gravity wave and orographic wave activity observed around the antarctic and arctic stratospheric vortices by the cosmic gps ro satellite constellation 1 polar stratospheric gravity wave activity is studied using data from the constellation observing system for meteorology ionosphere and climate cosmic global positioning system radio occultation gps ro waves with vertical wavelengths of 2 to 15 km are considered the temperature variance 2 is used as a measure of wave activity and is studied on isentropic surfaces large intermittent orographic wave activity is identified during austral spring 2007 above the patagonian andes and the antarctic peninsula where 2 in the stratosphere increases by up to a factor of 5 for periods of 5 days to a few weeks the 2 are also investigated in equivalent latitudes to allow a direct comparison with the changing vortex structure the october 2007 2 inside the antarctic vortex boundary region at 400 600 k is one and a half times that outside the vortex this region of enhanced 2 descends in time and is not observed during the decay of the arctic vortex during the boreal winter of 2006 2007 orographic wave activity is observed above scandinavia and greenland an analysis of the 400 k and the 450 k levels in both hemispheres shows a strong relationship between enhanced 2 and the location of the vortex edge suggesting that the waves observed are propagating poleward and are guided to higher altitudes by the vortex the line of sight of the occultations shows a preference for north south alignment indicating that cosmic favors the detection of orographic waves above the north south oriented mountain ranges considered here

archaean gold mineralisation in a normal motion shear zone at harbour lights leonora western australia although many archaean greenstone hosted mesothermal gold deposits are in steep reverse motion fault zones other fault geometries are prospective for mineralization harbour lights is one of a number of deposits at leonora hosted in a normal motion shear zone probably related to movement off the adjacent domal granitoid the deposit is also atypical in that mineralization predates the last deformation to affect the mine sequence but formed by similar processes to other mesothermal deposits in all respects other than the detail of shear zone geometry kinematics and timing

the effect of orographic gravity waves on antarctic polar stratospheric cloud occurrence and composition 1 a seasonal analysis of the relationship between mesoscale orographic gravity wave activity and polar stratospheric cloud psc composition occurrence around the whole of antarctica is presented gravity wave variances are derived from temperature measurements made with the constellation observing system for meteorology ionosphere and climate cosmic global positioning system radio occultation gps ro satellites data from the cloud aerosol lidar with orthogonal polarization caliop instrument onboard the cloud aerosol lidar and infrared pathfinder satellite observations calipso satellite are used to determine the psc composition class distribution and spatial volume the results show intermittent large wave activity above the antarctic peninsula which is coincident with large volumes of h2o ice pscs these ice psc volumes advect downstream where increases in nitric acid trihydrate nat psc volumes occur supporting the mountain wave seeding hypothesis during winter 2007 in the latitude range 60 s 70 s near the edge of the vortex and where temperatures are close to psc formation thresholds 30 of all pscs are attributable to orographic gravity waves in the separate composition classes around 50 of both h2o ice pscs and a high nat number density liquid nat mixture class of pscs are due to these waves while we show that planetary waves are the major determinant of psc presence at temperatures close to the nat formation threshold we also demonstrate the important role of mesoscale intermittent orographic gravity wave activity in accounting for the composition and distribution of pscs around antarctica

a statistical study of gravity waves in the polar regions based on operational radiosonde data gravity waves in the lower polar stratosphere are examined using operational radiosonde observations gathered from 33 stations over a period of 10 years both the potential and kinetic energies of the gravity waves vary annually and reach maxima in winter in the arctic and in spring in the antarctic in the antarctic spring a region of large gravity wave energy propagates downward following the movement of a zone of high static stability associated with southern hemispheric warming moreover the enhanced energy region and the high stability zone coincide in the horizontal plane and move gradually from 135 e 50 s to 45 w 70 s over the south pole the vertical and horizontal directions of wave propagation are examined using hodograph analysis in the vertical most gravity waves transfer energy upward in the arctic while the percentage of downward energy propagation is relatively high in winter and spring in the antarctic horizontally gravity waves propagate westward relative to the mean wind in the arctic while in the antarctic the dominant direction varies from station to station the correlation between gravity wave energy in the lower stratosphere and the mean wind is also examined in the arctic gravity wave energy is highly correlated with the surface wind though in the antarctic it correlates with the stratospheric wind these results suggest that gravity waves observed in the arctic are forced by topography whereas in antarctica some sources may exist in the stratosphere one such source candidate is likely to be the polar night jet

gravity wave generation around the polar vortex in the stratosphere revealed by 3 hourly radiosonde observations at syowa station intensive radiosonde observations were performed at syowa station 69 0 s 39 6 e over about 10 days in each of march june october and december 2002 to examine inertia gravity wave characteristics in the antarctic lower stratosphere based on the 3 hourly observation data two dimensional i e vertical wavenumber versus frequency spectra of wind fluctuations were examined utilizing a double fourier transform method clear signals of gravity waves whose phases propagate upward suggesting downward energy propagation are detected in june and october when the polar night jet pnj was present on the other hand downward phase propagation i e upward energy propagation components are dominant in all months there is a spectral peak around the inertial frequency in a wide range of vertical wavenumbers in december when the background wind was weak whereas large spectral densities are distributed over lower frequency regions in june and october these spectral characteristics are consistent with the results obtained using a gravity wave resolving global circulation model gcm by sato et al dynamical characteristics are examined separately for upward and downward propagating gravity waves in june using a hodograph analysis method as a result it is found that upward and downward propagating wave packets observed simultaneously in the same height regions have similar horizontal wavelengths and phase velocities this fact suggests that these gravity waves are generated from the same source with a similar mechanism when the wave packets were observed both the local rossby number and the residual in the nonlinear balance equation estimated using ncep ncar reanalysis data are large around the pnj situated slightly to the lower latitudes of syowa station therefore it is likely that the observed inertia gravity waves are generated by a spontaneous adjustment around the geostrophically unbalanced pnj and propagate toward syowa station the possibility of spontaneous gravity wave generation around the pnj is confirmed by comparison with the gcm simulation by sato et al

a gravity wave climatology for antarctica compiled from challenging minisatellite payload global positioning system champ gps radio occultations 1 the seasonal geographical and altitudinal dependence of gravity wave activity in the lower stratosphere over antarctica is presented gravity wave activity is estimated by calculating potential energy ep from radio occultation profiles obtained by the challenging minisatellite payload global positioning system champ gps experiment significant seasonal variation of wave activity is observed smaller wave activity in summer is attributed to waves with small phase velocities experiencing critical level filtering at other times of the year when wave activity is large less filtering occurs and the strong background wind is likely to cause doppler shifting of waves to longer vertical wavelengths which can reach larger amplitudes before saturating relationships between gravity wave activity and geographic location indicate that topography is a strong source for wave activity especially over the antarctic peninsula however wind rotation in this area was found to reduce the wave energy in summer at certain altitudes a strong enhancement of wave energy is observed at the edge of the polar vortex again reduced critical level filtering and doppler shifting in the area of the jet are likely to be major causes for this finding possible limitations to this study due to observational filtering are discussed

general aspects of a t213l256 middle atmosphere general circulation model 1 a high resolution middle atmosphere general circulation model gcm developed for studying small scale atmospheric processes is presented and the general features of the model are discussed the gcm has t213 spectral horizontal resolution and 256 vertical levels extending from the surface to a height of 85 km with a uniform vertical spacing of 300 m gravity waves gws are spontaneously generated by convection topography instability and adjustment processes in the model and the gcm reproduces realistic general circulation in the extratropical stratosphere and mesosphere the oscillations similar to the stratopause semiannual oscillation and the quasi biennial oscillation qbo in the equatorial lower stratosphere are also spontaneously generated in the gcm although the period of the qbo like oscillation is short 15 months the relative roles of planetary waves large scale gws and small scale gws in maintenance of the meridional structures of the zonal wind jets in the middle atmosphere are evaluated by calculating eliassen palm diagnostics separately for each of these three groups of waves small scale gws are found to cause deceleration of the wintertime polar night jet and the summertime easterly jet in the mesosphere while extratropical planetary waves primarily cause deceleration of the polar night jet below a height of approximately 60 km the meridional distribution and propagation of small scale gws are shown to affect the shape of the upper part of mesospheric jets the phase structures of orographic gws over the south andes and gws emitted from the tropospheric jet stream are discussed as examples of realistic gws reproduced by the t213l256 gcm

polar mesosphere and lower thermosphere dynamics 1 mean wind and gravity wave climatologies 1 mean wind and gravity wave climatologies are presented for the polar mesosphere and lower thermosphere mlt the data were derived using mf radars at davis 69 s 78 e and syowa 69 s 40 e in the antarctic and poker flat 65 n 147 w and andenes 69 n 16 e in the arctic the dynamics of the antarctic mlt are found to be significantly different from the arctic mlt summer maxima in both the westward and equatorward winds occur closer to the solstice in the antarctic than in the arctic the greater symmetry around the solstice suggests radiative effects may play a greater role in controlling the state of the antarctic mlt than in the arctic where dynamical effects appear to be more important gravity wave observations also suggest that wave drag may be greater in the arctic than in the antarctic the equatorward flow near the mesopause persists later in summer in the arctic than in the antarctic as do observations of polar mesospheric clouds and polar mesospheric summer echoes all three phenomena begin at about the same time in each hemisphere but end later in the arctic than in the antarctic it is proposed that the magnitude of the meridional winds can be used as a proxy for gravity wave driving and the consequent adiabatic cooling in the mlt seasonal variations in gravity wave activity are predominately combinations of annual and semiannual components significant hemispheric differences are observed for both the timing and magnitude of these seasonal variations

on the origins of mesospheric gravity waves 1 using hourly data from a three year simulation based on a gravity wave resolving general circulation model we have first inferred a global view of gravity wave sources and propagation affecting significantly the momentum balance in the mesosphere the meridional cross section of momentum fluxes suggests that there are a few dominant propagation paths originating from the subtropics in summer and the middle to high latitudes in winter these gravity waves are focused into the mesospheric jets in their respective seasons acting effectively to decelerate the jets the difference in the source latitudes likely contributes to the hemispheric asymmetries of the jets the horizontal distribution of the momentum fluxes indicates that the dominant sources are steep mountains and tropospheric westerly jets in winter and vigorous monsoon convection in summer the monsoon regions are the most important window to the middle atmosphere in summer because of the easterlies associated with the monsoon circulation

energy enhancements of gravity waves in the antarctic lower stratosphere associated with variations in the polar vortex and tropospheric disturbances 1 gravity waves in the antarctic lower stratosphere are examined using original operational radiosonde data obtained at syowa station 69 0 s 39 6 e with fine vertical resolution in the lower stratosphere the temporal variation in gravity wave energy depends on height in the height region of 13 15 km just above the tropopause the seasonal variation in gravity wave energy is not evident the wave energy is rather enhanced when the absolute value of potential vorticity in the upper troposphere becomes small over syowa station this fact implies that tropospheric disturbances affect the dynamical processes of gravity waves there however the gravity wave energy in the height region of 15 25 km shows clear seasonal variation having a maximum in spring the time variation in gravity wave energy is examined in detail in terms of the polar vortex by using the equivalent latitude coordinate energy enhancements occur when the edge of the polar vortex approaches syowa station and the enhancements are especially large when the polar vortex breaks down in spring these results suggest that height variation in the background atmosphere leads to the difference of wave characteristics between the two height regions the enhancements of wave energy are partly explained as modification of the wave structure by the background wind speed and the static stability but it is also likely that enhancements of wave activity contribute to the energy enhancement at the edge of the polar vortex in spring

falling sphere observations of anisotropic gravity wave motions in the upper stratosphere over australia a study of inertial scale gravity wave motions in the region of the atmosphere between 30 and 60 km has been undertaken using wind and temperature data derived from rocket borne falling sphere density experiments performed over woomera australia between 1962 nad 1976 the gross features of the wave field compare favorably with those found in similar northern hemispheric studies wave propagation is found to be both vertically and horizontally anisotropic a rotary spectral analysis indicates predominately upgoing wave energy suggesting that the majority of sources of these waves lie below 30 km a detailed statistical investigation of the waves made using the stokes parameters technique reveals that phase progression is also highly directional in the horizontal with a significant zonal component in summer but with a strong meridional component in winter propagation towards the southeast is inferred in summer with the waves possibly emanating from tropospheric sources in equatorial regions to the north of australia the technique also shows that on average the waves appear to have mean ellipse eccentricities f around 0 4 0 45 indirect estimates of a number of important wave parameters are made in particular v andw flux estimates are made over several height intervals the vertical gradient of density weighted flux implies wave induced mean flow accelerations of the order 0 1 1 ms 1day 1 this suggests that dissipating gravity waves are a significant source of the momentum residuals that are encountered in studies of satellite data from this region

seasonal variations of the gravity wave momentum flux in the antarctic mesosphere and lower thermosphere airglow imager and dynasonde imaging doppler interferometer idi radar wind measurements at halley station antarctica 75 6degreess 26 6degreesw have been used to estimate the seasonal variation of the vertical fluxes of horizontal momentum carried by high frequency atmospheric gravity waves the cross correlation coefficients between the vertical and horizontal wind perturbations were calculated from sodium na airglow imager data collected during the austral winter seasons of 2000 and 2001 these were combined with wind velocity variances from coincident radar measurements to estimate the daily averaged upper limit of the vertical flux of horizontal momentum due to gravity waves the resulting momentum flux at the na airglow altitudes while displaying a large day to day variability showed a marked rotation from the northwest to the southeast throughout the winter season calculations show that this rotation is consistent with seasonal changes in the wind field filtering of gravity waves below the na airglow region the calculations also indicate that while the magnitude of the meridional wind is small this filtering leads to the observed seasonal changes in the meridional momentum flux

lidar temperature measurements of gravity waves over kuhlungsborn 54 n from 1 to 105 km a winter summer comparison 1 since august 2002 temperature measurements from 1 to 105 km are performed at the leibniz institute of atmospheric physics in kuhlungsborn 54 n with a combination of different lidars results from 14 nights in winter and 31 in summer are presented nightly mean profiles and fluctuations with a temporal and vertical resolution of 15 min and 1 km respectively are derived in both seasons wave energy propagates upward phase propagates downward with vertical phase speeds of 0 25 to 1 9 m s phase speeds are generally larger in the mesosphere compared to the stratosphere because of decreasing static stability wave periods are found in the entire range of 1 8 hours given by experimental constraints with no preference for particular periods the observed vertical wavelengths cover the entire instrumental range of 5 50 km but the majority lies below 22 km in both seasons in single nights a few waves up to three dominate the wave spectrum and represent 45 65 of the entire variability wave amplitudes generally increase with altitude with a scale height of 18 22 km i e less than expected 14 km for propagation conserving momentum flux density the gravity wave energy loss changes with altitude and is different in both seasons local fluctuation minima nodes are often observed frequently colocated with convective instabilities temperature fluctuations are generally smaller in summer compared to winter maximum values are 10 and 25 k respectively applying gravity wave polarization relations to the mean winter and summer lidar temperature profiles the difference of fluctuations is basically determined by the background conditions especially at 60 80 km

role of gravity waves in the spatial and temporal variability of stratospheric temperature measured by cosmic formosat 3 and rayleigh lidar observations 1 this study utilizes cosmic satellite and lidar observations to examine the spatial and temporal variability of stratospheric temperature at a number of scales the geographic variation of the rms temperature difference between pairs of cosmic profiles shows a strong correspondence to previous climatologies of gravity wave activity in addition the second order structure functions we form can be directly related to the horizontal wave number power spectrum these structure functions for different seasons and altitudes display a close correspondence to previous studies which examined the form of the horizontal wave number power spectra our analysis suggests that the wavefield may be particularly affected by changes in the zonal wind between 15 and 25 km and that the wind reversal between tropospheric westerlies and stratospheric easterlies in summer strongly contributes to critical level filtering inspection also shows that longer horizontal wavelength waves are preferentially removed in this region at low altitudes the variability related to gravity waves shows a remarkably similar pattern as a function of horizontal separation in both hemispheres but is quite different at higher altitudes such contrast implies that seasonal variability at higher altitudes may be dominated by changes in propagation conditions in the lower stratosphere examination of temperature variability as a function of spatial and temporal separation indicates that gravity wave activity dominates stratospheric temperature variability and this has impacts on validation study site selection for example validation exercises in the summer hemisphere stratosphere are likely to be less affected by geophysical variability than those in the winter hemisphere

characteristics of atmospheric gravity wave activity in the polar regions revealed by gps radio occultation data with champ 1 using gps radio occultation data during 2001 2005 we studied the climatological behavior of atmospheric gravity waves in the polar stratosphere we calculated temperature fluctuations with vertical wavelengths shorter than 7 km and then determined the wave potential energy ep every month in a longitude latitude cell of 20 10 between 12 km and 33 km in the arctic region 50 90 n ep shows an annual variation with maximum in winter consistent with the zonal mean horizontal wind v and the eliassen palm e p flux fz the large fz values indicate higher planetary wave activity resulting in distortion of the polar vortex the unbalanced flow can then excite gravity waves through geostrophic adjustment in the antarctic region 50 90 s ep gradually increases during winter and reaches its maximum in spring before decreasing rapidly the time derivative of v coincides with the ep peak and the horizontal distribution of ep has a similar structure to v suggesting that the ep enhancement is closely related to the decay of the polar vortex during major warming events over the arctic the divergence of e p flux f was enhanced coinciding with large ep in the antarctic f strongly correlates with ep in spring gravity waves seem to be effectively generated through planetary wave transience and or breaking orographic generation of gravity waves seems to be important in limited areas only such as scandinavia and the antarctic peninsula showing that it is less important than the polar night jet in determining the climatological behavior of gravity waves

warm stratopause in the antarctic winter abstract the fact that the temperature near the stratopause in the polar night is remarkably higher in the antarctic than in the arctic is described the reason why the stratopause can exist in the polar night and be warmer in the antarctic is considered in terms of gravity waves and planetary waves

gravity waves appearing in a high resolution gcm simulation global characteristics of gravity waves in the lower stratosphere are examined using a gcm with high resolution in both the horizontal t106 corresponding to about 120 km and the vertical 600 m the bottom boundary condition of the model is that of an aquaplanet with perpetual february sea surface temperature the simulated gravity waves are in good agreement with mesosphere stratosphere troposphere mst radar observations at a middle latitude on the gravity wave structure and on the frequency spectra as a function of height the frequency spectra of simulated wind and temperature fluctuations are also examined as a function of latitude large values of spectral density are observed at frequencies higher than the inertial frequency f in a weak wind region around 20 km which is consistent with the characteristics of internal gravity waves an isolated peak is observed near f for horizontal wind spectra at latitudes higher than 108 while the energy is distributed in a wide range of frequency at lower latitudes where f approaches zero further analysis is performed of those fluctuations having periods shorter than 24 h and those having vertical wavelengths smaller than 5 km these are frequently analyzed as gravity waves using observation data the distribution of energy and momentum fluxes in the latitude height section is examined the result indicates that short period waves mostly propagate upward and poleward from the equatorial region the wave energy reaches about 508 lat at the 27 km altitude a negative positive maximum of vertical flux of meridional momentum y9w9 is seen above the subtropical jet in the northern southern hemisphere for small vertical scale gravity waves this is consistent with the preferred equatorward propagation of the wave indicated by a statistical analysis based on mst radar observations the ratio of potential to kinetic energy maximizes over the equator and decreases poleward the eliassen palm flux divergence associated with gravity waves is decelerative above the subtropical jet albeit small

microwave limb sounder observations of gravity waves in the stratosphere a climatology and interpretation high horizontal resolution temperature data from the microwave limb sounder mls are analyzed to obtain information about high intrinsic frequency gravity waves in the stratosphere global climatologies of temperature variance at solstice are computed using six years of data a linear gravity wave model is used to interpret the satellite measurements and to infer information about tropospheric wave sources globally uniform sources having several different spectral shapes are examined and the computed variances are filtered in three dimensional space in a manner that simulates the mls weighting functions the model is able to reproduce the observed zonal mean structure thus indicating that the observations reflect changes in background wind speeds and provide little information about the latitudinal variation of wave sources longitudinal variations in the summer hemisphere do reflect source variations since the modeled variances exhibit much less variation in this direction as a consequence of the zonal symmetry of the background winds a close correspondence between the mls variances and satellite observations of outgoing longwave radiation suggests that deep convection is the probable source for these waves the large variances observed over the tip of south america in winter are most certainly linked to orographic forcing but inferences about wave sources in northern hemisphere winter are difficult to make as a result of the high degree of longitudinal and temporal variability in the stratospheric winds comparisons of model results using different source spectra suggest that the tropospheric sources in the subtropics in summer have a broader phase speed spectrum than do sources at middle latitudes in winter

cosmic gps observations of northern hemisphere winter stratospheric gravity waves and comparisons with an atmospheric general circulation model 1 cosmic satellite temperature data are used to derive the 2006 07 winter mean stratospheric northern hemisphere potential energy ep from gravity waves with vertical wavelengths less than 7 km in grid cells of size 10 5 and to study longitudinal and latitudinal variability in cells of size 20 5 7 days large ep at 17 23 km is mostly associated with the sub tropical jet and shows significant longitudinal variability some contribution to total ep from local orographic sources may occur above the canadian rockies scandinavia and northern japan but not above the himalayas due to the background wind conditions many of the waves are likely to have low ground based phase speeds as observed by filtering around the 0 10 m s 1 background zonal wind cosmic results are compared with a t106l60 agcm confirming sub tropical jet related generation upward propagation and low phase speeds of the observed gravity waves

a general circulation model study of the orographic gravity waves over antarctica excited by katabatic winds 1 in this study we simulated orographic gravity waves ogws over antarctica using a t213l250 general circulation model gcm the gcm has a fine vertical resolution of 300 m throughout the middle atmosphere the simulation was run for a 1 year period results from 21 28 june were primarily considered ogws are excited by katabatic winds that travel down the surface slopes of the antarctic ice sheet a strong eastward katabatic wind blows over the west coast of the ross sea at the approach of the synoptic scale upper tropospheric westerly jets a quasi stationary ogw is then excited above the coast and propagates upward into the mesosphere an ogw appears sporadically during the antarctic winter and spring its amplitude is determined by the strength of the eastward katabatic wind dissipation of ogws within the middle atmosphere results in a localized deceleration of westerly winds greater than 30 m s 1 d 1 this in turn modifies the horizontal circulation in the polar vortex strong vertical mixing occurs within the mesosphere and is associated with wave breaking large temperature fluctuations associated with the ogws affect the formation or suppression of polar stratospheric clouds in the lower stratosphere katabatic wind excitation is the most powerful source of gravity waves over antarctica around the time of the winter solstice

rayleigh lidar observations of reduced gravity wave activity during the formation of an elevated stratopause in 2004 at chatanika alaska 65 n 147 w 1 we report rayleigh lidar measurements of nightly temperature profiles in the 40 80 km altitude region and 15 min relative density profiles in the 40 50 km altitude region at poker flat research range chatanika alaska 65 n 147 w in december january and february over three winters 2002 2003 2003 2004 and 2004 2005 we characterize the gravity wave activity in terms of the measurements of buoyancy period and relative density fluctuations and estimate the potential energy density and growth of potential energy density with altitude we use satellite and reanalysis data to analyze the synoptic structure of the stratospheric vortex and the aleutian anticyclone the planetary wave activity and the mean winds these three winters have a major stratospheric warming in 2002 2003 an extreme warming event in 2003 2004 resulting in an elevated stratopause and no warming in 2004 2005 the gravity wave activity shows significant interannual variability with an average potential energy density of 2 1 j kg in 2002 2003 1 1 j kg in 2003 2004 and 5 7 j kg in 2004 2005 we find a positive correlation of 0 74 between the gravity wave activity in the upper stratosphere and the winds in the lower stratosphere where the winds are lightest the reduction in gravity wave activity in 2002 2003 relative to 2004 2005 reflects the influence of the aleutian anticyclone that is present over chatanika in 2002 2003 but absent in 2004 2005 the occurrence of lower gravity wave activity in 2003 2004 when the aleutian anticyclone is present less often than in 2002 2003 supports recent modeling studies that indicate that the elevated stratopause is formed due to a reduction of gravity waves propagating upward into the mesosphere

rayleigh lidar observations of gravity wave activity in the winter upper stratosphere and lower mesosphere above davis antarctica 69 s 78 e 1 gravity wave activity in the upper stratosphere and lower mesosphere uslm is investigated using temperature data retrieved from a rayleigh lidar at davis antarctica 69 s 78 e during the 2007 and 2008 winters the temporal and height variabilities of waves with ground based periods greater than 2 h and vertical wavelengths between 4 km and 20 km are analyzed stratospheric gravity wave potential energy per unit mass shows a weaker correlation with stratospheric winds at davis than that reported in the arctic gravity waves dissipate above 40 km during winter while there is no dissipation in the autumn mesosphere a separate analysis of gravity waves with ground based periods of 2 6 h revealed lower dissipation in the winter mesosphere the seasonal cycle of gravity wave activity is evident throughout the uslm with peak activity observed during winter the gravity wave potential energy and vertical wavenumber power spectral density at davis are similar to that recorded at other high latitude sites

gravity wave characteristics in the lower atmosphere at south pole a 4 year 1993 1996 temperature and wind data set obtained from over 2000 high resolution balloon soundings at south pole is used to study gravity wave characteristics in the troposphere and lower stratosphere extensive analyses of energy density spectra and static stability are performed to present a comprehensive view of the gravity wave characteristics in the lower atmosphere at south pole our results show that the gravity waves are ubiquitous and often fairly strong at south pole even though the generation mechanisms are not clear gravity wave characteristics are in general similar to those obtained at other high latitude southern hemisphere stations potential energies vary between about 0 5 j kg and 5 j kg with season and altitude variations in kinetic energies are not well correlated with potential energy variations and range from 1 j kg to 11 j kg we observe significant seasonal variations of the slope and magnitude of the vertical wavenumber spectrum of temperature fluctuations especially in the stratosphere in general the gravity waves in the stratosphere are stronger weaker in austral spring fall wave activity in the troposphere has little seasonal dependence stability analysis shows that instabilities are more likely to occur in the troposphere than in the stratosphere the probability of wave instability is 13 7 in the troposphere and 5 4 in the stratosphere this is due to the less stable stratification in the troposphere where the buoyancy period averages 8 3 min compared to 4 9 min in the stratosphere dynamic shear instability is more likely to occur than convective instability 11 versus 2 6 in the troposphere and 4 7 versus 0 7 in the stratosphere due to the prevailing strong wind shear the instability probabilities vary seasonally with the austral winter exhibiting the highest probability of instabilities dynamic and convective instabilities combined in both the troposphere and stratosphere