convectively forced internal gravity waves results from two dimensional numerical experiments two dimensional numerical simulations were performed to investigate the nature of tropospheric internal gravity waves of the type which are observed to occur above active thermal convection over an unstable boundary layer these gravity waves are believed to be excited by a combination of pure thermal forcing and by the boundary layer eddies and cumulus clouds acting as obstacles to the flow in the presence of mean environmental wind shear large amplitude internal gravity waves were obtained in the simulations with amplitudes and horizontal scales similar to the 12 june 1984 aircraft observations over western nebraska this was a day with strong wind shear in the lowest 3 km above the ground and with scattered cumulus clouds topping the boundary layer the simulations show that there is significant difference between the early time solutions as might be predicted by linear theory and late time solutions for the boundary layer eddy structure a layer interaction occurs in which gravity waves of the stable layer are excited by the boundary layer convection there is evidence to suggest that this layer interaction occurs both with and without shear but that it is stronger in the presence of low level shear results indicate that shear or the obstacle effect is a more efficient generator of gravity waves than is the pure thermal forcing the simulations show that the gravity waves initially forced by the boundary layer eddies lead to a feedback mechanism that acts to organize the boundary layer eddies and the cumulus convection the solutions suggest that the character of fair weather convection moist or dry is a non local problem involving at times the full depth of the troposphere the clouds produced in the simulations have very little influence on the wave field or boundary layer eddy structure as they are relatively small cumuli on the other hand the clouds are strongly influenced by the interactions between the wave and eddy fields upshear growth of cumulus clouds similar to that which is frequently observed in nature is reproduced in the simulations the development of feeder feeder is used here in a dynamical sense only clouds on typically the upshear side of the cloud is found to be a result of the interaction between the gravity wave field and the dry and moist convection the relative phase velocity between the gravity waves and the cloud plays a crucial role in determining the character of the cumulus cloud growth in the present simulations these simulations suggest that the dynamics both internal and external to the boundary of a cumulus cloud is a complicated mix between wave dynamics and the usually considered convection dynamics a brief discussion of the implications of the present results to cloud boundary baroclinic instability dynamics is also presented

mjo related intraseasonal variation in the stratosphere gravity waves and zonal winds previous work has shown eastward migrating regions of enhanced temperature variance due to long vertical wavelength stratospheric gravity waves that are in sync with intraseasonal precipitation and tropopause wind anomalies associated with the madden julian oscillation mjo here the origin of these intraseasonal gravity wave variations is investigated with a set of idealized gravity wave resolving model experiments the experiments specifically test whether tropopause winds act to control gravity wave propagation into the stratosphere by a critical level filtering mechanism or play a role in gravity wave generation through an obstacle source effect all experiments use identical convective latent heating variability but the large scale horizontal wind profile is varied to investigate relationships between stratospheric gravity waves and zonal winds at different levels results show that the observed long vertical wavelength gravity waves are primarily sensitive to stratospheric zonal wind variations while tropopause wind variations have only a very small effect thus neither the critical level filter mechanism nor the obstacle source play much of a role in the observed intraseasonal gravity wave variations instead the results suggest that the stratospheric waves follow the mjo precipitation sources and tropopause wind anomalies follow the same sources we further find evidence of intraseasonal wave drag effects on the stratospheric circulation in reanalyzed winds the results suggest that waves drive intraseasonal stratospheric zonal wind anomalies that descend in altitude with increasing mjo phases 3 through 7 eastward anomalies descend further than westward suggesting that mjo related stratospheric waves cause larger eastward drag forces

experimental investigation of controls on cementation in carbonates experiments simulating carbonate diagenesis have been performed using natural oolitic and skeletal sediments in seawater at temperatures of 183 186 c and hydrostatic pressures of 6 10 mpa during the experiments both equant and granular columnar calcite cements were precipitated equant cements developed when both nucleation and growth rates were low due to mg 2 inhibition or to lower rates of caco 3 supply via aragonite dissolution the data show that the mg ca ratio of the pore fluid does not control calcite morphology directly during the experiments but rather the morphology is a function of nucleation and growth rate it is also suggested that the presence of organic matter may aid nucleation of caco 3

observational study of ionospheric irregularities and gps scintillations associated with the 2012 tropical cyclone tembin passing hong kong

rheological properties of water ice applications to satellites of the outer planets 1 abstract the icy moons of the outer solar system have not been quiescent bodies in part because many have a substantial water component and have experienced significant internal heating we can begin to understand the thermal evolution of the moons and the rate of viscous relaxation of surface topography because we now have good constraints on how ice in several of its polymorphic forms flows under deviatoric stress at planetary conditions details of laboratory derived flow laws for pure polycrystalline ice are reviewed in detail one of the more important questions at hand is the role of ice grain size grain size may be a dynamic quantity within the icy moons and it may or may not significantly affect rheology one recent beneficiary of revelations about grain size sensitive flow is the calculation of the rheological structure of europa s outer ice shell which may be no thicker than 20 km

gravity waves generated by a tropical cyclone during the step tropical field program a case study overflights of a tropical cyclone during the australian winter monsoon field experiment of the stratosphere troposphere exchange project step show the presence of two mesoscale phenomena a vertically propagating gravity wave with a horizontal wavelength of about 110 km and a feature with a horizontal scale comparable to that of the cyclone s entire cloud shield wavelength of 250 km or greater the larger feature is fairly steady though its physical interpretation is ambiguous the 110 km gravity wave is transient having maximum amplitude early in the flight and decreasing in amplitude thereafter its scale is comparable to that of 100 to 150 km diameter cells of low satellite brightness temperatures within the overall cyclone cloud shield these cells have lifetimes of 4 5 to 6 hours aircraft flights through the anvil show that these cells correspond to regions of enhanced convection higher cloud altitude and upwardly displaced potential temperature surfaces a three dimensional transient linear gravity wave simulation shows that the temporal and spatial distribution of meteorological variables associated with the 110 km gravity wave can be simulated by a slowly moving transient forcing at the anvil top having an amplitude of 400 600 m a lifetime of 4 5 6 hours and a size comparable to the cells of low brightness temperature the forcing amplitudes indicate that the zonal drag due to breaking mesoscale transient convective gravity waves is definitely important to the westerly phase of the stratopause semiannual oscillation and possibly important to the easterly phase of the quasi biennial oscillation there is strong evidence that some of the mesoscale gravity waves break below 20 km as well the effect of this wave breaking on the diabatic circulation below 20 km may be comparable to that of above cloud diabatic cooling

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

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

a global view of stratospheric gravity wave hotspots located with atmospheric infrared sounder observations 1 the main aim of this study is to find and classify hotspots of stratospheric gravity waves on a global scale the analysis is based on a 9 year record 2003 to 2011 of radiance measurements by the atmospheric infrared sounder airs aboard nasa s aqua satellite we detect gravity waves based on 4 3 m brightness temperature variances our method focuses on peak events i e strong gravity wave events for which the local variance considerably exceeds background levels we estimate the occurrence frequencies of these peak events for different seasons and time of day and use the results to find local maxima or hotspots in addition we use airs radiances at 8 1 m to simultaneously detect convective events including deep convection in the tropics and mesoscale convective systems at middle latitudes we classify the gravity wave sources based on seasonal occurrence frequencies for convection but also by means of time series analyses and topographic data our study reproduces well known hotspots of gravity waves e g the andes and the antarctic peninsula however the high horizontal resolution of the airs observations also allows us to locate numerous mesoscale hotspots which are partly unknown or poorly studied so far most of these mesoscale hotspots are found near orographic features like mountain ranges coasts lakes deserts or isolated islands this study will help to select promising regions and seasons for future case studies of gravity waves

statistics of cold cumulonimbus anvils based on enhanced infrared photographs infrared photographs from the atlantic geosynchronous satellite enhanced to resolve cold anvil temperatures of tropical clouds are analyzed statistically to determine their spatial temporal variability during the nasa u2 flight experiment of 1980 diurnal dependence varies regionally indicating topographic control via low level convergence and release of convective instability anvil growth rates area covered and duration are discussed for individual and merging anvil systems gradients of anvil temperatures implied by infrared photographs are shown to be caused in part by radial decrease in anvil depth i e to emissivities less than 1 an error in cloud top temperature of 10c is caused by 10 reduction in emissivity errors are near zero in dense actively growing portions of the anvil

a model study of gravity waves over hurricane humberto 2001 abstract atmospheric gravity waves are known to influence global circulations understanding these waves and their sources help to develop parameterizations that include their effects in climate and weather forecasting models deep convection is believed to be a major source for these waves and hurricanes may be particularly intense sources simulations of hurricane humberto 2001 are studied using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 humberto is simulated at both tropical storm and hurricane stages fourier transform and wavelet analysis are employed to investigate wave characteristics and their behavior in the lower stratosphere the fourier analysis gives a regional view of storm affects whereas wavelet analysis gives a local picture of isolated events analysis of the movement of convective sources and local winds gives further insight into the mechanisms that can cause gravity waves convectively generated grav

source spectra information derived from u s high resolution radiosonde data 1 a ray tracing model is used to study the climatology of the source properties for gravity waves in the lower stratosphere using 8 years of u s high resolution radiosonde data if the simulated total energy density and zonal momentum flux correlate well with those two parameters derived from the observations simultaneously we claim a best fit is found eighty five stations with sufficient completeness and quality are analyzed and we are able to obtain best fit source spectra for 61 of them two conditions are found to be necessary to achieve a best fit first the kinetic energy density and the zonal momentum flux derived from observations need to be highly correlated second the source altitude needs to be located right below the lower stratosphere since the observed gravity waves represent the average climatology of the cumulative effect on a monthly average basis of the various time varying physical sources together with their propagation from different altitudes all the sources we found are anisotropic with most of momentum flux directed upstream of the dominant wind direction this might be caused by wave propagation effects or the nature of the sources themselves the latitudinal variation of the horizontal wavelength of the source spectra corresponds well with that derived independently from the observations but other variable parameters do not show obvious latitudinal dependence a source spectrum type representing convection works well for lower latitudes while another more general source works better for middle to high latitudes the central u s and the north american monsoon region are two regions where it is difficult to obtain best fit source spectra we suspect that the reason for this is that during the summer mesoscale convective systems are dominant sources for inertia gravity waves which may not be well represented by our chosen spectral source functions

role of gravity waves in triggering deep convection during toga coare the role of gravity waves in the initiation of convection over oceanic regions during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare experiment is investigated first an autocorrelation method is applied to infrared temperature observations of convective events from satellite images it reveals that new deep convective cells often occur a few hours after a previous intense event at a typical distance of a few hundred kilometers such fast moving modes faster than 15 m s 21 are interpreted as the trace of gravity waves excited by previous convection and contributing to trigger further convection second the specific case of 11 12 december 1992 during which an active squall line is generated after the collapse of a previous mesoscale convective system mcs nearby is analyzed with a nonhydrostatic model the triggering of the second mcs is well reproduced explicitly owing to the use of the two way interactive grid nesting the convective source appears to emit pulses of gravity waves on a wide range of small scales on the contrary the troposphere response to the convective source exhibits a spectral simplicity a slowly evolving mode characterized by an ascent in the pbl and a compensating subsidence in the free troposphere favors shallow convection and inhibits deep convection respectively traveling modes propagating away from the convective source are characterized by a fast mode 50 m s21 and a slower mode 25 ms 21 associated with the convective and stratiform development of the source respectively in agreement with previous studies a budget analysis reveals the different factors leading to the deep convection triggering first an active pbl characterized by strong surface fluxes and mean ascent initiates shallow convection lasting about 2 h inhibited above by the subsiding motions maintaining a dry layer second horizontal advection of moist and cooler air at midlevels and detrainment from cumuli contribute to destroy the dry air layer capping the shallow convective layer finally vertical advection induced by the gravity waves passage modulates the vapor and temperature evolution ascending phases favor moistening and cooling whereas subsiding phases stop these effects delaying the deep convection onset the triggering occurs after a strong subsidence when the ascent phases of deep and shallow modes are combined

small scale motions observed by aircraft in the tropical lower stratosphere evidence for mixing and its relationship to large scale flows abstract measurments of temperature and ozone from instrumental aircraft in the tropical lower stratosphere show the presence of small scale disturbances generated by 1 underlying cumulus convection and 2 kelvin helmholtz instability the disturbances associated with underlying convection have peak to peak vertical parcel excursions of 300 m flying conditions were smooth suggesting an ensemble of gravity waves and little or no turbulent mixing it is nevertheless possible that these waves break at other altitudes leading to turbulent mixing and net fluxes of vertically stratified tracers disturbances attributed to kh instability implied vertical parcel excursions of 300 400 m the disturbances coincided with rough flying conditions suggesting turbulent mixing a linear stability analysis of the atmospheric basic state defined by high resolution radiosondes shows fastest growing waves with horizontal wavelengths of 1 4 1 8 km consistent with the aircraft observations the strong shears responsible

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

mineralogical and paramorphic textural changes generated in modern ooids by heat and compaction laboratory duplication of textures previously known only from naturally occurring ooids was accomplished for the first time on heated and experimentally compacted ooids 250 c 364 kg cm 2 crystals of neomorphic calcite developed replacing aragonitic ooids in places the original fabric survived preservation of concentric laminae in ooids during this process indicates absence of an intervening stage of void formation this polymorphic transformation is a wet process and temperature dependent

europa s crust and ocean origin composition and the prospects for life abstract we have considered a wide array of scenarios for europa s chemical evolution in an attempt to explain the presence of ice and hydrated materials on its surface and to understand the physical and chemical nature of any ocean that may lie below we postulate that following formation of the jovian system the europan evolutionary sequence has as its major links a initial carbonaceous chondrite rock b global primordial aqueous differentiation and formation of an impure primordial hydrous crust c brine evolution and intracrustal differentiation d degassing of europa s mantle and gas venting e hydrothermal processes and f chemical surface alteration our models were developed in the context of constraints provided by galileo imaging near infrared reflectance spectroscopy and gravity and magnetometer data low temperature aqueous differentiation from a carbonaceous ci or cm chondrite precursor without further chemical processing would result in a crust ocean enriched in magnesium sulfate and sodium sulfate consistent with galileo spectroscopy within the bounds of this simple model a wide range of possible layered structures may result the final state depends on the details of intracrustal differentiation devolatilization of the rocky mantle and hydrothermal brine reactions could have produced very different ocean crust compositions e g an ocean crust of sodium carbonate or sulfuric acid or a crust containing abundant clathrate hydrates realistic chemical physical evolution scenarios differ greatly in detailed predictions but they generally call for a highly impure and chemically layered crust some of these models could lead also to lateral chemical heterogeneities by diapiric upwellings and or cryovolcanism we describe some plausible geological consequences of the physical chemical structures predicted from these scenarios these predicted consequences and observed aspects of europa s geology may serve as a basis for further analys is and discrimination among several alternative scenarios most chemical pathways could support viable ecosystems based on analogy with the metabolic and physiological versatility of terrestrial microorganisms

model study of intermediate scale tropical inertia gravity waves and comparison to twp ice campaign observations abstracta 2 day inertia gravity wave igw was observed in high resolution radiosonde soundings of horizontal wind and temperature taken during the 2006 tropical warm pool international cloud experiment twp ice experiment in the darwin area the wave was observed in the stratosphere above darwin from 28 january to 5 february a similar wave event is observed in the european centre for medium range weather forecasts ecmwf operational data a comparison between the characteristics of the igw derived with the ecmwf data to the properties of the wave derived with the radiosonde data shows that the ecmwf data capture similar structure for this 2 day wave event but with a larger vertical wavelength a reverse ray tracing method is used to localize the source region using ecmwf data to define the atmospheric background conditions and wave properties observed in the soundings it is found that the 2 day wave event originated from deep convection in the indonesian region around 20 january the weather research

gravity wave momentum flux in the lower stratosphere over convection this work describes a method for estimating vertical fluxes of horizontal momentum carried by short horizontal scale gravity waves lambda sub x 10 100 km using aircraft measured winds in the lower stratosphere we utilize in situ wind vector and pressure altitude measurements provided by the meteorological measurement system mms on board the er 2 aircraft to compute the momentum flux vectors at the flight level above deep convection during the tropical experiment of the stratosphere troposphere exchange project step tropical data from flight 9 are presented here for illustration the vertical flux of horizontal momentum these observations points in opposite directions on either side of the location of a strong convective updraft in the cloud shield this property of internal gravity waves propagating from a central source compares favorably with previously described model results

near tropopause vertical motion within the trailing stratiform region of a midlatitude squall line abstract rawinsonde observations have been used to determine the flow structure in the vicinity of the tropopause atop the trailing stratiform precipitation region of an intense midlatitude squall line computations of vertical motion using the kinematic and thermodynamic methods show i upward motion in the mid to upper troposphere within the stratiform cloud and ii downward motion in a thin layer 2 3 km deep centered near the tropopause at cloud top the latter feature which has received little attention and explanation has recently been reported to exist above stratiform rain areas in the tropics as measured directly by a wind profiler on the tropical western pacific island pohnpei the thin layer of sinking at the top of the trailing stratiform region occurs along the sloping upper cloud boundary and is associated with downward sloping isentropes in the lower stratosphere to the rear of the convective line the deformation of the isentropes is associated with an upward bulging of the tropopause

satellite observed characteristics of midwest severe thunderstorm anvils abstract this paper presents analyses of the cloud top and anvil structure of severe thunderstorms as observed by goes for five sesame cases during 1979 and four non sesame cases during 1980 82 emphasis was placed on comparison of these observations with previous models and hypotheses for the so called v feature and thermal couplets in the infrared ir observations thermal couplets are comprised of a low temperature region generally at or upwind of the cloud summit old point near the vertex of the v and one or more higher temperature regions downshear of the cloud summit warm points within the interior of the v statistics of the various cloud top and anvil features were compiled and the different cases were compared all studied except one 8 june 1979 had the v feature the temperature difference between the claw in warm and cold points comprising the thermal couplet ranged from 7 to 17 c and the mean separation distance between these points was 21 44 km the observations also indicated th

deep burial diagenesis its implications for vertical movements of the crust uplift of the lithosphere and isostatic unroofing a review abstract various techniques of study of strata exposed at the surface in undeformed areas of the appalachian basin and ozark done imply that these strata have been heated to temperatures that suggest a former great depth of burial the data reveal that the strata have been much more deeply buried than previously thought if such former deep burial has taken place then subsequent uplift and erosion must also have taken place to bring these formerly deeply buried strata to the present land surface unexpectedly large amounts of uplift and erosion ranging from 4 3 to 7 km have re exposed these formerly deeply buried rocks this leads to the surprising conclusion that isostatic unroofing has stripped off thick sections of strata whose presence was previously unsuspected therefore the lithosphere in its isostatic unroofing of thick sequences of sedimentary strata has undergone much larger vertical motions than many geologists had previously estimated case histories in this review include strata of the silurian of the northern appalachian basin and of the ordovician of the ozark dome which reached interpreted maximum burial depths of 5 and 4 3 km respectively devonian strata in the catskill mountains of new york imply a former depth of burial of 6 5 km lower ordovician carbonate sequences of the northern appalachian basin imply a depth of burial in excess of 7 km middle ordovician strata from the same basin signify a depth of burial of approximately 5 km and devonian strata a paleodepth of 4 5 5 km such former great depths of burial of undeformed strata which are now exposed at the surface reflect large scale vertical movements of the crust and uplift of the lithosphere these drastic changes represent isostatic unroofing with widespread implications for paleogeography of a kind unrecognized at present

small scale wind fluctuations in the tropical tropopause layer from aircraft measurements occurrence nature and impact on vertical mixing abstractthe contribution of turbulent mixing to heat and tracer transport in the tropical tropopause layer ttl is poorly constrained partly due to a lack of direct observations here the authors use high resolution 20 hz airborne measurements to study the occurrence and properties of small scale 100 m wind fluctuations in the ttl 14 19 km over the tropical pacific the fluctuations are highly intermittent and appear localized within shallow 100 m patches furthermore active turbulent events are more frequent at low altitude near deep convection and within layers of low gradient richardson number a case study emphasizes the link between the turbulent events and the occurrence of inertio gravity waves having small horizontal or vertical scale in order to evaluate the impact of the observed fluctuations on tracer mixing their characteristics are examined during active events they are in broad agreement with inertial range turbulence theory the motions are close to 3d isotropic and the sp

dehydration of the upper troposphere and lower stratosphere by subvisible cirrus clouds near the tropical tropopause the extreme dryness of the lower stratosphere is believed to be caused by freeze drying of air as it enters the stratosphere through the cold tropical tropopause previous investigations have been focused on dehydration occurring at the tops of deep convective cloud systems however recent observations of a ubiquitous stratiform cirrus cloud layer near the tropical tropopause suggest the possibility of dehydration as air is slowly lifted by large scale motions in this study we have evaluated this possibility using a detailed ice cloud model simulations of ice cloud formation in the temperature minima of gravity waves wave periods of 1 2 hours indicate that large numbers of ice crystals will likely form due to the low temperatures and rapid cooling as a result the crystals do not grow larger than about 10 m fallspeeds are no greater than a few cm s 1 and little or no precipitation or dehydration occurs however ice clouds formed by large scale vertical motions with lifetimes of a day or more should have fewer crystals and more time for crystal sedimentation to occur resulting in water vapor depletions as large as 1 ppmv near the tropopause we suggest that gradual lifting near the tropical tropopause accompanied by formation of thin cirrus may account for the dehydration

numerical simulations of interactions between gravity waves and deep moist convection abstract this study uses a numerical model to simulate deep convection both in the tropics over the ocean and the midlatitudes over land the vertical grid that was used extends into the stratosphere allowing for the simultaneous examination of the convection and the vertically propagating gravity waves that it generates a large number of trajectories are used to evaluate the behavior of tracers in the troposphere and it is found that the tracers can be segregated into different types based upon their position in a diagram of normalized vertical velocity versus displacement conditional sampling is also used to identify updrafts in the troposphere and calculate their contribution to the kinetic energy budget of the troposphere in addition fourier analysis is used to characterize the waves in the stratosphere it was found that the waves simulated in this study have similarities to those observed and simulated by other researchers finally this study examines the wave energy flux as a means to provid

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

measurements of vertical eddy diffusivity across the tropopause using radio acoustic sounding system rass 1 a four day high temporal resolution mu radar rass data set was obtained under light wind conditions in august 1995 enabling retrieval of virtual temperatures up to 20 km this provided a unique opportunity to study the vertical eddy diffusivity k across the tropopause using rass brunt vaisala frequency n and radar spectral width co located six hourly radiosondes enabled calculation of k using radiosonde n and radar spectral width rass k decreased across the wmo tropopause from 0 39 0 05 m2s 1 in the uppermost kilometre of the troposphere to 0 27 0 03 m2s 1 in the lowermost kilometre of the stratosphere the equivalent radiosonde k were 0 43 0 06 m2s 1 and 0 31 0 07 m2s 1 respectively the wmo tropopause seems to provide a better definition than the cold point tropopause in separating the stratosphere from the troposphere when considering the mixing of minor constituents

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

the salt of europa the galileo mission to jupiter has provided strong evidence that its moon europa supports a deep water ocean covered by a layer of ice in his research commentary kargel discusses spectroscopic results reported in the same issue by mccord et al indicating that europa9s icy surface is paved with regions of hydrated salts interspersed with areas of pure ice the findings also suggest that the conductive salt water could be a giant electrical circuit and that europa9s unusual magnetic field could result from interactions with jupiter9s field

vertical short scale structures in the upper tropospheric and lower stratospheric temperature and ozone at la reunion island 20 8 s 55 3 e the distribution and the nature of vertical short scale structures observed in ozone and temperature are investigated in the upper troposphere and the lower stratosphere at la reunion island located in the vicinity of the southern subtropical barrier by using wavelet based methods a climatology of dominant wavelike patterns with short vertical wavelengths reveals the presence of localized structures on both the ozone and the temperature perturbations extracted from ozonesonde and temperature data up to the middle stratosphere some case studies are presented to identify the nature of short scale structures with 1 to 5 km vertical wavelengths in the troposphere and the stratosphere a climatology of short scale structures induced by gravity waves and the horizontal advection shows that short scale structures are mainly detected in the middle and upper troposphere and in the lower stratosphere the weak value of the coefficient r z that links the ozone and temperature perturbations induced by gravity waves is a major limit to detecting such short scale structures above 21 km altitude some structures with vertical wavelengths ranging from 1 to 5 km are attributed to gravity waves produced by convection in summer and the subtropical jet in winter or quasi horizontal large scale motions from both sides of the subtropical barrier

generation and trapping of gravity waves from convection with comparison to parameterization some parameterizations of gravity wave mean flow forcing in global circulation models gcms add realism by describing wave generation by tropospheric convection because the convection in gcms is itself a parameterized process these convectively generated wave parameterizations necessarily use many simplifying assumptions in this work the authors use a realistic simulation of wave generation by convection described in previous work which was validated by observations from the darwin area wave experiment dawex to test these assumptions and to suggest some possible improvements to the parameterizations in particular the authors find that wave trapping in the troposphere significantly modifies the spectrum of vertically propagating waves entering the stratosphere above convective wave sources and offer a linear method for computing wave transmission and reflection effects on the spectrum suitable for inclusion in the parameterizations the wave fluxes originate from both a time varying heating mechanism and an obstacle effect mechanism acting in the simulation methods for including both mechanisms in the parameterizations are described waves emanating from the obstacle effect remain very sensitive to the depth of penetration of latent heating cells into an overlying shear zone which will continue to make it difficult to accurately parameterize in a gcm where the convective cells are not resolved

flow strength of highly hydrated mg and na sulfate hydrate salts pure and in mixtures with water ice with application to europa 1 we selected two europan ice shell candidate highly hydrated sulfate salts for a laboratory survey of ductile flow properties mgso4 7h2o epsomite and na2so4 10h2o mirabilite called ms7 and ns10 respectively polycrystalline samples in pure form and in mixtures with water ice i were tested using our cryogenic high pressure creep apparatus at temperatures 232 t 294 k confining pressures p 50 and 100 mpa and strain rates 4 10 8 7 10 5 s 1 grain size of ns10 samples was 100 m the flow strength of pure ms7 was over 100 times that of polycrystalline ice i at comparable conditions that of pure ns10 over 20 times that of ice in terms of the creep law a n e q rt where r is the gas constant we determine parameter values of a 1012 1 mpa ns 1 n 5 4 and q 128 kj mol for pure ns10 composites of ice i and ns10 of volume fraction ns10 have flow strength c ns10 ns10j 1 ns10 iceij 1 j where j 0 5 making the effect on the flow of ice with low volume fractions of ns10 much like that of virtually undeformable hard rock inclusions being much stronger and denser than ice massive sulfate inclusions in the warmer ductile layer of the europan ice shell are less likely to be entrained in convective ice flow and more likely to be drawn to the base of the ice shell by gravitational forces and eventually expelled with only smaller dispersed sulfate inclusions at probable sulfate 0 2 the shell may be treated rheologically as pure polycrystalline ice with boundary conditions perhaps influenced by the high density and low thermal conductivity of the hydrated salts

occurrence frequency of convective gravity waves during the north american thunderstorm season 1 convective gravity waves are an important driver of the equator to pole circulation in the stratospheric summer hemisphere but their nature is not well known previous studies showing tight relationships between deep convection and convective waves mainly focus on tropical latitudes for midlatitudes most analyses are based on case studies here we present a new multiyear occurrence frequency analysis of convective waves at midlatitudes the study is based on radiance measurements made by the atmospheric infrared sounder airs satellite experiment during the north american thunderstorm season may to august in the years 2003 2008 for this study we optimized an existing algorithm to detect deep convection in airs data to be applicable at midlatitudes we also present a new detection algorithm for gravity waves in airs data based on a variance filter approach for 4 3 m brightness temperatures the new algorithm can detect plane wave perturbations in the altitude range from 20 to 65 km with vertical wavelengths larger than 15 km and horizontal wavelengths from 50 to 1000 km by analyzing spatial and temporal correlations of the individual airs observations it can be shown that more than 95 of the observed gravity waves in a core region over the north american great plains are related to deep convective clouds i e are likely being classified appropriately as convective waves we conclude that the core region is a good location to observe and characterize the properties of convective waves at midlatitudes the statistical analyses presented here are also valuable to validate parameterization schemes for convective gravity waves for completeness it should be mentioned that our analyses cover not only the u s midwest but the north american continent as well as the surrounding ocean regions in general our analysis also reveals interesting details about tropical convection and related gravity wave activity as well as the capability of the airs instrument to observe these

brine volcanism and the interior structures of asteroids and icy satellites abstract cryovolcanism is among the foremost processes responsible for modifying the surfaces of icy satellites volcanic brine petrogenesis in ammonia deficient satellites should mainly involve eutectic melting in relevant salt water systems carbonaceous chondrites provide useful insights into the compositions of salts and aqueously altered rock in icy satellites and asteroids c1 chondrites contain about one fifth by mass of salts in various states of hydration many aspects of the petrogenesis and physical volcanology of icy satellite brines should be well described in the system h2o mgso4 na2so4 minor components include sulfates of k ni mn and ca chondrites also contain abundant carbonates but these are probably not very important in brine magmatism due to their low solubilities under expected conditions chlorides are also unimportant under most circumstances because of the low cosmic abundance ratio of cl s soluble salts may have profound effects on the geology and structure of icy satellites and asteroids in some models late episodes of water volcanism are facilitated by high buoyant forces due to the relatively high densities of sulfate rich mantle and crustal layers in other models early hypersaline brine volcanism quickly yields to plutonic magmatism due to low crustal densities europa probably has a layered crust composed of anhydrous mg na sulfates near the base and a frozen or partially molten eutectic mixture of ice and hydrated mg and na sulfates near the surface ganymede may have a crust about 300 km thick composed of a 10 1 ratio of ice mirabilite and a mantle 500 km thick composed of 50 ice phases plus 50 hydrated mg and na sulfates

gravity wave characteristics over tromelin island during the passage of cyclone hudah 1 the time and spatial evolution of gravity wave characteristics are analysed using wavelets in vertical profiles of temperature and winds at tromelin island 15 53 s 54 31 e during the passage of the intense tropical cyclone hudah in the southern ocean indian basin in 2000 inertia gravity waves were observed in the upper troposphere and the lower stratosphere with dominant vertical wavelengths of 1 5 3 km horizontal wavelengths 2000 km and periods of 0 6 1 6 days large amounts of gravity wave energy were detected during landfalls of the tropical cyclone the distribution of total energy indicates that mesoscale convective structures such as tropical cyclones are important gravity wave sources in the upper troposphere

radiosonde observations of equatorial atmosphere dynamics over indonesia 2 characteristics of gravity waves this paper discusses the characteristics of gravity waves in the equatorial region revealed by analyzing radiosonde measurements of wind velocity and temperature fluctuations at 0 35 km with a height resolution of 150 m made every 5 7 hours between february 27 and march 22 1990 in east java indonesia we conducted hodograph analysis to delineate vertical and horizontal propagation characteristics and found that most gravity waves were generated in the middle of the troposphere and that they propagated upward into the stratosphere the amplitudes of wind velocity and temperature fluctuations due to gravity waves were larger in the stratosphere than in the troposphere the direction of horizontal propagation of gravity waves was rather uniformly distributed in the troposphere but it became eastward in the lower stratosphere being opposite to that of the mean winds because of quasi biennial oscillation the vertical wavenumber spectra of wind velocity were described fairly well by a saturated model spectrum although their amplitudes were smaller in the stratosphere a typical vertical wavelength was 2 2 5 km while the horizontal phase velocities were 5 7 and 12 m s in the troposphere and stratosphere respectively the amplitudes of small scale gravity waves were significantly larger in the equatorial stratosphere than at middle latitudes time height variation of the wind velocity variance due to gravity waves showed a clear correlation with that for high relative humidity which implies that cloud convection is an important mechanism of gravity wave generation in the equatorial region

europa s differentiated internal structure inferences from four galileo encounters radio doppler data from four encounters of the galileo spacecraft with the jovian moon europa have been used to refine models of europa s interior europa is most likely differentiated into a metallic core surrounded by a rock mantle and a water ice liquid outer shell but the data cannot eliminate the possibility of a uniform mixture of dense silicate and metal beneath the water ice liquid shell the size of a metallic core is uncertain because of its unknown composition but it could be as large as about 50 percent of europa s radius the thickness of europa s outer shell of water ice liquid must lie in the range of about 80 to 170 kilometers

mesoscale disturbances in the tropical stratosphere excited by convection observations and effects on the stratospheric momentum budget abstract the importance of the momentum flux of topographically generated mesoscale gravity waves to the extratropical middle atmosphere circulation has been well established for over a decade estimates of the zonal forcing due to tropical mesoscale gravity waves however are hampered by lack of data on their primarily convective sources the advent of aircraft measurements over tropical convective systems now makes such estimates possible without the use of ad hoc assumptions about amplitudes and phase speeds aircraft measurements from nasa s 1980 panama and 1987 step australia missions show that convectively generated disturbances observed just above the tropopause have horizontal scales comparable to those of the underlying anvils about 50 100 km with peak to peak isentropic surface variations of about 300 400 m satellite imagery of tropical anvil evolution indicates a typical lifetime of about five hours assuming that each convective system s impact on the stratosphere can be modeled as a time

isolating spatiotemporally local mixed rossby gravity waves using multi dimensional ensemble empirical mode decomposition tropical waves have relatively large amplitudes in and near convective systems attenuating as they propagate away from the area where they are generated due to the dissipative nature of the atmosphere traditionally nonlocal analysis methods such as those based on the fourier transform are applied to identify tropical waves however these methods have the potential to lead to the misidentification of local wavenumbers and spatial locations of local wave activities to address this problem we propose a new method for analyzing tropical waves with particular focus placed on equatorial mixed rossby gravity mrg waves the new tropical wave analysis method is based on the multi dimensional ensemble empirical mode decomposition and a novel spectral representation based on spatiotemporally local wavenumber frequency and amplitude of waves we first apply this new method to synthetic data to demonstrate the advantages of the method in revealing characteristics of mrg waves we further apply the method to reanalysis data 1 to identify and isolate the spatiotemporally heterogeneous mrg waves event by event and 2 to quantify the spatial inhomogeneity of these waves in a wavenumber frequency energy diagram in this way we reveal the climatology of spatiotemporal inhomogeneity of mrg waves and summarize it in wavenumber frequency domain the indian ocean is dominated by mrg waves in the period range of 8 12 days the western pacific ocean consists of almost equal energy distribution of mrg waves in the period ranges of 3 6 and 8 12 days respectively and the eastern tropical pacific ocean and the tropical atlantic ocean are dominated by mrg waves in the period range of 3 6 days the zonal wavenumbers mostly fall within the band of 4 15 with indian ocean has larger portion of higher wavenumber smaller wavelength components mrg waves

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

small scale gravity waves in the upper mesosphere and lower thermosphere generated by deep tropical convection a time dependent nonlinear fully compressible axisymmetric plane numerical model is used to simulate the generation of small scale gravity waves in the upper mesosphere and lower thermosphere by intense deep convection in the troposphere the simulations show that major convective storms in the tropics excite a broad spectrum of upper mesosphere lower thermosphere gravity waves above the storm centers the wave field includes a component that is guided in a thermal duct in the lower thermosphere and propagates horizontally outward from above the storm storms excite oscillations over the source which are initially confined to a stratospheric duct but leak into the thermospheric duct over time generating a long train of small scale ducted waves this ringing phenomenon persists for several hours after the storm has ended the ducted disturbances may propagate large distances from the source and explain observations of a strong summertime anisotropy favoring southward propagation of small scale waves observed in the airglow over adelaide more than 2000 km to the south of the storm events

general circulation model simulation of the semiannual oscillation of the tropical middle atmosphere abstract a study has been made of the evolution of the zonal mean zonal wind and temperature in a multiyear integration of the 40 level 3 3 6 resolution skyhi general circulation model gcm that has been developed at gfdl in the tropical upper stratosphere the mean wind variation is dominated by a strong semiannual oscillation sao the peak sao amplitude in the model is almost 25 m s 1 and occurs near the 1 mb level the phase of the sao near the stratopause is such that maximum westerlies occur shortly after the equinoxes these features are in good agreement with the available observations in addition the meridional width of the stratopause sao in the gcm compares well with observations a diagnostic analysis of the zonal mean momentum balance near the tropical stratopause was performed using the detailed fields archived during the gcm integration it appears that the easterly accelerations in the model sao are provided by a combination of i divergence of the meridional component of the el