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

measurements of gravity wave activity within and around the arctic stratospheric vortex lidar measurements of gravity wave activity have been conducted at eureka in the high arctic since 1993 the waves are detected by the fluctuations they induce in temperature it has been found that the amount of wave energy in the upper stratosphere is related to the position of the stratospheric polar vortex in each of the four winters reported here the wave activity was a maximum within the westerly jet at the edge of the vortex a minimum inside the vortex near its centre and intermediate outside the vortex the spectra of wave induced fluctuations show that it is at the longest resolved vertical wavelengths 8 to 15 km that wave energy is being influenced by the background meteorological conditions these findings are interpreted in terms of the doppler shifting and critical level filtering that is imposed by the background wind profile

the atmosphere of titan an analysis of the voyager 1 radio occultation measurements abstract two coherently related radio signals transmitted from voyager 1 at wavelengths of 13 cm s band and 3 6 cm x band were used to probe the equatorial atmosphere of titan the measurements were conducted during the occultation of the spacecraft by the satellite on november 12 1980 an analysis of the differential dispersive frequency measurements did not reveal any ionization layers in the upper atmosphere of titan the resolution was approximately 3 10 3 and 5 10 3 electrons cm 3 near the evening and morning terminators respectively abrupt signal changes observed at ingress and egress indicated a surface radius of 2575 0 0 5 km leading to a mean density of 1 881 0 002 g cm 3 for the satellite the nondispersive data were used to derive profiles in height of the gas refractivity and microwave absorption in titan s troposphere and stratosphere no absorption was detected the resolution was about 0 01 db km at the 13 cm wavelength the gas refractivity data which extend from the surface to about 200 km altitude were interpreted in two different ways in the first it is assumed that n 2 makes up essentially all of the atmosphere but with very small amounts of ch 4 and other hydrocarbons also present this approach yielded a temperature and pressure at the surface of 94 0 0 7 k and 1496 20 mbar respectively the tropopause which was detected near 42 km altitude had a temperature of 71 4 0 5 k and a pressure of about 130 mbar above the tropopause the temperature increased with height reaching 170 15 k near the 200 km level the maximum temperature lapse rate observed near the surface 1 38 0 10 k km corresponds to the adiabatic value expected for a dry n 2 atmosphere indicating that methane saturation did not occur in tbis region above the 3 5 km altitude level the lapse rate dropped abruptly to 0 9 0 1 k km and then decreased slowly with increasing altitude crossing zero at the tropopause for the n 2 atmospheric model the lapse rate transition at the 3 5 km level appears to mark the boundary between a convective region near the surface having the dry adiabatic lapse rate and a higher stable region in radiative equilibrium in the second interpretation of the refractivity data it is assumed instead that the 3 5 km altitude level corresponds to the bottom of a ch 4 cloud layer and that n 2 and ch 4 are perfectly mixed below this level these assumptions lead to an atmospheric model which below the clouds contains about 10 ch 4 by number density the temperature near the surface is about 95 k arguments concerning the temperature lapse rates computed from the radio measurements appear to favor models in which methane forms at most a limited haze layer high in the troposphere

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

titan s planetary boundary layer structure at the huygens landing site 1 huygens atmospheric structure instrument hasi for the first time performed an in situ measurement of the thermal structure in titan s atmosphere with a vertical resolution sufficient to analyze the planetary boundary layer pbl the vertical potential temperature profile reveals the presence of a weakly convective pbl with a surface layer thickness of 10 m and an outer layer with a depth of 300 m with a mean eddy diffusivity of only 7 4 10 3 m2 s 1 the turbulence in the pbl is weak the turbulent heat flux in the surface layer was upward but tiny 0 02 w m 2 indicating that the ground surface was marginally warmer than the air the surface heat flux is too small to cause a diurnal variation of the pbl except in the lowest few meters so the observed profile may be a nearly steady state feature within this season at the landing site in the surface layer the mean wind speed is likely to be less than 0 1 m s 1 given the tiny surface heat flux the buoyant production of turbulence is very weak the pbl structure reveals that the weather condition at the time and place of the huygens landing resembles a calm overcast day on earth but is clearly different from the pbl typical for the polar night

global gravity wave variances from aura mls characteristics and interpretation abstract the gravity wave gw resolving capabilities of 118 ghz saturated thermal radiances acquired throughout the stratosphere by the microwave limb sounder mls on the aura satellite are investigated and initial results presented because the saturated optically thick radiances resolve gw perturbations from a given altitude at different horizontal locations variances are evaluated at 12 pressure altitudes between 21 and 51 km using the 40 saturated radiances found at the bottom of each limb scan forward modeling simulations show that these variances are controlled mostly by gws with vertical wavelengths z 5 km and horizontal along track wavelengths of y 100 200 km the tilted cigar shaped three dimensional weighting functions yield highly selective responses to gws of high intrinsic frequency that propagate toward the instrument the latter property is used to infer the net meridional component of gw propagation by differencing the variances acquired from ascending a and descending d o

radio science measurements of atmospheric refractivity with mars global surveyor received 9 november 20u5 revised 10 january 2006 accepted 27 january 20u6 published 19 may 2006 1 radio occultation experiments with mars global surveyor measure the refractive index of the martian atmosphere from the surface to 250 km in geopotential height refractivity is proportional to neutral density at low altitudes and electron density at high altitudes with a transition at 75 km we use weighted least squares to decompose zonal refractivity variations into amplitudes and phases for observed wave numbers k 1 4 over the entire altitude range and use the results to analyze atmospheric structure and dynamics the data set consists of 147 refractivity profiles acquired in december 2000 at summer solstice in the martian northern hemisphere the measurements are at an essentially fixed local time sunrise and at latitudes from 67 to 70 n thermal tides appear to be responsible for much of the observed ionospheric structure from 80 to 220 km tides modulate the neutral density which in turn controls the height at which the ionosphere forms the resulting longitude dependent vertical displacement of the ionosphere generates distinctive structure in the fitted amplitudes particularly at k 3 within 50 km of the electron density peak height our k 3 observations are consistent with an eastward propagating semidiurnal tide with zonal wave number 1 relative to previous results our analysis extends the characterization of tides to altitudes well above and below the electron density peak in the neutral atmosphere refractivity variations from the surface to 50 km appear to arise from stationary rossby waves upon examining the full vertical range stationary waves appear to dominate altitudes below 75 km and thermal tides dominate altitudes above this transition region

a global morphology of gravity wave activity in the stratosphere revealed by the gps occultation data gps met using temperature profiles obtained by the gps met gps meteorology experiment from april 1995 to february 1997 we have extracted mesoscale temperature perturbations with vertical wavelengths ranging from 2 to 10 km and background brunt vaisala frequency squared n2 for each occultation event we can evaluate a potential energy ep which is assumed to be caused by atmospheric gravity waves the monthly mean values of ep at 15 20 km around japan showed an annual variation with an enhancement in winter which is consistent with the climatological behavior of the kinetic energy of gravity waves observed with the mu middle and upper atmosphere radar 34 9 n 136 0 e from 1985 to 1989 we have then derived the global distribution of ep at 20 30 km during northern hemisphere winter from november to february our analysis shows that the largest ep values are generally centered around the equator between 25 n and 25 s with considerable longitude variations longitudinal variations of ep at 20 30 km in a latitude range of 30 60 n are also analyzed resulting in larger ep values over the continents than over the pacific ocean using gps met data without antispoofing latitudinal variations of ep are determined in 15 45 km although large ep values are concentrated near the equator at 20 30 km ep tends to become larger at midlatitudes at 30 40 km and higher altitude regions at midlatitudes ep is found to be larger in winter months in both hemispheres height variations of ep indicate a decrease at 25 30 km and a monotonic increase above 30 km

satellite observations of atmospheric variances a possible indication of gravity waves the microwave limb sounder mls on the upper atmosphere research satellite has now produced the first global maps of small scale variances in the middle atmosphere initial analyses are presented here that suggest these variances are due to gravity waves and the technique used to extract gravity wave information from saturated radiance measurements is described observations at 30 80km altitudes show that the variances of horizontal scales less than 100km are strongly correlated with upper tropospheric convection surface topography and stratospheric jetstreams mls monthly averages during solstice periods suggest that the normalized variance amplitude grows exponentially with height in the stratosphere and saturates in the mesosphere as expected from wave breaking and dissipation at these altitudes

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

two boundary layers in titan s lower troposphere inferred from a climate model saturn s moon titan has a dense atmosphere but its thermal structure is poorly understood simulations with a three dimensional general circulation model suggest that titan has a lower atmospheric structure with two boundary layers a seasonal deep layer and a shallower one that develops during the course of each day

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 study of the dynamics of the equatorial lower stratosphere by use of ultra long duration balloons 2 gravity waves in the late southern winter of 1998 centre national d etudes spatiales cnes the french space agency released six 10 m diameter superpressure balloons from a location near quito ecuador three balloons collapsed soon after launching but the remaining three drifted westward for a few weeks at altitudes between 19 and 20 km two of those balloons crossed the pacific ocean before falling above the maritime continent while the other completed a revolution around the earth and crossed the pacific for a second time before its final fall despite the small number and the relatively short duration of the flights the balloons provided a unique in situ data set for the lower equatorial stratosphere this part 1 of a two part paper describes this data set and analyzes outstanding features in the planetary scales part 2 focuses on gravity wave scale it is argued that balloon trajectories over the pacific are primarily determined by the westward drift during the easterly phase of the equatorial quasi biennial oscillation qbo and the meridional velocity field of a mixed rossby gravity yanai wave with an apparent period of 4 days and zonal wave number 4 this wave appears to have two episodes of amplification during the balloon flights it is also argued that the balloons show evidence of oscillations with periods between 2 and 4 days and of a kelvin wave with an apparent period close to 10 days and zonal wave number 1 in this way the balloon behavior provided a pictorial view of air parcel trajectory in the equatorial lower stratosphere it is stated that larger balloon campaigns can provide excellent in situ data sets for studies on the dynamics and composition of the middle atmosphere

observations of intermediate scale diurnal waves in the equatorial mesosphere and lower thermosphere 1 the purpose of this study is to seek observational evidence for diurnal vertically propagating inertia gravity waves igws in the mesosphere and lower thermosphere mlt numerical modeling studies indicate that vertically propagating igws excited by tropical heating provide a significant source of momentum for the semiannual oscillation sao in the equatorial zonal mean winds the power spectrum of these waves has a strong diurnal component we analyze global patterns of ascending and descending node differences in mlt satellite temperatures which are assumed in this study to be proxies for waves of diurnal period juxtaposed upon the planetary scale features are localized variations with longitudinal wavelengths ranging from 25 to 50 and with vertical wavelengths between 13 and 25 km these intermediate scale variations are spatially coherent and persist for several weeks their amplitudes generally increase with altitude while their phase structures suggest both eastward and westward propagation the variance of wave numbers 9 17 in the mlt is examined in relation to the underlying stratospheric zonal mean zonal gradient winds stronger variances generally coincide with periods where the underlying zonal mean winds are relatively light or unidirectional the weak inverse association between variance strength and zonal wind magnitude is suggestive of a wave filtering mechanism

a study of mesoscale gravity waves over the north atlantic with satellite observations and a mesoscale model satellite microwave data are used to study gravity wave properties and variabilities over the northeastern united states and the north atlantic in the december january periods the gravity waves in this region found in many winters can reach the stratopause with growing amplitude the advanced microwave sounding unit a amsu a observations show that the wave occurrences are correlated well with the intensity and location of the tropospheric baroclinic jet front systems to further investigate the cause s and properties of the north atlantic gravity waves we focus on a series of wave events during 19 21 january 2003 and compare amsu a observations to simulations from a mesoscale model mm5 the simulated gravity waves compare qualitatively well with the satellite observations in terms of wave structures timing and overall morphology excitation mechanisms of these large amplitude waves in the troposphere are complex and subject to further investigations

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

two day wave observations of uars microwave limb sounder mesospheric water vapor and temperature 1 a two day wave disturbance is observed in the mesospheric temperature and water vapor on the basis of new version data from the upper atmosphere research satellite microwave limb sounder using two data segments during the austral summers january february of 1992 and 1993 and the asynoptic mapping method a strong wave signal is identified as having zonal wave number 3 and a westward period of about 2 1 days the wave amplitudes are located near the core of the summer easterly jet with strongest wave amplitudes as large as 11 k and 0 35 part per million by volume near the mesopause the temperature and water vapor wave strengths are highly correlated in time but their peaks are almost longitudinally out of phase poleward heat flux associated with upward wave energy propagation in the southern hemisphere points to baroclinic instability as the cause for the wave appearance a growing wave signature in water vapor is observed in regions of strong meridional gradient of water vapor near the mesopause wave breaking is suggested as moist polar air is displaced into the much drier subtropics and wave amplitude decays

gravity wave variance in lims temperatures part i variability and comparison with background winds abstract small scale features in temperature data from the limb infrared monitor of the stratosphere satellite experiment are isolated by subtracting profiles of globally mapped temperatures containing zonal waves 0 6 from inverted temperature profiles these features are interpreted as internal gravity waves the preponderance of the variance is associated with the longest wavelengths corresponding to the lowest frequencies inertio gravity waves the data include approximately 2000 daily soundings between late october 1978 and late may 1979 all longitudes latitudes from about 65 s to 85 n and altitudes from the tropopause to the middle mesosphere pressures from 100 to 0 1 mb zonal mean gravity wave variance is compared with background winds and variance maps are presented for five one week periods early november early january early february late march and early may time height plots of zonal mean wave variance and background winds in the latitude bands 45 55 s 5 s 5 n and 45 55 n ar

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

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

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

evolution of the bangong nujiang tethyan ocean insights from the geochronology and geochemistry of mafic rocks within ophiolites abstract the bangong nujiang suture zone bnsz is located in the central tibetan plateau and represents the relict of the bangong nujiang tethyan ocean bnto this paper presents zircon u pb ages and whole rock geochemical and sr nd isotope data for the ophiolitic rocks from the rutog dongco dongqiao amdo and dengqen areas from west to east in the bnsz zircon u pb ages obtained from five gabbros and one leucogabbro from the five areas are 169 2 167 2 187 2 184 2 177 3 and 164 2 ma respectively mafic rocks gabbros and basalts in the bnsz can be divided into morb like and oib type based on geochemical data the morb like rocks are tholeiitic and can be further divided into n and e morb subtypes marked by depleted and flat ree patterns respectively all morb like rocks show supra subduction zone ssz geochemical affinities such as mild enrichment in the large ion lithophile elements and depletion in the high field strength elements coupled with high and positive whole rock e nd t values 8 1 to 5 4 the oib type rocks which formed in the early cretaceous 132 108 ma are exposed in the dongco dongqiao and tarenben areas and they consist mostly of alkali basalts with within plate geochemical characteristics and positive e nd t values 5 9 to 4 5 on the basis of these new data combined with information from the literature we further support that the bnto was an intra oceanic arc backarc basin that existed between the north lhasa subterrane nlt and the south qiangtang subterrane sqt during the early middle jurassic this basin may have been active until the early cretaceous when the oib type basalts erupted

effects of tropospheric wind shear on the spectrum of convectively generated gravity waves abstract the authors examine the effects of tropospheric wind shear on the phase speed spectrum of gravity waves generated by tropical convection a two dimensional cloud resolving model is used to perform numerous squall line simulations with the vertical shear of the horizontal wind varied in three layers of the troposphere several simplified simulations using prescribed heating are also performed to elucidate the interactions of wind shear with thermal forcing it is found that the dominant phase speed range of convectively generated stratospheric gravity waves is primarily determined by the vertical scale of the tropospheric heating and is then modified by the tropospheric wind the gravity wave spectrum is especially sensitive to shear in the upper troposphere through a mechanism similar to critical level filtering such shear acts to reduce the momentum flux of waves propagating in the same direction as the storm relative mean wind through interaction with convective turrets shear in the upper t

global distribution of ct2 at altitudes 30 50 km from space borne observations of stellar scintillation 1 locally isotropic turbulence in the stratosphere consists of isolated sporadic patches with random values of temperature structure characteristic ct2 stellar scintillations measured aboard gomos envisat through the earth atmosphere provided the first global distribution of the effective characteristic ct eff2 averaged along sounding ray for zonal mean the largest values are achieved in winter polar regions this observed intense turbulence is probably related to the polar night jet relatively weak turbulence is observed at low latitudes turbulence intensity map is shown for altitude 42 km in the latitude band 35 where the maxima follow the sub solar latitude with enhancements located mainly over continents turbulence enhancements are not related with orography despite a noticeable correlation with typical regions of deep convection the overall distribution of ct eff2 displays a more complicated structure analyzed data suggest that the main turbulence sources at altitudes 40 km are instabilities of stratospheric circulation and gravity wave breaking

mls observations of atmospheric gravity waves over antarctica 1 stratospheric gravity waves over antarctica are studied with the radiance variances observed by upper atmosphere research satellite microwave limb sounder uars mls strong wave activities are found during august and september in 1992 1994 over the drake passage region 290 315 longitude and 50 s 70 s latitude where the enhancement seems associated with the topography of both south america and antarctic peninsula tips during the same period significant gravity wave activities are also evident along the antarctic coastal region the vertical growth of the wave variance shows a scale height of 14 km at low altitudes for both drake passage and the coastal regions but reduces substantially at high altitudes the growth rate transition occurs at a lower altitude in the drake passage region where the variance is larger the gravity wave activities observed near the antarctic may contribute significantly to the formation of polar stratospheric clouds psc because of the overlapping with the vortex edge and with the psc activities as observed by claes cryogenic limb array etalon spectrometer

tectonic environment and geodynamic significance of the neo cimmerian donqiao ophiolite bangong nujiang suture zone tibet the bangong nujiang suture zone is underlain by a discontinuous and roughly ew ophiolite belt around donqiao gyanco ophiolitic and metasedimentary palaeozoic series form nappes thrusted over jurassic flysch series all these series have undergone a late symmetrical folding accompanied by generally northward reverse faulting although strongly dismembered a complete ophiolitic sequence comprising harzburgites with large podiform type chromite deposits wehrlites cumulate gabbros sheeted dolerite dykes foliated garnet bearing amphibolites and pillow lavas has been found

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

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

global distribution of atmospheric waves in the equatorial upper troposphere and lower stratosphere agcm simulation of sources and propagation 1 the global distribution sources and propagation of atmospheric waves in the equatorial upper troposphere and lower stratosphere were investigated using an atmospheric general circulation model with t106l60 resolution 120 km horizontal and 550 m vertical resolution the quasibiennial oscillation qbo with a period of 1 5 2 years was simulated well without gravity wave drag parameterization the zonal wave number versus the frequency spectra of simulated precipitation represent realistic signals of convectively coupled equatorial trapped waves eqws the temperature spectra in the stratosphere also indicate dominant signals of eqws eqws with equivalent depths in the range of 8 90 m from the n 1 mode to n 2 mode were extracted separately each eqw in the stratosphere generally corresponded well with the source of each convectively coupled eqw activity in the troposphere the propagations of kelvin waves and n 0 eastward westward propagating eqws are strongly influenced by the walker circulation and the phase of the qbo potential energy associated with eqws is generally larger in the westerly than in the easterly shear phase of the qbo eqws with vertical wavelengths 7 km contribute up to 30 of total potential energy 7 km over the equator at an altitude of 20 30 km gravity waves generated by cumulus convection with periods 24 h are clearly visible over areas of africa the amazon and around indonesia and result in localized pe distributions in areas short distances from the source region comparisons of the model results and recent satellite observations are discussed

synoptic scale study of the arctic polar vortex s influence on the middle atmosphere 1 observations 1 we present nightly rayleigh lidar temperature measurements of the high latitude middle atmosphere taken at three arctic sites over similar time periods in midwinter the four reported case studies depict changes in the thermal structure of the stratosphere and lower mesosphere over a period of days to weeks that can be attributed to movement and interaction of the polar vortex the aleutian high and planetary waves as evidenced from the national center for environmental prediction tropospheric and stratospheric analyses in cases where substantial i e large horizontal scale movement of the vortex is observed it is noted that regional middle atmospheric arctic temperatures can change by tens of degrees in other cases we show that even very subtle i e small horizontal scale movement of the vortex system over similar timescales can result in notable temperature changes in the regional middle atmosphere it appears that the observed events are dependant on the location strength and structure of the polar vortex and aleutian high all of these synoptic scale measurements indicate a change in the local dynamical structure of the middle atmosphere and are discussed in regards to this issue

quasi biennial oscillation in vertical velocity inferred from trace gas data in the equatorial lower stratosphere vertical velocity variations associated with the quasi biennial oscillation qbo in the equatorial lower stratosphere are investigated with the halogen occultation experiment haloe data from 1993 to 1998 the vertical velocity is inferred from ascent rates of an annual cycle in total water h2o 2 ch4 profiles around the 20 60 hpa layer over the equator the zonally averaged ascent rates of total water anomalies exhibit qbo related variations with anomalies of 0 10 0 15 mm s 1 between 20 and 40 hpa at the equator whereas there scarcely exists an annual cycle in the ascent rates the qbo variation of the ascent rates shows that its positive anomalies precede negative anomalies of temperature and ozone variations by about 2 3 months at the equator and 30 60 hpa this phase relationship is in conflict with former results from several two dimensional model studies which have reported that vertical velocity variations are almost out of phase with temperature anomalies preceding ozone anomalies by a few months it is supposed that these differences could be caused by the observed large tendency of temperature anomalies which is related to the observed rapid acceleration of the qbo westerly an estimate of vertical advection of zonal momentum expected from the ascent rates suggests that the asymmetric acceleration of the zonal wind qbo can be explained by the qbo induced vertical velocity being asymmetric between the easterly and the westerly shear zones

global measurements of stratospheric mountain waves from space temperatures acquired by the cryogenic infrared spectrometers and telescopes for the atmosphere crista during shuttle mission sts 66 have provided measurements of stratospheric mountain waves from space large amplitude long wavelength mountain waves at heights of 15 to 30 kilometers above the southern andes mountains were observed and characterized with vigorous wave breaking inferred above 30 kilometers mountain waves also occurred throughout the stratosphere 15 to 45 kilometers over a broad mountainous region of central eurasia the global distribution of mountain wave activity accords well with predictions from a mountain wave model the findings demonstrate that satellites can provide the global data needed to improve mountain wave parameterizations and hence global climate and forecast models

occurrence characteristics of medium scale gravity waves observed in oh and oi nightglow over adelaide 34 5 s 138 5 e 1 this paper presents a 7 year climatology describing medium scale gravity waves observed in the menopause region covering the years from 1995 to 2001 the data comes from the oi and oh airglow observations of the three field photometer employed at the university of adelaide s buckland park australia 34 5 s 138 5 e about 1300 gravity wave events agw are identified during the years 1995 2001 these agw events usually persist for between 40 min and 4 hours the magnitudes range from 1 to 14 of the background intensities and peak at 2 for oi observations and at 3 for oh observations the observed periods range from 10 to 30 min and the horizontal phase speeds range from 20 to 250 m s 1 with dominant wave scales of 17 min 70 m s 1 for oi observations and 20 min 40 m s 1 for oh observations the intrinsic parameters are obtained by using medium frequency mf wind data observed at the same place the occurrence frequency of agw events peaks at 13 min 40 m s 1 for both oi and oh observations the occurrence rate of gravity waves has a major peak in summer and a minor peak in winter there is an obvious dominating southeastward direction for gravity waves with azimuths of 160 in summer and 130 in winter studies for gravity waves observed in various locations show a similar tendency of propagating meridionally toward the summer pole this implies that the tendency of propagating toward the summer pole may be a global trend for medium scale gravity waves observed in the mesopause region during summer gravity waves propagate against winds measured by mf radar in their dominating direction using the ray tracing method we found that the seasonal variation of winds limits the access of gravity waves to the observation height through reflection and critical coupling which is one of the causes leading to the seasonal behavior of gravity waves observed over adelaide

the structure and dynamics of titan s middle atmosphere titan s middle atmosphere is characterized by cyclostrophic winds and strong seasonal modulation cassini cirs observations obtained in northern winter indicate that the stratosphere near 1mbar i

late jurassic adakitic granodiorite in the dong co area northern tibet implications for subduction of the bangong nujiang oceanic lithosphere and related accretion of the southern qiangtang terrane abstract in this paper we present new major and trace element chemical data zircon u pb age data and zircon hf isotopic compositions for the dong co granodiorites dgs that were emplaced directly in the dong co ophiolites dos in the middle segment of the bangong nujiang suture zone bnsz northern tibet we use these new data to discuss the genesis of the dgs and implications for the evolution of the region the dgs have high contents of sio 2 al 2 o 3 na 2 o and sr high values of mg low contents of yb and y and markedly high sr y ratios indicating an adakitic affinity and we show that they were derived from the partial melting of subducted oceanic crust the dgs contain large numbers of inherited zircons that have similar shapes and peak ages to the detrital zircons in the accretionary wedge graywackes that surround the dgs suggesting that many of these sediments were assimilated during the formation of the dgs five dg samples yield the youngest zircon u pb ages of 155 160 ma indicating that the dgs formed during the late jurassic based on the present results and regional geological data we infer that the bangong nujiang oceanic lithosphere was subducted northwards beneath the southern qiangtang terrane during the formation of a continental arc system during the late jurassic the bangong nujiang oceanic lithosphere retreated rapidly after its initial subduction and the southern qiangtang terrane to the north of the bangong nujiang ocean acquired a massive amount of new oceanic material in the form of an accretionary wedge this wedge which included the dos and the mugagangri group became sufficiently large both in size and width for arc type magmas dgs to develop within it during the late jurassic

comparison of global distributions of zonal mean gravity wave variance inferred from different satellite instruments gravity wave temperature fluctuations acquired by the crista instrument are compared to previous estimates of zonal mean gravity wave temperature variance inferred from the lims mls and gps met satellite instruments during northern winter careful attention is paid to the range of vertical wavelengths resolved by each instrument good agreement between crista data and previously published results from lims mls and gps met are found key latitudinal features in these variances are consistent with previous findings from ground based measurements and some simple models we conclude that all four satellite instruments provide reliable global data on zonal mean gravity wave temperature fluctuations throughout the middle atmosphere

the two titan stellar occultations of 14 november 2003 1 we report the observation of two stellar occultations by titan on 14 november 2003 using stations in the indian ocean southern africa spain and northern and southern americas these occultations probed altitudes between 550 and 250 km 1 to 250 bar in titan s upper stratosphere the light curves reveal a sharp inversion layer near 515 6 km altitude 1 5 bar pressure level where the temperature increases by 15 k in only 6 km this layer is close to an inversion layer observed fourteen months later by the huygens hasi instrument during the entry of the probe in titan s atmosphere on 14 january 2005 fulchignoni et al 2005 central flashes observed during the first occultation provide constraints on the zonal wind regime at 250 km with a strong northern jet 200 m s 1 around the latitude 55 n wind velocities of 150 m s 1 near the equator and progressively weaker winds as more southern latitudes are probed the haze distribution around titan s limb at 250 km altitude is close to that predicted by the global circulation model of rannou et al 2004 in the southern hemisphere but a clearing north of 40 n is necessary to explain our data this contrasts with rannou et al s 2004 model which predicts a very thick polar hood over titan s northern polar regions simultaneous observations of the flashes at various wavelengths provide a dependence of q with q 1 8 0 5 between 0 51 and 2 2 m for the tangential optical depth of the hazes at 250 km altitude

the structure of titan s atmosphere from cassini radio occultations occultations from the prime and equinox missions abstract we present the results of six soundings of the atmosphere of titan by the radio occultation technique using the cassini spacecraft currently in orbit around saturn these occultations occurred during four separate targeted titan encounters in both the prime and equinox missions of cassini over 3 years they cover a wide range of latitude from 75 s to 79 n split so that three soundings are in the northern hemisphere and three are in the southern hemisphere techniques and error analysis are similar to schinder et al 2011 the six temperature altitude profiles presented here are compared to those earlier results of special interest is the sudden cooling observed at altitudes of 80 100 km in the two high northern winter soundings at 74 n and 80 n where the temperature drops by about 10 k over the course of 20 km the northern profiles also exhibit a transition between the troposphere and stratosphere that is much more abrupt than in the south and the northern tropopause temperatures are much cooler

stratospheric trailing gravity waves from new zealand abstractgravity waves are frequently observed in the stratosphere trailing long distances from mid to high latitude topography two such trailing wave events documented over new zealand are exami

global estimates of gravity wave momentum flux from high resolution dynamics limb sounder observations analyzed to derive global properties of gravity waves we describe a wavelet analysis technique that determines covarying wave temperature amplitude in adjacent temperature profile pairs the wave vertical wavelength as a function of height and the horizontal wave number along the line joining each profile pair the analysis allows a local estimate of the magnitude of gravity wave momentum flux as a function of geographic location and height on a daily basis we examine global distributions of these gravity wave properties in the monthly mean and on an individual day and we also show sample instantaneous wave events observed by hirdls the results are discussed in terms of previous satellite and radiosonde observational analyses and middle atmosphere general circulation model studies that parameterize gravity wave effects on the mean flow the high vertical and horizontal resolution afforded by the hirdls measurements allows the analysis of a wider range of wave vertical and horizontal wavelengths than previous studies and begins to show individual wave events associated with mountains and convection in high detail mountain wave observations show clear propagation to altitudes in the mesosphere

wintertime temperature maximum at the subtropical stratopause in a t213l256 gcm 1 a wintertime temperature maximum can be observed at the subtropical stratopause but does not appear in the radiative equilibrium temperature distribution this structure was well simulated using a high resolution general circulation model and examined in detail the stratopause temperature is latitudinally maximized in the winter subtropics because of a strong downwelling of the meridional circulation from summer tropics to winter subtropics passing above the stratopause its strong meridional flow consists of two parts a strong poleward flow in the winter subtropics with nearly vertically aligned contours of absolute angular momentum m and a strong cross equatorial flow toward winter hemisphere above the tropical stratopause with nearly horizontally aligned m contours the strong poleward flow in the winter subtropics is driven by a large eliassen palm e p flux convergence in a small absolute vorticity region the large e p flux convergence is due to extratropical planetary waves and asymmetric inertial instability on the other hand the strong cross equatorial flow is induced along the m contour to satisfy mass continuity with the strong poleward flow in the winter subtropics and exists in the easterly phase of s sao with a small latitudinal gradient of m the easterly of s sao during its mature phase acts as a corridor for cross equatorial meridional circulation while cross equatorial meridional circulation contributes to driving the easterly of s sao in its development phase

the structure of titan s atmosphere from cassini radio occultations abstract we present results from the two radio occultations of the cassini spacecraft by titan in 2006 which probed mid southern latitudes three of the ingress and egress soundings occurred within a narrow latitude range 31 34 s near the surface and the fourth at 52 8 s temperature altitude profiles for all four occultation soundings are presented and compared with the results of the voyager 1 radio occultation lindal g f wood g e hotz h b sweetnam d n eshleman v r tyler g l 1983 icarus 53 348 363 the hasi instrument on the huygens descent probe fulchignoni m et al 2005 nature 438 785 791 and cassini cirs results flasar f m et al 2005 science 308 975 978 achterberg r k conrath b j gierasch p j flasar f m nixon c a 2008b icarus 194 263 277 sources of error in the retrieved temperature altitude profiles are also discussed and a major contribution is from spacecraft velocity errors in the reconstructed ephemeris these can be reduced by using cirs data at 300 km to make along track adjustments of the spacecraft timing the occultation soundings indicate that the temperatures just above the surface at 31 34 s are about 93 k while that at 53 s is about 1 k colder at the tropopause the temperatures at the lower latitudes are all about 70 k while the 53 s profile is again 1 k colder the temperature lapse rate in the lowest 2 km for the two ingress dawn profiles at 31 and 33 s lie along a dry adiabat except within 200 m of the surface where a small stable inversion occurs this could be explained by turbulent mixing with low viscosity near the surface the egress profile near 34 s shows a more complex structure in the lowest 2 km while the egress profile at 53 s is more stable

crustal sources involved in continental arc magmatism a case study of volcan mocho choshuenco southern chile volcan mocho choshuenco a pleistocene holocene basaltic andesite to dacite shield volcano located at lat 40 s in the southern volcanic zone svz of the andes is built on the thinnest svz continental crust 30 km which consists largely of paleozoic sedimentary and metamorphic rocks and mesozoic plutons sr pb nd and o isotopic ratios of mocho choshuenco lavas 87 sr 86 sr 0 70399 to 0 70422 206 pb 204 pb 18 57 to 18 61 207 pb 204 pb 15 60 to 15 63 208 pb 204 pb 38 45 to 38 57 143 nd 144 nd 0 512787 to 0 512881 18 o 5 8 to 6 8 standard mean ocean water are similar to those of other svz centers and exhibit no correlation with indices of differentiation however incompatible trace element systematics indicate that evolved lavas have been contaminated by crustal plutonic rocks by 5 to 15 rb ba k ba rb la and k la ratios increase with increasing sio 2 content as a result of assimilation of orogenic calc alkalic plutonic rocks enriched in rb and k relative to ba and la xenoliths of plutonic rocks recovered from mocho choshuenco lavas are slightly more radiogenic in 87 sr 86 sr less radiogenic in 143 nd 144 nd and comparable in pb isotopic ratios and they have variable 18 o contents 87 sr 86 sr 0 70482 to 0 70557 206 pb 204 pb 18 60 to 18 64 207 pb 204 pb 15 60 to 15 62 208 pb 204 pb 38 53 to 38 56 143 nd 144 nd 0 512686 18 o 3 3 to 5 5 smow contamination of mocho choshuenco parental magmas by crustal melts with small isotopic contrast imposed little variation on isotopic heterogeneities existing in the parental compositions these heterogeneities probably were produced during magma crust interaction at the crust mantle boundary or in the lower crust

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

mesosphere inversion layers and stratosphere temperature enhancements 1 it has been known for at least 30 years that vertically narrow thermal layers form within the middle atmosphere two types of temperature enhancements the low latitude to midlatitude mesosphere inversion layer mil and the high latitude winter stratosphere temperature enhancement ste have both received much attention within the atmospheric science community because of their unexplained formation mechanisms and potential impacts on the middle atmosphere global circulation numerous experimental numerical and theoretical studies have attempted to explain certain aspects of these respective thermal layers but no one theory consistently and satisfactorily describes all the features observed we present a review of the literature and explicitly propose a classification scheme based on the different formation mechanisms suspected to cause these events for the mil we demonstrate that there are two subtypes the first one is tidally driven and tends to occur above 85 km this mil originates from large amplitude tidal waves propagating into the mesosphere and their subsequent nonlinear interactions with gravity waves which can often create the appearance of a double mil separated by approximately one vertical tidal wavelength 25 km the other subtype of mil is formed by a climatological planetary wave dissipation mechanism that occurs at a zero wind line the dissipation of the planetary wave tends to generate a mesoscale 1000 km inversion layer in the range of 65 80 km these two formation mechanisms explain a host of observed characteristics including the reason behind the downward progression of some mils and not others the different climatological nature of the two forms of mil events and the relative scarcity of mil observations at high latitudes the ste is believed to be generated by an altogether different process namely the nonlinear interaction between the polar vortex and planetary waves aleutian high the induced temperatures typically peak around 40 km and often exceed 300 k generating what appears to be a low hot stratopause when vertical temperature profiles are combined with synoptic analyses one observes that the ste is the consequence of high latitude vortex interactions creating a baroclinic atmosphere i e a downward adiabatic compression induced by an ageostropic flow we summarize the details of the relationship between this feature and sudden stratospheric warmings as well as the potential for in situ gravity wave generation we close with a review of currently unexplained mil ste features and offer new directions for future middle atmosphere thermal layer research

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

the evolution of the bangong nujiang neo tethys ocean evidence from zircon u pb and lu hf isotopic analyses of early cretaceous oceanic islands and ophiolites abstract we conducted in situ u pb analyses of zircons from three basalts and one gabbro from the zhonggang oceanic island one basalt from the zhaga oceanic island and one gabbro from the kangqiong ophiolite all located in the middle segments of the bangong nujiang suture zone of tibetan plateau as well as in situ hf isotope analyses of zircons from one gabbro from the zhonggang oceanic island to constrain the tectonic evolution of the bangong nujiang neo tethys ocean all samples contain numerous inherited zircons and all the zircons contain magmatic oscillatory zoning and have th u ratios exceeding 0 4 moreover the average ree content of these zircons is less than 2000 ppm and they display clear negative eu and variable positive ce anomalies indicating a magmatic origin la icp ms u pb dating of the zircons revealed three clear peaks in the age distribution at 248 255 162 168 and 117 120 ma lu hf isotopic analyses of zircons from the gabbro of the zhonggang oceanic island yielded a 269 ma crust mantle separation age taking into account the regional geology previous data and our new analyses we infer that the middle and western segments of the bangong nujiang neo tethys ocean had initially opened in the late permian 254 269 ma and that the ocean opened substantially between the late permian and the early triassic 248 255 ma in addition we infer that the initiation of subduction of the bangong nujiang neo tethys ocean took place at 162 168 ma which is middle jurassic the 117 120 ma age is the time when the oceanic islands and ophiolites were formed indicating that the bangong nujiang neo tethys ocean was to some extent still open at that time

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

evolving force balance during incipient subduction nearly half of all active subduction zones initiated during the cenozoic all subduction zones associated with active back arc extension have initiated since the eocene hinting that back arc extension may be intimately associated with an interval several tens of myr following subduction initiation that such a large proportion of subduction zones are young indicates that subduction initiation is a continuous process in which the net resisting force associated with forming a new subduction zone can be overcome during the normal evolution of plates subduction initiation is known to have occurred in a variety of tectonic settings old fracture zones transform faults and extinct spreading centers and through polarity reversal behind active subduction zones although occurring within different tectonic settings four known subduction initiation events izu bonin mariana ibm along a fracture zone tonga kermadec along an extinct subduction boundary new hebrides within a back arc and puysegur fiordland along a spreading center were typified by rapid uplift within the forearc followed by sudden subsidence other constraints corroborate the compressive nature of ibm and tonga kermadec during initiation using an explicit finite element method within a two dimensional domain we explore the evolving force balance during initiation in which elastic flexure viscous flow plastic failure and heat transport are all considered in order to tie theory with observation known tectonic settings of subduction initiation are used as initial and boundary conditions we systematically explore incipient compression of a homogeneous plate a former spreading center and a fracture zone the force balance is typified by a rapid growth in resisting force as the plate begins bending reaching a maximum value dependent on plate thickness but typically ranging from 2 to 3 1012 n m for cases that become self sustaining this is followed by a drop in stress once a shear zone extends through the plate the formation of a throughgoing fault is associated with rapid uplift on the hanging wall and subsidence on the footwall cumulative convergence not the rate of convergence is the dominant control on the force balance viscous tractions influence the force balance only if the viscosity of the asthenosphere is 1020 pa s and then only after plate failure following plate failure buoyancy of the oceanic crust leads to a linear increase with crustal thickness in the work required to initiate subduction the total work done is also influenced by the rate of lithospheric failure a self sustaining subduction zone does not form from a homogeneous plate a ridge placed under compression localizes subduction initiation but the resisting ridge push force is not nearly as large as the force required to bend the subducting plate the large initial bending resistance can be entirely eliminated in ridge models explaining the propensity for new subduction zones to form through polarity reversals a fracture zone fz placed in compression leads to subduction initiation with rapid extension of the overriding plate a fz must be underthrust by the older plate for 100 150 km before a transition from forced to self sustaining states is reached in fz models the change in force during transition is reflected by a shift from forearc uplift to subsidence subduction initiation is followed by trench retreat and back arc extension moderate resisting forces associated with modeled subduction initiation are consistent with the observed youth of pacific subduction zones the models provide an explanation for the compressive state of western pacific margins before and during subduction initiation including ibm and tonga kermadec in the eocene and the association of active back arcs with young subduction zones on the basis of our dynamic models and the relative poles of rotation between pacific and australia during the eocene we predict that the northern segment of the tonga kermadec convergent margin would have initiated earlier with a progressive southern migration of the transition between forced and self sustaining states

titan s middle atmospheric temperatures and dynamics observed by the cassini composite infrared spectrometer the composite infrared radiometer spectrometer cirs instrument on the nasa cassini saturn orbiter has been acquiring thermal emission spectra from the atmosphere of titan since orbit insertion in 2004 observation sequences for measuring stratospheric temperatures have been obtained using both a nadir mapping mode and a limb viewing mode the limb observations give better vertical resolution and give information from higher altitudes while the nadir observations provide more complete longitude coverage because the scale height of titan s atmosphere is large enough so that emission from a grazing ray is influenced by horizontal temperature variations in the atmosphere we have developed a twodimensional temperature retrieval algorithm for reducing the limb spectra which solves simultaneously for meridional and vertical temperature variations the analyzed nadir mapping data have sampled nearly all longitudes at latitudes from about 90 st o 60 n providing temperatures between pressure levels of about 5 to 0 2 mbar the limb data covers latitudes between about 75 s and 85 n and yields temperatures between about 1 and 0 005 mbar at a small number of longitudes the retrieved temperatures are consistent with early results from nadir observations flasar f m and 44 colleagues 2005 science 308 975 978 between 0 5 and 5 mbar where both results are valid with the warmest temperatures at the equator and much stronger meridional temperature gradients in the northern winter hemisphere than in the southern at higher altitudes not probed by nadir viewing the limb data reveal that the stratopause is nearly 20 k warmer in the northern polar regions than at the equator and southern hemisphere and that the altitude of the stratopause shifts from 0 1 mbar 300 km near the equator to 0 01 mbar 400 km poleward of about 40 n when the gradient wind equation is used to construct a zonal mean wind the reversal in sign of the temperature leads to capping of the winter westerly flow the core of the resulting jet is about 190 m s 1 in magnitude spans between 30 n and 60 n and peaks near 0 1 mbar estimates of the radiative heating associated with the radiative disequilibrium lead to a meridional overturning timescale of about three earth years

the structure of titan s atmosphere from cassini radio occultations one and two way occultations abstract we present the results of the remaining ten soundings of titan s atmosphere by radio occultations using the cassini spacecraft that have not been previously reported three were in 2008 and 2009 and used the ultra stable oscillator onboard the spacecraft the rest were in 2014 and 2016 after the uso had failed and were executed in two way mode comparison of the later soundings with those earlier in the cassini mission provide an indication of the seasonal change at mid latitudes the southern hemisphere has shown a dramatic cooling during the onset of autumn change in the northern hemisphere is noticeable but more subdued changes at low latitudes are even smaller the additional retrievals from 2008 to 2009 add a better constraint on the latitude structure of the previously reported destabilization of the temperature profiles at northern latitudes during winter and early spring they show that the most pronounced effect is at polar latitudes 70 n suggesting that they are associated with the descending circulation over the winter pole that has been proposed by several authors the full set of occultations indicates minimal variation with latitude and time in the troposphere likely attributable to the large atmospheric radiative damping time and efficient meridional heat transports but somewhat more variation near the surface which has a smaller thermal inertia

jupiter s ionosphere results from the first galileo radio occultation experiment the galileo spacecraft passed behind jupiter on december 8 1995 allowing the first radio occultation measurements of its ionospheric structure in 16 years at ingress 24 s 68 w the principal peak of electron density is located at an altitude of 900 km above the 1 bar pressure level with a peak density of 105 cm 3 and a thickness of 200 km at egress 43 s 28 w the main peak is centered near 2000 km altitude with a peak density of 2 104 cm 3 and a thickness of 1000 km two thin layers possibly forced by upwardly propagating gravity waves appear at lower altitudes in the ingress profile this is the first in a two year series of observations that should help to resolve long standing questions about jupiter s ionosphere

using satellite observations to constrain parameterizations of gravity wave effects for global models abstract small scale gravity waves are common features in atmospheric temperature observations in satellite observations these waves have been traditionally difficult to resolve because the footprint or resolution of the measurements precluded their detection or clear identification recent advances in satellite instrument resolution coupled to innovative analysis techniques have led in the last decade to some new global datasets describing the temperature variance associated with these waves such satellite observations have been considered the best hope for quantifying the global properties of gravity waves needed to constrain parameterizations of their effects for global models although global maps of averaged gravity wave temperature variance have now been published from a variety of different instruments on earth orbiting platforms these maps have not provided the needed constraints the present paper first summarizes what has been learned from traditional temporally and spatially averaged analyse

seasonal variability of vertical eddy diffusivity in the middle atmosphere 1 three year observations by the middle and upper atmosphere radar the vertical eddy diffusivity k due to atmospheric turbulence with spatial scales of 100 102 m has been computed from the echo power spectral width observed by the middle and upper atmosphere radar for almost every month from january 1986 to december 1988 the method of analysis follows lilly et al 1974 sato and woodman 1982 and hocking 1983a 1985 1988 and the contamination due to beam broadening vertical shear and transience has been removed although observations for horizontal wind speeds larger than approximately 40 m s such as occur near the tropopause jet stream in winter have been omitted because of excessive beam broadening sufficient numbers of observations have been accumulated to produce a reasonable climatology for the upper troposphere and lower stratosphere 6 20 km altitude and for the mesosphere 60 82 km altitude the monthly median of k shows a local maximum near the tropopause jet stream altitude it becomes larger in the mesosphere increasing gradually with height maxima of k are observed in winter near the tropopause and in summer in the mesosphere and the seasonal variability of k reaches approximately an order of magnitude a semiannual variability is apparent in the mesosphere with minima in the equinoctial seasons

timed saber observations of global gravity wave climatology and their interannual variability from stratosphere to mesosphere lower thermosphere the present study for the first time reports the global gravity wave activity in terms of their potential energy derived from timed saber observations right from the stratosphere to the mesosphere lower thermosphere mlt region the potential energy profiles obtained from saber temperature are validated by comparing them with ground based lidar observations over a low latitude site gadanki 13 5 n 79 2 e the stratospheric and mesospheric global maps of gravity wave energy showed pronounced maxima over high and polar latitudes of the winter hemisphere the interannual variability of the stratospheric gravity wave activity exhibited prominent annual oscillation over mid latitudes the equatorial gravity wave activity exhibited quasi biennial oscillation in the lower stratosphere and semi annual oscillation in the upper stratosphere the mlt region maps revealed summer hemispheric maxima over polar latitudes and secondary maxima over the equatorial region the results are discussed in the light of present understanding of global gravity wave observations the significance of the present study lies in emphasizing the importance of satellite measurements in elucidating gravity waves which is envisaged to have profound impact on parameterizing these waves

mesospheric temperature inversions as seen by isams in december 1991 a large number of mesospheric temperature inversion layers have been observed locally in recent decades notably by the network of french lidars it is shown in this paper that the improved stratospheric and mesospheric sounder on board the upper atmosphere research satellite is able to detect the presence of temperature inversions and thus allows the study of their occurrence and characteristics on a global scale during december 1991 inversions of large amplitude greater than 20 k are seen almost every day especially in mid latitudes with extent varying typically from 105 to 106 km several particularly large inversions were observed at the end of the month their correlation with assimilated stratospheric winds is consistent with the interpretation that gravity waves propagate unfiltered through the stratosphere in the regions of strong winds and break in the mesosphere the combination of high resolution lidar measurements and global satellite coverage is expected to lead to a better understanding of this significant feature of the winter mesosphere at middle latitudes

can slab melting be caused by flat subduction slab melting has been suggested as a likely source of adakitic arc magmas i e andesitic and dacitic magmas strongly depleted in y and heavy rare earth elements existing numerical and petrologic models however restrict partial melting to very young 5 ma oceanic crust typically at 60 80 km depth paradoxically most of the known pliocene quaternary adakite occurrences are related to subduction of 10 45 ma lithosphere which should not be able to melt under normal subduction zone thermal gradients we propose an unusual mode of subduction known as flat subduction occurring in 10 of the world s convergent margins that can produce the temperature and pressure conditions necessary for fusion of moderately old oceanic crust of the 10 known flat subduction regions worldwide eight are linked to present or recent 6 ma occurrences of adakitic magmas observations from chile ecuador and costa rica suggest a three stage evolution 1 steep subduction produces a narrow calc alkaline arc typically 300 km from the trench above the asthenospheric wedge 2 once flat subduction begins the lower plate travels several hundred kilometers at nearly the same depth thus remaining in a pressure temperature window allowing slab melting over this broad distance and 3 once flat subduction continues for several million years the asthenospheric wedge disappears and a volcanic gap results as in modern day central chile or peru the proposed hypothesis which reconciles thermal models with geochemical observations has broad implications for the study of arc magmatism and for the thermal evolution of convergent margins

a search for mountain waves in mls stratospheric limb radiances from the winter northern hemisphere data analysis and global mountain wave modeling 1 despite evidence from ground based data that flow over mountains is a dominant source of gravity waves gws for the northern hemisphere winter middle atmosphere gw related signals in global limb radiances from the microwave limb sounder mls on the upper atmosphere research satellite uars have shown little direct evidence of mountain waves we address this issue by combining a renewed analysis of mls limb track and limb scan radiances with global mountain wave modeling using the naval research laboratory mountain wave forecast model mwfm mls radiance variances show characteristics consistent with mountain waves such as enhanced variance over specific mountain ranges and annual variations that peak strongly in winter however direct comparisons of mls variance maps with mwfm simulated mountain wave climatologies reveal limited agreement we further develop a detailed mls gw visibility function that accurately specifies the three dimensional in orbit sensitivity of the mls limb track radiance measurement to a spectrum of gws with different wavelengths and horizontal propagation directions on postprocessing mwfm generated mountain wave fields through these mls visibility filters we generate mwfm variance maps that agree substantially better with mls radiance variances this combined data analysis and mls filtered mwfm modeling leads us to conclude that many mls variance enhancements can be associated with mountain waves forced by flow over specific mountainous terrain these include mountain ranges in europe e g scandinavia alps scotland ural putoran altai hangay and sayan mountains yablonovyy stanovoy khingan verkhoyansk and central ranges north america e g brooks range mackenzie mountains colorado rockies southeastern greenland and iceland our results show that given careful consideration of the in orbit sensitivity of the instrument to gws middle atmospheric limb radiances measured from uars mls as well as from the new mls instrument on the earth observing system eos satellite can provide important global information on mountain waves in the extratropical northern hemisphere stratosphere and mesosphere

upper atmosphere research satellite uars mls observation of mountain waves over the andes abstract stratospheric air temperature radiance fluctuations over the andes observed by the upper atmosphere research satellite uars microwave limb sounder mls are presented the mls radiance variances show strong annual variability over the andes mountains in south america which is closely correlated to the background wind conditions associated with mountain wave generation and propagation the variances are significantly larger in southern hemispheric winter when the winds in the troposphere and stratosphere over the andes are both westerly and mountain wave critical levels zerowind lines are absent the annual variation of mls radiance variance agrees well with data from radiosondes and output from the naval research laboratory nrl mountain wave forecast model mwfm over the same region and period the amplitude of the radiance variances seems to correlate well with the intensity of surface wind at upstream positions westward of the andes which is also related to the meridional temperature gradient in the region horizontal scale analysis suggests that mountain waves over the andes might have two preferential horizontal wavelengths at 110 and 400 km

interactions between gravity waves and planetary scale flow simulated by the gfdl skyhi general circulation model abstract in order to study interactions between gravity waves and planetary flow in the middle atmosphere a 3 latitude by 3 6 longitude version of the 40 level gfdl skyhi general circulation model is analyzed using bihourly sampled output data it is shown by a space time spectral analysis that gravity waves in the mean zonal westerlies easterlies mainly consist of westward eastward moving components and carry easterly westerly momentum upward and decelerate the mean zonal westerlies easterlies in the mesosphere zonal momentum flux convergence due to gravity waves accounts for nearly all of the eliassen palm e p flux divergence in the summer mesosphere this convergence accounts for 30 50 of that in the winter upper mesosphere however this percentage is probably an underestimate since the convergence is significantly enhanced in a high resolution 1 1 2 model currently being integrated vertical propagation of gravity waves is affected not only by the mean zonal wind but also

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 forcing in the stratosphere observational constraints from the upper atmosphere research satellite and implications for parameterization in global models 1 global models that include parameterized gravity wave effects have an excessively broad range of tuning parameters to choose from that allow a very broad range of gravity wave momentum forcing distributions we derive a set of constraints on gravity wave characteristics near the tropopause from databased estimates of gravity wave effects in the stratosphere we use 5 6 years of upper atmosphere research satellite data and uk met office analyzed wind and temperature fields to first derive estimates of the gravity wave mean flow forcing in the stratosphere we then compare these estimates to a suite of gravity wave model calculations to infer the constraints on the gravity wave characteristics near the tropopause these constraints apply to the portion of the gravity wave spectrum that dissipates in the stratosphere and does not include those that dissipate and drive the mesosphere we focus on equatorial and extratropical regions separately and find substantially different wave characteristics between the two we also find a seasonal variation in gravity wave characteristics in the extratropics near the equator gravity waves assist in driving the quasibiennial and semiannual oscillations and our constraints on gravity waves likely include a blend of characteristics of both ordinary gravity waves and some kelvin wave modes in the extratropics gravity wave forcing primarily assists in the annual winter to summer transition from westward to eastward winds

combining airs and mls observations for three dimensional gravity wave measurement gravity waves play a critical role in transporting energy and momentum between the troposphere stratosphere and mesosphere satellite measurements provide a powerful tool to investigate these waves across the globe however many present methods cannot yield reliable estimates of wave momentum fluxes or the directions of these fluxes here we present a new method which addresses this problem by combining observations from atmospheric infrared sounder airs and microwave limb sounder mls in three dimensions the method allows direct estimation of horizontal and vertical wavelengths as well as wave amplitude this in turn allows estimation of both wave momentum flux and the full 3 d direction of propagation crucially including the horizontal direction the method thus allows separation of the data into for example eastward and westward momentum fluxes allowing estimation of the net atmospheric forcing due to these waves we illustrate this method with a proof of concept study over the andes arguably the largest source of gravity waves in the world we further critically assess the advantages and disadvantages of our method our study highlights the importance of the difference between net and absolute measures of momentum flux