interaction of a tropical cyclone with a high amplitude midlatitude wave pattern waviness analysis trough deformation and track bifurcation an idealized scenario of extratropical transition et is investigated in which a tropical cyclone interacts with a high amplitude upper level wave pattern and well developed surface cyclones early during the interaction the external forcing of the upper level wave by the et system is quantified based on a metric for the waviness of the midlatitude flow local amplification of the wave pattern is diagnosed associated prominently with the trough downstream of et this amplified trough however exhibits pronounced anticyclonic breaking and thus in contrast to many previous et studies it is not clear that the amplification of the upper level wave propagates into the farther downstream region subsequently the et system merges with the upstream cyclone the upstream trough undergoes strong deformation and cyclonic breaking associated with straining due to the cyclonic circulation of the et system with the decay of this trough the et system weakens considerably and the upper level wave pattern changes locally to a zonal flow orientation this zonal flow pattern then extends into the downstream region and promotes the decay of the downstream baroclinic systems as in previous studies the evolution of et exhibits large sensitivity to the initial location of the tropical cyclone examining the steering flow s topology i e identifying the stagnation points and the streamlines emanating from these points helps to identify three different regimes a no et regime and two et regimes reminiscent of the northwest and northeast patterns respectively introduced previously by harr et al a stagnation point located on the axis of the upstream trough governs the bifurcation into no et and et regimes a stagnation point located on the axis of the downstream ridge governs the bifurcation into northwest and northeast patterns

the integrated effect of condensation in numerical simulations of extratropical cyclogenesis abstract by combining traditional sensitivity studies with techniques that focus on the conservation and invertibility properties of ertel s potential vorticity pv we illustrate the effect of latent heating on the structure and evolution of three simulated extratropical cyclones the cases include one continental cyclone development 15 december 1987 which we examine extensively and two cyclones over the western atlantic ocean 6 january 1983 and 5 january 1985 of somewhat greater intensity which are diagnosed to assess the generality of our findings for the continental case each storm featured a weaker cyclonic low level circulation when latent heating was removed from the simulation but the magnitude of the effect varied greatly in all cases the difference in intensity was attributed to velocities associated with a positive condensation produced pv anomaly above the warm front the amplification of the surface thermal perturbations was not strongly altered in even the case most affected by

on the role of a rossby wave train during the extratropical transition of hurricane helene 2006 three successive interactions of hurricane helene 2006 with a rossby wave train during the extratropical transition of helene over the north atlantic were investigated numerical experiments were performed with different horizontal resolutions and configurations over a domain that stretches from the eastern pacific to the western mediterranean to encompass helene and the whole rossby wave train in particular a cloud resolving run offered an explicit representation of strong diabatic effects involved in the three successive interactions while the circulation and moisture anomaly of helene were essential to its own reintensification it is shown that the rossby wave train played an important role in the track and intensity of helene and in explosive cyclogenesis downstream first the rossby wave train steered helene in such a way that a small difference in phasing resulted in large errors in the track of helene only a run at kilometre scale was able to correctly forecast the 5 day track of helene second through the formation of three filaments the rossby wave train created a quasi diurnal cycle in the intensity of helene helene responded with strong diabatic activity that prevented the superposition of an upstream trough and enhanced a downstream ridge finally model errors in the outflow of helene propagated downstream with the group speed of the rossby wave train leading to the loss of predictability of a tropical like cyclone over the mediterranean this study suggests that in addition to the horizontal resolution uncertainty from the model microphysics and from initial conditions need to be characterized to improve mid range forecast downstream from an extratropical transition copyright 2012 royal meteorological society

comments on the evolution and dynamical role of reduced upper tropospheric potential vorticity in intensive observing period one of fastex abstract the existence and production of reduced upper tropospheric potential vorticity rupv by heating is considered an objective technique is used that identifies anomalies of pv arising from a particular physical process here latent heat release the evolution of two rupv anomalies and a related diabatically increased lower tropospheric pv ilpv anomaly occurring during intensive observing period one of the cyclones from the fronts and atlantic storm track experiment fastex is examined using model analyses sounding data and trajectory calculations three distinct airflows are identified emanating from the ilpv anomaly each with a different evolution results show that rupv anomalies exist in the atmosphere and in a weaker form in numerical models the dynamical role of rupv anomalies is examined using a nonlinear balance pv inversion and reruns of the u k meteorological office limited area model this shows that instantaneously the flow and temperature perturbations associated with rupv an

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

dynamics of rossby wave packets in a quantitative potential vorticity potential temperature framework abstractrossby wave packets rwps have been associated with increased atmospheric predictability but also with the growth and propagation of forecast uncertainty to address the important question of under which conditions rwps imply high and low predictability a potential vorticity potential temperature pv framework is introduced to diagnose rwp dynamics finite amplitude rwps along the midlatitude waveguide are considered and are represented by the synoptic scale wavelike undulations of the tropopause the evolution of rwps is examined by the amplitude evolution of the individual troughs and ridges troughs and ridges are identified as pv anomalies on levels intersecting the midlatitude tropopause by partitioning the pv tendency equation individual contributions to the amplitude evolution are identified a novel aspect is that the important role of the divergent flow and the diabatic pv modification is quantified explicitly arguably prominent upper tropospheric divergent flow is associated

the resonant interaction of a tropical cyclone and a tropopause front in a barotropic model part ii frontal waves abstract the influence of frontal waves on the interaction of a tropical cyclone and a tropopause front is investigated in an idealized framework in a nondivergent barotropic model the front is represented by a vorticity step with a superimposed sinusoidal perturbation this gives rise to a jet that meanders to the north and south and can be viewed as a sequence of upper level troughs and ridges the model evolution depends sensitively on the position of the cyclone relative to the troughs and ridges here a bifurcation point is identified that is located on the trough axis at a distance where the zonal speed of the background flow equals the phase speed of the wave arbitrarily small displacements from this position determine whether a cyclone is advected toward the front or repelled only a limited range of wavelengths can lead to track bifurcations the largest effects are obtained for resonant frontal waves propagating with a phase speed matching the initial zonal translation speed of the cyclone we

first 40ar 39ar age constraints for the caledonian evolution of the trans european suture zone in ne germany from three rugen boreholes g14 rugen 5 loissin 1 across the caledonian deformation front four lower palaeozoic slate samples and three detrital muscovite concentrates from associated sandstones have been analysed by 40 ar 39 ar analysis microprobe analysis of the detrital muscovites show homogeneous but distinct chemical compositions for each concentrate particulate organic matter reflectance and illite crystallinity indicate that all the analysed whole rock samples have experienced anchizonal metamorphic conditions 40 ar 39 ar analysis of the samples from the g14 and loissin 1 wells give almost identical results muscovite concentrates define plateau ages of c 830 ma and show an isotopic rejuvenation of low temperature increments around 440 ma whole rock slate samples give plateau ages of c 440 ma and c 427 ma isotopic rejuvenation in the low temperature increments prior to 350 ma in the loissin 1 sample can be attributed to the permo carbonifereous volcanism which is known from this borehole in contrast samples from the borehole rugen 5 show a different isotope pattern a muscovite concentrate defines a plateau age of 609 ma two whole rock slate samples give internally discordant but identical 40 ar 39 ar spectra with consistent isotopic rejuvenation from high to low temperature increments from 510 ma to 420 ma while for the g14 and loissin 1 sandstone samples a baltica derived provenance can be assumed greywackes of rugen 5 indicate a cadomian influenced perigondwanan detrital source according to the results of whole rock slate samples the main caledonian tectonothermal event in ne germany occurred around the ordovician silurian boundary or in the early silurian 450 425 ma from these data the rugen palaeozoic appears as an allochthonous caledonian nappe complex which has been thrust much further onto the baltic shield than previously thought

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

wave breaking characteristics of midlatitude blocking in this article northern hemisphere winter midlatitude blocking is analysed through its wave breaking characteristics rossby wave breaking is identified as a key process in blocking occurrence as it provides the mechanism for the meridional reversal pattern typical of blocking two indices are designed to detect the major properties of wave breaking i e the orientation cyclonic anticyclonic direction of breaking or db index and the relative contribution of air masses warm cold relative intensity or ri index the use of the db index differentiates between the anticyclonic cases over europe and asia and the cyclonic events over the oceanic basins one of the three regions displaying cyclonic type was found over the atlantic ocean the other two being over the pacific ocean the first of these is located over the western side of the pacific and is dominated by warm air extrusions whereas the second is placed northward of the exit region of the jet stream where the meridional gradient is much weaker two european blocking types have been detected using the ri index which separates out the cases dominated by warm and cold air masses the latter cases in particular exhibited a well structured dipole with associated strong anomalies in both temperature and precipitation copyright 2011 royal meteorological society

lower tropospheric height tendencies associated with the shearwise and transverse components of quasigeostrophic vertical motion the recent suggestion that lower tropospheric cyclogenesis is predominantly a result of column stretching associated with the updraft portion of the shearwise quasigeostrophic qg vertical motion is quantified through direct calculation of 900 hpa height tendencies via the qg vorticity equation comparison of the separate lower tropospheric height tendencies associated with the shearwise and transverse portions of qg omega in a robust cyclogenesis event demonstrates that the shearwise updraft drives the largest part 80 of the cyclogenetic height falls at least through the end of the mature stage of the life cycle the lower tropospheric height falls and vorticity production near the sea level pressure minimum of the occluded surface cyclone are driven nearly equally by shearwise and transverse updrafts

vortex vortex interaction between hurricane nadine 2012 and an atlantic cut off dropping the predictability over the mediterranean operational ensemble forecasts for the western mediterranean exhibited high uncertainty while hurricane nadine was moving slowly over the eastern north atlantic in september 2012 the forecasts showed a bifurcation in the track of nadine a significant fraction predicting its landfall over the iberian peninsula and a high spread in the synoptic conditions downstream the forecast uncertainty was a major issue for planning observations during the first special observation period sop1 of the hydrological cycle in the mediterranean experiment hymex clustering the ensemble forecast of the european centre for medium range weather forecasts reveals two scenarios for interaction between nadine and an atlantic cut off which controls both the track of nadine and the synoptic conditions downstream the observed scenario of weak interaction is characterized by nadine moving westward and the cut off moving eastward the cut off then triggers precipitation over the cevennes in southeastern france the contrasting scenario of strong interaction is characterized by nadine and the cut off rotating around each other over the atlantic nadine then either merges with the cut off or makes landfall over the iberian peninsula the interaction between nadine and the cut off mimics the vortex vortex interaction previously observed between two tropical cyclones or two upper level vortices it differs from the usual interaction between a tropical cyclone and a larger trough during extratropical transition a critical distance of about 1000 km between nadine and the cut off distinguishes between the cases of weak and strong interaction in the ensemble forecast shifting the initial position of nadine in meso nh numerical experiments confirms the critical distance and suggests a bifurcation point in the relative position of nadine and the cut off the high forecast sensitivity to the vortex vortex interaction resulted in the lowest predictability over the mediterranean during the whole hymex sop1

the influence of the madden julian oscillation on northern hemisphere winter blocking abstractthe persistent and quasi stationary nature of atmospheric blocking is associated with long lasting extreme weather conditions that influence much of the northern hemisphere during boreal winter the madden julian oscillation mjo has been previously shown to influence important factors for blocking including rossby wave breaking and the north atlantic oscillation nao however the extent to which the mjo influences blocking across the northern hemisphere is not yet fully understood utilizing a two dimensional blocking index composites of north pacific north atlantic and european blocking are generated relative to mjo phase in the west and central pacific all mjo phases demonstrate significant changes in blocking particularly at high latitudes a significant decrease in east pacific and atlantic blocking occurs following phase 3 of the mjo characterized by enhanced convection over the tropical east indian ocean and suppressed convection in the west pacific the opposite signed mjo heatin

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

the impact of typhoon jangmi 2008 on the midlatitude flow part ii downstream evolution extratropical transition et of a tropical cyclone tc can modify the midlatitude flow and thus have implications for the weather and predictability in downstream regions such as north america or europe albeit recurving and undergoing et the downstream impact of typhoon jangmi in september 2008 during the thorpex pacific asian regional campaign t parc was weak in this study we explore the physical processes inhibiting the reintensification of jangmi and governing the forecast uncertainty during et the focus is on the relative contribution of the tc and the midlatitude flow quasi geostrophic diagnostics reveal that jangmi is located south of and in phase with a midlatitude trough jangmi does not couple with the region favourable for reintensification ahead of the trough and subsequently decays instead a weak frontal wave like cyclone develops the role of the phasing of typhoon jangmi and the midlatitude rossby wave pattern is tested in sensitivity experiments with the cosmo model in which jangmi has been relocated the simulations reveal two contrasting groups of scenarios the first group reflects the weak actual et and subsequent decay accompanied by a broad ridge over the pacific the second group is characterized by a strong et with extratropical reintensification the triggering of a pronounced rossby wave train and downstream cyclogenesis the displacement of jangmi s initial position in the two contrasting groups is less than 1 25 130 km in the frame moving with the environmental background flow a critical bifurcation point for the track of jangmi exists the relative position to this bifurcation point determines whether jangmi decays or reintensifies and triggers a rossby wave train a simple discrimination parameter is derived that allows for classifying the scenarios the observed behaviour gives a simple explanation for the reduced predictability of the track and of the midlatitude flow in downstream regions during et

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

a phase locking perspective on rossby wave amplification and atmospheric blocking downstream of recurving western north pacific tropical cyclones abstractthe extratropical transition et of tropical cyclones tcs can significantly influence the evolution of the midlatitude flow however the interaction between recurving tcs and upstream u

the microphysical building blocks of low level potential vorticity anomalies in an idealized extratropical cyclone abstractdiabatically generated low level potential vorticity pv anomalies in extratropical cyclones enhance near surface winds and influence the cyclone s development positive and negative pv anomalies in the warm frontal region of an extratropical cyclone simulated with an idealized moist baroclinic channel model are investigated to identify the microphysical processes that produce them using a novel method based on backward trajectories from the pv anomalies the contribution of different microphysical processes to the formation of the anomalies is quantified it is found that for each anomaly typically one specific microphysical process takes the leading role in its diabatic generation a large but rather weak low and midlevel positive anomaly is produced by depositional growth of ice and snow two smaller but stronger positive anomalies at lower levels are generated mainly by in cloud condensational heating at the warm front and below cloud rain evaporation and snow melting 200 km farther nor

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

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 antecedent large scale conditions of the perfect storms of late october and early november 1991 abstract the perfect storms pss were a series of three high impact extratropical cyclones ecs that impacted north america and the north atlantic in late october and early november 1991 the pss included the perfect storm in the northwest atlantic a second ec over the north atlantic that developed from the interaction of the ps with hurricane grace and a third ec over north america commonly known as the 1991 halloween blizzard the pss greatly impacted the north atlantic and north america with large waves coastal flooding heavy snow and accumulating ice and they also provided an opportunity to investigate the physical processes that contributed to a downstream baroclinic development dbd episode across north america that culminated in the ecs downstream baroclinic development resulted from an amplification of the large scale flow over the north pacific that was influenced by anomalous tropical convection the recurvature and extratropical transition of western north pacific tropical cyclone

the role of shearwise and transverse quasigeostrophic vertical motions in the midlatitude cyclone life cycle abstract the total quasigeostrophic qg vertical motion field is partitioned into transverse and shearwise couplets oriented parallel to and along the geostrophic vertical shear respectively the physical role played by each of these components of vertical motion in the midlatitude cyclone life cycle is then illustrated by examination of the life cycles of two recently observed cyclones the analysis suggests that the origin and subsequent intensification of the lower tropospheric cyclone responds predominantly to column stretching associated with the updraft portion of the shearwise qg vertical motion which displays a single dominant middle tropospheric couplet at all stages of the cyclone life cycle the transverse qg omega associated with the cyclones frontal zones appears only after those frontal zones have been established the absence of transverse ascent maxima and associated column stretching in the vicinity of the surface cyclone center suggests that the transverse plays little role i

downstream development associated with the extratropical transition of tropical cyclones over the western north pacific abstract the movement of a tropical cyclone into the midlatitudes involves interactions among many complex physical processes over a variety of space and time scales furthermore the extratropical transition et of a tropical cyclone may also result in a high amplitude rossby wave response that can extend to near hemispheric scales after an et event occurs over the western portion of a northern hemisphere ocean basin the high amplitude downstream response often forces anomalous midlatitude circulations for periods of days to a week these circulations may then be related to high impact weather events far downstream of the forcing by the et event in this study downstream development following et events over the western north pacific ocean is examined local eddy kinetic energy analyses are conducted on four cases of north pacific tropical cyclones of varying characteristics during et into varying midlatitude flow characteristics during 15 july 30 september 2005 the goal is to examine the impact of e

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

comparison of wave packets associated with extratropical transition and winter cyclones abstractdifferences in the development of wave packets associated with midlatitude cyclones and the extratropical transition et of tropical cyclones in the western north pacific wnp and atlantic basins are diagnosed observationally by compositing climate forecast system reanalysis cfsr data over a 32 yr period and applying the null hypothesis of no difference in the development structure propagation or downstream extent while the development of midlatitude cyclones during the fall august october and winter november march amplifies a preexisting wave packet moving through the midlatitude storm track et is associated with the quasi stationary amplification of the midlatitude flow the et cases involving the interaction of the decaying tc with a preexisting midlatitude trough are associated with a greater downstream amplitude and longer lasting downstream response than et cases that do not involve the interaction with a trough in the wnp et wave packets have greater amplitude than those asso

cyclogenesis downstream of extratropical transition analyzed by q vector partitioning based on flow geometry abstractduring extratropical transition et tropical cyclones exert a significant impact on the midlatitude circulation archetypical features of this impact are jet streak formation amplification of the downstream trough and modification of the associated downstream cyclogenesis this study investigates the relative importance of the jet streak and the upper level trough for cyclone development by quantifying the respective contributions to midtropospheric vertical motion using the q vector partitioning by j c jusem and r atlas their framework is here extended from quasigeostrophic theory to alternative balance the q vector under alternative balance involves the nondivergent wind instead of the geostrophic wind and therefore represents more accurately the balanced dynamics associated with vertical motion in particular downstream of et where the flow often exhibits significant curvature associated with the amplified trough an idealized et scenario and three real cases the cyclones downstream

perspicacious indicators of atmospheric blocking 1 a novel dynamically based approach is introduced to identify describe and diagnose atmospheric blocking events the approach is based upon the potential vorticity perspective and takes into account the three dimensional structure of the phenomenon it is argued that the essence of a blocking anomaly is located in the upper troposphere just below the tropopause the associated novel blocking indicators are derived from two dimensional fields at 6 hourly temporal resolution and provide information on the spatial scale shape amplitude and movement of blocks a northern hemisphere winter djf climatology for the era15 period 1979 1993 is presented and comments are made on the relationship between the indicators and previous blocking indices

the key role of diabatic outflow in amplifying the midlatitude flow a representative case study of weather systems surrounding western north pacific extratropical transition abstractrecurving tropical cyclones tcs undergoing extratropical transition et may substantially modify the large scale midlatitude flow pattern this study highlights the role of diabatic outflow in midlatitude flow amplification within the context of a review of the physical and dynamical processes involved in et composite fields of 12 western north pacific et cases are used as initial and boundary conditions for high resolution numerical simulations of the north pacific north american sector with and without the tc present it is demonstrated that a three stage sequence of diabatic outflow associated with different weather systems is involved in triggering a highly amplified midlatitude flow pattern 1 preconditioning by a predecessor rain event pre 2 tc extratropical flow interaction and 3 downstream flow amplification by a downstream warm conveyor belt wcb an ensemble of perturbed simulations demonstrates the robustness of these stages beyond earlier studies investigating pres recurv

the island scale internal wave climate of moorea french polynesia 1 analysis of five year records of temperatures and currents collected at moorea reveal strong internal wave activity at predominantly semi diurnal frequencies impacting reef slopes at depths 30 m around the entire island temperature changes of 1 5 c to 3 c are accompanied by surges of upward and onshore flow and vertical shear in onshore currents superimposed on annual temperature changes of approximately 3 c internal wave activity is high from oct may and markedly lower from jun sep the offshore pycnocline is broadly distributed with continuous stratification to at least 500 m depth and a subsurface fluorescence maximum above the strong nutricline at approximately 200 m minimum buoyancy periods range from 4 8 to 6 min with the maximum density gradient occurring at 50 to 60 m depth in summer and deepening to approximately 150 to 200 m in winter the bottom slope angle around all of moorea is super critical relative to the vertical stratification angle suggesting that energy propagating into shallow water is only a portion of total incident internal wave energy vertical gradient richardson numbers indicate dominance by density stability relative to current shear with relatively limited diapycnal mixing coherence and lagged cross correlation of semi diurnal temperature variation indicate complex patterns of inter site arrival of internal waves and no clear coherence or lagged correlation relationships among island sides semi diurnal and high frequency internal wave packets likely arrive on moorea from a combination of local and distant sources and may have important impacts for nutrient and particle fluxes in deep reef environments

role of moist processes in the tracks of idealized midlatitude surface cyclones abstractthe effects of moist processes on the tracks of midlatitude surface cyclones are studied by performing idealized mesoscale simulations in each simulation a finite amplitude surface cyclone is initialized on the warm air side of a zonal baroclinic jet for some simulations an upper level cyclonic anomaly upstream of the surface cyclone is also added initially sensitivities to the upper level perturbation and moist processes are analyzed by both performing a relative vorticity budget analysis and adopting a potential vorticity pv perspective whatever the simulation there is a systematic crossing of the zonal jet by the surface cyclone occurring after roughly 30 h a pv inversion tool shows that it is the nonlinear advection of the surface cyclone by the upper level pv dipole which explains the cross jet motion of the surface cyclone the simulation with an initial upper level cyclonic anomaly creates a stronger surface cyclone and a more intense upper level pv dipole than the simulation with

extratropical transition of tropical cyclones over the western north pacific part ii the impact of midlatitude circulation characteristics abstract two characteristic midlatitude circulation patterns labeled northwest and northeast are found to be associated with extratropical transition et of tropical cyclones over the western north pacific ocean although in both cases the tropical cyclone moves poleward ahead of a midlatitude trough the primary midlatitude circulation is either that trough or is a large quasi stationary cyclone to the northeast of the poleward moving tropical cyclone transition into a northwest pattern typically results in the development within 36 h of an intense extratropical cyclone that moves north northeast a tropical cyclone that moves into a northeast pattern enters into strong zonal flow between the primary midlatitude circulation and the subtropical ridge to the southeast these systems move rapidly eastward and do not intensify significantly during the 36 h following transition in part i of this study the et of typhoon ty david 1997 and the et of ty opal 1997 were investigated in terms of the form

a pv perspective on the vertical structure of mature midlatitude cyclones in the northern hemisphere development of extratropical cyclones can be seen as an interplay of three positive potential vorticity anomalies an upper level stratospheric intrusion low tropospheric diabatically produced potential vorticity pv and a warm anomaly at the surface acting as a surrogate pv anomaly this study based on the interim ecmwf re analysis era interim dataset quantifies the amplitude of the pv anomalies of mature extratropical cyclones in different regions in the northern hemisphere on a climatological basis a tracking algorithm is applied to sea level pressure slp fields to identify cyclone tracks surface potential temperatureanomalies duandverticalprofilesofpvanomalies dpvarecalculatedatthetimeofthecyclones minimumslpinaverticalcylinderaroundthesurfacecyclonecenter tocomparethecyclones characteristics they are grouped according to their location and intensity composite dpv profiles are calculated for each region and intensity class at the time of minimum slp and during the cyclone intensification phase in the maturestage allthree anomaliesare on averagelargerfor intense thanforweak wintercyclones e g 0 6 versus 0 2 potential vorticity units pvu 1 pvu 510 26 kk g 21 m 2 s 21 at lower levels and 1 5 versus 0 5 pvu at upper levels the regional variability of the cyclones vertical structure and the profile evolution is prominent cyclones in some regionsare moresensitiveto the amplitude ofa particularanomalythanin other regions values of du and low level dpv are on average larger in the western parts of the oceans than in the eastern parts results for summer are qualitatively similar except for distinctively weaker surface du values