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

classification and composite diagnosis of extratropical cyclogenesis events in the southwest pacific abstract characteristic patterns of cyclogenesis in the southwest pacific region are identified from a sample of 40 developing cyclones during 1990 94 cases were chosen objectively to ensure a realistic sampling of typical rather than ideal events a subjective classification based on synoptic scale upper tropospheric flow signatures prior to cyclone intensification suggested four classes into which all but three cases fell three categories each containing about a quarter of the population involved direct coupling with the upper jet they represent cyclone formation beneath i the poleward exit region of a 300 hpa jet upstream from a diffluent trough class u ii the confluent equatorward entrance region of the upper wind maximum e and iii the upper jet exit region where the jet is downstream from the upper trough class d these are analogous to previously identified categories for the western north atlantic region a fourth class involved cyclones forming beneath a preexisting intense up

analysis of the wind field evolution associated with the extratropical transition of bonnie 1998 abstract extratropical transition brings about a number of environmentally induced structural changes within a transitioning tropical cyclone of particular interest among these changes is the acceleration of the wind field away from the cyclone s center of circulation along with the outward movement of the radial wind maximum together termed wind field expansion previous informal hypotheses aimed at understanding this evolution do not entirely capture the observed expansion while a review of the literature shows no formal work done upon the topic beyond analyzing its occurrence this study seeks to analyze the physical and dynamical mechanisms behind the wind field expansion using model simulations of a representative transition case north atlantic tropical cyclone bonnie of 1998 the acceleration of the wind field along the outer periphery of the cyclone is found to be a function of the net import of absolute angular momentum within the cyclone s environment along inflowing trajectories this evolut

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

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

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

an application of potential vorticity inversion to improving the numerical prediction of the march 1993 superstorm in this study a methodology is proposed to improve the model initial conditions based on available surface temperature observations from ships buoys and drifters it is tested with the numerical prediction of the 12 14 march 1993 superstorm that is initialized at its incipient stage over the gulf of mexico in this methodology the authors make use of the piecewise potential vorticity pv inversion technique and treat the temperature errors at the lowest level as a surrogate pv anomaly after inverting the wind and mass perturbations from the surface thermal anomaly and its pertinent interior pv anomaly a three dimensional dynamically consistent set of errors are obtained and added to the model initial conditions to improve the representation of the lower troposphere over the data sparse ocean it is found that the numerical model prediction initialized with the modified initial conditions exhibits significant improvements in the early rapid deepening and the track of the superstorm over ocean the development of a prefrontal squall line and the central sea level pressure traces during the life cycle of the cyclone as verified against observations these results show that the methodology proposed is promising in improving the representation of lower tropospheric meteorological variables in the model initial conditions based on available surface observations over data sparse regions

extratropical transition of southwest pacific tropical cyclones part i climatology and mean structure changes a database of tropical cyclone best track and intensity information for the southwest pacific ocean basin is used to construct a 28 year climatology for tropical cyclones that move into middle latitudes of the nine or so tropical cyclones that form each year an average of about three can be expected to migrate south of 358s with the greatest fraction in march storms entering the tasman sea west of new zealand nz move almost due south on average and retain greater intensity than those to the east of nz where storms decay quickly while moving rapidly away to the southeast storms east of nz are embedded in a stronger more zonal flow than those to the west which move poleward ahead of a larger amplitude trough during el nino years tropical cyclones that move into middle latitudes exhibit stronger zonal motion and occur over a wider range of longitudes than during la nina years storm intensity is only weakly correlated with concurrent sst anomalies suggesting that atmospheric circulation is the dominant influence on storm properties average structure changes during extratropical transition et are identified using the ncep ncar reanalysis dataset for a subset of 33 transitioning storms during 1980 97 composites are used to construct a three dimensional conceptual model of the transformation from a mature hurricane to an asymmetric baroclinic midlatitude cyclone southwest pacific tropical cyclones encounter the baroclinic westerlies early in their lives accounting for their average eastward and poleward motion at maximum average intensity near 208s baroclinic effects are already important with warm frontogenesis appearing in the southeast quadrant and outflow aloft into a downstream subtropical wind maximum that moves poleward with the storm by 258s the average tc has lost the characteristic symmetric anticyclonic outflow aloft and acquired the characteristics of a baroclinic midlatitude storm including regions of warm and cold frontogenesis a vertical motion dipole and a westward tilt with height from about 308s poleward a second upper tropospheric wind maximum appears west of the storm with strengthening cyclonic vorticity advection aloft below about 400 hpa the storm retains the vertical warm cyclonic core as it migrates poleward

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

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

interpretation of the structure and evolution of adjoint derived forecast sensitivity gradients a 36 h adjoint based forecast sensitivity study of three response functions defined in the lower troposphere average temperature in an isolated region of the upper midwest r1 meridional temperature difference r2 and average zonal component of the wind r3 is conducted with the goal of providing a synoptic and dynamic interpretation of the sensitivity gradient structure and evolution in addition to calculating and interpreting the sensitivity gradients with respect to basic model variables along the model forecast trajectory a technique is outlined that allows for the calculation of the sensitivity gradients with respect to variables derivable from the model state vector including geopotential relative vorticity and divergence and a method for visualizing the sensitivities with respect to the horizontal components of the wind is proposed and demonstrated the sensitivity of r1 to all model and derived variables revealed that r1 was controlled by nearly adiabatic processes associated with the addition or generation of temperature perturbations upstream of the region in which r1 was defined for r2 the sensitivity gradients revealed the well known influence of confluent horizontal flow and vertical tilting of isentropes to increase the north south temperature gradient over the region within which r2 was defined the sensitivity of r3 to the components of the horizontal wind reveals that simply adding or generating an upstream zonal wind perturbation is insufficient to change the zonal wind at 36 h as these wind perturbations upstream of the domain within which r3 is defined are torqued by the coriolis force as they are advected toward the domain these results suggest adjoint derived sensitivities of quasi conserved response functions may be more easily interpretable than sensitivities calculated for nonconserved response functions

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 transformation of tropical storm agnes into an extratropical cyclone part i the observed fields and vertical motion computations abstract this is the first of two papers dealing with the transformation of tropical storm agnes june 1972 into an extratropical cyclone synoptic analyses and vertical motion patterns are used to describe the behavior of agnes over a five day period subsequent to initial landfall during which time agnes regained tropical storm strength prior to transforming into an extratropical cyclone and dissipating input data for all calculations are obtained from optimum interpolation objective analyses with a resolution of 1 latitude longitude in the horizontal and 100 mb in the vertical a modified 9 level version of krishnamurti s 1968a diagnostic balance model is discussed and applied to the data set to determine the fields of vertical motion redevelopment of agnes subsequent to initial landfall is the result of the spread of an area of appreciable cyclonic vorticity advection aloft over the periphery of the low level circulation devoid of significant baroclinicity unlike a corresponding midlatitude sto

the extratropical transitions of hurricanes felix and iris in 1995 abstract the extratropical transitions of hurricanes felix and iris in 1995 are examined and compared both systems affected northwest europe but only iris developed significantly as an extratropical system in both cases the hurricane interacts with a preexisting extratropical system over the western atlantic the remnants of the exhurricanes can be identified and tracked across the atlantic as separate low level potential vorticity pv anomalies the nature of the baroclinic wave involved in the extratropical transition is described from a pv perspective and shown to differ significantly between the two cases the role of vertical shear in modifying the hurricane structure during the early phase of the transition is investigated iris moved into a region of strong shear the high pv tower of iris developed a marked downshear tilt felix moved into a vertically sheared environment also but the shear was weaker than for iris and the pv tower of felix did not tilt much iris maintained its warm core struc

plate boundary deformation associated with the great sumatra andaman earthquake the sumatra andaman earthquake of 26 december 2004 is the first giant earthquake moment magnitude m w 9 0 to have occurred since the advent of modern space based geodesy and broadband seismology it therefore provides an unprecedented opportunity to investigate the characteristics of one of these enormous and rare events here we report estimates of the ground displacement associated with this event using near field global positioning system gps surveys in northwestern sumatra combined with in situ and remote observations of the vertical motion of coral reefs these data show that the earthquake was generated by rupture of the sunda subduction megathrust over a distance of 1 500 kilometres and a width of 150 kilometres megathrust slip exceeded 20 metres offshore northern sumatra mostly at depths shallower than 30 kilometres comparison of the geodetically and seismically inferred slip distribution indicates that 30 per cent additional fault slip accrued in the 1 5 months following the 500 second long seismic rupture both seismic and aseismic slip before our re occupation of gps sites occurred on the shallow portion of the megathrust where the large aceh tsunami originated slip tapers off abruptly along strike beneath simeulue island at the southeastern edge of the rupture where the earthquake nucleated and where an m w 7 2 earthquake occurred in late 2002 this edge also abuts the northern limit of slip in the 28 march 2005 m w 8 7 nias simeulue earthquake

inclusion of a tke boundary layer parameterization in the canadian regional finite element model abstract the formulation of the regional model recently implemented by the atmospheric environment service of canada for its operational 48 h nwp forecasts is presented the emphasis is put on the parameterization of the physical processes especially those affecting the atmospheric boundary layer the originality of this model in addition to the use of 3 d finite elements of variable meshes in both the horizontal and vertical and of being non nested as previously described by staniforth and daley consists in the treatment of the time dependent turbulent kinetic energy tke and the inclusion of the full diurnal cycle the overall organization of the model calculations it also presented in order to convey a more accurate description of this integrated system sample results from the well known case of the presidents day cyclone of 1979 and general performance are covered in the last section

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

deep crustal reflection recordings in australia 1957 1973 i data acquisition and presentation summary the australian bureau of mineral resources bmr has conducted experiments since 1957 to record deep crustal reflections these experiments were made initially during surveys conducted for other purposes in 1968 1969 bmr conducted experiments designed specifically for deep reflection recordings in the tertiary murray basin the precambrian willyama block and the palaeozoic tasman geosyncline in southeastern australia the amadeus basin in central australia and in the archaean in western australia bmr introduced digital recording in 1976 and since then successfully recorded several long deepcrustal profiles in this paper we describe and discuss only those recordings made with analogue equipment prior to 1973 apparent deep crustal reflections were recorded at most of the 46 sites investigated at 24 of these events occurred at times of 10 13 s at some sites where only one or two shots were recorded it was difficult to confirm late events as deep reflections where investigations were more comprehensive the events were consistent with deep reflections although in many places they lacked continuity the events showed peak frequencies of about 20 hz recording quality was improved with the use of 8 10 hz geophones in multiple in line arrays of 100 m or more and filters with a cut off about 14hz or less the quality was generally better in sedimentary basins than in areas of exposed basement rocks where several events occurred they generally showed a variety of dips making identification with simplified geological structure difficult it was not possible to interpret the reflection data alone in terms of crustal structure because of the limited data available and the large distances between most recording sites however the results are particularly useful in providing a preview of deep reflections that may be expected from future surveys in australia

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

the extratropical transition of tropical cyclone edisoana 1990 abstractdocumentation of southwest indian ocean swio tropical cyclones tcs and extratropical transition et events is sparse in the refereed literature the authors present a climatology of swio tc and et events for 1989 2013 the swio averages 9 tropical cyclones tcs per year in this modern era of these tcs 44 undergo extratropical transition et or four per year a case study of tc edisoana 1990 the most rapidly intensifying swio post et tc between 1989 and 2013 shows that extratropical interactions began when an approaching trough embedded in the subtropical jet stream stj induced et on 7 march as edisoana underwent et a subtropical ridge downstream amplified in response to poleward directed positive potential vorticity pv advection associated with diabatically convectively driven upper level outflow from tc edisoana this amplifying lower latitude ridge phased with a lower amplitude higher latitude ridge embedded in the polar front jet pfj resulting in the merger of the t