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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Topside observation of gravity waves

The AEPI (Atmospheric Emissions Photometric Imager) experiment on the ATLAS-1 shuttle mission (launched March 24, 1992) imaged the earth night airglow emission in O2 Atmospheric (0,0) bands, at 762.0 nm. Earthward views of O2 A bands show structure from gravity waves which exhibit extended horizontal structure with horizontal wavelenghts on the order of 50-100 km. These observations of the O2 A (0,0) bands are particularly interesting since in this wavelength the lower atmosphere absorbs all the earth-reflected emissions and most of the spectrally diffuse backgrounds. Herein we present observations of gravity waves using a topside airglow imaging technique.

Mende, S. B.↗
NASA NTRS1989

Gravity wave climatology at midlatitude from Rayleigh lidar data

Atmospheric sounding of the middle atmosphere by Rayleigh scattering has been performed in France for several years, from two stations with different orographic situations: one in the Alps, the Observatoire de Haute Provence, one on the Atlantic coast at Biscarosse. The vertical profiles of density and temperature are obtained with a temporal and spatial resolution of, respectively, 15 mn and 300 m between 30 and 80 km. A statistical study of the atmospheric fluctuations due to gravity waves was performed and the main results are presented: climatology of the gravity wave activity, distribution of energy versus vertical wave number and altitude, and comparison of the observations at the two sites. Conclusions are presented on the saturation of the wave field, the filtering by the mean wind, the transfer of energy and momentum into the atmosphere.

Wilson, R.↗
NASA NTRS1986

Climatology of gravity waves over Poker Flat, Alaska for 1983

An analysis of short-period wind fluctuations over Poker Flat, Alaska, obtained using the Poker Flat mesosphere-stratosphere-troposphere radar is presented. Results are shown for the troposphere and lower stratosphere as well as for the upper mesosphere and lower thermosphere. Contours depict various levels of wind variance (m2s-2). These results pertain only to wind fluctuation periods lying between one and six hours. These particular fluctuations are generally considered to arise primarily from atmospheric gravity waves. Insofar as this is true, the figure thus describes a general climatology of gravity waves at high latitudes.

Balsley, B. B.↗
NASA NTRS1983

Short-period atmospheric gravity waves - A study of their statistical properties and source mechanisms

Gravity waves for the one year period beginning 19 October 1976 around Palisades, New York, are investigated to determine their statistical properties and sources. The waves have typical periods of 10 min, pressure amplitudes of 3 Pa and velocities of 30 m/s. In general, the largest, amplitude waves occur during late fall and early winter when the upper tropospheric winds directly overhead are fastest and the static stability of the lower troposphere is greatest. Mean wave amplitudes correlate highly with the product of the mean maximum wind speed and the mean low level stratification directly aloft. A distinct diurnal variation of wave amplitudes with the largest waves occurring in the pre-dawn hours is also observed as a result of the increased static stability then. The majority of waves are generated by shear instability; however, a number of waves are generated by distant sources such as nuclear detonations or large thunderstorms. The waves with distant sources can be distinguished on the basis of their generally much higher coherency across the grid and velocities that depart markedly from the wind velocity at any point in the sounding.

Gedzelman, S. D.↗
NASA NTRS1985

Modulational development of nonlinear gravity-wave groups

Observations of the development of nonlinear surface gravity-wave groups are presented, and the amplitude and phase modulations are calculated using Hilbert-transform techniques. With increasing propagation distance and wave steepness, the phase modulation develops local phase reversals whose locations correspond to amplitude minima or nodes. The concomitant frequency modulation develops jumps or discontinuities. The observations are compared with recent similar results for wavetrains. The observations are modelled numerically using the cubic nonlinear Schroedinger equation. The motivation is twofold: to examine quantitatively the evolution of phase as well as amplitude modulation, and to test the inviscid predictions for the asymptotic behavior of groups versus long-time observations. Although dissipation rules out the recurrence, there is a long-time coherence of the groups. The phase modulation is found to distinguish between dispersive and soliton behavior.

Chereskin, T. K.↗
NASA NTRS1986

Horizontal wind perturbations and their relation to transient internal gravity waves

Horizontal winds as measured with the Saskatoon MF radar exhibit wind fluctuations which have preferred directions toward north or south in the period range 0 to 60 min at heights between about 60 and 110 km. Longer period perturbations (approx 1-6 h) tend to have an additional maximum of direction frequencies in the E-W sector.The polarization effect analyzed for more than 6 years shows regular changes with season. The main features of the seasonal variations of the direction distributions can be explained by directional filtering of vertically propagating nonstationary gravity waves and appropriate changes of the wave source strength and position in the troposphere. The N-S polarization of the gravity-wave field appears to result in meridional wind reversals with height above the mesopause.

Ebel, A.↗
NASA NTRS2002

Rayleigh-Taylor Gravity Waves and Quasiperiodic Oscillation Phenomenon in X-ray Binaries

Accretion onto compact objects in X-ray binaries (black hole, neutron star (NS), white dwarf) is characterized by non-uniform flow density profiles. Such an effect of heterogeneity in presence of gravitational forces and pressure gradients exhibits Rayleigh-Taylor gravity waves (RTGW). They should be seen as quasiperiodic wave oscillations (QPO) of the accretion flow in the transition (boundary) layer between the Keplerian disk and the central object. In this paper the author shows that the main QPO frequency, which is very close to the Keplerian frequency, is split into separate frequencies (hybrid and low branch) under the influence of the gravitational forces in the rotational frame of reference. The RTGWs must be present and the related QPOs should be detected in any system where the gravity, buoyancy and Coriolis force effects cannot be excluded (even in the Earth and solar environments). The observed low and high QPO frequencies are an intrinsic signature of the RTGW. The author elaborates the conditions for the density profile when the RTGW oscillations are stable. A comparison of the inferred QPO frequencies with QPO observations is presented. The author finds that hectohertz frequencies detected from NS binaries can be identified as the RTGW low branch frequencies. The author also predicts that an observer can see the double NS spin frequency during the NS long (super) burst events when the pressure gradients and buoyant forces are suppressed. The Coriolis force is the only force which acts in the rotational frame of reference and its presence causes perfect coherent pulsations with a frequency twice of the NS spin. The QPO observations of neutron binaries have established that the high QPO frequencies do not go beyond of the certain upper limit. The author explains this observational effect as a result of the density profile inversions. Also the author demonstrates that a particular problem of the gravity waves in the rotational frame of reference in the approximation of very small pressure gradients is reduced to the problem of the classical oscillator in the rotational frame of reference which was previously introduced and applied for the interpretation of kHZ QPO observation by Osherovich & Titarchuk.

Titarchuk, Lev↗
NASA NTRS1989

The separated polar winter stratopause - A gravity wave driven climatological feature

An examination of satellite-derived temperatures reveals that the winter polar stratopause is usually elevated and warmer than the adjacent midlatitude stratopause. This separated stratopause occurs in both hemispheres, but is more pronounced and persistent in the southern winter. It descends with time towards spring and exhibits week-to-week variability. Observational diagnostics and results from a two-dimensional model suggest that gravity-wave driving can account for this separated polar stratopause by driving a meridional circulation, with downwelling over the winter pole. In the model, the solar heating pattern induces stronger winter westerlies than summer easterlies, which leads to a stronger gravity-wave-driven circulation in the winter hemisphere. Spherical geometry and the high latitude location of the winter westerly jet combine to yield a concentrated region of downwelling. Model results suggest that descent of the temperature maximum with time is probably caused by wave/mean-flow interaction.

Hitchman, Matthew H.↗
DOE OSTI2023

Lightning Rings and Gravity Waves: Insights Into the Giant Eruption Plume From Tonga's Hunga Volcano on 15 January 2022

Abstract On 15 January 2022, Hunga Volcano in Tonga produced the most violent eruption in the modern satellite era, sending a water‐rich plume at least 58 km high. Using a combination of satellite‐ and ground‐based sensors, we investigate the astonishing rate of volcanic lightning (>2,600 flashes min −1 ) and what it reveals about the dynamics of the submarine eruption. In map view, lightning locations form radially expanding rings. We show that the initial lightning ring is co‐located with an internal gravity wave traveling >80 m s −1 in the stratospheric umbrella cloud. Buoyant oscillations of the plume's overshooting top generated the gravity waves, which enhanced turbulent particle interactions and triggered high‐current electrical discharges at unusually high altitudes. Our analysis attributes the intense lightning activity to an exceptional mass eruption rate (>5 × 10 9 kg s −1 ), rapidly expanding umbrella cloud, and entrainment of abundant seawater vaporized from magma‐water interaction at the submarine vent.

58 GEOSCIENCES↗
NASA NTRS1983

Internal gravity waves in Titan's atmosphere observed by Voyager radio occultation

The radio scintillations caused by scattering from small-scale irregularities in Titan's neutral atmosphere during a radio occultation of Voyager 1 by Titan are investigated. Intensity and frequency fluctuations occurred on time scales from about 0.1 to 1.0 sec at 3.6 and 13 cm wavelengths whenever the radio path passed within 90 km of the surface, indicating the presence of variations in refractivity on length scales from a few hundred meters to a few kilometers. Above 25 km, the altitude profile of intensity scintillations closely agrees with the predictions of a simple theory based on the characteristics of internal gravity waves propagating with little or no attenuation through the vertical stratification in Titan's atmosphere. These observations support a hypothesis of stratospheric gravity waves, possibly driven by a cloud-free convective region in the lowest few kilometers of the stratosphere.

Hinson, D. P.↗
NASA NTRS2022

Conjugate Effect of the 2011 Tohoku Reflected Tsunami-Driven Gravity Waves in the Ionosphere

This study presents the conjugate ionospheric disturbances triggered by the 2011 Tohoku-Oki reflected tsunami oceanic waves using the ground-based Global Navigation Satellite System (GNSS) total electron content (TEC) observations. We found that the equatorward and westward propagating nighttime medium-scale traveling ionospheric disturbances (MSTIDs) occurred over Japan and Australia simultaneously following the tsunami oceanic waves reflected by the Emperor Seamount Chain in the northern hemisphere. The atmospheric gravity waves driven by reflected tsunami oceanic waves are hypothesized to be the source to trigger the conjugate MSTIDs by transporting the polarization electric fields along the field line to the conjugate hemisphere. Moreover, only the southwestward propagating MSTIDs have this conjugate effect, which could be due to the wavefront orientation. The Perkins instability could also be involved in the interhemispheric coupling process. This study provides the first observational evidence that the reflected tsunami can induce conjugate ionospheric disturbances through electrodynamic forcing.

tsunami, gravity waves, GPS TEC↗