subrainband structure and dynamic characteristics in the principal rainband of typhoon hagupit 2008 abstractthe principal rainband in tropical cyclones is currently depicted as a solitary and continuous precipitation region however the airborne radar observations of the principal rainband in typhoon hagupit 2008 reveal multiple subrainband structures these subbands possess many characteristics of the squall lines with trailing stratiform in the midlatitudes and are different from those documented in previous principal rainband studies the updraft and reflectivity cores are upright and elevated the updraft is fed by a low level radial outflow from the inner side the tangential wind speed shows a clear midlevel jet on the inner side of the reflectivity core except for the structural similarities the dynamics of the subbands is also similar to the squall lines the local environment near the subbands shows little convective inhibition modest instability and vertical wind shear the temperature retrieval shows a cold pool structure in the stratiform precipitation region the estimated vertical w

monsoon gyres of the northwest pacific influences of enso the mjo and the pacific japan pattern abstractan objective definition of monsoon gyres in the northwest pacific was developed in order to construct a gyre climatology over a 31 yr period 53 gyres were identified with a median formation location at 16 5 n 135 e more than 80 formed during july september more than half of gyres developed during el nino periods at a median location 1200 km farther to the east southeast than during la nina cyclonic winds at 850 hpa extended across a diameter of more than 4000 km with maximum tangential wind near the 1000 km radius a precipitation maximum extended westward for several thousand kilometers south of the gyre typhoons were most common north and east of the gyre centers more than 70 of gyres developed during large amplitude mjo events with a strong preference for real time multivariate mjo rmm phases 5 7 in boreal summer these phases contain circulation and convective anomalies that coincide most closely with those of the climatological monsoon trough gyres are most likely to form when

distribution of helicity cape and shear in tropical cyclones abstract the previous study of helicity cape and shear in hurricane bonnie 1998 was extended to all eight tropical cyclones sampled by nasa during the convection and moisture experiments camex storms were categorized as having large or small ambient vertical wind shear with 10 m s 1 as the dividing line in strongly sheared storms the downshear mean helicity exceeded the upshear mean by a factor of 4 as in the previous study the helicity differences resulted directly from the tropical cyclone response to ambient shear with enhanced in up out flow and veering of the wind with height present downshear cape in strongly sheared storms was 60 larger downshear mean inflow near the surface and the depth of the inflow layer each were 4 times larger downshear at more than 30 of observation points outside the 100 km radius in the downshear right quadrant midlatitude empirical parameters indicated a strong likelihood of supercells no such points existed upshear in highly sheared storms much small

cloud to ground lightning in hurricane andrew the spatial and temporal distribution of cloud to ground lightning was examined in hurricane andrew of 1992 lightning locations available from the national lightning detection network were superimposed on infrared satellite images to relate lightning activity to hurricane cloud structure a distinct radial variation occurred in time averaged flash density with a weak maximum in the eye wall a region of near zero flash density 40 to 100 km from the center and a steady increase to a large maximum in the outer rainbands 190 km from the center this radial distribution is consistent with the convective structure of mature hurricanes eye wall lightning tended to be episodic occurring almost exclusively prior to and during periods of intensification of the storm during these periods negative flashes occurred several kilometers inward from the highest eye wall cloud tops in the region of the largest radar reflectivity positive eye wall flashes while small in number tended to occur directly under the highest cloud tops the results are suggestive of a normal dipole in sign but outwardly tilted along the sloping eye wall in general hurricane flash characteristics resembled those for a background data set of nonhurricane flashes from the same area the exception occurred for negative flashes in the eye wall which had a much smaller mean peak current than the background 25 3 ka versus 44 9 ka

an observational study of a coastal barrier jet induced by a landfalling typhoon abstractin this study the structure and evolution of a coastal barrier jet cbj along the east coast of taiwan is documented using operational doppler radars the formation of the cbj was control

concentric eyewall formation in typhoon sinlaku 2008 part iii horizontal momentum budget analyses abstract this is a follow up work to two prior studies examining secondary eyewall formation sef in typhoon sinlaku 2008 this study shows that in the sef region the majority of the elevated

the kinematic structure of hurricane gloria 1985 determined from nested analyses of dropwindsonde and doppler radar data abstract a set of three dimensional filtered multiply nested objective analyses has been completed for the wind field of hurricane gloria for 0000 utc 25 september 1985 at this time gloria was one of the most intense hurricanes ever observed in the atlantic basin with a minimum sea level pressure of 919 mb the nested analyses based on observations from airborne doppler radar and omega dropwindsondes simultaneously describe eyewall and synoptic scale features and are the most comprehensive analyses of a single hurricane constructed to date the analyses have been used to document the multiscale kinematic structure of gloria and to investigate the relationship between the kinematic fields and the motion of the vortex the analyses indicate that the vortex was unusually barotropic the radius of maximum wind rmw was nearly vertical below 500 mb with a slight inward slope with height between 750 and 550 mb the strongest azimuthal mean tangential winds were found well above the boundary layer near

revisiting azimuthally asymmetric moist instability in the outer core of sheared tropical cyclones abstractthis study revisits the characteristics and physical processes of the azimuthally asymmetric distribution of moist instability in the outer core of vertically sheared tropical cyclones tcs

the multiple vortex nature of tropical cyclogenesis abstract this study explores the extent to which potential vorticity pv generation and superposition were relevant on a variety of scales during the genesis of tropical storm allison allison formed close to shore and the combination of continuous doppler radar satellite aircraft and surface observations allows for the examination of tropical cyclogenesis in great detail preceding allison s genesis pv superposition on the large scale created an environment where decreased vertical shear and increased instability surface fluxes and low level cyclonic vorticity coexisted this presented a favorable environment for meso scale pv production by widespread convection and led to the formation of surface based meso scale vortices termed convective burst vortices cbvs the cbvs seemed to form in association with intense bursts of convection and rotated around each other within the meso circulation field one cbv eventually superposed with a mesoscale convective vortex mcv resulting in a mor

downdrafts and the evolution of boundary layer thermodynamics in hurricane earl 2010 before and during rapid intensification abstractusing a combination of noaa p 3 aircraft tail doppler radar noaa and nasa dropsondes and buoy and drifter based sea surface temperature data different types of downdrafts and their infl

the role of observed environmental conditions and precipitation evolution in the rapid intensification of hurricane earl 2010 abstractan investigation into the possible causes of the rapid intensification ri of hurricane earl 2010 is carried out using a combination of global analyses aircraft doppler radar data and observations from passive microwave satellites and a long range lightning network results point to an important series of events leading to and just after the onset of ri all of which occur despite moderate 7 12 m s 1 vertical wind shear present beginning with an initially vertically misaligned vortex observations indicate that asymmetric deep convection initially left of shear but not distinctly up or downshear rotates into more decisively upshear regions following this convective rotation the vortex becomes aligned and precipitation symmetry increases the potential contributions to intensification from each of these structural changes are discussed the radial distribution of intense convection relative to the radius of maximum wind rmw determined from doppler wind retrievals is estimated from

distributions of shallow to very deep precipitation convection in rapidly intensifying tropical cyclones abstractshear relative distributions of four types of precipitation convection in tropical cyclones tcs are statistically analyzed using 14 years of tropical rainfall measuring mission trmm precipitation radar pr data the dataset of 1139 trmm pr overpasses of tropical storms through category 2 hurricanes over global tc prone basins is divided by future 24 h intensity change it is found that increased and widespread shallow precipitation defined as where the 20 dbz radar echo height 6 km around the storm center is a first sign of rapid intensification ri and could be used as a predictor of the onset of ri the contribution to total volumetric rain and latent heating from shallow and moderate precipitation 20 dbz echo height between 6 and 10 km in the inner core is greater in ri storms than in non ri storms while the opposite is true for moderately deep 20 dbz echo height between 10 and 14 km and very deep precipitation 20 dbz echo height 14 km the authors argue that ri is more likely

effects of asymmetric sst distribution on straight moving typhoon ewiniar 2006 and recurving typhoon maemi 2003 abstractthe effects of asymmetric sea surface temperature sst distribution on the tropical cyclone tc motion around east asia have been examined using the weather research and forecasting model for the straight moving typhoon ewiniar 2006 and recurving typhoon maemi 2003 the sst tc motion relationships associated with the two different tcs and the physical mechanism of recurvature are investigated in the context of the potential vorticity tendency framework a zonally asymmetric sst distribution alters the tc translating direction and speed which is ascribable to the interaction between a tc and the environmental current associated with asymmetric sst forcing a north south sst gradient has an insignificant role in the tc motion it is noted that the straight moving i e northward moving tc deflects toward the region of warmer sst when sst is zonally asymmetric a contribution of the horizontal advection including asymmetric flow induced by asymmetric forcing is dominant for the deflection t

an idealized numerical study of shear relative low level mean flow on tropical cyclone intensity and size abstractgiven comparable background vertical wind shear vws magnitudes the initially imposed shear relative low level mean flow lmf is hypothesized to modify the structure and convective featu

an investigation of spiral gravity waves radiating from tropical cyclones using a linear nonhydrostatic model abstracta recent study showed observational and numerical evidence for small scale gravity waves that radiate outward from tropical cyclones these waves are wrapped into tight spirals by the radia

life of a six hour hurricane hurricane claudette developed from a weak vortex in 6 h as deep convection shifted from downshear into the vortex center despite ambient vertical wind shear exceeding 10 m s 1 six hours later it weakened to a tropical storm and 12 h after the hurricane stage a circulation center could not be found at 850 hpa by aircraft reconnaissance at hurricane strength the vortex contained classic structure seen in intensifying hurricanes with the exception of 7 12 c dewpoint depressions in the lower troposphere upshear of the center these extended from the 100 km radius to immediately adjacent to the eyewall where equivalent potential temperature gradients reached 6 k km 1 the dry air was not present prior to intensification suggesting that it was associated with vertical shear induced subsidence upshear of the developing storm it is argued that weakening of the vortex was driven by cooling associated with the mixing of dry air into the core and subsequent evaporation and cold downdrafts evidence suggests that this mixing might have been enhanced by eyewall instabilities after the period of rapid deepening the existence of a fragile small but genuinely hurricane strength vortex at the surface for 6 h presents difficult problems for forecasters such a temporary hurricane in strongly sheared flow might require a different warning protocol than longer lasting hurricane vortices in weaker shear

effects of vertical wind shear on the intensity and structure of numerically simulated hurricanes a series of numerical simulations of tropical cyclones in idealized large scale environments is performed to examine the effects of vertical wind shear on the structure and intensity of hurricanes the simulations are performed using the nonhydrostatic pennsylvania state university national center for atmospheric research fifth generation mesoscale model using a 5 km fine mesh and fully explicit representation of moist processes when large scale vertical shears are applied to mature tropical cyclones the storms quickly develop wavenumber one asymmetries with upward motion and rainfall concentrated on the left side of the shear vector looking downshear in agreement with earlier studies the asymmetries develop due to the storm s response to imbalances caused by the shear the storms in shear weaken with time and eventually reach an approximate steady state intensity that is well below their theoretical maximum potential intensity as expected the magnitude of the weakening increases with increasing shear all of the storms experience time lags between the imposition of the large scale shear and the resulting rise in the minimum central pressure while the lag is at most a few hours when the storm is placed in very strong 15 m s21 shear storms in weaker shears experience much longer lag times with th e5ms 21 shear case showing no signs of weakening until more than 36 h after the shear is applied these lags suggest that the storm intensity is to some degree predictable from observations of largescale shear changes in all cases both the development of the asymmetries in core structure and the subsequent weakening of the storm occur before any resolvable tilt of the storm s vertical axis occurs it is hypothesized that the weakening of the storm occurs via the following sequence of events first the shear causes the structure of the eyewall region to become highly asymmetric throughout the depth of the storm second the asymmetries in the upper troposphere where the storm circulation is weaker become sufficiently strong that air with high values of potential vorticity and equivalent potential temperature are mixed outward rather than into the eye this allows the shear to ventilate the eye resulting in a loss of the warm core at upper levels which causes the central pressure to rise weakening the entire storm the maximum potential vorticity becomes concentrated in saturated portions of the eyewall cloud aloft rather than in the eye third the asymmetric features at upper levels are advected by the shear causing the upper portions of the vortex to tilt approximately downshear the storm weakens from the top down reaching an approximate steady state intensity when the ventilated layer can descend no farther due to the increasing strength and stability of the vortex at lower levels

simulation of the downshear reformation of a tropical cyclone abstractthe downshear reformation of tropical storm gabrielle 2001 was simulated at 1 km horizontal resolution using the weather research and forecasting wrf model the environmental shear tilted the initial parent vortex downshear left and forced azimuthal wavenumber 1 kinematic thermodynamic and convective asymmetries the combination of surface enthalpy fluxes and a lack of penetrative downdrafts right of shear allowed boundary layer moist entropy to increase to a maximum downshear right this contributed to convective instability that fueled the downshear convection within this convection an intense mesovortex rapidly developed with maximum boundary layer relative vorticity reaching 2 2 10 2 s 1 extreme vortex stretching played a key role in the boundary layer spinup of the mesovortex cyclonic vorticity remained maximized in the boundary layer and intensified upward with the growth of the convective plume the circulation associated with the mesovortex and adjacent localized cyclonic vorti

assessing the influence of upper tropospheric troughs on tropical cyclone intensification rates after genesis abstractthe role of upper tropospheric troughs on the intensification rate of newly formed tropical cyclones tcs is analyzed this study focuses on tcs forming in the presence of upper tropospheric troughs in the north atlantic basin between 1980 and 2014 tcs were binned into three groups based upon the 24 h intensification rate starting at the time of genesis rapid tc genesis rtcg slow tc genesis stcg and neutral tc genesis ntcg composite analysis shows rtcg events are characterized by amplified upper tropospheric flow with the largest upshear displacement between the tc and trough of the three groups rtcg events are associated with greater quasigeostrophic qg ascent in upshear quadrants of the tc forced by differential vorticity advection by the thermal wind especially around the time of genesis this pattern of qg ascent closely matches the rtcg composite of infrared brightness temperatures conversely ntcg events are associated with an upper tropospheric trough that is closest to the

intensity and inner core structure of typhoon haiyan 2013 near landfall doppler radar analysis abstractthe intensity and inner core structure of an extremely intense tropical cyclone typhoon haiyan 2013 were examined using real time ground based doppler radar products from the guiuan radar over the period of about 2 5 h immediately before the storm approached guiuan in eastern samar philippines haiyan s wind fields from 2 to 6 km altitude were retrieved by the ground based velocity track display gbvtd technique from the doppler velocity data the gbvtd retrieved maximum wind speed reached 101 m s 1 at 4 km altitude on the right side of the track the relatively fast forward speed of haiyan about 11 m s 1 increased maximum wind speed on the right hand side of the storm azimuthal mean tangential wind increased with height from 2 to 5 km and a local maximum of 86 m s 1 occurred at 5 km altitude the central pressure was estimated as 906 hpa with an uncertainty of 4 hpa by using the gbvtd retrieved tangential wind and by assuming gradient wind balance the radius of maximum radar reflecti

the roles of asymmetric inflow forcing induced by outer rainbands in tropical cyclone secondary eyewall formation abstractthis study analyzes the secondary eyewall formation sef process in an idealized cloud resolving simulation of a tropical cyclone in particular the unbalanced boundary layer response to asymmetric inflow forcing induced by outer rainbands orbs is examined in order to understand the mechanisms driving the sustained convection outside the primary eyewall during the early phase of sef the enhancement of convection in the sef region follows the formation and inward contraction of an orb the azimuthal distribution of the enhanced convection is highly asymmetric but regular generally along a half circle starting from the downwind portion of the orb it turns out that the descending radial inflow in the middle and downwind portions of the orb initiates maintains a strong inflow in the boundary layer the latter is able to penetrate into the inner core region sharpens the gradient of radial velocity and reinforces convergence consequently warm and moist air is continuously lifted up at the lead

dynamics of the stratiform sector of a tropical cyclone rainband abstractairborne doppler radar documented the stratiform sector of a rainband within the stationary rainband complex of hurricane rita the stratiform rainband sector is a mesoscale feature consisting of nearly uniform precipitation and weak vertical velocities from collapsing convective cells upward transport and associated latent heating occur within the stratiform cloud layer in the form of rising radial outflow beneath downward transport is organized into descending radial inflow in response to two regions of latent cooling in the outer upper regions of the rainband sublimational cooling introduces horizontal buoyancy gradients which produce horizontal vorticity and descending inflow similar to that of the trailing stratiform region of a mesoscale convective system within the zone of heavier stratiform precipitation melting cooling along the outer rainband edge creates a midlevel horizontal buoyancy gradient across the rainband that drives air farther inward beneath the brightband the organi

low wavenumber structure and evolution of the hurricane inner core observed by airborne dual doppler radar abstract the asymmetric dynamics of the hurricane inner core region is examined through a novel analysis of high temporal resolution three dimensional wind fields derived from airborne dual doppler radar seven consecutive composites of hurricane olivia s 1994 wind field with 30 min time resolution depict a weakening storm undergoing substantial structural changes the symmetric and asymmetric mechanisms involved in this transformation are considered separately to zeroth order the weakening of the primary circulation is consistent with the axisymmetric vortex spindown theory of eliassen and lystad for a neutrally stratified atmosphere vertical shear however increased dramatically during the observation period leading to a strong projection of the convection onto an azimuthal wavenumber 1 pattern oriented along the maximum vertical shear vector recent theoretical ideas elucidating the dynamics of vortices in vertical shear are used to help explain this asymmetry the role of asymmetric vorticity d

the unexpected rapid intensification of tropical cyclones in moderate vertical wind shear part i overview and observations abstracta satellite based investigation is performed of a class of tropical cyclones tcs that unexpectedly undergo rapid intensification ri in moderate vertical wind shear between 5 and 10 m s

the effect of relative flow on the asymmetric structure in the interior of hurricanes abstract asymmetric structure of tropical cyclones simulated by the geophysical fluid dynamics laboratory high resolution triply nested movable mesh hurricane model was analyzed emphasis was placed on the quasi steady component of the asymmetric structure in the region of the eyewall it was found that the asymmetry was primarily caused by the relative wind that is the flow entering and leaving the storm region relative to the moving storm a set of idealized numerical experiments was first performed both with a constant and a variable coriolis parameter f and the addition of basic flows that were either constant or sheared with height analysis was then made for one case of hurricane gilbert 1988 to demonstrate that the quasi steady asymmetric structure analyzed in the idealized studies could be identified in this real data case vorticity analysis in the variable f experiment indicated that quasi steady asymmetries resulted in the eyewall region through the effect of vorticity advection due to

external influences on hurricane intensity part iii potential vorticity structure abstract the interaction of hurricane elena 1985 with a baroclinic wave was reexamined using both potential vorticity pv and a formulation for eliassen palm fluxes in cylindrical coordinates the hurricane began to deepen rapidly as a narrow upper level positive pv anomaly became nearly superposed over the low level center the intensification appeared to represent an evaporation wind feedback activated by constructive interference of the pv anomalies enhanced convection associated with this process eroded the upper pv anomaly and prevented it from crossing the hurricane and reversing the intensification the eliassen palm flux divergence showed that maximum eddy activity remained in the upper troposphere prior to the reintensification this activity was produced in part because the action of the outflow anticyclone of the hurricane contributed to synoptic scale wave breaking the upper level pv anomaly that approached the center was much narrower in extent than the original synoptic scale trough th

the effect of vertical shear on tropical cyclone intensity change abstract the effect of vertical shear on tropical cyclone intensity change is usually explained in terms of ventilation where heat and moisture at upper levels are advected away from the low level circulation which inhibits development a simple two layer diagnostic balance model is used to provide an alternate explanation of the effect of shear when the upper layer wind in the vortex environment differs from that in the lower layer the potential vorticity pv pattern associated with the vortex circulation becomes tilted in the vertical the balanced mass field associated with the tilted pv pattern requires an increased midlevel temperature perturbation near the vortex center it is hypothesized that this midlevel warming reduces the convective activity and inhibits the storm development previous studies have shown that diabatic heating near the storm center acts to reduce the vertical tilt of the vortex circulation these studies have also shown that there is an adiabatic process that acts to redu

performance evaluation of the u s national lightning detection network in eastern new york 2 location accuracy we have evaluated the location accuracy of the u s national lightning detection network nldn via comparison of individual nldn stroke locations with their corresponding stroke terminations as determined from multiple site video recordings of local cloud to ground lightning flashes the video records used in this analysis were acquired in the vicinity of albany new york during the summers of 1994 and 1995 seasons corresponding to the initial and final phases of the upgrade of the nldn to the improved accuracy from combined technology impact configuration for 1994 a total of 751 strokes were located in common between the video and nldn data sets yielding median and mean values of the nldn video location separation of 2 21 km and 3 74 km respectively constraint of the 1994 data to the best video locations those with a semimajor axis value of the 50 error ellipse less than 500 m yielded a subset of 53 strokes with median and mean values of the nldn video location separation of 2 61 km and 4 74 km respectively for 1995 a total of 219 strokes were located in common yielding median and mean values of the nldn video location separation of 442 m and 865 m respectively constraint of the 1995 data to that year s best video locations those with a semimajor axis value of the 50 error ellipse less than 200 m yielded a subset of 79 common strokes with median and mean values of the nldn video location separation of 435 m and 625 m respectively the impact upgrade of the nldn apparently has resulted in about a fivefold increase in location accuracy a special subset of 11 strokes occurred in 1995 these were located by the nldn and observed to terminate on local structures of accurately known location for these 11 strokes the median and mean values of the nldn location error are 518 m and 484 m respectively a result quite consistent with the overall nldn video location comparison and the claimed 500 m median location accuracy for the upgraded network indeed we argue that removal of an apparent residual bias in the nldn locations ultimately could yield a median location accuracy in this region approaching 250 m finally we find that the nldn location error is a function of the estimated stroke peak current with the weakest peak currents having the poorest locations for both years for the 1995 data strokes with peak currents of intermediate magnitude 20 30 ka were the most accurately located

convective structure of hurricanes as revealed by lightning locations cloud to ground lightning flash locations were examined for nine atlantic basin hurricanes using data from the national lightning detection network a common radial distribution in ground flash density was evident a weak maximum in the eyewall region a clear minimum 80 100 km outside the eyewall and a strong maximum in the vicinity of outer rainbands 210 290 km radius these results are consistent with the authors previous study of hurricane andrew none of the storms showed this characteristic radial structure during prehurricane stages the results support the division of precipitation in the hurricane into three distinct regimes the eyewall is a unique phenomenon but shares some attributes with deep weakly electrified oceanic monsoonal convection the region outside the eyewall and under the central dense overcast has characteristics of the trailing stratiform region of mesoscale convective systems including a relatively high fraction of positive polarity flashes the outer bands with mean maximum flash density at the 250 km radius contain the vast majority of ground flashes in the storms eyewall lightning defined as that within 40 km of the center was examined for four moderate to strong hurricanes such lightning occurred episodically during hurricane stage with 93 of hourly intervals containing no detected flashes eyewall lightning outbreaks over water always occurred at the beginning of or during times of intensification but often were indicative of the imminent end of deepening it is proposed that the existence of such inner core lightning might reveal the presence of an eyewall cycle for the one storm with available aircraft reconnaissance data eyewall cycles were reliably identified by the occurrence of inner core lightning and inner core lightning appeared only during such cycles suggestions are made as to how eyewall flashes in existing hurricanes might be used to help predict hurricane intensity change

the relationship between storm motion vertical wind shear and convective asymmetries in tropical cyclones abstract the influence of the direction of storm motion on the azimuthal distribution of electrified convection in 35 atlantic basin tropical cyclones from 1985 to 1999 was examined using data from the national lightning detection network in the inner 100 km flashes most often occurred in the front half of storms with a preference for the right front quadrant in the outer rainbands r 100 300 km flashes occurred predominantly to the right of motion although the maximum remained in the right front quadrant the results are shown to be consistent with previous studies of asymmetries in rainfall radar reflectivity and vertical motion with respect to tropical cyclone motion the motion effect has been attributed to the influence of asymmetric friction in the tropical cyclone boundary layer the authors previously found a strong signature in the azimuthal distribution of lightning with respect to vertical wind shear because both effects show clearly vertical wind shear and storm motion must themse

a composite study of the interactions between tropical cyclones and upper tropospheric troughs abstract the objective of this study is to understand how interactions with upper tropospheric troughs affect the intensity of tropical cyclones the study includes all named atlantic tropical cyclones between 1985 and 1996 to minimize other factors affecting intensity change times when storms are over subcritical sea surface temperatures 26 c or near landfall are removed from the sample a trough interaction is defined to occur when the eddy momentum flux convergence calculated over a 300 600 km radial range is greater than 10 m s 1 day 1 the trough interaction cases are separated into four composites i favorable superposition tropical cyclone intensifies with an upper tropospheric potential vorticity pv maximum within 400 km of the tropical cyclone center ii unfavorable superposition iii favorable distant interaction upper pv maximum between 400 and 1000 km from the tropical cyclone center and iv unfavorable distant interaction for comparison two additional composites are cre

a numerical study of convective scale structures in the outer cores of sheared tropical cyclones 1 updraft traits in different vertical wind shear magnitudes

polarimetric radar observations of the persistently asymmetric structure of tropical cyclone ingrid abstract tropical cyclone ingrid had a distinctly asymmetric reflectivity structure with an offshore maximum as it passed parallel to and over an extended coastline near a polarimetric weather radar located near darwin northern australia for the first time in a tropical cyclone polarimetric weather radar microphysical analyses are used to identify extensive graupel and rain hail mixtures in the eyewall the overall microphysical structure was similar to that seen in some other asymmetric storms that have been sampled by research aircraft both environmental shear and the land sea interface contributed significantly to the asymmetry but their relative contributions were not determined the storm also underwent very rapid changes in tangential wind speed as it moved over a narrow region of open ocean between a peninsula and the tiwi islands the time scale for changes of 10 m s 1 was of the order of 1 h there were also two distinct types of rainbands observed large scale principal bands with embedded d

potential vorticity diagnosis of a simulated hurricane part ii quasi balanced contributions to forced secondary circulations although the forced secondary circulations fscs associated with hurricane like vortices have been previously examined understanding is still limited to idealized axisymmetric flows and forcing functions in this study the individual contributions of latent heating frictional and dry dynamical processes to the fscs of a hurricane vortex are separated in order to examine how a hurricane can intensify against the destructive action of vertical shear and how a warm cored eye forms this is achieved by applying a potential vorticity pv inversion and quasi balanced omega equations system to a cloud resolving simulation of hurricane andrew 1992 during its mature stage with the finest grid size of 6 km it is shown that the latent heating fsc tilting outward with height acts to oppose the shear forced vertical tilt of the storm and part of the upward mass fluxes near the top of the eyewall is detrained inward causing the convergence aloft and subsidence warming in the hurricane eye the friction fsc is similar to that of the ekman pumping with its peak upward motion occurring near the top of the planetary boundary layer pbl in the eye about 40 of the pbl convergence is related to surface friction and the rest to latent heating in the eyewall in contrast the dry dynamical forcing is determined by vertical shear and system relative flow when an axisymmetric balanced vortex is subjected to westerly shear a deep countershear fsc appears across the inner core region with the rising sinking motion downshear upshear and easterly sheared horizontal flows in the vertical the shear fsc is shown to reduce the destructive roles of the large scale shear imposed as much as 40 including its forced vertical tilt moreover the shear fsc intensity is near linearly proportional to the shear magnitude and the wavenumber 1 vertical motion asymmetry can be considered as the integrated effects of the shear fscs from all the tropospheric layers the shear fsc can be attributed to the laplacian of thermal advection and the temporal and spatial variations of centrifugal force in the quasi balanced omega equation and confirms the previous finding of the development of wavenumber 1 cloud asymmetries in hurricanes hurricane eye dynamics are presented by synthesizing the latent heating fsc with previous studies the authors propose to separate the eye formation from maintenance processes the upper level inward mass detrainment forces the subsidence warming and the formation of an eye the surface pressure fall and increased rotation in the eyewall this increased rotation will induce an additional vertical pressure gradient force to balance the net buoyancy generated by the subsidence warming for the maintenance of the hurricane eye in this sense the negative vertical shear in tangential wind in the eyewall should be considered as being forced by the subsidence warming and maintained by the rotation in the eyewall

effects of low level flow orientation and vertical shear on the structure and intensity of tropical cyclones abstractthis article explores the simultaneous effect of vertical wind shear vws and low level mean flow lmf on tropical cyclone tc structure evolution the structural evolution of 180 wester

satellite derived rain rates in vertically sheared tropical cyclones 1 when tropical cyclones interact with environmental vertical wind shear they often take on an asymmetric structure prior observational and modeling studies have identified a preference for rainfall enhancement in the directions that are down shear and also to the left of the shear vector in the northern hemisphere this study composites hundreds of snapshots of the rain fields for atlantic tropical cyclones between 1988 2004 taken from satellite borne passive microwave radiometer estimates quadrant mean rain rates are fairly symmetrical in weakly sheared hurricanes for cases with shear greater than 10 m s 1 the favored downshear and left of shear quadrants have a factor of two greater rain rates in the inner core than the non favored quadrants beyond 100 km from the center this asymmetry increases to a factor of four or more the magnitude of the asymmetry is greater for tropical storms although the mean rain rates are less

relationships between tropical cyclone intensity and eyewall structure as determined by radial profiles of inner core infrared brightness temperature abstractradial profiles of infrared brightness temperature for 2405 different satellite observations from 14 western north pacific tropical cyclones tcs from the 2012 season were analyzed and compared to intensity and changes in intensity four critical points along the inner core of each infrared ir brightness temperature bt profile were identified coldest cloud top cct first overshooting top fot and lower l45 and upper u45 extent of the inner eyewall radial movement of the mean cct point outward with increasing tc intensity combined with subsequent warming of the mean l45 point with intensity highlighted structure changes that are consistent with eye and eyewall development when stratified by latitude and vertical wind shear the cct point moved radially outward for all cases notably at higher intensities for lower latitude tcs and at lower intensities for higher latitude tcs the majority of the warming of the l45 point with increasing intensity occurred for low latitude and low s

external influences on hurricane intensity part i outflow layer eddy angular momentum fluxes abstract outflow layer winds were objectively analyzed every 12 h for 6 days during the life cycle of hurricane elena 1985 a high correlation was found between angular momentum fluxes by azimuthal eddies at large radii and central pressure changes in the storm 27 33 h later momentum flux by eddies exceeded that by the azimuthal mean outside the 800 km radius while vortex spinup by the eddies reached instantaneous magnitudes as large as 25 m s 1 day outflow maxima and minima repeatedly appeared more than 1000 km from the hurricane center and tracked inward with time the results provide evidence of significant environmental control on the behavior of the storm after reaching hurricane strength elena experienced a major secondary intensification associated with a large inward cyclonic eddy momentum flux produced by the passage of a middle latitude trough north of the hurricane an outflow maximum appeared radially inside of the eddy momentum source consistent with balanced vortex theory and tracke

observations of lightning in convective supercells within tropical storms and hurricanes cloud to ground cg lightning observations from land based lightning detection networks now allow monitoring this component of the electrical structure of tropical storms and hurricanes within a few hundred kilometers of the united states coastline several case studies confirm the long held opinion that lightning is rather common within the outer rainbands the general absence of cg lightning within the interior of mature tropical cyclones is also apparent on the other hand bursts of cg lightning near the circulation center of developing storms appear to precede periods of further deepening the cg events are associated with convective supercells whose anvil canopies can often obscure much of the underlying storm near eyewall cg bursts preceding periods of intensification were noted in hurricanes diana 1984 and florence 1988 a detailed case study of the 1987 unnamed tropical storm that struck the texas louisiana coastline reveals that lightning was associated with two large supercells these supercells appeared to be the trigger for the development of a closed circulation that formed several hours after the apparent low pressure center made landfall further studies of lightning may provide additional insight into the role of convective supercells in tropical storm intensification it may also provide a useful diagnostic of impending deepening

diagnosing forecast errors in tropical cyclone motion abstractthis paper reports on the development of a diagnostic approach that can be used to examine the sources of numerical model forecast error that contribute to degraded tropical cyclone tc motion forecasts tropical cyclone motion forecasts depend upon skillful prediction of the environment wind field and by extension the synoptic scale weather systems nearby the tc while previous research suggests that the deep layer mean dlm steering flow typically approximates the actual tc motion it is shown that the motion of even mature tcs can depart from the dlm steering flow an optimal environmental steering flow is defined which varies the vertical extent of the steering layer and the radius over which tc vorticity and divergence are removed errors in predicted tc motion are quantified using a diagnostic equation that accounts for not only differences in the synoptic scale flow but also differences in the depth and radius used to define the steering flow differences in the latter two parameters a

electrification and lightning in idealized simulations of a hurricane like vortex subject to wind shear and sea surface temperature cooling abstractrelationships between intensity fluctuations cloud microphysics lightning variations and electrical structures within idealized tropical cyclones are investigated with the cloud resolving collaborative model for multiscale atmospheric simulation commas an initial strong tropical cyclone is subjected to either steady state control conditions ctrl increased wind shear shear or a reduction in sea surface temperature sst in ctrl nearly all the lightning 95 occurred in the outer region 100 r 300 km and was overall very episodic in the inner core r 100 km consistent with observations the inner core updrafts were weaker and experienced greater depletion of cloud water by warm rain processes which in contrast to the deeper updrafts in the rainband convection reduced the mixed phase cloud depth and confined the bulk of the charging and lightning initiations to lower levels notably larger flash rates were produced in the asymmetric inner core of the shear case with the ma

shear relative asymmetries in tropical cyclone eyewall slope abstractrecent studies have analyzed the azimuthal mean slope of the tropical cyclone tc eyewall this study looks at the shear relative azimuthal variability of different metrics of eyewall slope the 20 dbz surface the radius of maximum wind rmw and an angular momentum m surface passing through the rmw the data used are doppler radar composites from the noaa hurricane research division hrd this study examines 34 tcs with intensities ranging from 3 to 75 m s 1 and shear magnitudes ranging from 0 to 10 m s 1 calculation of the mean slope in each quadrant for all cases shows that rmw slope has the strongest asymmetry with downshear slope larger than upshear in 62 of cases slopes of momentum surfaces and dbz surfaces are also greater downshear in some cases 65 for m and 47 for dbz but there is more variance than in the rmw slope the azimuthal phase of maximum slope occurs most often downshear particularly downshear left consistent with the depiction of a mean vortex tilt approximate

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

rainfall characteristics of recurving tropical cyclones over the western north pacific abstracta dataset of 88 recurving western north pacific tropical cyclones from 2004 to 2015 is investigated for rainfall characteristics during their period of recurvature the tcs are categorized into two groups based on different large scale patterns from empirical orthogonal function analysis group 1 is characterized by an intense midlatitude baroclinic zone and close distance between the zone and tc while group 2 is characterized by a weaker midlatitude baroclinic zone and more remote distance between the zone and tc at the time of recurvature the results show the large scale environment has substantial impact on tc rainfall patterns in group 1 as the tc approaches and is embedded into the baroclinic zone a relatively strong interaction between the tc and midlatitudes occurs which is reflected by a rapid increase of environmental vertical wind shear and tc translation speed the alignment of the shear vector and motion vector and a sharp contrast of temperature and moisture higher rainfall an

cloud to ground lightning in tropical cyclones a study of hurricanes hugo 1989 and jerry 1989 abstract cloud to ground lightning characteristics of two atlantic cyclones of 1989 hurricanes hugo and jerry are presented statistics on the number of flashes location polarity peak currents and multiplicity number of strokes per flash are examined in an 18 h period divided into prelandfall and postlandfall categories land based and aircraft lower fuselage radar data are also analyzed to determine the nature of the precipitation in which lightning is detected jerry is found to be more electrically active than hugo with 691 flashes detected compared with 33 flashes for hugo the majority of these flashes regardless of the polarity are located in the right front and right rear quadrants of the hurricanes almost exclusively in outer convective rainbands one reason for the large difference in the number of flashes between the two storms is the presence of many convective rainbands in jerry compared to only a few in hugo more than 20 of the flashes in each storm have a positive polarity me

tropical cyclone motion and evolution in vertical shear abstract the motion and the evolution of tropical cyclone like vortices in an environmental flow with vertical shear are investigated using a baroclinic primitive equation model the study focuses on the fundamental dynamics of a baroclinic vortex in vertical shear the influence of vortex structure and the role of diabatic heating the results show that the initial response of the vortex to the vertical shear is to tilt downshear as soon as the tilt develops the upper level anticyclonic and lower level cyclonic circulations begin to interact with each other as a result of these interactions the tilted axis of the vortex reaches a stable state after an initial adjustment which varies with the structure of the vortex its environmental flow shear and the cumulus convective heating the motion of an adiabatic vortex in vertical shear is controlled by both the steering of the environmental flow and vertical coupling mechanisms most of the vortices move with the environmental flow at about 650 hpa or

on the initial development of asymmetric vertical motion and horizontal relative flow in a mature tropical cyclone embedded in environmental vertical shear in this paper the authors focus on the initial development of asymmetric vertical motion and horizontal relative flow in a mature tropical cyclone tc embedded in an environmental vertical shear the fully compressible nonhydrostatic tc model was used to perform a series of numerical experiments with a mature tc with different intensities embedded in shear with different magnitudes and different vertical profiles results show that the development of both the wavenumber 1 asymmetric vertical motion and horizontal relative flow for a tc embedded in vertical shear is quite sensitive to both the magnitude and the vertical profile of wind shear as well as the intensity of the tc itself diagnostic analysis based on the quasi balanced potential vorticity inversion indicates that the balanced dynamics can only explain a small portion of the asymmetric vertical motion and relative flow the unbalanced processes contribute predominantly to the developmentoftheasymmetricflowinthesimulations itisshownthattheeyewallofamaturetcplaysarole somewhat like a material cylinder embedded in an environmental flow with vertical shear the interaction between the environmental shear and the eyewall produces vertical gradient of convergence divergence of horizontal wind around the lateral edge of the eyewall this forces much stronger asymmetric vertical motion than the balanced processes do and drives significant horizontal relative divergent flow over the storm core which opposes vertical shear and reduces the vertical tilt of the storm axis in addition the budget analysis for the axisymmetric tangential wind demonstrates that the asymmetric flow plays a dominant role in weakening the storm top down

origin and maintenance of the long lasting outer mesoscale convective system in typhoon fengshen 2008 abstractouter mesoscale convective systems omcss are long lasting heavy rainfall events separate from the inner core rainfall that have previously been shown to occur in 22 of western north pacific tropical cyclones tcs environmental conditions accompanying the development of 62 omcss are contrasted with the conditions in tcs that do not include an omcs the development kinematic structure and maintenance mechanisms of an omcs that occurred to the southwest of typhoon fengshen 2008 are studied with weather research and forecasting model simulations quick scatterometer quikscat observations and the simulations indicate the low level tc circulation was deflected around the luzon terrain and caused an elongated north south moisture band to be displaced to the west such that the omcs develops in the outer region of fengshen rather than spiraling into the center strong northeasterly vertical wind shear contributed to frictional convergence in the boundary layer and then the large moisture flux

analyzing simulated convective bursts in two atlantic hurricanes part i burst formation and development abstractunderstanding the structure and evolution of the tropical cyclone tc inner core remains an elusive challenge in tropical meteorology especially the role of transient asymmetric features such as localized strong updrafts known as convective bursts cbs this study investigates the formation of cbs and their role in tc structure and evolution using high resolution simulations of two atlantic hurricanes dean in 2007 and bill in 2009 with the weather research and forecasting wrf model several different aspects of the dynamics and thermodynamics of the tc inner core region are investigated with respect to their influence on tc convective burst development composites with cbs show stronger radial inflow in the lowest 2 km and stronger radial outflow from the eye to the eyewall around z 2 4 km than composites without cbs asymmetric vorticity associated with eyewall mesovortices appears to be a major factor in some of the radial flow anomalies that lead to cb development the anomalous outfl

eye and eyewall traits as determined with the noaa wp 3d lower fuselage radar abstracteye and eyewall traits were ascertained for 209 images from 37 tropical cyclones tcs using the lower fuselage 5 6 cm radar aboard the two national oceanic and atmospheric administration wp 3ds these tcs were almost entirely from the atlantic basin and were sampled from 1997 to 2012 for the eye these traits included area maximum diameter and roundness for the eyewall the traits included area completeness maximum width maximum reflectivity value and location number of local reflectivity maxima and mean rain rate these variables were compared to tc intensity and motion characteristics from the best track dataset and environmental characteristics from the statistical hurricane intensity prediction scheme interrelationships between eyewall features revealed that eyewall reflectivity features became more homogeneous as eye and eyewall areas shrank and maximum reflectivity and rain rate increased as the eyewall became wider and more complete as the tc intensified the eye area decreased

the effects of vertical wind shear on the distribution of convection in tropical cyclones abstract the influence of vertical wind shear on the azimuthal distribution of cloud to ground lightning in tropical cyclones was examined using flash locations from the national lightning detection network the study covers 35 atlantic basin tropical cyclones from 1985 99 while they were over land and within 400 km of the coast over water a strong correlation was found between the azimuthal distribution of flashes and the direction of the vertical wind shear in the environment when the magnitude of the vertical shear exceeded 5 m s 1 more than 90 of flashes occurred downshear in both the storm core defined as the inner 100 km and the outer band region r 100 300 km a slight preference for downshear left occurred in the storm core and a strong preference for downshear right in the outer rainbands the results were valid both over land and water and for depression storm and hurricane stages it is argued that in convectively active tropical cyclones deep divergent circulations oppose the ver

kinematics of the secondary eyewall observed in hurricane rita 2005 abstractairborne doppler radar data collected from the concentric eyewalls of hurricane rita 2005 provide detailed three dimensional kinematic observations of the secondary eyewall feature the secondary eyewall radar echo shows a ring of heavy precipitation containing embedded convective cells which have no consistent orientation or radial location the axisymmetric mean structure has a tangential wind maximum within the reflectivity maximum at 2 km altitude and an elevated distribution of its strongest winds on the radially outer edge the corresponding vertical vorticity field contains a low level maximum on the inside edge which is part of a tube of increased vorticity that rises through the center of the reflectivity tower and into the midlevels the secondary circulation consists of boundary layer inflow that radially overshoots the secondary eyewall a portion of this inflowing air experiences convergence and supergradient forces that cause the air to rise and flow radially outward back into th

a high resolution record of atmospheric 14c based on hulu cave speleothem h82 abstract the development of a calibration of atmospheric radiocarbon 14c is a significant scientific goal because it provides the means to link the numerous 14c dated paleoclimate records to a common timescale with absolutely dated records and thereby improve our understanding the relationships between the carbon cycle and climate change currently few calibration datasets that directly sample the atmospheric 14c reservoir are available beyond the end of the dendro dated holocene tree ring record at 12 6 kyr bp before 1950 ad in the absence of suitable true atmospheric records 14c calibrations beyond this age limit are based largely on marine data that are complicated by the marine reservoir effect which may have varied over the glacial cycle in this paper we present a high resolution record of u th series and 14c measurements from hulu cave speleothem h82 spanning 10 6 26 8 kyr bp corrections for detrital 230th are negligible and the contribution of 14c free geologic carbon to the speleothem calcite is small 5 6 and is stable across major climate shifts the time series provides a 16 kyr record of atmospheric 14c as well as an updated age model for the existing hulu cave 18o record the 14c data are in good overall agreement with existing marine and terrestrial 14c records but comparisons with the cariaco basin marine 14c record through the deglacial interval reveal that the cariaco reservoir age appears to have varied during parts of the younger dryas and heinrich stadial 1 cold events this highlights the importance of developing extended high resolution marine and terrestrial 14c records as a means of detecting changes in ocean circulation over the glacial cycle

examining polarimetric radar observations of bulk microphysical structures and their relation to vortex kinematics in hurricane arthur 2014 abstractdual polarization radar observations were taken of hurricane arthur prior to and during landfall providing needed insight into the microphysics of tropical cyclone precipitation a total of 30 h of data were composited and analyzed by annuli capturing storm features eyewall inner rainbands and outer rainbands and by azimuth relative to the deep layer environmental wind shear vector polarimetric radar variables displayed distinct signatures indicating a transition from convective to stratiform precipitation in the downshear right to downshear left quadrants which is an organization consistent with the expected kinematic asymmetry of a sheared tropical cyclone in the downshear right quadrant vertical profiles of differential reflectivity zdr and copolar correlation coefficient hv were more vertically stretched within and above the melting layer at all annuli which is attributed to convective processes an analysis of specific differential phase kdp indicated that nonspherical ice particle

vertical structure of tropical cyclone rainbands as seen by the trmm precipitation radar abstractten years of data from the tropical rainfall measurement mission satellite s precipitation radar trmm pr show the vertical structure of tropical cyclone rainbands radar echo statistics show that rainbands have a two layered structure with distinct modes separated by the melting layer the ice layer is a combination of particles imported from the eyewall and ice left aloft as convective cells collapse this layering is most pronounced in the inner region of the storm and the layering is enhanced by storm strength the inner region rainbands are vertically confined by outflow from the eyewall but nevertheless are a combination of strong embedded convective cells and robust stratiform precipitation both of which become more pronounced in stronger cyclones changes in rainband coverage vertical structure and the amount of active convection indicate a change in the nature of rainbands between the regions inward and outward of a radius of approximately 200 km beyond this radius rainbands consis

extreme helicity and intense convective towers in hurricane bonnie abstract helicity was calculated in hurricane bonnie 1998 using tropospheric deep dropsonde soundings from the nasa convection and moisture experiment large helicity existed downshear of the storm center with respect to the ambient vertical wind shear it was associated with veering semicircular hodographs created by strong vortex scale radial vertical flow induced by the shear the most extreme values of helicity among the largest ever reported in the literature occurred in the vicinity of deep convective cells in the downshear left quadrant these cells reached as high as 17 5 km and displayed the temporal and spatial scales of supercells convective available potential energy cape averaged 861 j kg 1 downshear but only about one third as large upshear the soundings nearest the deep cells were evaluated using two empirical supercell parameters that make use of cape helicity and or shear these parameters supported the possible existence of supercells as a consequence of the exceptional hel

vertical motion characteristics of tropical cyclones determined with airborne doppler radial velocities abstract vertical motions in seven atlantic hurricanes are determined from data recorded by doppler radars on research aircraft the database consists of doppler velocities and reflectivities from vertically pointing radar rays collected along radial flight legs through the hurricane centers the vertical motions are estimated throughout the depth of the troposphere from the doppler velocities and bulk estimates of particle fallspeeds portions of the flight tracks are subjectively divided into eyewall rainband stratiform and other regions characteristics of the vertical velocity and radar structure are described as a function of altitude for the entire dataset and each of the four regions in all of the regions more than 70 of the vertical velocities range from 2 to 2 m s 1 the broadest distribution of vertical motion is in the eyewall region where 5 of the vertical motions are 5 m s 1 averaged over the entire dataset the mean vertical velocity is upward at all altitudes mean downward mot

observed boundary layer wind structure and balance in the hurricane core part i hurricane georges abstract the gps dropsonde allows observations at unprecedentedly high horizontal and vertical resolution and of very high accuracy within the tropical cyclone boundary layer these data are used to document the boundary layer wind field of the core of hurricane georges 1998 when it was close to its maximum intensity the spatial variability of the boundary layer wind structure is found to agree very well with the theoretical predictions in the works of kepert and wang in particular the ratio of the near surface wind speed to that above the boundary layer is found to increase inward toward the radius of maximum winds and to be larger to the left of the track than to the right while the low level wind maximum is both more marked and at lower altitude on the left of the storm track than on the right however the expected supergradient flow in the upper boundary layer is not found with the winds being diagnosed as close to gradient balance the tropical cyclone boundary layer model of kepert and wan

an axisymmetric view of concentric eyewall evolution in hurricane rita 2005 abstractmultiplatform observations of hurricane rita 2005 were collected as part of the hurricane rainband and intensity change experiment rainex field campaign during a concentric eyewall stage of the storm s life cycle that occurred during 21 22 september satellite aircraft dropwindsonde and doppler radar data are used here to examine the symmetric evolution of the hurricane as it underwent eyewall replacement during the approximately 1 day observation period developing convection associated with the secondary eyewall became more symmetric and contracted inward latent heating in the emergent secondary eyewall led to the development of a distinct toroidal overturning circulation with inertially constrained radial inflow above the boundary layer and compensating subsidence in the moat region properties that are consistent broadly with the balanced vortex response to an imposed ring of diabatic heating outside the primary eyewall the primary eyewall s convection became more asymmetric during

a subtropical cyclonic gyre associated with interactions of the mjo and the midlatitude jet abstractthis paper describes a large cyclonic gyre that lasted several days in the northwest pacific during july 1988 cyclonic winds at 850 hpa extended beyond the 2000 km radius with a radius of maximum winds of 700 800 km the gyre exhibited clear skies within and north of its center active convection extended 4000 km in longitude to its south the madden julian oscillation mjo was in its active phase in the indian ocean prior to gyre formation consistent with earlier studies diabatic heating in the mjo was associated with an anomalous upper tropospheric westerly jet over the northeast asian coast and a jet exit region over the northwest pacific repeated equatorward wave breaking events developed downwind of the jet exit region one such event left behind a region of lower tropospheric cyclonic vorticity and convection in the subtropics that played a key role in the gyre formation a second wave breaking event produced strong subsidence north of the mature gyre that contributed to its convective a

asymmetric distribution of convection associated with tropical cyclones making landfall along the south china coast this study examines the convection distribution associated with 18 tcs that made landfall along the south china coast during 1995 and 2005 cloud top temperatures from high resolution satellite imageries of the geosynchronous meteorological satellite 5 are used as proxy of strong convection it is found that convection tends to be enhanced on the western side of the tc as it makes landfall in 10 of the cases in agreement with the conclusion of some previous studies four cases have stronger convection on the eastern side this deviation from the general rule appears to be related to the tcs being more slow moving or their interaction of the tc with another land surface prior to its making landfall along the south china coast for the remaining cases in which no significant asymmetries in convection can be identified the vertical wind shear appears to enhance convection on the east side

tropical cyclone formation in a sheared environment a case study abstract the development of hurricane danny 1997 from depression to hurricane was examined using cloud to ground lightning data reconnaissance aircraft data and satellite imagery vertical wind shear between 850 and 200 hpa of 5 11 m s 1 produced persistent downshear convective outbreaks that became progressively more intense and closer to the center during the development early in the period the storm intensified steadily in the presence of this downshear convection during the last and most intense outbreak a second vortex appeared to develop within the convection evidence is presented that the new downshear vortex became the dominant vortex and absorbed the original based on these events it is hypothesized that the presence of moderate vertical wind shear accelerated the early development process equivalent potential temperature fields within 500 m of the surface were examined only well after the period of vortex interaction did the characteristic mature tropical cyclone radial profile of eq

convective bursts downdraft cooling and boundary layer recovery in a sheared tropical storm abstracttropical storm edouard 2002 experienced episodic outbreaks of convection downshear within the storm core in the presence of 11 15 m s 1 of ambient vertical wind shear these outbreaks lasted 2 6 h and were followed by long periods with no deep convection flights from u s air force reconnaissance aircraft within the boundary layer were used to investigate the cause of one such oscillation low equivalent potential temperature e air filled the boundary layer as convection ceased creating a 4 6 k deficit in e within the convective region soundings within 110 km of the center were supportive of convective downdrafts with midlevel relative humidity below 15 and large downdraft cape deep convection ceased within 75 km of the center for more than 8 h tangential velocity reached hurricane force locally during the convective outbreak then became nearly symmetric after convection stopped arguably as a result of axisymmetrization and the storm weakened nevertheless the corresponding lack of

observations of the eyewall structure of typhoon sinlaku 2008 during the transformation stage of extratropical transition abstracta unique dataset observing the life cycle of typhoon sinlaku was collected during the observing system research and predictability experiment thorpex pacific asian regional campaign t parc in 2008 in this study observations of the transformation stage of the extratropical transition of sinlaku are analyzed research flights with the naval research laboratory p 3 and the u s air force wc 130 aircraft were conducted in the core region of sinlaku data from the electra doppler radar eldora dropsondes aircraft flight level and satellite atmospheric motion vectors were analyzed with the recently developed spline analysis at mesoscale utilizing radar and aircraft instrumentation samurai software with a 1 km horizontal and 0 5 km vertical node spacing the samurai analysis shows marked asymmetries in the structure of the core region in the radar reflectivity and three dimensional wind field the highest radar reflectivities were found in the left of shear semicircle and maximum ascent was

quadrant dependent evolution of low level tangential wind of a tropical cyclone in the shear flow abstractthis study investigates the quadrant by quadrant evolution of the low level tangential wind near the eyewall of an idealized simulated mature tropical cyclone embedded in a unidirectional shear flow it is found that the quadrant averaged tangential wind in the right of shear quadrants weakens continuously while that in the left of shear quadrants experiences a two stage evolution a quasi steady stage followed by a weakening stage after the imposing of vertical wind shear this leads to a larger weakening rate in the right of shear and a stronger jet in the left of shear quadrants the budget analysis shows that the quadrant dependent evolution of tangential wind is controlled through the balance between the generalized coriolis force gcf i e the radial advection of absolute angular momentum and the advection terms the steady decreasing of the gcf is primarily responsible for the continuous weakening of jet strength in the right of shear quadrants for the left of shear quadrants the quas

mesoscale aspects of the downshear reformation of a tropical cyclone the downshear reformation of tropical storm gabrielle 2001 was investigated using radar reflectivity and lightning data that were nearly continuous in time as well as frequent aircraft reconnaissance flights initially the storm was a marginal tropical storm in an environment with strong 850 200 hpa vertical wind shear of 12 13 m s 1 and an approaching upper tropospheric trough both the observed outflow and an adiabatic balance model calculation showed that the radial vertical circulation increased with time as the trough approached convection was highly asymmetric with almost all radar return located in one quadrant left of downshear in the storm reconnaissance data show that an intense mesovortex formed downshear of the original center this vortex was located just south of rather than within a strong downshear left lightning outbreak consistent with tilting of the horizontal vorticity associated with the vertical wind shear the downshear mesovortex contained a 972 hpa minimum central pressure 20 hpa lower than minimum pressure in the original vortex just 3 h earlier the mesovortex became the new center of the storm but weakened somewhat prior to landfall it is argued that dry air carried around the storm from the region of upshear subsidence as well as the direct effects of the shear prevented the reformed vortex from continuing to intensify despite the subsequent weakening of the reformed center it reached land with greater intensity than the original center it is argued that this intensification process was set into motion by the vertical wind shear in the presence of an environment with upward motion forced by the upper tropospheric trough in addition the new center formed much closer to the coast and made landfall much earlier than predicted such vertical shear induced intensity and track fluctuations are important to understand especially in storms approaching the coast

what is the key feature of convection leading up to tropical cyclone formation abstractinfrared brightness temperature data are used to investigate convective evolution during tropical cyclone tc formation in a quasi lagrangian framework more than 150 named atlantic storms

the convective evolution and rapid intensification of hurricane earl 2010 abstractthe relationship between an inner core r 100 km lightning outbreak and the subsequent rapid intensification ri of hurricane earl 2010 is examined using lightning strikes recorded by the world wide lightning location network wwlln and in situ observations from various aircraft missions moderate 8 4 m s 1 northeasterly deep layer 850 200 hpa vertical wind shear caused by outflow from hurricane danielle existed over earl at the beginning of a prolonged period of ri over 70 of the lightning strikes within a 500 km radius occurred downshear with a preference toward downshear right in the outer rainbands in agreement with previous studies the location of inner core strikes in earl differed markedly from previous studies the inner core lightning activity precessed from left of shear to upshear an extremely rare event beginning just prior to the onset of ri diagnosis of the vortex tilt midway through the lightning precession showed this convection was occurring downtilt in the ups

convective scale variations in the inner core rainbands of a tropical cyclone airborne doppler radar documented a variety of convective scale structures within the inner core rainbands of hurricane rita 2005 as predicted by past studies wind shear determined azimuthal variations in the convection all convective scale circulations had radial inflow at low levels upward motion and outflow in the midtroposphere convective cells at smaller radii contained a low level tangential jet determined largely by tangential acceleration due to angular momentum conservation uy r term while cells at larger radii contained a low level and or midlevel jet determined jointly by the uy r and vertical advection terms the outflow was at a higher lower altitude for the outer inner cells radial variations in the convective cells are attributable to differencesin buoyancy and vertical shear of the radial wind u z more buoyant updrafts at larger radii enhance vertical advection of y creating local tangential jets at midlevels at smaller radii the stronger low level radial inflow contributes to a greater u z confining convectively generated jets to low levels the low level tangential jet and convectively generated pressure gradients produce outward pointing supergradient acceleration that decelerates the boundary layer inflow consequently this supergradient flow will enhance convergence and convection at the radius of inner rainbandcells increasing the likelihoodof secondary eyewall formation it is hypothesized that a critical zone for secondary eyewall formation exists where sufficiently high u z consistently constrains the altitudes of convectively generated supergradient flow so that convection in this radial zone leads to a newly developed eyewall once an incipient secondary eyewall forms at a certain radius subsidence occurring along its inner edge separates it from the primary eyewall