the poleward motion of extratropical cyclones from a potential vorticity tendency analysis abstractthe poleward propagation of midlatitude storms is studied using a potential vorticity pv tendency analysis of cyclone tracking composites in an idealized zonally symmetric moist gcm a detailed pv budget reveals the important role of the upper level pv and diabatic heating associated with latent heat release during the growth stage the classic picture of baroclinic instability emerges with an upper level pv to the west of a low level pv associated with the cyclone this configuration not only promotes intensification but also a poleward tendency that results from the nonlinear advection of the low level anomaly by the upper level pv the separate contributions of the upper and lower level pv as well as the surface temperature anomaly are analyzed using a piecewise pv inversion which shows the importance of the upper level pv anomaly in advecting the cyclone poleward the pv analysis also emphasizes the crucial role played by latent heat release in the poleward motion of the cyclone the l

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

objective classification of extratropical cyclogenesis extratropical cyclones experience vastly different genesis conditions at the first point of their tracks a novel method is introduced to characterize this variability and classify genesis events by computing 30 diagnostic variables that describe the synoptic scale environment of 16029 genesis events in the northern hemisphere extratropics using era interim reanalyses from 2000 2011 these variables are referred to as precursors and include parameters characterizing upper level forcing low level baroclinicity thermodynamic stability surface fluxes and moist processes the genesis events spread over a large portion of the 30 dimensional precursor phase space and no obvious clusters occur which highlights the high variability of cyclogenesis processes and indicates that they form in a continuum rather than a few distinct categories a projection of the genesis events to the first two principle components pc of the precursor phase space allows reducing the dimensionality and introducing a meaningful segmentation of the genesis events in five classes the first two pcs are characterized by upper level forcing e g the amplitude of the upper level potential vorticity pv anomaly and low tropospheric diabatic processes e g precipitation and diabatically produced low level pv respectively the first of the five identified classes constitutes the center of the pc1 pc2 phase space and represents average conditions composites reveal that the four classes of events characterized by large positive or negative scores of pc1 and pc2 occur in distinct and strongly differing flow regimes characterized by the strength of the upper level forcing the structure of the upper level jet and the amplitude of low level moist processes and baroclinicity the four classes also have clearly differing geographical distributions many well known cyclogenesis events fall within classes characterized by strong low level moist processes with or without strong upper level forcing also discussed are the robustness of the method and the linkage to classical concepts of cyclone classifications

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

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

simulations of the potential vorticity structure and budget of fronts 87 iop8 dropsonde observations in the cold fronts sampled during the joint british french fronts 87 experiment along the west coast of europe have shown that the dry and moist potential vorticity fields q d and q e respectively have significant anomalies on the mesoscale the processes associated with these anomalies during a 12 h period encompassing the observation time have been examined by simulating the q d and q e structures observed near the cold front of iop8 using the meteo france mesoscale peridot model and by developing and using an eulerian potential vorticity budget module high resolution dropsonde rawinsonde and doppler radar observations are used as verification of the simulated potential vorticity structures initial and boundary conditions are obtained from three different analysis systems the simulated potential vorticity structures are sensitive to the initial conditions because the analyses over the data sparse atlantic ocean vary significantly from one analysis system to another of the seven persistent mesoscale potential vorticity features identified in the observations five were simulated reasonably well using at least one of the initial analyses and examined with the potential vorticity budget the low level pre frontal positive q d anomaly along the length of the cold front is maintained through a balance between lagrangian source sink terms dominated by differential diabatic heating and vertical advection within the main frontal updraught this balance maintains the q d anomaly in a region of near zero q d tendency between areas of q d generation near the surface and q d destruction in the middle troposphere a mid tropospheric region of negative q e directly behind the surface cold front appears to be produced by a weak but persistent generation by the solenoid term in the region of strong humidity gradients along the back edge of the mid tropospheric cloud shield this position and the model evolution suggest that the solenoid created region of negative q e can lead to enhanced mid tropospheric updraughts through conditional symmetric instability or a combination of conditional symmetric instability and large scale forcing the magnitudes of regions of negative q d and q e on the anticyclonic side of the upper level jet decrease throughout the simulation due to horizontal momentum diffusion while a post frontal low level negative q e region is generated principally by temperature and moisture diffusion

long lived rossby wave trains as precursors to strong winter cyclones over europe the statistical connection between strong surface cyclones over europe and long lived upper tropospheric rossby wave trains is examined for the northern hemisphere winter season using 45 years of reanalysis data dates are selected for which the surface pressure anomaly over central europe is below a threshold yielding the 5 of lowest values composites of upper tropospheric meridional wind for these dates including a lead or lag in time display clear signs of a wave train the composite wave train lives for over two weeks and propagates eastward over more than 360 longitude the phase speed of individual lows and highs by contrast is close to zero and the same is true for the composite surface low there is a pronounced northward shift of the wave train as it propagates over the north american east coast although this composite wave train is statistically highly significant there is large scatter about the mean an index is defined that quantifies the similarity of the upper tropospheric meridional wind pattern for an arbitrary date with the composite wave train for a certain lead or lag given large positive values of the index there is an enhanced probability of a strong surface cyclone over central europe a few days later comparison with a previous study focusing on pacific cyclones shows noteworthy differences

quantifying the climatological relationship between extratropical cyclone intensity and atmospheric precursors 1 we introduce a novel technique in which linear regression analysis is applied to clusters of tracked cyclones to statistically assess the factors controlling cyclone development we illustrate this technique by evaluating the differences between cyclones forming in the west and east north atlantic herein termed west and east atlantic cyclones enhanced cyclone intensity 2 days after genesis is found to be associated with deeper upper level troughs upstream of the cyclone center at the genesis time in both west and east atlantic cyclones however whilst west atlantic cyclones are also enhanced by the presence of strong fronts east atlantic cyclones are not instead east atlantic cyclones exhibit an enhancement when diabatically generated midlevel potential vorticity is present with the enhancement being of approximately equal magnitude to that associated with the potential vorticity in the upper level trough this is consistent with the paradigm of latent heat release in the warm conveyor belt region playing an important role in the development of east atlantic cyclones

diagnosing the influence of diabatic processes on the explosive deepening of extratropical cyclones a novel version of the classical surface pressure tendency equation pte is applied to era interim reanalysis data to quantitatively assess the contribution of diabatic processes to the deepening of extratropical cyclones relative to effects of temperature advection and vertical motions the five cyclone cases selected lothar and martin in december 1999 kyrill in january 2007 klaus in january 2009 and xynthia in february 2010 all showed explosive deepening and brought considerable damage to parts of europe for xynthia klaus and lothar diabatic processes contribute more to the observed surface pressure fall than horizontal temperature advection during their respective explosive deepening phases while kyrill and martin appear to be more baroclinically driven storms the powerful new diagnostic tool presented here can easily be applied to large numbers of cyclones and will help to better understand the role of diabatic processes in future changes in extratropical storminess

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

the role of moist processes in the formation and evolution of mesoscale snowbands within the comma head of northeast u s cyclones abstract the role of moist processes in regulating mesoscale snowband life cycle within the comma head portion of three northeast u s cyclones is investigated using piecewise potential vorticity pv inversion modeling experiments and potential temperature tendency budgets snowband formation in each case occurred along a mesoscale trough that extended poleward of a 700 hpa low this 700 hpa trough was associated with intense frontogenetical forcing for ascent a variety of pv evolutions among the cases contributed to midlevel trough formation and associated frontogenesis however in each case the induced flow from diabatic pv anomalies accounted for a majority of the midlevel frontogenesis during the band s life cycle highlighting the important role that latent heat release plays in band evolution simulations with varying degrees of latent heating show that diabatic processes associated with the band itself were critical to the development and maintenance of the band however changes in the meso

dynamical aspects of the life cycle of the winter storm lothar 24 26 december 1999 dynamical aspects of the life cycle of the winter storm lothar 24 26 december 1999 are investigated with the aid of the european centre for medium range weather forecasts analysis data and mesoscale model simulations neither of these datasets capture the full amplitude of the observed extreme pressure fall and surface wind speeds but they do help identify a range of key dynamical and physical features that characterize the development of this unusual event the analysis and interpretation is primarily based upon the evolution of the lower and upper level potential vorticity pv field complemented by three dimensional trajectory calculations lothar originated in the western atlantic and travelled as a shallow low level cyclone of moderate intensity towards europe this translation took place below and slightly to the south of a very intense upper level jet and was accompanied by continuous and intense condensational heating that sustained a pronounced positive low level pv anomaly not unlike the concept of a diabatic rossby wave no significant pv anomalies were evident at the tropopause level during this early phase of the life cycle the surface cyclone intensified rapidly when the shallow cyclone approached the jet stream axis the circulation induced by the diabatically produced low tropospheric pv anomaly on steeply sloping isentropic surfaces that transect the intense upper level jet contributed significantly to the rapid formation of a narrow and deep tropopause fold this stratospheric pv anomaly virtually merged with the diabatically produced ephemeral pv feature to form a vertically aligned tower of positive pv at the time of maximum storm intensity a sensitivity study with a dry adiabatic hindcast simulation shows no pv tower configuration and only a very weak surface development and confirms the primary importance of the cloud diabatic heating for the tropopause fold formation and the rapid bottom up intensification of lothar a comparison of the anomalously high atlantic sea surface temperatures in december 1999 with the water vapour source regions for the latent heat release that accompanied the rapid intensification phase of lothar shows a close relationship this is of importance when discussing the possible implications of climate variability and change on the development of north atlantic winter storms copyright 2002 royal meteorological society

the dynamical consequences for tropopause folding of pv anomalies induced by surface frontal collapse it has been noted previously that during frontal collapse dynamical processes lead to the formation of potential vorticity pv anomalies in the vicinity of the surface front these processes can either be associated with diffusion in the presence of the tight temperature gradients or with intrusion into the atmosphere of the vanishingly thin layer adjacent to the surface this paper explores the dynamical consequences of these pv anomalies on the parent baroclinic wave cyclone the method used is to find the vertical motion attributable to these anomalies the location and magnitude of this vertical motion is clearly key to the dynamical influence of the anomalies as we are dealing with a three dimensional evolving cyclone with an emergent tropopause fold the calculation of vertical motion needs to be capable of accounting for the role of the highly deformed tropopause hence we develop and use a nonlinear balance model approach the result shows that the pv anomalies near the surface front induce downward vertical motion at the tropopause fold and thus they act to amplify this feature this role of diffusion associated with surface frontal collapse is the key finding of this paper an analysis is made of the role of upper and lower level pv anomalies on the overall rate of the wave development

dynamical characterization of the fastex cyclogenesis cases summary a series of diagnostics based on the automatic tracking of cyclones is applied to the 25 life cycles captured during the fastex field experiment the tracking enables a setting of the various cases into a common frame of reference that moves with the system time filtering is used to further separate the events into a basic state and perturbations information is obtained on environmental properties such as strain or baroclinicity combining these diagnostics it is shown that instability mechanisms based on the existence of potential vorticity strips or the control of these instabilities by deformation may be involved in the initial genesis of a number of cases but do not seem to characterize specific types nor to determine a systematic behaviour on the other hand it is shown that rapid deepening phases leading eastern atlantic systems to their maximum amplitude happens suddenly and at the same time as crossing the jet stream even in the absence of a clear additional upper level feature for cold air systems development means meeting a diffluent zone this is unlike the american east coast systems that are associated with an exit entrance complex another remarkable feature is the generation of a frontal waveas a re sult of the parent vorticity maximum being apparently stretched and split this has occurred in 25 of cases a number of other properties of the fastex cases are shown such as several occurrences of large

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

mineralogy and geochemistry of volcanic and plutonic rocks from the boundaries of the caroline plate tectonic implications abstract chemical and mineralogical data from rocks dredged at six sites along plate boundaries around the caroline sea define at least three separate igneous suites three sites were located in the sorol trough along the caroline pacific plate boundary and three sites were located in the ayu trough along the caroline philippine plate boundary geophysical data suggest that both features have originated through processes of crustal extension weathered basalts with mid ocean ridge basalt morb affinities were recovered from the base of the northern margin of the sorol trough fresh transitional to alkalic pillow basalts from a seamount in the central part of the trough have geochemical and sr isotopic characteristics similar to enriched morb or volcanics associated with off ridge volcanism a suite of tholeiitic rocks consisting of high mg basalt ferrobasalt and a variety of mafic to ultramafic rocks dredged from the western section of the sorol trough has chemical and mineralogical characteristics of other intraplate tholeiitic suites like those from hawaii the ferrobasalts could have been derived from a high mg basaltic liquid through fractional crystallization of olivine clinopyroxene and plagioclase the geochemical data indicate that both morb and hot spot type sources have been involved in the generation of magmas beneath the sorol trough furthermore the highly metamorphosed and tectonized mafic to ultramafic rocks recovered with the tholeiites suggest that a significant component of shear accompanied crustal accretion along leaky transform faults within the sorol trough the chemical and isotopic characteristics of fresh to weathered pillow lava fragments from the axial rift and eastern margin of the ayu trough suggest that a morb type source was tapped during crustal accretion along a central spreading centre an assemblage of metabasalts metagabbros and silicic plutonic rocks plagiogranites recovered from a scarp along the western margin of the trough have petrologic and chemical features analogous to rocks from plutonic complexes in ophiolites and some oceanic ridges the plagiogranites could be differentiates from a relatively hydrous morb magma but cannot be related to the slightly lil enriched basalts in the ayu trough by crystal fractionation two separate mantle sources are implicated metamorphic features in the plutonic rocks are inferred to be the result of hydrothermal and dynamic events associated with the inception of spreading and to subsequent tectonism which exposed them the petrochemistry of rocks from the ayu and sorol troughs is consistent with the hypothesis that crustal accretion occurred along the northern and western boundaries of the caroline plate and further suggests that a variety of sub oceanic mantle sources have been involved in the genesis of the crust in each region

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

effects of cloud diabatic heating on the early development of the fastex iop17 cyclone a set of numerical simulations is used to study the first development phase of the fastex cyclone a particularly well sampled frontal cyclone system that developed on the trailing front of a primary large scale baroclinic wave during intensive observation period 17 iop17 of fastex the fronts and atlantic storm track experiment the role of diabatically induced vertical circulations is investigated with a combination of diagnostic tools including a generalized omega equation and keyser s psi vector technique applied to the model outputs the full physics simulation shows a good agreement with observed data particularly the splitting of the upper level flow into a pair of jet streaks analysis of the contributions to the vertical ageostrophic transverse circulations near the jet streak pair structure shows that a positive feedback exists between the storm s dynamical configuration and the diabatic processes in the second part of the paper this interpretation is confirmed by a sensitivity analysis excluding cloud processes results suggest that after initial baroclinic growth the storm evolves towards a purely diabatic deepening regime leading to a diabatic rossby wave mechanism as proposed by recent wave cisk conditional instability of the second kind theoretical studies

a lagrangian based analysis of extratropical cyclones ii a detailed case study a detailed case study analysis is undertaken of the occurrence of significant coherent ensembles of trajectories cets that accompany atlantic cyclogenesis the approach is based upon the lagrangian based analysis scheme introduced in part i the analysis reveals the existence of several distinct moist ascending and dry descending cets two types of moist ascending cets associated with strong condensational processes ascend from the boundary layer of the warm sector either in the close vicinity of the cyclone centre or in the trailing cold frontal region the latter is the main contributor to the precipitation along the cold front during the early phase of the development another type of moist cets distinguished by maximum water vapour flux travels at low levels through the warm sector and ascends to mid tropospheric levels in the warm frontal region where it produces strong precipitation around the time of maximum storm intensity cets with an upper level origin are linked to the classical dry intrusion different cets correspond to strong descent of upper level tropospheric air that penetrated to the lower troposphere the movement of stratospheric air toward the centre of the maturing cyclone and an event of stratosphere to troposphere exchange upstream of the upper level trough two different visualizations of time sequences of the moist ascending cets indicate that they represent well defined flexible tubes or airstreams that exist over a time period comparable with the duration of the main cyclone intensification they provide a translating flexible but coherent river bed for the quasi continuous ascent of moist boundary layer air to the upper troposphere these tubes are akin to the concept of warm conveyor belts and the present analysis method objectively diagnoses their geometrical and physical characteristics and potential vorticity pattern some consideration is also given to the relationship of cets and tropospheric rivers and to possible shortcomings of the approach

frontal wave cyclogenesis in the north atlantic a climatological characterisation the ambient conditions during cyclogenesis on fronts in the north atlantic na are characterised climatologically in the era interim dataset these secondary cyclones which grow from frontal waves are typically small in scale shallow and deepen rapidly and pose a challenge to forecasters and numerical weather prediction models frontal wave development has been studied intensively in the past based on observations e g fastex real case studies or analytical models in this study frontal wave cyclogenesis is studied from a climatological perspective and is detected by a combination of two automated identification methods for the period between 1979 and 2014 a climatology of frontal wave cyclogenesis is presented horizontal composites provide an estimate of the climatological mean of conditions during frontal wave cyclogenesis which may prove useful in the assessment of the realism of proposed idealized models of frontogenesis the findings are also compared with assumptions made in earlier idealized studies of frontal waves the composites reveal coherent structures of diabatically generated low level pv in the lower troposphere neutral moist static stability at cyclogenesis and an ambient lower troposphere close to saturation the vertical pv structure in the east na is more vertically aligned than in the west na and pv anomalies from the upper and lower levels reach deeper into the mid troposphere which indicates an enhanced phase lock between the two anomalies previous studies suggest the existence of an upper limit of along frontal stretching above which frontal wave development is strongly suppressed the presented multi decadal analysis confirms its existence in a range between 0 6 and 0 8 10 5 s 1 finally a climatology of along frontal stretching for the na is presented and compared to the fraction of cyclogenesis forming on frontal waves

secondary cyclogenesis along an occluded front leading to damaging wind gusts windstorm kyrill january 2007 abstractwindstorm kyrill affected large parts of europe in january 2007 and caused widespread havoc and loss of life in this study the formation of a secondary cyclone kyrill ii along the occluded front of the mature cyclone kyrill and the occurrence of severe wind gusts as kyrill ii passed over germany are investigated with the help of high resolution regional climate model simulations kyrill underwent an explosive cyclogenesis south of greenland as the storm crossed poleward of an intense upper level jet stream later in its life cycle secondary cyclogenesis occurred just west of the british isles the formation of kyrill ii along the occluded front was associated i with frontolytic strain and ii with strong diabatic heating in combination with a developing upper level shortwave trough sensitivity studies with reduced latent heat release feature a similar development but a weaker secondary cyclone revealing the importance of diabatic processes during the formation of kyrill ii kyrill ii moved

relationship between convection over central america and the intensity of the jet stream bearing on the 1999 december european storms during 26 28 december 1999 two very powerful and devastating extratropical cyclones hit western europe these two storms were associated with an upper level zonal jet remarkable in its intensity and its large extension over the atlantic ocean in this study we focus on the relationship between the exceptional features of this jet stream and some heavy precipitation that occurred over central america during mid december a rossby wave train excited by strong convective activity over this area is likely to play a key role in this teleconnection to assess this tropical extratropical interaction several numerical experiments have been performed with the french global model arpege firstly the effects of convection have been neutralized within a domain localized over central america then to combine the model with observations a new strategy has been devised within a selected window the parametrized latent heat release has been deduced from tropical rainfall measuring mission trmm precipitation data translated in terms of a potential vorticity hereafter pv source and incorporated into the model using pv inversion these simulations show in particular that the convective activity over central america triggers a wave train that moves poleward and eastward with the group velocity finally to strengthen the north atlantic jet stream leading to windstorms lothar and martin copyright 2011 royal meteorological society

rifting in the northern norwegian greenland sea thermal tests of asymmetric spreading the analysis of heat flow seismic and topographic data collected in the northern norwegian greenland sea reveals an asymmetric evolution of the eurasian and north american plates these data are compared to predictions from three kinematic models of extension which produce asymmetry about the knipovich ridge 1 uniform asymmetric pure shear 2 lithospheric simple shear and 3 rift ridge jumping the data are consistent with a range of deformation scenarios from one ridge jump occurring at about 25 m y after the initiation of spreading to continuous asymmetric extension the simple shear model can match the data only when a detachment fault dips more steeply than 45 under svalbard tectonic and heat flow evidence suggests that asymmetry may have evolved from a combination of all three models when the mohns ridge propagating to the east encountered the preexisting northward trending spitsbergen shear zone the direction of ridge propagation shifted to the north being influenced by the abrupt change in the regional stress field at the shear zone ridge axis intersection as a result the nascent knipovich ridge entered into and propagated along the shear zone consequently formerly active shear faults became the new detachment surfaces along which new crust is minted and asymmetrically extended the high level of deviatoric stress about the mohns and knipovich ridge intersection may cause a gradual eastward migration of the knipovich ridge resulting in multiple zones of magma intrusion off axial bands of high heat flow and volcanism located along the barents sea and svalbard margin along the yermak plateau and on continental svalbard just southeast of the yermak plateau may be evidence for this migration propagation from the nansen ridge may have entered the same shear zone from the north explaining the creation of the small molloy ridge and off axis volcanism on the yermak plateau

a five year radar based climatology of tropopause folds and deep convection over wales united kingdom abstracta five year 2006 10 radar based climatology of tropopause folds and convective storms was constructed for wales united kingdom to determine how deep moist convection is modulated by tropopause folds based on the continuous high resolution data from a very high frequency vhf wind profiling radar located at capel dewi wales 183 tropopause folds were identified tropopause folds were most frequent in january with a secondary maximum in july based on data from the u k weather radar network a climatology of 685 convective storms was developed the occurrence of convective storms was relatively high year round except for an abrupt minimum in february april multicellular lines 43 5 were the most common morphology with a maximum in october followed by isolated cells 33 1 with a maximum in may september and nonlinear clusters 23 4 with a maximum in november january convective storms were associated with 104 56 8 of the tropopause folds identified in this study with the associ

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

case study of potential vorticity tower in three explosive cyclones over eastern asia abstractthree cases of explosively developing extratropical cyclones over eastern asia are analyzed using era interim data the morphological characteristics of the upper tropospheric potential vorticity pv were examined the common feature of all of these three cases is a hook shaped high pv streamer wrapping counterclockwise around the center of surface cyclones on the southern and eastern sides and an arch shaped low pv tongue that wrapped the high pv hook head from the north the hook shaped high pv tongue overlaps with the maximum centers of both the relative vorticity and static stability parameter indicating the stratospheric nature of the pv source inside the hook shaped high pv tongue the analysis indicates that there existed a deep tower of high pv above the surface cyclone at the time when these cyclones underwent explosive cyclogenesis the high pv in the upper troposphere originates from the polar stratospheric pv reservoir associated with the tropopause folding process the high pv in the

synoptic and dynamic aspects of an extreme springtime saharan dust outbreak in march 2004 a large scale strong and persistent outbreak of saharan dust on to the adjacent tropical and subtropical atlantic ocean was observed in satellite imagery surface observations show that the event was accompanied by unusual weather conditions across large parts of north africa including low temperatures and strong winds over the sahara extreme precipitation in libya and a heat wave on the guinea coast the dust outbreak was associated with an unseasonally southerly position of the intertropical convergence zone and a delayed northward progression of the african monsoon the dust front was initially related to a density current caused by strong evaporational cooling along a precipitating cloud band that penetrated into the northern sahara ahead of an upper level trough at later stages massive upper level convergence sinking low level divergence and an explosive anticyclogenesis over northwest africa caused strong northerly flow and a quick spreading of the dust front to the south and west the strong pressure gradients over north africa were further enhanced by the formation of a cyclone ahead of the upper trough a dynamical analysis based on potential vorticity pv theory provides new insights into the generation of north african harmattan surges using a pv inversion it is shown that the explosive anticyclogenesis was caused largely by unbalanced dynamics related to the density current divergent outflow from the precipitation over libya and inertial instability in the entrance region of the strong subtropical jet and tropical plume along the eastern side of the upper trough these processes enhanced the effects of the balanced advection of negative vorticity and cold air by the large scale wave moreover we show the importance of an explosive cyclogenesis event over the central north atlantic for the amplification of the downstream wave associated with the penetration of the cold front into north africa copyright 2006 royal meteorological society

the linkage between the warm and the cold conveyor belts in an idealized extratropical cyclone abstractthis study continues the investigation of airstreams in idealized moist baroclinic waves and addresses the formation of the cold conveyor belt ccb its linkage to the warm conveyor belt wcb and their impact on the development of a midlatitude cyclone the ccb is identified as a coherent bundle of trajectories characterized by weak ascent and a strong increase of potential vorticity pv along the flow in contrast to the wcb defined as the trajectories with maximum ascent the authors illuminate the role of the two conveyor belts in the formation of two strong pv anomalies that form in the upper wcb negative pv anomaly and lower troposphere ccb positive pv anomaly respectively and thereby establish a link between these airstreams and relevant aspects of the dynamics of extratropical cyclones the ccb moves close to the surface along the colder side of the bent back front and experiences a pv increase as it passes below a region of maximum latent heat release at midtropospheric level

reexamining the dynamics of short scale diabatic rossby waves and their role in midlatitude moist cyclogenesis abstract as a step toward a more comprehensive study of the physical processes that underlie explosive cyclogenesis a two dimensional semigeostrophic model with a now standard parameterization of latent heat release is used to diagnose the structure energetics and propagation characteristics of short scale diabatic normal modes in a moist baroclinic atmosphere with the eady basic state upon revisiting the inviscid problem it is found that when a thermodynamically consistent vertical profile of latent heat release is used the short wave cutoff vanishes and growth rates become independent of zonal wavelength for zonal wavelengths shorter than approximately 1900 km the destabilized short scale modes identified previously as diabatic rossby waves owe their existence to the continuous generation of potential vorticity by moist processes associated with warm air advection rising motion and latent heat release to determine if these short scale diabatic rossby wave modes continue to grow at small

role of the low frequency deformation field on the explosive growth of extratropical cyclones at the jet exit part i barotropic critical region abstract by using new theoretical results on perturbation growth in spatially and temporally complex quasigeostrophic flows this paper investigates the role of the large scale deformation field on extratropical cyclones and especially on their explosive growth in the jet exit region theoretical ideas are tested by decomposing the atmospheric flow into a high and a low frequency part and by analyzing four dimensional variational data assimilation 4dvar reanalysis data of the fronts and atlantic storm track experiment fastex during february 1997 as well as reanalysis data for the end of december 1999 regions where the low frequency deformation magnitude is greater than the absolute value of the low frequency vorticity are shown to correspond to regions where synoptic disturbances at the same level tend to be located these regions in the upper troposphere are intrinsically related to the horizontal inhomogeneities of the low frequency large scale upper tropospheric jet but cannot be detected by look

subduction erosion crustal structure and an evolutionary model of the northern yap subduction zone new observations from the latest geophysical survey the yap subduction zone is a distinctive erosive margin with an extremely slow convergence rate the high relief of the subducting plate generated by horst and graben structures and seamounts leads to attenuation of the crust in this study we present the latest geophysical data collected by the chinese research vessel kexue to investigate subduction erosion at the yap subduction zone and develop subduction models for yap subduction zone structures we show an anomalous distance between the yap trench and the adjacent volcanic arc the steep slope of the trench arcward a frontal prism and rare sediment in the trench all typical features of erosive margins we propose that the high relief subducting plate has led to erosion of the overlying plate and that different subduction processes controlled locally by the topography of the subducting plate have modified the yap subduction zone numerous normal faults increase the relief of the seafloor entering the trench and an anomalously large slope angle along the trench reflects uplift of the fore arc high via seamount subduction in addition the thin crust of the subducted horst and graben structures along with the normal faults might have eroded the fore arc crust and subsequently eroded the yap arc crust during subduction these subduction erosional processes at the yap trench provide one of the best cases of an erosive margin in the world particularly for a subduction zone with an extremely slow convergence rate

life cycle study of a diabatic rossby wave as a precursor to rapid cyclogenesis in the north atlantic dynamics and forecast performance abstractthe life cycle of a north atlantic cyclone in december 2005 that included a rapid propagation phase as a diabatic rossby wave drw is investigated by means of operational analyses and deterministic forecasts from the ecmwf a quasigeostrophic omega diagnostic has been applied to assess the impact of upper level forcing during the genesis propagation and intensification phase respectively the system was generated in the gulf of mexico as a mesoscale convective vortex mcv influenced by vertical motion forcing from a nearby upper level trough the drw propagation phase was characterized by a shallow low level diabatically produced potential vorticity pv anomaly that rapidly propagated along the southern border of an intense baroclinic zone no significant upper level forcing could be identified during this phase of the development eventually explosive intensification occurred as the region of vertical motion forced by an approaching upper level trough reached the position of the drw the

secondary frontal waves in the north atlantic region a dynamical perspective of current ideas the current understanding of the dynamics of secondary cyclogenesis on frontal systems in the north atlantic region is reviewed these secondary cyclones are often poorly forecast and in extreme cases can have damaging consequences but because of their small scales and potential for rapid growth detailed observations and analyses are limited in this paper recent work is described and compared it is argued that on the synoptic scale the development of primary baroclinic waves is well understood but on the subscales of these systems where the secondaries develop there is a wider variety of mechanisms which may cause or modify cyclone growth this variety may be reflected in a wider range of resulting systems various dynamical models have been postulated secondary frontal waves are seen as the instability of a low level potential vorticity strip or warm band at a front with possible finite amplitude triggering by upper level features latent heating is thought to provide a suitable unstable potential vorticity strip but the degree to which the latent heating contributes to the instability itself is a matter of dissent secondary systems are often shallow so boundary layer processes are important but the influence of these is not well understood laboratory experiments have suggested that the boundary layer will act to suppress instability in general frontogenetic strain flow while acting to intensify the basic state front suppresses wave development in contrast recent work suggests that a frontolytic strain flow may be important in enhancing the development of one class of waves the fastex experiment an international field study of north atlantic secondary cyclogensis has recently attempted to observe these systems in detail it is hoped that the data which have been obtained will help to resolve some of the outstanding issues in this field

role of salient potential vorticity elements in an event of frontal wave cyclogenesis extratropical cyclogenesis is usually accompanied by both an upper level trough and a surface front with its cloud diabatic accoutrements in the present study these distinctive structures are interpreted as salient elements of the atmosphere s potential vorticity pv distribution and their role examined for one particular event of frontal wave cyclogenesis the strategy adopted is a form of diagnosis by pv dismemberment it entails adopting a successful forecast with a limited area model as a surrogate for the actual event and then performing a sequence of simulations with modified initial conditions that correspond in each case to the removal of one or more of the salient pv elements this approach provides an assessment of the relative significance of the individual elements permits an insightful comparison of various extant theories of cyclogenesis and pinpoints the particular pv elements influencing the event s predictability it is shown that the replication of the simulated cyclone requires an adequate representation both of specific fine scale pv features at tropopause levels and of the diabatically maintained low level pre frontal pv band thus a tenable theory of cyclogenesis that incorporates this not atypical event should both recognize and help clarify the dependence of cyclogenesis upon the relative locations movement scales and structures of the aforementioned salient pv elements

diabatic rossby waves in the southern hemisphere diabatic rossby waves drws are a special type of low level cyclone with a self maintaining mechanism given an environment of moderate or strong baroclinicity and abundant moisture under certain conditions these shallow cyclones associated with a cyclonic low level pv anomaly can serve as precursors for explosive cyclone intensification the present study is the first to investigate drws in the southern hemisphere sh two typical drw case studies are presented and a sophisticated algorithm is used to detect drws in operational analysis data from 2001 to 2012 drws occur in all ocean basins and seasons with a maximum in summer on average about four drws are found per month and 12 intensify explosively thereby they contribute 6 to the total set of explosively deepening extratropical cyclones in the sh drw tracks originate slightly closer to the equator than normal extratropical cyclones and they follow the convergence zones eastward and poleward this results in a climatological drw track density similar to a spiral from the western south pacific ending in the eastern south indian ocean broken only by the andes typical synoptic situations associated with drw genesis are identified the categories include i low level pv generation by upper level induced lifting ii low level jet induced diabatic pv generation and iii transformation of the low tropospheric pv anomaly from another system

a 10 yr climatology of diabatic rossby waves in the northern hemisphere abstractdiabatic rossby waves drws are low tropospheric positive potential vorticity pv anomalies in moist and sufficiently baroclinic regions they regenerate continuously by moist diabatic processes and potentially develop into explosively intensifying cyclones in this study a specific drw tracking algorithm is developed and applied to operational ecmwf analyses to compile a first climatology of drws in the northern hemisphere for the years 2001 10 drws are more frequent over the north pacific than over the north atlantic with on average 81 and 43 systems per year respectively less than 15 of these systems intensify explosively on average 12 per year over the pacific and 5 over the atlantic drws are most frequent in summer but most of the explosively intensifying drws occur in autumn and winter drws are generated typically between 30 50 n over the eastern parts of the continents and the western central parts of the oceans they propagate fairly zonally along the midlatitude baroclinic zone

a model aided study of the origin and evolution of the anomalously high potential vorticity in the inner region of a rapidly deepening marine cyclone abstract high spatial and temporal resolution fields generated by a mesoscale prediction model are used to study a case of rapid marine cyclogenesis 26 mb in 12 h within the context of potential vorticity pv thinking the case which occurred on 23 february 1987 near the east coast of the united states was well simulated by the model as was verified by ship reports and satellite imagery three components of the cyclone were investigated 1 a surface thermal anomaly or surrogate pv anomaly 2 a low level diabatically produced pv anomaly in and near the frontal cloud band and 3 a dry pv anomaly of upper tropospheric and lower stratosphoric origin trajectory tracing revealed that the surface thermal anomaly was caused primarily by northward transport of warm air into the central region of the low although surface sensible heat flux also contributed to the warm anomaly a sensitivity experiment run with the flux withheld showed that it had little impact on the depth of the storm furthermore

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

the role of secondary cyclones and cyclone families for the north atlantic storm track and clustering over western europe secondary cyclones are those that form in association with a pre existing primary cyclone typically along a trailing cold front in previously studied cases they have been shown to cause extreme damage across europe particularly when multiple cyclones track over the same location in rapid succession known as cyclone clustering to determine the dynamical relationship between primary and secondary cyclones over the north atlantic a frontal identification algorithm is partnered with a cyclone identification method to objectively identify secondary cyclones in 35 extended winter periods using reanalysis data cyclones are grouped into cyclone families consisting of a single primary cyclone and one or more secondary cyclones this paper aims to quantify the differences between secondary and primary cyclones over the north atlantic and how cyclone families contribute to episodes of cyclone clustering across western europe secondary cyclones are shown to occur most frequently in the central and eastern north atlantic whereas primary cyclones are commonly found over the western north atlantic cyclone families have their strongest presence over the north atlantic ocean and contribute more than 50 of cyclones over the main north atlantic storm track a final category solo cyclones which are not associated with cyclogenesis on any connected fronts are most commonly identified over continental regions as well as the mediterranean sea primary cyclones are associated with the development of an environment that is favourable for secondary cyclone growth enhanced rossby wave breaking following primary cyclone development leads to an increase in the upper level jet speed and a decrease in low level stability secondary cyclogenesis commonly occurs in this region of anomalously low stability close to the european continent during periods of cyclone clustering secondary cyclones are responsible for approximately 50 of the total number of cyclones the increase in jet speed and decrease in static stability initiated by the primary cyclones acts to concentrate the genesis region of secondary cyclones and direct the cyclones that form along a similar track while there is an increase in the secondary cyclogenesis rate near western europe during periods of european clustering the basin wide secondary cyclogenesis rate decreases during these periods thus the large scale environment redistributes secondary cyclones during periods of clustering rather than increasing the total number of secondary cyclones

application of a new wind gust parameterization multiscale case studies performed with the canadian regional climate model 1 the implementation of a physically based parameterization scheme for computation of wind gusts in a numerical regional climate model rcm is described in this paper the method is based on an innovative approach proposed by brasseur 2001 that assumes that gusts occurring at the surface result from the deflection of air parcels flowing higher in the boundary layer our parameterization scheme is developed so as to use quantities available at each model time step consequently the gusts are also computed for each of these time steps to illustrate the performances of this novel method gusts simulated for two severe midlatitude windstorms with the canadian rcm at various resolutions are compared with observed gust speeds the study is carried out concurrently for the complex terrain of switzerland and for the smoother topography of belgium a preliminary analysis indicates that this parameterization performs equally well over flat and over mountainous regions it also responds properly in the strengthening as well as the weakening phases of wind storms the storm dependent results rely on the model configuration associated with the downscaling procedure as well as on the accuracy of the simulated flow fields the model response is dependent on the resolved topography distribution and height and on the types of lower boundary conditions that affect the stability of the boundary layer the simulated gusts are generally more realistic at higher resolution over the complex topography of switzerland but are less sensitive to resolution over the flat terrain as in belgium on the basis of these two storms this study also shows that simple scaling coefficients relating gust speeds and resolution are not an appropriate method for addressing such issues

seasonality and interannual variability of the westerly jet in the tibetan plateau region abstract in this study 40 yr ecmwf re analysis era 40 data are used for the description of the seasonal cycle and the interannual variability of the westerly jet in the tibetan plateau region to complement results based on the analysis of monthly mean horizontal wind speeds an occurrence based jet climatology is constructed by identifying the locations of the jet axes at 6 hourly intervals throughout 1958 2001 thus a dataset describing the highly transient and localized features of jet variability is obtained during winter and summer the westerly jet is located respectively to the south and north of the tibetan plateau during the spring and autumn seasons there are jet transitions from south to north and vice versa the median dates for these transitions are 28 april and 12 october the spring transition is associated with large interannual variations while the fall transition occurs more reliably within a 3 week period the strength of the jet exhibits a peculiar seasonal cycle during northw

the role of large scale atmospheric flow and rossby wave breaking in the evolution of extreme windstorms over europe we investigate the relationship between large scale atmospheric flow and the evolution of the most extreme windstorms affecting western continental europe the 25 most destructive western continent

the dynamical structure of intense mediterranean cyclones this paper presents and analyzes the three dimensional dynamical structure of intense mediterranean cyclones the analysis is based on a composite approach of the 200 most intense cyclones during the period 1989 2008 that have been identified and tracked using the output of a coupled ocean atmosphere regional simulation with 20 km horizontal grid spacing and 3 hourly output it is shown that the most intense mediterranean cyclones have a common baroclinic life cycle with a potential vorticity pv streamer associated with an upper level cyclonic rossby wave breaking which precedes cyclogenesis in the region and triggers baroclinic instability it is argued that this common baroclinic life cycle is due to the strongly horizontally sheared environment in the mediterranean basin on the poleward flank of the quasi persistent subtropical jet the composite life cycle of the cyclones is further analyzed considering the evolution of key atmospheric elements as potential temperature and pv as well as the cyclones thermodynamic profiles and rainfall it is shown that most intense mediterranean cyclones are associated with warm conveyor belts and dry air intrusions similar to those of other strong extratropical cyclones but of rather small scale before cyclones reach their mature stage the streamer s role is crucial to advect moist and warm air towards the cyclones center these dynamical characteristics typical for very intense extratropical cyclones in the main storm track regions are also valid for these mediterranean cases that have features that are visually similar to tropical cyclones

understanding the regeneration stage undergone by surface cyclones crossing a midlatitude jet in a two layer model the present paper provides a rationale for the regeneration stage undergone by surface cyclones when they cross a baroclinic jet from its anticyclonic shear warm side to its cyclonic shear cold side in a two layer quasigeostrophic model to do so the evolution of finite amplitude synoptic cyclones in various baroclinic zonal flows is analyzed baroclinic zonal flows with uniform horizontal shears are first considered while the anticyclonic shear allowsamuchmoreefficientandsustainableextractionofpotentialenergythanthecyclonicshear thegrowth of the lower layer eddy kinetic energy eke is shown to be highly dependent on the choice of the parameter values an increased vertical shear leads to a more rapid eke increase in the anticyclonic shear than in the cyclonic shear whereas increasing the vertically averaged potential vorticity gradient or the barotropic shear stabilizes the eke more in the former shear than in the latter finally vertical velocities arising from the nonlinear interaction between synoptic cyclones are shown to favor eke growth in the cyclonic shear rather than in the anticyclonic one the evolution of cyclones initialized on the warm side of a meridionally confined baroclinic jet is then investigated the lower layer cyclone crosses the jet axis and undergoes two distinct growth stages the first growth stage results from the classical baroclinic interaction and is mainly driven by linear interaction between the cyclones and the jet the second growth stage is mainly a nonlinear process it is triggered by the verticalvelocitiescreated by the three dimensionalstructureofthe cyclonic disturbances whenthey reach the cyclonic side of the jet

baroclinic transition of a long lived mesoscale convective vortex abstract the period 5 15 june 2003 during the field phase of the bow echo and mesoscale convective vortex mcv experiment bamex was noteworthy for the wide variety of mesoscale convective systems mcss that occurred of particular interest was a long lived mcv that formed in the trailing stratiform region of an mcs over west texas at 0600 utc 10 june this mcv was noteworthy for its i longevity as it can be tracked from 0600 utc 10 june to 1200 utc 14 june ii development of a surface cyclonic circulation and attendant 2 to 4 hpa sea level pressure perturbation iii ability to retrigger convection and produce widespread rains over several diurnal heating cycles and iv transition into a baroclinic surface cyclone with distinct frontal features baroclinic transition defined here as the acquisition of surface fronts occurred as the mcv interacted with a remnant cold front left behind by a predecessor extratropical cyclone over the great lakes region although the mcv developed well def

the impact of coriolis approximations on the environmental sensitivity of idealized extratropical cyclones the precise influence of climate change on extratropical cyclone genesis and evolution is an important but as yet unsolved problem given their physical and economic impact on a large portion of the planet s population however extratropical cyclones are also affected by the competing influences of forcing mechanisms at a wide range of spatial scales complicating the problem while the advent of idealized numerical modeling has allowed great strides in addressing these complications and achieving some qualitative consensus in the literature there is still some quantitative disagreement about response magnitude and where local maxima and minima in the response may be located thus the advantages inherent in the variety of idealized numerical modeling methods used to address this problem are also a drawback as it can be difficult to draw one to one comparisons across experiments although the effects of particular model architecture choices such as microphysical and cumulus schemes are well documented others are less understood in this study we examine the role of coriolis approximations by comparing a new set of etc sensitivity experiments using a linear plane approximation to an existing set of extratropical sensitivity experiments using a constant f plane approximation etcs within the new plane experiment are found to generally decrease in strength with temperature as measured by both minimum sea level pressure and maximum eddy kinetic energy eke a small increase in eke is observed at the warmest temperatures likely due to diabatic influences disrupting flow within the warm conveyor belt while seemingly contradictory to the previous f plane results the two experiments are instead found to be qualitatively similar upon further inspection with an offset of approximately 8 k this offset is primarily due to the coriolis approximations although the initial stability profile affected by the coriolis approximation has a marginal influence

fastex iop17 cyclone introductory synoptic study with field data this paper introduces the study of the early development phase of the iop17 frontal cyclone of the fastex field experiment fronts and atlantic storm track experiment with the support of observations from fastex observing platforms a synoptic description highlights the development of mesoscale features of interest in the operational meteo france arpege action de recherche petite echelle grand echelle analysis cycle i e cloud head dry wedge and upper level jet outflow a discussion attempts to isolate two significant differences of the present cyclone life cycle compared with previous well known conceptual models of maritime cyclone life cycles i the indirect role of an upper level precursor in triggering the surface low ii the existence of a diabatic regime taking over from the baroclinic development to sustain the deepening rate of the cyclone these two mechanisms are the subject of two companion papers

origin and tectonic evolution of the caroline ridge and the sorol trough western tropical pacific from admittance and a tectonic modeling analysis abstract an independent caroline sea plate surrounded by prominent seismotectonic features is said to exist in the western tropical pacific the caroline sea plate is a transient feature existing only when the caroline philippine sea plate boundary is jumping to the caroline pacific boundary the origin and the tectonic evolution of the caroline ridge sorol trough region which forms the northern part of the caroline pacific plate boundary are examined using a standard admittance analysis a tectonic modeling study and additional direct gravity and magnetic analyses the observed admittance function is fitted well by shallow airy model in the 250 125 km 0 025 k 1 wavelength region whose average crustal thickness t c is 20 km and also by thin plate flexure model of isostasy within the diagnostic waveband of 250 80 km 0 025 k 1 with an effective elastic thickness t e of 5 7 km a simple interpretation of the observed admittance function is that the local airy model of isostasy is the main support mechanism in the study region for the longer wavelength more fundamental topography corresponding to that of the caroline ridge the caroline ridge is inferred to have formed in a near ridge tectonic setting on top of oceanic lithosphere which was young thin and weak at the time of emplacement the tectonic model study after an explanation for rifting along the mendana fracture zone in the nazca plate suggests that the sorol trough formed in the 17 7 ma interval splitting the caroline ridge into two longitudinal halves the rifting along the sorol trough which took place in the manner described in weissel and karner 1989 flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension j geophys res 94 13 919 13 950 necking of unbroken lithosphere post dated the formation of the caroline ridge by 10 15 m y during which time t e in the region increased to 5 10 km the rifting necking along the sorol trough represents a second loading event in the region the combined gravity effects of the rifting as well as the increase in the t e in the region from essentially nil to 5 10 km is reflected in the agreement between the observed admittance and the regional model with a 5 7 km t e in the wavelength region 80 km these results are consistent with the findings and the suggestions of the previous investigators in the region in that 1 the caroline ridge was constructed in the late oligocene by hot spot volcanism on top of oligocene seafloor of the caroline sea back arc basin 2 the eauripik rise genetically related to the caroline ridge formed on young and weak caroline basin lithosphere and is supported by airy manner crustal thickening and that 3 the lithosphere of the caroline ridge was young at the time of rifting necking along the sorol trough on the basis of the current results and the findings of the previous workers a tentative hypothetical rheological model for the crustal density structure of the caroline ridge sorol trough is also given the caroline sea plate appears to be bounded in the north and south by e w trending boundaries that deform diffusely while more normal narrow n s trending boundaries exhibiting more localized albeit slow deformation bound the plate in the east and west

diminutive frontal waves a link between fronts and cyclones abstract a number of recent publications have dealt with cyclone identification and tracking following on this paper extends the typical cyclone life cycle back in time to embrace a new feature called a diminutive frontal wave one aim is to improve predictability by extending tracks this is particularly important for small cyclonic windstorms which can often be missed in postprocessed output from operational ensemble and climate runs the recognition of diminutive waves requires a new front relative low level vorticity partition the parts are labeled frontal vorticity and disturbance vorticity and are computed respectively from front parallel and cross front low level wind components a diminutive frontal wave then lies wherever there is a local along front maximum in the disturbance vorticity computations require local coordinates these are conveniently provided at all grid points by objective front diagnostics analysis of cyclone type transitions over the north atlantic in opera

cenozoic tectonic and depth age evolution of the indonesian gateway and associated back arc basins abstract we reconstruct the tectonic and paleo age and depth history of the indonesian seaway and associated southeast asian back arc basins to create a comprehensive paleogeographic framework for the region during the cenozoic we combine published tectonic models with revised models of the evolution of back arc basins based on available marine magnetic anomaly data and a recently published high resolution 1 min marine gravity anomaly grid which reveals many fine scale tectonic features previously not resolved reconstructions of the now subducted ceno tethys ocean floor are integrated with a revised absolute plate motion reference frame for the indian ocean based on moving hotspots all marginal seas north of australia formed in a back arc setting with the caroline and celebes seas opening north of a northward dipping subduction zone and the solomon sea south of a southward dipping subduction zone north of australia we suggest that the evolution of the two sub basins of the caroline sea from 36 to 25 ma followed different seafloor spreading patterns with the western sub basin being influenced by the manus hotspot our model suggests that collision between the melanesian and the caroline arcs led to cessation of oceanic crustal production in the caroline basin shortly before 25 ma combined geophysical and geological observations suggest that several major tectonic events occurred north of australia at around 45 ma roughly at the time when australia started moving northwards at fast rates similar to the present we suggest that this event is related to a relocation of the subduction zone nw of australia under the philippine sea plate due to a collision and subsequent accretion of old pacific plate material to the northward subducting australian plate our gridded oceanic paleo depth maps capture the history of marginal seas north of australia and the stepwise destruction of the ceno tethys ocean floor in the northern wharton basin and the west pacific providing boundary conditions for both paleoceanograpic and geodynamic models a regional analysis of basement depth anomalies reveals that median negative anomalous depth of several back arc basins is of the order of 650 800 m with a range of 300 1100 m accompanied by negative regional heatflow anomalies suggesting that mantle driven dynamic topography plays a larger role in modulating regional basement depth than previously suggested regional shear wave mantle tomography cross sections highlight that all marginal basins that exhibit large negative dynamic topography are underlain by massive buried slab material in the lower portion of the upper mantle and or below the transition zone supporting the notion that the observed paired negative dynamic topography and heatflow anomalies are due to basin formation above slab burial grounds

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

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