mesoscale vortices in the weddell sea region antarctica abstract preliminary results of investigations of antarctic mesocyclones in the weddell sea region are presented for the antarctic summer periods 1983 88 based on noaa and meteor satellite images a total of 195 mesoscale vortices scale less than 1000 km were observed and classified using a simple classification scheme depending on lifetime and cortex diameter the highest frequency of vortices was found over the ice free part of the eastern weddell sea mean synoptic conditions for vortices with scales less than 400 km near halley station indicate an offshore flow being most favorable for their development a case study with satellite images surface measurements synoptic analyses derived from tovs data shows the evolution of several mesoscale vortices in a pool of cold air in the eastern weddell sea

bed load grain velocities and sediment transport rates theoretical consideration of the dynamics of bed load sediment transport leads to expressions for bed grain velocity and sediment transport rate as respectively ub a u u c and ib a tan u u c 0 c agreeing in form with many previous analyses the grain velocity equation agrees well with all experimentally determined velocities of single grains moving over fixed rough beds if a is allowed to vary with bed roughness and saltation height values of u c for such overriding grains are substantially less than normally accepted values the sediment transport rate equation predicts plane bed experimental data well over five orders of magnitude of ib values of a tan increase significantly from lower to upper stage plane beds due to an increase in a with suspended sediment concentration but also due to a decrease in tan with increasing transport stage and grain size as predicted by bagnold

secondary eyewall formation in an idealized tropical cyclone simulation balanced and unbalanced dynamics abstractthe secondary eyewall formation sef in an idealized simulation of a tropical cyclone tc is examined from the perspective of both the balanced and unbalanced dynamics and through the tangential wind vt budget analysis it is found that the expansion of the azimuthal mean vt above the boundary layer occurs prior to the development of radial moisture convergence in the boundary layer the vt expansion results primarily from the inward angular momentum transport by the mid to lower tropospheric inflow induced by both convective and stratiform heating in the spiral rainbands in response to the vt broadening is the development of radial inflow convergence and the supergradient flow near the top of the inflow boundary layer results from the vt budget analysis show that the combined effect of the mean advection and the surface friction is to spin down vt in the boundary layer while the eddy processes eddy radial and vertical advection contribute positively to the spinup of vt in the sef region

case studies of developing east pacific easterly waves this paper contains a study of developing east pacific easterly waves observed during the summer of 1991 with aircraft in situ and radar data and geosynchronous infrared satellite imagery the circulation and divergence profiles surface momentum and entropy fluxes as well as 700 mb and 975 mb saturated and actual equivalent potential temperatures were measured repeatedly for three disturbances that evolved into east pacific hurricanes as the disturbances develop the level of maximum updraught mass flux decreases which leads to increased convergence at low levels this process appears to be coupled to an increase in the mid level relative humidity which in turn suppresses the development of convective downdraughts comparison of the respective tendencies of convergence and surface friction to spin up and spin down a developing disturbance suggests that friction is unimportant in the early stages of development however as the surface circulation develops the two effects become comparable in magnitude if surface friction is deposited through a fairly deep layer of the troposphere the observations appear to rule out boundary layer ekman balance in these developing systems though more accurate observations of the eddy fluxes of absolute vorticity into such systems are needed to answer this question with certainty

climatological aspects of mesoscale cyclogenesis over the ross sea and ross ice shelf regions of antarctica abstract a one year 1988 statistical study of mesoscale cyclogenesis near terra nova bay and byrd glacier antarctica was conducted using high resolution digital satellite imagery and automatic weather station data results indicate that on average two one mesoscale cyclones form near terra nova bay byrd glacier each week confirming these two locations as mesoscale cyclogenesis areas the maximum minimum weekly frequency of mesoscale cyclones occurred during the summer winter the satellite survey of mesoscale vortices was extended over the ross sea and ross ice shelf results suggest southern maric byrd land as another area of mesoscale cyclone formation also frequent mesoscale cyclonic activity was noted over the ross sea and ross ice shelf where on average six and three mesoscale vortices were observed each week respectively with maximum minimum frequency during summer winter in both regions the majority 70 80 of the vortices were of comma cloud type and were shallow only a

on the dynamics of sediment suspension by residual reynolds stresses confirmation of bagnold s theory bagnold s dynamic theory for sediment suspension requires that the immersed weight of suspended grains over unit bed area is supported by an upward directed residual reynolds stress yy arising from asymmetrical shear turbulence the present paper presents an analysis of previously published turbulence data which confirms the existence of this residual stress and indicates its generation in the lowermost part of the buffer layer of turbulent shear flows the magnitude of yy is estimated as about 0 3 yx calculations from experimental data on suspended fine sand transport over upper phase beds reveals that yy is in approximate equilibrium with the weight stress due to the suspended load

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

a characteristic life cycle of upper tropospheric cyclogenetic precursors during the experiment on rapidly intensifying cyclones over the atlantic erica abstract this paper documents a characteristic life cycle of upper tropospheric precursors to surface cyclogenesis observed during the field phase of the experiment on rapidly intensifying cyclones over the atlantic erica december 1988 february 1989 this life cycle begins with the development of an elongated region of lower dynamic tropopause that forms in association with an intensifying midtropospheric jet front over central north america the elongated disturbance subsequently compacts into a more circular configuration prior to crossing the east coast of north america and frequently is associated with rapid surface cyclogenesis offshore a representative example of the life cycle outlined above is documented through a detailed case study of the upper precursor associated with the second erica intensive observation period iop 2 cyclone emphasis is placed upon i description of the tropopause structure and evolution during the upper precursor life cycle ii diagnosis of mechanisms leading to t

the role of vortical hot towers in the formation of tropical cyclone diana 1984 abstract a high resolution 3 km horizontal grid spacing near cloud resolving numerical simulation of the formation of hurricane diana 1984 is used to examine the contribution of deep convective processes to tropical cyclone formation this study is focused on the 3 km horizontal grid spacing simulation because this simulation was previously found to furnish an accurate forecast of the later stages of the observed storm life cycle the numerical simulation reveals the presence of vortical hot towers or cores of deep cumulonimbus convection possessing strong vertical vorticity that arise from buoyancy induced stretching of local absolute vertical vorticity in a vorticity rich prehurricane environment at near cloud resolving scales these vortical hot towers are the preferred mode of convection they are demonstrated to be the most important influence to the formation of the tropical storm via a two stage evolutionary process i preconditioning of the local environment via diabatic production of mul

a comparison of the vorticity dynamics governing the oceanic bomb cyclone of 4 5 january 1989 and the super derecho of 8 may 2009

the impact of moist frontogenesis and tropopause undulation on the intensity size and structural changes of hurricane sandy 2012 abstractthis study examines the relative roles of moist frontogenesis and tropopause undulation in determining the intensity size and structural changes of hurricane sandy using a high resolution cloud resolving model a 138 h simulation reproduces sandy s four distinct development stages i rapid intensification ii weakening iii steady maximum surface wind but with large continued sea level pressure slp falls and iv reintensification results show typical correlations between intensity changes sea surface temperature and vertical wind shear during the first two stages the large slp falls during the last two stages are mostly caused by sandy s northward movement into lower tropopause regions associated with an eastward propagating midlatitude trough where the associated lower stratospheric warm air wraps into the storm and its surrounding areas the steady maximum surface wind occurs because of the widespread slp falls with weak gradients lacking significant inward advection of absolute

the sting at the end of the tail damaging winds associated with extratropical cyclones strong surface winds often accompany the low level jets that occur along the cold fronts of extratropical cyclones but there is evidence that the strongest surface winds occur in a distinctly different part of a certain class of cyclone the most damaging extratropical cyclones go through an evolution that involves the formation of a bent back front and cloud head separated from the main polar front cloud band by a dry slot when the cyclone attains its minimum central pressure the trailing tip of the cloud head bounding the bent back front forms a hook which goes on to encircle a seclusion of warm air the most damaging winds occur near the tip of this hook the sting at the end of the tail observations of the great storm of october 1987 in south east england are re examined in some detail to study this phenomenon the cloud head is shown to have a banded structure consistent with the existence of multiple mesoscale slantwise circulations air within these circulations leaves the hooked tip of the cloud head and enters the dry slot much faster than the rate of travel of the cloud head tip implying rapid evaporation and diabatic cooling immediately upwind of the area of damaging surface winds the circumstantial evidence from the observational study leads one to hypothesize that the mesoscale circulations and the associated evaporative heat sinks may play an active role in strengthening the damaging winds regardless of how important this role may be the evolution of the cloud pattern seen in satellite imagery is a useful tool for nowcasting the occurrence and location of the worst winds copyright 2004 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

derecho and mcs development evolution and multiscale interactions during 3 5 july 2003 abstract from 3 to 5 july 2003 during the bow echo and mesoscale convective vortex experiment bamex multiple mesoscale convective systems mcss 1 and 2 and derechos derechos an as a bw and be progressed across a preferred upper midwest corridor the derechos evolved in a favorable synoptic scale environment however the environmental details associated with each derecho such as the characteristics of the initial surface boundary the formation position relative to the upper level jet stream the presence of an upper level mesoscale disturbance and the cape shear environment varied from derecho to derecho the mcss and derechos composed three distinct convective episodes multiple mesoscale interactions between the mcss and derechos and the environment altered the character and longevity of these episodes the first convective episode consisted of derecho a which formed from merging derechos an and as northern and southern systems respectively the 200 hpa deep cold pool associated with d

the vertical structure of mesoscale convective vortices abstract simulations of two cases of developing mesoscale convective vortices mcvs are examined to determine the dynamics governing the origin and vertical structure of these features although one case evolves in strong vertical wind shear and the other evolves in modest shear the evolutions are remarkably similar in addition to the well known mesoscale convergence that spins up vorticity in the midtroposphere the generation of vorticity in the lower troposphere occurs along the convergent outflow boundary of the parent mesoscale convective system mcs lateral transport of this vorticity from the convective region back beneath the midtropospheric vorticity center is important for obtaining a deep column of cyclonic vorticity however this behavior would be only transient without a secondary phase of vorticity growth in the lower troposphere that results from a radical change in the divergence profile favoring lower tropospheric convergence following the decay of the nocturnal mcs subsequent con

intensification of hurricane sandy 2012 through extratropical warm core seclusion abstracthurricane sandy s landfall along the new jersey shoreline at 2330 utc 29 october 2012 produced a catastrophic storm surge stretching from new jersey to rhode island that contributed to damage in excess of 50 billion the sixth costliest u s tropical cyclone on record since 1900 and directly caused 72 fatalities hurricane sandy s life cycle was marked by two upper level trough interactions while it moved northward over the western north atlantic on 26 29 october during the second trough interaction on 29 october sandy turned northwestward and intensified as cold continental air encircled the warm core vortex and sandy acquired characteristics of a warm seclusion the aim of this study is to determine the dynamical processes that contributed to sandy s secondary peak in intensity during its warm seclusion phase using high resolution numerical simulations the modeling results show that intensification occurred in response to shallow low level convergence below 850 hpa that was consistent with th

some aspects of hurricane inner core dynamics and energetics abstract the energy cycle of the mature hurricane resides in the secondary circulation that passes through the storm s eyewall by equating the generation of energy in this cycle to boundary layer dissipation an upper bound on wind speed is derived this bound depends on the degree of thermodynamic disequilibrium between the tropical ocean and atmosphere on the difference between sea surface and outflow absolute temperatures and also on the ratio between the enthalpy exchange and surface drag coefficients such a bound proves to be an excellent predictor of maximum wind speeds in two different axisymmetric numerical models and does not appear to depend on the existence of the hurricane eye but further consideration of the detailed dynamics of the eye and eyewall show that the intensification of hurricanes is accelerated by feedbacks associated with a component of eye subsidence forced by radial turbulent diffusion of momentum this radial momentum diffusion is an inevitable by product of the strong fr

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

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

mesoscale cyclone activity over antarctica during 1991 2 near the antarctic peninsula a survey of mesoscale cyclogenesis near the antarctic peninsula has been carried out for 1991 based on digital satellite imagery collected at palmer station slightly higher cyclonic activity was found over the bellingshausen sea sector bss than in the weddell sea sector wss both sides were characterized by a pronounced formation maximum in summer and a minimum in winter comma clouds were the dominant vortex type and their average diameter was around 370 km trajectories show that many vortices in the bss move northeastward toward the drake passage with some of the most well developed moving north northeastward to the southern tip of south america bringing severe weather conditions to that area little systematic motion was noted over the wss the fraction of mesoscale cyclones with middle and or high cloud on the west side of the antarctic peninsula was much higher than on the east side these numerous and deep mesoscale cyclones are a consequence of the frequent outbreaks of cold air associated with synoptic scale cyclones that move cold air northward over the relatively warm bellingshausen sea with convective instability resulting this happens much less often in the wss where low level baroclinic instability and vortex stretching are the dominant formation mechanisms and air sea interaction is usually much less vigorous due to the stabilizing influence of the extended sea ice cover

distribution and characteristics of mesoscale cyclones in the antarctic ross sea eastward to the weddell sea abstract the mesoscale cyclone activity observed in the portion of antarctica that faces the south pacific ocean and weddell sea area is summarized from a study of 1991 in general area normalized results reveal much greater mesoscale cyclonic activity over the ross sea ross ice shelf and southern marie byrd land than on both sides of the antarctic peninsula more than 50 of the observed mesoscale vortices are of the comma cloud type the average diameter of mesoscale vortices is approximately 200 km near terra nova bay 270 km near byrd glacier and 280 km near siple coast near the antarctic peninsula the average diameter is about 370 km over the bellingshausen sea and 380 km on the weddell sea side the largest percentage of deep vortices occurs over the bellingshausen sea sector 38 of all cases where convective instability frequently occurs over the ross sea ross ice shelf and weddell sea sectors the majority of the mesoscale vortices are low cloud features that probably do not exceed the 700

relationship between the track and structural evolution of hurricane sandy 2012 using a regional ensemble abstractan ensemble of 72 weather research and forecasting wrf model simulations is evaluated to examine the relationship between the track of hurricane sandy 2012 and its structural evolution

heavy precipitation associated with southern appalachian cold air damming and carolina coastal frontogenesis in advance of weak landfalling tropical storm marco 1990 abstract an analysis is presented of tropical storm marco 1990 a storm that dropped copious amounts of rain over the southeast united states marco was noteworthy because of its role in the formation and evolution of two distinct episodes of cold air damming and coastal frontogenesis over georgia and the carolinas these mesoscale features led to greater than 300 mm of precipitation in 2 days over the near coastal southeast united states much of the rain occurred while marco was over 400 km away this case is further complicated by two other nearby tropical cyclones which affected marco s track and the overall rainfall distribution synoptic and mesoscale analyses of the development of the coastal front and cold air damming episodes show that the location of marco helped to orient low level winds toward the appalachians as rain developed inland a pocket of relatively cool air the cool pool formed near the mountain slopes and was partially blocked by the higher terrain low level analyses show t

tropical transition of hurricane chris 2012 over the north atlantic ocean a multiscale investigation of predictability abstracttropical cyclones that evolve from a nontropical origin and undergo tropical transition tt play a prominent role in cyclogenesis in the north atlantic ocean they pose a special challenge

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

simulations of topographically forced mesocyclones in the weddell sea and the ross sea region of antarctica abstract mesocyclones mcs are a frequently observed phenomenon in the coastal regions of antarctica numerical simulations of topographically forced mcs in the weddell sea and the ross sea region are presented using a three dimensional mesoscale weather forecast model simulations are performed for an idealized case without synoptic forcing three realistic cases of smaller mcs with diameters of 200 300 km and two larger systems with diameters of up to 1000 km the simulation results show that the orography of the coastal regions can play an important role in mesocyclogenesis one key factor is the katabatic wind system which is able to initiate low level mcs in areas of suitable orography structure the second key factor is the support of the synoptic environment leading to vorticity production by vertical stretching of the synoptically supported katabatic winds besides this stretching mechanism katabatic winds can have a second impact on the generation of mcs by transporting cold air into the coa

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

sedimentary evidence of hurricane strikes in western long island new york 1 evidence of historical landfalling hurricanes and prehistoric storms has been recovered from backbarrier environments in the new york city area overwash deposits correlate with landfalls of the most intense documented hurricanes in the area including the hurricanes of 1893 1821 1788 and 1693 a d there is little evidence of intense hurricane landfalls in the region for several hundred years prior to the late 17th century a d the apparent increase in intense hurricane landfalls around 300 years ago occurs during the latter half of the little ice age a time of lower tropical sea surface temperatures multiple washovers laid down between 2200 and 900 cal yr b p suggest an interval of frequent intense hurricane landfalls in the region our results provide preliminary evidence that fluctuations in intense hurricane landfall in the northeastern united states were roughly synchronous with hurricane landfall fluctuations observed for the caribbean and gulf coast suggesting north atlantic wide changes in hurricane activity

season dependent distributions and profiles of seven super typhoons 2014 in the northwestern pacific ocean from satellite cloud images this paper extends a former study on super typhoon s formation in winter to its seasonal dependence on distribution and profiles it aims to enhance understanding and predictability of the super typhoons to reduce their impacts on human beings and properties in the regions where they pass by or influence a framework by integrating remote sensing imagery and image processing techniques is implemented to analyze the seven super typhoons of concern in both summer and winter seasons in the northwestern pacific ocean conventionally typhoons occur in summer in the northern hemisphere while owing to increased climate variability in recent decades the occurrence of typhoons in winter is increased and a large number of super typhoons are observed surprisingly three summer super typhoons neoguri july rammasun july and halong august and four winter super typhoons phanfone october vongfong october nuri november and hagupit december happened in 2014 their physical responses of tracks distributions profiles and intensifications are examined the 3 d profiles of typhoons derived from surface cloud images are used to investigate the in depth distributions of the cloud tops results show that southwest airflows and cold fronts and southwest airflows enhance the summer and winter typhoons respectively to become super typhoons eventually within the zones of lat 15 20 and 10 20 n and long 110 135 and 133 138 e in summer and winter respectively the lat 20 n is likely the boundary for the super typhoons occurrence and a turning point of the typhoons two major tracks with the first track moving in the westerly direction and the second track inclining in the northerly direction three crucial findings are obtained first of all it is observed that track 1 inclined toward the latitude with an inclination angle theta 1 and track 2 inclined toward track 1 with an inclination angle theta 2 using both inclination angles the patterns of the super typhoons were approximately described second the inclination angle theta 1 of the winter super typhoons is represented with smaller values and a narrower range 10 26 than those 13 40 of the summer super typhoons after the turning point both inclination angles theta 2 of winter and summer super typhoons varied with a wider range of 25 65 and 35 to 50 respectively the winter super typhoons exhibit higher intensities than the summer super typhoons third it is further confirmed that a mechanism through which cold fronts and southwest airflows enhance the typhoons causes them to become super typhoons the cold front is a new aspect of the leading edge of cooler air masses in typhoon environments exerting a greater temperature gradient between the front and typhoon circulation that ultimately affects the track of typhoons and increases the intensity of typhoons

an adiabatic simulation of the erica iop 4 storm an example of quasi ideal frontal cyclone development abstract numerical experiments with dry inviscid models started from small normal mode perturbations in baroclinic jet flows provide examples of ideal baroclinic cyclone development this paper examines with use of the pennsylvania state university national center for atmospheric research mesoscale model cyclone development under conditions that resemble the ideal experiments in lacking initial surface fronts and in neglecting latent heating and surface fluxes but that differ from most ideal experiments in including surface friction and an initial large upper level disturbance the initial state of the simulation is that of the intense explosive experiment on rapidly intensifying cyclones over the atlantic intensive observation period 4 storm issues highlighted are the timing and rate of deepening the rapidity and intensity of frontal formation the frontal structure the airflow relative to the cyclone and fronts and the nature of the occlusion and warm core seclusion processes principal findings

bedload stresses and sediment transport theory a correction a previous proposal leeder 1977 to test the magnitude of the solid transmitted stresses due to bedload transport failed to confirm bagnold s theory because the applied fluid stress contribution was not corrected for sidewall drag once this correction is made there is a reasonable correspondence of theory and experiment

the extratropical transition of tropical cyclones part i cyclone evolution and direct impacts abstractextratropical transition et is the process by which a tropical cyclone upon encountering a baroclinic environment and reduced sea surface temperature at higher latitudes transforms into an extratropical cyclone this process is influenced by and influences phenomena from the tropics to the midlatitudes and from the meso to the planetary scales to extents that vary between individual events motivated in part by recent high impact and or extensively observed events such as north atlantic hurricane sandy in 2012 and western north pacific typhoon sinlaku in 2008 this review details advances in understanding and predicting et since the publication of an earlier review in 2003 methods for diagnosing et in reanalysis observational and model forecast datasets are discussed new climatologies for the eastern north pacific and southwest indian oceans are presented alongside updates to western north pacific and north atlantic ocean climatologies advances in understanding and in some cases mode

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

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

the 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

the march 1993 superstorm cyclogenesis incipient phase synoptic and convective scale flow interaction and model performance abstract the incipient stages of the 12 14 march 1993 superstorm ss93 cyclogenesis over the gulf of mexico are examined noteworthy aspects of ss93 include 1 it is the deepest extratropical cyclone ever observed over the gulf of mexico during the 1957 96 period and 2 existing operational prediction models performed poorly in simulating the incipient cyclogenesis over the northwestern gulf of mexico a dynamic tropopause dt analysis shows that ss93 is triggered by a potent potential vorticity pv anomaly as it crosses extreme northern mexico and approaches the gulf of mexico the low level environment over the western gulf of mexico is warmed moistened and destabilized by a persistent southerly flow ahead of the approaching pv anomaly ascent and a lowering of the dt associated with a lowering of the potential temperature ahead of the pv anomaly contributes to further destabilization that is realized in the form of a massive convective outbreak an examination of the national centers for envi

application of the eliassen balanced model to real data tropical cyclones abstract the eliassen balanced vortex model assumes gradient balance of the azimuthal mean flow this assumption was tested by calculating mean and eddy terms in the radial momentum equation in the synoptic scale environments of two tropical cyclones the azimuthally averaged gradient balance was accurate to within 15 25 in the free atmosphere outside the core even in the asymmetric outflow layer balanced secondary circulations correlated well with circulations that included gradient thermal wind imbalance terms although the balanced model lacks galilean invariance balanced circulations were largely insensitive to use of a fixed coordinate or a coordinate moving with the storm this occurred because changes in eddy heat and angular momentum fluxes largely offset one another the two dimensional balanced solutions provide a reasonably robust measure of circulations induced by azimuthal eddy processes in the tropical cyclone environment nevertheless individual forcing functions such as the commonly

the present day simulation and twenty first century projection of the climatology of extratropical transition in the north atlantic abstractthis study explores the simulations and twenty first century projections of extratropical transition et of tropical cyclones tcs in the north atlantic with a newly developed global climate model the forecast oriented low ocean resolution flor version of the geophysical fluid dynamics laboratory gfdl coupled model version 2 5 cm2 5 flor exhibits good skill in simulating present day et properties e g cyclone phase space parameters a version of flor in which sea surface temperature sst biases are artificially corrected through flux adjustment flor fa shows much improved simulation of et activity e g annual et number this result is largely attributable to better simulation of basinwide tc activity which is strongly dependent on larger scale climate simulation flor fa is also used to explore changes of et activity in the twenty first century under the representative concentration pathway rcp 4 5 scenario a contrasting pattern is found in which regional tc density increas

influence of coupling on atmosphere sea ice and ocean regional models in the ross sea sector antarctica air sea ice ocean interactions in the ross sea sector form dense waters that feed the global thermohaline circulation in this paper we develop the new limited area ocean sea ice atmosphere coupled model tango to simulate the ross sea sector tango is built up by coupling the atmospheric limited area model mar to a regional configuration of the ocean sea ice model nemo a method is then developed to identify the mechanisms by which local coupling affects the simulations tango is shown to simulate realistic sea ice properties and atmospheric surface temperatures these skills are mostly related to the skills of the stand alone atmospheric and oceanic models used to build tango nonetheless air temperatures over ocean and winter sea ice thickness are found to be slightly improved in coupled simulations as compared to standard stand alone ones local atmosphere ocean feedbacks over the open ocean are found to significantly influence ocean temperature and salinity in a stand alone ocean configuration the dry and cold air produces an ocean cooling through sensible and latent heat loss in a coupled configuration the atmosphere is in turn moistened and warmed by the ocean sensible and latent heat loss is therefore reduced as compared to the stand alone simulations the atmosphere is found to be less sensitive to local feedbacks than the ocean effects of local feedbacks are increased in the coastal area because of the presence of sea ice it is suggested that slow heat conduction within sea ice could amplify the feedbacks these local feedbacks result in less sea ice production in polynyas in coupled mode with a subsequent reduction in deep water formation

influence of the orographic roughness of glacier valleys across the transantarctic mountains in an atmospheric regional model glacier valleys across the transantarctic mountains are not properly taken into account in climate models because of their coarse resolution nonetheless glacier valleys control katabatic winds in this region and the latter are thought to affect the climate of the ross sea sector frsater formation to snow mass balance the purpose of this paper is to investigate the role of the production of turbulent kinetic energy by the subgrid scale orography in the transantarctic mountains using a 20 km atmospheric regional model a classical orographic roughness length parametrization is modified to produce either smooth or rough valleys a one year simulation shows that katabatic winds in the transantarctic mountains are strongly improved using smooth valleys rather than rough valleys pressure and temperature fields are affected by the representation of the orographic roughness specifically in the transantarctic mountains and over the ross ice shelf a smooth representation of escarpment regions shows better agreement with automatic weather station observations than a rough representation this work stresses the need to improve the representation of subgrid scale orography to simulate realistic katabatic flows this paper also provides a way of improving surface winds in an atmospheric model without increasing its resolution

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

an analysis of a relatively rare case of continental blocking planetary and synoptic scale analyses of a relatively rare continental blocking event that occurred over north america during the spring of 1980 are undertaken to determine whether or not this event was different from its counterparts which occur over oceanic regions the planetary scale analysis demonstrates that during the spring season a ridge was located further inland over the north american continent and amplified with respect to climatology the position of this ridge may have been linked to a broad region of colder than normal sea surface temperatures found over the north central pacific during the spring season and much of the previous winter simple sutcliffe type and thermodynamic analyses of the accompanying lower tropospheric warm anomaly associated with the ridging show that lower tropospheric temperature advection and subsidence associated with anticyclonic vorticity advection by the time mean thermal wind produced much of the anomalous warmth a simple synoptic scale analysis was performed using both the zwack okossi zo equation and potential vorticity pv thinking approaches these complementary analyses demonstrated that synoptic scale cyclones were instrumental in the formation and maintenance and or intensification of this blocking event the pv analysis demonstrated that low pv air was swept polewards and then was advected over the blocking region sustaining the broad region of low potential vorticity associated with the block over north america the zo analysis showed that the advection of anticyclonic vorticity was the most important mechanism forcing geopotential height rises at 500 hpa over the block centre the region of low pv and zo height rises could be associated with the anticyclonic shear side of an upstream jet maximum typically found in association with developing and or intensifying blocking events thus negative pv advection correlated significantly with calculated zo height rises finally it is suggested that a favourable phase relationship between the upstream cyclones and the large scale ridge is necessary for block development or intensification

reexamining the cold conveyor belt abstract despite the popularity of the conveyor belt model for portraying the airflow through midlatitude cyclones questions arise as to the path of the cold conveyor belt the lower tropospheric airflow poleward of and underneath the warm front some studies beginning with carlson s analysis of the eastern u s cyclone of 5 december 1977 depict the cold conveyor belt moving westward reaching the northwest quadrant of the storm turning abruptly anticyclonically rising to jet level and departing the cyclone downstream hereafter the anticyclonic path other studies depict the cold conveyor belt reaching the northwest quadrant turning cyclonically around the low center and remaining in the lower troposphere the cyclonic path to clarify the path of the cold conveyor belt the present study reexamines carlson s analysis of the cold conveyor belt using an observational and mesoscale numerical modeling study of the 5 december 1977 cyclone this reexamination raises several previously unappreciated

idealized simulations of the antarctic katabatic wind system with a three dimensional mesoscale model the katabatic wind system represents a key factor for the near surface wind field of the antarctic region idealized simulations with a three dimensional mesoscale model are performed to investigate the development of the antarctic katabatic wind system and its sensitivity to physical boundary conditions in particular channeling effects and the thermodynamic forcing close to the coastline the simulated cases represent wintertime cases with complete sea ice coverage and no sea ice as well as a realistic summertime situation for the wintertime situations a large impact of the presence of open water on the three dimensional structure of the wind field close to the coast can be shown whereas the effects on the katabatic wind over the continent are relatively small near surface wind speeds over the continental slope for the summertime case have strengths comparable to those of the wintertime cases but reveal a distinct daily cycle due to the daily course of the radiation fluxes the formation of shallow mesoscale circulations is simulated after 2 4 days of simulation in ice free coastal areas in these regions low level convergence diabatic heating and the cold air advection associated with the katabatic flow leads to low level baroclinicity and cyclonic vorticity production

simulation of the mesocyclonic activity in the ross sea antarctica the mesocyclonic activity in the southwestern ross sea is examined with emphasis on its forcing by katabatic winds the three dimensional version of the meso gamma scale primitive equation model modele atmospherique regional is used in which a representation of cloud microphysical processes has been introduced idealized boundary conditions are prescribed in particular the ocean is assumed to be completely ice free or partially ice covered the former case corresponds to a fall situation that coincides with the climatological maximum of estimated precipitation at mcmurdo station on ross island due to the propagation of katabatic winds over the ocean boundary layer fronts form clouds are generated in the fronts a surface pressure trough also forms and extends northeastward from terra nova bay mesocyclones are simulated in the trough when the ocean is ice free strong sensible heat fluxes toward the atmosphere amplify the strength of the trough up to typically observed values tn this case snow precipitation is associated with the boundary layer fronts and occurs in particular over mcmurdo sound it is also found that latent heat release due to precipitation formation in the fronts does not significantly affect the deepening of the trough

formation of winter supertyphoons haiyan 2013 and hagupit 2014 through interactions with cold fronts as observed by multifunctional transport satellite this paper incorporates remote sensing imagery and image processing techniques to analyze typhoons evolution into supertyphoons through interactions with cold fronts in the western pacific ocean the purpose is to enhance understanding and predictability of the tracks and profiles of supertyphoons evolutions of typhoons haiyan 2013 and hagupit 2014 into supertyphoons were studied the 3 d profiles of weather systems were reconstructed using multifunctional transport satellite ir cloud images when interactions between typhoon and cold front happened enhancements of typhoons were observed causing typhoons haiyan and hagupit to strengthen power and evolve into supertyphoons the origins of typhoons haiyan and hagupit are closely located at 152 50e 05 12n and 151 30e 04 19n respectively both typhoons went through the philippine sea in the zone of 112 52e 146 11e the lowest values of central pressures of typhoons haiyan and hagupit occurred along their paths at the positions 128 41e 10 16n and 131 06e 11 00n respectively their distances from cold front and average speed of their movement were dominating parameters for the formation of winter supertyphoons the supertyphoon haiyan showed higher intensity than the supertyphoon hagupit each of the two typhoons roughly consisted of two paths with the first path moving westerly and the second path northerly the two typhoons evolved into supertyphoons at the turning points of the two paths the first paths were about 2330 and 2050 km for typhoons haiyan and hagupit respectively

the life cycle of an extratropical marine cyclone part ii mesoscale structure and diagnostics abstract this is the second of two articles describing the evolving structure and selected physical processes within an intense extratropical marine cyclone observed during the experiment on rapidly intensifying cyclones over the atlantic erica field program part i describes the 24 h frontal cyclone evolution through 6 h horizontal analyses of observations taken by specially deployed observing systems from air land and sea part ii presents frontal scale and precipitation structures and physical processes from analyses based primarily on research aircraft observations taken during three phases of the cyclone s life cycle horizontal analyses at 350 m above ground level describe the cyclone s mesoscale frontal baroclinic structure and associated flow patterns the vertical structure and evolution of the cyclone s cold front warm front and bent back front are illustrated in cross sectional analyses of potential temperature wind velocity potential vorticity pv front relative transverse flow vecto

atmospheric sensitivity to sst near the kuroshio extension during the extratropical transition of typhoon tokage abstract it is hypothesized that the tropical to extratropical transition of a cyclone in the western north pacific can be sensitive to the underlying sea surface temperature sst distribution this hypothesis was tested through a case study of typhoon tokage using a series of high resolution simulations by the weather research forecast wrf numerical weather prediction model simulations were carried out for a control sst distribution and for sst distributions with imposed warm and cold perturbations of 1 5 c maximum amplitude in the vicinity of the kuroshio extension the simulations with the warm sst perturbation yielded a cyclone slightly weaker than in the control sst case about 2 days after transition in contrast the cold sst perturbation case yielded a cyclone with a central pressure 10 hpa lower than in the control case at the same point in the storm s life cycle apparently due to its more northward track and hence closer proximity to an approaching upper level trough and perhaps in associati

a cyclone phase space derived from thermal wind and thermal asymmetry abstract an objectively defined three dimensional cyclone phase space is proposed and explored cyclone phase is described using the parameters of storm motion relative thickness asymmetry symmetric nonfrontal versus asymmetric frontal and vertical derivative of horizontal height gradient cold versus warm core structure via the thermal wind relationship a cyclone s life cycle can be analyzed within this phase space providing substantial insight into the cyclone structural evolution an objective classification of cyclone phase is possible unifying the basic structural description of tropical extratropical and hybrid cyclones into a continuum stereotypical symmetric warm core tropical cyclone and asymmetric cold core extratropical cyclone life cycles are illustrated using 1 navy operational global atmospheric prediction system nogaps operational analyses and 2 5 ncep ncar reanalyses the transitions between cyclone phases are clearly illustrated within the phase space including extratro

mesoscale cyclogenesis dynamics over the southwestern ross sea antarctica previous work has shown that frequent mesoscale cyclogenesis adjacent to franklin island is linked to the strong and persistent katabatic winds from east antarctica which funnel into terra nova bay and then blow out over the southwestern ross sea four mesoscale cyclones that formed near terra nova bay between february 16 and 20 1988 are examined to more clearly define the governing mechanisms these events are investigated using all available observations including automatic weather station data high resolution satellite images satellite soundings and hemispheric synoptic analyses the first two cyclones formed on low level baroclinic zones established by the synoptic scale advection of warm moist air toward the cold continental air blowing gently from east antarctica in the second case baroclinic instability of this small scale cold front was apparently triggered by the enhanced upward vertical motion associated with the approach of a midtropospheric trough the third mesocyclone formed shortly after on a baroclinic zone over the polar plateau the second vortex completely disrupted the usual katabatic drainage over the plateau and forced warm moist air over the coastal slopes all three cyclones moved to the north in the prevailing cyclonic flow but the plateau vortex lasted for only 6 hours the fourth mesoscale low formed in conjunction with an abrupt and intense surge of katabatic air from terra nova bay which resharpened the coastal baroclinic zone at the same time a transiting midtropospheric trough probably associated with lower tropospheric upward vertical motion apparently accelerated the katabatic winds and triggered the vortex formation a similar katabatic wind forced mesocyclone formed near byrd glacier the two vortices moved to the east southeast and northeast respectively apparently being steered by the generating katabatic airstreams and merged just to the north of the ross ice shelf the combined vortex reintensified as another trough passed overhead and moved eastward to west antarctica where it dissipated two days later

synoptic controls on precipitation pathways and snow delivery to high accumulation ice core sites in the ross sea region antarctica 1 dominant storm tracks to two ice core sites on the western margin of the ross sea antarctica skinner saddle sks and evans piedmont glacier are investigated to establish key synoptic controls on snow accumulation this is critical in terms of understanding the seasonality source regions and transport pathways of precipitation delivered to these sites in situ snow depth and meteorological observations are used to identify major accumulation events in 2007 2008 which differ considerably between sites in terms of their magnitude and seasonal distribution while snowfall at evans piedmont glacier occurs almost exclusively during summer and spring skinner saddle receives precipitation year round with a lull during the months of april and may cluster analysis of daily back trajectories reveals that the highest accumulation days at both sites result from fast moving air masses associated with synoptic scale low pressure systems there is evidence that short duration pulses of snowfall at sks also originate from mesocyclone development over the ross ice shelf and local moisture sources changes in the frequency and seasonal distribution of these mechanisms of precipitation delivery will have a marked impact on annual accumulation over time and will therefore need careful consideration during the interpretation of stable isotope and geochemical records from these ice cores

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 mesoscale vortex over halley station antarctica abstract a detailed analysis of the evolution and structure of a mesoscale vortex and associated cloud comma that developed at the eastern edge of the weddell sea antarctica during the early part of january 1986 is presented the system remained quasi stationary for over three days close to the british research station halley 75 36 s 26 42 w and gave severe weather with gale force winds and prolonged snow the formation and development of the system were investigated using conventional surface and upper air meteorological observations taken at halley analyses from the u k meteorological office 15 level model and satellite imagery and sounder data from the tiros n noaaseries of polar orbiting satellites the thermal structure of the vortex was examined using atmospheric profiles derived from radiance measurements from the tiros operational vertical sounder details of the wind field were examined using cloud motion vectors derived from a sequence of advanced very high resolution radiometer images

mesoscale cyclogenesis over the southwestern ross sea linked to strong katabatic winds abstract two years of automatic weather station aws observations and satellite images have been used to study mesoscale cyclogenesis along the transantarctic mountains twice daily regional sea level pressure analyses revealed the frequent formation of mesoscale cyclones adjacent to two regions where the discharge of cold boundary layer air from east antarctica is concentrated near terra nova bay franklin island and byrd glacier between one and two new vortices on average formed each week in the former location with weak frequency maxima in december march and august september there was a large difference between the cyclogenetic activity in the two years the aws array expanded in 1985 and resolved another cyclogenetic area near byrd glacier this feature was half as active as the franklin island area and exhibited many of the same characteristics about half of the byrd glacier cyclones developed simultaneously with vortices near franklin island these developments are the result of a dry baroclinic

potential vorticity analysis of tropical cyclone intensification the interaction of marginal tropical storm danny 1985 with an upper tropospheric positive potential vorticity anomaly was examined the intensification mechanism proposed earlier for mature hurricane elena appears to be valid for danny as well despite significant differences in the synoptic scale environment and in the stage of the tropical cyclone prior to the interaction both storms experienced rapid pressure falls as a relatively smallscale positive upper potential vorticity anomaly began to superpose with the low level tropical cyclone center the interaction is described in terms of a complex interplay between vertical wind shear diabatic heating and mutual advection among vortices at and below the level of the outflow anticyclone despite this complexity the superposition principle appears to be conceptually useful to describe the intensification of tropical cyclones during such interactions