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

three dimensional properties of andes mountain waves observed by satellite a case study the southern andes region has been clearly identified in previous satellite and balloon observations and in global models as a hot spot of small scale gravity wave activity with monthly mean momentum fluxes exceeding 10 times background values in fall winter and spring seasons this makes this region a focus of interest for global circulation and climate studies we analyze a case study on 8 may 2006 combining observations from the atmospheric infrared sounder instrument on the aqua satellite and the high resolution dynamics limb sounder instrument of the aura satellite to form a three dimensional picture of the wave field the observations show a widespread wave pattern over the southern andes extending eastward over the south atlantic simulations with the weather research forecasting model clearly identify the waves as orographic in origin but the observed wave pattern is far from the simple two dimensional wave field forced by steady flow over a mountain ridge the morphology of the pattern is consistent with three dimensional linear theoretical calculations of downstream propagation and latitudinal focusing of mountain waves into the stratospheric jet the observations confirm the importance of this process in the stratosphere and we find the process also occurring in the global analysis and forecasts from the european centre for medium range weather forecasting our analysis evaluates some strengths and weaknesses of current orographic wave drag parameterizations in global models and the relevance of parameterization assumptions in global models with high resolution copyright 2011 by the american geophysical union

total electron content behavior over japan during geomagnetic storms 1 the total electron content tec obtained from gps signals is used to study ionospheric dynamics over japan during geomagnetically disturbed conditions the numerous tec measurements are averaged in cells with a size 1 5 1 5 geographic scale and formatted as time series within the years 2000 2002 to extract the storm time changes of tec the diurnal and 27 day periodicities are subsequently removed diurnal variations are removed by replacing absolute tec values in each cell with their relative deviations rtec from medians the hourly rtec values from all cells within the central 4 wide band over japan area are then approximated by a plane surface this surface is represented by two parameters its value at the center rt and the slope b along the main axis taken as constants of the linear regression the 27 day periodicity was approximated by fourier waves with main period of 640 hours and two harmonics separately for rt and b and subtracted from them the analysis of rt and b behavior during a number of geomagnetic storms allowed us to reveal several repeatable features of average tec behavior it was found that tec behavior during the storms is similar to that of fof2 at the f region and was local time dependent a marked poleward expansion of the equatorial ionosphere crest region at the end of recovery phase is persistently observed feature produced probably by intensified eastward zonal winds such an expansion of equatorial ionosphere is observed also during isolated substorms outside main geomagnetic storms an oscillation like change of positive and negative disturbances with period of 24 hours is observed during a 4 day period following a moderate storm in the absence of geomagnetic activity driver that effect is probably caused by the alternative expansion and contraction of equatorial ionosphere

a modeling study of stratospheric waves over the southern andes and drake passage abstractlarge amplitude stratospheric gravity waves over the southern andes and drake passage as observed by the atmospheric infrared sounder airs on 8 9 august 2010 are modeled and studied using a deep 0 70 km version of the coupled ocean atmosphere mesoscale prediction system coamps model the simulated tropospheric waves are generated by flow over the high central andes ridge and the patagonian peaks in the southern andes some waves emanating from patagonia propagate southeastward across drake passage into the stratosphere over a horizontal distance of more than 1000 km the wave momentum flux is characterized by a tropospheric maximum over patagonia that splits into two comparable maxima in the stratosphere one located directly over the terrain and the other tilting southward with altitude using spatial ray tracing techniques and flow conditions derived from the numerical simulation the authors find that waves that originate from the high ridge in the central andes are absorbed by a critica

alpine gravity waves lessons from map regarding mountain wave generation and breaking the two month special observing period of the mesoscale alpine programme map in autumn 1999 included a variety of complex mountain wave events seven wave events were carefully analyzed compared with numerical models and described in published papers these detailed investigations revealed some common dynamical elements i e the importance of low level processes involving the slow moving boundary layer low level wind shear causing either wave absorption or decoupling spilling upstream blocking and latent heat release based on these studies it is clear that any quantitative prediction of mountain wave generation must take full account of these lower troposphere processes the newest numerical models show significant skill in simulating these effects using these models the climatology of waves over the alps can be studied copyright 2007 royal meteorological society

seafloor hydrothermal alteration at an archaean mid ocean ridge a hydrothermally metamorphosed altered greenstone complex capped by bedded cherts exposed in the north pole pilbara carton western australia is interpreted as an accretionary complex it is distinc tive in being characterised by both duplex structure and an oceanic crust stratigraphy this complex is shown to represent an archaean upper oceanic crust with a mid ocean ridge hydrothermal meta morphism that increases in grade stratigraphically downward three mineral zones have been defined zone a of the zeolite facies the prehnite pumpellyite facies or the lower greenschist facies at high xco2 condition zone b of the greenschist facies and zone c of the greenschist amphibolite transition facies in zone a metabasites ca al silicates including ca zeolites prehnite and pumpellyite are absent and epidote clinozoisite is extremely rare instead abundant carbonates are present with chlorite suggesting high xco2 composition in the fluid on the other hand in zones b and c metabasites where ca amphibole epidote clinozoisite chlorite ca na plagioclase are the dominant assemblages carbonate is not identified the metamorphic conditions boundary of zones b c were estimated to be about 350 uc at a pressure of 0 5 kbar fluid compositions coexisting with archaean greenstones at the transition between zones b and c were estimated by thermodynamic calculation in the cafmasch system t 350 370 uc p 150 1000 bar at xco2 of 0 012 0 140 such values are higher than present day vent fluids collected near mid ocean ridges with low xco2 values up to 0 005 the archaean seawater depth at the mid ocean ridge was estimated to be 1600 m at xco2 0 06 using a depth to boiling point curve for a fluid the carbonation due to high xco2 hydrothermal fluids occurred near the ridge axis before or was coincident with ridge metamorphism

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

observations and numerical simulations of mountain waves in the presence of directional wind shear three research aircraft observed small amplitude gravity waves over the south western french alps on 13 november 1999 during the mesoscale alpine programme map radiosonde ascents and global positioning system dropsondes deployed by map research aircraft indicate that the upstream flow was characterized by topographic blocking below 2 km and low level directional wind shear associated with a synoptic scale depression that extended above the alpine crest the in situ vertical velocity data from the three research aircraft and backscatter from lidar onboard the low level and upper level aircraft exhibit gravity wave signatures in the lower troposphere that are characterized by relatively short horizontal wavelengths on a scale of 5 km or less the in situ flight level and backscatter data also suggest a rapid decrease in the wave amplitude with height due to a directional critical layer that partially absorbs wave energy in the lower to middle troposphere in concert with a decrease in the scorer parameter with height that traps the wave energy numerical simulation results obtained from the non hydrostatic coupled ocean atmosphere mesoscale prediction system model using a horizontal resolution of 556 m indicate the presence of low level wave breaking above the highest peaks and confirm the presence of trapped waves and a directional critical level results based on linear theory and nonlinear model simulations suggest that the absorption of wave energy associated with the directional critical layer has an important impact on the wave characteristics including the momentum flux copyright 2006 royal meteorological society

high gravity wave activity observed in patagonia southern america generation by a cyclone passage over the andes mountain range fil pulido manuel arturo consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet nordeste instituto de modelado e innovacion tecnologica universidad nacional del nordeste facultad de ciencias exactas naturales y agrimensura instituto de modelado e innovacion tecnologica argentina

momentum flux estimates for south georgia island mountain waves in the stratosphere observed via satellite abstract we show high resolution satellite observations of mountain wave events in the stratosphere above south georgia island in the remote southern atlantic ocean and compute the wave momentum fluxes for these events the fluxes are large and they imply important drag forces on the circulation small island orography is generally neglected in mountain wave parameterizations used in global climate models because limited model resolution treats the grid cell containing the island as ocean rather than land our results show that satellite observations can be used to quantitatively constrain mountain wave momentum fluxes and they suggest that mountain waves from island topography may be an important missing source of drag on the atmospheric circulation

what is the source of the stratospheric gravity wave belt in austral winter abstractduring austral winter and away from orographic maxima or hot spots stratospheric gravity waves in both satellite observations and interim european centre for medium range weather forecasts ecmwf re analysis era interim data reveal enhanced amplitudes in a broad midlatitude belt extending across the southern ocean from east of the andes to south of new zealand the peak latitude of this feature slowly migrates poleward from 50 to 60 s wave amplitudes are much weaker across the midlatitude pacific ocean these features of the wave field are in striking agreement with diagnostics of baroclinic growth rates in the troposphere associated with midlatitude winter storm tracks and the climatology of the midlatitude jet this correlation suggests that these features of the stratospheric gravity wave field are controlled by geographical variations of tropospheric nonorographic gravity wave sources in winter storm tracks spontaneous adjustment emission from the midlatitude winter jet frontogenesi

observations and simulations of a large amplitude mountain wave breaking over the antarctic peninsula 1 a case study of a large amplitude orographic gravity wave occurring over the antarctic peninsula is presented based on observations from the vorcore balloon campaign and on mesoscale numerical simulations the vorcore campaign september 2005 to february 2006 consisted in the flight of 27 superpressure balloons in the core of the southern hemisphere stratospheric polar vortex at altitudes of 16 19 km from september 2005 to february 2006 on 7 october 2005 one of the balloons exploded as it was flying above the antarctic peninsula the observations collected by another balloon that was flying during the same time period above the peninsula suggest the presence of a very intense gravity wave peak to peak amplitude of the order of 25 30 m s 1 in zonal and meridional velocity disturbances the wave packet is likely undersampled in the balloon observations because of its high intrinsic frequency but the balloon data set is complemented with high resolution numerical simulations carried out with the weather research and forecast model the simulations are validated by comparison with the balloon measurements and show that the wave was breaking in the lower stratosphere at the time and height where the balloon exploded the simulations highlight several consequences of the mountain wave on the stratosphere forcing of the mean flow generation of secondary inertia gravity waves and turbulence and mixing in particular the momentum fluxes are calculated and are found to compare well with the estimates from balloon measurements the large values found are likely extreme values which raises the issue of their representativity to discuss this the balloon measurements are used in conjunction with operational analyses to estimate the frequency of such large amplitude gravity waves i e to provide an estimate of their intermittency

large amplitude gravity waves above the southern andes the drake passage and the antarctic peninsula 1 above the southern andes range and its prolongation in the antarctic peninsula large amplitude mountain and shear gravity waves observed with weather research and forecasting wrf mesoscale model simulations during winter 2009 are analyzed two specific reasons motivated this study 1 a decade of satellite observations of temperature fluctuations in the stratosphere allowing us to infer that this region may be launching the largest amplitude gravity waves into the upper atmosphere and 2 the recent design of a research program to investigate these features in detail the southern andes antarctic gravity wave initiative saangria the simulations are forced with era interim data from the european centre for medium range weather forecasts the approach selected for the regional downscaling is based on consecutive integrations with weekly reinitialization with 24 h of spin up and the outputs during this period are excluded from the analysis from 1 june to 31 august 2009 five case studies were selected on the basis of their outstanding characteristics and large wave amplitudes in general one or two prevailing modes of oscillation are identified after applying continuous wavelet transforms at constant pressure levels and perpendicularly to the nominal orientation of the dominant wave crests in all cases the dominant modes are characterized by horizontal wavelengths around 50 km their vertical wavelengths depending on a usually strong background wind shear are estimated to be between 2 and 11 km the corresponding intrinsic periods range between 10 and 140 min in general the estimated vertical wavelength intrinsic period maximizes minimizes around 250 300 hpa the synoptic circulation for each case is described zonal and meridional components of the vertical flux of horizontal momentum are shown in detail for each case including possible horizontal wavelengths between 12 and 400 km large values of this flux are observed at higher pressure levels decreasing with increasing height after a progressive deposition of momentum by different mechanisms as expected in the wintertime upper troposphere and lower stratosphere in this region a prevailing zonal component is negative almost everywhere with the exception of one case above the northern tip of the antarctic peninsula a comparison with previous experimental results reported in the region from in situ and remote sensing measurements suggests a good agreement with the momentum flux profiles computed from the simulations partial wave reflection near the tropopause was found as considerable departures from equipartition between potential and kinetic wave energy are obtained in all cases and at all pressure levels this ratio was always less than 1 below the lower stratosphere

the gravity wave response above deep convection in a squall line simulation abstract high frequency gravity waves generated by convective storms likely play an important role in the general circulation of the middle atmosphere yet little is known about waves from this source this work utilizes a fully compressible nonlinear numerical two dimensional simulation of a midlatitude squall line to study vertically propagating waves generated by deep convection the model includes a deep stratosphere layer with high enough resolution to characterize the wave motions at these altitudes a spectral analysis of the stratospheric waves provides an understanding of the necessary characteristics of the spectrum for future studies of their effects on the middle atmosphere in realistic mean wind scenarios the wave spectrum also displays specific characteristics that point to low physical mechanisms within the storm responsible for their forcing understanding these forcing mechanisms and the properties of the storm and atmosphere that control them are crucial first steps toward developing

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

orographic wave drag over the southern ocean a linear theory perspective abstractrecent studies suggest that stratospheric wind biases in global and climate models in the southern hemisphere may result from insufficient orographic wave drag particularly over the southern ocean in the latitude belt centered near 60 s in this study contributions to the stratospheric wave drag along 60 s from three neighboring orographic wave sources are evaluated using a multiple layer linear wave model with large scale wind and stratification profiles derived from the interim ecmwf re analysis era interim between the years 1991 and 2010 the orographic wave sources include the patagonian peaks in the southern andes the antarctic peninsula and the island of south georgia the climatological and dynamical aspects of the wave drag and its dependence on tropospheric winds are investigated the results suggest that these orographic wave sources may have significant contributions to the stratospheric drag over the southern ocean through meridional spreading of the wave momentum flux aloft assoc

sensitivity of mesoscale gravity waves to the baroclinicity of jet front systems abstract this study investigates the sensitivity of mesoscale gravity waves to the baroclinicity of the background jet front systems by simulating different life cycles of baroclinic waves with a high resolution mesoscale model four simulations are made starting from two dimensional baroclinic jets having different static stability and wind shear in order to obtain baroclinic waves with significantly different growth rates in all experiments vertically propagating mesoscale gravity waves are simulated in the exit region of upper tropospheric jet streaks a two dimensional spectral analysis demonstrates that these gravity waves have multiple components with different wave characteristics the short scale wave components that are preserved by a high pass filter with a cutoff wavelength of 200 km have horizontal wavelengths of 85 161 km and intrinsic frequencies of 3 11 times the coriolis parameter the medium scale waves that are preserved by a bandpass filter with 200 and 600 km cutoff wavelengths ha

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

observation and analysis of a large amplitude mountain wave event over the antarctic peninsula 1 we use measurements from the atmospheric infrared sounder airs on the aqua satellite to observe the 3 dimensional structure of a gravity wave event over the antarctic peninsula and determine the horizontal and vertical wavelengths propagation direction and temperature amplitude and from these we estimate wave momentum flux using theoretical knowledge of the weighting functions and radiative transfer for airs radiance measurements at temperature sensitive channels in the infrared we derive a method of estimating wave temperature amplitude directly from the radiance measurements comparison of the radiance based temperature amplitudes to the temperature amplitude in airs retrieved temperature fields shows close agreement because the radiances have 3 times better horizontal resolution than the retrievals our analysis suggests we can routinely observe important geophysical properties of waves with horizontal wavelengths as short as 80 km using airs radiances we further analyze a nearly identical wave event appearing in the european centre for medium range forecasts ecmwf temperature and wind fields from both assimilation and forecast data analysis of the ecmwf data and nearby radiosonde wind profiles allows the interpretation as a mountain wave event forced by flow over the topography of the antarctic peninsula

three dimensional characteristics of stratospheric mountain waves during t rex abstract measurements from the national science foundation national center for atmospheric research nsf ncar gulfstream v g v obtained during the recent terrain induced rotor experiment t rex indicate marked differences in the character of the wave response between repeated flight tracks across the sierra nevada which were separated by a distance of approximately 50 km observations from several of the g v research flights indicate that the vertical velocities in the primary wave exhibited variations up to a factor of 2 between the southern and northern portions of the racetrack flight segments in the lower stratosphere with the largest amplitude waves most often occurring over the southern flight leg which has a terrain maximum that is 800 m lower than the northern leg multiple racetracks at 11 7 and 13 1 km altitudes indicate that these differences were repeatable which is suggestive that the deviations were likely due to vertically propagating mountain waves that varied systematically in am

the effect of varying the source spectrum of a gravity wave parameterization in a middle atmosphere general circulation model climate simulations of the middle atmosphere circulation with general circulation models are now starting to include parameterizations of the momentum flux deposition due to unresolved gravity wave spectra a current uncertainty in the application of such parameterizations is the specification of the imposed gravity wave spectrum the aim of this work is to quantify the effect of varying within a realistic range the source spectrum of a gravity wave parameterization in a general circulation model results from two simulations with the gravity wave spectrum launched at two different heights the surface and the 110 hpa pressure level respectively are compared noteworthy differences found in the simulated middle atmosphere response include the following 1 the average temperature in the southern winter upper stratosphere is about 40 k warmer in the experiment with the surface as the launching height virtually eliminating the typical cold polar bias that affects many general circulation models 2 stronger easterlies in the subtropical summer mesosphere again in the experiment with the surface as the launching height diagnostics of the parameterized gravity waves indicate that in the experiment with the surface as the launching height the net zonal momentum flux transported by the gravity waves is negative just above the troposphere at middle latitudes this negative net momentum flux facilitates the deceleration of the mesospheric winter westerlies the meridional circulation induced by such deceleration is thereafter responsible for the substantial polar winter warming in contrast in summer the negative net momentum flux limits the upper mesospheric deceleration of the easterlies in the experiment with launching height at 110 hpa the gravity wave net momentum flux is instead zero by construction at the launching height