Internal Atmospheric Gravity Waves Research Articles

Quasi-Lagrangian superpressure balloon measurements of gravity-wave momentum fluxes in the polar stratosphere of both hemispheres

[1] Superpressure balloons were flown in 2002 and 2005 in the winter polar vortices of both hemispheres. The balloons can drift for months in the stratosphere acting as quasi-Lagrangian tracers of air-parcel motions. The meteorological datasets acquired are used to retrieve small-scale internal atmospheric gravity wave parameters using wavelet techniques. For the first time, gravity wave momentum fluxes are estimated over wide geographical areas and the results will help constrain gravity wave parameterization schemes used in general circulation climate models. The importance of mountain waves is confirmed, with largest fluxes observed in the lee of Greenland and the Antarctic Peninsula. However, significant momentum fluxes are also observed over the oceans, showing the importance of other wave generation mechanisms.

Wave Flow Simulations Over Arctic Leads

We investigate the flow over Arctic leads using a mesoscale numerical model, typical of both summer and winter, under idealised conditions. We find that Arctic leads may be the source of standing atmospheric internal gravity waves during both seasons. The summertime wave may be compared with the wave generated by a small ridge, though with the phase reversed. The mechanism for exciting the wave is found to be the internal boundary layer developing due to horizontal variations in surface temperature and roughness length. During the more exploratory wintertime simulations, with substantial temperature difference between the lead and the ice surface, we find that secondary circulations and intermittent wave-breaking may occur. The effects of the lead appear far downstream.

The ionospheric effect of atmospheric gravity waves excited prior to strong earthquake

We have computed perturbations in the nighttime mid-latitude F2 region ionosphere that could be produced by internal atmospheric gravity waves generated before strong earthquakes through ionospheric Joule heating due to the seismogenic electric field of short duration. There is a strong anisotropy of the atmospheric gravity wave effect with respect to the imminent earthquake epicentre, the electron density changes being maximum poleward and equatorward of the epicentre and being minimum eastward and westward of it. It should be noted that the duration of the electron density perturbation in the F2 region ionosphere is much longer than the duration of the primary precursor of an earthquake – the enhancement of the vertical electric field at the Earth’s surface, which initiates the atmospheric gravity wave generation. This fact is important from the practical point of view of predicting catastrophic earthquakes.

Recent Advances in Bolide Entry Modeling: A Bolide Potpourri

In this paper, we will review recent research on numerous aspects of bolide entry into a planetary atmosphere, including such topics as the entry dynamics, energetics, ablation, deceleration, fragmentation, luminosity, mechanical wave generation processes, a total (panchromatic) power budget including differential and integral efficiencies versus time, etc. Fragmentation, triggered by stagnation pressures exceeding the bolide breaking strength, has been subsequently included in either a collective or non-collective wake behavior limit. We have also utilized the differential panchromatic luminous efficiency of ReVelle and Ceplecha (2002) to compute bolide luminosity. In addition we also introduce the concept of the differential and integral acoustic/infrasonic efficiency and generalized it to the case of mechanical wave efficiency including internal atmospheric gravity waves generated during entry. Unlike the other efficiencies which are assumed to be a constant multiple of the luminous efficiency, the acoustic efficiency is calculated independently using a “first principles” approach. All of these topics have been pursued using either a homogeneous or a porous meteoroid model with great success. As a direct result, porosity seems to be a rather good possibility for explaining anomalous meteoroid behavior in the atmosphere.

Solitary Wave in Linear ODE with Variable Coefficients**The project supported by National Natural Science Foundation of China (Nos. 40045016, 40175016 and 40035010)

In this paper, the linear ordinary differential equations with variable coefficients are obtained from the controlling equations satisfied by wavelet transform or atmospheric internal gravity waves, and these linear equations can be further transformed into Weber equations. From Weber equations, the homoclinic orbit solutions can be derived, so the solitary wave solutions to linear equations with variable coefficients are obtained.

Theory of the Eulerian tail in the spectra of atmospheric and oceanic internal gravity waves

Observed atmospheric and oceanic internal wave spectra, when analysed in an Eulerian frame of reference, exhibit a large-wavenumber ‘tail’. In one-dimensional vertical-wavenumber (k3) spectra, it is typically proportional to |k3|−3.In 1989, K. R. Allen and R. I. Joseph showed that a large-wavenumber tail was to be anticipated as a consequence of Eulerian nonlinearity, and they derived relations for the coefficients of both horizontal and vertical spectra of the form |k|−3. The coefficients were obtained only for the wave-induced vertical-displacement spectra, and only for an input spectrum having a certain ‘canonical’ frequency variation derived on other grounds.The present work builds on that of Allen & Joseph. It is more general in some respects, more limited in others. It provides a more transparent form of analysis, it treats a broad class of wave variables, and it does so for input (Lagrangian) spectra that can be chosen by the user, free from any constraint to canonical or other restricted forms. It provides relations whereby the full Eulerian spectrum may be determined numerically, once the input spectrum has been chosen, and it provides analytic forms applicable at large wavenumbers for horizontally isotropic spectra. The derived one-dimensional vertical-wavenumber spectra are discussed in relation to observations.Certain shortcomings in the development, both as given by Allen & Joseph and as found here, are identified and discussed.

A Possible Mechanism of Superrotation of the Atmosphere of Venus

A hypothesis is proposed for the mechanism of superrotation of the atmosphere of Venus involving the following processes. Winds near the planet's surface, making up part of the Hadley cell, flow past the surface relief and excite internal atmospheric gravity waves. While moving upward, these waves become unstable and collapse generating turbulent eddies. Some portion of the energy of these eddies is transferred to a two-dimensional flow, which is maintained also at the expense of instability of large-scale motions. In this flow, the inverse energy cascade (transition from smaller eddies to larger eddies), or negative viscosity, appears as a key element of this mechanism. Large-scale quasi-two-dimensional turbulent eddies transfer their energy to Rossby planetary waves which, in turn, transmit it to a zonal flow. Based on this hypothesis and the existing experimental data, the time period over which superrotation is established, as well as the vertical and horizontal eddy viscosity coefficients, is estimated. In parallel, arguments in favor of the proposed hypothesis are obtained.

Thermospheric meridional winds in the vicinity of the auroral zone: observations and modelling

Optical Fabry-Perot interferometer measurements of the Doppler shift of the 557.7 nm OI emission were used to obtain the meridional thermospheric wind velocities at heights of the E-layer in the pre-midnight sector of the ionosphere at Loparskaya (68 °N, 33 °E geographic). They distinctly reveal a decrease in the mean meridional wind velocity when passing across the auroral zone from the pole to the equator, and also the near-counterphase character of the wind velocity fluctuations on both sides of the precipitation zone. The observed behaviour of the meridional wind has been reproduced in the modelling calculations using the global ionosphere-thermosphere model and interpreted in terms of the ion-neutral coupling due to the momentum interchange and generation of atmospheric internal gravity waves.

The total ozone content and orography

Systematical differences of the Total Ozone Content over high mountains (The Pamirs, Andes) and westward located plains are revealed. The changes in the total ozone over mountains are preliminary interpreted in terms of the upward propagation of atmospheric internal gravity waves generated when the horizontal wind iniciates upward motions when it meets an obstacle — the mountain ridge.

Earth's atmosphere in dynamic coupling envisaged through atmospheric tides and atmospheric gravity waves: A view on the past‐present‐future research

In 1982–1985 an international scientific endeavor was attempted as the Middle Atmosphere Program, contributing successfully to exploring the last unknown part of the atmosphere on the planet Earth, the middle atmosphere. Now it seems timely for us to consider the whole atmosphere, which extends from the ground to the upper atmosphere and further into space as an entity. Each part of the atmosphere couples not only horizontally (globally) but also vertically. While the horizontal coupling is mainly important for conventional meteorology, the vertical one is significant, say, for space physics and, probably, future meteorology and will be the present topic. Atmospheric waves play an important role for the dynamic coupling of the atmosphere, transporting energy, momentum, and material mainly from below and releasing on the way in their propagation upward. Already in the last century, the existence of the tidal dynamo for the geomagnetic Sq variation in the upper atmosphere was known as a manifestation of the dynamic coupling by atmospheric tides. Atmospheric internal gravity waves are now found to play an important role, among many others, in the general circulation of the middle atmosphere which is another manifestation of the dynamic coupling of the atmosphere. Reviewing remarkable progress in the last 40 years in the research of this subject, the author has suggested that frontiers of the future research would be to develop a GCM (General Circulation Model) to include the upper atmosphere and to establish an equatorial atmosphere observation system.

Rocket vapor trail releases revisited: Turbulence and the scale of gravity waves: Implications for the imaging Doppler interferometry/incoherent scatter radar controversy

The rate of diffusion of a trimethyl aluminum trail released by a Skylark rocket over Woomera, Australia (31°S, 137°E), in 1969 is interpreted in terms of molecular and turbulent diffusion, and is related to the scale of internal atmospheric gravity wave winds. Implications for disagreement between imaging Doppler interferometry and incoherent scatter radar winds are explored.

Global variations of thermospheric winds and temperatures caused by substorm energy injection

Two numerical simulations of the thermospheric response to magnetospheric energy injection have been performed using a zonally averaged, time‐dependent model of neutral composition, dynamics, and energy budget. The simulations are distinguished by the duration of the source. The first simulation has an energy injection of 1 hour, representative of substorm type forcing, and the second one has a 12‐hour energy injection, representative of main storm type forcing. They were performed under the condition of equinox at solar minimum. In the first simulation, large‐scale atmospheric gravity waves (AGWs), generated by the substorm energy via Joule heating of ionospheric currents, are clearly identified in the wind‐field in a meridional plane as well as in the temporal and spacial variations of the total energy density of air above about 130 km height. These waves reach the equator after about 3 hours and propagate into the opposite hemisphere. The horizontal propagation speed is close to the speed of sound (for example, roughly 440 m/s at about 150 km altitude and 670 m/s at about 260 km altitude). Snapshots of the wind system affected by the substorm energy injection show a “four‐cell” pattern between the poles. Above 260 km, the cells have the opposite rotational direction to those below. These small‐scale features in the wind system are indicative of the internal atmospheric gravity waves with the vertical phase propagation. From a term analysis of the energy conservation equation, it is identified that the dominant energy process associated with the propagation of AGWs is adiabatic compressional heating and/or expansive cooling process. It can be concluded that the energy oscillations at middle and low latitude are mainly produced by AGWs propagating from high latitude during the substorm. The second simulation indicated that horizontal and vertical advections, vertical heat conduction, and infrared radiative cooling by nitric oxide are important in addition to adiabatic compressional heating and/or expansive cooling. It is suggested that short‐duration energy injection preferentially generates AGWs which dominate the energy oscillations at low latitudes through adiabatic heating and cooling. Long‐duration energy injection is more effective in generating a meridional circulation which transfers energy by both advective and adiabatic processes.

A study of meteor radar winds from two locations in the British Isles

Winds and tides have been measured by a two-station meteor radar system which has increased spatial resolution compared with single station radars used in the past. Narrow radar beams, pointing SW from Sheffield (53.5°N, 1.6°W) and 30°N of W from Shrivenham (51.5°N, 1.6°W), are arranged to converge over the U.K. MST radar site near Aberystwyth, thus defining a unique atmospheric volume in which meteor wind components are simultaneously measured from the two radar sites. The resultant ‘true’, or local, wind vector is compared with the spatially averaged vector obtained with the aid of beams pointing SW and NW from Sheffield only. It is found that the ‘true’ and averaged tidal winds are in good agreement, as expected from their large scale sizes, and that the main advantages of the dual station technique lie in the resolution of a small scale structure such as that related to internal atmospheric gravity waves. By the simultaneous deployment of two-station meteor radar, MST radar and LIDAR, such waves may now be studied through a large vertical section of the atmosphere in a geographically localized area.

Radial energy transport by magnetospheric ULF waves: Effects of magnetic curvature and plasma pressure

The “radial” transport of energy by internal ULF waves, stimulated by dayside magnetospheric boundary oscillations, is analyzed in the framework of one‐fluid magnetohydrodynamics. (The term radial is used here to denote the direction orthogonal to geomagnetic flux surfaces.) The model for the inhomogeneous magnetospheric plasma and background magnetic field is axisymmetric and includes radial and parallel variations in the magnetic field, magnetic curvature, plasma density, and low but finite plasma pressure. The radial mode structure of the coupled fast and intermediate MHD waves is determined by numerical solution of the inhomogeneous wave equation; the parallel mode structure is characterized by a WKB approximation. Ionospheric dissipation is modeled by allowing the parallel wave number to be complex. For boundary oscillations with frequencies in the range from 10 to 48 mHz, and using a dipole model for the background magnetic field, the combined effects of magnetic curvature and finite plasma pressure are shown to (1) enhance the amplitude of field line resonances by as much as a factor of 2 relative to values obtained in a cold plasma or box‐model approximation for the dayside magnetosphere; (2) increase the energy flux delivered to a given resonance by a factor of 2–4; and (3) broaden the spectral width of the resonance by a factor of 2–3. The effects are attributed to the existence of an “Alfvén buoyancy oscillation,” which approaches the usual shear mode Alfvén wave at resonance, but unlike the shear Alfvén mode, it is dispersive at short perpendicular wavelengths. The form of dispersion is analogous to that of an internal atmospheric gravity wave, with the magnetic tension of the curved background field providing the restoring force and allowing radial propagation of the mode. For nominal dayside parameters, the propagation band of the Alfvén buoyancy wave occurs between the location of its (field line) resonance and that of the fast mode cutoff that exists at larger radial distances.

Post-sunset F-region vertical velocity variations at magnetic equator

The vertical drift velocity of the F-region in the post-sunset period at the magnetic equatorial station Trivandrum has been studied using a HF phase path sounder. The study revealed the presence of quasi-periodic fluctuations with periods in the range 4 30 min superposed on a steady vertical motion as a regular feature of the equatorial F-region in the post-sunset period. The fluctuations in the vertical velocity arc attributed to the east west electric field fluctuations generated by internal atmospheric gravity waves. The vertical velocity fluctuations can provide the necessary seed perturbations for the growth of equatorial spread- F irregularities.

Internal atmospheric gravity waves near the coast of Antarctica

Two gravity wave events as observed at Georg von Neumayer Station in Antarctica are described and analyzed. Wind and temperature are recorded at a meteorological tower. Surface pressure time series are available from four sites so that rather exact evaluations of phase speed and wavelength are possible. Radiosonde ascents provide information on the structure of the atmosphere above the boundary layer.

Airborne synthetic aperture radar imagery of atmospheric gravity waves

We analyze the oceanic “imprints” of atmospheric internal gravity waves detected in airborne synthetic aperture radar (SAR) images collected off the west coast of Vancouver Island, British Columbia, in June 1990. A sequence of SAR images taken over a period of 2.5 hours reveals that the waves traveled with group velocities of 3–6 m s−1 toward the northwest, counter to the 10 m s−1 surface winds. Wave crests were oriented normal to the coast and had lateral extents of several tens of kilometers. Observed wavelengths ranged from 1.2 to 2.3 km, while calculated wave periods ranged from 3 to 8 min. A comparison of the observed wave properties with values derived from a simple three‐layer density model of the troposphere suggest that the waves were low‐mode oscillations trapped within a 0.75‐km‐thick temperature inversion overlying a 1‐km‐thick weakly stratified marine boundary layer. Wave propagation was counter to the wind shear within the inversion layer. Generation of the internal wave groups appears to have occurred near the southern boundary of the stable marine air mass, where it bordered a convectively active air mass that was intruding northward along the coast.

A microbarograph for internal gravity wave studies in Antarctica

Measurement of pressure fluctuations provides the best means of detecting atmospheric internal gravity waves at the Earth's surface. We have developed an instrument which is sufficiently sensitive to detect the small pressure fluctuations associated with such waves yet robust enough for deployment in an Antarctic environment. The instrument incorporates several novel features, both in its design and in the method of deployment used. A prototype instrument has been successfully deployed at the British Antarctic Survey's Halley Station during 1989. The design of an experiment using an array of six improved instruments is briefly described.

Stokes Diffusion by Atmospheric Internal Gravity Waves

Abstract Owing to the stochastic action of Stokes drift induced by a spectrum of noninteracting gravity waves, a parcel of air subject to a spectrum of randomly superposed waves will be displaced, on average, an increasing distance from an initial position as time goes on. The effect of this drift on an ensemble of parcels is to induce a diffusive-like growth in time of the mean-square separation between parcels. We refer to this process as Stokes diffusion. We have calculated trajectories for an ensemble of parcels moving under the influence of a spectrum of gravity waves and have found vertical diffusion coefficients inferred from the dispersion of parcels on the order of 102 m s−2, which is comparable to the values usually attributed to turbulence. If a constituent is distributed as a function of potential temperature, the dispersion due to conservative waves is not apt to accomplish a significant vertical transport. However, if the constituent has a significant gradient on wave-perturbed potential tem...

MORTI: A mesopause oxygen rotational temperature imager

A new instrument for the measurement of integrated rotational temperature and emission rate of the O 2 Atmospheric (0–1) nightglow layer at 95 km and for the characterization of internal atmospheric gravity waves passing through this layer has been built and successfully tested. It bears the acronym MORTI for mesopause oxygen rotational temperature imager. MORTI is a spatial spectral scanning Fabry-Perot spectrometer in which the etalon is a narrow band interference filter and the detector is a CCD camera. This design makes for a compact, stable, high-resolution, ground-based instrument of large throughput, currently capable of measuring emission rate fluctuations of ± 2% and integrated temperature fluctuations of ± 2 K. Appending a conical mirror at the top provides an annular field of view 108 km across at 95 km altitude, and imposing a field stop at the vertex of this cone ensures the orthogonal separation of the image into a radial, spectral dimension and an azimuthal, spatial dimension. This separation makes possible the horizontal tracking of perturbations of the layer in both temperature and emission rate as functions of time, from which the horizontal wave velocity and the wave period may be found. As an example, the temperature and emission rate fluctuations of the O 2 Atmospheric (0–1) band over Puerto Rico on April 5/6, 1989, measured during the AIDA '89 campaign, are shown to imply a wave of 126 min period and 712 km horizontal wavelength.