global RAy Tracer (GROGRAT...equatorial wave modes and a broad spectrum of gravity waves (GWs) Kelvin waves are one of the main drivers of the quasi-biennial oscil- lation ( QBO ) of the...and dy- namics in the stratosphere and mesosphere (even at high lati- tudes) are modulated or influenced by the QBO , showing the importance of the

A study of the dynamics of the equatorial lower stratosphere by use of ultra-long-duration balloons, 2, Gravity waves

NASA Astrophysics Data System (ADS)

Hertzog, A.; Vial, F.

2001-10-01

This study is the companion paper of Vial et al. [this issue]. A campaign of ultra-long-duration, superpressure balloons in the equatorial lower stratosphere was held in September 1998. By conception these balloons evolve on isopycnic surfaces. Pressure and position were measured every 12 min, which enable to infer the characteristics of gravity waves with periods between 1 hour and 1 day in this region of the atmosphere. The intrinsic-frequency spectra of horizontal wind fluctuations exhibit a -2 slope, while the one associated with vertical-wind fluctuations is flat. Significant inhomogeneity of the wave activity is observed, and the variance of the shortest frequency waves is found to be linked to the position of the balloons with respect to the Intertropical Convergence Zone. On average, the total energy associated with gravity waves in the period range studied in this paper is found to be ˜ 7 J kg-1. Calculations of momentum flux have also been undertaken. It appears that there is an approximate equipartition of flux between eastward and westward propagating gravity waves and that the absolute value of the flux is 8-12 × 10-3 m2 s-2 at 20 km. A larger flux is also observed above convective regions. These values suggest that gravity waves may carry the largest part of the Eliassen-Palm flux required for the driving of the quasi-biennial oscillation.

One billion year-old Mid-continent Rift leaves virtually no clues in the mantle

NASA Astrophysics Data System (ADS)

Bollmann, T. A.; Frederiksen, A. W.; van der Lee, S.; Wolin, E.; Revenaugh, J.; Wiens, D.; Darbyshire, F. A.; Aleqabi, G. I.; Wysession, M. E.; Stein, S.; Jurdy, D. M.

2017-12-01

We measured the relative arrival times of more than forty-six thousand teleseismic P waves recorded by seismic stations of Earthscope's Superior Province Rifting Earthscope Experiment (SPREE) and combined them with a similar amount of such measurements from other seismic stations in the larger region. SPREE recorded seismic waves for two and a half years around the prominent, one billion year-old Mid-continent Rift structure. The curvilinear Mid-continent Rift (MR) is distinguished by voluminous one billion year-old lava flows, which produce a prominent gravity high along the MR. As for other seismic waves, these lava flows along with their underplated counterpart, slightly slow down the measured teleseismic P waves, on average, compared to P waves that did not traverse structures beneath the Mid-continent Rift. However, the variance in the P wave arrival times in these two groups is nearly ten times higher than their average difference. In a seismic-tomographic inversion, we mapped all measured arrival times into structures deep beneath the crust, in the Earth's mantle. Beneath the crust we generally find relatively high P velocities, indicating relatively cool and undeformable mantle structures. However, the uppermost mantle beneath the MR shows several patches of slightly decreased P velocities. These patches are coincident with where the gravity anomalies peak, in Iowa and along the northern Minnesota/Wisconsin border. We will report on the likelihood that these anomalies are indeed a remaining mantle-lithospheric signature of the MR or whether these patches indirectly reflect the presence of the lava flows and their underplated counterparts at the crust-mantle interface. Other structures of interest and of varying depth extent in our tomographic image locate at 1) the intersection of the Superior Craton with the Penokean Province and the Marshfield Terrane west of the MR in southern Minnesota, 2) the intersection of the Penokean, Yavapai, and Mazatzal Terranes along the eastern edge of the Michigan arm of the MR, and 3) beneath Lake Nipigon, north of Lake Superior. Our tomographic image also reveals an intricate distribution of deep high-velocity anomalies, including in the lower mantle, potentially related to Mesozoic subduction of the Kula and/or Farallon Plates.

New statistical analysis of the horizontal phase velocity distribution of gravity waves observed by airglow imaging

NASA Astrophysics Data System (ADS)

Matsuda, Takashi S.; Nakamura, Takuji; Ejiri, Mitsumu K.; Tsutsumi, Masaki; Shiokawa, Kazuo

2014-08-01

We have developed a new analysis method for obtaining the power spectrum in the horizontal phase velocity domain from airglow intensity image data to study atmospheric gravity waves. This method can deal with extensive amounts of imaging data obtained on different years and at various observation sites without bias caused by different event extraction criteria for the person processing the data. The new method was applied to sodium airglow data obtained in 2011 at Syowa Station (69°S, 40°E), Antarctica. The results were compared with those obtained from a conventional event analysis in which the phase fronts were traced manually in order to estimate horizontal characteristics, such as wavelengths, phase velocities, and wave periods. The horizontal phase velocity of each wave event in the airglow images corresponded closely to a peak in the spectrum. The statistical results of spectral analysis showed an eastward offset of the horizontal phase velocity distribution. This could be interpreted as the existence of wave sources around the stratospheric eastward jet. Similar zonal anisotropy was also seen in the horizontal phase velocity distribution of the gravity waves by the event analysis. Both methods produce similar statistical results about directionality of atmospheric gravity waves. Galactic contamination of the spectrum was examined by calculating the apparent velocity of the stars and found to be limited for phase speeds lower than 30 m/s. In conclusion, our new method is suitable for deriving the horizontal phase velocity characteristics of atmospheric gravity waves from an extensive amount of imaging data.

A Revised Method of Presenting Wavenumber-Frequency Power Spectrum Diagrams That Reveals the Asymmetric Nature of Tropical Large-scale Waves

NASA Technical Reports Server (NTRS)

Chao, Winston C.; Yang, Bo; Fu, Xiouhua

2007-01-01

The popular method of presenting wavenumber-frequency power spectrum diagrams for studying tropical large-scale waves in the literature is shown to give an incomplete presentation of these waves. The so-called "convectively-coupled Kelvin (mixed Rossby-gravity) waves" are presented as existing only in the symmetric (antisymmetric) component of the diagrams. This is obviously not consistent with the published composite/regression studies of "convectively-coupled Kelvin waves," which illustrate the asymmetric nature of these waves. The cause of this inconsistency is revealed in this note and a revised method of presenting the power spectrum diagrams is proposed. When this revised method is used, "convectively-coupled Kelvin waves" do show anti-symmetric components, and "convectively-coupled mixed Rossby-gravity waves (also known as Yanai waves)" do show a hint of symmetric components. These results bolster a published proposal that these waves be called "chimeric Kelvin waves," "chimeric mixed Rossby-gravity waves," etc. This revised method of presenting power spectrum diagrams offers a more rigorous means of comparing the General Circulation Models (GCM) output with observations by calling attention to the capability of GCMs in correctly simulating the asymmetric characteristics of the equatorial waves.

Is tropospheric weather influenced by solar wind through atmospheric vertical coupling downward control?

NASA Astrophysics Data System (ADS)

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

2017-04-01

More than four decades have passed since a link between solar wind magnetic sector boundary structure and mid-latitude upper tropospheric vorticity was discovered (Wilcox et al., Science, 180, 185-186, 1973). The link has been later confirmed and various physical mechanisms proposed but apart from controversy, little attention has been drawn to these results. To further emphasize their importance we investigate the occurrence of mid-latitude severe weather in the context of solar wind coupling to the magnetosphere-ionosphere-atmosphere (MIA) system. It is observed that significant snowstorms, windstorms 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 after arrivals of high-speed solar wind streams from coronal holes (Prikryl et al., Ann. Geophys., 27, 1-30, 2009; Prikryl et al., J. Atmos. Sol.-Terr. Phys., 149, 219-231, 2016) is corroborated for the southern hemisphere. A 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., Space Sci. Rev., 54, 297-375, 1990) show that propagating waves originating in the 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 thus initiating convection to form cloud/precipitation bands (Prikryl et al., Ann. Geophys., 27, 31-57, 2009). 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.

A model for gravity-wave spectra observed by Doppler sounding systems

NASA Technical Reports Server (NTRS)

Vanzandt, T. E.

1986-01-01

A model for Mesosphere - Stratosphere - Troposphere (MST) radar spectra is developed following the formalism presented by Pinkel (1981). Expressions for the one-dimensional spectra of radial velocity versus frequency and versus radial wave number are presented. Their dependence on the parameters of the gravity-wave spectrum and on the experimental parameters, radar zenith angle and averaging time are described and the conditions for critical tests of the gravity-wave hypothesis are discussed. The model spectra is compared with spectra observed in the Arctic summer mesosphere by the Poker Flat radar. This model applies to any monostatic Doppler sounding system, including MST radar, Doppler lidar and Doppler sonar in the atmosphere, and Doppler sonar in the ocean.

Thermospheric gravity waves - Observations and interpretation using the transfer function model (TFM)

NASA Technical Reports Server (NTRS)

Mayr, H. G.; Harris, I.; Herrero, F. A.; Spencer, N. W.; Varosi, F.; Pesnell, W. D.

1990-01-01

This paper presents some numerical experiments performed with the TFM to study the various wave components excited in the auroral regions that propagate through the thermosphere and lower atmosphere, and to demonstrate the properties of realistic source geometries. The model is applied to the interpretation of satellite measurements, and gravity waves seen in the thermosphere of Venus are discussed. Gravity waves are prominent in the terrestrial thermosphere polar region and can be excited by perturbations in Joule heating and Lorentz force due to magnetospheric processes. Observations from the Dynamics Explorer-2 satellite are used to illustrate the complexity of the phenomenon and to review the TFM that is utilized.

Summary of NASA Advanced Telescope and Observatory Capability Roadmap

NASA Technical Reports Server (NTRS)

Stahl, H. Phil; Feinberg, Lee

2006-01-01

The NASA Advanced Telescope and Observatory (ATO) Capability Roadmap addresses technologies necessary for NASA to enable future space telescopes and observatories operating in all electromagnetic bands, from x-rays to millimeter waves, and including gravity-waves. It lists capability priorities derived from current and developing Space Missions Directorate (SMD) strategic roadmaps. Technology topics include optics; wavefront sensing and control and interferometry; distributed and advanced spacecraft systems; cryogenic and thermal control systems; large precision structure for observatories; and the infrastructure essential to future space telescopes and observatories.

Gravity dual of spin and charge density waves

NASA Astrophysics Data System (ADS)

Jokela, Niko; Järvinen, Matti; Lippert, Matthew

2014-12-01

At high enough charge density, the homogeneous state of the D3-D7' model is unstable to fluctuations at nonzero momentum. We investigate the end point of this instability, finding a spatially modulated ground state, which is a charge and spin density wave. We analyze the phase structure of the model as a function of chemical potential and magnetic field and find the phase transition from the homogeneous state to be first order, with a second-order critical point at zero magnetic field.

Summary of NASA Advanced Telescope and Observatory Capability Roadmap

NASA Technical Reports Server (NTRS)

Stahl, H. Philip; Feinberg, Lee

2007-01-01

The NASA Advanced Telescope and Observatory (ATO) Capability Roadmap addresses technologies necessary for NASA to enable future space telescopes and observatories operating in all electromagnetic bands, from x-rays to millimeter waves, and including gravity-waves. It lists capability priorities derived from current and developing Space Missions Directorate (SMD) strategic roadmaps. Technology topics include optics; wavefront sensing and control and interferometry; distributed and advanced spacecraft systems; cryogenic and thermal control systems; large precision structure for observatories; and the infrastructure essential to future space telescopes and observatories.

Generation and Upper Atmospheric Propagation of Acoustic Gravity Waves according to Numerical Modeling and Radio Tomography

NASA Astrophysics Data System (ADS)

Vorontsov, Artem; Andreeva, Elena; Nesterov, Ivan; Padokhin, Artem; Kurbatov, Grigory

2016-04-01

The acoustic-gravity waves (AGW) in the upper atmosphere and ionosphere can be generated by a variety of the phenomena in the near-Earth environment and atmosphere as well as by some perturbations of the Earth's ground or ocean surface. For instance, the role of the AGW sources can be played by the earthquakes, explosions, thermal heating, seisches, tsunami waves. We present the examples of AGWs excited by the tsunami waves traveling in the ocean, by seisches, and by ionospheric heating by the high-power radio wave. In the last case, the gravity waves are caused by the pulsed modulation of the heating wave. The AGW propagation in the upper atmosphere induces the variations and irregularities in the electron density distribution of the ionosphere, whose structure can be efficiently reconstructed by the method of the ionospheric radio tomography (RT) based on the data from the global navigational satellite systems (GNSS). The input data for RT diagnostics are composed of the 150/400 MHz radio signals from the low-orbiting (LO) satellites and 1.2-1.5 GHz radio signals from the high-orbiting (HO) satellites with their orbits at ~1000 and ~20000 km above the ground, respectively. These data enable ionospheric imaging on different spatiotemporal scales with different spatiotemporal resolution and coverage, which is suitable, inter alia, for tracking the waves and wave-like features in the ionosphere. In particular, we demonstrate the maps of the ionospheric responses to the tornado at Moore (Oklahoma, USA) of May 20, 2013, which are reconstructed from the HO data. We present the examples of LORT images containing the waves and wavelike disturbances associated with various sources (e.g., auroral precipitation and high-power heating of the ionosphere). We also discuss the results of modeling the AGW generation by the surface and volumetric sources. The millihertz AGW from these sources initiate the ionospheric perturbation with a typical scale of a few hundred km at the heights corresponding to the middle atmosphere and ionosphere. The results of numerical modeling based on the solution of the equation of geophysical hydrodynamics agree with the observations.

Optimization schemes for the inversion of Bouguer gravity anomalies

NASA Astrophysics Data System (ADS)

Zamora, Azucena

Data sets obtained from measurable physical properties of the Earth structure have helped advance the understanding of its tectonic and structural processes and constitute key elements for resource prospecting. 2-Dimensional (2-D) and 3-D models obtained from the inversion of geophysical data sets are widely used to represent the structural composition of the Earth based on physical properties such as density, seismic wave velocities, magnetic susceptibility, conductivity, and resistivity. The inversion of each one of these data sets provides structural models whose consistency depends on the data collection process, methodology, and overall assumptions made in their individual mathematical processes. Although sampling the same medium, seismic and non-seismic methods often provide inconsistent final structural models of the Earth with varying accuracy, sensitivity, and resolution. Taking two or more geophysical data sets with complementary characteristics (e.g. having higher resolution at different depths) and combining their individual strengths to create a new improved structural model can help achieve higher accuracy and resolution power with respect to its original components while reducing their ambiguity and uncertainty effects. Gravity surveying constitutes a cheap, non-invasive, and non-destructive passive remote sensing method that helps to delineate variations in the gravity field. These variations can originate from regional anomalies due to deep density variations or from residual anomalies related to shallow density variations [41]. Since gravity anomaly inversions suffer from significant non-uniqueness (allowing two or more distinct density structures to have the same gravity signature) and small changes in parameters can highly impact the resulting model, the inversion of gravity data represents an ill-posed mathematical problem. However, gravity studies have demonstrated the effectiveness of this method to trace shallow subsurface density variations associated with structural changes [16]; therefore, it complements those geophysical methods with the same depth resolution that sample a different physical property (e.g. electromagnetic surveys sampling electric conductivity) or even those with different depth resolution sampling an alternative physical property (e.g. large scale seismic reflection surveys imaging the crust and top upper mantle using seismic velocity fields). In order to improve the resolution of Bouguer gravity anomalies, and reduce their ambiguity and uncertainty for the modeling of the shallow crust, we propose the implementation of primal-dual interior point methods for the optimization of density structure models through the introduction of physical constraints for transitional areas obtained from previously acquired geophysical data sets. This dissertation presents in Chapter 2 an initial forward model implementation for the calculation of Bouguer gravity anomalies in the Porphyry Copper-Molybdenum (Cu-Mo) Copper Flat Mine region located in Sierra County, New Mexico. In Chapter 3, we present a constrained optimization framework (using interior-point methods) for the inversion of 2-D models of Earth structures delineating density contrasts of anomalous bodies in uniform regions and/or boundaries between layers in layered environments. We implement the proposed algorithm using three different synthetic gravitational data sets with varying complexity. Specifically, we improve the 2-dimensional density structure models by getting rid of unacceptable solutions (geologically unfeasible models or those not satisfying the required constraints) given the reduction of the solution space. Chapter 4 shows the results from the implementation of our algorithm for the inversion of gravitational data obtained from the area surrounding the Porphyry Cu-Mo Cooper Flat Mine in Sierra County, NM. Information obtained from previous induced polarization surveys and core samples served as physical constraints for the inversion parameters. Finally, in order to achieve higher resolution, Chapter 5 introduces a 3-D theoretical framework for the joint inversion of Bouguer gravity anomalies and surface wave dispersion using interior-point methods. Through this work, we expect to contribute to the creation of additional tools for the development of 2- and 3-D models depicting the Earth's geological processes and to the widespread use of constrained optimization techniques for the inversion of geophysical data sets.

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

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

NASA Astrophysics Data System (ADS)

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

2016-09-01

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

Generation of internal solitary waves by frontally forced intrusions in geophysical flows.

PubMed

Bourgault, Daniel; Galbraith, Peter S; Chavanne, Cédric

2016-12-06

Internal solitary waves are hump-shaped, large-amplitude waves that are physically analogous to surface waves except that they propagate within the fluid, along density steps that typically characterize the layered vertical structure of lakes, oceans and the atmosphere. As do surface waves, internal solitary waves may overturn and break, and the process is thought to provide a globally significant source of turbulent mixing and energy dissipation. Although commonly observed in geophysical fluids, the origins of internal solitary waves remain unclear. Here we report a rarely observed natural case of the birth of internal solitary waves from a frontally forced interfacial gravity current intruding into a two-layer and vertically sheared background environment. The results of the analysis carried out suggest that fronts may represent additional and unexpected sources of internal solitary waves in regions of lakes, oceans and atmospheres that are dynamically similar to the situation examined here in the Saguenay Fjord, Canada.

Measuring ocean waves from space; Proceedings of the Symposium, Johns Hopkins University, Laurel, MD, Apr. 15-17, 1986

NASA Technical Reports Server (NTRS)

Beal, Robert C. (Editor)

1987-01-01

Papers are presented on ocean-wave prediction; the quasi-universal form of the spectra of wind-generated gravity waves at different stages of their development; the limitations of the spectral measurements and observations of the group structure of surface waves; the effect of swell on the growth of wind wave; operational wave forecasting; ocean-wave models, and seakeeping using directional wave spectra. Consideration is given to microwave measurements of the ocean-wave directional spectra; SIR research; estimating wave energy spectra from SAR imagery, with the radar ocean-wave spectrometer, and SIR-B; the wave-measurement capabilities of the surface contour radar and the airborne oceanographic lidar; and SIR-B ocean-wave enhancement with fast-Fourier transform techniques. Topics discussed include wave-current interaction; the design and applicability of Spectrasat; the need for a global wave monitoring system; the age and source of ocean swell observed in Hurricane Josephine; and the use of satellite technology for insulin treatment.

LIGO - The Laser Interferometer Gravitational-Wave Observatory

NASA Technical Reports Server (NTRS)

Abramovici, Alex; Althouse, William E.; Drever, Ronald W. P.; Gursel, Yekta; Kawamura, Seiji; Raab, Frederick J.; Shoemaker, David; Sievers, Lisa; Spero, Robert E.; Thorne, Kip S.

1992-01-01

The goal of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Project is to detect and study astrophysical gravitational waves and use data from them for research in physics and astronomy. LIGO will support studies concerning the nature and nonlinear dynamics for gravity, the structures of black holes, and the equation of state of nuclear matter. It will also measure the masses, birth rates, collisions, and distributions of black holes and neutron stars in the universe and probe the cores of supernovae and the very early universe. The technology for LIGO has been developed during the past 20 years. Construction will begin in 1992, and under the present schedule, LIGO's gravitational-wave searches will begin in 1998.

A morphological study of waves in the thermosphere using DE-2 observations

NASA Technical Reports Server (NTRS)

Gross, S. H.; Kuo, S. P.; Shmoys, J.

1986-01-01

Theoretical model and data analysis of DE-2 observations for determining the correlation between the neutral wave activity and plasma irregularities have been presented. The relationships between the observed structure of the sources, precipitation and joule heating, and the fluctuations in neutral and plasma parameters are obtained by analyzing two measurements of neutral atmospheric wave activity and plasma irregularities by DE-2 during perigee passes at an altitude on the order of 300 to 350 km over the polar cap. A theoretical model based on thermal nonlinearity (joule heating) to give mode-mode coupling is developed to explore the role of neutral disturbance (winds and gravity waves) on the generation of plasma irregularities.

Towards Crustal Structure of Java Island (Sunda Arc) from Ambient Seismic Noise Tomography

NASA Astrophysics Data System (ADS)

Widiyantoro, Sri; Zulhan, Zulfakriza; Martha, Agustya; Saygin, Erdinc; Cummins, Phil

2015-04-01

In our previous studies, P- and S-wave velocity structures beneath the Sunda Arc were successfully imaged using a global data set and a nested regional-global tomographic method was employed. To obtain more detailed P- and S-wave velocity structures beneath Java, in the central part of the Sunda Arc, we then used local data sets, i.e. newline from the MErapi AMphibious EXperiment (MERAMEX) and the Meteorological, Climatological and Geophysical Agency (MCGA), as well as employed a double-difference technique for tomographic imaging. The results of the imaging show e.g. that P- and S-wave velocities are significantly reduced in the uppermost mantle beneath central Java. In order to obtain detailed crustal structure information beneath Java, the Ambient Noise Tomography (ANT) method was used. The application of this method to the MERAMEX data has produced a good crustal model beneath central Java. We continue our experiment to image crustal structure of eastern Java. We have used seismic waveform data recorded by 22 MCGA stationary seismographic stations and 25 portable seismographs installed for 2 to 8 weeks. The data were processed to obtain waveforms of cross-correlated noise between pairs of seismographic stations. Our preliminary results presented here indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly (as shown by our tomographic images). In future work we will install more seismographic stations in eastern Java as well as in western Java to conduct ANT imaging for the whole of Java Island. The expected result combined with the mantle velocity models resulting from our body wave tomography will allow for accurate location of earthquake hypocenters and determination of regional tectonic structures. Both of these are valuable for understanding seismic hazard in Java, the most densely populated island in the world.

Deep Europe today: Geophysical synthesis of the upper mantle structure and lithospheric processes over 3.5 Ga

USGS Publications Warehouse

Artemieva, I.M.; Thybo, H.; Kaban, M.K.; ,

2006-01-01

We present a summary of geophysical models of the subcrustal lithosphere of Europe. This includes the results from seismic (reflection and refraction profiles, P- and S-wave tomography, mantle anisotropy), gravity, thermal, electromagnetic, elastic and petrological studies of the lithospheric mantle. We discuss major tectonic processes as reflected in the lithospheric structure of Europe, from Precambrian terrane accretion and subduction to Phanerozoic rifting, volcanism, subduction and continent-continent collision. The differences in the lithospheric structure of Precambrian and Phanerozoic Europe, as illustrated by a comparative analysis of different geophysical data, are shown to have both a compositional and a thermal origin. We propose an integrated model of physical properties of the European subcrustal lithosphere, with emphasis on the depth intervals around 150 and 250 km. At these depths, seismic velocity models, constrained by body-and surface-wave continent-scale tomography, are compared with mantle temperatures and mantle gravity anomalies. This comparison provides a framework for discussion of the physical or chemical origin of the major lithospheric anomalies and their relation to large-scale tectonic processes, which have formed the present lithosphere of Europe. ?? The Geological Society of London 2006.

Seasonality of submesoscale dynamics in the Kuroshio Extension

NASA Astrophysics Data System (ADS)

Rocha, Cesar B.; Gille, Sarah T.; Chereskin, Teresa K.; Menemenlis, Dimitris

2016-11-01

Recent studies show that the vigorous seasonal cycle of the mixed layer modulates upper ocean submesoscale turbulence. Here we provide model-based evidence that the seasonally changing upper ocean stratification in the Kuroshio Extension also modulates submesoscale (here 10-100 km) inertia-gravity waves. Summertime restratification weakens submesoscale turbulence but enhances inertia-gravity waves near the surface. Thus, submesoscale turbulence and inertia-gravity waves undergo vigorous out-of-phase seasonal cycles. These results imply a strong seasonal modulation of the accuracy of geostrophic velocity diagnosed from submesoscale sea surface height delivered by the Surface Water and Ocean Topography satellite mission.

Analytic solutions for Long's equation and its generalization

NASA Astrophysics Data System (ADS)

Humi, Mayer

2017-12-01

Two-dimensional, steady-state, stratified, isothermal atmospheric flow over topography is governed by Long's equation. Numerical solutions of this equation were derived and used by several authors. In particular, these solutions were applied extensively to analyze the experimental observations of gravity waves. In the first part of this paper we derive an extension of this equation to non-isothermal flows. Then we devise a transformation that simplifies this equation. We show that this simplified equation admits solitonic-type solutions in addition to regular gravity waves. These new analytical solutions provide new insights into the propagation and amplitude of gravity waves over topography.

Three waves for quantum gravity

NASA Astrophysics Data System (ADS)

Calmet, Xavier; Latosh, Boris

2018-03-01

Using effective field theoretical methods, we show that besides the already observed gravitational waves, quantum gravity predicts two further massive classical fields leading to two new massive waves. We set a limit on the masses of these new modes using data from the Eöt-Wash experiment. We point out that the existence of these new states is a model independent prediction of quantum gravity. We then explain how these new classical fields could impact astrophysical processes and in particular the binary inspirals of neutron stars or black holes. We calculate the emission rate of these new states in binary inspirals astrophysical processes.

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.

Magnetic Ripples Observed by Low-altitude Satellites and their Relation to Micro-barometric and Ground Magnetic Variations

NASA Astrophysics Data System (ADS)

Iyemori, T.; Aoyama, T.; Nakanishi, K.; Odagi, Y.; Sanoo, Y.; Yokoyama, Y.; Yamada, A.

2017-12-01

The `magnetic ripples' are small scale magnetic fluctuations observed in upper ionosphere by low altitude satellites such as CHAMP or Swarm, and they are spatial structure of field-aligned currents along satellite orbit. They are observed almost always in mid- and low-latitudes. From their geographical and seasonal characteristics, they are supposed to be caused by the atmospheric waves which propagates from lower atmosphere to the ionosphere. Although the global distribution and its local time or seasonal variation of the amplitude of magnetic ripples, or the correlation with meteorological phenomena such as typhoons strongly suggest the cumulus convection as the main origin, we need to clarify which mode of atmospheric waves, i.e., acoustic wave or internal gravity wave, mainly contributes to the magnetic ripples and what meteorological condition correspond them. For those purposes, we analyze ground based magnetic and micro-barometric variations. We try to make quantitative estimation of the contribution from both acoustic and internal mode of gravity waves, acoustic resonance, etc. by calculating PSD (power spectral density) of pressure and ground magnetic variations. In this paper, we present their basic characteristics and discuss the relation with magnetic ripples. [Acknowledgments]: The ground observations have been supported by many people including students at our graduate school and by the collaboration with other institutions.

Estimates of Lagrangian particle transport by wave groups: forward transport by Stokes drift and backward transport by the return flow

NASA Astrophysics Data System (ADS)

van den Bremer, Ton S.; Taylor, Paul H.

2014-11-01

Although the literature has examined Stokes drift, the net Lagrangian transport by particles due to of surface gravity waves, in great detail, the motion of fluid particles transported by surface gravity wave groups has received considerably less attention. In practice nevertheless, the wave field on the open sea often has a group-like structure. The motion of particles is different, as particles at sufficient depth are transported backwards by the Eulerian return current that was first described by Longuet-Higgins & Stewart (1962) and forms an inseparable counterpart of Stokes drift for wave groups ensuring the (irrotational) mass balance holds. We use WKB theory to study the variation of the Lagrangian transport by the return current with depth distinguishing two-dimensional seas, three-dimensional seas, infinite depth and finite depth. We then provide dimensional estimates of the net horizontal Lagrangian transport by the Stokes drift on the one hand and the return flow on the other hand for realistic sea states in all four cases. Finally we propose a simple scaling relationship for the transition depth: the depth above which Lagrangian particles are transported forwards by the Stokes drift and below which such particles are transported backwards by the return current.

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

NASA Technical Reports Server (NTRS)

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

1997-01-01

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

Unexpected Occurrence of Mesospheric Frontal Gravity Wave Events Over South Pole (90°S)

NASA Astrophysics Data System (ADS)

Pautet, P.-D.; Taylor, M. J.; Snively, J. B.; Solorio, C.

2018-01-01

Since 2010, Utah State University has operated an infrared Advanced Mesospheric Temperature Mapper at the Amundsen-Scott South Pole station to investigate the upper atmosphere dynamics and temperature deep within the vortex. A surprising number of "frontal" gravity wave events (86) were recorded in the mesospheric OH(3,1) band intensity and rotational temperature images (typical altitude of 87 km) during four austral winters (2012-2015). These events are gravity waves (GWs) characterized by a sharp leading wave front followed by a quasi-monochromatic wave train that grows with time. A particular subset of frontal gravity wave events has been identified in the past (Dewan & Picard, 1998) as "bores." These are usually associated with wave ducting within stable mesospheric inversion layers, which allow them to propagate over very large distances. They have been observed on numerous occasions from low-latitude and midlatitude sites, but to date, very few have been reported at high latitudes. This study provides new analyses of the characteristics of frontal events at high latitudes and shows that most of them are likely ducted. The occurrence of these frontal GW events over this isolated region strongly supports the existence of horizontally extensive mesospheric thermal inversion layers over Antarctica, leading to regions of enhanced stability necessary for GW trapping and ducting.

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.

Oscillatory interfacial instability between miscible fluids

NASA Astrophysics Data System (ADS)

Shevtsova, Valentina; Gaponenko, Yuri; Mialdun, Aliaksandr; Torregrosa, Marita; Yasnou, Viktar

Interfacial instabilities occurring between two fluids are of fundamental interest in fluid dynamics, biological systems and engineering applications such as liquid storage, solvent extraction, oil recovery and mixing. Horizontal vibrations applied to stratified layers of immiscible liquids may generate spatially periodic waving of the interface, stationary in the reference frame of the vibrated cell, referred to as a "frozen wave". We present experimental evidence that frozen wave instability exists between two ordinary miscible liquids of similar densities and viscosities. At the experiments and at the numerical model, two superimposed layers of ordinary liquids, water-alcohol of different concentrations, are placed in a closed cavity in a gravitationally stable configuration. The density and viscosity of these fluids are somewhat similar. Similar to the immiscible fluids this instability has a threshold. When the value of forcing is increased the amplitudes of perturbations grow continuously displaying a saw-tooth structure. The decrease of gravity drastically changes the structure of frozen waves.

Educing the emission mechanism of internal gravity waves in the differentially heat rotating annulus

NASA Astrophysics Data System (ADS)

Rolland, Joran; Hien, Steffen; Achatz, Ulrich; Borchert, Sebastian; Fruman, Mark

2016-04-01

Understanding the lifecycle of gravity waves is fundamental to a good comprehension of the dynamics of the atmosphere. In this lifecycle, the emission mechanisms may be the most elusive. Indeed, while the emission of gravity waves by orography or convection is well understood, the so-called spontaneous emission is still a quite open topic of investigation [1]. This type of emission usually occur very near jet-front systems in the troposphere. In this abstract, we announce our numerical study of the question. Model systems of the atmosphere which can be easily simulated or built in a laboratory have always been an important part of the study of atmospheric dynamics, alongside global simulations, in situ measurements and theory. In the case of the study of the spontaneous emission of gravity waves near jet-front systems, the differentially heated rotating annulus set up has been proposed and extensively used. It comprises of an annular tank containing water: the inner cylinder is kept at a cold temperature while the outer cylinder is kept at a warm temperature. The whole system is rotating. Provided the values of the control parameters (temperature, rotation rate, gap between the cylinders, height of water) are well chosen, the resulting flow mimics the troposphere at midlatitudes: it has a jet stream, and a baroclinic lifecycle develops on top of it. A very reasonable ratio of Brunt-Väisälä frequency over rotation rate of the system can be obtained, so as to be as close to the atmosphere as possible. Recent experiments as well as earlier numerical simulations in our research group have shown that gravity waves are indeed emitted in this set up, in particular near the jet front system of the baroclinic wave [2]. After a first experimental stage of characterising the emitted wavepacket, we focused our work on testing hypotheses on the gravity wave emission mechanism: we have tested and validated the hypothesis of spontaneous imbalance generated by the flow in geostrophic balance. For the first stage of this investigation, we separated the flow between a balance and an imbalanced part at first order in Rossby number: the balanced pressure field was computed through an inversion of the potential vorticity equation [3]. The balanced horizontal velocity field and buoyancy were then computed using the geostrophic and hydrostatic balance conditions. We first checked that this decomposition gave on the one hand a large scaled balanced flow, comprising mostly of the baroclinic wave, and on the other hand a small scale flow comprising mostly of the gravity wave signal. We then proceeded with the central stage of the validation: we simulated the tangent linear dynamics of the imbalanced part of the flow [4]. The equations are linearised about the balanced part, and any imbalances forces the modeled imbalanced part. The output of this simulation compares very well with the actual imbalanced part, thus confirming that the observed gravity waves are indeed generated through spontaneous imbalance. To our knowledge, this is the first demonstration of emission by this mechanism in a flow which is not idealised: a flow which can be obtained as a result of a numerical simulation of primitive equations or actually observed in a laboratory experiment. References [1] R. Plougonven, F. Zhang, Internal gravity waves from atmospheric jets and fronts, Rev. Geophys. 52, 33-76 (2014). [2] S. Borchert, U. Achatz, M.D. Fruman, Spontaneous Gravity wave emission in the differentially heated annulus, J. Fluid Mech. 758, 287-311 (2014). [3] F. Zhang, S.E . Koch, C. A. Davis, M. L. Kaplan, A Survey of unbalanced flow diagnostics and their application, Adv. Atmo. Sci. 17, 165-183 (2000). [4] S. Wang, F. Zhang, Source of gravity waves within a vortex dipole jet revealed by a linear model, J. Atmo. Sci. 67, 1438-1455 (2010).

Investigation of the role of gravity waves in the generation of equatorial bubbles

NASA Technical Reports Server (NTRS)

Johnson, Francis S.; Coley, William R.

1995-01-01

The following areas of interest in this progress report are: (1) the continuation of software development in the examination of F-region gravity-wave power using in-situ data from the Atmosphere Explorer (AE-E); (2) the inquiry into the use of the San Marco data for the study of the initiation and growth of bubbles, particularly when the satellite passes through the early evening hours at relatively high altitudes, and the development of bubbles using not only the San Marco data but includes the use of airglow observations made in Hawaii; and (3) the promising development in the observation of distinct well formed waves at about 400 km altitude in the equatorial region. These waves look very much like waves seen over the polar cap that are attributed to internal gravity waves in the neutral atmosphere driving ionization up and down the magnetic field lines. These equatorial waves show no modulation of the total ion concentration.

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

Universal planetary tectonics (supertectonics)

NASA Astrophysics Data System (ADS)

Kochemasov, G. G.

2009-04-01

Universal planetary tectonics (supertectonics) G. Kochemasov IGEM of the Russian Academy of Sciences, Moscow, Russia, kochem.36@mail.ru The wave planetology [1-3 & others] proceeds from the following: "planetary structures are made by orbits and rotations". A uniform reason makes uniform structures. Inertia-gravity waves arising in planetary bodies due to their movements in Keplerian elliptical orbits with periodically changing accelerations warp these bodies in such way that they acquire polyhedron shapes (after interference of standing waves of four directions). Strong Newtonian gravity makes bodies larger than ~400 to 500 km in diameter globular and polyhedra are rarely seen. Only geomorphologic, geologic and geophysical mapping can develop these hidden structures. But small bodies, normally less than ~ 300 to 400 km in diameter, often show parts of the polyhedra, rarely fully developed forms (the asteroid Steins and satellite Amalthea present rather perfect forms of "diamond"). Depending on warping wavelengths (they make harmonics) various Plato's figures superimposed on each other can be distinguished. The fundamental wave 1 produces a tetrahedron, intrinsically dichotomic figure in which a vertex (contraction) always is opposed to a face (expansion). From the recent examples the best is the saturnian northern hexagon (a face) opposed to the southern hurricane (a vertex). The first overtone wave 2 is responsible for creation of structural octahedra. Whole ‘diamonds" and their parts are known [4, 5]. Other overtones produce less developed (because of smaller wave amplitudes) planetary shapes complicating main forms. Thus, the first common structural peculiarity of planetary bodies is their polyhedron nature. Not less important is the second common structural peculiarity. As all globular or smaller more or less isometric bodies rotate, they have an angular momentum. It is inevitably different in tropic and extra-tropic belts having uneven radii or distances to the rotation axe. But this unevenness is undesirable because it creates tectonic stresses and increases energetic status that is against the natural tendency to minimize these physical characteristics. So, a body tends to lower angular momentum of tropics and increase it in extra-tropics. With the same angular velocity it remains only mass and radius to play in this tendency. Tropical belt is destructed (for an example, the lithosphere disintegration in solid bodies), extra-tropical belts add dense material (plumes), expand - the constructive tendency [6]. Both tectonic peculiarities-polyhedrons and constructive - destructive tendencies - are common for celestial bodies of various classes. They are characteristic for our star, planets, satellites and small bodies. That is why a term "supertectonics" seems rather suitable. References: [1] Kochemasov G.G. Concerted wave supergranulation of the solar system bodies // 16th Russian-American microsymposium on planetology, Abstracts, Moscow, Vernadsky Inst. (GEOKHI), 1992, 36-37. [2] Kochemasov G.G. Tectonic dichotomy, sectoring and granulation of Earth and other celestial bodies // Proceedings of the International Symposium on New Concepts in Global Tectonics, "NCGT-98 TSUKUBA", Geological Survey of Japan, Tsukuba, Nov 20-23, 1998, p. 144-147. [3] Kochemasov G.G. Theorems of wave planetary tectonics // Geophys. Res. Abstr., 1999, V.1, №3, 700. [4] Kochemasov G.G. Plato' polyhedra as shapes of small icy satellites // Geophys. Res. Abstracts, Vol. 10, 2008, EGU2008-A-01271, CD-ROM; [5] Kochemasov G.G. (1999) "Diamond" and "dumb-bells"-like shapes of celestial bodies induced by inertia-gravity waves // 30th Vernadsky-Brown microsymposium on comparative planetology, Abstracts, Moscow, Vernadsky Inst.,, 49-50; [6] Kochemasov G.G. Tectonics of rotating celestial globes // Vernadsky-Brown microsymposium 48, 20-22 Oct. 2008, Moscow, Abstr. m48_20.

Ocean dynamics studies. [of current-wave interactions

NASA Technical Reports Server (NTRS)

1974-01-01

Both the theoretical and experimental investigations into current-wave interactions are discussed. The following three problems were studied: (1) the dispersive relation of a random gravity-capillary wave field; (2) the changes of the statistical properties of surface waves under the influence of currents; and (3) the interaction of capillary-gravity with the nonuniform currents. Wave current interaction was measured and the feasibility of using such measurements for remote sensing of surface currents was considered. A laser probe was developed to measure the surface statistics, and the possibility of using current-wave interaction as a means of current measurement was demonstrated.

Gravity and geoid anomalies of the Philippine Sea: Evidence on the depth of compensation for the negative residual water depth anomaly

NASA Technical Reports Server (NTRS)

Bowin, C.

1982-01-01

A negative free-air gravity anomaly which occurs in the central part of the Philippine Sea was examined to determine the distribution and nature of possible regional mass excesses or deficiencies. Geoid anomalies from GEOS-3 observation were positive. A negative residual geoid anomaly consistent with the area of negative free-air gravity anomalies were found. Theoretical gravity-topography and geoid-topography admittance functions indicated that high density mantle at about 60 km dept could account for the magnitudes of the gravity and residual geoid anomaly and the 1 km residual water depth anomaly in the Philippine Sea. The negative residual depth anomaly may be compensated for by excess density in the uppermost mantle, but the residual geoid and regional free-air gravity anomalies and a slow surface wave velocity structure might result from low-density warm upper mantle material lying beneath the zone of high-density uppermost mantle. From a horizontal disk approximation, the depth of the low-density warm mantle was estimated to be on the order of 200 km.

Theoretical frameworks for testing relativistic gravity. 5: Post-Newtonian limit of Rosen's theory

NASA Technical Reports Server (NTRS)

Lee, D. L.; Caves, C. M.

1974-01-01

The post-Newtonian limit of Rosen's theory of gravity is evaluated and is shown to be identical to that of general relativity, except for the PPN parameter alpha sub 2, which is related to the difference in propagation speeds for gravitational and electromagnetic waves. Both the value of alpha sub 2 and the value of the Newtonian gravitational constant depend on the present cosmological structure of the Universe. If the cosmological structure has a specific but presumably special form, the Newtonian gravitational constant assumes its current value, alpha sub 2 is zero, the post-Newtonian limit of Rosen's theory is identical to that of general relativity--and standard solar system experiments cannot distinguish between the two theories.

Theoretical frameworks for testing relativistic gravity. V - Post-Newtonian limit of Rosen's theory

NASA Technical Reports Server (NTRS)

Lee, D. L.; Ni, W.-T.; Caves, C. M.; Will, C. M.

1976-01-01

The post-Newtonian limit of Rosen's theory of gravity is evaluated and is shown to be identical to that of general relativity, except for the post-Newtonian parameter alpha sub 2 (which is related to the difference in propagation speeds for gravitational and electromagnetic waves). Both the value of alpha sub 2 and the value of the Newtonian gravitational constant depend on the present cosmological structure of the Universe. If the cosmological structure has a specific (but presumably special) form, the Newtonian gravitational constant assumes its current value, alpha sub 2 is zero, the post-Newtonian limit of Rosen's theory is identical to that of general relativity - and standard solar system experiments cannot distinguish between the two theories.

Stochastic Lagrangian dynamics for charged flows in the E-F regions of ionosphere

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

Tang Wenbo; Mahalov, Alex

2013-03-15

We develop a three-dimensional numerical model for the E-F region ionosphere and study the Lagrangian dynamics for plasma flows in this region. Our interest rests on the charge-neutral interactions and the statistics associated with stochastic Lagrangian motion. In particular, we examine the organizing mixing patterns for plasma flows due to polarized gravity wave excitations in the neutral field, using Lagrangian coherent structures (LCS). LCS objectively depict the flow topology-the extracted attractors indicate generation of ionospheric density gradients, due to accumulation of plasma. Using Lagrangian measures such as the finite-time Lyapunov exponents, we locate the Lagrangian skeletons for mixing in plasma,more » hence where charged fronts are expected to appear. With polarized neutral wind, we find that the corresponding plasma velocity is also polarized. Moreover, the polarized velocity alone, coupled with stochastic Lagrangian motion, may give rise to polarized density fronts in plasma. Statistics of these trajectories indicate high level of non-Gaussianity. This includes clear signatures of variance, skewness, and kurtosis of displacements taking polarized structures aligned with the gravity waves, and being anisotropic.« less

Stokes waves revisited: Exact solutions in the asymptotic limit

NASA Astrophysics Data System (ADS)

Davies, Megan; Chattopadhyay, Amit K.

2016-03-01

The Stokes perturbative solution of the nonlinear (boundary value dependent) surface gravity wave problem is known to provide results of reasonable accuracy to engineers in estimating the phase speed and amplitudes of such nonlinear waves. The weakling in this structure though is the presence of aperiodic "secular variation" in the solution that does not agree with the known periodic propagation of surface waves. This has historically necessitated increasingly higher-ordered (perturbative) approximations in the representation of the velocity profile. The present article ameliorates this long-standing theoretical insufficiency by invoking a compact exact n -ordered solution in the asymptotic infinite depth limit, primarily based on a representation structured around the third-ordered perturbative solution, that leads to a seamless extension to higher-order (e.g., fifth-order) forms existing in the literature. The result from this study is expected to improve phenomenological engineering estimates, now that any desired higher-ordered expansion may be compacted within the same representation, but without any aperiodicity in the spectral pattern of the wave guides.

ON THE SOURCE OF ASTROMETRIC ANOMALOUS REFRACTION

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

Taylor, M. Suzanne; McGraw, John T.; Zimmer, Peter C.

2013-03-15

More than a century ago, astronomers using transit telescopes to determine precise stellar positions were hampered by an unexplained periodic shifting of the stars they were observing. With the advent of CCD transit telescopes in the past three decades, this unexplained motion, termed 'anomalous refraction' by these early astronomers, is again being observed. Anomalous refraction is described as a low-frequency, large angular scale ({approx}2 Degree-Sign ) motion of the entire image plane with respect to the celestial coordinate system as observed and defined by astrometric catalogs. These motions, of typically several tenths of an arcsecond amplitude with timescales on themore » order of 10 minutes, are ubiquitous to ground-based drift-scan astrometric measurements regardless of location or telescopes used and have been attributed to the effect of tilting of equal-density layers of the atmosphere. The cause of this tilting has often been attributed to atmospheric gravity waves, but this cause has never been confirmed. Although theoretical models of atmospheric refraction show that atmospheric gravity waves are a plausible cause of anomalous refraction, an observational campaign specifically directed at defining this relationship provides clear evidence that anomalous refraction is not consistent with the passage of atmospheric gravity waves. The source of anomalous refraction is found to be meter-scale, slowly evolving quasi-coherent dynamical structures in the boundary layer below 60 m above ground level.« less

Precursor wave structure, prereversal vertical drift, and their relative roles in the development of post sunset equatorial spread-F

NASA Astrophysics Data System (ADS)

Abdu, Mangalathayil; Sobral, José; alam Kherani, Esfhan; Batista, Inez S.; Souza, Jonas

2016-07-01

The characteristics of large-scale wave structure in the equatorial bottomside F region that are present during daytime as precursor to post sunset development of the spread F/plasma bubble irregularities are investigated in this paper. Digisonde data from three equatorial sites in Brazil (Fortaleza, Sao Luis and Cachimbo) for a period of few months at low to medium/high solar activity phases are analyzed. Small amplitude oscillations in the F layer true heights, representing wave structure in polarization electric field, are identified as upward propagating gravity waves having zonal scale of a few hundred kilometers. Their amplitudes undergo amplification towards sunset, and depending on the amplitude of the prereversal vertical drift (PRE) they may lead to post sunset generation of ESF/plasma bubble irregularities. On days of their larger amplitudes they appear to occur in phase coherence on all days, and correspondingly the PRE vertical drift velocities are larger than on days of the smaller amplitudes of the wave structure that appear at random phase on the different days. The sustenance of these precursor waves structures is supported by the relatively large ratio (approaching unity) of the F region-to- total field line integrated Pedersen conductivities as calculated using the SUPIM simulation of the low latitude ionosphere. This study examines the role of the wave structure relative to that of the prereversal vertical drift in the post sunset spread F irregularity development.

Inventory of File sref.t03z.pgrb212_SPC.prob_1hrly.grib2

Science.gov Websites

analysis Total Precipitation [prob] prob >0.25 002 cloud base U-GWD 1 hour fcst Zonal Flux of Gravity Precipitation [prob] prob >0.25 007 cloud base U-GWD 2 hour fcst Zonal Flux of Gravity Wave Stress [prob ;0.25 012 cloud base U-GWD 4 hour fcst Zonal Flux of Gravity Wave Stress [prob] prob =1 013 entire

Gravity wave generation from jets and fronts: idealized and real-case simulations

NASA Astrophysics Data System (ADS)

Plougonven, Riwal; Arsac, Antonin; Hertzog, Albert; Guez, Lionel; Vial, François

2010-05-01

The generation of gravity waves from jets and fronts remains an outstanding issue in the dynamics of the atmosphere. It is important to explain and quantify this emission because of the several impacts of these waves, in particular the induced momentum fluxes towards the middle atmosphere, and their contribution to turbulence and mixing, e.g. in the region of the tropopause. Yet, the mechanisms at the origin of these waves have been difficult to identify, the fundamental reason for this being the separation between the time scales of balanced motions and gravity waves. Recent simulations of idealized baroclinic life cycles and of dipoles have provided insights into the mechanisms determining the characteristics and the amplitude of gravity waves emitted by jets. It has been shown in particular that the environmental strain and shear play a crucial role in determining the characteristics and location of the emitted waves, emphasizing jet exit regions for the appearance of coherent low-frequency waves. It has also been shown how advection of relatively small-scales allow to overcome the separation of time scales alluded to above. Recent results, remaining open questions and ongoing work on these idealized simulations will be briefly summarized. Nevertheless, unavoidable shortcomings of such idealized simulations include the sensitivity of the emitted waves to model setup (resolution, diffusion, parameterizations) and uncertainty regarding the realism of this aspect of the simulations. Hence, it is necessary to compare simulations with observations in order to assess their relevance. Such comparison has been undertaken using the dataset from the Vorcore campaign (Sept. 2005 - Feb. 2006, Hertzog, J. Atmos. Ocean. Techno. 2007) during which 27 superpressure balloons drifted as quasi-Lagrangian tracers in the lower stratosphere above Antarctica and the Southern Ocean. High-resolution simulations (dx = 20 km) have been carried out using the Weather Research and Forecast model for nearly two months. The realism of the simulated gravity waves is established based on systematic comparison with the observations and on case studies. The simulations are then used to quantify the importance and characteristics of gravity waves emitted from jets and fronts above the Southern Ocean. In particular, application of results from the idealized simulations to real cases, with a check provided by observations, will be discussed.

QBO Modulation of the Mesopause Gravity Wave Momentum Flux over Tierra del Fuego

NASA Technical Reports Server (NTRS)

De Wit, R. J.; Janches, D.; Fritts, D. C.; Hibbins, R. E.

2016-01-01

The interannual variability of the mesosphere and lower thermosphere (MLT) gravity wave momentum flux over southern mid latitudes (53.7degS) has been studied using more than 7 years of meteor radar observations at Ro Grande, Argentina. A modulation, with periods similar to that of the equatorial stratospheric quasi-biennial oscillation (QBO), is observed in the vertical flux of zonal as well as meridional momentum. The QBO signal is largest in the zonal component during summer and is in phase with the stratospheric QBO at 50 hPa (approx. 21 km). The relation between the stratospheric QBO and the QBO modulation in the MLT gravity wave forcing (derived from the divergence of the momentum flux) was found to be consistent with that expected from the Holton-Tan effect coupled to the interhemispheric coupling mechanism. These results provide the first observational support for the existence of the midlatitude gravity wave forcing anomalies as hypothesized in the interhemispheric coupling mechanism.

Extreme gravity tests with gravitational waves from compact binary coalescences: (I) inspiral-merger

NASA Astrophysics Data System (ADS)

Berti, Emanuele; Yagi, Kent; Yunes, Nicolás

2018-04-01

The observation of the inspiral and merger of compact binaries by the LIGO/Virgo collaboration ushered in a new era in the study of strong-field gravity. We review current and future tests of strong gravity and of the Kerr paradigm with gravitational-wave interferometers, both within a theory-agnostic framework (the parametrized post-Einsteinian formalism) and in the context of specific modified theories of gravity (scalar-tensor, Einstein-dilaton-Gauss-Bonnet, dynamical Chern-Simons, Lorentz-violating, and extra dimensional theories). In this contribution we focus on (i) the information carried by the inspiral radiation, and (ii) recent progress in numerical simulations of compact binary mergers in modified gravity.

Mechanistic Studies of Combustion and Structure Formation During Synthesis of Advanced Materials

NASA Technical Reports Server (NTRS)

Varma, A.; Lau, C.; Mukasyan, A. S.

2001-01-01

Combustion in a variety of heterogeneous systems, leading to the synthesis of advanced materials, is characterized by high temperatures (2000-3500 K) and heating rates (up to 10(exp 6) K/s) at and ahead of the reaction front. These high temperatures generate liquids and gases which are subject to gravity-driven flow. The removal of such gravitational effects is likely to provide increased control of the reaction front, with a consequent improvement in control of the microstructure of the synthesized products. Thus, microgravity (mu-g) experiments lead to major advances in the understanding of fundamental aspects of combustion and structure formation under the extreme conditions of the combustion synthesis (CS) wave. In addition, the specific features of microgravity environment allow one to produce unique materials, which cannot be obtained under terrestrial conditions. The current research is a logic continuation of our previous work on investigations of the fundamental phenomena of combustion and structure formation that occur at the high temperatures achieved in a CS wave. Our research is being conducted in three main directions: 1) Microstructural Transformations during Combustion Synthesis of Metal-Ceramic Composites. The studies are devoted to the investigation of particle growth during CS of intermetallic-ceramic composites, synthesized from nickel, aluminum, titanium, and boron metal reactants. To determine the mechanisms of particle growth, the investigation varies the relative amount of components in the initial mixture to yield combustion wave products with different ratios of solid and liquid phases, under 1g and mu-g conditions; 2) Mechanisms of Heat Transfer during Reactions in Heterogeneous Media. Specifically, new phenomena of gasless combustion wave propagation in heterogeneous media with porosity higher than that achievable in normal gravity conditions, are being studied. Two types of mixtures are investigated: clad powders, where contact between reactants occurs within each particle, and mixtures of elemental powders, where interparticle contacts are important for the reaction; and 3) Mechanistic Studies of Phase Separation in Combustion of Thermite Systems. Studies are devoted to experiments on thermite systems (metal oxide-reducing metal) where phase separation processes occur to produce alloys with tailored compositions and properties. The separation may be either gravity-driven or due to surface forces, and systematic studies to elucidate the true mechanism are being conducted. The knowledge obtained will be used to find the most promising ways of controlling the microstructure and properties of combustion-synthesized materials. Low-gravity experiments are essential to create idealized an environment for insights into the physics and chemistry of advanced material synthesis processes.

Lithosphere-asthenosphere interaction beneath Ireland from joint inversion of teleseismic P-wave delay times and GRACE gravity

NASA Astrophysics Data System (ADS)

O'Donnell, J. P.; Daly, E.; Tiberi, C.; Bastow, I. D.; O'Reilly, B. M.; Readman, P. W.; Hauser, F.

2011-03-01

The nature and extent of the regional lithosphere-asthenosphere interaction beneath Ireland and Britain remains unclear. Although it has been established that ancient Caledonian signatures pervade the lithosphere, tertiary structure related to the Iceland plume has been inferred to dominate the asthenosphere. To address this apparent contradiction in the literature, we image the 3-D lithospheric and deeper upper-mantle structure beneath Ireland via non-linear, iterative joint teleseismic-gravity inversion using data from the ISLE (Irish Seismic Lithospheric Experiment), ISUME (Irish Seismic Upper Mantle Experiment) and GRACE (Gravity Recovery and Climate Experiment) experiments. The inversion combines teleseismic relative arrival time residuals with the GRACE long wavelength satellite derived gravity anomaly by assuming a depth-dependent quasilinear velocity-density relationship. We argue that anomalies imaged at lithospheric depths probably reflect compositional contrasts, either due to terrane accretion associated with Iapetus Ocean closure, frozen decompressional melt that was generated by plate stretching during the opening of the north Atlantic Ocean, frozen Iceland plume related magmatic intrusions, or a combination thereof. The continuation of the anomalous structure across the lithosphere-asthenosphere boundary is interpreted as possibly reflecting sub-lithospheric small-scale convection initiated by the lithospheric compositional contrasts. Our hypothesis thus reconciles the disparity which exists between lithospheric and asthenospheric structure beneath this region of the north Atlantic rifted margin.

Group-kinetic theory and modeling of atmospheric turbulence

NASA Technical Reports Server (NTRS)

Tchen, C. M.

1989-01-01

A group kinetic method is developed for analyzing eddy transport properties and relaxation to equilibrium. The purpose is to derive the spectral structure of turbulence in incompressible and compressible media. Of particular interest are: direct and inverse cascade, boundary layer turbulence, Rossby wave turbulence, two phase turbulence; compressible turbulence, and soliton turbulence. Soliton turbulence can be found in large scale turbulence, turbulence connected with surface gravity waves and nonlinear propagation of acoustical and optical waves. By letting the pressure gradient represent the elementary interaction among fluid elements and by raising the Navier-Stokes equation to higher dimensionality, the master equation was obtained for the description of the microdynamical state of turbulence.

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.

1993-01-01

The Control-B simulation experiment was designed to improve on the Control-A experiment performed with the GMASS model. This experiment addressed several inadequacies with the first smooth terrain numerical simulation by including: (1) increased nested-grid resolution to better define the simulated gravity waves, (2) increased horizontal diffusion to remove outflow boundary condition noise, and (3) the use of reanalyzed rawinsonde data and surface observations in the initial state to increase the definition of the observed jet streak as well as other low-level features. A smoothed-terrain dry simulation with the nested-grid GMASS model has revealed many important aspects of the processes which resulted in the generation of gravity waves in the region and time when and where they were observed. However, the vertical structure, number, and characteristics of the waves are still quite different from observed waves as diagnosed thus necessitating future improved simulations. However, this control simulation has produced substantial insight into processes which occur on many spatial scales over a 30 hour time period thus allowing one to draw promising inferences as to the mechanisms for the complex process which occurred in nature during the CCOPE case study. The theoretical aspects of the project have focus on understanding the nature of the ageostrophic circulations which are produced in idealized models of the atmosphere in which the troposphere is modeled in one of two ways. The first model assumes that the lower atmosphere can be represented as a single layer of homogeneous fluid whose upper surface is free to exhibit vertical displacement. Two-dimensional internal convergence (divergence) occurring during the adjustment to an asymptotic equilibrium state from an ageostrophic initial state whose momentum structure is representative of a midlatitude localized zonal wind anomaly will cause the free upper surface of the homogeneous atmosphere to rise (fall), and therefore the response can be viewed as being physically three-dimensional. The second model assumes that the troposphere can be represented by an unbounded continuously stratified Boussinesq fluid of constant Brunt-Vaisala frequency N, where the vertical gradient of the basic state potential temperature profile allows for the existence of vertically propagating internal inertia-gravity waves.

Gravity Waves in the Atmospheres of Mars and Venus

NASA Astrophysics Data System (ADS)

Tellmann, Silvia; Paetzold, Martin; Häusler, Bernd; Bird, Michael K.; Tyler, G. Leonard; Hinson, David P.; Imamura, Takeshi

2016-10-01

Gravity waves are ubiquitous in all stably stratified planetary atmospheres and play a major role in the redistribution of energy and momentum. Gravity waves can be excited by many different mechanisms, e.g. by airflow over orographic obstacles or by convection in an adjacent layer.Gravity waves on Mars were observed in the lower atmosphere [1,2] but are also expected to play a major role in the cooling of the thermosphere [3] and the polar warming [4]. They might be excited by convection in the daytime boundary layer or by strong winter jets in combination with the pronounced topographic diversity on Mars.On Venus, gravity waves play an important role in the mesosphere above the cloud layer [5] and probably below. Convection in the cloud layer is one of the most important source mechanisms but certain correlations with topography were observed by different experiments [6,7,8].Temperature height profiles from the radio science experiments on Mars Express (MaRS) [9] and Venus Express (VeRa) [10] have the exceptionally high vertical resolution necessary to study small-scale vertical gravity waves, their global distribution, and possible source mechanisms.Atmospheric instabilities, which are clearly identified in the data, can be investigated to gain further insight into possible atmospheric processes contributing to the excitation of gravity waves.[1] Creasey, J. E., et al.,(2006), Geophys. Res. Lett., 33, L01803, doi:10.1029/2005GL024037.[2]Tellmann, S., et al.(2013), J. Geophys. Res. Planets, 118, 306-320, doi:10.1002/jgre.20058.[3]Medvedev, A. S., et al.(2015), J. Geophys. Res. Planets, 120, 913-927. doi:10.1002/2015JE004802.[4] Barnes, J. R. (1990), J. Geophys. Res., 95, B2, 1401-1421.[5] Tellmann, S., et al. (2012), Icarus, 221, 471 - 480.[6] Blamont, J.E. et al., (1986) 231, 1422-1425.[7] Bertaux J.-L., et al. (2016), J. Geophys. Res., Planets, in press.[8] Piccialli, A., et al. (2014), Icarus, 227, 94 - 111.[9] Pätzold, M., et al. (2016), Planet. Space Sci., 127, 44 - 90.[10] Häusler, B. et al., (2006). 1315-1335.

Sensitivity of Middle Atmospheric Temperature and Circulation in the UIUC Mesosphere-Stratosphere-Troposphere GCM to the Treatment of Subgrid-Scale Gravity-Wave Breaking

NASA Technical Reports Server (NTRS)

Yang, Fanglin; Schlesinger, Michael E.; Andranova, Natasha; Zubov, Vladimir A.; Rozanov, Eugene V.; Callis, Lin B.

2003-01-01

The sensitivity of the middle atmospheric temperature and circulation to the treatment of mean- flow forcing due to breaking gravity waves was investigated using the University of Illinois at Urbana-Champaign 40-layer Mesosphere-Stratosphere-Troposphere General Circulation Model (MST-GCM). Three GCM experiments were performed. The gravity-wave forcing was represented first by Rayleigh friction, and then by the Alexander and Dunkerton (AD) parameterization with weak and strong breaking effects of gravity waves. In all experiments, the Palmer et al. parameterization was included to treat the breaking of topographic gravity waves in the troposphere and lower stratosphere. Overall, the experiment with the strong breaking effect simulates best the middle atmospheric temperature and circulation. With Rayleigh friction and the weak breaking effect, a large warm bias of up to 60 C was found in the summer upper mesosphere and lower thermosphere. This warm bias was linked to the inability of the GCM to simulate the reversal of the zonal winds from easterly to westerly crossing the mesopause in the summer hemisphere. With the strong breaking effect, the GCM was able to simulate this reversal, and essentially eliminated the warm bias. This improvement was the result of a much stronger meridional transport circulation that possesses a strong vertical ascending branch in the summer upper mesosphere, and hence large adiabatic cooling. Budget analysis indicates that 'in the middle atmosphere the forces that act to maintain a steady zonal-mean zonal wind are primarily those associated with the meridional transport circulation and breaking gravity waves. Contributions from the interaction of the model-resolved eddies with the mean flow are small. To obtain a transport circulation in the mesosphere of the UIUC MST-GCM that is strong enough to produce the observed cold summer mesopause, gravity-wave forcing larger than 100 m/s/day in magnitude is required near the summer mesopause. In the tropics, only with the AD parameterization can the model produce realistic semiannual oscillations.

Observations and modeling of the effects of waves and rotors on submeso and turbulence variability within the stable boundary layer over central Pennsylvania

NASA Astrophysics Data System (ADS)

Suarez Mullins, Astrid

Terrain-induced gravity waves and rotor circulations have been hypothesized to enhance the generation of submeso motions (i.e., nonstationary shear events with spatial and temporal scales greater than the turbulence scale and smaller than the meso-gamma scale) and to modulate low-level intermittency in the stable boundary layer (SBL). Intermittent turbulence, generated by submeso motions and/or the waves, can affect the atmospheric transport and dispersion of pollutants and hazardous materials. Thus, the study of these motions and the mechanisms through which they impact the weakly to very stable SBL is crucial for improving air quality modeling and hazard predictions. In this thesis, the effects of waves and rotor circulations on submeso and turbulence variability within the SBL is investigated over the moderate terrain of central Pennsylvania using special observations from a network deployed at Rock Springs, PA and high-resolution Weather Research and Forecasting (WRF) model forecasts. The investigation of waves and rotors over central PA is important because 1) the moderate topography of this region is common to most of the eastern US and thus the knowledge acquired from this study can be of significance to a large population, 2) there have been little evidence of complex wave structures and rotors reported for this region, and 3) little is known about the waves and rotors generated by smaller and more moderate topographies. Six case studies exhibiting an array of wave and rotor structures are analyzed. Observational evidence of the presence of complex wave structures, resembling nonstationary trapped gravity waves and downslope windstorms, and complex rotor circulations, resembling trapped and jump-type rotors, is presented. These motions and the mechanisms through which they modulate the SBL are further investigated using high-resolution WRF forecasts. First, the efficacy of the 0.444-km horizontal grid spacing WRF model to reproduce submeso and meso-gamma motions, generated by waves and rotors and hypothesized to impact the SBL, is investigated using a new wavelet-based verification methodology for assessing non-deterministic model skill in the submeso and meso-gamma range to complement standard deterministic measures. This technique allows the verification and/or intercomparison of any two nonstationary stochastic systems without many of the limitations of typical wavelet-based verification approaches (e.g., selection of noise models, testing for significance, etc.). Through this analysis, it is shown that the WRF model largely underestimates the number of small amplitude fluctuations in the small submeso range, as expected; and it overestimates the number of small amplitude fluctuations in the meso-gamma range, generally resulting in forecasts that are too smooth. Investigation of the variability for different initialization strategies shows that deterministic wind speed predictions are less sensitive to the choice of initialization strategy than temperature forecasts. Similarly, investigation of the variability for various planetary boundary layer (PBL) parameterizations reveals that turbulent kinetic energy (TKE)-based schemes have an advantage over the non-local schemes for non-deterministic motions. The larger spread in the verification scores for various PBL parameterizations than initialization strategies indicates that PBL parameterization may play a larger role modulating the variability of non-deterministic motions in the SBL for these cases. These results confirm previous findings that have shown WRF to have limited skill forecasting submeso variability for periods greater than ~20 min. The limited skill of the WRF at these scales in these cases is related to the systematic underestimation of the amplitude of observed fluctuations. These results are implemented in the model design and configuration for the investigation of nonstationary waves and rotor structures modulating submeso and mesogamma motions and the SBL. Observations and WRF forecasts of two wave cases characterized by nonstationary waves and rotors are investigated to show the WRF model to have reasonable accuracy forecasting low-level temperature and wind speed in the SBL and to qualitatively produce rotors, similar to those observed, as well as some of the mechanisms modulating their development and evolution. Finally, observations and high-resolution WRF forecasts under different environmental conditions using various initialization strategies are used to investigate the impact of nonlinear gravity waves and rotor structures on the generation of intermittent turbulence and valley transport in the SBL. Evidence of the presence of elevated regions of TKE generated by the complex waves and rotors is presented and investigated using an additional four case studies, exhibiting two synoptic flow regimes and different wave and rotor structures. Throughout this thesis, terrain-induced gravity waves and rotors in the SBL are shown to synergistically interact with the surface cold pool and to enhance low-level turbulence intermittency through the development of submeso and meso-gamma motions. These motions are shown to be an important source of uncertainty for the atmospheric transport and dispersion of pollutants and hazardous materials under very stable conditions. (Abstract shortened by ProQuest.).

Radio scintillations observed during atmospheric occultations of Voyager: Internal gravity waves at Titan and magnetic field orientations at Jupiter and Saturn. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Hinson, D. P.

1983-01-01

The refractive index of planetary atmospheres at microwave frequencies is discussed. Physical models proposed for the refractive irregularities in the ionosphere and neutral atmosphere serve to characterize the atmospheric scattering structures, and are used subsequently to compute theoretical scintillation spectra for comparison with the Voyager occultation measurements. A technique for systematically analyzing and interpreting the signal fluctuations observed during planetary occultations is presented and applied to process the dual-wavelength data from the Voyager radio occultations by Jupiter, Saturn, and Titan. Results concerning the plasma irregularities in the upper ionospheres of Jupiter and Saturn are reported. The measured orientation of the irregularities is used to infer the magnetic field direction at several locations in the ionospheres of these two planets; the occultation measurements conflict with the predictions of Jovian magnetic field models, but generally confirm current models of Saturn's field. Wave parameters, including the vertical fluxes of energy and momentum, are estimated, and the source of the internal gravity waves discovered in Titan's upper atmosphere is considered.

The family of anisotropically scaled equatorial waves

NASA Astrophysics Data System (ADS)

RamíRez GutiéRrez, Enver; da Silva Dias, Pedro Leite; Raupp, Carlos; Bonatti, Jose Paulo

2011-04-01

In the present work we introduce the family of anisotropic equatorial waves. This family corresponds to equatorial waves at intermediate states between the shallow water and the long wave approximation model. The new family is obtained by using anisotropic time/space scalings on the linearized, unforced and inviscid shallow water model. It is shown that the anisotropic equatorial waves tend to the solutions of the long wave model in one extreme and to the shallow water model solutions in the other extreme of the parameter dependency. Thus, the problem associated with the completeness of the long wave model solutions can be asymptotically addressed. The anisotropic dispersion relation is computed and, in addition to the typical dependency on the equivalent depth, meridional quantum number and zonal wavenumber, it also depends on the anisotropy between both zonal to meridional space and velocity scales as well as the fast to slow time scales ratio. For magnitudes of the scales compatible with those of the tropical region, both mixed Rossby-gravity and inertio-gravity waves are shifted to a moderately higher frequency and, consequently, not filtered out. This draws attention to the fact that, for completeness of the long wave like solutions, it is necessary to include both the anisotropic mixed Rossby-gravity and inertio-gravity waves. Furthermore, the connection of slow and fast manifolds (distinguishing feature of equatorial dynamics) is preserved, though modified for the equatorial anisotropy parameters used δ ∈ < 1]. New possibilities of horizontal and vertical scale nonlinear interactions are allowed. Thus, the anisotropic shallow water model is of fundamental importance for understanding multiscale atmosphere and ocean dynamics in the tropics.

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.

A gravitational test of wave reinforcement versus fluid density models

NASA Technical Reports Server (NTRS)

Johnson, Jacqueline Umstead

1990-01-01

Spermatozoa, protozoa, and algae form macroscopic patterns somewhat analogous to thermally driven convection cells. These bioconvective patterns have attracted interest in the fluid dynamics community, but whether in all cases these waves were gravity driven was unknown. There are two conflicting theories, one gravity dependent (fluid density model), the other gravity independent (wave reinforcement theory). The primary objectives of the summer faculty fellows were to: (1) assist in sample collection (spermatozoa) and preparation for the KC-135 research airplane experiment; and (2) to collaborate on ground testing of bioconvective variables such as motility, concentration, morphology, etc., in relation to their macroscopic patterns. Results are very briefly given.

Dynamical response of the summer MLT to tropospheric global warming: Results from a mechanistic GCM with resolved gravity waves

NASA Astrophysics Data System (ADS)

Becker, E.

2009-04-01

The sensitivity of the mesosphere and lower thermosphere (MLT) to climate variability of the troposphere is largely controlled by the generation, propagation, and dissipation of gravity waves (GWs). Conventional climate models cannot fully describe this sensitivity since GWs must be parameterized by invoking strong assumptions. Since the Eliassen-Palm flux (EPF) of low-frequency inertia GWs is negligible, the main contribution to the EPF divergence at high latitudes of the MLT is due to mid- and high-frequency GWs with periods of a few hours or less. In order to resolve at least a good portion of these waves in a GCM, a high spatial resolution from the boundary layer to the lower thermosphere is required. Furthermore, both the generation and dissipation of resolved GWs is expected to depend strongly on the details of the parameterization of turbulence. The present study proposes a new formulation of the Kuehlungsborn mechanistic general circulation model (KMCM) with high spatial resolution and Smagorinsky-type horizontal and vertical diffusion coefficients that are both scaled by the Richardson criterion. This model version allows for an explicit and self-consistent simulation of the gravity-wave drag in the MLT. A sensitivity experiment is conducted in which the main changes associated with tropospheric global warming are imposed by the differential heating, i.e., reduced static stability in the lower troposphere along with a reduced equator-to-pole temperature difference and enhanced latent heating in the intertropical convergence zone. These changes result in both a stronger Lorenz energy cycle and enhanced gravity-wave activity in the upper troposphere at middle latitudes. The altered gravity-wave sources result in the following remote effects in the summer MLT: downward shift of the residual circulation, as well as lower temperatures and reduced easterlies below the mesopause. These changes are consistent with enhanced turbulent diffusion and dissipation below the mesopause due to larger gravity-wave amplitudes.

Simulations of wave propagation and disorder in 3D non-close-packed colloidal photonic crystals with low refractive index contrast.

PubMed

Glushko, O; Meisels, R; Kuchar, F

2010-03-29

The plane-wave expansion method (PWEM), the multiple-scattering method (MSM) and the 3D finite-difference time-domain method (FDTD) are applied for simulations of propagation of electromagnetic waves through 3D colloidal photonic crystals. The system investigated is not a "usual" artificial opal with close-packed fcc lattice but a dilute bcc structure which occurs due to long-range repulsive interaction between electrically charged colloidal particles during the growth process. The basic optical properties of non-close-packed colloidal PhCs are explored by examining the band structure and reflection spectra for a bcc lattice of silica spheres in an aqueous medium. Finite size effects and correspondence between the Bragg model, band structure and reflection spectra are discussed. The effects of size, positional and missing-spheres disorder are investigated. In addition, by analyzing the results of experimental work we show that the fabricated structures have reduced plane-to-plane distance probably due to the effect of gravity during growth.

Fate of Large-Scale Structure in Modified Gravity After GW170817 and GRB170817A

NASA Astrophysics Data System (ADS)

Amendola, Luca; Kunz, Martin; Saltas, Ippocratis D.; Sawicki, Ignacy

2018-03-01

The coincident detection of gravitational waves (GW) and a gamma-ray burst from a merger of neutron stars has placed an extremely stringent bound on the speed of GWs. We showed previously that the presence of gravitational slip (η ) in cosmology is intimately tied to modifications of GW propagation. This new constraint implies that the only remaining viable source of gravitational slip is a conformal coupling to gravity in scalar-tensor theories, while viable vector-tensor theories cannot now generate gravitational slip at all. We discuss structure formation in the remaining viable models, demonstrating that (i) the dark-matter growth rate must now be at least as fast as in general relativity (GR), with the possible exception of that beyond the Horndeski model, and (ii) if there is any scale dependence at all in the slip parameter, it is such that it takes the GR value at large scales. We show a consistency relation that must be violated if gravity is modified.

Equatorial waves in a stratospheric GCM: Effects of vertical resolution. [GCM (general circulation model)

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

Boville, B.A.; Randel, W.J.

1992-05-01

Equatorially trapped wave modes, such as Kelvin and mixed Rossby-gravity waves, are believed to play a crucial role in forcing the quasi-biennial oscillation (QBO) of the lower tropical stratosphere. This study examines the ability of a general circulation model (GCM) to simulate these waves and investigates the changes in the wave properties as a function of the vertical resolution of the model. The simulations produce a stratopause-level semiannual oscillation but not a QBO. An unfortunate property of the equatorially trapped waves is that they tend to have small vertical wavelengths ([le] 15 km). Some of the waves, believed to bemore » important in forcing the QBO, have wavelengths as short as 4 km. The short vertical wavelengths pose a stringent computational requirement for numerical models whose vertical grid spacing is typically chosen based on the requirements for simulating extratropical Rossby waves (which have much longer vertical wavelengths). This study examines the dependence of the equatorial wave simulation of vertical resolution using three experiments with vertical grid spacings of approximately 2.8, 1.4, and 0.7 km. Several Kelvin, mixed Rossby-gravity, and 0.7 km. Several Kelvin, mixed Rossby-gravity, and inertio-gravity waves are identified in the simulations. At high vertical resolution, the simulated waves are shown to correspond fairly well to the available observations. The properties of the relatively slow (and vertically short) waves believed to play a role in the QBO vary significantly with vertical resolution. Vertical grid spacings of about 1 km or less appear to be required to represent these waves adequately. The simulated wave amplitudes are at least as large as observed, and the waves are absorbed in the lower stratosphere, as required in order to force the QBO. However, the EP flux divergence associated with the waves is not sufficient to explain the zonal flow accelerations found in the QBO. 39 refs., 17 figs., 1 tab.« less

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.

Wavelength dependence of eddy dissipation and Coriolis force in the dynamics of gravity wave driven fluctuations in the OH nightglow

NASA Technical Reports Server (NTRS)

Hickey, M. P.

1988-01-01

This paper examines the effect of inclusion of Coriolis force and eddy dissipation in the gravity wave dynamics theory of Walterscheid et al. (1987). It was found that the values of the ratio 'eta' (where eta is a complex quantity describing the ralationship between the intensity oscillation about the time-averaged intensity, and the temperature oscillation about the time-averaged temperature) strongly depend on the wave period and the horizontal wavelength; thus, if comparisons are to be made between observations and theory, horizontal wavelengths will need to be measured in conjunction with the OH nightglow measurements. For the waves with horizontal wavelengths up to 1000 km, the eddy dissipation was found to dominate over the Coriolis force in the gravity wave dynamics and also in the associated values of eta. However, for waves with horizontal wavelengths of 10,000 km or more, the Coriolis force cannot be neglected; it has to be taken into account along with the eddy dissipation.

Wave equations in conformal gravity

NASA Astrophysics Data System (ADS)

Du, Juan-Juan; Wang, Xue-Jing; He, You-Biao; Yang, Si-Jiang; Li, Zhong-Heng

2018-05-01

We study the wave equation governing massless fields of all spins (s = 0, 1 2, 1, 3 2 and 2) in the most general spherical symmetric metric of conformal gravity. The equation is separable, the solution of the angular part is a spin-weighted spherical harmonic, and the radial wave function may be expressed in terms of solutions of the Heun equation which has four regular singular points. We also consider various special cases of the metric and find that the angular wave functions are the same for all cases, the actual shape of the metric functions affects only the radial wave function. It is interesting to note that each radial equation can be transformed into a known ordinary differential equation (i.e. Heun equation, or confluent Heun equation, or hypergeometric equation). The results show that there are analytic solutions for all the wave equations of massless spin fields in the spacetimes of conformal gravity. This is amazing because exact solutions are few and far between for other spacetimes.

Electric Current Activated Combustion Synthesis and Chemical Ovens Under Terrestrial and Reduced Gravity Conditions

NASA Technical Reports Server (NTRS)

Unuvar, C.; Fredrick, D.; Anselmi-Tamburini, U.; Manerbino, A.; Guigne, J. Y.; Munir, Z. A.; Shaw, B. D.

2004-01-01

Combustion synthesis (CS) generally involves mixing reactants together (e.g., metal powders) and igniting the mixture. Typically, a reaction wave will pass through the sample. In field activated combustion synthesis (FACS), the addition of an electric field has a marked effect on the dynamics of wave propagation and on the nature, composition, and homogeneity of the product as well as capillary flow, mass-transport in porous media, and Marangoni flows, which are influenced by gravity. The objective is to understand the role of an electric field in CS reactions under conditions where gravity-related effects are suppressed or altered. The systems being studied are Ti+Al and Ti+3Al. Two different ignition orientations have been used to observe effects of gravity when one of the reactants becomes molten. This consequentially influences the position and concentration of the electric current, which in turn influences the entire process. Experiments have also been performed in microgravity conditions. This process has been named Microgravity Field Activated Combustion Synthesis (MFACS). Effects of gravity have been demonstrated, where the reaction wave temperature and velocity demonstrate considerable differences besides the changes of combustion mechanisms with the different high currents applied. Also the threshold for the formation of a stable reaction wave is increased under zero gravity conditions. Electric current was also utilized with a chemical oven technique, where inserts of aluminum with minute amounts of tungsten and tantalum were used to allow observation of effects of settling of the higher density solid particles in liquid aluminum at the present temperature profile and wave velocity of the reaction.

Effect of Baffle on Gravity-Gradient-Excited Slosh Waves and Spacecraft Moment and Angular-Momentum Fluctuations in Microgravity

NASA Technical Reports Server (NTRS)

Hung, R. J.; Lee, C. C.

1995-01-01

The dynamical behavior of fluids affected by the asymmetric gravity gradient acceleration has been investigated. In particular, the effects of surface tension on partially filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank with and without baffles are studied. Results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient acceleration indicate that the gravity gradient acceleration is equivalent to the combined effect of a twisting force and a torsional moment acting on the spacecraft. The results are clearly seen from one-up one-down and one-down one-up oscillations in the cross-section profiles of two bubbles in the vertical (r, z)-plane of the rotating dewar, and from the eccentric contour of the bubble rotating around the axis of the dewar in a horizontal (r, theta)-plane. As the viscous force, between liquid and solid interface, greatly contributes to the damping of slosh wave excitation, a rotating dewar with baffles provides more areas of liquid-solid interface than that of a rotating dewar without baffles. Results show that the damping effect provided by the baffles reduces the amplitude of slosh wave excitation and lowers the degree of asymmetry in liquid-vapor distribution. Fluctuations of angular momentum and fluid moment caused by the slosh wave excited by gravity gradient acceleration with and without baffle boards are also investigated. It is also shown that the damping effect provided by the baffles greatly reduces the amplitudes of angular momentum and fluid moment fluctuations.

Intermittency of gravity wave momentum flux in the mesopause region observed with an all-sky airglow imager

NASA Astrophysics Data System (ADS)

Cao, Bing; Liu, Alan Z.

2016-01-01

The intermittency of gravity wave momentum flux (MF) near the OH airglow layer (˜87 km) in the mesopause region is investigated for the first time using observation of all-sky airglow imager over Maui, Hawaii (20.7°N, 156.3°W), and Cerro Pachón, Chile (30.3°S, 70.7°W). At both sites, the probability density function (pdf) of gravity wave MF shows two distinct distributions depending on the magnitude of the MF. For MF smaller (larger) than ˜16 m2 s-2 (0.091 mPa), the pdf follows a lognormal (power law) distribution. The intermittency represented by the Bernoulli proxy and the percentile ratio shows that gravity waves have higher intermittency at Maui than at Cerro Pachón, suggesting more intermittent background variation above Maui. It is found that most of the MF is contributed by waves that occur very infrequently. But waves that individually contribute little MF are also important because of their higher occurrence frequencies. The peak contribution is from waves with MF around ˜2.2 m2 s-2 at Cerro Pachón and ˜5.5 m2 s-2 at Maui. Seasonal variations of the pdf and intermittency imply that the background atmosphere has larger influence on the observed intermittency in the mesopause region.

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.

Wave turbulence in a two-layer fluid: Coupling between free surface and interface waves

NASA Astrophysics Data System (ADS)

Falcon, Eric; Issenmann, Bruno; Laroche, Claude

2017-11-01

We experimentally study gravity-capillary wave turbulence on the interface between two immiscible fluids of close density with free upper surface. We locally measure the wave height at the interface between both fluids by means of a highly sensitive laser Doppler vibrometer. We show that the inertial range of the capillary wave turbulence regime is significantly extended when the upper fluid depth is increased: The crossover frequency between the gravity and capillary wave turbulence regimes is found to decrease whereas the dissipative cut-off frequency of the spectrum is found to increase. We explain these observations by the progressive decoupling between waves propagating at the interface and the ones at the free surface, using the full dispersion relation of gravity-capillary waves in a two-layer fluid of finite depths. The cut-off evolution is due to the disappearance of parasitic capillaries responsible for the main wave dissipation for a single fluid. B. Issenmann, C. Laroche & E. Falcon, EPL 116, 64005 (2016) published online 16 feb. 2017. This work has been partially supported by CNRS (1-year postdoctoral funding), ANR Turbulon 12-BS04-0005, and ANR Dysturb 2017.

Jet-front systems nearing strongly stratified region in differentially heated, rotating stratified annulus

NASA Astrophysics Data System (ADS)

Rolland, Joran; Achatz, Ulrich

2017-04-01

The differentially heated, rotating annulus configuration has been used for a long time as a model system of the earth troposphere. It can easily reproduce thermal wind and baroclinic waves in the laboratory. It has recently been shown numerically that provided the Rossby number, the rotation rate and the Brunt-Väisälä frequency were well chosen, this configuration also reproduces the spontaneous emission of gravity waves by jet front systems [1]. This offers a very practical configuration in which to study an important process of emission of atmospheric gravity waves. It has also been shown experimentally that this configuration can be modified in order to add the possibility for the emitted wave to reach a strongly stratified region [2]. It thus creates a system containing a model troposphere where gravity waves are spontaneously emitted and can propagate to a model stratosphere. For this matter a stratification was created using a salinity gradient in the experimental apparatus. Through double diffusion, this generates a strongly stratified layer in the middle of the flow (the model stratosphere) and two weakly stratified region in the top and bottom layers (the model troposphere). In this poster, we present simulations of this configuration displaying baroclinic waves in the top and bottom layers. We aim at creating jet front systems strong enough that gravity waves can be spontaneously emitted. This will thus offer the possibility of studying the wave characteristic and mechanisms in emission and propagation in details. References [1] S. Borchert, U. Achatz, M.D. Fruman, Spontaneous Gravity wave emission in the differentially heated annulus, J. Fluid Mech. 758, 287-311 (2014). [2] M. Vincze, I. Borcia, U. Harlander, P. Le Gal, Double-diffusive convection convection and baroclinic instability in a differentially heated and initially stratified rotating system: the barostrat instability, Fluid Dyn. Res. 48, 061414 (2016).

Gravity Wave Energetics Determined From Coincident Space-Based and Ground-Based Observations of Airglow Emissions

NASA Technical Reports Server (NTRS)

2000-01-01

Significant progress was made toward the goals of this proposal in a number of areas during the covered period. Section 5.1 contains a copy of the originally proposed schedule. The tasks listed below have been accomplished: (1) Construction of space-based observing geometry gravity wave model. This model has been described in detail in the paper accompanying this report (Section 5.2). It can simulate the observing geometry of both ground-based, and orbital instruments allowing comparisons to be made between them. (2) Comparisons of relative emission intensity, temperatures, and Krassovsky's ratio for space- and ground-based observing geometries. These quantities are used in gravity wave literature to describe the effects of the waves on the airglow. (3) Rejection of Bates [1992], and Copeland [1994] chemistries for gravity wave modeling purposes. Excessive 02(A(sup 13)(Delta)) production led to overproduction of O2(b(sup 1)(Sigma)), the state responsible for the emission of O2. Atmospheric band. Attempts were made to correct for this behavior, but could not adequately compensate for this. (4) Rejection of MSX dataset due to lack of coincident data, and resolution necessary to characterize the waves. A careful search to identify coincident data revealed only four instances, with only one of those providing usable data. Two high latitude overpasses and were contaminated by auroral emissions. Of the remaining two mid-latitude coincidences, one overflight was obscured by cloud, leaving only one ten minute segment of usable data. Aside from the statistical difficulties involved in comparing measurements taken in this short period, the instrument lacks the necessary resolution to determine the vertical wavelength of the gravity wave. This means that the wave cannot be uniquely characterized from space with this dataset. Since no observed wave can be uniquely identified, model comparisons are not possible.

Rayleigh lidar observations of gravity wave activity in the upper stratosphere at Urbana, Ill.

NASA Technical Reports Server (NTRS)

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

1988-01-01

During 13 nights of Rayleigh lidar measurements at Urbana, Ill. in 1984 to 1986, thirty-six quasi-monochromatic gravity waves were observed in the 35 to 50 km altitude region of the stratosphere. The characteristics of the waves are compared with other lidar and radar measurements of gravity waves and the theoretical models of wave saturation and dissipation phenomena. The measured vertical wavelengths ranged from 2 to 11.5 km and the measured vertical phase velocities ranged from 10 to 85 cm/s. The vertical wavelengths and vertical phase velocities were used to infer observed wave periods which ranged from 100 to 1000 min and horizontal wavelengths which ranged from 70 to 2000 km. Dominant wave activity was found at vertical wavelengths between 2 to 4 km and 7 to 10 km. No significant seasonal variations were evident in the observed parameters. Vertical and horizontal wavelengths showed a clear tendency to increase with wave periods, which is consistent with recent sodium lidar studies of quasi-monochromatic waves near the mesopause. An average amplitude growth length of 20.9 km for the rms wind perturbations was estimated from the data. Kinetic energy density associated with the waves decreased with height, suggesting that waves in this altitude region were subject to dissipation or saturation effects.

A revised method of presenting wavenumber-frequency power spectrum diagrams that reveals the asymmetric nature of tropical large-scale waves

NASA Astrophysics Data System (ADS)

Chao, Winston C.; Yang, Bo; Fu, Xiouhua

2009-11-01

The popular method of presenting wavenumber-frequency power spectrum diagrams for studying tropical large-scale waves in the literature is shown to give an incomplete presentation of these waves. The so-called “convectively coupled Kelvin (mixed Rossby-gravity) waves” are presented as existing only in the symmetric (anti-symmetric) component of the diagrams. This is obviously not consistent with the published composite/regression studies of “convectively coupled Kelvin waves,” which illustrate the asymmetric nature of these waves. The cause of this inconsistency is revealed in this note and a revised method of presenting the power spectrum diagrams is proposed. When this revised method is used, “convectively coupled Kelvin waves” do show anti-symmetric components, and “convectively coupled mixed Rossby-gravity waves (also known as Yanai waves)” do show a hint of symmetric components. These results bolster a published proposal that these waves should be called “chimeric Kelvin waves,” “chimeric mixed Rossby-gravity waves,” etc. This revised method of presenting power spectrum diagrams offers an additional means of comparing the GCM output with observations by calling attention to the capability of GCMs to correctly simulate the asymmetric characteristics of equatorial waves.

Global ERS 1 and 2 and NSCAT observations: Upwind/crosswind and upwind/downwind measurements

NASA Astrophysics Data System (ADS)

Quilfen, Y.; Chapron, B.; Bentamy, A.; Gourrion, J.; El Fouhaily, T.; Vandemark, D.

1999-05-01

This paper presents an analysis of the wind speed dependence of upwind/downwind asymmetry (UDA) and upwind-crosswind anisotropy (UCA) as derived from global C band VV-polarized ERS 1 and 2 and Ku band VV- and HH-polarized NASA scatterometer (NSCAT) data. Interpretation of the results relies on identifying relationships between the differing frequencies and incidence angles that are consistent with Bragg scattering theory from gravity-capillary waves. It is shown that globally derived parameters characterizing UDA and UCA hold information on the wind dependence of short gravity and gravity-capillary wave growth and dissipation. In particular, the UCA behavior is found quadratic for both the C and Ku band, peaking at moderate wind speeds. In addition, the dual-frequency results appear to map out the expected, more rapid adjustment of centimeter-scale (Ku band) waves to the wind direction at light winds. However, as wind increases, the directionality associated with these shorter waves saturates at a lower speed than for the slightly longer waves inferred at C band. It is suggested that this observed phenomenon may be related to increasing wave-drift interactions that can potentially inhibit short-scale surface wave growth along the wind direction. Concerning UDA properties, our present analysis reveals that the NSCAT and ERS 1 and 2 scatterometers give quite different results. Our preliminary interpretation is that C band measurements may be easier to interpret using composite Bragg scattering theory and that upwind/downwind contrasts are mainly supported by short gravity waves.

Drake Antarctic Agile Meteor Radar first results: Configuration and comparison of mean and tidal wind and gravity wave momentum flux measurements with Southern Argentina Agile Meteor Radar

NASA Astrophysics Data System (ADS)

Fritts, D. C.; Janches, D.; Iimura, H.; Hocking, W. K.; Bageston, J. V.; Leme, N. M. P.

2012-01-01

A new generation meteor radar was installed at the Brazilian Antarctic Comandante Ferraz Base (62.1°S) in March 2010. This paper describes the motivations for the radar location, its measurement capabilities, and comparisons of measured mean winds, tides, and gravity wave momentum fluxes from April to June of 2010 and 2011 with those by a similar radar on Tierra del Fuego (53.8°S). Motivations for the radars include the “hotspot” of small-scale gravity wave activity extending from the troposphere into the mesosphere and lower thermosphere (MLT) centered over the Drake Passage, the maximum of the semidiurnal tide at these latitudes, and the lack of other MLT wind measurements in this latitude band. Mean winds are seen to be strongly modulated at planetary wave and longer periods and to exhibit strong coherence over the two radars at shorter time scales as well as systematic seasonal variations. The semidiurnal tide contributes most to the large-scale winds over both radars, with maximum tidal amplitudes during May and maxima at the highest altitudes varying from ˜20 to >70 ms-1. In contrast, the diurnal tide and various planetary waves achieve maximum winds of ˜10 to 20 ms-1. Monthly mean gravity wave momentum fluxes appear to reflect the occurrence of significant sources at lower altitudes, with relatively small zonal fluxes over both radars, but with significant, and opposite, meridional momentum fluxes below ˜85 km. These suggest gravity waves propagating away from the Drake Passage at both sites, and may indicate an important source region accounting in part for this “hotspot.”

Drake Antarctic Agile Meteor Radar (DrAAMER) First Results: Configuration and Comparison of Mean and Tidal Wind and Gravity Wave Momentum Flux Measurements with SAAMER

NASA Technical Reports Server (NTRS)

Fritts, D. C.; Janches, D.; Iimura, H.; Hocking, W. K.; Bageston, J. V.; Pene, N. M.

2011-01-01

A new-generation meteor radar was installed at the Brazilian Antarctic Comandante Ferraz Base (62.1degS) in March 2010. This paper describes the motivations for the radar location, its measurement capabilities, and comparisons of measured mean winds, tides, and gravity wave momentum fluxes from April to June of 2010 and 2011 with those by a similar radar on Tierra del Fuego (53.8degS). Motivations for the radars include the "hotspot" of small-scale gravity wave activity extending from the troposphere into the mesosphere and lower thermosphere (MLT) centered over the Drake Passage, the maximum of the semidiurnal tide at these latitudes, and the lack of other MLT wind measurements in this latitude band. Mean winds are seen to be strongly modulated at planetary wave and longer periods and to exhibit strong coherence over the two radars at shorter time scales as well as systematic seasonal variations. The semidiurnal tide contribute most to the large-scale winds over both radars, with maximum tidal amplitudes during May and maxima at the highest altitudes varying from approx.20 to >70 m/s. In contrast, the diurnal tide and various planetary waves achieve maximum winds of approx.10 to 20 m/s. Monthly-mean gravity wave momentum fluxes appear to reflect the occurrence of significant sources at lower altitudes, with relatively small zonal fluxes over both radars, but with significant, and opposite, meridional momentum fluxes below approx.85 km. These suggest gravity waves propagating away from the Drake Passage at both sites, and may indicate an important source region accounting in part for this "hotspot".

A statistical study of variations of internal gravity wave energy characteristics in meteor zone

NASA Technical Reports Server (NTRS)

Gavrilov, N. M.; Kalov, E. D.

1987-01-01

Internal gravity wave (IGW) parameters obtained by the radiometer method have been considered by many other researchers. The results of the processing of regular radiometeor measurements taken during 1979 to 1980 in Obninsk (55.1 deg N, 36.6 deg E) are presented.

Identification of Stratospheric Waves in Ozone in the Tropics from OMI High Spectral Resolution Measurements

NASA Technical Reports Server (NTRS)

Ziemke, J. R.; Liu, X.; Bhartia, P. K.

2007-01-01

Previous studies using Total Ozone Mapping Spectrometer (TOMS) measurements have identified several types of tropical waves in the stratosphere. These waves include Kelvin waves, mixed Rossby-gravity waves, equatorial Rossby waves, and global normal modes. All of these detected waves occur when their zonal phase speeds are opposite the zonal winds in the low-mid stratosphere associated with the Quasi-biennial Oscillation (QBO). Peak-to-peak amplitudes in all cases are typically 5 DU. While total ozone data from TOMS is sensitive in detecting these tropical waves, they provide each day only a single horizontal cross-sectional map. The high spatial and spectral resolution of the Aura Ozone Monitoring Instrument (OMI) provides a unique means to evaluate 3D structure in these waves including their propagation characteristics. Ozone profiles retrieved from OMI radiances for wavelengths 270-310 nm are utilized to examine the nature of these wave disturbances extending from the lower to upper stratosphere.

Ring dynamics

NASA Technical Reports Server (NTRS)

Borderies, Nicole

1989-01-01

Theoretical models of planetary-ring dynamics are discussed in a detailed analytical review and illustrated with graphs and diagrams. The streamline concept is introduced, and the phenomena associated with the transport of angular momentum are described. Particular attention is then given to (1) broad rings like those of Saturn (shepherding, density-wave excitation, gaps, bending-wave excitation, multiringlet structures, inner-edge shepherding, and the possibility of polar rings around Neptune), (2) narrow rings like those of Uranus (shepherding, ring shapes, and a self-gravity model of rigid precession), and (3) ring arcs like those seen in stellar-occultation observations of Neptune.

Derivation of gravity wave intrinsic parameters and vertical wavelength using a single scanning OH(3-1) airglow spectrometer

NASA Astrophysics Data System (ADS)

Wüst, Sabine; Offenwanger, Thomas; Schmidt, Carsten; Bittner, Michael; Jacobi, Christoph; Stober, Gunter; Yee, Jeng-Hwa; Mlynczak, Martin G.; Russell, James M., III

2018-05-01

For the first time, we present an approach to derive zonal, meridional, and vertical wavelengths as well as periods of gravity waves based on only one OH* spectrometer, addressing one vibrational-rotational transition. Knowledge of these parameters is a precondition for the calculation of further information, such as the wave group velocity vector.OH(3-1) spectrometer measurements allow the analysis of gravity wave ground-based periods but spatial information cannot necessarily be deduced. We use a scanning spectrometer and harmonic analysis to derive horizontal wavelengths at the mesopause altitude above Oberpfaffenhofen (48.09° N, 11.28° E), Germany for 22 nights in 2015. Based on the approximation of the dispersion relation for gravity waves of low and medium frequencies and additional horizontal wind information, we calculate vertical wavelengths. The mesopause wind measurements nearest to Oberpfaffenhofen are conducted at Collm (51.30° N, 13.02° E), Germany, ca. 380 km northeast of Oberpfaffenhofen, by a meteor radar.In order to compare our results, vertical temperature profiles of TIMED-SABER (thermosphere ionosphere mesosphere energetics dynamics, sounding of the atmosphere using broadband emission radiometry) overpasses are analysed with respect to the dominating vertical wavelength.

Theoretical and lidar studies of the density response of the mesospheric sodium layer to gravity wave perturbations

NASA Technical Reports Server (NTRS)

Shelton, J. D.; Gardner, C. S.

1981-01-01

The density response of atmospheric layers to gravity waves is developed in two forms, an exact solution and a perturbation series solution. The degree of nonlinearity in the layer density response is described by the series solution whereas the exact solution gives insight into the nature of the responses. Density perturbation in an atmospheric layer are shown to be substantially greater than the atmospheric density perturbation associated with the propagation of a gravity wave. Because of the density gradients present in atmospheric layers, interesting effects were observed such as a phase reversal in the linear layer response which occurs near the layer peak. Once the layer response is understood, the sodium layer can be used as a tracer of atmospheric wave motions. A two dimensional digital signal processing technique was developed. Both spatial and temporal filtering are utilized to enhance the resolution by decreasing shot noise by more han 10 dB. Many of the features associated with a layer density response to gravity waves were observed in high resolution density profiles of the mesospheric sodium layer. These include nonlinearities as well as the phase reversal in the linear layer response.

Mesoscale variations in acoustic signals induced by atmospheric gravity waves.

PubMed

Chunchuzov, Igor; Kulichkov, Sergey; Perepelkin, Vitaly; Ziemann, Astrid; Arnold, Klaus; Kniffka, Anke

2009-02-01

The results of acoustic tomographic monitoring of the coherent structures in the lower atmosphere and the effects of these structures on acoustic signal parameters are analyzed in the present study. From the measurements of acoustic travel time fluctuations (periods 1 min-1 h) with distant receivers, the temporal fluctuations of the effective sound speed and wind speed are retrieved along different ray paths connecting an acoustic pulse source and several receivers. By using a coherence analysis of the fluctuations near spatially distanced ray turning points, the internal wave-associated fluctuations are filtered and their spatial characteristics (coherences, horizontal phase velocities, and spatial scales) are estimated. The capability of acoustic tomography in estimating wind shear near ground is shown. A possible mechanism describing the temporal modulation of the near-ground wind field by ducted internal waves in the troposphere is proposed.

Gravity waves produced by the total solar eclipse of 1 August 2008

NASA Astrophysics Data System (ADS)

Marty, Julien; Francis, Dalaudier; Damien, Ponceau; Elisabeth, Blanc; Ulziibat, Munkhuu

2010-05-01

Gravity waves are a major component of atmospheric small scale dynamics because of their ability to transport energy and momentum over considerable distances and of their interactions with the mean circulation or other waves. They produce pressure variations which can be detected at the ground by microbarographs. The solar intensity reduction which occurs in the atmosphere during solar eclipses is known to act as a temporary source of large scale gravity waves. Despite decades of research, observational evidence for a characteristic bow-wave response of the atmosphere to eclipse passages remains elusive. A new versatile numerical model (Marty, J. and Dalaudier, F.: Linear spectral numerical model for internal gravity wave propagation. J. Atmos. Sci. (in press)) is presented and applied to the cooling of the atmosphere during a solar eclipse. Calculated solutions appear to be in good agreement with ground pressure fluctuations recorded during the total solar eclipse of 1 August 2008. To the knowledge of the authors, this is the first time that such a result is presented. A three-dimensional linear spectral numerical model is used to propagate internal gravity wave fluctuations in a stably stratified atmosphere. The model is developed to get first-order estimations of gravity wave fluctuations produced by identified sources. It is based on the solutions of the linearized fundamental fluid equations and uses the fully-compressible dispersion relation for inertia-gravity waves. The spectral implementation excludes situations involving spatial variations of buoyancy frequency or background wind. However density stratification variations are taken into account in the calculation of fluctuation amplitudes. In addition to gravity wave packet free propagation, the model handles both impulsive and continuous sources. It can account for spatial and temporal variations of the sources allowing to cover a broad range of physical situations. It is applied to the case of solar eclipses, which are known to produce large-scale bow waves on the Earth's surface. The asymptotic response to a Gaussian thermal forcing travelling at constant velocity as well as the transient response to the 4 December 2002 eclipse are presented. They show good agreement with previous numerical simulations. The model is then applied to the case of the 1 August 2008 solar eclipse. Ground pressure variations produced by the response to the solar intensity reduction in both stratosphere and troposphere are calculated. These synthetic signals are then compared to pressure variations recorded by IMS (International Monitoring System) infrasound stations and a temporary network specifically set up in Western Mongolia for this occasion. The pressure fluctuations produced by the 1 August 2008 solar eclipse are in a frequency band highly disturbed by atmospheric tides. Pressure variations produced by atmospheric tides and synoptic disturbances are thus characterized and removed from the signal. A low frequency wave starting just after the passage of the eclipse is finally brought to light on all stations. Its frequency and amplitude are close to the one calculated with our model, which strongly suggest that this signal was produced by the total solar eclipse.

Interactions between gravity waves and cold air outflows in a stably stratified uniform flow

NASA Technical Reports Server (NTRS)

Lin, Yuh-Lang; Wang, Ting-An; Weglarz, Ronald P.

1993-01-01

Interactions between gravity waves and cold air outflows in a stably stratified uniform flow forced by various combinations of prescribed heat sinks and sources are studied using a hydrostatic two-dimensional nonlinear numerical model. The formation time for the development of a stagnation point or reversed flow at the surface is not always directly proportional to the Froude number when wave reflections exist from upper levels. A density current is able to form by the wave-otuflow interaction, even though the Froude number is greater than a critical value. This is the result of the wave-outflow interaction shifting the flow response to a different location in the characteristic parameter space. A density current is able to form or be destroyed due to the wave-outflow interaction between a traveling gravity wave and cold air outflow. This is proved by performing experiments with a steady-state heat sink and an additional transient heat source. In a quiescent fluid, a region of cold air, convergence, and upward motion is formed after the collision between two outflows produced by two prescribed heat sinks. After the collision, the individual cold air outflows lose their own identity and merge into a single, stationary, cold air outflow region. Gravity waves tend to suppress this new stationary cold air outflow after the collision. The region of upward motion associated with the collision is confined to a very shallow layer. In a moving airstream, a density current produced by a heat sink may be suppressed or enhanced nonlinearly by an adjacent heat sink due to the wave-outflow interaction.

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.

Frequencies of gravity-capillary waves on highly curved interfaces with edge constraints

NASA Astrophysics Data System (ADS)

Shankar, P. N.

2007-06-01

A recently developed technique to calculate the natural frequencies of gravity-capillary waves in a confined liquid mass with a possibly highly curved free surface is extended to the case where the contact line is pinned. The general technique is worked out in detail for the cases of rectangular and cylindrical containers of circular section, the cases for which experimental data are available. The results of the present method are in excellent agreement with all earlier experimental and theoretical data for the flat static interface case [Benjamin and Scott, 1979. Gravity-capillary waves with edge constraints. J. Fluid Mech. 92, 241-267; Graham-Eagle, 1983. A new method for calculating eigenvalues with applications to gravity-capillary waves with edge constraints. Math. Proc. Camb. Phil. Soc. 94, 553-564; Henderson and Miles, 1994. Surface-wave damping in a circular cylinder with a fixed contact line. J. Fluid Mech. 275, 285-299]. However, the present method is applicable even when the contact angle is not π/2 and the static interface is curved. As a consequence we are able to work out the effects of a curved meniscus on the results of Cocciaro et al. [1993. Experimental investigation of capillary effects on surface gravity waves: non-wetting boundary conditions. J. Fluid Mech. 246, 43-66] where the measured contact angle was 62∘. We find that the meniscus does indeed account, as suggested by Cocciaro et al., for the earlier discrepancy between theory and experiment of about 20 mHz and there is now excellent agreement between the two.

A note on specific variability of long surface gravity waves and drag coefficient in coastal upwelling zone

NASA Astrophysics Data System (ADS)

Krzyścin, Janusz

1990-01-01

In this paper we solve analytically wave kinematic equations and the wave energy transport equation, for basic long surface gravity wave in the coastal upwelling zone. Using Gent and Taylor's (1978) parameterization of drag coefficient (which includes interaction between long surface waves and the air flow) we find variability of this coefficient due to wave amplification and refraction caused by specific surface water current in the region. The drag coefficient grows towards the shore. The growth is faster for stronger current. When the angle between waves and the current is less than 90° the growth is mainly connected with the waves steepness, but when the angle is larger, it is caused by relative growth of the wave phase velocity.

Ionospheric and satellite observations for studying the dynamic behavior of typhoons and the detection of severe storms and tsunamis

NASA Technical Reports Server (NTRS)

Hung, R. J.; Smith, R. E.

1978-01-01

Atmospheric acoustic-gravity waves associated with severe thunderstorms, tornadoes, typhoons (hurricanes) and tsunamis can be studied through the coupling between the ionosphere and the troposphere. Reverse ray tracing computations of acoustic-gravity waves observed by an ionospheric Doppler sounder array show that wave sources are in the nearby storm systems and that the waves are excited prior to the storms. Results show that ionospheric observations, together with satellite observations, can contribute to the understanding of the dynamical behavior of typhoons, severe storms and tsunamis.

Evidence of gravity wave-tidal interaction observed near the summer mesopause at Poker Flat, Alaska

NASA Technical Reports Server (NTRS)

Wang, Ding-Yi; Fritts, David C.

1991-01-01

An analysis of gravity wave-tidal interaction observed near the mesopause by the MST radar at Poker Flat in July of 1986 is presented. The observations revealed daily mean wind maxima of about 60 m/sec westward and 20 m/sec southward with daily mean momentum fluxes, contributed by gravity waves with periods less than 1 hour of 4-5 sq m/sec sq eastward and 1-2 sq m/sec sq northward. Considerable hourly height variability was found to exist for both winds and momentum fluxes. A significant modulation of the fluxes by tidal winds was observed, characterized by out-of-phase correlations over a number of heights.

Evidence at Mesospheric Altitude of Deeply Propagating Atmospheric Gravity Waves Created by Orographic Forcing over the Auckland Islands (50.5ºS) During the Deepwave Project

NASA Astrophysics Data System (ADS)

Pautet, P. D.; Ma, J.; Taylor, M. J.; Bossert, K.; Doyle, J. D.; Eckermann, S. D.; Williams, B. P.; Fritts, D. C.

2014-12-01

The DEEPWAVE project recently took place in New Zealand during the months of June and July 2014. This international program focused on investigating the generation and deep propagation of atmospheric gravity waves. A series of instruments was operated at several ground-based locations and on-board the NSF Gulfstream V aircraft. 26 research flights were performed to explore possible wave sources and their effects on the middle and upper atmosphere. On July 14th, a research flight was conducted over the Auckland Islands, a small sub Antarctic archipelago located ~450km south of New Zealand. Moderate southwesterly tropospheric wind (~25m/s) was blowing over the rugged topography of the islands, generating mountain wave signature at the flight altitude. Spectacular small-scale gravity waves were simultaneously observed at the mesopause level using the USU Advanced Mesospheric Temperature Mapper (AMTM). Their similarity with the model-predicted waves was striking. This presentation will describe this remarkable case of deep wave propagation and compare the measurements obtained with the instruments on-board the aircraft with forecasting and wave propagation models.

Cosmic Tsunamis in Modified Gravity: Disruption of Screening Mechanisms from Scalar Waves.

PubMed

Hagala, R; Llinares, C; Mota, D F

2017-03-10

Extending general relativity by adding extra degrees of freedom is a popular approach for explaining the accelerated expansion of the Universe and to build high energy completions of the theory of gravity. The presence of such new degrees of freedom is, however, tightly constrained from several observations and experiments that aim to test general relativity in a wide range of scales. The viability of a given modified theory of gravity, therefore, strongly depends on the existence of a screening mechanism that suppresses the extra degrees of freedom. We perform simulations, and find that waves propagating in the new degrees of freedom can significantly impact the efficiency of some screening mechanisms, thereby threatening the viability of these modified gravity theories. Specifically, we show that the waves produced in the symmetron model can increase the amplitude of the fifth force and the parametrized post Newtonian parameters by several orders of magnitude.

Cosmic Tsunamis in Modified Gravity: Disruption of Screening Mechanisms from Scalar Waves

NASA Astrophysics Data System (ADS)

Hagala, R.; Llinares, C.; Mota, D. F.

2017-03-01

Extending general relativity by adding extra degrees of freedom is a popular approach for explaining the accelerated expansion of the Universe and to build high energy completions of the theory of gravity. The presence of such new degrees of freedom is, however, tightly constrained from several observations and experiments that aim to test general relativity in a wide range of scales. The viability of a given modified theory of gravity, therefore, strongly depends on the existence of a screening mechanism that suppresses the extra degrees of freedom. We perform simulations, and find that waves propagating in the new degrees of freedom can significantly impact the efficiency of some screening mechanisms, thereby threatening the viability of these modified gravity theories. Specifically, we show that the waves produced in the symmetron model can increase the amplitude of the fifth force and the parametrized post Newtonian parameters by several orders of magnitude.

Search for Earthquake-Induced Prompt Gravity Signals in Gravimetric Data: Data Analysis and a New Observation Model

NASA Astrophysics Data System (ADS)

Kimura, M.; Kame, N.; Watada, S.; Ohtani, M.; Araya, A.; Imanishi, Y.; Ando, M.; Kunugi, T.

2017-12-01

Seismic waves radiated from an earthquake rupture induces density perturbations of the medium, which in turn generates prompt gravity changes at all distances before the arrival of seismic waves. Detection of the gravity signal before the seismic one is a challenge in seismology. In this study, we searched for the prompt gravity changes from the 2011 Tohoku-Oki earthquake in data recorded by gravimeters, seismometers, and tiltmeters. Predicted changes from the currently used simplified model were not identified using band-pass filtering and multi-station stacking even though sufficient signal-to-noise ratios were achieved. Our data analysis raised discrepancy between the data and the theoretical model. To interpret the absence of signals in the data, we investigated the effect of self-gravity deformation on the measurement of gravitational acceleration, which has been ignored in the existing theory. We analytically calculated the displacement of the observation station induced by the prompt gravity changes in an infinite homogeneous medium, and showed that before the arrival of P waves each point in the medium moves at an acceleration identical to the applied gravity change, i.e., free-falls. As a result of the opposite inertial force, gravity sensors attached to the medium lose their sensitivity to the prompt gravity changes. This new observation model incorporated with the self-gravity effect explains the absence of such prompt signals in the acceleration data. We have shown the negative observability in acceleration, but there remains a possibility of detection of its spatial gradients or spatial strain. For a future detection experiment, we derived an analytical expression of the theoretical gravity gradients from a general seismic source described as a moment tensor.

Mesoscale disturbances in the tropical stratosphere excited by convection - Observations and effects on the stratospheric momentum budget

NASA Technical Reports Server (NTRS)

Pfister, Leonhard; Scott, Stanley; Loewenstein, Max; Bowen, Stuart; Legg, Marion

1993-01-01

Aircraft temperature and pressure measurements as well as satellite imagery are used to establish the amplitudes and the space and time scale of potential temperature disturbances over convective systems. A conceptual model is proposed for the generation of mesoscale gravity waves by convection. The momentum forcing that a reasonable distribution of convection might exert on the tropical stratosphere through convectively excited mesoscale gravity waves of the observed amplitudes is estimated. Aircraft measurements show that presence of mesoscale disturbances in the lower stratospheric temperature, disturbances that appear to be associated with underlying convection. If the disturbances are convectively excited mesoscale gravity waves, their amplitude is sufficient that their breakdown in the upper stratosphere will exert a zonal force comparable to but probably smaller than the planetary-scale Kelvin waves.

Ground-based Observations for the Upper Atmosphere at King Sejong Station, Antarctica

NASA Astrophysics Data System (ADS)

Jee, Geonhwa; Kim, Jeong-Han; Lee, Changsup; Kim, Yong Ha

2014-06-01

Since the operation of the King Sejong Station (KSS) started in Antarctic Peninsula in 1989, there have been continuous efforts to perform the observation for the upper atmosphere. The observations during the initial period of the station include Fabry-Perot Interferometer (FPI) and Michelson Interferometer for the mesosphere and thermosphere, which are no longer in operation. In 2002, in collaboration with York University, Canada, the Spectral Airglow Temperature Imager (SATI) was installed to observe the temperature in the mesosphere and lower thermosphere (MLT) region and it has still been producing the mesopause temperature data until present. The observation was extended by installing the meteor radar in 2007 to observe the neutral winds and temperature in the MLT region during the day and night in collaboration with Chungnam National University. We also installed the all sky camera in 2008 to observe the wave structures in the MLT region. All these observations are utilized to study on the physical characteristics of the MLT region and also on the wave phenomena such as the tide and gravity wave in the upper atmosphere over KSS that is well known for the strong gravity wave activity. In this article, brief introductions for the currently operating instruments at KSS will be presented with their applications for the study of the upper atmosphere

Einstein Inflationary Probe (EIP)

NASA Technical Reports Server (NTRS)

Hinshaw, Gary

2004-01-01

I will discuss plans to develop a concept for the Einstein Inflation Probe: a mission to detect gravity waves from inflation via the unique signature they impart to the cosmic microwave background (CMB) polarization. A sensitive CMB polarization satellite may be the only way to probe physics at the grand-unified theory (GUT) scale, exceeding by 12 orders of magnitude the energies studied at the Large Hadron Collider. A detection of gravity waves would represent a remarkable confirmation of the inflationary paradigm and set the energy scale at which inflation occurred when the universe was a fraction of a second old. Even a strong upper limit to the gravity wave amplitude would be significant, ruling out many common models of inflation, and pointing to inflation occurring at much lower energy, if at all. Measuring gravity waves via the CMB polarization will be challenging. We will undertake a comprehensive study to identify the critical scientific requirements for the mission and their derived instrumental performance requirements. At the core of the study will be an assessment of what is scientifically and experimentally optimal within the scope and purpose of the Einstein Inflation Probe.

Modeling Volcanic Eruption Parameters by Near-Source Internal Gravity Waves.

PubMed

Ripepe, M; Barfucci, G; De Angelis, S; Delle Donne, D; Lacanna, G; Marchetti, E

2016-11-10

Volcanic explosions release large amounts of hot gas and ash into the atmosphere to form plumes rising several kilometers above eruptive vents, which can pose serious risk on human health and aviation also at several thousands of kilometers from the volcanic source. However the most sophisticate atmospheric models and eruptive plume dynamics require input parameters such as duration of the ejection phase and total mass erupted to constrain the quantity of ash dispersed in the atmosphere and to efficiently evaluate the related hazard. The sudden ejection of this large quantity of ash can perturb the equilibrium of the whole atmosphere triggering oscillations well below the frequencies of acoustic waves, down to much longer periods typical of gravity waves. We show that atmospheric gravity oscillations induced by volcanic eruptions and recorded by pressure sensors can be modeled as a compact source representing the rate of erupted volcanic mass. We demonstrate the feasibility of using gravity waves to derive eruption source parameters such as duration of the injection and total erupted mass with direct application in constraining plume and ash dispersal models.

Modeling Volcanic Eruption Parameters by Near-Source Internal Gravity Waves

PubMed Central

Ripepe, M.; Barfucci, G.; De Angelis, S.; Delle Donne, D.; Lacanna, G.; Marchetti, E.

2016-01-01

Volcanic explosions release large amounts of hot gas and ash into the atmosphere to form plumes rising several kilometers above eruptive vents, which can pose serious risk on human health and aviation also at several thousands of kilometers from the volcanic source. However the most sophisticate atmospheric models and eruptive plume dynamics require input parameters such as duration of the ejection phase and total mass erupted to constrain the quantity of ash dispersed in the atmosphere and to efficiently evaluate the related hazard. The sudden ejection of this large quantity of ash can perturb the equilibrium of the whole atmosphere triggering oscillations well below the frequencies of acoustic waves, down to much longer periods typical of gravity waves. We show that atmospheric gravity oscillations induced by volcanic eruptions and recorded by pressure sensors can be modeled as a compact source representing the rate of erupted volcanic mass. We demonstrate the feasibility of using gravity waves to derive eruption source parameters such as duration of the injection and total erupted mass with direct application in constraining plume and ash dispersal models. PMID:27830768

Transition from geostrophic turbulence to inertia-gravity waves in the atmospheric energy spectrum.

PubMed

Callies, Jörn; Ferrari, Raffaele; Bühler, Oliver

2014-12-02

Midlatitude fluctuations of the atmospheric winds on scales of thousands of kilometers, the most energetic of such fluctuations, are strongly constrained by the Earth's rotation and the atmosphere's stratification. As a result of these constraints, the flow is quasi-2D and energy is trapped at large scales—nonlinear turbulent interactions transfer energy to larger scales, but not to smaller scales. Aircraft observations of wind and temperature near the tropopause indicate that fluctuations at horizontal scales smaller than about 500 km are more energetic than expected from these quasi-2D dynamics. We present an analysis of the observations that indicates that these smaller-scale motions are due to approximately linear inertia-gravity waves, contrary to recent claims that these scales are strongly turbulent. Specifically, the aircraft velocity and temperature measurements are separated into two components: one due to the quasi-2D dynamics and one due to linear inertia-gravity waves. Quasi-2D dynamics dominate at scales larger than 500 km; inertia-gravity waves dominate at scales smaller than 500 km.

Transition from geostrophic turbulence to inertia–gravity waves in the atmospheric energy spectrum

PubMed Central

Callies, Jörn; Ferrari, Raffaele; Bühler, Oliver

2014-01-01

Midlatitude fluctuations of the atmospheric winds on scales of thousands of kilometers, the most energetic of such fluctuations, are strongly constrained by the Earth’s rotation and the atmosphere’s stratification. As a result of these constraints, the flow is quasi-2D and energy is trapped at large scales—nonlinear turbulent interactions transfer energy to larger scales, but not to smaller scales. Aircraft observations of wind and temperature near the tropopause indicate that fluctuations at horizontal scales smaller than about 500 km are more energetic than expected from these quasi-2D dynamics. We present an analysis of the observations that indicates that these smaller-scale motions are due to approximately linear inertia–gravity waves, contrary to recent claims that these scales are strongly turbulent. Specifically, the aircraft velocity and temperature measurements are separated into two components: one due to the quasi-2D dynamics and one due to linear inertia–gravity waves. Quasi-2D dynamics dominate at scales larger than 500 km; inertia–gravity waves dominate at scales smaller than 500 km. PMID:25404349

Interannual variability in the gravity wave drag - vertical coupling and possible climate links

NASA Astrophysics Data System (ADS)

Šácha, Petr; Miksovsky, Jiri; Pisoft, Petr

2018-05-01

Gravity wave drag (GWD) is an important driver of the middle atmospheric dynamics. However, there are almost no observational constraints on its strength and distribution (especially horizontal). In this study we analyze orographic GWD (OGWD) output from Canadian Middle Atmosphere Model simulation with specified dynamics (CMAM-sd) to illustrate the interannual variability in the OGWD distribution at particular pressure levels in the stratosphere and its relation to major climate oscillations. We have found significant changes in the OGWD distribution and strength depending on the phase of the North Atlantic Oscillation (NAO), quasi-biennial oscillation (QBO) and El Niño-Southern Oscillation. The OGWD variability is shown to be induced by lower-tropospheric wind variations to a large extent, and there is also significant variability detected in near-surface momentum fluxes. We argue that the orographic gravity waves (OGWs) and gravity waves (GWs) in general can be a quick mediator of the tropospheric variability into the stratosphere as the modifications of the OGWD distribution can result in different impacts on the stratospheric dynamics during different phases of the studied climate oscillations.

Hindcasting of Equatorial Spread F Using Seasonal Empirical Models

NASA Astrophysics Data System (ADS)

Aswathy, R. P.; Manju, G.

2018-02-01

The role of gravity waves in modulating equatorial spread F (ESF) day-to-day variability is investigated using ionosonde data at Trivandrum (geographic coordinates, 8.5°N, 77°E; mean geomagnetic latitude -0.3°N) a magnetic equatorial location. A novel empirical model that incorporates the combined effects of electrodynamics and gravity waves in modulating ESF occurrence during autumnal equinox season was presented by Aswathy and Manju (2017). In the present study, the height variations of the requisite gravity wave seed perturbations for ESF are examined for the vernal equinoxes, summer solstices, and winter solstices of different years. Subsequently, the empirical model, incorporating the electrodynamical effects and the gravity wave modulation, valid for each of the seasons is developed. Accordingly, for each season, the threshold curve may be demarcated provided the solar flux index (F10.7) is known. The empirical models are validated using the data for high, moderate, and low solar activity years corresponding to each season. In the next stage, this model is to be fine tuned to facilitate the prediction of ESF well before its onset.

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.

Structure of the southern Rio Grande rift from gravity interpretation

NASA Technical Reports Server (NTRS)

Daggett, P. H.; Keller, G. R.; Wen, C.-L.; Morgan, P.

1986-01-01

Regional Bouguer gravity anomalies in southern New Mexico have been analyzed by two-dimensional wave number filtering and poly-nomial trend surface analysis of the observed gravity field. A prominent, regional oval-shaped positive gravity anomaly was found to be associated with the southern Rio Grande rift. Computer modeling of three regional gravity profiles suggests that this anomaly is due to crustal thinning beneath the southern Rio Grande rift. These models indicate a 25 to 26-km minimum crustal thickness within the rift and suggest that the rift is underlain by a broad zone of anomalously low-density upper mantle. The southern terminus of the anomalous zone is approximately 50 km southwest of El Paso, Texas. A thinning of the rifted crust of 2-3 km relative to the adjacent Basin and Range province indicates an extension of about 9 percent during the formation of the modern southern Rio Grande rift. This extension estimate is consistent with estimates from other data sources. The crustal thinning and anomalous mantle is thought to result from magmatic activity related to surface volcanism and high heat flow in this area.

Hydrodynamic Controls on Muddy Sedimentary Fabric Development on Low-Gradient Shelves: Atchafalaya Chenier Plain Subaqueous Delta

NASA Astrophysics Data System (ADS)

Denommee, K.; Bentley, S. J.; Harazim, D.; Macquaker, J.

2016-02-01

Short sediment cores and geophysical data collected on the Southwest Louisiana Chenier Plain inner shelf have been studied in order to examine the sedimentary products of current-wave-enhanced sediment gravity flows (CWESGFs), a type of sediment gravity flow where the driving energy required to transport sediment across low-gradient settings is augmented by the near-bed orbital velocity of surface gravity wave and near-bed currents. Sedimentary fabrics observed on the SWLA shelf document the following flow evolution: (1) the erosion of the underlying substrate in response to wave-generated shear stresses in the bottom boundary layer, followed by (2) the deposition of ripple a crossbeded unit during wave-mediated oscillatory motions in low-viscosity suspension; (3) the deposition of subtle intercalated laminae during laminar flow at higher suspended sediment concentrations; followed by the deposition of (4) normally graded sediments during the waning phases of the flow. Significantly, the sedimentary fabrics deposited by CWESGFs on SWLA shelf show diagnostic variations from CWESGF-generated sedimentary fabrics observed on the Eel and Amazon shelves. Differences between the observed sedimentary fabrics are hypothesized to result from variations in the relative contribution of near-bed currents, wave orbital velocities, and bed slope (gravity) to the driving energy of the CWESGF, and as such can be catalogued as diagnostic recognition criteria using a prismatic ternary diagram where current-, wave-, and gravity-dominated end members form the vertices of a triangle, and wave period forms the prism axis. In this framework forcing mechanisms can be represented quantitatively, based on wave period and the relative contribution of each of the CWESGF velocity terms. This framework can be used to explore relationships between hydrodynamics and CWESGF fabrics, providing geologists with a tool with which to better recognize the depositional products of CWESGFs in the rock record; allowing for more accurate paleoenvironmental interpretations of extensive muddy successions.

Multi-instrument gravity-wave measurements over Tierra del Fuego and the Drake Passage - Part 1: Potential energies and vertical wavelengths from AIRS, COSMIC, HIRDLS, MLS-Aura, SAAMER, SABER and radiosondes

NASA Astrophysics Data System (ADS)

Wright, Corwin J.; Hindley, Neil P.; Moss, Andrew C.; Mitchell, Nicholas J.

2016-03-01

Gravity waves in the terrestrial atmosphere are a vital geophysical process, acting to transport energy and momentum on a wide range of scales and to couple the various atmospheric layers. Despite the importance of these waves, the many studies to date have often exhibited very dissimilar results, and it remains unclear whether these differences are primarily instrumental or methodological. Here, we address this problem by comparing observations made by a diverse range of the most widely used gravity-wave-resolving instruments in a common geographic region around the southern Andes and Drake Passage, an area known to exhibit strong wave activity. Specifically, we use data from three limb-sounding radiometers (Microwave Limb Sounder, MLS-Aura; HIgh Resolution Dynamics Limb Sounder, HIRDLS; Sounding of the Atmosphere using Broadband Emission Radiometry, SABER), the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) GPS-RO constellation, a ground-based meteor radar, the Advanced Infrared Sounder (AIRS) infrared nadir sounder and radiosondes to examine the gravity wave potential energy (GWPE) and vertical wavelengths (λz) of individual gravity-wave packets from the lower troposphere to the edge of the lower thermosphere ( ˜ 100 km). Our results show important similarities and differences. Limb sounder measurements show high intercorrelation, typically > 0.80 between any instrument pair. Meteor radar observations agree in form with the limb sounders, despite vast technical differences. AIRS and radiosonde observations tend to be uncorrelated or anticorrelated with the other data sets, suggesting very different behaviour of the wave field in the different spectral regimes accessed by each instrument. Evidence of wave dissipation is seen, and varies strongly with season. Observed GWPE for individual wave packets exhibits a log-normal distribution, with short-timescale intermittency dominating over a well-repeated monthly-median seasonal cycle. GWPE and λz exhibit strong correlations with the stratospheric winds, but not with local surface winds. Our results provide guidance for interpretation and intercomparison of such data sets in their full context.

Small-Scale Structure in Saturn's Rings

NASA Astrophysics Data System (ADS)

Rehnberg, Morgan

2017-08-01

The rings of Saturn are the largest and most complex in the Solar System. Decades of observation from ground- and space-based observatories and spacecraft missions have revealed the broad structure of the rings and the intricate interactions between the planet's moons and its rings. Stellar occultations observed by the Ultraviolet Imaging Spectrograph's High Speed Photometer onboard the Cassini spacecraft now enable the direct study of the small-scale structure that results from these interactions. In this dissertation, I present three distinct phenomena resulting from the small-scale physics of the rings. Many resonance locations with Saturn's external satellites lie within the main (A and B) rings. Two of these satellites, Janus and Epimetheus, have a unique co-orbital relationship and move radially to switch positions every 4.0 years. This motion also moves the resonance locations within the rings. As the spiral density waves created at these resonances interact, they launch an enormous solitary wave every eight years. I provide the first-ever observations of this never-predicted phenomenon and detail a possible formation mechanism. Previous studies have reported a population of kilometer-scale aggregates in Saturn's F ring, which likely form as a result of self-gravitation between ring particles in Saturn's Roche zone. I expand the known catalog of features in UVIS occultations and provide the first estimates of their density derived from comparisons with the A ring. These features are orders of magnitude less dense than previously believed, a fact which reconciles them with detections made by other means. Theory and indirect observations indicate that the smallest regular structures in the rings are wavelike aggregates called self-gravity wakes. Using the highest-resolution occulta- tions, I provide the first-ever direct detection of these features by identifying the gaps that represent the minima of the wakes. I demonstrate that the distribution of these gaps is con- sistent with the broad brightness asymmetries previously observed in the rings. Furthermore, the presence of spiral density waves affects the formation of self-gravity waves.

Anisotropic models of the upper mantle

NASA Technical Reports Server (NTRS)

Regan, J.; Anderson, D. L.

1983-01-01

Long period Rayleigh wave and Love wave dispersion data, particularly for oceanic areas, were not simultaneously satisfied by an isotropic structure. Available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy, an elastic dispersion, sphericity, and gravity. The resulting models, for the average Earth, average ocean and oceanic regions divided according to the age of the ocean floor, are quite different from previous results which ignore the above effects. The models show a low velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies. The correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggested.

Observations and a model of gravity-wave variability in the middle atmosphere

NASA Technical Reports Server (NTRS)

Fritts, D. C.; Vincent, R. A.

1986-01-01

A major goal was to determine what portion of the gravity-wave frequency spectrum accounted for the majority of the momentum flux and divergence, as this has important implications for the middle atmosphere response. It was found that approx. 70% of the total flux and divergence was due to wave motions with observed periods less than 1 hour, consistent with expectations based on the shape of the observed gravity-wave spectrum (FrItts, 1984). This dominance of the momentum flux and divergence by high-frequency motions implies a potential for the modulation of those quantities by large-amplitude motions at lower frequencies. A second, striking aspect of the velocity and momentum flux data is its dramatic diurnal variability, particularly at certain levels. This variability is illustrated with the momentum flux, computed in 8-hr blocks. The dominant contributions here are due to waves with periods less than 1 hr. The variability with height and size of the mean square velocity in the west beam and the momentum flux, energed over the 3-day period. A detailed analysis of the various tidal motions present during this data interval was performed, and it was determined that variations in the zontal wind profile imposed by the diurnal tidal motion are probably responsible for the modulation of the gravity-wave amplitudes and momentum fluxes.

Stratospheric Horizontal Wavenumber Spectra of Winds, Potential Temperature, and Atmospheric Tracers Observed by High-Altitude Aircraft

NASA Technical Reports Server (NTRS)

Bacmeister, Julio T.; Eckermann, Stephen D.; Newman, Paul A.; Lait, Leslie; Chan, K. R.; Loewenstein, Max; Proffitt, Michael H.; Gary, Bruce L.

1996-01-01

Horizontal wavenumber power spectra of vertical and horizontal wind velocities, potential temperatures, and ozone and N(2)O mixing ratios, as measured in the mid-stratosphere during 73 ER-2 flights (altitude approx. 20km) are presented. The velocity and potential temperature spectra in the 100 to 1-km wavelength range deviate significantly from the uniform -5/3 power law expected for the inverse energy-cascade regime of two-dimensional turbulence and also for inertial-range, three-dimensional turbulence. Instead, steeper spectra approximately consistent with a -3 power law are observed at horizontal scales smaller than 3 km for all velocity components as well as potential temperature. Shallower spectra are observed at scales longer than 6 km. For horizontal velocity and potential temperature the spectral indices at longer scales are between -1.5 and -2.0. For vertical velocity the spectrum at longer scales become flat. It is argued that the observed velocity and potential temperature spectra are consistent with gravity waves. At smaller scales, the shapes are also superficially consistent with a Lumley-Shur-Weinstock buoyant subrange of turbulence and/or nonlinear gravity waves. Contemporaneous spectra of ozone and N(sub 2)O mixing ratio in the 100 to 1-km wavelength range do conform to an approximately uniform -5/3 power law. It is argued that this may reflect interactions between gravity wave air-parcel displacements and laminar or filamentary structures in the trace gas mixing ratio field produced by enstropy-cascading two-dimensional turbulence.

Simulations of the Boundary Layer Between a White Dwarf and Its Accretion Disk

NASA Astrophysics Data System (ADS)

Balsara, Dinshaw S.; Fisker, Jacob Lund; Godon, Patrick; Sion, Edward M.

2009-09-01

Using a 2.5D time-dependent numerical code we recently developed, we solve the full compressible Navier-Stokes equations to determine the structure of the boundary layer (BL) between the white dwarf (WD) and the accretion disk in nonmagnetic cataclysmic variable systems. In this preliminary work, our numerical approach does not include radiation. In the energy equation, we either take the dissipation function (Φ) into account or we assume that the energy dissipated by viscous processes is instantly radiated away (Φ = 0). For a slowly rotating nonmagnetized accreting WD, the accretion disk extends all the way to the stellar surface. There, the matter impacts and spreads toward the poles as new matter continuously piles up behind it. We carry out numerical simulations for different values of the alpha-viscosity parameter (α), corresponding to different mass accretion rates. In the high viscosity cases (α = 0.1), the spreading BL sets off a gravity wave in the surface matter. The accretion flow moves supersonically over the cusp making it susceptible to the rapid development of gravity wave and/or Kelvin-Helmholtz shearing instabilities. This BL is optically thick and extends more than 30° to either side of the disk plane after only 3/4 of a Keplerian rotation period (tK = 19 s). In the low viscosity cases (α = 0.001), the spreading BL does not set off gravity waves and it is optically thin.

Modeling the QBO—Improvements resulting from higher‐model vertical resolution

PubMed Central

Zhou, Tiehan; Shindell, D.; Ruedy, R.; Aleinov, I.; Nazarenko, L.; Tausnev, N. L.; Kelley, M.; Sun, S.; Cheng, Y.; Field, R. D.; Faluvegi, G.

2016-01-01

Abstract Using the NASA Goddard Institute for Space Studies (GISS) climate model, it is shown that with proper choice of the gravity wave momentum flux entering the stratosphere and relatively fine vertical layering of at least 500 m in the upper troposphere‐lower stratosphere (UTLS), a realistic stratospheric quasi‐biennial oscillation (QBO) is modeled with the proper period, amplitude, and structure down to tropopause levels. It is furthermore shown that the specified gravity wave momentum flux controls the QBO period whereas the width of the gravity wave momentum flux phase speed spectrum controls the QBO amplitude. Fine vertical layering is required for the proper downward extension to tropopause levels as this permits wave‐mean flow interactions in the UTLS region to be resolved in the model. When vertical resolution is increased from 1000 to 500 m, the modeled QBO modulation of the tropical tropopause temperatures increasingly approach that from observations, and the “tape recorder” of stratospheric water vapor also approaches the observed. The transport characteristics of our GISS models are assessed using age‐of‐air and N2O diagnostics, and it is shown that some of the deficiencies in model transport that have been noted in previous GISS models are greatly improved for all of our tested model vertical resolutions. More realistic tropical‐extratropical transport isolation, commonly referred to as the “tropical pipe,” results from the finer vertical model layering required to generate a realistic QBO. PMID:27917258

Generalized framework for testing gravity with gravitational-wave propagation. I. Formulation

NASA Astrophysics Data System (ADS)

Nishizawa, Atsushi

2018-05-01

The direct detection of gravitational waves (GWs) from merging binary black holes and neutron stars marks the beginning of a new era in gravitational physics, and it brings forth new opportunities to test theories of gravity. To this end, it is crucial to search for anomalous deviations from general relativity in a model-independent way, irrespective of gravity theories, GW sources, and background spacetimes. In this paper, we propose a new universal framework for testing gravity with GWs, based on the generalized propagation of a GW in an effective field theory that describes modification of gravity at cosmological scales. Then, we perform a parameter estimation study, showing how well the future observation of GWs can constrain the model parameters in the generalized models of GW propagation.

The generation of a zonal-wind oscillation by nonlinear interactions of internal gravity waves

NASA Astrophysics Data System (ADS)

Campbell, Lucy

2003-11-01

Nonlinear interactions of internal gravity waves give rise to numerous large-scale phenomena that are observed in the atmosphere, for example the quasi-biennial oscillation (QBO). This is an oscillation in zonal wind direction which is observed in the equatorial stratosphere; it is characterized by alternating regimes of easterly and westerly shear that descend with time. In the past few decades, a number of theories have been developed to explain the mechanism by which the QBO is generated. These theories are all based on ``quasi-linear'' representations of wave-mean-flow interactions. In this presentation, a fully nonlinear numerical simulation of the QBO is described. A spectrum of gravity waves over a range of phase speeds is forced at the lower boundary of the computational domain and propagates upwards in a density-stratified shear flow. As a result of the absorption and reflection of the waves at their critical levels, regions of large shear develop in the background flow and propagate downwards with time.

Very high resolution observations of waves in the OH airglow at low latitudes.

NASA Astrophysics Data System (ADS)

Franzen, Christoph; Espy, Patrick J.; Hibbins, Robert E.; Djupvik, Amanda A.

2017-04-01

Vibrationally excited hydroxyl (OH) is produced in the mesosphere by the reaction of atomic hydrogen and ozone. This excited OH radiates a strong, near-infrared airglow emission in a thin ( 8 km thick) layer near 87 km. In the past, remote sensing of perturbations in the OH Meinel airglow has often been used to observe gravity, tidal and planetary waves travelling through this region. However, information on the highest frequency gravity waves is often limited by the temporal and spatial resolution of the available observations. In an effort to expand the wave scales present near the mesopause, we present a series of observations of the OH Meinel (9,7) transition that were executed with the Nordic Optical Telescope on La Palma (18°W, 29°N). These measurements are taken with a 10 s integration time (24 s repetition rate), and the spatial resolution at 87 km is as small as 10 m, allowing us to quantify the transition between the gravity and acoustic wave domains in the mesosphere.

Effect of gravity waves on the North Atlantic circulation

NASA Astrophysics Data System (ADS)

Eden, Carsten

2017-04-01

The recently proposed IDEMIX (Internal wave Dissipation, Energy and MIXing) parameterisation for the effect of gravity waves offers the possibility to construct consistent ocean models with a closed energy cycle. This means that the energy available for interior mixing in the ocean is only controlled by external energy input from the atmosphere and the tidal system and by internal exchanges. A central difficulty is the unknown fate of meso-scale eddy energy. In different scenarios for that eddy dissipation, the parameterized internal wave field provides between 2 and 3 TW for interior mixing from the total external energy input of about 4 TW, such that a transfer between 0.3 and 0.4 TW into mean potential energy contributes to drive the large-scale circulation in the model. The impact of the different mixing on the meridional overturning in the North Atlantic is discussed and compared to hydrographic observations. Furthermore, the direct energy exchange of the wave field with the geostrophic flow is parameterized in extended IDEMIX versions and the sensitivity of the North Atlantic circulation by this gravity wave drag is discussed.

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.

Statistical comparisons of gravity wave features derived from OH airglow and SABER data

NASA Astrophysics Data System (ADS)

Gelinas, L. J.; Hecht, J. H.; Walterscheid, R. L.

2017-12-01

The Aerospace Corporation's near-IR camera (ANI), deployed at Andes Lidar Observatory (ALO), Cerro Pachon Chile (30S,70W) since 2010, images the bright OH Meinel (4,2) airglow band. The imager provides detailed observations of gravity waves and instability dynamics, as described by Hecht et al. (2014). The camera employs a wide-angle lens that views a 73 by 73 degree region of the sky, approximately 120 km x 120 km at 85 km altitude. Image cadence of 30s allows for detailed spectral analysis of the horizontal components of wave features, including the evolution and decay of instability features. The SABER instrument on NASA's TIMED spacecraft provides remote soundings of kinetic temperature profiles from the lower stratosphere to the lower thermosphere. Horizontal and vertical filtering techniques allow SABER temperatures to be analyzed for gravity wave variances [Walterscheid and Christensen, 2016]. Here we compare the statistical characteristics of horizontal wave spectra, derived from airglow imagery, with vertical wave variances derived from SABER temperature profiles. The analysis is performed for a period of strong mountain wave activity over the Andes spanning the period between June and September 2012. Hecht, J. H., et al. (2014), The life cycle of instability features measured from the Andes Lidar Observatory over Cerro Pachon on March 24, 2012, J. Geophys. Res. Atmos., 119, 8872-8898, doi:10.1002/2014JD021726. Walterscheid, R. L., and A. B. Christensen (2016), Low-latitude gravity wave variances in the mesosphere and lower thermosphere derived from SABER temperature observation and compared with model simulation of waves generated by deep tropical convection, J. Geophys. Res. Atmos., 121, 11,900-11,912, doi:10.1002/2016JD024843.

Oblique wave trapping by vertical permeable membrane barriers located near a wall

NASA Astrophysics Data System (ADS)

Koley, Santanu; Sahoo, Trilochan

2017-12-01

The effectiveness of a vertical partial flexible porous membrane wave barrier located near a rigid vertical impermeable seawall for trapping obliquely incident surface gravity waves are analyzed in water of uniform depth under the assumption of linear water wave theory and small amplitude membrane barrier response. From the general formulation of the submerged membrane barrier, results for bottom-standing and surface-piercing barriers are computed and analyzed in special cases. Using the eigenfunction expansion method, the boundary-value problems are converted into series relations and then the required unknowns are obtained using the least squares approximation method. Various physical quantities of interests like reflection coefficient, wave energy dissipation, wave forces acting on the membrane barrier and the seawall are computed and analyzed for different values of the wave and structural parameters. The study will be useful in the design of the membrane wave barrier for the creation of tranquility zone in the lee side of the barrier to protect the seawall.

Infragravity waves in the ocean as a source of acoustic-gravity waves in the atmosphere

NASA Astrophysics Data System (ADS)

Zabotin, Nikolay A.; Godin, Oleg A.

2013-04-01

Infragravity waves (IGWs) are surface gravity waves in the ocean with periods longer than the longest periods (~30s) of wind-generated waves. IGWs propagate transoceanic distances with very little attenuation in deep water and, because of their long wavelengths (from ~1 km to hundreds of km), provide a mechanism for coupling wave processes in the ocean, ice shelves, the atmosphere, and the solid Earth. Here, we build on recent advances in understanding spectral and spatial variability of background infragravity waves in deep ocean to evaluate the IGW manifestations in the atmosphere. Water compressibility has a minor effect on IGWs. On the contrary, much larger compressibility and vertical extent of the atmosphere makes it necessary to treat IGW extension into the atmosphere as acoustic-gravity waves. There exist two distinct regimes of IGW penetration into the atmosphere. At higher frequencies, one has surface waves in the atmosphere propagating horizontally along the ocean surface and prominent up to heights of the order of the wavelength. At lower frequencies, IGWs are leaky waves, which continuously radiate their energy into the upper atmosphere. The transition between the two regimes occurs at a frequency of the order of 3 mHz, with the exact value of the transition frequency being a function of the ocean depth, the direction of IGW propagation and the vertical profiles of temperature and wind velocity. The transition frequency decreases with increasing ocean depth. Using recently obtained semi-empirical model of power spectra the IGWs over varying bathymetry [Godin O. A., Zabotin N. A., Sheehan A. F., Yang Z., and Collins J. A. Power spectra of infragravity waves in a deep ocean, Geophys. Res. Lett., under review (2012)], we derive an estimate of the flux of the mechanical energy from the deep ocean into the atmosphere due to IGWs. Significance will be discussed of the IGW contributions into the field of acoustic-gravity waves in the atmosphere.

Irreversible transport in the stratosphere by internal waves of short vertical wavelength

NASA Technical Reports Server (NTRS)

Danielsen, Edwin F.; Hipskind, R. S.; Starr, Walter L.; Vedder, James F.; Gaines, Steven E.; Kley, Dieter; Kelley, Ken K.

1991-01-01

Measurements performed during stratospheric flights of the U-2 aircraft confirm that cross-jet transport is dominated by waves, not by large-scale circulations. Monotonic gradients of trace constituents normal to the jet axis, with upper stratospheric tracers increasing poleward and tropospheric tracers increasing equatorward, are augmented by large-scale confluence as the jet intensifies during cyclogenesis. These gradients are rotated, intensified, and significantly increased in areas as their mixing ratio surfaces are folded by the differential transport of a very low frequency transverse wave. The quasi-horizontal transport produces a laminar structure with stable layers rich in upper stratospheric tracers alternating vertically with less stable layers rich in tropospheric tracers. The transport proceeds toward irreversibility at higher frequency, shear-gravity waves extend the folding to smaller horizontal scales.

A numerical experiment on the formation of the tropopause inversion layer associated with an explosive cyclogenesis: possible role of gravity waves

NASA Astrophysics Data System (ADS)

Otsuka, Shigenori; Takeshita, Megumi; Yoden, Shigeo

2014-12-01

The tropopause inversion layer (TIL) is a persistent layer with high static stability. Although some mechanisms for the formation of the TIL have been proposed, the time evolution of the TIL under realistic conditions especially when factoring in the contribution of small-scale processes such as gravity waves is not well understood. To gain an understanding of this factor, we conducted a numerical experiment on an explosive cyclogenesis in mid-latitudes using a nonhydrostatic regional atmospheric model. Although the TIL in the model is consistent with previous observations in the sense that it is stronger in the negative vorticity areas, the relationship is clear only in the development and mature stages of a cyclone, suggesting that the evolution of the cyclone plays an important role in the formation of the TIL. To ascertain the effects of gravity waves on the TIL, vertical convergence at the tropopause is analyzed. Histograms of maximum buoyancy frequency squared within the TIL show that regions of vertical convergence have higher , in addition to regions with high ∂ 2 w/ ∂ z 2, implying that waves having downward phase propagation also play an important role in the dynamical formation of the TIL. This tendency is clearer in regions of negative relative vorticity at the tropopause. By taking account of the fact that the gravity wave activities associated with the cyclone and the jet streak are enhanced during the development and mature stages of the cyclone, vertical convergence due to gravity waves associated with synoptic weather systems can be seen to be a key process in the formation of the negative correlation between the strength of the TIL and the local relative vorticity at the tropopause.

The gravitational wave stress–energy (pseudo)-tensor in modified gravity

NASA Astrophysics Data System (ADS)

Saffer, Alexander; Yunes, Nicolás; Yagi, Kent

2018-03-01

The recent detections of gravitational waves by the advanced LIGO and Virgo detectors open up new tests of modified gravity theories in the strong-field and dynamical, extreme gravity regime. Such tests rely sensitively on the phase evolution of the gravitational waves, which is controlled by the energy–momentum carried by such waves out of the system. We here study four different methods for finding the gravitational wave stress–energy pseudo-tensor in gravity theories with any combination of scalar, vector, or tensor degrees of freedom. These methods rely on the second variation of the action under short-wavelength averaging, the second perturbation of the field equations in the short-wavelength approximation, the construction of an energy complex leading to a Landau–Lifshitz tensor, and the use of Noether’s theorem in field theories about a flat background. We apply these methods in general relativity, Jordan–Fierz–Brans–Dicky theoy, and Einstein-Æther theory to find the gravitational wave stress–energy pseudo-tensor and calculate the rate at which energy and linear momentum is carried away from the system. The stress–energy tensor and the rate of linear momentum loss in Einstein-Æther theory are presented here for the first time. We find that all methods yield the same rate of energy loss, although the stress–energy pseudo-tensor can be functionally different. We also find that the Noether method yields a stress–energy tensor that is not symmetric or gauge-invariant, and symmetrization via the Belinfante procedure does not fix these problems because this procedure relies on Lorentz invariance, which is spontaneously broken in Einstein-Æther theory. The methods and results found here will be useful for the calculation of predictions in modified gravity theories that can then be contrasted with observations.

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.

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.

Electric Field Effects in Self-Propagating High-Temperature Synthesis under Microgravity Conditions

NASA Technical Reports Server (NTRS)

Unuvar, C.; Frederick, D. M.; Shaw, B. D.; Munir, Z. A.

2003-01-01

Self-propagating high-temperature synthesis (SHS) has been used to form many materials. SHS generally involves mixing reactants together (e.g., metal powders) and igniting the mixture such that a combustion (deflagration) wave passes though the mixture. The imposition of an electric field (AC or DC) across SHS reactants has been shown to have a marked effect on the dynamics of wave propagation and on the nature, composition, and homogeneity of the product . The use of an electric field with SHS has been termed "field-assisted SHS". Combustion wave velocities and temperatures are directly affected by the field, which is typically perpendicular to the average wave velocity. The degree of activation by the field (e.g., combustion rate) is related to the current density distribution within the sample, and is therefore related to the temperature-dependent spatial distribution of the effective electrical conductivity of reactants and products. Furthermore, the field can influence other important SHS-related phenomena including capillary flow, mass-transport in porous media, and Marangoni flows. These phenomena are influenced by gravity in conventional SHS processes (i.e., without electric fields). As a result the influence of the field on SHS under reduced gravity is expected to be different than under normal gravity. It is also known that heat loss rates from samples, which can depend significantly on gravity, can influence final products in SHS. This research program is focused on studying field-assisted SHS under reduced gravity conditions. The broad objective of this research program is to understand the role of an electric field in SHS reactions under conditions where gravity-related effects are suppressed. The research will allow increased understanding of fundamental aspects of field-assisted SHS processes as well as synthesis of materials that cannot be formed in normal gravity.

Gravity Waves in the Martian Atmosphere detected by the Radio Science Experiment MaRS on Mars Express

NASA Astrophysics Data System (ADS)

Tellmann, S.; Pätzold, M.; Häusler, B.; Tyler, G. L.; Hinson, D. P.

2013-09-01

Gravity waves are an ubiquitous feature in all stably stratified planetary atmospheres. They are known to play a significant role in the energy and momentum budget of the Earth, and they are assumed to be of importance for the redistribution of energy and momentum throughout the Martian atmosphere.

Gravity Probe-B Spacecraft attitude control based on the dynamics of slosh wave-induced fluid stress distribution on rotating dewar container of cryogenic propellant

NASA Technical Reports Server (NTRS)

Hung, R. J.; Lee, C. C.; Leslie, F. W.

1991-01-01

The dynamical behavior of fluids, in particular the effect of surface tension on partially-filled rotating fluids, in a full-scale Gravity Probe-B Spacecraft propellant dewar tank imposed by various frequencies of gravity jitters have been investigated. Results show that fluid stress distribution exerted on the outer and inner walls of rotating dewar are closely related to the characteristics of slosh waves excited on the liquid-vapor interface in the rotating dewar tank. This can provide a set of tool for the spacecraft dynamic control leading toward the control of spacecraft unbalance caused by the uneven fluid stress distribution due to slosh wave excitations.

Gravity wave initiated convection

NASA Astrophysics Data System (ADS)

Hung, R. J.

1990-09-01

The vertical velocity of convection initiated by gravity waves was investigated. In one particular case, the convective motion-initiated and supported by the gravity wave-induced activity (excluding contributions made by other mechanisms) reached its maximum value about one hour before the production of the funnel clouds. In another case, both rawinsonde and geosynchronous satellite imagery were used to study the life cycles of severe convective storms. Cloud modelling with input sounding data and rapid-scan imagery from GOES were used to investigate storm cloud formation, development and dissipation in terms of growth and collapse of cloud tops, as well as, the life cycles of the penetration of overshooting turrets above the tropopause. The results based on these two approaches are presented and discussed.

Acoustic-gravity waves in atmospheric and oceanic waveguides.

PubMed

Godin, Oleg A

2012-08-01

A theory of guided propagation of sound in layered, moving fluids is extended to include acoustic-gravity waves (AGWs) in waveguides with piecewise continuous parameters. The orthogonality of AGW normal modes is established in moving and motionless media. A perturbation theory is developed to quantify the relative significance of the gravity and fluid compressibility as well as sensitivity of the normal modes to variations in sound speed, flow velocity, and density profiles and in boundary conditions. Phase and group speeds of the normal modes are found to have certain universal properties which are valid for waveguides with arbitrary stratification. The Lamb wave is shown to be the only AGW normal mode that can propagate without dispersion in a layered medium.

Structure of the Lithosphere and Asthenosphere beneath the Western US from Simultaneous Multi-Parameter Inversion

NASA Astrophysics Data System (ADS)

Steck, L.; Maceira, M.; Herrmann, R. B.; Ammon, C. J.

2012-12-01

Joint inversion of multiple datasets should produce more realistic images of Earth structure. Here we simultaneously invert surface wave dispersion, gravity, and receiver functions to determine structure of the crust and upper mantle of the western United States. To date our receiver function dataset, from the EARS system, spans California and western Nevada, but it will be expanded to include the entire study area as the project continues. Rayleigh and Love dispersion data come from multiple filter analysis of regional earthquakes, while the PACES and GRACE campaigns provide the gravity measurements. Our starting model is comprised of an oceanic PREM model west of the Pacific coast, a western US model between that and the eastern front of the Rocky Mountains, and a continental PREM model east of the Rocky Mountain Front. Our inversion reduces surface wave residuals by 57% and receiver function residuals by about 10%, when the two datasets are weighted equally. Gravity residuals are reduced to less than 3 Mgal. Results are consistent with numerous previous studies in the region. In general, the craton exhibits higher velocities than the tectonically active regions to its west. We see high mid-crustal velocities under the Snake River Plain and the Colorado Plateau. In the lower crust we observe lowest velocities in the western Basin and Range and under the Colorado Mineral Belt. At 80km depth we see broad low velocities fanning out from the Snake River Plain associated with the mantle plume feeding Yellowstone Caldera. Other high and low velocity anomalies along the west coast and to the east are likely related to ongoing subduction processes beneath the western US.

Quantum solitonic wave-packet of a meso-scopic system in singularity free gravity

NASA Astrophysics Data System (ADS)

Buoninfante, Luca; Lambiase, Gaetano; Mazumdar, Anupam

2018-06-01

In this paper we will discuss how to localise a quantum wave-packet due to self-gravitating meso-scopic object by taking into account gravitational self-interaction in the Schrödinger equation beyond General Relativity. In particular, we will study soliton-like solutions in infinite derivative ghost free theories of gravity, which resolves the gravitational 1 / r singularity in the potential. We will show a unique feature that the quantum spread of such a gravitational system is larger than that of the Newtonian gravity, therefore enabling us a window of opportunity to test classical and quantum properties of such theories of gravity in the near future at a table-top experiment.

Waves in the middle and upper atmosphere of Mars as seen by the Radio Science Experiment MaRS on Mars Express

NASA Astrophysics Data System (ADS)

Tellmann, S.; Paetzold, M.; Häusler, B.; Hinson, D. P.; Peter, K.; Tyler, G. L.

2017-12-01

Atmospheric waves play a crucial role in the Martian atmosphere. They are responsible for the redistribution of momentum, energy and dust and for the coupling of the different atmospheric regions on Mars. Almost all kinds of waves have been observed in the lower atmosphere (e.g. stationary and transient waves, baroclinic waves as well as migrating and non-migrating thermal tides, gravity waves, etc...). Atmospheric waves are also known to exist in the middle atmosphere of Mars ( 70-120 km, e.g. by the SPICAM instrument on Mars Express). In the thermosphere, thermal tides have been observed e.g. by radio occultation or accelerometer measurements on MGS. Recently, the NGIMS instrument on MAVEN reported gravity waves in the thermosphere of Mars. Radio Science profiles from the Mars Express Radio Science experiment MaRS on Mars Express can analyse the temperature, pressure and neutral number density profiles in the lower atmosphere (from a few hundred metres above the surface up to 40-50 km) and electron density profiles in the ionosphere of Mars. Wavelike structures have been detected below the main ionospheric layers (M1 & M2) and in the topside of the ionosphere. The two coherent frequencies of the MaRS experiment allow to discriminate between plasma density fluctuations in the ionosphere and Doppler related frequency shifts caused by spacecraft movement. A careful analysis of the observed electron density fluctuations in combination with sensitivity studies of the radio occultation technique will be used to classify the observed fluctuations. The MaRS experiment is funded by DLR under grant 50QM1401.

Waves in the middle and upper atmosphere of Mars as seen by the Radio Science Experiment MaRS on Mars Express

NASA Astrophysics Data System (ADS)

Tellmann, Silvia Anna; Paetzold, Martin; Häusler, Bernd; Hinson, David P.; Peter, Kerstin; Tyler, G. Leonard

2017-10-01

Atmospheric waves play a crucial role for the dynamics in the Martian atmosphere. They are responsible for the redistribution of momentum, energy and dust and the coupling of the different atmospheric regions on Mars.Almost all kinds of waves have been observed in the lower atmosphere (e.g. stationary and transient waves, baroclinic waves as well as migrating and non-migrating thermal tides, and gravity waves). Atmospheric waves are also known to exist in the middle atmosphere of Mars (~70-120 km, e.g. by the SPICAM instrument on Mars Express). In the thermosphere, thermal tides have been observed e.g. by radio occultation or accelerometer measurements on MGS. Recently, the NGIMS instrument on MAVEN reported gravity waves in the thermosphere of Mars.Radio Science profiles from the Mars Express Radio Science experiment MaRS on Mars Express can analyse the temperature, pressure and neutral number density profiles in the lower atmosphere (from a few hundred metres above the surface up to ~ 40-50 km) and electron density profiles in the ionosphere of Mars.Wavelike structures have been detected below the main ionospheric layers (M1 & M2) and in the topside of the ionosphere. The two coherent frequencies of the MaRS experiment allow to discriminate between plasma density fluctuations in the ionosphere and Doppler related frequency shifts caused by spacecraft movement.A careful analysis of the observed electron density fluctuations in combination with sensitivity studies of the radio occultation technique will be used to classify the observed fluctuations.The MaRS experiment is funded by DLR under grant 50QM1401.

Longitudinal Waves Organize and Control Plants and Other Life

NASA Astrophysics Data System (ADS)

Wagner, Orvin E.

2002-04-01

Since the discovery of longitudinal waves in plants (W-waves) in 1988 I have taken data related to influences of these waves. These data include spacings between structures on plants, sap flow data, electrical data from probes traceable to effects produced by these waves, data related to the influences of gravity, data related to these waves traveling between plants and on and on. All of the data suggest that these waves provide a basis for a unified theory for plant growth and development. They likely provide a basis for growth and development for all life. The wave influences are present on the microscopic level in live plants but may not show in the microscopic pieces of material often scrutinized by the usual researcher. It is this author's conclusion that the waves mentioned are important in all life and provide what we call life which has been so difficult to pinpoint in previous work. The waves show in dead material but generally are of a much smaller amplitude than in resonating live material. In the wave theory one might compare something alive to a properly operating laser. See the

Tsunami and acoustic-gravity waves in water of constant depth

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

Hendin, Gali; Stiassnie, Michael

2013-08-15

A study of wave radiation by a rather general bottom displacement, in a compressible ocean of otherwise constant depth, is carried out within the framework of a three-dimensional linear theory. Simple analytic expressions for the flow field, at large distance from the disturbance, are derived. Realistic numerical examples indicate that the Acoustic-Gravity waves, which significantly precede the Tsunami, are expected to leave a measurable signature on bottom-pressure records that should be considered for early detection of Tsunami.

A quantum trampoline for ultra-cold atoms

NASA Astrophysics Data System (ADS)

Robert-de-Saint-Vincent, M.; Brantut, J.-P.; Bordé, Ch. J.; Aspect, A.; Bourdel, T.; Bouyer, P.

2010-01-01

We have observed the interferometric suspension of a free-falling Bose-Einstein condensate periodically submitted to multiple-order diffraction by a vertical 1D standing wave. This scheme permits simultaneously the compensation of gravity and coherent splitting/recombination of the matter waves. It results in high-contrast interference in the number of atoms detected at constant height. For long suspension times, multiple-wave interference is revealed through a sharpening of the fringes. We characterize our atom interferometer and use it to measure the acceleration of gravity.

Effect of small floating disks on the propagation of gravity waves

NASA Astrophysics Data System (ADS)

De Santi, F.; Olla, P.

2017-04-01

A dispersion relation for gravity waves in water covered by disk-like impurities embedded in a viscous matrix is derived. The macroscopic equations are obtained by ensemble-averaging the fluid equations at the disk scale in the asymptotic limit of long waves and low disk surface fraction. Various regimes are identified depending on the disk radii and the thickness and viscosity of the top layer. Semi-quantitative analysis in the close-packing regime suggests dramatic modification of the dynamics, with orders of magnitude increase in wave damping and wave dispersion. A simplified model working in this regime is proposed. Possible applications to wave propagation in an ice-covered ocean are discussed and comparison with field data is provided.

Propagation of inertial-gravity waves on an island shelf

NASA Astrophysics Data System (ADS)

Bondur, V. G.; Sabinin, K. D.; Grebenyuk, Yu. V.

2015-09-01

The propagation of inertial-gravity waves (IGV) at the boundary of the Pacific shelf near the island of Oahu (Hawaii), whose generation was studied in the first part of this work [1], is analyzed. It is shown that a significant role there is played by the plane oblique waves; whose characteristics were identified by the method of estimating 3D wave parameters for the cases when the measurements are available only for two verticals. It is established that along with the descending propagation of energy that is typical of IGVs, wave packets ascend from the bottom to the upper layers, which is caused by the emission of waves from intense jets of discharged waters flowing out of a diffusor located at the bottom.

Mechanical energy transport. [during stellar turbulences

NASA Technical Reports Server (NTRS)

Stein, R. F.; Leibacher, J. W.

1980-01-01

The properties, generation, and dissipation mechanisms of acoustic, gravity and Alfven waves are described, whose restoring forces are pressure, buoyancy, and magnetic tension, respectively. For acoustic waves, generation by turbulent convective motions and by the Eddington Valve thermal overstability is discussed, considering the 'five-minute' oscillation; dissipation is possible either by radiation or shocks. Generation of gravity waves by penetrative convective motions and by shear arising from supergranule motions is reviewed, and dissipation due to wave breaking, interaction with the mean horizontal fluid flow, and very severe radiative damping is considered. Attention is given to Alfven wave generation by convective motions and thermal overstability, and to dissipation by mode coupling, wave decay, current dissipation, and particle collisions producing Joule or viscous heating.

Development and application of gravity-capillary wave fourier analysis for the study of air-sea interaction physics

NASA Astrophysics Data System (ADS)

MacKenzie Laxague, Nathan Jean

Short ocean waves play a crucial role in the physical coupling between the ocean and the atmosphere. This is particularly true for gravity-capillary waves, waves of a scale (O(0.01-0.1) m) such that they are similarly restored to equilibrium by gravitational and interfacial tension (capillary) effects. These waves are inextricably linked to the turbulent boundary layer processes which characterize near-interfacial flows, acting as mediators of the momentum, gas, and heat fluxes which bear greatly on surface material transport, tropical storms, and climatic processes. The observation of these waves and the fluid mechanical phenomena which govern their behavior has long posed challenges to the would-be observer. This is due in no small part to the delicacy of centimeter-scale waves and the sensitivity of their properties to disruption via tactile measurement. With the ever-growing interest in satellite remote sensing, direct observations of short wave characteristics are needed along coastal margins. These zones are characterized by a diversity of physical processes which can affect the short-scale sea surface topography that is directly sensed via radar backscatter. In a related vein, these observations are needed to more fully understand the specific hydrodynamic relationship between young, wind-generated gravity-capillary waves and longer gravity waves. Furthermore, understanding of the full oceanic current profile is hampered by a lack of observations in the near-surface domain (z = O(0.01-0.1) m), where flows can differ greatly from those at depth. Here I present the development of analytical techniques for describing gravity-capillary ocean surface waves in order to better understand their role in the mechanical coupling between the atmosphere and ocean. This is divided amongst a number of research topics, each connecting short ocean surface waves to a physical forcing process via the transfer of momentum. One involves the examination of the sensitivity of short ocean surface waves to atmospheric forcing. Another is the exploration of long wave-short wave interactions and their effects on air-sea interaction vis-a-vis hydrodynamic modulation. The third and final topic is the characterization of the gravity-capillary regime of the wavenumber-frequency spectrum for the purpose of retrieving near-surface, wind-driven current. All of these fit as part of the desire to more fully describe the mechanism by which momentum is transferred across the air-sea interface and to discuss the consequences of this flux in the very near-surface layer of the ocean. Gravity-capillary waves are found to have an outsize share of ocean surface roughness, with short wave spectral peaks showing a connection to turbulent atmospheric stress. Short wave modulation is found to occur strongest at high wavenumbers at the lowest wind speeds, with peak modulation occurring immediately downwind of the long wave crest. Furthermore, short scale roughness enhancement is found to occur upwind of the long wave crest for increasing wind forcing magnitude. Observations of the near-surface current profile show that flows retrieved via this method agree well with the results of camera-tracked dye. Application of this method to data collected in the mouth of the Columbia River (MCR) indicates the presence of a near-surface current component that departs considerably from the tidal flow and orients into the wind stress direction. These observations demonstrate that wind speed-based parameterizations may not be sufficient to estimate wind drift and hold implications for the way in which surface material (e.g., debris or spilled oil) transport is estimated when atmospheric stress is of relatively high magnitude or is steered off the mean wind direction.

Tracing Acoustic-Gravity Waves from the Ocean into the Ionosphere

NASA Astrophysics Data System (ADS)

Zabotin, N. A.; Godin, O. A.; Bullett, T. W.; Negrea, C.

2013-12-01

Ionospheric manifestations of tsunamis provide dramatic evidence of a connection between wave processes in the ocean and in the atmosphere. But tsunamis are only a transient feature of a more general phenomenon, infragravity waves (IGWs). IGWs are permanently present surface gravity waves in the ocean with periods longer than the longest periods (~30 s) of wind-generated waves. IGWs propagate transoceanic distances and, because of their long wavelengths (from ~1 km to hundreds of km), provide a mechanism for coupling wave processes in the ocean, atmosphere, and the solid Earth. The notion that tsunamis may generate waves in the upper atmosphere has existed for a long time but no quantitative coupling theory for the background waves has been proposed. We provide a strict physical justification for the influence of the background IGWs on the upper atmosphere. Taking into account both fluid compressibility and the gravity in a coupled atmosphere-ocean system, we show that there exist two distinct regimes of IGW penetration into the atmosphere. At higher frequencies, one has evanescent waves in the atmosphere propagating horizontally along the ocean surface. At lower frequencies, IGWs continuously radiate their energy into the upper atmosphere in the form of acoustic gravity waves (AGWs). The transition frequency depends on the ocean depth; it varies slowly near 3 mHz for typical depth values and drops to zero sharply only for extremely large depths. Using semi-empirical model of the IGW power spectrum, we derive an estimate of the flux of the mechanical energy and mechanical momentum from the deep ocean into the atmosphere due to background IGWs and predict specific forcing on the atmosphere in coastal regions. We compare spectra of wave processes in the ionosphere measured using Dynasonde technique over Wallops Island, VA and San Juan, PR and interpret the differences in terms of the oceanic effects. We conclude that AGWs of oceanic origin may have an observable impact on the upper atmosphere and describe techniques for experimental verification of this finding.

Waves in the Mesosphere of Venus as seen by the Venus Express Radio Science Experiment VeRa

NASA Astrophysics Data System (ADS)

Tellmann, Silvia; Häusler, B.; Hinson, D. P.; Tyler, G.; Andert, T. P.; Bird, M. K.; Imamura, T.; Pätzold, M.; Remus, S.

2013-10-01

The Venus Express Radio Science Experiment (VeRa) has retrieved more than 700 profiles of the mesosphere and troposphere of Venus. These profiles cover a wide range of latitudes and local times, enabling study of atmospheric wave phenomena over a range spatial scales at altitudes of 40-90 km. In addition to quasi-horizontal waves and eddies on near planetary scales, diurnally forced eddies and thermal tides, small-scale gravity waves, and turbulence play a significant role in the development and maintenance of atmospheric super-rotation. Small-scale temperature variations with vertical wavelengths of 4 km or less have wave amplitudes reaching TBD km in the stable atmosphere above the tropopause, in contrast with much weaker temperature perturbations observed in the middle cloud layer below. The strength of gravity waves increases with latitude in both hemispheres. The results suggest that convection at low latitudes and topographical forcing at high northern latitudes—possibly in combination with convection and/or Kelvin-Helmholtz instabilities—play key roles in the genesis of gravity waves. Further, thermal tides also play an important role in the mesosphere. Diurnal and semi-diurnal wave modes are observed at different latitudes and altitudes. The latitudinal and height dependence of the thermal tide modes will be investigated.

Making Waves in the Sky off of Africa

NASA Image and Video Library

2017-12-08

On June 26, 2016, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this natural-color image of cloud gravity waves off the coast of Angola and Namibia. “I [regularly] look at this area on Worldview because you quite often have these gravity waves,” said Bastiaan Van Diedenhoven, a researcher for Columbia University and NASA's Goddard Institute for Space Studies interested in cloud formations. “On this day, there was so much going on—so many different waves from different directions—that they really started interfering.” A distinctive criss-cross pattern formed in unbroken stretches hundreds of kilometers long. Similar to a boat’s wake, which forms as the water is pushed upward by the boat and pulled downward again by gravity, these clouds are formed by the rise and fall of colliding air columns. Off of west Africa, dry air coming off the Namib desert—after being cooled by the night—moves out under the balmy, moist air over the ocean and bumps it upwards. As the humid air rises to a higher altitude, the moisture condenses into droplets, forming clouds. Gravity rolls these newly formed clouds into a wave-like shape. When moist air goes up, it cools, and then gravity pushes it down again. As it plummets toward the earth, the moist air is pushed up again by the dry air. Repeated again and again, this process creates gravity waves. Clouds occur at the upward wave motions, while they evaporate at the downward motions. Such waves will often propagate in the morning and early afternoon, said Van Diedenhoven. During the course of the day, the clouds move out to sea and stretch out, as the dry air flowing off the land pushes the moist ocean air westward. NASA Earth Observatory image by Jesse Allen, using data from the Land Atmosphere Near real-time Capability for EOS (LANCE). via @NASAEarth go.nasa.gov/29Btxcy NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

NASA capabilities roadmap: advanced telescopes and observatories

NASA Technical Reports Server (NTRS)

Feinberg, Lee D.

2005-01-01

The NASA Advanced Telescopes and Observatories (ATO) Capability Roadmap addresses technologies necessary for NASA to enable future space telescopes and observatories collecting all electromagnetic bands, ranging from x-rays to millimeter waves, and including gravity-waves. It has derived capability priorities from current and developing Space Missions Directorate (SMD) strategic roadmaps and, where appropriate, has ensured their consistency with other NASA Strategic and Capability Roadmaps. Technology topics include optics; wavefront sensing and control and interferometry; distributed and advanced spacecraft systems; cryogenic and thermal control systems; large precision structure for observatories; and the infrastructure essential to future space telescopes and observatories.

Dynamical Meteorology of the Equatorial and Extratropical Stratosphere

NASA Technical Reports Server (NTRS)

Dunkerton, Tomothy

1999-01-01

Observational studies were performed of westward propagating synoptic scale waves in the tropical troposphere, the structure of monsoon circulations in the upper troposphere and lower stratosphere, and zonally propagating features in deep tropical convection. The effect of the quasi-biennial oscillation (QBO) were investigated, and a numerical study of the QBO was performed using a two-dimensional model, highlighting the role of gravity waves in the momentum balance of the QBO. Vertical coupling of the troposphere and stratosphere was examined in polar regions on intraseasonal and interannual timescales. A deep circumpolar mode was discovered, now known as the Arctic Oscillation.

On the generation and evolution of internal gravity waves

NASA Technical Reports Server (NTRS)

Lansing, F. S.; Maxworthy, T.

1984-01-01

The tidal generation and evolution of internal gravity waves is investigated experimentally and theoretically using a two-dimensional two-layer model. Time-dependent flow is created by moving a profile of maximum submerged depth 7.7 cm through a total stroke of 29 cm in water above a freon-kerosene mixture in an 8.6-m-long 30-cm-deep 20-cm-wide transparent channel, and the deformation of the fluid interface is recorded photographically. A theoretical model of the interface as a set of discrete vortices is constructed numerically; the rigid structures are represented by a source distribution; governing equations in Lagrangian form are obtained; and two integrodifferential equations relating baroclinic vorticity generation and source-density generation are derived. The experimental and computed results are shown in photographs and graphs, respectively, and found to be in good agreement at small Froude numbers. The reasons for small discrepancies in the position of the maximum interface displacement at large Froude numbers are examined.

Quantum Cause of Gravity Waves and Dark Matter

NASA Astrophysics Data System (ADS)

Goradia, Shantilal; Goradia Team

2016-09-01

Per Einstein's theory mass tells space how to curve and space tells mass how to move. How do they tell''? The question boils down to information created by quantum particles blinking ON and OFF analogous to `Ying and Yang' or some more complex ways that may include dark matter. If not, what creates curvature of space-time? Consciousness, dark matter, quantum physics, uncertainty principle, constants of nature like strong coupling, fine structure constant, cosmological constant introduced by Einstein, information, gravitation etc. are fundamentally consequences of that ONE TOE. Vedic philosophers, who impressed Schrodinger so much, called it ATMA split in the categories of AnuAtma (particle soul), JivAtma (life soul) and ParamAtma (Omnipresent soul) which we relate to quantum physics, biology and cosmology. There is no separate TOE for any one thing. The long range relativistic propagations of the strong and weak couplings of the microscopic black holes in are just gravity waves. What else could they be?

Hamiltonian formalism for Perturbed Black Hole Spacetimes

NASA Astrophysics Data System (ADS)

Mihaylov, Deyan; Gair, Jonathan

2017-01-01

Present and future gravitational wave observations provide a new mechanism to probe the predictions of general relativity. Observations of extreme mass ratio inspirals with millihertz gravitational wave detectors such as LISA will provide exquisite constraints on the spacetime structure outside astrophysical black holes, enabling tests of the no-hair property that all general relativistic black holes are described by the Kerr metric. Previous work to understand what constraints LISA observations will be able to place has focussed on specific alternative theories of gravity, or generic deviations that preserve geodesic separability. We describe an alternative approach to this problem--a technique that employs canonical perturbations of the Hamiltonian function describing motion in the Kerr metric. We derive this new approach and demonstrate its application to the cases of a slowly rotating Kerr black hole which is viewed as a perturbation of a Schwarzschild black hole, of coupled perturbations of black holes in the second-order Chern-Simons modified gravity theory, and several more indicative scenarios. Deyan Mihaylov is funded by STFC.

The Science of Gravitational Waves with Space Observatories

NASA Technical Reports Server (NTRS)

Thorpe, James Ira

2013-01-01

After decades of effort, direct detection of gravitational waves from astrophysical sources is on the horizon. Aside from teaching us about gravity itself, gravitational waves hold immense promise as a tool for general astrophysics. In this talk I will provide an overview of the science enabled by a space-based gravitational wave observatory sensitive in the milli-Hertz frequency band including the nature and evolution of massive black holes and their host galaxies, the demographics of stellar remnant compact objects in the Milky Way, and the behavior of gravity in the strong-field regime. I will also summarize the current status of efforts in the US and Europe to implement a space-based gravitational wave observatory.

Refraction of coastal ocean waves

NASA Technical Reports Server (NTRS)

Shuchman, R. A.; Kasischke, E. S.

1981-01-01

Refraction of gravity waves in the coastal area off Cape Hatteras, NC as documented by synthetic aperture radar (SAR) imagery from Seasat orbit 974 (collected on September 3, 1978) is discussed. An analysis of optical Fourier transforms (OFTs) from more than 70 geographical positions yields estimates of wavelength and wave direction for each position. In addition, independent estimates of the same two quantities are calculated using two simple theoretical wave-refraction models. The OFT results are then compared with the theoretical results. A statistical analysis shows a significant degree of linear correlation between the data sets. This is considered to indicate that the Seasat SAR produces imagery whose clarity is sufficient to show the refraction of gravity waves in shallow water.

Gravitational waves in ghost free bimetric gravity

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

Mohseni, Morteza, E-mail: m-mohseni@pnu.ac.ir

2012-11-01

We obtain a set of exact gravitational wave solutions for the ghost free bimetric theory of gravity. With a flat reference metric, the theory admits the vacuum Brinkmann plane wave solution for suitable choices of the coefficients of different terms in the interaction potential. An exact gravitational wave solution corresponding to a massive scalar mode is also admitted for arbitrary choice of the coefficients with the reference metric being proportional to the spacetime metric. The proportionality factor and the speed of the wave are calculated in terms of the parameters of the theory. We also show that a F(R) extensionmore » of the theory admits similar solutions but in general is plagued with ghost instabilities.« less

Momentum and energy deposition in late-type stellar atmospheres and winds

NASA Technical Reports Server (NTRS)

Hartmann, L.; Macgregor, K. B.

1980-01-01

The present study calculates the response of the outer atmospheres of cool low-gravity stars to the passage of the mechanical energy fluxes of solar magnitude in the form of acoustic waves and Alfven waves. It is shown that Alfven waves are efficient in generating outflow, and can account for the order of magnitude of observed mass loss in late-type luminous stars. However, unless these magnetic waves undergo some dissipation within several stellar radii of the surface, the predicted terminal velocities of the resulting stellar winds are far too high. Alfven wave dissipation should give rise to extended warm chromospheres in low-gravity late-type stars, a prediction which can be observationally tested.

Integrated geophysical and geological study of the tectonic framework of the 38th parallel lineament in the vicinity of its intersection with the extension of the New Madrid fault zone. Annual progress report, fiscal year 1979

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

Braile, L.W.; Hinze, W.J.; Sexton, J.L.

1979-09-01

An integrated gravity, magnetic, crustal seismic refraction, and basement geology study is being conducted of the northeastern extension of the New Madrid Fault Zone in the vicinity of the 38th Parallel Lineament. Gravity and magnetic anomaly maps prepared of this area plus regional seismicity suggest that the basement structural feature associated with the New Madrid seismicity extends northeasterly into southern Indiana to at least 39/sup 0/N latitude. Gravity and subsurface data indicate that the Rough Creek Fault Zone, a major element of the 38th Parallel Lineament, is the northern boundary of a complex graben which formed in late Precambrian-early Paleozoicmore » time and since has been reactivated. Surface wave studies indicate that the crustal thickness of the northern Mississippi Embayment is probably in the range of 50 to 55 km, and the structure of the crust obtained from these studies is highly suggestive of a failed rift. 40 figures, 3 tables.« less

Stellar occultation spikes as probes of atmospheric structure and composition. [for Jupiter

NASA Technical Reports Server (NTRS)

Elliot, J. L.; Veverka, J.

1976-01-01

The characteristics of spikes observed in occultation light curves of Beta Scorpii by Jupiter are discussed in terms of the gravity-gradient model. The occultation of Beta Sco by Jupiter on May 13, 1971, is reviewed, and the gravity-gradient model is defined as an isothermal atmosphere of constant composition in which the refractivity is a function only of the radial coordinate from the center of refraction, which is assumed to lie parallel to the local gravity gradient. The derivation of the occultation light curve in terms of the atmosphere, the angular diameter of the occulted star, and the occultation geometry is outlined. It is shown that analysis of the light-curve spikes can yield the He/H2 concentration ratio in a well-mixed atmosphere, information on fine-scale atmospheric structure, high-resolution images of the occulted star, and information on ray crossing. Observational limits are placed on the magnitude of horizontal refractivity gradients, and it is concluded that the spikes are the result of local atmospheric density variations: atmospheric layers, density waves, or turbulence.

Wave like signatures in aerosol optical depth and associated radiative impacts over the central Himalayan region

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

Shukla, K. K.; Phanikumar, D. V.; Kumar, K.  Niranjan

2015-10-01

In this study, we present a case study on 16 October 2011 to show the first observational evidence of the influence of short period gravity waves in aerosol transport during daytime over the central Himalayan region. The Doppler lidar data has been utilized to address the daytime boundary layer evolution and related aerosol dynamics over the site. Mixing layer height is estimated by wavelet covariance transform method and found to be ~ 0.7 km, AGL. Aerosol optical depth observations during daytime revealed an asymmetry showing clear enhancement during afternoon hours as compared to forenoon. Interestingly, Fourier and wavelet analysis ofmore » vertical velocity and attenuated backscatter showed similar 50-90 min short period gravity wave signatures during afternoon hours. Moreover, our observations showed that gravity waves are dominant within the boundary layer implying that the daytime boundary layer dynamics is playing a vital role in transporting the aerosols from surface to the top of the boundary layer. Similar modulations are also evident in surface parameters like temperature, relative humidity and wind speed indicating these waves are associated with the dynamical aspects over Himalayan region. Finally, time evolution of range-23 height indicator snapshots during daytime showed strong upward velocities especially during afternoon hours implying that convective processes through short period gravity waves plays a significant role in transporting aerosols from the nearby valley region to boundary layer top over the site. These observations also establish the importance of wave induced daytime convective boundary layer dynamics in the lower Himalayan region.« less

A fast wind-farm boundary-layer model to investigate gravity wave effects and upstream flow deceleration

NASA Astrophysics Data System (ADS)

Allaerts, Dries; Meyers, Johan

2017-11-01

Wind farm design and control often relies on fast analytical wake models to predict turbine wake interactions and associated power losses. Essential input to these models are the inflow velocity and turbulent intensity at hub height, which come from prior measurement campaigns or wind-atlas data. Recent LES studies showed that in some situations large wind farms excite atmospheric gravity waves, which in turn affect the upstream wind conditions. In the current study, we develop a fast boundary-layer model that computes the excitation of gravity waves and the perturbation of the boundary-layer flow in response to an applied force. The core of the model is constituted by height-averaged, linearised Navier-Stokes equations for the inner and outer layer, and the effect of atmospheric gravity waves (excited by the boundary-layer displacement) is included via the pressure gradient. Coupling with analytical wake models allows us to study wind-farm wakes and upstream flow deceleration in various atmospheric conditions. Comparison with wind-farm LES results shows excellent agreement in terms of pressure and boundary-layer displacement levels. The authors acknowledge support from the European Research Council (FP7-Ideas, Grant No. 306471).

Dispersion and transport of hypersaline gravity currents in the presence of internal waves at a pycnocline

NASA Astrophysics Data System (ADS)

Hogg, C. A. R.; Pietrasz, V. B.; Ouellette, N. T.; Koseff, J. R.

2015-12-01

Desalination of seawater offers a source of potable water in arid regions and during drought. However, hypersaline discharge from desalination facilities presents environmental risks, particularly to benthic organisms. The risks posed by salt levels and chemical additives, which can be toxic to local ecosystems, are typically mitigated by ensuring high levels of dilution close to the source. We report on laboratory flume experiments examining how internal waves at the pycnocline of a layered ambient density stratification influence the transport of hypersaline effluent moving as a gravity current down the slope. We found that some of the hypersaline fluid from the gravity current was diverted away from the slope into an intrusion along the pycnocline. A parametric study investigated how varying the energy of the internal wave altered the amount of dense fluid that was diverted into the pycnocline intrusion. The results are compared to an analytical framework that compares the incident energy in the internal wave to potential energy used in diluting the gravity current. These results are significant for desalination effluents because fluid diverted into the intrusion avoids the ecologically sensitive benthic layer and disperses more quickly than if it had continued to propagate along the bed.

Gravity waves generated by a tropical cyclone during the STEP tropical field program - A case study

NASA Technical Reports Server (NTRS)

Pfister, L.; Chan, K. R.; Bui, T. P.; Bowen, S.; Legg, M.; Gary, B.; Kelly, K.; Proffitt, M.; Starr, W.

1993-01-01

Overflights of a tropical cyclone during the Australian winter monsoon field experiment of the Stratosphere-Troposphere Exchange Project (STEP) show the presence of two mesoscale phenomena: a vertically propagating gravity wave with a horizontal wavelength of about 110 km and a feature with a horizontal scale comparable to that of the cyclone's entire cloud shield. The larger feature is fairly steady, though its physical interpretation is ambiguous. The 110-km gravity wave is transient, having maximum amplitude early in the flight and decreasing in amplitude thereafter. Its scale is comparable to that of 100-to 150-km-diameter cells of low satellite brightness temperatures within the overall cyclone cloud shield; these cells have lifetimes of 4.5 to 6 hrs. These cells correspond to regions of enhanced convection, higher cloud altitude, and upwardly displaced potential temperature surfaces. The temporal and spatial distribution of meteorological variables associated with the 110-km gravity wave can be simulated by a slowly moving transient forcing at the anvil top having an amplitude of 400-600 m, a lifetime of 4.5-6 hrs, and a size comparable to the cells of low brightness temperature.

Spacetime Singularities in Quantum Gravity

NASA Astrophysics Data System (ADS)

Minassian, Eric A.

2000-04-01

Recent advances in 2+1 dimensional quantum gravity have provided tools to study the effects of quantization of spacetime on black hole and big bang/big crunch type singularities. I investigate effects of quantization of spacetime on singularities of the 2+1 dimensional BTZ black hole and the 2+1 dimensional torus universe. Hosoya has considered the BTZ black hole, and using a "quantum generalized affine parameter" (QGAP), has shown that, for some specific paths, quantum effects "smear" the singularities. Using gaussian wave functions as generic wave functions, I found that, for both BTZ black hole and the torus universe, there are families of paths that still reach the singularities with a finite QGAP, suggesting that singularities persist in quantum gravity. More realistic calculations, using modular invariant wave functions of Carlip and Nelson for the torus universe, offer further support for this conclusion. Currently work is in progress to study more realistic quantum gravity effects for BTZ black holes and other spacetime models.

Weight optimization of ultra large space structures

NASA Technical Reports Server (NTRS)

Reinert, R. P.

1979-01-01

The paper describes the optimization of a solar power satellite structure for minimum mass and system cost. The solar power satellite is an ultra large low frequency and lightly damped space structure; derivation of its structural design requirements required accommodation of gravity gradient torques which impose primary loads, life up to 100 years in the rigorous geosynchronous orbit radiation environment, and prevention of continuous wave motion in a solar array blanket suspended from a huge, lightly damped structure subject to periodic excitations. The satellite structural design required a parametric study of structural configurations and consideration of the fabrication and assembly techniques, which resulted in a final structure which met all requirements at a structural mass fraction of 10%.

Implications for seismic hazard from new gravity data in Napa and vicinity, California

NASA Astrophysics Data System (ADS)

Morgan, K.; Langenheim, V. E.; Ritzinger, B. T.

2015-12-01

New gravity data refine the basin structure beneath the city of Napa, California and suggest continuity of the West Napa fault to the SE, near the city of Vallejo. Previous regional gravity data defined a basin 2-3 km deep beneath Napa where the 2014 M6.0 South Napa and the 2000 M4.9 Yountville earthquakes caused considerable damage. Higher ground motions were also recorded within the area of the gravity low. About 100 new gravity measurements sharpen gravity gradients along the eastern margin of the gravity low, where there was a concentration of red-tagged buildings from the 2014 earthquake. The new data also confirm the presence of an intrabasinal, arch, defined by slightly higher gravity values (~ 1 mGal) in the center of the basin and marked by the edge of a significant magnetic high (~150 nT). This arch coincides with the highest concentration of red-tagged buildings from the 2014 earthquake. Comparison of the potential-field anomalies with rock types encountered in water wells suggests that the arch is underlain by sediments which thin to the south where they are underlain by thick Sonoma Volcanics.. We speculate that the concentration of damage may be caused by shallowing of the basement or by a thicker sequence of basin sediments in the arch or both. Red-tagged buildings from the Yountville earthquake are near the western edge of the basin defined by significant potential-field gradients of the West Napa fault. A sharp basin boundary or guided waves along the fault may have contributed to concentration of damage in this area. Although the potential-field gradients decrease south of Napa, our new gravity data define a gradient aligned to the SE beneath the town of Vallejo. The gradient resides within Mesozoic basement rocks because it traverses outcrops of Great Valley Sequence. Although these data cannot prove Quaternary slip on this structure, its trend and location may indicate continuation of the West Napa fault to the SE.

Spontaneous generation of bending waves in isolated Milky Way-like discs

NASA Astrophysics Data System (ADS)

Chequers, Matthew H.; Widrow, Lawrence M.

2017-12-01

We study the spontaneous generation and evolution of bending waves in N-body simulations of two isolated Milky Way-like galaxy models. The models differ by their disc-to-halo mass ratios, and hence by their susceptibility to the formation of a bar and spiral structure. Seeded from shot noise in the particle distribution, bending waves rapidly form in both models and persist for many billions of years. Waves at intermediate radii manifest as corrugated structures in vertical position and velocity that are tightly wound, morphologically leading and dominated by the m = 1 azimuthal Fourier component. A spectral analysis of the waves suggests they are a superposition of modes from two continuous branches in the Galactocentric radius-rotational frequency plane. The lower frequency branch is dominant and is responsible for the corrugated, leading and warped structure. Over time, power in this branch migrates outward, lending credence to an inside-out formation scenario for the warp. Our power spectra qualitatively agree with results from linear perturbation theory and a WKB analysis, both of which include self-gravity. Thus, we conclude that the waves in our simulations are self-gravitating and not purely kinematic. These waves are reminiscent of the wave-like pattern recently found in Galactic star counts from the Sloan Digital Sky Survey and smoothly transition to a warp near the disc's edge. Velocity measurements from Gaia data will be instrumental in testing the true wave nature of the corrugations. We also compile a list of 'minimum requirements' needed to observe bending waves in external galaxies.

Rossby-gravity waves in tropical total ozone data

NASA Technical Reports Server (NTRS)

Stanford, J. L.; Ziemke, J. R.

1993-01-01

Evidence for Rossby-gravity waves in tropical data fields produced by the European Center for Medium Range Weather Forecasts (ECMWF) was recently reported. Similar features are observable in fields of total column ozone from the Total Ozone Mapping Spectrometer (TOMS) satellite instrument. The observed features are episodic, have zonal (east-west) wavelengths of 6,000-10,000 km, and oscillate with periods of 5-10 days. In accord with simple linear theory, the modes exhibit westward phase progression and eastward group velocity. The significance of finding Rossby-gravity waves in total ozone fields is that (1) the report of similar features in ECMWF tropical fields is corroborated with an independent data set and (2) the TOMS data set is demonstrated to possess surprising versatility and sensitivity to relatively smaller scale tropical phenomena.