diagnosis of the downstream ridging associated with extratropical transition using short term ensemble forecasts abstract the dynamical mechanisms that led to downstream ridging during the extratropical transition et of typhoons tokage and nabi are evaluated using data drawn from a cycling ensemble kalman filter coupled with the weather research and forecasting model wrf during both transitions the ensemble covariances indicate that the 350 k potential vorticity pv at the apex of the ridge which is used to define the ridge structure is proportional to the amount of precipitation along the baroclinic zone to the northeast of the tropical cyclone tc and at some times to the upper tropospheric divergence above the tropical cyclone multivariate regression calculations indicate that the frontal precipitation has the largest impact on the ridge amplitude and area during tokage s transition while the tc divergence has roughly equal impact during some times of nabi s transition the amount of precipitation along the baroclinic zone is modulated by the lower tropospheric frontogenesis and moisture flux on the

research aircraft measurements of jet stream geostrophic and ageostrophic winds abstract radar altimeter and inertial navigation wind velocity measurements from research aircraft are shown to give the ageostrophic wind velocity distribution within a jet stream system near the tropopause results from one case study reveal cross height contour ageostrophic winds exceeding 20 m s 1 and centripetal acceleration induced ageostrophic winds approaching 100 m s 1 in the exit region of a jet streak which has entered into the trough region of a synoptic wave diagnostic calculations are made of the horizontal velocity divergence and the geostrophic and ageostrophic components of the observed wind velocity acceleration the results suggest caution in the application of near straight jet streak dynamics and the geostrophic momentum approximation to jet streak systems embedded within large amplitude synoptic wave regimes

potential vorticity in hurricane gloria abstract potential vorticity pv analysts for hurricane gloria of 1985 are derived from nested objective wind analyses of omega dropwindsonde and airborne doppler radar data the analyses resolve eyewall scale features in the inner vortex core and embed analyses of these features within the larger scale environment since three dimensional geopotential height fields required for evaluation of pv are not available in the core they are derived using the balance equation in the process of deriving the heights the degree of gradient balance is evaluated the 500 mb tangential winds in the core averaged azimuthally on the four cardinal points are close to gradient balance outside the radius of maximum wind the resulting depiction of pv is the first presented for a real hurricane due to data deficiencies immediately outside the doppler region as well as inside the eye smoothing of the wind data using a filter with a minimum 25 km spatial scale is required to derive a balanced geopotential height distr

ageostrophic geopotential fluxes in downstream and upstream development of baroclinic waves abstract with the use of a simple primitive equation model it is demonstrated that the convergence divergence of ageostrophic geopotential fluxes can be a major source sink of kinetic energy for both downstream and upstream development of baroclinic waves and can play a dominant role during the early stages of wave development it is also shown that both surface friction and effects lead to an asymmetry in the upstream versus downstream development with downstream development much stronger a total group velocity is defined based on ageostrophic fluxes and its relationship to the rate of wave packet spreading and to convective and absolute instability is discussed

an analysis of hurricane opal s forecast track errors using quasigeostrophic potential vorticity inversion abstract hurricane opal s landfall in october 1995 forms the basis of a serious hurricane forecast problem the potential for hurricane conditions over land with insufficient warning time official national hurricane center nhc a division of the tropical prediction center forecasts predicted landfall and passage inland over the eastern united states at a later time than observed because of underestimation of the northward component of the steering flow by the national centers for environmental prediction s ncep operational models and other hurricane track models the goal of this paper is to isolate the cause of the poor forecast of meridional storm motion in ncep s early eta model by using quasigeostrophic potential vorticity qgpv inversion qgpv inversion permits decomposition of the steering flow into contributions from different synoptic scale features the inversion procedure is applied to the eta analysis and 48 h eta forecast valid at 1200 utc 5 october 1995 analyses from the european centre

oriented precipitates of quartz and amphibole in clinopyroxene of metabasites from the greek rhodope a product of open system precipitation during eclogite granulite amphibolite transition in metabasites from the high grade metamorphic kimi complex of the greek rhodope lamellae of quartz and amphibole were observed together with either rutile or titanite precipitates in the cores of clinopyroxene that underwent a prolonged exhumation history from eclogite via granulite and amphibolite facies conditions lamellae are crystallographically oriented along clinopyroxene cleavage planes 010 and interpreted as the result of precipitation during a two step intracrystalline compositional adjustment from an omphacite to a ca tschermak rich clinopyroxene and finally to diopside even though retrograde diffusion profiles develop in clinopyroxene the diffusion rates of highly charged ions like si4 al3 and ti4 are too slow so precipitates rich in si4 quartz al3 amphibole and ti4 rutile or titanite form as viable kinetic alternatives these precipitation reactions are not possible isochemically and additional exchange of ions with the matrix is required for precipitation to occur this exchange of mainly rapidly diffusing low charge ions is postulated to proceed by bulk diffusion self diffusion and does not require special pathways or fluid even though these may play an additional role during metamorphism this hitherto undescribed process of precipitation made possible by diffusional exchange with the matrix through an intact host crystal lattice is termed here as open system precipitation osp no prior ca eskola rich ultrahigh pressure uhp composition of omphacite is required to explain the observed precipitates it is proposed that many precipitation phenomena that were hard to explain in a closed system scenario can now be explained more readily by osp calculation of an original solid solution composition as in an uhp phase from precipitate and host mineral analyses becomes imprecise to the degree that bulk diffusion and hence osp have been important

the impact of extratropical transition on the downstream flow an idealized modelling study with a straight jet the interaction of a tropical cyclone undergoing extratropical transition et with the midlatitude synoptic scale flow is investigated using full physics numerical experiments with idealized initial conditions the emphasis is on the impact on the midlatitude flow downstream of the et event the midlatitude flow is represented by a balanced straight jet stream as the tropical cyclone approaches the jet a ridge trough couplet and a distinct jet streak form in the upper level flow a midlatitude cyclone develops rapidly downstream of the et system and the further evolution is characterized by downstream baroclinic development based on hovmoller diagrams the upper level development is interpreted as the excitation and subsequent dispersion of a rossby wave train on the potential vorticity gradient associated with the jet the characteristics of this wave train are sensitive to the structure of the jet and to moist processes in the midlatitudes the tropical cyclone undergoing et acts as a sustained forcing for the wave train and the structure of the et system impacts the development most significantly one to two wavelengths downstream of et piecewise inversion of potential vorticity complemented by the partitioning of the flow into its rotational and divergent parts is applied to assess the impact of the et system quantitatively both the cyclonic circulation and the outflow of the tropical cyclone are important contributors to the formation and amplification of the ridge trough couplet the outflow anomaly reduces the eastward motion of the ridge trough couplet significantly and thus promotes phase locking between the tropical cyclone and the upper level pattern copyright 2008 royal meteorological society

extratropical transition of tropical cyclones over the western north pacific part i evolution of structural characteristics during the transition process abstract the development of extratropical cyclone structural characteristics that resulted from the extratropical transition of typhoon ty david 1997 and ty opal 1997 over the western north pacific is examined david moved poleward ahead of a midlatitude trough that was moving eastward as the dominant midlatitude circulation feature over the western north pacific during the transition david coupled with the midlatitude trough which led to the evolution of an intense cyclone that became the primary circulation over the north pacific although opal also moved poleward ahead of a midlatitude trough the principal midlatitude feature over the western north pacific was a preexisting stationary cyclone over the kamchatka peninsula during transition opal weakened and became a secondary cyclone to the preexisting primary north pacific cyclone the structural characteristics of the evolving extratropical cyclone with respect to each case are examined in the context of the interaction between a vortex an

interaction of a baroclinic vortex with background shear application to hurricane movement abstract most extant studies of tropical cyclone movement consider a barotropic vortex on a plane however observations have shown that real tropical cyclones are strongly baroclinic with broad anticyclones aloft also the distribution of the large scale potential vorticity gradient in the tropical atmosphere is very nonuniform these properties may substantially influence the movement of such storms note that the anticyclone above a hurricane will interact with the lower hurricane vortex and induce storm motion such interaction can be caused by both the direct effect of ambient vertical shear and the effect of vertical variation of the background potential vorticity gradient in this paper an attempt to isolate the effect of background vertical shear is made the hurricane is represented in a two layer quasigeostrophic model as a point source of mass and zero potential vorticity air in the upper layer collocated with a point cyclone in the lower layer the model is integrated by the method of co

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

postlandfall tropical cyclone reintensification in a weakly baroclinic environment a case study of hurricane david september 1979 abstract an analysis is conducted from a potential vorticity pv perspective of the reintensification of tropical storm david over the northeastern united states in september 1979 david a major long lived hurricane originated near the cape verde islands in late august 1979 it made final landfall in georgia on 4 september 1979 and weakened rapidly thereafter the noteworthy aspect of david was its subsequent reintensification approximately 27 h after landfall as a warm core disturbance in a weakly baroclinic environment in this regard the redevelopment of david is unlike the classical extratropical transformation of a tropical storm in a strongly baroclinic environment that has been documented in the literature the authors analysis of the evolution of the dynamical tropopause subsequent to storm landfall revealed that david reintensified in response to tropopause lifting upward displacement of the dynamic tropopause ahead of a nondeepening and otherwise very weak upper tropospheric disturbance

the influence of tropical cyclones on heat waves in southeastern australia 1 heat waves in southeastern australia in summer are commonly associated with slow moving surface high pressure systems which result in warm northerly flow from the continental interior the underlying dynamical pattern of heat waves in this region is associated with propagating rossby waves which grow in amplitude and eventually overturn forming an upper level anticyclonic potential vorticity anomaly the influence of tropical cyclones on the development of these anomalies is investigated here tropical cyclones may affect heat waves in this region indirectly as the divergent outflow at upper levels perturbs the rossby wave guide leading to downstream development however the effect may also be direct through the advection of anomalously anticyclonic potential vorticity from regions of deep convection in the vicinity of tropical cyclones into the upper level anticyclone our research shows that this direct reinforcement of the anticyclone is likely to be more important in the formation of severe heat waves in southeastern australia

a potential vorticity based study of the role of diabatic heating and friction in a numerically simulated baroclinic cyclone abstract a particularly intense case of western atlantic baroclinic cyclogenesis was investigated in this study specifically the roles of latent heat of condensation and surface friction were examined from the potential vorticity or pv thinking perspective the methodology used for this study involves three key components 1 a full physics mesoscale model which provides a continuous and dynamically consistent dataset and provides full user control over physical processes 2 a partitioned pv integration which temporally integrates the accumulation of pv due to various physical processes in the model s eulerian framework and 3 the piecewise inversion method of davis and emanuel which calculates the balanced wind and mass field associated with particular pv anomalies potential vorticity features obtained through the partitioned integration technique were inverted to yield their direct contributions to the total circulation in addition sensitivity studies were carried out to determine the overal

simulations of the extratropical transition of tropical cyclones contributions by the midlatitude upper level trough to reintensification abstract the extratropical cyclone development processes during the reintensification stage of an extratropical transition from a tropical cyclone tc are described using numerical simulations three control simulations without a tropical cyclone present examine the extratropical cyclogenesis associated with upper level troughs that are characterized as weak moderate and strong when no tropical cyclone is included in the simulation the minimum surface pressures attained with the weak moderate and strong troughs are 1003 991 and 977 mb respectively in all three cases the low tilts northwestward with height during intensification and the rainfall pattern and eventual occlusion are representative of classic extratropical cyclone development the interactions of a tropical cyclone with each of the three midlatitude circulation patterns are compared with the control simulations to illustrate the contributions to the extratropical transition of the tropical cyclone in the three trough with tc case

northern hemisphere rossby wave initiation events on the extratropical jet a climatological analysis abstracta climatology of rossby wave initiation rwi events on the northern hemisphere mid latitude jet is compiled by applying an objective rwi identification algorithm to the era interim re analysis dataset in winter rwi events occur most frequently over the northwestern pacific and less often over the north atlantic in summer the total number of rwi events is lower than in winter and the north pacific rwi region shifts towards the tibetan plateau composite analysis of the large scale flow prior to during and after winter north pacific rwi events shows an upstream wave train propagating across asia on the arctic waveguide prior to rwi the composite wave forms on a relatively weak zonal jet streak exhibits a baroclinic structure and is strongly amplified by latent heat release in the warm conveyor belt of a deepening surface cyclone moreover the wave forms in a region of large scale upper level deformation upstream of a pre existing ridge further active tropical convection affects the longit

using tropopause maps to diagnose midlatitude weather systems the use of potential vorticity pv allows the efficient description of the dynamics of nearly balanced atmospheric flow phenomena but the distribution of pv must be simply represented for ease in interpretation representations of pv on isentropic or isobaric surfaces can be cumbersome as analyses of several surfaces spanning the troposphere must be constructed to fully apprehend the complete pv distribution following a brief review of the relationship between pv and nearly balanced flows it is demonstrated that the tropospheric pv has a simple distribution and as a consequence an analysis of potential temperature along the dynamic tropopause here defined as a surface of constant pv allows for a simple representation of the upper tropospheric and lower stratospheric pv the construction and interpretation of these tropopause maps which may be termed isertelic analyses of potential temperature are described in addition techniques to construct dynamical representations of the lower tropospheric pv and near surface potential temperature which complement these isertelic analyses are also suggested case studies are presented to illustrate the utility of these techniques in diagnosing phenomena such as cyclogenesis tropopause folds the formation of an upper trough and the effects of latent heat release on the upper and lower troposphere

the extratropical transition of hurricane irene 1999 a potential vorticity perspective extratropical transition et of tropical cyclones is common in all ocean basins where tropical cyclones recurve polewards after the tropical cyclone experiences et a rapid deepening can take place resulting in the development of a very large and deep extratropical cyclone the et of hurricane irene 1999 was an example of such an explosive et irene formed in the caribbean and experienced et as it moved poleward resulting in a low pressure system which deepened 39 hpa in 24 hours according to the met office analyses the extent to which the hurricane was responsible for the explosive extratropical development has been determined by performing met office unified model forecasts from initial states with and without the hurricane the circulation and temperature anomalies associated with the hurricane were removed from the initial state using potential vorticity inversion the moisture anomaly co located with the hurricane core was also removed the results show that an extratropical cyclogenesis event takes place regardless of the presence of the hurricane in the initial conditions however the hurricane makes a significant difference to the track and central mean sea level pressure evolution of the resulting extratropical cyclone when irene was present the track of the extratropical cyclone was more zonal and the cyclone deepening rate was twice as fast as when irene was not present these effects appear to be particularly associated with a negative potential vorticity anomaly and enhanced divergent flow in the region of the upper level outflow of the transforming hurricane rather than with the hurricane vortex results also show that the presence of the hurricane resulted in a significant downstream surface low development in the eastern atlantic copyright 2004 royal meteorological society

the downstream impact of tropical cyclones on a developing baroclinic wave in idealized scenarios of extratropical transition the interaction of a tropical cyclone with a developing baroclinic wave is investigated in an idealized scenario of extratropical transition et the impact of et is examined by comparing and analyzing two numerical baroclinic wave experiments a traditional experiment in which baroclinic development is excited by a localized upper level perturbation on a realistic jet profile and an experiment in which additionally a model tropical cyclone is inserted south of the jet at the initial time et occurs in a wavy upper level flow while baroclinic surface systems are still weak the characteristic direct impact of et on the midlatitude flow is the formation of a distinct jet streak and the amplification of a ridge trough couplet in the adjacent downstream region the subsequent rapid cyclogenesis downstream is a direct consequence of these upper level flow modifications this faster and stronger development constitutes the amplification of the leading edge of downstream development both the upper level wave pattern and the surface development are subsequently amplified in the region further downstream the formation of the ridge adjacent to the intensified downstream cyclone is analyzed in detail to elucidate the next stage in the downstream dispersion of the et impact ridge building in the et scenario exhibits characteristics distinct from those in the life cycle experiment wave breaking feedback from the modified low level frontal structure and diabatic processes all contribute to the high amplitude wave pattern downstream of et the downstream impact of et is highly sensitive to the initial storm location and intensity the considerable amplification of the leading edge found in the reference experiment is the most widespread and rapidly propagating impact we thus speculate that this leading edge represents an optimal location of the midlatitude circulation where et can lead to the most significant impact on the downstream flow copyright 2010 royal meteorological society

diagnosis of the source of gfs medium range track errors in hurricane sandy 2012 abstractmedium range forecasts of hurricane sandy s track were characterized by widely diverging solutions with some suggesting that sandy would make landfall over the mid atlantic region of the united states while others forecast the storm to move due east to the north of bermuda here dynamical processes responsible for the eastward tracking forecasts are diagnosed using an 80 member ensemble of experimental global forecast system gfs forecasts initialized five days prior to landfall comparing the ensemble members with tracks to the east against those with tracks to the west indicates that the eastern members were characterized by a lower amplitude upper tropospheric anticyclone on the poleward side of sandy during the first 24 h of the forecast which in turn was associated with a westerly perturbation steering wind the amplification of this ridge in each set of members was modulated by differences in the advection of potential vorticity pv by the irrotational wind associated with sandy s seco

piecewise tendency diagnosis of dynamical processes governing the development of an upper tropospheric mobile trough abstract the intensification and evolution of midlatitude upper tropospheric mobile troughs may be viewed in terms of the isentropic advection and deformation of the tropopause potential vorticity gradient the potential vorticity viewpoint allows one to qualitatively assess observed events in the context of existing theories of mobile trough genesis such as baroclinic instability or downstream development in order to quantitatively determine the role of distinct dynamical process the method of piecewise tendency diagnosis or ptd is developed ptd is an extension of piecewise potential vorticity inversion applied to height tendencies with the forcing terms in the quasigeostrophic height tendency equation partitioned into potential vorticity advection associated with distinct dynamical processes a particular case of mobile trough genesis which occurred during 1 4 december 1980 over north america is diagnosed using ptd although about 20 of the intensification of the trough was due to superposition

the impact of tropical remnants on extratropical cyclogenesis case study of hurricanes danielle and earl 1998 abstract the importance of remnant tropical cyclone tc circulation and moisture structures is investigated for a simultaneous extratropical transition et event involving ex hurricanes danielle and earl september 1998 although both storms undergo prolonged periods of reintensification following et the forcings involved in each of their redevelopment processes differ fundamentally a review of the tropical and baroclinic et modes in the north atlantic stresses the importance of jet front structures to the nature of the reintensification process ex hurricane danielle begins to redevelop in the eastern half of the basin in the downstream poleward sector of an intensifying polar jet the system undergoes a tropical mode of reintensification resulting in a troposphere deep warm environment surrounding the storm devoid of near surface fronts and maintained by strong tropopause folds at its periphery ex hurricane earl reintensifies near the eastern seaboard according to a baroclinic mode under the i

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

evidence from the rb sr system for 4 4 ga alteration of chondrules in the allende cv3 parent body the timing and processes of alteration in the cv parent body are investigated by the analysis of sr isotopes major and trace elements and petrographic type and distribution of the secondary minerals nepheline and sodalite in 22 chondrules from the allende cv3 chondrite the sr isotopic compositions of the chondrules are scattered around the 4 0 ga reference line on the 87sr 86sr evolution diagram indicating that the chondrules have been affected by late thermal alteration event s in the parent body the degree of alteration determined for individual chondrules based on the distribution of nepheline and sodalite is unrelated to the disturbance of the rb sr system suggesting that the alteration process that produced nepheline and sodalite is different from the thermal process that disturbed the rb sr system of the chondrules considering the geochemical behavior of rb and sr the main host phase of sr in chondrules is likely to be mesostasis which could be most susceptible to late thermal alteration as there is a poor connection between the alteration degree determined from abundances of nepheline and sodalite and the disturbance of rb sr isotopic system we consider the mesostasis to provide a constraint on the late parent body alteration process from this point of view 23 mesostasis rich chondrules including those from literature data were selected the selected chondrules are closely correlated on the 87sr 86sr evolution diagram with an inferred age of 4 36 0 08 ga this correlation would represent an age of the final major sr isotopic redistribution of the chondrules in the parent body

the extratropical transition and precipitation distribution of hurricane floyd 1999 abstract several recent landfalling tropical cyclones e g dennis floyd and irene 1999 have highlighted a need for a refinement in the forecasting paradigms and techniques in the area of quantitative precipitation forecasting floyd proved to be a particularly challenging forecast problem as it was accompanied by catastrophic flooding over large regions of the east coast in spite of its relatively quick northward movement the extent and intensity of the precipitation distribution was strongly modulated by the storm s interaction with a midlatitude trough in an attempt to better understand and quantify the relevant dynamics during this interaction potential vorticity pv and quasigeostrophic perspectives are utilized as floyd approached the east coast precipitation shifted to the left of the storm track due to the presence of a deep midlatitude trough in the ohio valley the juxtaposition of a cold core pv anomaly associated with the midlatitude trough and a warm core pv anomaly associated with

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

remote impact of north atlantic hurricanes on the mediterranean during episodes of intense rainfall in autumn 2012 autumn is the most favourable season for tropical cyclones to undergo extratropical transition and interact with the midlatitude flow over the north atlantic autumn is also the season when intense rainfall over the mediterranean is often triggered by rossby wave breaking the impact of tropical cyclones on downstream wave breaking is investigated here during three episodes of intense rainfall which were the target of hymex hydrological cycle in mediterranean experiment in autumn 2012 five day simulations of hurricanes leslie rafael and sandy were performed with the meso nh model in a domain encompassing the north atlantic and the mediterranean control simulations were compared to simulations in which the hurricanes were filtered out from the initial conditions in each case the hurricane locally impeded the forward progression of an upstream trough then reintensified as an extratropical cyclone during the wrap up of the trough the local impact of leslie and rafael on the midlatitude flow quickly propagated downstream along a polar jet and amplified rossby wave breaking but decreased the intensity of the forecast precipitation over the mediterranean the local impact of sandy propagated downstream along a subtropical jet in addition to the polar jet and resulted in a weak impact of the forecast precipitation on the mediterranean this study suggests that the interaction of tropical cyclones with the midlatitude flow over the western north atlantic may be considered a perturbation to rather than a source of downstream wave breaking

the balanced dynamical nature of a rapidly intensifying oceanic cyclone abstract aided with a numerical simulation the authors diagnose the synoptic scale evolution of an intense extratropical cyclone over the western atlantic ocean from the perspective of balanced dynamics using potential vorticity inversion techniques the authors show that even during the period of largest growth rate early in the life cycle the balance equations capture much of the nondivergent wind irrotational wind and height tendency fields the structure of the cyclone evolves from a maximum amplitude at the tropopause to a maximum amplitude at the surface as the system moves offshore the vertical phase structure remains slightly upshear tilted throughout less than one quarter wavelength cyclogenesis is interpreted in terms of a baroclinic wave propagating through a varying basic state in which surface development is rapid because of the sudden response of the wave structure to a changing environment the mature cyclone structure strongly resembles cases of continental cyclones except that t

the influence of the downstream state on extratropical transition hurricane earl 1998 case study abstract the multitude of tropical extratropical interactions that occur during an extratropical transition et complicate the prediction and diagnosis of these extreme events this study focuses on the analysis of a double et and reintensification event that took place between 5 and 7 september 1998 ex hurricanes earl and danielle reintensified rapidly over the western and eastern north atlantic respectively a set of simulations designed to test the sensitivity of earl s et to features in the downstream state was run using a set of idealizations for a numerical model s initial and boundary conditions downstream of ex hurricane earl dynamic tropopause analyses and the pv thinking paradigm applied under the eady model highlight important developmental and structural differences between the tests in fact two distinct solution modes are diagnosed both in the control and in the sensitivity tests earl s et proceeds according to a baroclinic mode of redevelopment whereas danielle displays distinct

dynamics of a local alpine flooding event in october 2011 moisture source and large scale circulation alpine heavy precipitation events often affect small catchments although the circulation pattern leading to the event extends over the entire north atlantic the various scale interactions involved are particularly challenging for the numerical weather prediction of such events unlike previous studies focusing on the southern alps here a comprehensive study of a heavy precipitation event in the northern alps in october 2011 is presented with particular focus on the role of the large scale circulation in the north atlantic european region during the event exceptionally high amounts of total precipitable water occurred in and north of the alps this moisture was initially transported along the flanks of a blocking ridge over the north atlantic subsequently strong and persistent northerly flow established at the upstream flank of a trough over europe and steered the moisture towards the northern alps lagrangian diagnostics reveal that a large fraction of the moisture emerged from the west african coast where a subtropical upper level cut off low served as an important moisture collector wave activity flux diagnostics show that the ridge was initiated as part of a low frequency large scale rossby wave train while convergence of fast transients helped to amplify it locally in the north atlantic a novel diagnostic for advective potential vorticity tendencies sheds more light on this amplification and further emphasizes the role of the ridge in amplifying the trough over europe operational forecasts misrepresented the amplitude and orientation of this trough for the first time this study documents an important pathway for northern alpine flooding in which the interaction of synoptic scale to large scale weather systems and of long range moisture transport from the tropics are dominant moreover the trapping of moisture in a subtropical cut off near the west african coast is found to be a crucial precursor to the observed european high impact weather

rossby wave initiation by recurving tropical cyclones in the western north pacific abstractthe interaction of recurving tropical cyclones tcs with midlatitude rossby waves during extratropical transition et can significantly alter the midlatitude flow configuration this study provides a climatological investigation of rossby wave initiation rwi by transitioning tcs in the specific configuration of an initially zonal midlatitude waveguide and elucidates physical processes governing ab initio flow amplification during et recurving tcs interacting with a zonally oriented waveguide in the western north pacific wnp basin from 1979 to 2013 are categorized into cases initiating rossby waves tc rwi or not tc norwi interactions with a zonally oriented waveguide occurred for 22 7 of the recurving tcs and one third of these resulted in tc rwi in the presence of a tc the probability of rwi on a zonally oriented waveguide is 3 times larger than in situations without a tc the occurrence of tc rwi exhibits a seasonality and is relatively more common during boreal summer than in aut

baroclinic instability in an environment of small stability to slantwise moist convection part i two dimensional models abstract in the semigeostrophic system the growth rate of baroclinic waves varies with the inverse square root of the potential vorticity which acts as the effective static stability recent observations in the ascent regions of middle latitude cyclones show that the effective potential vorticity for saturated air is very near zero in this paper we examine the structure and rate of growth of baroclinic cyclones when the effective potential vorticity is small for upward saturated displacements but large in regions of descent analytic solutions for two dimensional disturbances in a two layer semigeostrophic model and numerical simulations using a multilevel semigeostrophic model show that when the effective potential vorticity is small in regions of upward motion growth rates are modestly increased and the region of ascent intensifies and collapses onto a thin ascending sheet in the limit of zero moist potential vorticity the fastest growing wave has a finite growth rate which is about 2 5 times the