interpretations of observed climatological patterns in stratospheric gravity wave variance observational analyses of gravity waves in the stratosphere have revealed various climatological patterns in gravity wave activity seasonal geographical and vertical variations have all been observed in this work a linear model of gravity wave propagation is applied to investigate the underlying causes of some of the observed patterns a collection of monochromatic gravity waves that represent a broad spectrum of wavenumbers and frequencies is input at 6 km altitude in the model propagation of the waves through realistic background atmospheric wind and stability fields is treated with linear ray theory and a simple saturation condition to limit amplitudes to stable values the wave spectrum at the 6 km source height is specified to be constant at all latitudes longitudes and times so the variability that appears at higher altitudes is due entirely to background atmosphere variations before the model results are compared to the observations the spectrum of waves is filtered in a way that mimics the limitations of each of the observation techniques the filtering is described in terms of vertical wavelength and is referred to as the observational filter in a vertically varying background wind gravity waves are doppler shifted in intrinsic frequency and refracted to different vertical wavelengths as they propagate vertically through the atmosphere the observational filter and the wave refraction effects can thus couple in interesting ways that have not been explicitly considered in previous work the model shows that this coupling can give rise to geographical seasonal and vertical variations in gravity wave observations without any variations in the spectrum or amplitude of gravity wave sources in the troposphere thus careful consideration of both the background wind profile and observational filter can greatly affect the interpretation of the observed climatological patterns in gravity wave activity

inertia gravity waves observed in the lower stratosphere over macquarie island abstract this study examines the properties of inertia gravity waves observed in the lower stratosphere over macquarie island how these properties vary with season and the likely source of the waves the waves are observed in high resolution upper air ozonesonde soundings of wind and temperature released from macquarie island during the 1994 ashoe maesa program the properties of the inertia gravity waves observed in the soundings are quantified using hodograph and rotary spectral analyses the analyzed waves have horizontal wavelengths between 100 and 1000 km vertical wavelengths between about 1 and 7 km intrinsic frequencies between f and 2f and horizontal trace speeds between 50 and 30 m s 1 there appears to be a seasonal cycle in the inertia gravity wave activity in the lower stratosphere the minimum being in the austral winter when the background zonal flow is strong and westerly and its vertical shear is positive in contrast the variance of the horizontal perturbation winds does not show a

downward control of the mean meridional circulation and temperature distribution of the polar winter stratosphere abstract 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 stratopause and by 20 at 30 km when gravity wave drag is not included

latitudinal and seasonal variations of inertial gravity wave activity in the lower atmosphere over central china 1 gravity wave activities and background dynamical structure in the troposphere and lower stratosphere tls over five stations at latitudes from 10 n to 40 n were statistically studied by using the data from radiosonde observation on a twice daily basis at 0800 and 2000 lt the background dynamical structure exhibits evident latitudinal and seasonal variations and has a profound influence on inertial gravity waves in the tls in the analyses of inertial gravity waves according to the background structures the observation height coverage is divided into two segments which are the tropospheric 0 10 km and lower stratospheric segments 18 25 km the observational results indicate that the tropospheric jet is the most important excitation source for gravity waves both in the troposphere and lower stratosphere and it plays different roles in determining the morphology of gravity waves in these two segments the jet excited gravity waves in the troposphere can propagate both upward and downward and only part of the upward propagating waves can penetrate into the stratosphere because of the doppler shifting by the jet while in the lower stratosphere gravity waves excited by the tropospheric jet propagate upward most differences between the tropospheric and lower stratospheric results can be explained from the linear dispersion relations of gravity waves and the doppler shifting by the strong tropospheric jet however such an explanation is qualitative rather than quantitative generally the observations reveal that the tropospheric gravity waves are mainly controlled by their excitation sources implying the wave characteristics may be regarded as at least an indicator of the wave excitation source characteristics these results suggest that in order to attain a more realistic source parameterization for gravity waves propagating in the middle and upper atmosphere more attention should be paid to the gravity waves in the troposphere moreover the causes of the pronounced peak of lower stratospheric gravity wave intensity at tropical latitudes revealed by previous observations are also discussed

gravity wave and equatorial wave morphology of the stratosphere derived from long term rocket soundings fluctuations in vertical profiles of atmospheric temperature and horizontal wind in the 20 60 km altitude range have been isolated from meteorological rocket measurements during 1977 87 at 15 widely separated sites the seasonal geographical and vertical variability of the variance of horizontal velocities u 2 2 and relative temperature perturbations t 2 were studied the bulk of the variance of both quantities in the 2 10 km and 2 20 km vertical wavelength bands was associated with gravity wave motions although in depth study of the wave polarization shows that planetary scale equatorial wave modes contribute to the variance at equatorial sites annual mean variances varied widely among the 15 stations suggesting appreciable geographical variability in stratospheric wave activity

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

radiosonde observations of gravity waves in the lower stratosphere over davis antarctica radiosonde observations made from davis station antarctica 68 6 s 78 0 e between 2001 and 2012 are used to compile a climatology of lower stratosphere inertial gravity wave characteristics wavelet analysis extracts single wave packets from the wind and temperature perturbations wavelet parameters combined with linear gravity wave theory allow for the derivation of a wide range of wave characteristics observational filtering associated with this analysis preferentially selects inertial gravity waves with vertical wavelengths less than 2 3 km the vertical propagation statistics show strong temporal and height variations the waves propagate close to the horizontal and are strongly advected by the background wind in the wintertime notably around half of the waves observed in the stratosphere above davis between early may and mid october propagate downward this feature is distributed over the observed stratospheric height range based on the similarity between the upward and downward propagating waves and on the vertical structure of the nonlinear balance residual in the polar winter stratosphere it is concluded that a source due to imbalanced flow that is distributed across the winter lower stratosphere best explains the observations calculations of kinetic and potential energies and momentum fluxes highlight the potential for variations in results due to different analysis techniques

simple bouguer gravity anomaly field and the inferred crustal structure of continental ecuador the simple bouguer gravity anomaly field of continental ecuador corresponds closely to the physiographic provinces of the country the sierra which includes the andes and their foothills is characterized by a pronounced low with values to 292 mgal which reflects the deep andean root bouguer anomalies over the oriente become less negative away from the sierra chiefly in response to progressive thinning of continental crust eastward the costa between the sierra and the pacific shore in the north has the most positive on land bouguer anomalies 162 mgal so far known in the western hemisphere this part of the costa is underlain by an ancient oceanic plate now welded to the northwestern corner of the otherwise continental south american plate

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

inertia gravity waves revealed in radiosonde data at jang bogo station antarctica 74 37 s 164 13 e 2 potential sources and their relation to inertia gravity waves

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

wavelet analysis of stratospheric gravity wave packets over macquarie island 1 wave parameters we describe a technique to detect gravity wave packets in high resolution radiosonde soundings of horizontal wind and temperature the vertical profiles of meridional and zonal wind speeds are transformed using the morlet wavelet and regions of high wind variance in height wavenumber space are identified as gravity wave packets application of the stokes parameter analysis to horizontal wind and temperature profiles of the reconstructed wave packets yields the wave parameters the technique was applied to twice daily radiosonde launches at macquarie island 55 s 159 e between 1993 and 1995 a strong seasonal cycle in the total wave variance was found with a maximum in winter the amount of wave energy propagating downward from the upper stratosphere also maximized in winter waves propagated predominately toward the southwest in winter but in summer propagation directions were approximately isotropic the intrinsic frequencies were close to the inertial frequency and the waves had inferred horizontal wavelengths of several hundred kilometers

gravity wave characteristics in the southern hemisphere revealed by a high resolution middle atmosphere general circulation model abstractgravity wave characteristics in the middle to high latitude southern hemisphere are analyzed using simulation data over 3 yr from a high resolution middle atmosphere general circulation model without using any gravity wave parameterizations gravity waves have large amplitudes in winter and are mainly distributed in the region surrounding the polar vortex in the middle and upper stratosphere while the gravity wave energy is generally weak in summer the wave energy distribution in winter is not zonally uniform but it is large leeward of the southern andes and antarctic peninsula linear theory in the three dimensional framework indicates that orographic gravity waves are advected leeward significantly by the mean wind component perpendicular to the wavenumber vector results of ray tracing and cross correlation analyses are consistent with this theoretical expectation the leeward energy propagation extends to several thousand kilometers which explains part of the gravity wave distribution aro

seasonal variations in lower stratospheric gravity wave energy above the falkland islands 1 the gravity wavefield in the lower stratosphere between 15 km and 22 km altitude above mount pleasant airport 51 49 s 58 26 w on the falkland islands is studied using over 2100 high resolution radiosonde soundings from 2002 to 2010 the seasonal variation in vertical direction of propagation shows a small decrease in numbers of upward propagating waves that is related to critical level filtering however there is a very large increase in numbers of downward propagating waves between july and september this is attributed to the proximity of the edge of the polar vortex there is a seasonal variation in gravity wave energy density with a large peak during the austral autumn equinox this is markedly different to results in the literature both from rothera on the antarctic peninsula and stations on the main antarctic continent this seasonal pattern has been shown to be linked to variations in the sources of upward propagating gravity waves the seasonal variation in gravity wave characteristics above mount pleasant airport seen in our results suggests that the gravity wavefield in this region is determined by a combination of different gravity wave sources located above and below the lower stratosphere

a mesoscale gravity wave event observed during ccope iii wave environment and probable source mechanisms abstract synoptic and special mesoscale observations taken during the cooperative convective precipitation experiment ccope are used to describe the multiscale environment of a gravity wave event understand the wave environment interactions that led to the development of severe thunderstorms and asses possible wave generation mechanisms the storms formed sequentially as a packet of gravity waves propagated across a stationary thunderstorm outflow boundary convection developed most rapidly in that part of the mesonetwork in which existed the combination of relatively high parcel buoyant energy weak restraining inversion strong storm downdraft potential and substantial vertical wind shear associated with a mesoscale jet streak synoptic scale analysis reveals that the waves were excited north of a stationary front and within the right exit region of the jet streak as it approached a stationary ridge in the 300 mb height field strong indications of unbalanced flow were diagnosed within the gravit

recent developments in gravity wave effects in climate models and the global distribution of gravity wave momentum flux from observations and models recent observational and theoretical studies of the global properties of small scale atmospheric gravity waves have highlighted the global effects of these waves on the circulation from the surface to the middle atmosphere the effects of gravity waves on the large scale circulation have long been treated via parametrizations in both climate and weather forecasting applications in these parametrizations key parameters describe the global distributions of gravity wave momentum flux wavelengths and frequencies until recently global observations could not define the required parameters because the waves are small in scale and intermittent in occurrence recent satellite and other global datasets with improved resolution along with innovative analysis methods are now providing constraints for the parametrizations that can improve the treatment of these waves in climate prediction models research using very high resolution global models has also recently demonstrated the capability to resolve gravity waves and their circulation effects and when tested against observations these models show some very realistic properties here we review recent studies on gravity wave effects in stratosphere resolving climate models recent observations and analysis methods that reveal global patterns in gravity wave momentum fluxes and results of very high resolution model studies and we outline some future research requirements to improve the treatment of these waves in climate simulations copyright 2010 royal meteorological society and crown in the right of canada

gravity waves in the tropical lower stratosphere an observational study of seasonal and interannual variability radiosonde observations made at cocos islands 12 s 97 e in the indian ocean between september 1992 and june 1998 are used to study seasonal and interannual variations in gravity wave activity in the lower stratosphere 18 25 km the islands are located in a region of generally strong convection that occurs at all times of the year with the period of strongest convective activity between december and july wet season the prevailing zonal winds during the observational period and height range are westward with a quasi biennial oscillation qbo superimposed time series of wave energy show that largest wave amplitudes occur during the wet season when convection is strongest but a qbo like variation is also apparent maximum energy densities of about 25 j kg 1 occur early 1993 1995 and 1997 at the times when the westward shears are largest wave energy is found to be propagating upward and in the horizontal there is considerable azimuthal anisotropy with predominate eastward propagation against the prevailing wind upward fluxes of zonal momentum flux u w are estimated by combining the temperature and wind information fluxes show a similar temporal behavior to the energy the motion and temperature fields are dominated by waves with vertical wavelengths 2 km using a stokes parameter analysis it is found that the intrinsic frequencies are on average 2 3 times the inertial frequency corresponding to intrinsic periods of 20 25 hours horizontal wavelengths between 200 and 2000 km are inferred with a mean value of about 1000 km the mean intrinsic phase speeds are about 10 ms 1 but ground based phase speeds are centered on 0 ms 1

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

a climatology of gravity wave motions in the mesopause region at adelaide australia abstract a statistical study of gravity wave motions in the mesosphere and lower thermosphere measured with a mf partial reflection radar located at buckland park new adelaide 35 s 138 e in the period november 1933 to december 1984 is presented the analyses am confined to waves with ground based periods between 1 and 24 h time height cross sections show that the mean square amplitudes u 2 and v 2 of the zonal and meridional perturbation velocities respectively vary in a predominantly semiannual manner such that the minima in wave activity coincide with the reversals in the zonal circulation in the middle atmosphere in most instances v 2 is greater than u 2 which together with the small but nonzero u v fluxes shows that the gravity wave field is partially polarized a technique similar to that used to analyse partially polarized electromagnetic waves suggests that on a seasonal basis the wave field is polarized by about 10 to 20 but for shorter periods the degree of polarization may be signi

seasonal cycle of orographic gravity wave occurrence above small islands in the southern hemisphere implications for effects on the general circulation 1 orographic gravity waves generated by flow over the topography of small islands in the southern oceans have been observed from orbit with the atmospheric infrared sounder on the aqua satellite we examine the occurrence frequencies of these waves in the stratosphere at 40km above 14 islands and examine geographical and seasonal changes our results show that these small island mountain waves occur commonly in the stratosphere in the may september season though not every day differing seasonal variations are evident at different islands and the seasonal variations are closely related to latitude and prevailing wind patterns we also examine interannual variability in 2years of data and the relationships between occurrence frequencies momentum fluxes and stratospheric and surface winds the results suggest that stratospheric winds have a first order limiting effect on the observations of these island mountain waves in atmospheric infrared sounder airs data surface wind direction and island orographic relief have an additional but secondary influence on the island mountain wave occurrence frequencies in airs data the implications are that these wave events are extremely common and that on many days when the waves are not observed in airs data they have likely dissipated and induced a drag force on the atmosphere below the 40km observation level observations of momentum flux during these wave events also permit a first estimate of their importance to the general circulation of the southern hemisphere

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

estimation of gravity wave momentum flux and phase speeds from quasi lagrangian stratospheric balloon flights part ii results from the vorcore campaign in antarctica the stratospheric gravity wave field in the southern hemisphere is investigated by analyzing observations collected by 27 long duration balloons that flew between september 2005 and february 2006 over antarctica and the southern ocean the analysis is based on the methods introduced by boccara et al in a companion paper special attention is given to deriving information useful to gravity wave drag parameterizations employed in atmospheric general circulation models the balloon dataset is used to map the geographic variability of gravity wave momentum fluxes in the lower stratosphere this flux distribution is found to be very heterogeneous with the largest time averaged value 28 mpa observed above the antarctic peninsula this value exceeds by a factor of 10 the overall mean momentum flux measured during the balloon campaign zonal momentum fluxes were predominantly westward whereas meridional momentum fluxes were equally northward and southward a local enhancement of southward flux is nevertheless observed above adelie land and is attributed to waves generated by katabatic winds for which the signature is otherwise rather small in the balloon observations when zonal averages are performed oceanic momentum fluxes are found to be of similar magnitude to continental values 2 5 3 mpa stressing the importance of nonorographic gravity waves over oceans last gravity wave intermittency is investigated mountain waves appear to be significantly more sporadic than waves observed above the ocean

vertical fluctuation energy in united states high vertical resolution radiosonde data as an indicator of convective gravity wave sources 1 convectively generated internal gravity waves at extratropical latitudes are difficult to identify by climatological analysis of the temperature and horizontal wind fields from radiosonde profiles using traditional analysis methods here we show that by analyzing ascent rate profiles we define a new variable vertical fluctuation energy ve we can identify convection sources in climatological analyses analysis of a 9 year time series 1998 2006 of united states high vertical resolution radiosonde data shows that ve maximizes in summer in midlatitudes within the troposphere 2 8 9 km and peaks at local afternoon early evening during the summer over most of the contiguous united states furthermore the apparent dominant vertical wavelength based on fourier analysis of the low pass filtered ascent rate fluctuations also increase and decrease with ve both on diurnal and seasonal timescales ve in the lower stratosphere however does not show this same relationship to convection but analysis of the vertical wavelength does show some of the features seen in tropospheric ve unlike midlatitude stations ve within both the troposphere and the lower stratosphere over tropical western pacific island stations is highly correlated with convective precipitation and inversely correlated with outgoing longwave radiation we interpret this difference by using the 4 d gravity wave regional or global ray tracer ray tracing model with a source spectrum representative of a convection source

seasonal variations of gravity wave activity in the lower stratosphere over an antarctic peninsula station an 8 year series of 965 high resolution radiosonde soundings over rothera 67 degrees s 68 degrees w on the antarctic peninsula are used to study gravity wave characteristics in the lower stratosphere the gravity wave energy is shown to have a seasonal variation with peaks at the equinoxes the largest peak is around the spring equinox during the winter months and extending into the spring there is both an enhancement in the downward propagating wave activity and a reduction in the amount of critical level filtering of upward propagating mountain waves the horizontal propagation directions of the gravity waves were determined using hodographs it was found that there is a predisposition toward northward and westward propagating waves above rothera this is in agreement with previous observations of gravity wave momentum flux in the wintertime mesosphere over rothera these results are consistent with a scenario whereby the stratospheric gravity wavefield above rothera is determined by a combination of wind flow over topography generating waves from below and sources such as the edge of the polar stratospheric vortex generating waves from above especially during winter and spring

generation of mesoscale gravity waves in upper tropospheric jet front systems abstract multiply nested mesoscale numerical simulations with horizontal resolution up to 3 3 km are performed to study the generation of mesoscale gravity waves during the life cycle of idealized baroclinic jet front systems long lived vertically propagating mesoscale gravity waves with horizontal wavelengths 100 200 km are simulated originating from the exit region of the upper tropospheric jet streak in a manner consistent with past observational studies the residual of the nonlinear balance equation is found to be a useful index in diagnosing flow imbalance and predicting wave generation the imbalance diagnosis and model simulations suggest that balance adjustment as a generalization of geostrophic adjustment is likely responsible for generating these mesoscale gravity waves it is hypothesized that through balance adjustment the continuous generation of flow imbalance from the developing baroclinic wave will lead to the continuous radiation of gravity waves

lidar observations of persistent gravity waves with periods of 3 10 h in the antarctic middle and upper atmosphere at mcmurdo 77 83 s 166 67 e persistent dominant and large amplitude gravity waves with 3 10 h periods and vertical wavelengths 20 30 km are observed in temperatures from the stratosphere to lower thermosphere with an fe boltzmann lidar at mcmurdo antarctica these waves exhibit characteristics of inertia gravity waves in case studies yet they are extremely persistent and have been present during every lidar observation we characterize these 3 10 h waves in the mesosphere and lower thermosphere using lidar temperature data in june from 2011 to 2015 a new method is applied to identify the major wave events from every lidar run longer than 12 h a continuous 65 h lidar run on 28 30 june 2014 exhibits a 7 5 h wave spanning 60 h and 6 5 h and 3 4 h waves spanning 40 and 45 h respectively over the course of 5 years 323 h of data in june reveal that the major wave periods occur in several groups centered from 3 5 to 7 5 h with vertical phase speeds of 0 8 2 m s these 3 10 h waves possess more than half of the spectral energy for 93 of the time a rigorous prewhitening postcoloring technique is introduced for frequency power spectra investigation the resulting spectral slopes are unusually steep 2 7 below 100 km but gradually become shallower with increasing altitude reaching about 1 6 at 110 km two dimensional fast fourier transform spectra confirm that these waves have a uniform dominant vertical wavelength of 20 30 km across periods of 3 5 10 h these statistical features shed light on the wave source and pave the way for future research

wavelet analysis of stratospheric gravity wave packets over macquarie island 2 intermittency and mean flow accelerations we calculate the mean flow accelerations due to gravity wave packets observed in the lower stratosphere over macquarie island 55 s 159 e between february 1994 and april 1995 the parameters of the wave packets were extracted from twice daily radiosonde soundings using a wavelet based analysis method introduced by zink and vincent this issue the deduced wave parameters are used to directly compute momentum flux profiles in the lower stratosphere and the shortcomings of this approach to assess mean flow accelerations are discussed we then use the observed wave packets as an input spectrum in a linear ray tracing model the vertical extent of the detected wave packets allows us to define an expression for wave intermittency which enables us to compute zonal accelerations in the stratosphere and mesosphere in the stratosphere the waves produce an acceleration of the mean flow in accordance with predictions in the mesosphere the inferred wave drag is 2 3 times larger than previous observational and theoretical estimates

characteristics of inertio gravity waves revealed in rawinsonde data observed in korea during 20 august to 5 september 2002 1 characteristics of inertio gravity waves igws observed at six operational rawinsonde stations in korea from 20 august to 5 september 2002 and their relationship with convective sources are investigated several types of convective systems including mesoscale convective complexes and typhoon rusa passed the korean peninsula during the observing period to categorize the observed waves with and without convective sources wet and dry periods are defined at each observing site using hourly precipitation and satellite data although waves with extremely large values of intrinsic frequency and vertical wavelength are observed mostly in wet periods the mean values of wave parameters for wet and dry periods are similar low frequency igws can originate far from and long before the observing sites implying that it is unreasonable to correlate convective sources and observed waves at the same location and time for better correlation of the observed waves and their sources a three dimensional ray tracing model is used a new wet case is defined on the basis of the occurrence of convection when and where a ray locates in mid to upper troposphere characteristics of the observed waves for new wet and dry cases differ significantly the intrinsic frequency is larger but the horizontal wavelength is much smaller for wet than dry cases sources for wet cases are mostly convective clouds located northeast and southeast of the observing sites below 5 km this is clearly distinguished from dry cases where sources are located mostly in the northwest above 15 km and southeast far from the observing sites below 5 km

southern hemisphere extratropical gravity wave sources and intermittency revealed by a middle atmosphere general circulation model abstractsouthern hemisphere extratropical gravity wave activity is examined using simulations from a free running middle atmosphere general circulation model called kanto that contains no gravity wave parameterizations the total absolute gravity wave momentum flux mf and its intermittency diagnosed by the gini coefficient are examined during january and july the mf and intermittency results calculated from the kanto model agree well with results from satellite limb and superpressure balloon observations the analysis of the kanto model simulations indicates the following results nonorographic gravity waves are generated in kanto in the frontal regions of extratropical depressions and around tropopause level jets regions with lower higher intermittency in the july midstratosphere become more less intermittent by the mesosphere as a result of lower level wave removal the gravity wave intermittency is low and nearly homogeneous throughout the sh middle atmosphere during january this indicates t

interstation correlation of high latitude lower stratosphere gravity wave activity evidence for planetary wave modulation of gravity waves over antarctica 1 four years of operational radiosonde balloon flights from three australian stations in eastern antarctica casey 66 3 s 110 0 e davis 68 6 s 78 0 e and mawson 67 6 s 62 9 e are analyzed to derive lower stratosphere 12 20 km altitude gravity wave information from perturbations in wind and temperature gravity wave activity and seasonal behavior was found to be similar to that seen in earlier studies from antarctica interstation comparisons of zonal wind and gravity wave activity showed very high correlations throughout the entire data set between mawson and davis stations 600 km distant with a lag near 0 5 days the correlations between casey and davis 1400 km apart were lower but still significant with a lag near 1 day there is no significant correlation between stratospheric gravity wave activity and surface winds our results suggest a pattern of winds and waves moving eastward over the stations with a speed near 15 m s 1 as this is comparable to planetary wave speeds we interpret our results as being evidence for a significant planetary wave induced modulation of the zonal wind and the gravity wave field although we are unable to identify the mechanism by which this operates our work suggests that the high latitude lower stratosphere gravity wave fields are relatively uniform on spatial scales of 500 1000 km and on timescales of around 0 5 1 days

inertia gravity wave generation by the tropospheric midlatitude jet as given by the fronts and atlantic storm track experiment radio soundings 1 generation of inertia gravity waves by the midlatitude tropospheric jet is studied on the basis of the data obtained from the radio soundings over the north atlantic during the fronts and atlantic storm track experiment campaign a sample of 224 radio soundings is used to analyze the wave activity as a function of the distance to the jet it is shown that radio soundings displaying the most intense gravity wave activity both in the stratosphere and in the troposphere are the ones closest to the jet axis thus the jet region is the dominant source of gravity waves in this region far from orography further examination allows for identification of two specific regions of the flow that are associated with intense gravity wave activity the vicinity of the maximum of the jet velocity and the regions of strong curvature of the jet the detailed case studies we provide suggest that geostrophic adjustment is the dynamical mechanism responsible for the generation of large amplitude inertia gravity waves in the regions of the strong curvature of the wind the generation of waves in the vicinity of the regions where the wind veers in the deep troughs of the geopotential appears to be systematic

cracking and water seepage of xiashu loess used as landfill cover under wetting drying cycles this paper intends to investigate the anti seepage characteristics of xiashu loess used as landfill cover under wetting drying cycles a series of tests were performed to systematically evaluate the surface cracks pores the hydraulic conductivity and water seepage of the soil under wetting drying cycles the cracking tests indicated that the cracking intensity factor cif increased with the number of wetting drying cycles after three wetting drying cycles the cif gradually reached a stable value the influence of the compactness of the compacted clay was significant to cracking after four drying wetting cycles the cif of compacted clay with relatively low compactness 1 65 g cm3 w 5 25 was 0 15 and the cif of compacted clay with higher compactness 1 65 g cm3 w 3 21 was only 0 06 with the increase in the number of wetting drying cycles the accumulated pore volume of the soil particles increased and the maximum pore size was nearly unchanged after four drying wetting cycles the proportion and average diameter of macro pore in the soil particles were both increased however the proportion and average diameter of the meso pore slightly decreased furthermore the proportion and average diameter of the micro pores were unchanged after four wetting drying cycles the hydraulic conductivity of the compacted soil was at 8 3 10 7 1 5 10 5cm s which was increased about three orders of magnitude compared with the compacted soil without cracks the hydraulic conductivity of compacted soil increased linearly as cracks increased the hydraulic conductivity of compacted soil also gradually increased to a stable value as the pore volume increased after 1 month of wetting drying cycles the cracks of soil with low compactness had extended to a depth of 15 cm below the soil surface while the cracks of soil with higher compactness only reached a depth of 5 cm

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