inertia gravity waves associated with deep convection observed during the summers of 2005 and 2007 in korea 1 characteristics of inertia gravity waves associated with convection are investigated in the lower stratosphere using high resolution radiosonde data observed from 18 june to 15 july of 2005 and 2007 in korea three dimensional ray tracing model and reanalysis data are used to investigate the propagation and the sources of the observed waves the observed waves associated with convections are discriminated based on the existence of convections when and where the rays reach the average height range of convective clouds waves observed in 2005 and 2007 show similar spectral characteristics but wave energy in 2007 is significantly larger than in 2005 the observed waves propagate from three source regions the northeastern southeastern and western regions around korea they show preferential propagation directions based on their sources and convections from the western region generate larger amplitude gravity waves than the other two regions the spectral characteristics of the observed waves are determined largely by those of the convective forcing along with the wave propagation condition associated with background wind and stability the significantly larger mean wave energy in 2007 occurs because more observed waves originate from the western region of korea in 2007 than in 2005 where convective forcing is much larger than in the other source regions

gravity wave and orographic wave activity observed around the antarctic and arctic stratospheric vortices by the cosmic gps ro satellite constellation 1 polar stratospheric gravity wave activity is studied using data from the constellation observing system for meteorology ionosphere and climate cosmic global positioning system radio occultation gps ro waves with vertical wavelengths of 2 to 15 km are considered the temperature variance 2 is used as a measure of wave activity and is studied on isentropic surfaces large intermittent orographic wave activity is identified during austral spring 2007 above the patagonian andes and the antarctic peninsula where 2 in the stratosphere increases by up to a factor of 5 for periods of 5 days to a few weeks the 2 are also investigated in equivalent latitudes to allow a direct comparison with the changing vortex structure the october 2007 2 inside the antarctic vortex boundary region at 400 600 k is one and a half times that outside the vortex this region of enhanced 2 descends in time and is not observed during the decay of the arctic vortex during the boreal winter of 2006 2007 orographic wave activity is observed above scandinavia and greenland an analysis of the 400 k and the 450 k levels in both hemispheres shows a strong relationship between enhanced 2 and the location of the vortex edge suggesting that the waves observed are propagating poleward and are guided to higher altitudes by the vortex the line of sight of the occultations shows a preference for north south alignment indicating that cosmic favors the detection of orographic waves above the north south oriented mountain ranges considered here

gravity waves around the subtropical jet of the southern winter in an atmospheric general circulation model 1 gravity wave gw activities around the subtropical jet of the southern winter june are analyzed using atmospheric general circulation model outputs of t106l60 in order to clarify roles of gws in maintaining the zonal mean zonal wind dominant gws are characterized with periods of 10 24 hours relative to the ground and with horizontal and vertical wavelengths of about 600 700 km and 2 2 4 4 km respectively these gws propagate both upward and downward from the jet and westward relative to the mean zonal wind most of the upward propagating waves do not reach the upper stratosphere due to negative vertical wind shear of the zonal wind in the lower stratosphere dominant upward fluxes of easterly momentum due to the non stationary gws extend zonally along 30 s above the jet remarkable ep flux convergence due mostly to these gws is seen around 100 hpa at 30 s and explains up to 30 of the total ep flux convergence

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

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

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

origin evolution and finescale structure of the st valentine s day mesoscale gravity wave observed during storm fest part i origin and evolution abstract on 14 15 february 1992 a long lived mesoscale gravity wave was observed over the storm scale operational and research meteorology fronts experiment systems test observational network a precipitation band formed and intensified as the wave moved across kansas and missouri the disturbance was tracked for 14 h surface dual doppler radar and wind profiler analyses as well as isentropic analyses derived from a special rawinsonde network are used to examine the origin and evolution of this wave the wave originated at the leading edge of a dry air mass associated with downslope flow in the lee of the rockies the earliest surface pressure signatures of wave motion began as a dry air mass associated with the downslope flow ascended a warm front east of a lee cyclone a weak rainband developed simultaneously with the wave at the leading edge of the dry air mass the mesoscale gravity wave and convection remained tied to the leading edge of the advancing dry air mass during the first 8 10 h of

inertia gravity waves spontaneously generated by jets and fronts part i different baroclinic life cycles abstract the spontaneous generation of inertia gravity waves in idealized life cycles of baroclinic instability is investigated using the weather research and forecasting model two substantially different life cycles of baroclinic instability are obtained by varying the initial zonal jet the wave generation depends strongly on the details of the baroclinic wave s development in the life cycle dominated by cyclonic behavior the most conspicuous gravity waves are excited by the upper level jet and are broadly consistent with previous simulations of o sullivan and dunkerton in the life cycle that is dominated by anticyclonic behavior the most conspicuous gravity waves even in the stratosphere are excited by the surface fronts although the fronts are no stronger than in the cyclonic life cycle the anticyclonic life cycle also reveals waves in the lower stratosphere above the upper level trough of the baroclinic wave these waves have not been previously identified in idealized simulations the sensiti

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

convectively generated gravity waves and their effect on the cloud environment this study uses a two dimensional cloud resolving model to examine how convectively generated gravity waves modify the environment of an isolated convective cloud the model is initialized with an idealized sounding and the cloud is initiated by adding a locally buoyant perturbation the modeled convection generates a spectrum of gravity waves with vertical wavelengths that are harmonics of the depth of the troposphere it is shown that the first three wave modes significantly modify the cloud environment the modification of the cloud environment is quantified in terms of the convective available potential energy cape and convective inhibition cin the first two wave modes travel fastest away from the cloud and are responsible for the changes in cape whereas the third wave mode causes low level lifting and hence a reduction in cin the maximum far field perturbations in cape and cin are approximately 15 and 33 of the initial background values respectively these results agree with previous studies of more organized convection predicting the existence of a region surrounding the convective system that favors the development of new convection

numerical simulations of a gravity wave event over ccope part iii the role of a mountain plains solenoid in the generation of the second wave episode abstract mesoscale model simulations have been performed of the second episode of gravity waves observed in great detail in previous studies on 11 12 july 1981 during the cooperative convective precipitation experiment the dominant wave simulated by the model was mechanically forced by the strong updraft associated with a mountain plains solenoid mps as this updraft impinged upon a stratified shear layer above the deep well mixed boundary layer that developed due to strong sensible heating over the absaroka mountains the gravity wave was created this wave rapidly weakened as it propagated eastward however explosive convection developed directly over the remnant gravity wave as an eastward propagating density current produced by a rainband generated within the mps leeside convergence zone merged with a westward propagating density current in eastern montana the greatly strengthened cool pool resulting from this new convection then generated a bore wave that appeared to be continuous with the move

millennial scale glacial meltwater pulses and their effect on the spatiotemporal benthicδ18o variability 1 ratios of oxygen isotope values obtained from foraminiferal calcite are one of the most established paleoceanographic proxies they are used in the context of estimating variations in ice volume ocean temperature and salinity and provide a means to date marine sediment cores across different ocean basins our study addresses the question how the 18o of the deglacial meltwater signal propagates into the interior ocean when large scale millennial scale reorganizations of the atlantic meridional overturning circulation amoc are present analyzing a series of idealized tracer injection experiments conducted with an earth system model we find that a substantial weakening of the amoc leads to a massive delay in the export of the glacioeustatic oxygen isotope signal into the deep ocean whereas the atlantic pacific lag in benthic oxygen isotope signals is not increased furthermore it is shown that an amoc cessation causes a decoupling of 18o propagation time and water mass age in particular in the deep pacific our results lend further support to the notion that benthic oxygen isotope records obtained from stacks are not a useful global chronostratigraphic tool during periods of millennial scale global ocean circulation changes the regionally varying delay effect of the deglacial sea level signal studied here adds onto existing uncertainties in the interpretation and decomposition of benthic oxygen isotope in terms of sea level temperature and hydrographic variations

numerical simulations of a gravity wave event over ccope part ii waves generated by an orographic density current a mesoscale numerical model and detailed observations are used to investigate the generation and maintenance of a mesoscale gravity wave event observed in eastern montana on 11 july 1981 during the cooperative convective precipitation experiment ccope it is shown that the interaction between an orographic density current and a mountain barrier leads to the generation of the gravity waves the simulation results suggest the following four stage conceptual model during stage i shortly after sunset the remnant up branch of a thermally driven upslope flow east of the rockies was driven back toward the mountain by the pressure gradient force associated with a cool pool over north dakota the nocturnal stable layer over eastern montana was strengthened during passage of this density current during the 1 2 h transition period of stage ii the advancing density current became blocked as it encountered the higher terrain an isentropic ridge developed above the original warm lee trough due to strong adiabatic cooling caused by the sustained upward motion in the presence of orographic blocking during stage iii an even stronger upward motion center formed to the east of the density current head updraft in response to an eastward horizontal pressure gradient force produced by the isentropic ridge in stage iv as the density current head collapsed and downward motion developed to the west of the original updraft in quadrature phase with the isentropic perturbation a gravity wave was generated this wave propagated eastward with the mean wind opposite to the motion of the earlier density current and was maintained by the strong wave duct established earlier by the density current thus the mountain plains circulation may at times generate mesoscale gravity waves and deep convection hours after diurnal heating has ended

an analysis of frontogenesis in numerical simulations of baroclinic waves abstract using a primitive equation pe model we revisit two canonical flows that were previously studied using a semigeostrophic equation sg model in a previous paper the authors showed that the pe and the sg models can have significantly different versions of the large scale dynamics here they report on the implications of this difference for frontogenesis the program for the study of frontogenesis developed by b j hoskins and collaborators is followed to show how in the pe version of the canonical cases the surface warm front develops before the cold front and why the upper level front is a long nearly continuous feature going from ridge to trough the frontogenesis experienced by an air parcel is computed following the parcel to illustrate better the mechanisms involved as the present calculations are carried out longer than most previous ones the relation of the upper frontogenesis to the formation of the upper level cutoff cyclone is also examined trajectory and three dimensional g

a comparative study of large amplitude gravity wave events abstract two large amplitude gravity waves were observed over the midwestern united states on 5 and 14 january 1989 during the university of illinois winter precipitation program on both days an extensive amount of data was recorded including data from two radars and a radiosonde facility the waves originated near missouri registered pressure fluctuations as large as 10 mb and produced distinct precipitation bands along their updraft regions the waves were long lived and maintained their identity over 1000 km a distance several times their wave lengths the synoptic features at the surface were dissimilar a deep cyclone was present on 5 january while a leeside trough was present on 14 january however the middle and upper tropospheric flow patterns were similar in both cases the axis of a trough was immediately upstream of the gravity wave genesis area and a jet streak had just propagated through the base of the trough toward a downstream ridge soundings taken near the gravity waves were re

consistent vertical and horizontal resolution abstract simple physical relations namely the rossby ratio between vertical and horizontal scales in quasi geostrophic flow and the dispersion relation for internal gravity waves are used to estimate the vertical resolution consistent with a given horizontal resolution using these relations we find that virtually all large scale models and observing systems have inadequate vertical resolutions in models the excess horizontal resolution can lead to increased model noise rather than improved accuracy in observing systems the finer horizontal scales can be severely misrepresented

a case study of cyclogenesis using a model hierarchy abstract it is universally agreed that cyclogenesis in midlatitudes occurs through baroclinic conversion of the potential energy available from an initial state the mechanical process by which that conversion takes place is a perennial subject of discussion at least as far back as the 1950s it was recognized that in any practical forecast problem the initial condition is influential observational research continues to confirm the prevalence of tropopause level perturbations preceding surface cyclogenesis the observations also suggest that the growing disturbances have time varying vertical structures relating these observations to the classical linear theory of baroclinic instability is not immediately obvious since in the latter the precise form of the initial condition is not important and the theory predicts cyclogenesis with a fixed in time vertical structure these differences between theory and observations are but a few of the many that have been recognized and treated in modified theorie

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

numerical simulation of the large amplitude mesoscale gravity wave event of 15 december 1987 in the central united states abstract an observational study employing spectral methods is first made to establish a background for a modeling effort of the mesoscale gravity wave event of 15 december 1987 the waves are found to have wavelengths of 100 160 km phase speeds of approximately 30 m s 1 and lifetimes of over 6 h conditions for their maintenance are evaluated indicating the presence of a wave duct and a supportive role for wave cisk convection shearing instability and geostrophic adjustment are all implicated as possible source mechanisms for the observed waves the case is then simulated with the pennsylvania state university national center for atmospheric research mm4 mesoscale forecast model with the following primary objectives i to test the model s ability to simulate a mesoscale gravity wave event ii to examine in detail the environments of mesoscale gravity wave development and iii to investigate the mechanisms of mesoscale gravity wave generation and maintenance the full physics control experim

a case study of long gravity wave crests in noctilucent clouds and their origin in the upper tropospheric jet stream atmospheric gravity waves with very long crests of 450 500 km length and short horizontal wavelengths of about 20 km were observed in noctilucent clouds and were studied in detail for the first time the gravity waves were slowly moving in opposite direction to the background wind indicating their forced generation outside the mesopause region a ray tracing analysis using meteorological reanalysis and empirical atmospheric model data shows that a source of such peculiar gravity waves observed in noctilucent clouds was located near the tropopause and could be associated with the jet stream at altitudes 8 10 km two considered examples of very long wave crests confirm a significant role of the upper tropospheric jet stream as a source of gravity waves and reveal that these waves could propagate without critical levels to the mesopause in summertime

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

a study of cyclone mesoscale structure with emphasis on a large amplitude inertia gravity wave abstract an analysis is presented of prominent mesoscale structure in a moderately intense cyclone with emphasis on a long lived large amplitude inertia gravity wave igw that moved through the northeastern united states on 4 january 1994 available national weather service wsr 88d doppler radar and wind profiler observations are employed to illustrate the rich time dependent three dimensional structure of the igw as the igw amplified peak crest to trough pressure falls exceeded 13 hpa 30 min 1 it also accelerated away from the cyclone reaching a peak forward speed of 35 40 m s 1 across eastern new england the igw was one of three prominent mesoscale features associated with the cyclone the others being a weak offshore precursor warm frontal wave and an onshore band of heavy snow snow bomb in which peak hourly snowfalls of 10 15 cm were observed none of these three prominent mesoscale features were well forecast by existing operational prediction models particularly with regard to preci

holocene ethnobotanical and paleoecological record of human impact on vegetation in the little tennessee river valley tennessee abstract human occupation and utilization of plant resources have affected vegetation in the lower little tennessee river valley of east tennessee for 10 000 yr changes in indian cultures and land use are documented by radiocarbon chronologies lithic artifacts ceramics settlement patterns and ethnobotanical remains from 25 stratified archaeological sites within the holocene alluvial terrace the ethnobotanical record consists of 31 500 fragments 13 7 kg of wood charcoal identified to species and 7 7 kg of carbonized fruits seeds nutshells and cultigens from 956 features pollen and plant macrofossils from small ponds both in the uplands and on lower stream terraces record local vegetational changes through the last 1500 to 3000 yr human impact increased after cultigens including squash and gourd were introduced ca 4000 yr b p during the archaic cultural period forest clearance and cultivation disturbed vegetation on both the floodplain and lower terraces after 2800 yr b p during the woodland period permanent indian settlements and maize and bean agriculture extended to higher terraces 1 5 km from the floodplain by the mississippian period 1000 to 300 yr b p after 300 yr b p extensive land clearance and cultivation by historic overhill cherokee and euro americans spread into the uplands beyond the river valley

wavelet analysis and the governing dynamics of a large amplitude mesoscale gravity wave event along the east coast of the united states detailed diagnostic analyses are performed upon a mesoscale numerical simulation of a well observed gravity wave event that occurred on 4 january 1994 along the east coast of the united states the value of using wavelet analysis to investigate the evolving gravity wave structure and of using potential vorticity pv inversion to study the nature of the flow imbalance in the wave generation region is demonstrated the cross stream lagrangian rossby number the residual in the nonlinear balance equation and the unbalanced geopotential height field obtained from pv inversion are each evaluated for their usefulness in diagnosing the flow imbalance all of these fields showed clear evidence of strong imbalance associated with a middle to upper tropospheric jet streak and tropopause fold upstream of the large amplitude gravity wave several hours before the wave became apparent at the surface analysis indicates that a train of gravity waves was continuously generated by geostrophic adjustment in the exit region of the unbalanced upper level jet streak as it approached the inflection axis in the height field immediately downstream of the maximum imbalance associated with the tropopause fold a split front in the middle troposphere characterized by the advance of the dry conveyor belt above the warm front was overtaken by one of these propagating waves during this merger process a resonant interaction resulted which promoted the rapid amplification and scale contraction of both the incipient wave nonlinear wave development and the split front frontogenesis the gravity wave and front aloft became inseparable following this merger the situation became even more complex within a few hours as the vertical motion enhanced by this front wave interaction acted upon a saturated potentially unstable layer to produce elevated moist convection an analysis of the temporal changes in the vertical profile of wave energy flux suggests that moist convective downdraughts efficiently transported the wave energy from the midlevels downward beneath the warm front surface where the wave became ducted however pure ducting was not sufficient for maintaining and amplifying the waves rather wave cisk conditional instability of the second kind was crucial this complex sequence of nonlinear interactions produced a long lived large amplitude gravity wave that created hazardous winter weather and disrupted society over a broad and highly populated area although gravity waves with similar appearance to this large amplitude wave of depression occasionally have been seen in other strong cyclogenesis cases involving a jet streak ahead of the upper level trough axis it is unknown whether other such events share this same sequence of interactions

the synoptic setting and possible energy sources for mesoscale wave disturbances abstract thirteen case studies of mesoscale wave disturbances characterized by either a singular wave of depression or wave packets with periods of 1 4 h horizontal wavelengths of 50 500 km and surface pressure perturbation amplitudes of 0 2 7 0 mb are reviewed to isolate common synoptic features for these cases and to shed light on possible energy sources for the waves a strong thermal inversion in the lower troposphere north of a frontal boundary and a jet streak propagating toward a ridge axis in the upper troposphere are commonly observed in all the cases in general the area of wave activity is bounded by the jet axis to the west or northwest a surface front to the southeast an inflection axis between the trough and ridge axes to the southwest and the ridge axis to the northeast the conditions specified by lindzen and tung as being necessary to form a wave duct which include the existence of the lower tropospheric inversion seem to be met in many of these cases this suggests that a du

a potential vorticity diagnostic approach to upper level frontogenesis within a developing baroclinic wave the process of tropopause folding is studied in the context of the life cycle of baroclinic waves previous studies of upper level frontogenesis have emphasized the role of the vertical circulation in driving stratospheric air down into the midtroposphere here a potential vorticity based approach is adopted that focuses on the generation of a folded tropopause to facilitate comparison of the two approaches the diagnosis is applied to the upper level front previously simulated and studied by rotunno et al the potential vorticity approach clarifies the primary role played by the horizontal nondivergent wind in producing a fold and explains why folding should be a common aspect of baroclinic development between the trough and upstream ridge prolonged subsidence within a region of weak system relative flow generates a tropopause depression oriented at an angle to the large scale flow the large scale vertical shear then locally increases the slope of the tropopause eventually leading to a tropopause fold in contrast tropopause folding in the base of the trough is caused by the nondivergent cyclonic circulation associated with the surface thermal wave the winds associated with the thermal wave amplify the potential vorticity wave aloft and these winds which decrease with height rapidly generate a tropopause fold within the trough

a review of the structure and dynamics of upper level frontal zones abstract this article presents a review of upper level fronts with the intent of synthesizing observational and modeling studies into a conceptual and dynamical description of these fronts and their evolution relative to the life cycle of midlatitude baroclinic waves the discussion begins by tracing present day concepts concerning the structure of upper level frontal systems which are based on composite analyses of radiosonde and aircraft data from their origins in the pioneering analyses of upper air data in the 1930s perspectives from scales both smaller and larger than upper level frontal systems are provided respectively by considering the effects of turbulent processes on frontal structure and dynamics and by relating variations in frontal structure to the evolution of the baroclinic waves that provide the dynamical environment for upper level frontogenesis the dynamics of upper level fronts are shown to comprise the interactions between the primary geostrophic and secondary ageostrophic cir

dynamics of upper level frontogenesis in baroclinic waves abstractthis paper reports a diagnosis of the structure and dynamics of upper level fronts ulfs simulated with a high resolution weather research and forecasting model with diabatic heating versus one without diabatic heating the ulfs of both simulations develop in about 6 days as integral parts of intensifying baroclinic waves each has a curvilinear structure along the southern edge of a relatively narrow long tongue of high potential vorticity in which stratospheric air is subducted to different tropospheric levels by synoptic scale subsidence it resembles a veil in the sky of varying thickness across the midsection upstream of the trough of the baroclinic wave the 3d frontogenetical function is shown to be a necessary and sufficient metric for quantifying the rate of development of ulfs its value is mostly associated with the contribution of the 3d ageostrophic velocity component upper level frontogenesis is attributable to the joint direct influence of the vortex stretching process and the defo