the dynamics of polar jet streams as depicted by the meteosat wv channel radiance field abstract a polar jet stream flowing over northern europe is investigated using both the radiosounding network and the meteosat water vapor wv channel imagery a maximum radiance band associated with the polar jet stream is shown to accurately delineate the tropopause break a major difference in the subtropical jet stream radiative signature is noted however an analytic approximation of the radiative transfer equation is established for the meteosat wv channel and leads to the conclusion that the radiance field away from the polar frontal zones is representative of the temperature field on a water vapor isosteric surface

a new look at deformation as a diagnostic for large scale flow abstractdeformation plays a key role in atmospheric dynamics because it provides a dynamical measure of the interaction between different scales such as in frontogenesis a climatology of deformation constructed from interim ecmwf re analysis era interim data 1979 2013 reveals four main processes associated with deformation 1 frontogenesis at lower levels 2 movement and evolution of jet streams in the upper troposphere 3 orographic blocking and 4 rossby wave breaking the merits of deformation as an additional perspective are discussed for these processes on the basis of case studies and composite analyses in conjunction with analytic solutions this study shows that deformation can be used to unambiguously detect orographic blocking through the local strength of the flow diversion around orography moreover the deformation signature for orographic blocking observed in case studies and composites closely resembles the analytic solution for two dimensional flow around an obstacle the climatolo

a high resolution one layer model of breaking planetary waves in the stratosphere numerical integrations of a one layer hemispheric model of the winter stratosphere have been carried out at very high resolution of the order of a fraction of a degree of latitude the numerical experiments simulate planetary wave breaking and polar vortex erosion under conditions far closer to the real winter stratosphere than those assumed in earlier critical layer models the model has implications for stratospheric photochemistry and the antarctic ozone hole problem

convective mixing in a tropopause fold we present a case study of the passage of a tropopause fold over the uk behind a cold front with emphasis on the mixing caused by convection extending into the fold the event took place on 15 16 january 1999 and was the subject of intensive observations using the met office c130 aircraft and the mesosphere stratosphere troposphere mst radar at aberystwyth here we concentrate on radar and satellite observations during the afternoon of 16 january when the surface cold front had passed over the uk a tongue of moist air moved north eastwards over wales at 700 hpa at this time which because of the very dry air in the fold above resulted in potential instability the resulting convection was clearly observed in noaa satellite images the mst radar depicted the passage of the cold front and tropopause fold as a layer of high echo power and vertical wind shear ascending with time spectral widths showed the fold to be free of turbulence until 1200 utc on 16 january when convection was observed reaching into the frontal zone and generating turbulence eddy dissipation and diffusivity rates of 8 6 mw kg 1 and 8 5 m2s 1 respectively were derived for this event to place these figures in context they are compared with corresponding rates derived for sixteen other passages of tropopause folds over the radar each resulting from shear rather than convective instability the convective event is found to be comparable to the strongest shear events and to correspond to moderate turbulence as experienced by an aircraft this process is of potential importance for atmospheric chemistry because it mixes boundary layer air directly with stratospheric air over a timescale of 1 2 hours copyright 2004 royal meteorological society

tropopause folding at satellite observed spatial gradients 2 development of an empirical model 1 we develop an empirical model that estimates the horizontal distribution of tropopause folds based primarily on a robust relationship between upper tropospheric specific humidity gradients and tropopause folding the specific humidity gradients are resolved by the altered water vapor awv product developed from the goes imager water vapor channel unexpectedly no proportional relationship was found between tropopause fold size and awv gradient magnitude beyond the one to one occurrence of strong gradients at tropopause folds this indicates that tropopause folds do not commonly reach a steady state mass of ozone inside the fold rather the mass of air must be controlled at least as much by the age of the fold and dynamical dispersion mechanisms that are not linearly related to the strength of the corresponding tropopause depression this has important implications for the interpretation of lidar imagery and in situ ozone data at tropopause folds in lieu of this result a uniform fold size is assigned at all locations of modeled folding on the basis of the average of the folds used in parameterization the model estimates the distribution of actively developing and residual tropopause folds which is a useful method of tracking the dispersal of all stratospherically enhanced air in the troposphere and is unique to this observation based model of tropopause folding

oxygen isotopic composition and chemical correlations in meteorites and the terrestrial planets recent models attempting to explain non mass dependent oxygen isotopic anomalies in meteorites and planets posit that they may have originated within the gas phase of the solar nebula which suggests the potential for correlations of non mass dependent oxygen isotopic anomalies with other chemical fractionations generated during cooling and condensation of the nebula we have examined three specific issues possible correlations of 17o with i oxidation state ii bulk chondrite chemistry and iii bulk planetary properties isolated grains and chondrules from several carbonaceous chondrite groups exhibit good to weak positive correlations between 17o and olivine fayalite content and whole rock ureilite samples show a positive correlation of 17o with olivine fayalite content these are consistent with oxidation of fe metal by 17o 18o enriched oxygen in the precursor materials that formed these objects in contrast oxygen isotopic and major element compositions of ferromagnesian phases in ordinary chondrite chondrules and in bulk chondrites do not show a correlation thus there is no compelling evidence that oxidation of nebular materials was tightly linked to gas species carrying anomalous o using average chondrite group compositions we demonstrate that significant negative correlations of refractory lithophile element mg and refractory siderophile element ni with 17o exist refractory inclusions cais and aoas are modally rare in many chondrite types that exhibit substantial range in 17o thus the refractory component in these chondrites must occur in a crypto component e g material dissolved in chondrule melts during chondrule formation significant positive correlations of moderately volatile elements mg with 17o are not simply explained by incomplete mixing of 16o enriched refractory grains but are broadly consistent with nebula based mechanisms of non mass dependent oxygen isotope fractionation the estimated compositions of the primitive mantles of the earth mars and 4 vesta have some compositional redox and isotopic properties that vary with heliocentric distance however 17o does not vary monotonically in this sequence indicating a decoupling of planetary o isotopic composition from other compositional characteristics

a simulation and diagnostic study of water vapor image dry bands abstract a limited area mesoscale prediction system lamps model simulation and special 3 hour radiosonde dataset are used to investigate warm dry bands in 6 7 m water vapor satellite imagery on 6 7 march 1982 the purpose is to reveal processes resulting in the formation and evolution of the dry features that appear as curving dark streaks in the imagery model soundings are input to a radiative transfer algorithm to generate synthetic 6 7 m equivalent blackbody temperatures tb which are compared with those from the visible infrared spin scan radiometer atmospheric sounder aboard the geostationary operational environmental satellite simulated and radiosonde derived vertical velocity and humidity also are compared with the images finally trajectories are calculated from both radiosonde data and lamps output the model reproduces major characteristics of the observed tb field a development dry image feature occurs in conjunction with an upper level shortwave trough and an advective feature

extratropical tropopause transition layer characteristics from high resolution sounding data 1 accurate determination of the tropopause is important for applications such as dynamical analysis and forecasting radiative transfer calculations and the diagnosis of chemical transport in the atmosphere in this paper we examine how well the extratropical tropopause is determined in the national centers for environmental prediction high resolution global forecast system gfs model analysis over the continental united states using high resolution aircraft and radiosonde data the gfs analyses and sounding data compare well with rms differences of approximately 600 m which is comparable to the vertical resolution of the model the gfs tropopause is a good proxy in areas without in situ observations but near the subtropical jet the gfs analysis often mistakenly identifies the secondary rather than the primary tropopause we also explore an alternative method to identify the tropopause by fitting a smoothed step function to the static stability profile this new approach provides a measure of the depth of the troposphere stratosphere transition and facilitates the study of the dynamical behavior of the tropopause region in particular using the transition depth we are able to identify the statistical behavior of temperature in profiles with deep or shallow tropopause transition layers

break up of a stratospheric streamer observed by mst radar the break up of a stratospheric streamer over the british isles is described using satellite mesosphere stratosphere troposphere mst radar and in situ observations together with european centre for medium range weather forecasts analyses the streamer started as a thin ribbon of high potential vorticity to the west of the british isles as this was strained by the background flow it broke up into a series of mesoscale vortices mst radar and ozonesonde observations delineated a tropopause fold to the west of the initial streamer taking the form of a thin layer of stratospheric air embedded in a deep layer of descending upper tropospheric air the fold appears to have been mixed out by small scale turbulence as the streamer broke up this break up also generated strong inertia gravity waves which broke just above the tropopause introducing extensive mixing to the lowermost stratosphere one of the mesoscale vortices returned over the mst radar showing a very indistinct tropopause typical of a synoptic scale cut off low this vortex was also responsible for the development of a rain band on its eastern flank which brought significant rainfall to the british isles at a time when the synoptic flow pattern was strongly anticyclonic

a new chemical lagrangian model of the stratosphere clams 1 formulation of advection and mixing 1 recent satellite observations and dynamical studies have demonstrated the existence of filamentary structures in chemical tracer fields in the stratosphere it is also evident that such features are often below the spatial resolution of the highest resolution eulerian models that have been used up to the present time these observations have motivated the development of a novel chemical lagranigan model of the stratosphere clams that is based on a lagrangian transport of tracers the description of clams is divided into two parts part 1 this paper concentrates on the lagrangian dynamics i e on the calculation of trajectories and on a completely new mixing algorithm based on a dynamically adaptive grid while part 2 describes the chemical integration and initialization procedure the mixing of different air masses in clams is driven by the large scale horizontal flow deformation and takes into account the mass exchange between the nearest neighbors determined by delaunay triangulation here we formulate an isentropic i e two dimensional version of the model and verify the mixing algorithm using tracer distributions measured during the space shuttle crista 1 experiment where highly resolved stratospheric structures were observed in early november 1994 a comparison of the measured southern hemispheric n2o distribution with clams results allows the intensity of simulated mixing to be optimized the long term robustness of the transport scheme is investigated in a case study of the 1996 1997 northern hemisphere polar vortex this study further provides a dynamical framework for investigations of chemical arctic ozone destruction discussed in part 2

static stability in the extratropical tropopause region abstract idealized axisymmetric anomalies of potential vorticity pv on a midlatitude f plane and their related response in terms of balanced wind and temperature are investigated with special focus on the static stability in the tropopause region the pv anomalies are specified such that they can be interpreted as the result of conservative advection in the tropopause region across the gradients of a prescribed background atmosphere with piecewise constant buoyancy frequency squared n2 related cyclones and anticyclones are treated identically except for the sign of the tropopause potential temperature anomaly composite profiles of n2 are computed for which the thermal tropopause is used as a common reference level and where the number of cyclones in the composite equals the number of anticyclones one obtains a pronounced peak of n2 just above the tropopause and slightly enhanced values below the tropopause in comparison with the background profile within the framework of pv inversion various mechan

detection and prediction of warm season midtropospheric vortices by the rapid update cycle the authors perform a statistical and dynamical analysis of midtropospheric mesoscale vortices captured by analyses from the rapid update cycle version 2 ruc 2 during the period 1 may to 31 august 1999 a total of 203 vortices meeting conditions of an automated algorithm were found of these 86 were observed to form within organized convection and were termed mesoscale convective vortices mcvs mcvs were favored over a broad area from eastern colorado and western nebraska to the mississippi river valley essentially collocated with the loci of organized convection the remaining 117 vortices termed dry vortices clustered in the immediate lee of the rocky mountains and over the southeastern united states vortices arising from convection had considerably greater intensity and longevity than dry vortices they were roughly five times more likely to be involved with the triggering of new convection a relationship was found between intensity and longevity such that there appears to be a maximum vortex lifetime that can be estimated from its maximum intensity vortices arising from convection had markedly greater humidity and water vapor mixing ratio underneath their centers compared to dry vortices consistent with many dry vortices having a topographic origin and mcvs arising from organized convection parameters such as horizontal scale background vertical wind shear and horizontal deformation were not systematically related to intensity or longevity prediction of mesoscale vortices by the ruc 2 was examined for a subsample of all cases in general the ruc 2 was able to predict the evolution of vortices once analyzed but had virtually no skill at predicting 12 h in advance the formation of the vortices however forecasts of organized convection should still benefit from accurate predictions of long lived vortex tracks

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

evolution of a mesoscale upper tropospheric vorticity maximum and comma cloud from a cloud free two dimensional potential vorticity anomaly a diagnostic case study is presented in which output from the limited area forecast version of the meteorological office operational unified model was used together with water vapour and cloud imagery from the meteosat satellite the case chosen for study was an archetypally simple example in which a long narrow strip of air with high potential vorticity pv in the upper troposphere strictly a tropopause depression became unstable and rolled up into fairly ling lived mesoscale vortices for much of the time the vortices were cloud free and they were dynamically pure examples of very small upper air pv anomalies moving relative to the strata beneath as such they provided a good test of theoretical deductions from the pv invertability principle and of the performance of the dynamical components of the forecast model the evolution of the mesoscale vortices as revealed in the satellite imagery was well handled by the unified model indicating that the small scales were reproduced well by the model dynamics even though they were not fully defined by the routine observations fed into the model as the vortices began to form the stretching deformation along the axis of the initial pv strip was very small and the 900 km spacing of the vortices was broadly consistent with theoretical expectations for the wavelength of instabilities growing on such a pv strip a detailed analysis of one of the mesoscale vortices throughout its 3 day lifetime showed that its maximum potential vorticity and absolute vorticity decreased with time as it travelled within the circulation of large scale anticyclonic gyre by the end of the second day when cloud first formed the vortex had become a weak upper tropospheric shear line 500 km long sandwiched between a pair of anticyclonic mesoscale vortices 900 km apart the meteosat imagery revealed a characteristic two component structure both in the water vapour channel and when the cloud eventually formed in the infrared channel too this structure which resembled that seen on other occasions is explained in terms of a particular combination of vertical motion and advection in the region of sharp humidity gradients alongside dry stratospheric air that had intruded into the upper troposphere

diagnostic study of a narrow cold frontal rainband and severe winds associated with a stratospheric intrusion a diagnostic study of a severe wind event associated with a cold front is presented based on output from an operational numerical weather prediction model together with radar and satellite imagery and detailed surface observations an intrusion of stratospheric air initially with a potential vorticity of 2 pv units is shown as part of a backward tilted filament to have plunged down to the lower troposphere where it was associated with a narrow cold frontal rainband at its leading edge and produced severe wind gusts up to 70 knots a close correspondence in time and space is revealed between these surface events and the appearance in the model of a pocket of diluted stratospheric air with pv 1 at the 2 km level the stratospheric intrusion produced two distinguishable wind surges one behind the narrow cold frontal rainband and another mainly dry about 200 km farther behind the strength of the winds was attributable to the downward transport of momentum as part of the large scale dynamics local moist processes played only a minor role at coarse resolution the radar echo from the narrow cold frontal rainband resembled line convection but it is shown that there were significant differences between this event and the archetypal form of line convection often seen in the british isles

a northern hemispheric climatology of cross tropopause exchange for the era15 time period 1979 1993 1 a 15 year climatology of cross tropopause exchange in the extratropical northern hemisphere is presented based upon a previously developed lagrangian methodology and reanalysis data from the european centre for medium range weather forecasts ecmwf for the years 1979 1993 for this time period no apparent trends exist for upward troposphere to stratosphere tst and downward stratosphere to troposphere stt cross tropopause transport the seasonal cycles of hemispherically integrated tst and stt and the zonally integrated meridional exchange distributions show relatively little interannual variability the 15 year averaged geographical distribution of stt reveals significant deviations from zonal symmetry and pronounced seasonal variability stt occurs predominantly over the atlantic and pacific storm track regions during winter spring and autumn and also over the mediterranean in winter and spring in contrast during summer stt maxima are located over the continents particularly over southeastern europe and central asia tst is less variable and is strongest near the southern tip of greenland and the aleutian islands during all seasons aspects of the interannual variability of the geographical exchange distributions are investigated over the atlantic stt varies significantly in line with the changing storm tracks during different phases of the north atlantic oscillation nao whereas tst does less so special consideration is given to vertically deep exchange where the exchange air parcels transfer rapidly from the lowermost stratosphere to the boundary layer or vice versa these processes occur mainly during winter and exhibit pronounced maxima over the north american west deep stt and east deep tst coasts

fragmentation of stratospheric intrusions evidence is presented pointing to the existence of rich and coherent subsynoptic and mesoscale flow features at tropopause levels these features are related to and evolve from the classical v shaped intrusions of stratospheric air down to tropospheric elevations it is shown that intrusions can develop into elongated 2000 3000 km and slender 200 km streamers and that thereafter such a streamer can roll up to form a train of stalactite shaped vortex subentities with an accompanying substantial thinning of the intervening filament in addition there are indications that the vortices themselves can develop a spirallike interior structure of interleaved stratospheric and tropospheric air these inferences are based upon two independent but complementary sources analysis of the potential vorticity distribution on tropopause transcending isentropic surfaces derived from the analysis fields of the european centre for medium range weather forecasts either directly or indirectly using a contour advection technique and imagery from the water vapor channel of the european space agency meteosat 4 satellite streamers were observed to occur with a frequency of approximately one per week over central and southern europe during the winter of 1991 1992 the fragmentation is linked to the instability or self development of a filament of enhanced potential vorticity and it can modify or instigate surface weather systems moreover by inducing a substantial and rapid enlargement of the intrusion s surface area it greatly enhances the potential for local irreversible mixing of stratospheric and tropospheric air

tropopause folds in era interim global climatology and relation to extreme weather events tropopause folds are intimately linked to upper level frontogenesis and jet stream dynamics they play an important role for stratosphere troposphere exchange the dynamical coupling of upper and lower tropospheric levels and for generating severe weather events this study presents a global climatology of tropopause folds using era interim reanalysis data from 1979 to 2012 and a refined version of a previously developed 3 d labeling and fold identification algorithm this algorithm objectively separates stratospheric and tropospheric air in complex situations e g in regions with strong low level inversions and in extratropical cyclones where diabatically generated potential vorticity anomalies typically occur three classes of tropopause folds are defined shallow medium and deep and their geographical distribution vertical extent and seasonal cycle are investigated most shallow folds occur along the subtropical jet stream in agreement with previous studies hot spots of medium and deep tropopause folds are found west of australia and along the coast of antarctica in the southern hemisphere and around the east coast of north america in the northern hemisphere seasonal cycles show maxima in winter for all fold classes medium and deep folds are frequently associated with surface wind gust and precipitation extremes as quantified for folds over the southern indian ocean wind gust extremes occur mainly in an elongated band upstream and equatorward of folds whereas precipitation extremes occur mainly east and poleward of folds overall in the considered region about 20 of medium folds and 33 of deep folds are associated with surface wind or precipitation extremes in the vicinity of the fold

interpretation of satellite imagery of a rapidly deepening cyclone model output and observational data are used to interpret in detail satellite images of a distinctive cloud system several hundred kilometres long which was observed before and during rapid cyclonic development that occurred over england conceptual models are forwarded which account for the structure of the major cloud areas and upper level moisture fields as observed by water vapour imagery immediately prior to and following the onset of vigorous cyclogenesis the cloud system corresponded to what r b weldon refers to as a baroclinic leaf cloud and was characterized by ana cold frontal ascent the baroclinic leaf lay within an area of enhanced ascent ahead of a major upper level trough a jet streak which originated upstream propagated rapidly around the base of the upper trough a tongue of dry air centred on the left flank of this jet streak lay immediately upstream of the leaf cloud and had a major influence on its subsequent development this intrusion of dry air was well represented by the meteorological office fine mesh model which showed it as a pronounced tongue of recently descended air with high potential vorticity which originated in the upper troposphere and lower stratosphere rapid cyclogenesis occurred as the dry intrusion overran low level air of high w within a warm conveyor belt at the southern tip of the leaf cloud interaction of the dry intrusion and baroclinic leaf cloud is shown to be particularly important in accounting for the detailed distribution of weather it also suggests a way of pinpointing the location and timing of vigorous cyclogenesis

greenschist facies metamorphism of the burgess shale and its implications for models of fossil formation and preservation metamorphosed silty mudstones of the burgess shale and stephen shale formations record a poly metamorphic history an early greenschist facies event associated with burial by paleozoic strata produced a nearly ubiquitous bedding parallel cleavage s1 tectonic exhumation during the formation of the southern canadian rocky mountains produced a domainal subgreenschist facies retrograde overprint in which a high angle crenulation cleavage s2 was developed whereas all rocks have experienced these two events the degree of deformation and fossil pre servation varies with position relative to the cathedral escarpment this paleosubmarine cliff resulted in a zone of reduced deformation within adjacent strata by buttressing them during burial and deflecting deformation during orogenesis fossil bearing strata are composed of a typical greenschist assemblage of muscovite chlorite quartz albite are devoid of clays and contain an average of 0 28 organic carbon this typical metamudstone assemblage is consiste

climatology of tropopause folds over a european arctic station esrange 1 eleven years september 1996 to august 2007 of continuous measurements of three dimensional wind and backscattered signal strength observed with esrange radar esrad have been utilized to study the annual and interannual variation of tropopause folds over an arctic station two typical tropopause fold events one is associated with a streamer type of system and the other with a cutoff low are selected and are characterized with the help of synoptic charts and potential vorticity pv analysis typical characteristics of radar parameters during the passage of folds are identified such as the sudden rise in the tropopause altitude high reflectivity layer sloping downward from the tropopause beneath the jet stream and intensification of the jet stream these characteristics are utilized to discern the tropopause fold in the radar data the climatology of tropopause folds exhibits a pronounced annual cycle with a large number of folds in winter and fewer in summer the annual cycle of folds is more or less similar in all the years however significant interannual variation is observed with winter periods exhibiting maximum interannual variability the climatology of folds and its annual cycle are compared and contrasted with similar climatological studies available in the literature the differences in the climatologies are discussed in light of differences in the algorithms and the spatial variability of fold frequency

dynamics in the extratropical tropopause region a case of transition between dynamically active and passive tracer advection it is argued that certain aspects of tracer patterns and related stirring by the flow in the extratropical tropopause region can be understood in terms of a transition between dynamically active and passive tracer advection called active to passive tracer transition in the framework of surface quasi geostrophic dynamics a specific initial value problem is defined and investigated it features a gradual transition between the two paradigms of tracer advection and allows a clear interpretation thanks to the idealized nature of the model setup physical reasoning and anecdotal evidence from previous studies suggest that at least in specific cases this interpretation is relevant for the real atmosphere copyright 2005 royal meteorological society

a global view of the extratropical tropopause transition layer from atmospheric chemistry experiment fourier transform spectrometer o3 h2o and co 1 the global behavior of the extratropical tropopause transition layer extl is investigated using o 3 h 2 o and co measurements from the atmospheric chemistry experiment fourier transform spectrometer ace fts on canada s scisat 1 satellite obtained between february 2004 and may 2007 the extl depth is derived using h 2 0 0 3 and co 0 3 correlations the extl top derived from h 2 0 0 3 shows an increase from roughly 1 1 5 km above the thermal tropopause in the subtropics to 3 4 km 2 5 3 5 km in the north south polar region implying somewhat weaker troposphere stratosphere transport in the southern hemisphere the extl bottom extends 1 km below the thermal tropopause indicating a persistent stratospheric influence on the troposphere at all latitudes the extl top derived from the co 0 3 correlation is lower at 2 km or 345 k 1 5 km or 335 k in the northern southern hemisphere its annual mean coincides with the relative temperature maximum just above the thermal tropopause the vertical co gradient maximizes at the thermal tropopause indicating a local minimum in mixing within the tropopause region the seasonal changes in and the scales of the vertical h 2 o gradients show a similar pattern as the static stability structure of the tropopause inversion layer til which provides observational support for the hypothesis that h 2 o plays a radiative role in forcing and maintaining the structure of the til

dynamics and geometry of extratropical cyclones in the upper troposphere by a neighbor enclosed area tracking algorithm abstractthis study shows that the morphological characteristics of upper tropospheric extratropical eddies are closely related to the background flow in the northern hemisphere winter enclosed surfaces of 300 hpa relative vorticity are identified by using the neighbor enclosed area tracking algorithm and the periphery of these surfaces are approximated by ellipses eddies are classified into five categories according to the approximate ellipse eddies having an oblateness of less than 0 6 are classified as near circle or are otherwise classified as northeast southwest ne sw northwest southeast nw se north south or west east according to the direction of the major axis in the wintertime climatology ne sw oriented cyclones are collocated with the jet stream while nw se oriented cyclones mostly reside north of the jet in interannual variability moreover the frequency of ne sw cyclones is slightly correlated with the arctic oscillation ao index while the frequency of nw se cyclones is high

the advection of high resolution tracers by low resolution winds abstract the usefulness of any simulation of atmospheric tracers using low resolution winds relies on both the dominance of large spatial scales in the strain and time dependence that results in a cascade in tracer scales here a quantitative study on the accuracy of such tracer studies is made using the contour advection technique it is shown that although contour stretching rates are very insensitive to the spatial truncation of the wind field the displacement errors in filament position are sensitive a knowledge of displacement characteristics is essential if lagrangian simulations are to be used for the inference of airmass origin a quantitative lower estimate is obtained for the tracer scale factor tsf the ratio of the smallest resolved scale in the advecting wind field to the smallest trustworthy scale in the tracer field for a baroclinic wave life cycle the tsf 6 1 0 3 while for the northern hemisphere wintertime lower stratosphere the tsf 5 5 0 5 when using the most stringent

deep tropospheric gravity waves created by leeside cold fronts abstract the water vapor channel of the geostationary operational environmental satellite goes 8 reveals narrow 30 km wide elongated 500 1000 km bands that propagate southward on the eastern side of the rocky mountains from colorado to texas two events in which surface and wind profiler observations show that these bands are associated with leeside cold fronts are documented in detail and several other cases are summarized the wind profilers observe vertical motions exceeding 1 m s 1 in narrow plumes at the leading edge of the fronts in broader zones in the upper troposphere and in the lower stratosphere these cause vertical displacements of up to 1 km and are responsible for the signature in water vapor images the bands occur when the rocky mountains block either arctic leeside cold fronts coming from the north or northeast or pacific cold fronts coming from the northwest the blocking changes the frontal orientation and disrupts geostrophic thermal wind balance near the terrain modified fron

convective injection into stratospheric intrusions 1 stratospheric intrusions tropopause folds are known to be major contributors to stratosphere troposphere exchange the specific mixing processes that lead to irreversible exchange between stratospheric intrusions and the surrounding troposphere however are not entirely understood this study presents direct observations of moist convection penetrating into stratospheric intrusions the characteristics of convective injection are shown by using in situ aircraft measurements radar reflectivities and model analyses convective injection is observed at altitudes up to 5 km above the bottom of a stratospheric intrusion aircraft measurements from the stratosphere troposphere analyses of regional transport 2008 start08 experiment show that convective injection in stratospheric intrusions can be uniquely identified by coincident observations of water vapor greater than about 100 ppmv and ozone greater than about 125 ppbv trajectory analyses show that convective injection can impact transport in both directions from troposphere to stratosphere and from stratosphere to troposphere we present a conceptual model of the synoptic meteorological conditions conducive to convective injection in stratospheric intrusions in particular convective injection is found to be associated with a split front where the upper level frontal boundary outruns the surface cold front

characteristics of tropopause folds over arctic latitudes 1 characteristics of tropopause folds over arctic latitudes have been studied using vhf radar measurements supplemented by balloon measurements the variation of the radar parameters during the passage of tropopause folds is discussed in detail to our knowledge these observations constitute the first spaced antenna sa radar measurements during the passage of tropopause folds this allows us to compare the parameters detectable using this mode with those observed using other configurations such as the doppler beam swinging dbs technique in general the structural characteristics such as the slope of folds seem to be similar at arctic latitudes to that at midlatitudes however the height of the tropopause and the axis of the jet stream and hence the folding are found to be lower by 1 2 km than their counterparts in midlatitudes in the case studies the radar derived parameters such as the signal to noise ratio snr and vertical shear of horizontal wind clearly show the upper air frontal zone the frontal circulation conceived from vertical velocity including the warm conveyer belt flow and the dry intrusion is clearly visible in the first case whereas it is masked by high amplitude mountain lee waves in the second case further the frontal zone seems to be acting as a critical layer to mountain lee wave activity by absorbing filtering the wave activity the aspect angles derived from the present analysis agree well with those estimated by vertical beam spectral width but are small in comparison with those estimated by the power ratio method the mean full correlation analysis fca turbulent velocity is estimated using the esrad data obtained during the passage of 15 tropopause folds the mean eddy diffusion coefficients kz near the tropopause and in the upper portion of the fold where strong turbulence is seen in case studies are found to be 3 54 and 6 4 m2 s 1 respectively utilizing the mean kz and the mean ozone gradient obtained from ozonesondes values the ozone fluxes across the tropopause and topside of the fold due to turbulence are estimated as 0 71 m s 1 ppbv and 0 32 m s 1 ppbv respectively although the flux across the tropopause is more than that occurring near the fold the exchange occurring through folds could be more significant to the tropospheric chemical budget

tropopause folds and cross tropopause exchange a global investigation based upon ecmwf analyses for the time period march 2000 to february 2001 1 a new methodology is proposed to identify folds of the dynamical tropopause taken as the 2 potential vorticity pv units pvu isosurface from global analysis data sets from the european centre for medium range weather forecasts ecmwf it consists of a three dimensional subdivision of the atmosphere into stratospheric and tropospheric parts and a subsequent examination of multiple tropopause crossings in vertical profiles of the analyses the method is applied to a 1 year period starting in march 2000 seasonal mean fold frequency distributions show that folds occur preferentially in the subtropics with maximum frequencies of about 30 pronounced maxima are located in the subtropical bands that extend from 20 e to 120 e on both hemispheres during summer generally subtropical folds are comparatively shallow deep folds occur most frequently in midlatitudes during winter over eastern north america and the western north atlantic with maximum frequencies of about 1 detailed investigation of the relationship between individual folds and cross tropopause exchange events reveals that on the average individual folds in the extratropics are associated with larger exchange mass fluxes compared to the subtropics however due to the much higher frequency of subtropical folds the percentage of exchange events that are associated with tropopause folds is larger near 20 40 latitude 50 70 than further poleward 20 30 during winter and 10 20 during summer this indicates that tropopause folds are the key feature for cross tropopause exchange in the subtropics whereas in the extratropics other tropopause structures are at least of equal importance

the palette of fronts and cyclones within a baroclinic wave development abstract a study is undertaken of the concurrent development of fronts and cyclones within a growing baroclinic wave the dynamical framework for the study is that of the semigeostrophic adiabatic flow of a uniform potential vorticity atmosphere that is sandwiched between two horizontal plates on an f plane a three dimensional spectral model is used to examine the growth to finite amplitude of the normal modes of this system for basic states that comprise of a symmetric jetlike baroclinic flow with and without a superposition of a uniform barotropic shear of either cyclonic or anticyclonic vorticity it is demonstrated that the presence of such lateral shear in the ambient environment exerts a profound influence upon the ensuing palette of fronts and cyclones on the synoptic scale this flow component influences the scale and strength of the individual surface highs and lows and also modifies the extent of their lateral drift away from and their relative movement along the baroclinic zone aloft t

the link between cut off lows and rossby wave breaking in the southern hemisphere the climatological link between cut off low col pressure systems that occur from 20 to 50 s and rossby wave breaking rwb in the southern hemisphere sh is examined for 1979 2008 it is shown that cols are associated with either rwb events 89 or with potential vorticity pv intrusions where there is north south advection of high pv air 11 in the vast majority of cols the rwb events occur upstream on or before the day of the col formation the evolution of the pv geopotential heights static stability absolute vorticity and temperature advection fields during the cols are consistent with the formation of high pv anomalies that induce cyclonic circulations as predicted by theory rwb plays a key role in producing the split flow associated with cols in the sh which in turn produces absolute vorticity anomalies by shear curvature vorticity conversion and creates static stability anomalies the cols associated with rwb at 330 k are deeper and more persistent than those associated with 350 k rwb and surface processes differ depending on the isentropic surface on which the associated rwb occurs the seasonality of the rwb and cols are similar and is linked to the seasonal march of the westerly jets copyright 2010 royal meteorological society

tropical upper tropospheric potential vorticity intrusions during sudden stratospheric warmings abstractthe intrusion of lower stratospheric extratropical potential vorticity into the tropical upper troposphere in the weeks surrounding the occurrence of sudden stratospheric warmings ssws is examined the analysis reveals that ssw related pv intrusions are significantly stronger penetrate more deeply into the tropics and exhibit distinct geographic distributions compared to their climatological counterparts while climatological upper tropospheric and lower stratospheric utls pv intrusions are generally attributed to synoptic scale rossby wave breaking it is found that ssw related pv intrusions are governed by planetary scale wave disturbances that deform the extratropical meridional pv gradient maximum equatorward as these deformations unfold planetary scale wave breaking along the edge of the polar vortex extends deeply into the subtropical and tropical utls in addition the material pv deformations also reorganize the geographic structure of the utls waveguide which alters where synopti

the role of tropical cyclones in the formation of tropical upper tropospheric troughs abstract tropical upper tropospheric troughs tutts also known as midoceanic troughs are elongated troughs that appear in summer monthly averaged maps of the upper tropospheric flow over the oceans the transient part of these climatological features is composed of tutt cells and their origin is the subject of this study tutt cells often occur to the east of tropical cyclones a nonlinear shallow water model on the sphere was used in a simplified study of the interactions between tropical cyclones and the circumpolar vortex based on the results of these simulations and keeping in mind their limitations it is proposed that dispersion of short rossby wave energy is a possible mechanism to explain the formation of tutt cells to the east of tropical cyclones the model simulations suggest that two types of tutt cells may form to the east of tropical cyclones when embedded in cyclonic or weak anticyclonic shear the trough to the east of the tropical cyclone may broaden resulting in the formation of an

on the relation of 6 7 μm water vapour features to isentropic distributions of potential vorticity currently available isentropic maps of potential vorticity ipv maps are of low resolution in this note we examine the possibility of using 6 7 m satellite derived water vapour measurements to obtain higher resolution information about ipv distributions while attempts to relate the two data sets analytically have so far proved unsuccessful a qualitative comparison shows very similar features in both our results suggest that over limited areas it may be possible to use 6 7 m brightness temperatures to obtain approximate contours for water vapour mixing ratio on a particular isentropic surface in the upper troposphere for areas free of high clouds these contours are expected to parallel the ipv contours on this surface in a case study the resulting map exhibits dramatically increased horizontal resolution compared with present ipv maps detailing an intriguing upper tropospheric feature at sub synoptic scales

tropospheric intrusions associated with the secondary tropopause 1 deep intrusions of tropospheric air into the lower stratosphere above the subtropical jet are investigated using new observations and meteorological analyses these intrusions are characterized by low ozone concentration and low static stability the low ozone layer is consistently observed from ozonesonde profiles and satellite remote sensing data from aura hirdls the intruding layer occurs along and under the poleward extending tropical tropopause which becomes the secondary tropopause in middle to high latitudes the association of the ozone and the thermal structure provides evidence for the physical significance of the subtropical tropopause break and the secondary tropopause the core of the intruding layer is typically between 370 and 400 k potential temperature 15 km but the vertical extent of the intrusion can impact ozone above 400 k the lower boundary of the overworld two intrusion events over the continental united states in the spring of 2007 are analyzed to show the spatial extent and the temporal evolution of the intruding air mass these examples demonstrate the effectiveness of potential temperature lapse rate i e static stability as a diagnostic for the intrusion event comparison with the potential vorticity field is made to show the complementarity of the two dynamical fields the static stability diagnostic provides a tool to map out the horizontal extent of the intruding layer and to investigate its evolution furthermore the diagnostic makes it possible to forecast the intrusion event for field studies

breaking waves at the tropopause in the wintertime northern hemisphere climatological analyses of the orientation and the theoretical lc1 2 classification abstract breaking waves on the tropopause are viewed as potential vorticity pv streamers on middle world isentropic levels a northern hemisphere winter climatology of the streamers spatial distribution and meridional orientation is derived from the 40 yr ecmwf re analysis era 40 dataset and used to assess the nature and frequency of occurrence of breaking synoptic scale waves the streamers are grouped into two classes related to the so called cyclonic lc2 and anticyclonic lc1 patterns and the ambient wind strength and wind shear is also noted it is shown that the occurrence of cyclonic and anticyclonic pv streamers exhibits a distinct spatial variability in the horizontal and the vertical the majority of cyclonic pv streamers are found on lower isentropic levels that intersect the tropopause at more poleward latitudes whereas anticyclonic streamers predominate at higher elevations in the subtropics an analysis of the streamer patterns for the two phases of the north atlantic oscillation

the presidents day cyclone of 18 19 february 1979 influence of upstream trough amplification and associated tropopause folding on rapid cyclogenesis abstract a diagnostic analysis of an amplifying polar jet trough system and associated tropopause fold which preceded the 19 february 1979 presidents day cyclone is presented the analysis is based on conventional radiosonde data infrared and visible satellite imagery 6 7 m water vapor measurements from the temperature humidity infrared radiometer thir and ozone measurements from the total ozone mapping spectrometer toms the case study indicates that dynamically forced meso scale vertical circulations played an important role in the extrusion of stratospheric air along the axis of a polar jet and the subsequent development of the storm system specific findings include 1 tropopause folding accompanying an amplifying polar jet trough system occurred along the axis of the intensifying polar jet in response to subsidence forced by geostrophic deformation patterns associated with the jet streak 2 the folding process extruded dry stratosphere air marked by high values of potential vorticity dow

intrusions into the lower stratospheric arctic vortex during the winter of 1991 1992 investigations of the kinematics of the lower stratospheric arctic vortex during the winter of 1991 1992 using the contour advection with surgery technique reveal three distinct events in which there was substantial intrusion of midlatitude air into the vortex in apparent contradiction of the view that the polar vortex constitutes an isolated air mass two of these events in late january and mid february were well documented they were predicted in high resolution forecasts by the european centre for medium range weather forecasts most clearly in experimental forecasts with reduced diffusion direct confirmation of the presence of the intrusions and of their calculated locations was provided by aerosol observations from the airborne differential absorption laser lidar aboard the nasa dc 8 taken as part of the second airborne arctic stratospheric expedition campaign aerosol rich air of midlatitude origin was seen in the expected position of the intrusions the reality of the february event was also confirmed by in situ measurements from the nasa er 2 such events may be significant for the chemical processes taking place within the winter vortex the intrusions were evidently related to the meteorology of the northern stratosphereduring this winter and in particular to persistent tropospheric blocking over the northeastern atlantic ocean and western europe and concomitant ridging into the lower stratospheric vortex in this region nevertheless preliminary investigations have indicated that such events are not uncommon in other northern hemisphere winters although no such events were found in the southern hemisphere during the antarctic winter of 1987

substructure of a map streamer a study is undertaken of the substructure of an upper level potential vorticity streamer that approached the european alps during the field phase of the mesoscale alpine programme map the diagnosis is based upon a lagrangian forward projection lfp technique which can provide a spatial refinement of the operational european centre for medium range weather forecasts analysis fields the reconstructed fields capture several notable fine scale features of the streamer s structure that include spiral arms of a vortex like feature and a richly structured western flank to the streamer comprising a deep primary fold surmounted by a significant secondary fold with an intermediate distinctive striation that extends back into the stratosphere these features are not at variance with independent high resolution satellite water vapour images and measurements gathered during a flight mission using an airborne water vapour differential absorption lidar dial instrument and hence lend a measure of credence to both the lfp approach and the dial measurements moreover the analysis sheds light on the evolution and dynamics of the streamer s vortices the origin of the folds the mismatch between the satellite observations and fields from other sources and also has implications for stratosphere troposphere exchange and the accompanying chemical mixing copyright 2003 royal meteorological society

influence of upstream diabatic heating upon an alpine event of heavy precipitation abstract narrow extended troughs associated with elongated streamers of potential vorticity pv are a frequent feature of upper tropospheric flow and they can instigate or modify surface weather systems in this study consideration is given to the generation of one particular pv streamer that was itself a dynamical precursor of a heavy precipitation event in the alpine region it is shown that the streamer s parturition over the eastern north atlantic is linked to a prior event of cyclo and frontogenesis upstream over the western north atlantic diagnostic trajectory analysis and heuristic simulations with a limited area nwp model suggest that the streamer s origin is influenced crucially by the following chain of physical processes cloud diabatic heating associated with the upstream cyclogenesis enhances a downstream negative pv anomaly in the upper troposphere and the flow associated with this anomaly subsequently helps transform a farther downstream preexisting broad positive pv anomaly into an elo

heavy precipitation on the alpine southside an upper level precursor analyses of four separate autumnal events of very heavy precipitation on the southern slopes of the european alps indicate that each was accompanied by a strikingly similar anomaly at upper tropospheric levels it took the form of a narrow 500km deep 4km and elongated 2000 km streamer of intruded stratospheric air sic high potential vorticity air extending north south from the british isles to the western mediterranean in each case the streamer translated comparatively slowly eastward and the storm event ensued as its forward flank approached the alpine ridge empirical indicators and theoretical considerations support the thesis that the streamer is an ubiquitous dynamically significant and distinctive precursor of storms on the alpine southside

identification and era 15 climatology of potential vorticity streamers and cutoffs near the extratropical tropopause abstract a novel approach is introduced to identify potential vorticity pv streamers and cutoffs as indicators of rossby wave breaking near the extratropical tropopause and to compile climatologies of these features on different isentropic surfaces the method is based on a contour searching algorithm that identifies the dynamical tropopause 2 potential vorticity units pvu pvu 1 10 6 k kg 1 m2 s 1 isoline on isentropic surfaces the contour is then analyzed to search for cutoffs and filament like streamers whereas the identification of cutoffs is unambiguous the one for streamers requires the specification of two parameters that determine the width and length of the contour feature to be classified as a streamer this technique has been applied to the pv distribution in the northern hemisphere on isentropes from 295 to 360 k during the time period from 1979 to 1993 using the 15 yr european centre for medium range weather forecasts ecmwf re analysis era 15 the climatology reveals a pronou

frontal instability generated by tropospheric potential vorticity anomalies the development of secondary disturbances on a two dimensional front is described using a linear stability analysis a two stage process is envisaged in which first strong frontogenesis produces condensation at the front this leads to the generation of a lower tropospheric zone of high potential vorticity pv lying along the front as frontogenesis weakens the second stage is entered in which an essentially steady front is susceptible to the growth of linear normal modes along the front owing to the existence of the pv anomaly or equivalently the frontal rainband thus for a typical band of width 160 km a frontal wave of some 800 km is produced with a growth rate of about 1 day 1 the dynamics of these modes is examined by considering both the realistic frontal flow as well as idealized strips of pv anomalies the idealized case is potentially applicable to a variety of meteorological situations such as upper jet streaks useful insight is gained from an analysis of the energetics of the modes this shows that for narrow frontal pv anomalies the waves main energy source is the basic kinetic energy and further they have a negative vertical heat flux recent observations suggest that frontal waves are indeed characterized by such a heat flux as most frontal zones involve significant condensation and therefore are likely to exhibit a lower tropospheric pv maximum it is stressed that studies of frontal waves need to include this aspect of the frontal structure

transport out of the lower stratospheric arctic vortex by rossby wave breaking the fine scale structure in lower stratospheric tracer transport during the period of the two arctic airborne stratospheric expeditions january and february 1989 december 1991 to march 1992 is investigated using contour advection with surgery calculations these calculations show that rossby wave breaking is an ongoing occurrence during these periods and that air is ejected from the polar vortex in the form of long filamentary structures there is good qualitative agreement between these filaments and measurements of chemical tracers taken aboard the nasa er 2 aircraft the ejected air generally remains filamentary and is stretched and mixed with midlatitude air as it is wrapped around the vortex this process transfers vortex air into midlatitudes and also produces a narrow region of fine scale filaments surrounding the polar vortex among other things this makes it difficult to define a vortex edge the calculations also show that strong stirring can occur inside as well as outside the vortex

tracer lamination in the stratosphere a global climatology vertical soundings of stratospheric ozone often exhibit laminated tracer structures characterized by strong vertical tracer gradients the change in time of these gradients is used to define a tracer lamination rate it is shown that this quantity can be calculated by the cross product of the horizontal temperature and horizontal tracer gradients a climatology based on uars satellite borne ozone data and on ozone like pseudotracer data is presented three stratospheric regions with high lamination rates were found the part of the stratospheric overworld which is influenced by the polar vortex the part of the lowermost stratosphere which is influenced by the tropopause and a third region in the subtropical lower stratosphere mainly characterized with strong vertical shear high lamination rates in the stratospheric overworld were absent during summer whereas in the lowermost stratosphere high lamination rates were found year round this is consistent with the occurrence and seasonal variation of the horizontal tracer gradient and vertical shear necessary for tilting the tracer surfaces during winter high lamination rates associated with the stratospheric polar vortex are present down to 100 hpa several features of the derived climatology are roughly consistent with earlier balloonborne studies the patterns in the southern and northern hemisphere are comparable but details differ as anticipated from a less disturbed and more symmetric southern polar vortex

global characteristics of medium scale tropopausal waves observed in ecmwf operational data global characteristics and seasonal variation of medium scale zonal wavelengths of 2000 3000 km waves observed around the midlatitude tropopause are examined using 6 hourly european centre for medium range weather forecasts operational data over four years 1990 93 covering both hemispheres medium scale waves and synoptic scale waves are extracted using time filters and their characteristics are compared hovmoller diagrams indicate the existence of medium scale waves in the southern hemisphere as well as in the northern hemisphere the zonal wavelengths of medium scale waves are slightly larger in the southern hemisphere than in the northern hemisphere medium scale waves are mostly active in three regions the north atlantic in winter dec jan feb the north pacific in spring mar apr may mam and the south indian ocean in autumn mam these regions are roughly corresponding to and slightly downstream of storm tracks where synoptic waves are dominant significant differences in seasonal variation of the intensity between the two kinds of waves are also found the maximum of wave amplitudes is seen around the tropopause at latitudes slightly higher than the jet stream axis where the meridional gradient of the quasigeostrophic potential vorticity qpv is maximized the positive large qpv gradient is attributed to the atmospheric structure around the midlatitude tropopause that is located in vertical westerly shear of the jet stream this fact suggests that the medium scale waves are waves trapped around the midlatitude tropopause

potential vorticity anomalies of the lowermost stratosphere a 10 yr winter climatology abstract inspection of the potential vorticity pv distribution on isentropic surfaces in the lowermost stratosphere reveals the ubiquitous presence of numerous subsynoptic positive pv anomalies to examine the space time characteristics of these anomalies a combined identification and tracking tool is developed that can catalog each individual anomaly s effective amplitude location overall spatial structure and movement from genesis to lysis a 10 yr winter climatology of such anomalies in the northern hemisphere is derived for the period 1991 2001 based upon the 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 the climatology indicates that the anomalies are frequently evident above high topography and in a quasi annular band at about 70 n are long lived days to weeks and that their effective amplitude is typically 2 pv units pvu higher than that of the ambient environment in addition the derived climatologies and associated composites pose questions

structure and dynamics of an alpine potential vorticity banner a detailed analysis is undertaken of the primary alpine shear zone that occurred on 1 october 1999 during the mesoscale alpine programme this shear zone emanates from the south western alpine tip in north westerly flow conditions develops in response to the alpine scale flow splitting and separates the northerly mistral wind to the south west of the alps from the quasi stagnant air within the alpine wake the study is based on in situ flight level and dropsonde data from two research aircraft the data are used for the construction of an objective analysis in a cross section perpendicular to the shear zone and for diagnostic computations of the potential vorticity pv flux between vertically stacked flight legs the observed flow structure is compared with simulation results of the swiss model and the non hydrostatic canadian mesoscale compressible community model mc2 operating at horizontal resolutions of 14 and 3 km respectively immediately downstream of the topography the observed shear zone has a surprisingly quasi steady structure that becomes evident provided a slow westward migration is accounted for further downstream the shear zone shows increased signs of transience near the surface it has an overall width of 150 km but narrows to about 25 km near the top of the mistral inversion at a height of 2 km detailed analysis shows that the shear zone has a complex substructure consisting of at least three positive and three negative pv filaments these shear lines are characterized by a pronounced vertical coherence in the mixed layer and throughout most of the inversion layer one of the banners is also evident in low level tracer constituents diagnostic computations of the pv flux along the banners using the generalized bernoulli theorem reveal that most of the associated pv flux is due to vertically oriented vorticity within the inversion layer within the shear zone there is a spanwise circulation of appreciable strength it consists of a deformation flow with the axes of deformation oriented perpendicular to the shear zone this deformation flow in effect squeezes the pv banners and thereby makes them resilient with respect to dissipation and barotropic instabilities detailed intercomparison with numerical model results shows that models with a grid spacing below 15 km are able to capture the overall structure of the shear zone the mc2 model in addition credibly replicates some of the finer scale sub structure of the shear zone in particular at low levels the high predictability and steadiness of the pv banners supports the idea that individual banners are generated by flow separation and or gravity wave breaking events upstream it is argued that the overall width of the shear zone is thus in effect determined by the geometry of the upstream topography and the dynamical processes that govern the downstream advection of the pv banners copyright 2003 royal meteorological society

chemical discontinuity at the extratropical tropopause and isentropic stratosphere troposphere exchange pathways diagnosed using aura mls data 1 the chemical discontinuity at the extratropical tropopause extp and stratosphere troposphere exchange ste pathways are investigated using the long lived chemical species carbon monoxide co and ozone o3 measured by the aura microwave limb sounder mls a relative coordinate tropopause latitude tplat is developed based on potential vorticity pv from the goddard earth observing system version 5 geos 5 data assimilation system tplat is defined as the shortest geographic distance along an isentropic surface from the extratropical tropopause extp to an observation location our results show that this coordinate highlights the sharp chemical discontinuities at the extp more clearly than the widely used equivalent latitude coordinate geographical distributions of ste pathways and barriers are investigated based on meridional gradients in o3 abundances in the new tplat coordinate in conjunction with analysis of rossby wave breaking between 330 k and 360 k in northern hemispheric nh winter dec jan feb nh ste pathways are seen mainly above the northeast pacific in nh summer jun jul aug the nh pathway covers all longitudes at 330 k however it is mainly located above asia at 340 k and above the atlantic and the north pacific at 350 k and 360 k in the southern hemisphere sh there is a weaker ste region above the eastern indian ocean and the southwestern pacific at and above 350 k in sh winter and a stronger ste region over the southeastern pacific at these levels during sh summer in addition this study shows nh pv gradients are slightly stronger near the extp in summer than in winter even though the subtropical jet is weaker and rossby wave breaking is stronger in summer than in winter

rossby wave breaking in the southern hemisphere wintertime upper troposphere abstract the characteristics of rossby wave propagation and breaking in the southern hemisphere upper troposphere during winter are examined although the southern hemisphere subtropical jet is more zonally symmetric than that of the northern hemisphere there are still significant zonal variations in the upper tropospheric flow in particular the flow within a given sector 120 longitude can generally be characterized into one of four different configurations i a single jet ii a broken subtropical jet iii a polar jet at the upstream end of the subtropical jet or iv a polar jet at the downstream end of the subtropical jet using potential vorticity thinking and barotropic wind shear arguments it is argued that the characteristics of the rossby wave propagation and breaking will differ between each flow configuration consistent with these arguments examination of potential vorticity maps and contour advection calculations show differing wave breaking characteristics in particular t

water vapor heterogeneity related to tropopause folds over the north atlantic revealed by airborne water vapor differential absorption lidar 1 airborne differential absorption lidar dial measurements of tropospheric water vapor and aerosol clouds are presented from transfers across the north atlantic on 13 15 may and 16 18 june 2002 the intense dynamical activity over the atlantic is reflected in complex structures like deep tropopause folds extended dry layers and tilted aerosol filaments intrusions with h2o mixing ratios below 0 03 g kg 1 regularly develop along the storm track over intense cyclones and correspond to analyzed european centre for medium range weather forecasts ecmwf or simulated mm5 potential vorticity anomalies sloping folds are typically 1 km thick in vertical profiles but on horizontal sections resemble long filaments with widths of a few hundred kilometers filaments of solid roughly micron sized particles occur inside and along the axes of the tropopause folds the particles most likely originate in forest fires from where they are injected to the lower stratosphere by deep convection and later on reenter the troposphere in developing baroclinic disturbances their laminar appearance indicates that these intrusions have not yet been mixed but are eroded on timescales significantly larger than a few days by stretching thinning stirring and only finally turbulent diffusion mm5 mesoscale model simulations and with less accuracy also ecmwf analyses are capable of reproducing the dynamical structures associated with the observed dry intrusions however deep inside the intrusions where scales are small even the mm5 simulated water vapor mixing ratios are more than twice those observed the large dynamical range of water vapor mixing ratios 3 orders of magnitude and large gradients 2 g kg 1 km 1 at the intrusions boundaries constitute a challenge for future space borne water vapor dial systems

wave breaking and mixing at the subtropical tropopause abstract this paper discusses rossby wave breaking on the isentropic surfaces that intersect the subtropical tropopause using winds and isentropic potential vorticity from high resolution meteorological analysis the focus is both on particular aspects of individual wave breaking events as well as on more general aspects such as the spatial and temporal distribution of the mixing associated with these events the direction and intensity of wave breaking is shown to exhibit the same dependence on stagnation points in the wind field as that seen in previous highly idealized numerical model studies wave breaking that results in stratospheric intrusions into the troposphere can be categorized as weak or strong depending on the development of filaments or larger coherent vortices or cutoff lows the events presented show a deep vertical structure that approximately spans the region between the 330 k and 370 k isentropic surfaces where the tropopause is steeply sloping through the subtropical jets this i

baroclinic wave breaking and the internal variability of the tropospheric circulation abstract a simple model of the tropospheric circulation based on a 10 level primitive equation model is forced by linearly relaxing the potential temperature toward an idealized zonally symmetric equilibrium field the model equations are integrated in time until a statistically steady state is obtained the local relationship between the state of the background flow the direction of wave propagation and subsequent wave breaking at the tropopause level is then investigated maps of potential vorticity pv on isentropic surfaces are analyzed and all four different types of wave breaking described recently by peters and waugh are shown to occur it is found that cyclonic wave breaking events are usually initiated by poleward fluxes of wave activity and anticyclonic events by equatorward fluxes composites are then used to show that equatorward fluxes are associated with a jet that is locally broad and weak with relatively strong isentropic pv gradients to its equatorward flank by contrast poleward

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

quantification of filaments penetrating the subtropical barrier a method based on contour advection is introduced that aims to quantify the formation of filaments both equatorward and poleward of the subtropical barrier it is applied to diagnosed potential vorticity fields for every day of january and february in 1997 and 1998 an isosurface of modified potential vorticity is found to represent the region of largest isentropic gradients of potential vorticity and is hence assumed as the tropopause tropopause penetrating structures filaments forming in contour advected potential vorticity fields are identified and statistics of the abundance of such structures are derived filamentation as measured by this method exhibits a large temporal variability on the scale of days to weeks for example tropospheric cutoff systems developing in the wake of rossby wave breaking events cause strong filamentation to occur in the lowermost stratosphere the timescales governing filamentation are a function of altitude reflecting the differing types and amplitudes of waves inducing filamentation at different isentropic levels zonal asymmetries arise as rossby waves favorably break near the end of the north atlantic storm track a difference in the intensities of filamentation in january and february of 1997 and 1998 suggests that the relatively low values of ozone in the lowermost stratosphere observed in 1997 are related to increased filamentation induced stratosphere troposphere exchange compared to 1998 for example around 30 more filaments are found in the hemispheric and bimonthly mean at the 330 k isentropic surface in january and february of 1997 than during the same months of 1998 single events can represent most of the filamentation occurring in a month and hence interannual variability in the frequency of filamentation can be considerable