application of the compressible nonhydrostatic balanced omega equation in estimating diabatic forcing for parameterization of inertia gravity waves case study of moist baroclinic waves using wrf abstractthe parameterization of inertia gravity waves igws is of considerable importance in general circulation models among the challenging issues faced in studies concerned with parameterizati

climatology of short period gravity waves observed over northern australia during the darwin area wave experiment dawex and their dominant source regions 1 the darwin area wave experiment dawex was designed to investigate the generation and propagation of gravity waves from intense regions of localized convection that occur regularly over northern australia in the vicinity of darwin during the premonsoon period this multinational program was conducted during the austral spring 2001 using a range of coordinated optical radar and in situ balloon measurements as part of this program all sky image observations of short period gravity wave events in the near infrared oh nightglow emission altitude 87 km were made from two well separated sites in northern australia wyndham 15 5 s 128 1 e and katherine 14 5 s 132 3 e over a 10 day period during november 2001 a total of 25 extensive wave events were observed during this period from which the dominant horizontal wave characteristics were determined to be wavelength 25 35 km and observed phase speed 27 75 m s yielding observed periods from 7 to 14 min consistent with previous measurements at other low latitude sites a key finding of this study was a marked anisotropy in the wave propagation headings with over 3 4 of the events exhibiting a strong southward component of motion and a clear preference for wave progression over the azimuthal range se to ssw although this range encompasses gravity waves originating locally from the darwin area the majority of the wave events exhibited propagation headings consistent with more distant sources located to the north and northwest of australia assuming deep convection was the dominant mechanism for the waves the strong asymmetry in their velocity distribution appears to result from a combination of nonuniformity in the geographic occurrence of thunderstorms coupled together with significant wind filtering effects at the source altitude and within the middle atmosphere these results are consistent with long range short period wave propagation most probably in the form of ducted waves possibly from intense convective regions located 1000 km to the north over the indonesian island chain

momentum flux spectrum of convectively forced internal gravity waves and its application to gravity wave drag parameterization part ii impacts in a gcm waccm abstract impacts of a spectral parameterization of gravity wave drag gwd induced by cumulus convection gwdc in the ncar whole atmosphere community climate model waccm1b are investigated in the spectral gwdc parameterization reference wave momentum flux spectrum is launched at cloud top and analytically calculated based on the physical properties of convection and the large scale flow the cloud top wave momentum flux is strong mainly in the tropics and midlatitude storm track regions and exhibits anisotropy and spatiotemporal variability the anisotropy and variability are determined by the distributions and variations of convective activities the moving speed of convection and horizontal wind and stability in convection regions zonal mean zonal gwdc has a maximum of 13 27 37 50 m s 1 day 1 in the mesosphere in january july impacts of gwdc on zonal wind appear mainly in the low to midlatitudes of the upper stratosphere and mesosphere in these regions biases of zonal wind with respect to

a model study of zonal forcing in the equatorial stratosphere by convectively induced gravity waves a two dimensional cloud resolving model is used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi biennial oscillation qbo of the zonal winds in the equatorial stratosphere a simulation with constant background stratospheric winds is compared to simulations with background winds characteristic of the westerly and easterly qbo phases respectively in all three cases a broad spectrum of both eastward and westward propagating gravity waves is excited in the constant background wind case the vertical momentum flux is nearly constant with height in the stratosphere after correction for waves leaving the model domain in the easterly and westerly shear cases however westward and eastward propagating waves respectively are strongly damped as they approach their critical levels owing to the strongly scale dependent vertical diffusion in the model the profiles of zonal forcing induced by this wave damping are similar to profiles given by critical level absorption but displaced slightly downward the magnitude of the zonal forcing is of order 5 m s21 day21 it is estimated that if 2 of the area of the tropics were occupied by storms of similar magnitude mesoscale gravity waves could provide nearly 1 4 of the zonal forcing required for the qbo

the occurrence and significance of biogenic opal in the regolith abstract biogenic opal produced by vascular plants diatoms and siliceous sponges have been found in soils and terrestrial sediments of all continents except antarctica since the middle of the 19th century the opal particles range in size from fine silt to fine sand almost all soils contain detectable opal up to levels of 2 3 and a significant number contain values in excess of 5 even higher values have been found from soils and sediments of all continents in a wide range of soil types the most important factor is poor soil drainage and seasonal to permanent water logging this encourages the proliferation of silica producing organisms such conditions have been found in the soils and aquatic sediments of the monsoonal tropics tropical rain forests temperate forests tropical savanna tropical islands semi arid grasslands and savanna and temperate woodland and grassland the presence of a volcanic substrate also appears favourable in some cases but is not necessary biogenic opal preferentially collects in the a horizon of soils and to a lesser extent in the b horizon this preferential distribution facilitates identification of palaeosols in stacked soil sequences biogenic opal is also a component of windblown dust even in arid environments biogenic opal is significant to regolith processes in a number of ways firstly as in the case in marine environments it is likely to be important in silica cycling and storage because of its greater lability compared to quartz secondly dissolution and reprecipitation of opal a as opal ct or micro quartz may play a role in cementation and silicification of regolith to form silica hardpans and silcrete thirdly the organisms that form biogenic opal can have considerable palaeoenvironmental significance and be valuable in reconstructing regolith evolution finally some forms of biogenic silica in particular sponge spicules can present a health hazard their high abundance in some soils and sediments needs to be considered when assessing the health implications of airborne dust

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 three dimensional simulation of a tropical squall line convective organization and thermodynamic vertical transport abstract three dimensional convective scale simulations of an african squall line observed during the french copt 81 experiment are presented three simulations with different representations of large scale forcing are performed on a domain of 50 km along the line by 80 km across the line they exhibit a similar circulation pattern characteristic of a squall line but differ in intensity the first simulation supposes an unperturbed environment and produces a slow moving squall line 7 m s 1 with weaker total precipitation rate then observed 25 the second one includes a representation of observed thermodynamic and dynamic environment modifications and produces a fast moving squall line 10 m s 1 still weaker than observations 50 or the rain rate the third simulation takes into account the forcing induced by the rear inflow jet as depicted by smull and houze and observed on that day it allows the system to reach an intensity in agreement with observations the convective region 30 km wid

a numerical study of gravity waves induced by convection associated with typhoon rusa 1 typhoon rusa 2002 is simulated using a three dimensional mesoscale model mm5 and the characteristics of gravity waves generated by convection associated with the typhoon are investigated the gravity waves in the stratosphere propagate in two directions northwestward and southeastward according to the convective bands propagating in the same directions although the typhoon itself moves north northeastward spectral analyses show that the inertio gravity waves igws in the stratosphere generated by rusa have a dominant horizontal wavelength of 300 600 km a vertical wavelength of 3 11 km and a period of 6 11 hrs a large fraction of the igws is filtered out in the upper troposphere and stratosphere mainly due to the critical level filtering process the decreased magnitude of the momentum flux with height in a non filtered region is likely due to the damping process with a minor contribution by the wave breaking process that can occur exclusively near the critical level phase speeds

convection generated high frequency gravity waves as observed by mst radar and simulated by wrf model over the indian tropical station of gadanki using a mesosphere stratosphere troposphere mst radar operating at 53 mhz the present work reports that during the development of convection over the indian tropical station of gadanki at 16 38 17 30 ut universal time on 06 june 2011 all these three source mechanisms played important roles in determining the characteristics of high frequency internal atmospheric gravity waves generated 1 latent heating of convection 2 mechanical oscillation of up and down drafts associated with convection and 3 obstacle effect of wind flows over convective towers near the tropopause level in general it is found that while the depth of latent heating determines the vertical wavelength of gravity waves the oscillation frequency of up and down drafts determines the observed frequency of waves from the study of vertical structure of vertical wind velocities and phases of three waves 13 17 and 26 min generated during this event it is observed that while the 13 min and 26 min oscillations are associated with mechanical oscillator mechanism the 17 min oscillation is associated with obstacle effect analyses fourier morlet wavelet transforms and maximum entropy method mem of all the three components of wind velocities measured by the mst radar show that there is a clear association of gravity waves generated with convection and the vertical propagation characteristics of the gravity waves are found to be in good agreement with theoretical expectations with the back ground atmospheric information obtained by using the data of gps radiosondes era interim and ncep ncar reanalyses high resolution wrf model simulations support the present observations that in turn will help in a large way to the progress of parameterization of convection generated high frequency gravity waves in general circulation models the present work also finds that water molecules induced distinct atmospheric polarized refractive index structures are in existence which is in accordance with an earlier report on this subject

a numerical study of three dimensional gravity waves triggered by deep tropical convection and their role in the dynamics of the qbo abstract a 3d mesoscale model is used to study the structure of convectively triggered gravity waves in the tropics and their role in the dynamics of the middle atmosphere simulations with three stratospheric background zonal wind cases are examined in the first case the background wind profile is constant the other two are representative of the easterly and westerly phases of the quasi biennial oscillation qbo spectral analysis is used to link the structure of the triggered gravity waves to the dominant vertical wavelength of the latent heating within the convection in the qbo wind shear cases upward propagating gravity waves are damped as they approach their critical layer the signature of critical layer absorption is clearly visible in the profiles of vertical momentum flux divergence in the simulations with open boundary conditions the response to vertical momentum flux divergence takes the form of large dynamic pressure differences between the east and west boundaries together with acceler

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

a numerical investigation of the organization and interaction of the convective and stratiform regions of tropical squall lines abstract a set of 13 two dimensional numerical simulations based on the 22 and 23 june soundings from the convectionprofonde tropicale in 1981 copt81 experiment in west africa is used to study the organization and interactionof the convective and stratiform regions of squall line type convective systems the initial wind profiles arecharacterized by the african easterly jet aej and the tropical easterly jet tej located at about 3 5 km and14 km respectively the physical processes that generate and maintain the mesoscale inflow at the rear of squall line type mesoscaleconvective systems are thereby examined horizontal potential temperature gradients generated by a combinationof latent heat release in the convective region and unsaturated mesoscale descent both modulated by evaporation cause a horizontal pressure gradient and generate horizontal line parallel vorticity the rear inflow is a consequenceof these processes the convective activity induces a significant upscale influence ahead of the

gravity waves in the tropical lower stratosphere a model study of seasonal and interannual variability a model study is presented to clarify the relationship between gravity wave properties observed in the stratosphere and the sources for the waves presumed to be in the troposphere the observations are balloon borne radiosondes launched from cocos island in the tropical indian ocean 12 s 97 e and the analysis of these data is described in a companion paper vincent and alexander this issue the dominant time variations in the observed gravity wave activity are annual and quasi biennial patterns in the zonal momentum flux and kinetic energy density the background zonal winds at this site vary with the same periods and these are known to be capable of causing dramatic variations in the observable properties of the waves even if the sources for the waves are constant in time the results presented here clarify 1 the nature of the sources for the gravity waves observed in the stratosphere 2 the limitations of the observations for observing the full range of gravity wave perturbations potentially present in the atmosphere and 3 the role the observed waves can play in forcing the quasibiennial oscillation qbo in the zonal winds at this latitude the stratospheric waves appear to originate near the height of the tropopause so the source is apparently related to deep convection no seasonal or interannual variations in the convection need be assumed to understand the observations the waves at the tropopause appear to have a phase speed distribution that is narrowly confined near zero phase speed relative to the ground the source is likely related to slowly propagating tropospheric convection and the wind near the tropopause variations observed in the stratospheric data are caused by both the wind shear in the stratosphere and the ability of waves with these characteristics to propagate vertically without severe dissipation higher phase speed waves may be present and could carry significant momentum flux vertically into the stratosphere and mesosphere but would be extremely difficult to see in these radiosonde data the observed waves can contribute substantially to the descent of the eastward shear zones characteristic of the westerly phase of the qbo in the lower stratosphere zonal winds

recognition of maximum flooding events in mixed siliciclastic carbonate systems key to global chronostratigraphic correlation the maximum flooding event within a depositional sequence is an important datum for correlation because it represents a virtually synchronous horizon this event is typically recognized by a distinctive physical surface and or a significant change in microfossil assemblages relative fossil abundance peaks in siliciclastic deposits from shoreline to continental slope environments in a passive margin setting recognition of maximum flooding events in mixed siliciclastic carbonate sediments is more complicated because the entire section usually represents deposition in continental shelf environments with varying rates of biologic and carbonate productivity versus siliciclastic influx hence this event cannot be consistently identified simply by relative fossil abundance peaks factors such as siliciclastic input carbonate productivity sediment accumulation rates and paleoenvironmental conditions dramatically affect the relative abundances of microfossils failure to recognize these complications can lead to a sequence stratigraphic interpretation that substantially overestimates the number of depositional sequences of 1 to 10 m y duration

a numerical study of stratospheric gravity waves triggered by squall lines observed during the toga coare and copt 81 experiments a 3d mesoscale model is used to study the structure and intensity of stratospheric gravity waves generated by tropical convection two prototypical cases are examined a squall line observed during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare over the pacific warm pool and a west african squall line observed during the convection profonde tropicale 1981 copt 81 experiment gravity waves generated by these two squall lines are compared with those generated by a previously investigated event over northern australia although the individual squall lines vary in intensity the stratospheric gravity waves generated by the various storms have surprisingly similar amplitudes the similarity in the wave amplitudes arises because within each storm there is a positive correlation between the updraft intensity and the height of the level of neutral buoyancy when the level of neutral buoyancy is relatively high the atmospheric density in the region of wave generation is relatively low and this reduction in density tends to weaken the convectively triggered waves thereby compensating for the stronger updraft velocities in the more intense storms the sensitivity of the azimuthal distribution of the convectively generated gravity waves to the upper tropospheric and lower stratospheric wind profile is also examined in the absence of critical level absorption the motion of the storm relative to the stratospheric winds appears to be the single most important factor determining the azimuthal distribution of the waves stationary storm relative waves similar to mountain waves may also be generated when there is a strong storm relative stratospheric wind the interaction of the gravity waves with shear layers representative of the eastward and westward phases of the quasi biennial oscillation qbo is also examined an analysis of the domain averaged momentum budget supports the claim that the drag exerted by critical level absorption of convectively generated gravity waves plays a nontrivial role in the downward propagation of the qbo

stratospheric variability of wave activity and parameters in equatorial coastal and tropical sites during the west african monsoon recent numerical studies in stratospheric dynamics and its variability as well as climate have highlighted the need of more observational analyses to improve simulation of the west african monsoon wam in this paper activity and spectral characteristics of short scale vertical waves wavelengths 4 km are analysed in equatorial coastal and tropical lower stratosphere during the wam a first detailed description of such waves over west africa is derived from high resolution vertical profiles of temperature and horizontal wind obtained during intensive observation period of the african monsoon multidisciplinary analyses amma campaign 2006 monthly variation of wave energy density is revealed to trace the progression of the inter tropical convergence zone itcz over west africa mesoscale inertia gravity waves structures with vertical and horizontal wavelengths of 1 5 2 5 and 400 1100 km respectively and intrinsic frequencies of 1 1 2 2 f or periods 2 days are observed in the tropical ls with intense activity during july and august when the wam is installed over the tropical west africa over equatorial region gravity waves with intrinsic frequencies of 1 4 4 f or periods 5 2 days vertical wavelength of 2 1 km and long horizontal wavelengths of 1300 km are intense during the wam coastal phase from july to october gravity waves with intrinsic frequencies of 1 2 3 8 f or periods 6 days vertical wavelength of 2 1 km and horizontal wavelengths of 1650 km are less intense during the wam sahelian phase of the wam march june unlike potential energy density kinetic energy density is observed to be a good proxy for the activity of short scale vertical waves during the wam because quasi inertial waves are dominant long term wave activity variation from january 2001 to december 2009 highlights strong year to year variation superimposed on convective activity and quasi biennial oscillation like variations especially above tropical stations

some genetic implications of silica and aluminosilicates in peat and coal abstract the inorganic content of okefenokee peat in the absence of a significant detrital contribution is a function of sponge spicule phytolith and diatom abundance in addition to the degree of organic matter decomposition and the frequency of fires the detrital component quartz dominates ash composition where it is present no clear correlation has been observed between the inorganic content of coals examined in this study and their maceral composition vitrinite rich coals have a wide range of ash yield these observations suggest that the minerals have been introduced detritally rather than accumulated as a result of peat degradation quartz in the coals appears to be detrital and the presence of 2m 1 mica indicates that there is also a detrital contribution to the clay minerals present

the impacts of seawater mg ca and temperature on element incorporation in benthic foraminiferal calcite on geological timescales oceanic mg2 and ca2 vary with changing rates of weathering seafloor spreading and dolomite formation accurate reconstruction of the ratio between mg2 and ca2 in seawater mg casw may potentially be reconstructed using foraminiferal mg ca ratios since both temperature and seawater mg ca impact foraminiferal mg ca successful reconstruction of mg casw requires quantification of both these parameters independently on foraminiferal mg ca as well as their combined effect on mg incorporation here we present the combined and isolated impacts of temperature and mg casw on mg incorporation in two model species the benthic hyaline i e perforate foraminifer elphidium crispum and porcelaneous i e miliolid foraminifer quinqueloculina sp using controlled growth experiments specimens of these two species were kept at four different temperatures ranging from 10 to 27 c and three mg casw s 3 4 6 4 and 8 5 mol mol resulting in 12 experimental conditions newly grown calcite was analyzed for a number of elements na mg and sr by laser ablation icp ms results show that although the mg ca varied by more than an order of magnitude between species the sensitivity of mg incorporation with respect to temperature appeared not to be influenced by mg casw by extension these results may also help improving accuracy in the reconstruction of past mg casw based on foraminifera with contrasting mg ca

numerical modeling of gravity wave generation by deep tropical convection although convective clouds are known to generate internal gravity waves the mechanisms responsible are not well understood the present study seeks to clarify the dynamics of wave generation using a high resolution numerical model of deep convection over the tiwi islands australia the numerical calculations presented explicitly resolve both the mesoscale convective cloud cluster and the gravity waves generated as the convective clouds evolve they excite gravity waves which are prominent features of the model solutions in both the troposphere and stratosphere the source location is variable in time and space but is related to the development of individual convective cells the largest amplitude gravity waves are generated when the cloud tops reach the upper troposphere a new analysis technique is introduced in which the nonlinear terms in the governing equations are taken as the forcing for linear gravity waves the analysis shows that in the present calculation neither the shear nor the diabatic heating are the dominant forcing terms instead the wave source is most easily understood when viewed in a frame of reference moving with the wind at the level of neutral buoyancy whereupon the source may be described as a vertically oriented oscillating convective updraft this description is consistent with the properties of the modeled stratospheric waves

kelvin waves and the quasi biennial oscillation an observational analysis a method is derived for estimating the kelvin wave contribution to the vertical flux of westerly momentum in the equatorial stratosphere which is based on temperature and geopotential perturbations this method is used to estimate the momentum transfer due to kelvin wave activity as derived from the cryogenic limb array etalon spectrophotometer claes temperature data set for the onset of the westerly phase of the qbo during 1992 and the first few months of 1993 that is during the first part of the upper atmosphere research satellite uars mission the results are compared with the zonal winds as observed by the high resolution doppler imager hrdi also flown on board uars and the united kingdom meteorological office ukmo data assimilation model product a correlative data set to the uars mission the analysis shows that although the kelvin wave momentum flux convergence is occasionally sufficient to account for the observed qbo westerly acceleration the observed flux is sporadic in nature and virtually disappears during the second half of the sample when the westerly vertical shear zone approaches the 100 hpa level an estimate of the total westerly momentum flux necessary to produce the observed descent of the westerly phase of the qbo is made using the transformed eulerian mean tem formalism the results suggest that kelvin waves are not sufficient to force the descent of the westerly phase of the qbo there appears to be a need for enhanced westerly forcing throughout the descent of the westerly phase of the qbo this enhanced forcing is most likely provided by gravity waves that are unresolved by the satellite observations these results are in agreement with the results derived from general circulation models

impact of a convectively forced gravity wave drag parameterization in ncar ccm3 a parameterization of gravity wave drag forced by subgrid scale cumulus convection gwdc proposed by chun and baik is implemented into the national center for atmospheric research community climate model ncar ccm3 and its effect on perpetual january and july climate is investigated the cloud top gravity wave stress is concentrated in the intertropical convergence zone where persistent deep cumulus clouds exist the resultant zonal wind acceleration due to the breaking of convectively forced gravity waves is predominantly found in the tropical lower stratosphere with westerly acceleration above cloud top and easterly acceleration just below it since the parameterized gravity waves are stationary relative to convective clouds wave breaking occurs mainly in the tropical lower stratosphere where the zonal wind is weak enough for wave saturation it is shown that the gwdc parameterization significantly alleviates the systematic model biases of zonal mean zonal wind and temperature in particular excessive easterlies in the tropical stratosphere and excessive cold temperatures in the tropical lower stratosphere are reduced by more than 50 by including the gwdc parameterization the horizontal wind divergence field in the tropical upper troposphere and lower stratosphere is also significantly improved with the gwdc parameterization the impact of the gwdc parameterization extends to mid to high latitudes through planetary wave activity in the winter hemisphere the increased amplitude of zonal wavenumber 3 in the january northern hemisphere and the increased amplitude of zonal wavenumber 2 in the july southern hemisphere lead to significant improvements in model performance the impact of the gwdc parameterization on eliassen palm ep flux divergence forcing by stationary waves is generally opposite to that by transient waves in the extratropics especially in the northern hemisphere wintertime hence the zonal mean zonal wind change by the gwdc parameterization occurs mainly in the tropics by direct gravity wave drag forcing

a coordinated study of 1 h mesoscale gravity waves propagating from logan to boulder with crrl na doppler lidars and temperature mapper we present the first coordinated study using two lidars at two separate locations to characterize a 1 h mesoscale gravity wave event in the mesopause region the simultaneous observations were made with the student training and atmospheric research star na doppler lidar at boulder co and the utah state university na doppler lidar and temperature mapper at logan ut on 27 november 2013 the high precision possessed by the star lidar enabled these waves to be detected in vertical wind the mean wave amplitudes are 0 44 m s in vertical wind and 1 in relative temperature at altitudes of 82 107 km those in the zonal and meridional winds are 6 1 and 5 2 m s averaged from 84 to 99 km the horizontal and vertical wavelengths inferred from the mapper and lidars are 219 4 and 16 0 0 3 km respectively the intrinsic period is 1 3 h for the airglow layer doppler shifted by a mean wind of 17 m s the wave packet propagates from logan to boulder with an azimuth angle of 135 clockwise from north and an elevation angle of 3 from the horizon the observed phase difference between the two locations can be explained by the traveling time of the 1 h wave from logan to boulder which is about 2 4 h the wave polarization relations are examined through the simultaneous quantifications of the three wind components and temperature this study has developed a systematic methodology for fully characterizing mesoscale gravity waves inspecting their intrinsic properties and validating the derivation of horizontal wave structures by applying multiple instruments from coordinated stations

kelvin wave variability near the equatorial tropopause observed in gps radio occultation measurements 1 temperature fields in the equatorial upper troposphere and lower stratosphere derived from gps radio occultation measurements for 2001 2002 show evidence for planetary scale kelvin waves these waves have a characteristic eastward phase tilt with height and typical vertical wavelengths of 4 8 km the kelvin waves exhibit coherent vertical structure over 12 25 km with maximum amplitudes near the tropical tropopause 17 km the waves are often quasi stationary near the tropopause but exhibit regular eastward propagation in the lower stratosphere with periods near 20 days the quasi stationary waves modulate the climatological cold tropopause over indonesia the transient lower stratospheric waves show enhanced amplitudes coincident with the descending westerly shear phase of the quasi biennial oscillation qbo correlations with outgoing long wave radiation olr data show that global temperature patterns over 12 17 km with characteristic kelvin wave structure vary coherently with transient deep convection over indonesia

global observations of gravity waves from high resolution dynamics limb sounder temperature measurements a yearlong record of temperature amplitude and vertical wavelength 1 global observations of gravity waves have been performed using the high resolution dynamics limb sounder hirdls temperature data a background field that was derived by dynamically calculating 31 day 15 day means to block the stationary component and the slowly varying planetary scale waves was first subtracted from the hirdls temperature measurements an additional step was then taken to remove rapidly moving planetary scale waves by developing an along track temperature filter which was created by averaging the profiles within a 1000 km along track window finally each individual temperature perturbation vertical profile was analyzed using a fast fourier transform to estimate gravity wave temperature amplitudes and vertical wavelengths the investigation of the monthly mean gravity wave temperature amplitudes for the year 2006 found that gravity wave activity in the stratosphere is highly variable with season and can be very orographically dependent especially in the winter extratropics the monthly zonal means show that the peak vertical wavelengths correspond closely to the peak amplitudes the increasing amplitudes and vertical wavelengths are faster and generated at lower altitudes in the winter extratropical and high latitude stratosphere than those in the summer tropical stratosphere this is consistent with the lower source altitudes of orographic gravity waves in the extratropics and high latitudes and the higher source altitudes of convectively generated gravity waves in the tropics three cases were studied for the observed gravity waves over large mountain ranges using the european centre for medium range weather forecasts wind data investigations of episodes of enhanced gravity wave activity over the southern andes the cascade range and the rockies in winter months of 2006 indicate that orographic gravity waves refract downwind from the mountains and propagate along the direction of the intense winds by way of contrast observations of gravity waves around the himalayas show a strong relationship with the cyclones in that region

the inorganic chemistry of peat from the maunachira channel swamp system okavango delta botswana abstract the okavango delta is a large 18000 km2 low gradient 1 3600 alluvial fan situated in the semi arid kalahari basin of northern botswana seasonal floodwaters from tropical angola disperse on the fan creating both perennial 6000 km2 and seasonal 7000 to 12000 km2 swamps ninety five percent of this water is lost annually by evapotranspiration organic rich sediment peat is a major sediment of the perennial swamps peat formation commences during senescence of the plants when certain nutrients are recycled while others are lost by rainwater leaching further changes in chemistry occur during subaqueous decay of the plants which involve both gains and losses of constituents decaying plants trap detrital mineral matter which becomes an integral part of the peat the main sources and forms of inorganic matter in the peat are allochthonous kaolinite 40 and quartz 20 and both allochthonous and autochthonous phytolithic silica 30 several inorganic components fe k p na ca and mg which make up the remaining 10 are associated with the organic fraction ion exchange plays only a minor part in their uptake and it seems that these metals are taken up during bacterial activity in the peat the weight proportion of inorganic matter ash decreases downstream mainly due to a decrease in allochthonous mineral matter volume percentage also decreases but is low throughout generally less than five percent this study has revealed that the low quantity allochthonous mineral matter is the main reason for the long term survival of this ecosystem uptake of soluble ions by the peat is important in off setting evaporative concentration of metals

convectively generated internal gravity waves in the lower atmosphere of venus part ii mean wind shear and wave mean flow interaction abstract this paper is the second of a two part study that numerically investigates internal gravity wave generation by convection in the lower atmosphere of venus part i of this study considers gravity wave generation and propagation in the absence of mean wind shear in part ii the venus westward superrotation is included and wave mean flow interaction is assessed both lower atmosphere convection and cloud level convection play active roles in the dynamics of the stable layer from 31 to 47 km altitude when mean wind shear is present this result contrasts with the simulation without mean wind shear presented in part i where cloud level convection was primarily responsible for gravity wave generation in the stable layer in the presence of mean wind shear upward entrainment from lower atmosphere convection and downward penetration from cloud level convection are comparable in magnitude convectively generated internal gravity waves have horizontal wavelengths 25 30 km comparable to horizontal sc

gravity wave activity associated with tropical convection detected in toga coare sounding data upper air sounding data collected at santa cruz 10 s 165 e in the western tropical pacific ocean during november 1992 february 1993 have been used to estimate the gravity wave activity in the upper troposphere and lower stratosphere large amplitude gravity waves with vertical wavelengths of 2 5 km were found in almost all the soundings time series describing the wave activity in two height ranges 10 17 km the upper troposphere and 17 24 km the lower stratosphere are presented and compared to simple measures of the convective cloud activity there is enhanced gravity wave activity associated with increased convection on intraseasonal timescales

climatology of the equatorial lower stratosphere abstract twenty years of radiosonde data have been analyzed in an attempt to develop a latitudinal structure climatology of winds temperature and geopotential at 30 and 50 mb in the equatorial stratosphere the fine latitudinal resolution provided by the wmo station network reveals several interesting features in the latitudinal structure of the annual and quasi biennial cycles which dominate this region for example the westerly and easterly acceleration phases of the quasi biennial oscillation are markedly different westerly accelerations appear first at the equator spreading outward with time to higher latitude and an more intense on average than the easterly accelerations the easterly accelerations are more uniform in latitude but leer uniform in time sometimes occurring in two stages the quasi biennial wind and temperature oscillations are symmetric about the equator while the annual harmonic in zonal wind is antisymmetric about the equator but is not proportional to the coriolis paramete

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

quasi biennial and higher period oscillations in the mean winds in the mesosphere and lower thermosphere over saskatoon 52 n 107 w the mesospheric zonal and meridional winds over saskatoon 52 n 107 w show significant qbo quasi biennial oscillations with periods of 2 01 2 42 2 30 2 37 and 2 31 years at 94 91 88 85 and 82 km respectively in the meridional north component and 2 51 2 88 2 52 2 29 and 2 61 years in the zonal east component mostly not matching with the qbo 2 50 years of equatorial stratospheric winds also significant higher periodicities 4 years are seen in the mesospheric winds indicating that qbo and higher periodicities in the midlatitude mesosphere could be highly distorted forms of stratospheric wind qbo and or may have altogether different origins e g el nino southern oscillation effects

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

plant impact on the biogeochemical cycle of silicon and related weathering processes abstract the contribution of plants to the biogeochemical cycle of si and related weathering processes was studied in an equatorial rainforest ecosystem congo where the biologic turnover of si is high 58 to 76 kg ha y litterfall leaves a soil profile and groundwaters were analysed phytoliths and organic matter have a similar distribution with depth in the soil profile the model of a bicompartmental distribution of organic matter is applied to phytolith distribution and shows that about 92 of the biogenic silica input is rapidly recycled while about 8 of the biogenic silica input supplies a stable pool of phytoliths with a lower turnover reprecipitation of silica was observed at the base of the soil profile indicating a local geochemical environment that is oversaturated with respect to amorphous silica a balance in biogeochemical cycle of si requires that the vegetation absorb dissolved silicon released from weathering of minerals which otherwise would be available for mineral neoformation or export from the profile towards regional drainages plant uptake of si increases the chemical weathering rate without increasing the denudation rate this study shows that the uptake storage and release of si by the vegetation have to be taken into account when using dissolved si for tracing chemical weathering dynamics

quantification of gravity wave forcing in driving the stratospheric quasi biennial oscillation 1 using long term rayleigh lidar temperature observations during april 1998 april 2005 in the lower stratospheric region momentum flux divergence of the gravity waves of periods 0 5 1 and 2 4 hours are estimated over gadanki 13 5 n 79 2 e india monthly mean zonal winds from ncep ncar reanalysis data over gadanki at two pressure levels 10 and 20 hpa are used to study the characteristics of the quasi biennial oscillation qbo and its month to month acceleration this observed mean flow acceleration is compared with that estimated from the momentum flux divergence of gravity waves which led to a better insight into the role of gravity waves in driving the qbo the present analysis reveals that the contribution of gravity waves towards the westerly phase of qbo varies from 10 60 while that during easterly phase from 10 30 the present study thus quantifies the role of gravity waves in driving the easterly and westerly phases of qbo

secondary gravity waves generated by breaking mountain waves over europe a strong mountain wave observed over central europe on 12 january 2016 is simulated in 2d under two fixed background wind conditions representing opposite tidal phases the aim of the simulation is to investigate the breaking of the mountain wave and subsequent generation of nonprimary waves in the upper atmosphere the model results show that the mountain wave first breaks as it approaches a mesospheric critical level creating turbulence on horizontal scales of 8 30 km these turbulence scales couple directly to horizontal secondary waves scales but those scales are prevented from reaching the hermosphere by the tidal winds which act like a filter initial secondary waves that can reach the thermosphere range from 60 to 120 km in horizontal scale and are influenced by the scales of the horizontal and vertical forcing associated with wave breaking at mountain wave zonal phase width and horizontal wavelength scales large scale nonprimary waves dominate over the whole duration of the simulation with horizontal scales of 107 300 km and periods of 11 22 minutes the thermosphere winds heavily influence the time averaged spatial distribution of wave forcing in the thermosphere which peaks at 150 km altitude and occurs both westward and eastward of the source in the 2 ut background simulation and primarily eastward of the source in the 7 ut background simulation the forcing amplitude is 2 that of the primary mountain wave breaking and dissipation this suggests that nonprimary waves play a significant role in gravity waves dynamics and improved understanding of the thermospheric winds is crucial to understanding their forcing distribution

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

paleosols in laterite and silcrete profiles evidence from the south east margin of the australian precambrian shield abstract laterite and silcrete profiles are common in the arid and semi arid areas of the australian precambrian shield a vast planar surface masked by the regolith much of the geological history of the shield subsequent to its early development is recorded in ancient cover rocks and younger basin sediments which occur in important stratigraphic sequences particularly on the margins of the shield within these sequences stratigraphically associated or as companion materials weathering zones and paleosols were developed which individually and as assemblages of layers and horizons record the history of weathering and of soil formation since the proterozoic laterite and silcrete profiles are seen to be assemblages of paleosols stratigraphically associated deposits and companion materials which were formed in response to changes in groundwater conditions at particular times in the past the paleosols record the evolution of the regolith older weathering zones and bleached rocks were features of successive landscapes after the early palaeozoic ferruginous mottling ferricrete and silcrete pans were formed after the early cainozoic ferricretes and mottled clay paleosols some of which have been described as laterite were formed during and after the pliocene materials in laterite and silcrete profiles are overlain in places by calcretes formed after the early pleistocene and by younger soils the assemblages are distinctive and are characteristic of particular morpholithogical provinces

darwin area wave experiment dawex field campaign to study gravity wave generation and propagation 1 a field campaign studying aspects of the atmospheric dynamics from the ground to the lower thermosphere was conducted in australia during october to december 2001 this darwin area wave experiment dawex involved participation from nine institutions in the usa japan and australia and focused on studying wave perturbations in the middle atmosphere in conjunction with detailed observations of tropospheric moist convection the experiment involved extended deployment of six airglow imagers medium frequency radars and a boundary layer wind profiler tropospheric convection was observed by meteorological radars including the australian bureau of meteorology research centre c band polarized radar this paper provides an overview of the experimental setup and also discusses the basic meteorological fields during the experiment including some examples of convective activity near darwin wind and temperature fields extending up into the lower thermosphere were constructed on the basis of campaign observations and the ukmo global meteorological analysis these fields can be used for the modeling of gravity wave propagation through the middle atmosphere

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

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

multiscale variability of deep convection in relation to large scale circulation in toga coare deep convection over the indo pacific oceanic warm pool in the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare occurred in cloud clusters which grouped together in regions favoring their occurrence these large groups of cloud clusters produced large scale regions of satellite observed cold cloud top temperature this paper investigates the manner in which the cloud clusters were organized on time and space scales ranging from the seasonal mean pattern over the whole warm pool region to the scale of individual cloud clusters and their relationship to the large scale circulation and sea surface temperature sst the dominant convective variability was associated with the intraseasonal oscillation iso a large eastward propagating ensemble of cloud clusters marked the iso s progress the meridional structure of the iso was strongly affected by the seasonal cycle with a southward shift from the northern hemisphere in october november to the southern hemisphere in january february the sst had an intraseasonal signal in lagged quadrature with the cold cloudiness and rainfall in coare the sst increased decreased during the convectively suppressed active phases of the iso enhanced low level westerly winds occurred toward the later stages of the enhanced convection periods of the iso though not always centered at the equator the strongest westerlies tended to be located between two synoptic scale cyclonic gyres which were often not symmetric about the equator in the low level wind field this asymmetry in the anomalous equatorial low level westerlies may have different implications for the oceanic response in the coupled atmosphere ocean system than those centered on the equator the cyclonic gyres contained highly concentrated deep convection and in four cases the gyres developed into tropical cyclones within the envelope marking the convectively active phase of the iso cloud clusters were frequently concentrated into westward propagating disturbances with a local periodicity of similar to 2 days these 2 day disturbances have been identified in earlier spectral studies and appear to be related to westward propagating inertio gravity waves in coare they typically contained numerous cloud clusters which underwent a distinct diurnal cycle most of the cloud clusters embedded in the 2 day disturbances moved westward though some were stationary and a few moved eastward a cloud duster tracking program identified groups of clusters lime dusters that exhibited continuity in time and space in the most convectively active period of the iso the tracking program identified almost the entire iso cloud ensemble as a long lasting trackable superconvective system this observation indicates the lack of a distinct scale separation between convection and large scale disturbances during the most intense convective periods in coare

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

the palaeoecological and palaeoclimatic significance of miocene freshwater diatomite deposits from southern new south wales australia abstract the bonnie doon member of the bunyan formation is a relatively extensive diatomite deposited over about 100 ka during the mid to late miocene the diatomite was deposited in a shallow eutrophic slightly alkaline lake with low salinity and turbidity the deposit consists of well laminated massive and bioturbated and dark organic rich diatomine facies which are dominated by melosira granulata the deposit is cyclic at three scales 1 paired laminae of diatomite and diatomite plus clay the thickness of which varies with a period of 11 6 23 2 and 51 2 yr 2 packets of varves variable thickness composed of 10 25 paired laminae each and 3 megascopic cycles about 1 m thick of laminated diatomite grading up into massive and or brecciated diatomite and thence into bioturbated dark coloured diatomite these cycles are interpreted as 1 strong annually seasonal variations in temperature and or light availability 2 packets reflecting wide variations in solar activity and 3 longer term climatic instability with a period less than or equal to 8 ka which produced cycles we interpret as shallowing upwards variations in the lake levels on this basis we conclude that strong climatic seasonality existed at this locality during the late miocene as well as longer term climatic cycles

medium frequency radar studies of gravity wave seasonal variations over hawaii 22 n 160 w 1 using simple numerical filters estimates of wind variances with period bands of 0 1 to 1 hour and 1 to 5 hours have been derived from data taken with the medium frequency radar on the island of kauai hawaii 22 n 160 w the observations cover altitudes of 70 to 90 km and extend over the years 1990 2000 the results show seasonal and interannual variations of the wind variances which can be attributed to atmospheric gravity waves the mean zonal wind has mainly an annual variation below an altitude of 83 km and a semiannual variation above the gravity waves have maximum intensity at the solstices below 83 km but at higher altitudes the times of the maxima shift to the equinoxes numerical simulations suggest this behavior results from the dependence of gravity wave generation and propagation on the background wind and temperature

some effects of model resolution on simulated gravity waves generated by deep mesoscale convection abstract over the past decade numerous numerical modeling studies have shown that deep convective clouds can produce gravity waves that induce a significant vertical flux of horizontal momentum such studies used models with horizontal grid spacings of o 1 km and produced strong gravity waves with horizontal wavelengths greater than about 20 km this paper is an examination of how simulated gravity waves and their momentum flux are sensitive to model resolution it is shown that increases in horizontal resolution produce more power in waves with shorter horizontal wavelengths this change in the gravity waves spectra influences their vertical propagation in some cases gravity waves that were vertically propagating in coarse simulations become vertically trapped in fine simulations which strongly influences the vertical flux of horizontal momentum

impact of a spectral gravity wave parameterization on the stratosphere in the met office unified model abstract the impact of a parameterized spectrum of gravity waves on the simulation of the stratosphere in the met office unified model um is investigated in the extratropical mesosphere the gravity wave forcing acts against the mean zonal wind and it dominates over the resolved wave forcing in the extratropical stratosphere the gravity wave forcing gives a small acceleration in the direction of the mean zonal wind both summer and winter stratospheric jets have improved maximum strength and tilt with height when the parameterized gravity wave forcing is included although the southern winter jet is still more vertically aligned than in observational analyses the timing of the seasonal breakdown of the southern winter vortex is also improved by the addition of gravity wave forcing in the tropics the most obvious impact is that the model reproduces the quasi biennial oscillation qbo with a realistic mean and range of periods it also reproduces most of the observed asymmetries between the easterl

gravity wave generation in the lower stratosphere due to passage of the typhoon 9426 orchid observed by the mu radar at shigaraki 34 85 n 136 10 e 1 intense gravity wave activities were investigated in the lower stratosphere during the typhoon 9426 strong vertical winds were observed just a few hours before the arrival of the typhoon center at the mu radar site about 30 min to 1 hour after the typhooncenter had passed a considerable reduction in vertical wind amplitude was detected dominant gravity waves showed time period in the range of 7 8 min 15 min and 40 60 min in the upper troposphere and lower stratosphere in the vicinity of the central region of the typhoon a gravity wave was observed which was monochromatic in nature with a vertical wavelength 3 km between 1 5 km and 23 km height in the lower stratosphere the horizontal wavelength for the prominent period was detected in the range of 10 15 km for 15 min wave period and 25 50 km for 40 60 min wave period the vertical wavelength of these waves was examined from 2 5 km to 4 0 km in the horizontal direction the intrinsic group velocity was estimated between 9 2 and 11 2 m s near the tropopause the average direction of group velocity was assessed at about 20 3 from the horizontal the generation of gravity wave like features in the lower stratosphere is believed induced by convection as the low temperature of the clouds indicates a deep penetration over the radar region as seen in the satellite gms images index terms 3314 meteorology and atmospheric dynamics convective processes 3334 meteorology and atmospheric dynamics middle atmosphere dynamics 0341 0342 3329 meteorology and atmospheric dynamics mesoscale meteorology 3384 meteorology and atmospheric dynamics waves and tides 6952 radio science radar atmospheric physics keywords convective updrafts gravity waves troposphere lower stratosphere