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

a comparison of inner and outer spiral rainbands in a numerically simulated tropical cyclone abstractthe simulated inner and outer spiral rainbands in a tropical cyclone are compared in this study the inner rainbands are generally active immediately outside the eyewall in the rapid filamentation zone while the outer rainbands are active in regions outside about 3 times the radius of maximum wind the inner rainbands are characterized by the convectively coupled vortex rossby waves the movement of the outer rainbands follows the low level vector winds associated with the azimuthally averaged low level flow and the radially outward cross band flow caused by the downdraft induced cold pool in the boundary layer convective cells in outer rainbands are typical of convective systems and move cyclonically and radially outward inward at large small radii net upward vertical mass transports vmts appear throughout the depth of the troposphere in the whole inner rainband region while net downward vmts are found below 4 km height in the outer rainband region in the whole inner rainband region on

glaciological and marine geological controls on terminus dynamics of hubbard glacier southeast alaska hubbard glacier located in southeast alaska is the world s largest nonpolar tidewater glacier it has been steadily advancing since it was first mapped in 1895 occasionally the advance creates an ice or sediment dam that blocks a tributary fjord russell fiord the sustained advance raises the probability of long term closure in the near future which will strongly impact the ecosystem of russell fiord and the nearby community of yakutat here we examine a 43 year record of flow speeds and terminus position to understand the large scale dynamics of hubbard glacier our long term record shows that the rate of terminus advance has increased slightly since 1895 with the exception of a slowed advance between approximately 1972 and 1984 the short lived closure events in 1986 and 2002 were not initiated by perturbations in ice velocity or environmental forcings but were likely due to fluctuations in sedimentation patterns at the terminus this study points to the significance of a coupled system where short term velocity fluctuations and morainal shoal development control tidewater glacier terminus position

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

numerical simulation of cyclone sidr using a cloud resolving model characteristics and formation process of an outer rainband abstractcyclone sidr one of the most devastating tropical cyclones that resulted in several thousand deaths and substantial damages developed in the north indian ocean and made landfall over the bangladesh coast on 15 november 2007 observation and simulation results show that sidr was embedded in a nonuniform environment and contained an intense outer rainband to the east of its center and a significant frontal band to the northwest a detailed study of the outer rainband is performed by numerical simulation the eastern band was a long quasi straight shape in the meridional direction that remained stationary relative to the cyclone center this band was composed of convective cells that developed southeast of the center within a synoptic scale convergence zone and propagated along the band toward the northeast quadrant the speed of the downwind propagating cells was greater than that of the cyclone which resulted in a convective cluster northeast of the center only the downwind portion of the band

doppler profiler and radar observations of boundary layer variability during the landfall of tropical storm gabrielle abstract detailed observations of boundary layer structure were acquired on 14 september 2001 prior to and during the landfall of tropical storm gabrielle the mobile integrated profiling system mips and the shared mobile atmospheric research and teaching radar smart r were collocated at the western florida coastline near venice very close to the wind center at landfall prior to landfall the boundary layer was rendered weakly stable by a long period of evaporational cooling and mesoscale downdrafts within extensive stratiform precipitation that started 18 h before landfall the cool air mass was expansive with an area within the 23 c surface isotherm of about 50 000 km2 east northeasterly surface flow transported this cool air off the west coast of florida toward the convergent warm core of the gabrielle and promoted the development of shallow warm and cold fronts that were prominent during the landfall phase airflow properties of the boundary layer around the coastal zone are examined using

objective convective updraft identification and tracking part 1 structure and thermodynamics of convection in the rainband regions of two hurricane simulations to better understand the life cycles of convective elements in numerical model simulations a convective updraft tracking algorithm dubbed the statistical and programmable objective updraft tracker spout is developed spout identifies updraft cores in horizontal slices through a given model data set links these cores in three dimensions to form vertically coherent updrafts and then tracks updrafts in time via estimates of the mean local advection spout is evaluated in idealized hurricane simulations from both the regional atmospheric modeling system rams and weather research and forecasting wrf in both simulations spout indicates most updrafts live less than 60 min but some can persist for over 2 h updrafts are typically manifested as shallow cumulus cumulus congestus and deep cumulonimbus overall there is reasonable agreement between the vigor of convection and the amount of localized conditional convective instability also the majority of updrafts attain a tilted structure that is in accordance with the localized vertical wind shear nonetheless there are striking differences between models with the higher resolution wrf simulation producing around twice as many updrafts as rams moreover the wrf updrafts are significantly weaker this paper highlights the utility of spout for studying convective life cycles in high resolution numerical simulations and provides some basic features of convection in two hurricane simulations

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

azimuthal distribution of deep convection environmental factors and tropical cyclone rapid intensification a perspective from hwrf ensemble forecasts of hurricane edouard 2014 abstractforecasts from the operational hurricane weather research and forecasting hwrf based ensemble prediction system for hurricane edouard 2014 are analyzed to study the differences in both the tropical cyclone inner core structure and large scale environment between rapidly intensifying ri and non intensifying ni ensemble members an analysis of the innercore structure reveals that as deep convection wraps around from the downshear side of the storm to the upshear left quadrant for ri members vortex tilt and asymmetry reduce rapidly and ri occurs for ni members deep convection stays trapped in the downshear downshear right quandrant and storms do not intensify the budget calculation of tangential wind tendency reveals that the positive radial eddy vorticity flux for ri members contributes significantly to spinning up the tangential wind in the middle and upper levels and reduces vortex tilt the negative eddy vorticity flux for ni members spins down the tangential wind in the middle and u

wind profiles in tropical cyclone stratiform rainbands over land abstractobservations of 14 stratiform periods in outer tropical cyclone rainbands are used to evaluate wind structure using a velocity azimuth display vad technique applied to kamx miami weather surveillance radar 1988 doppler wsr 88d data these 14 cases occurred over land in southern florida from tropical storm fay and hurricanes gustav and ike during 2008 profiles show a maximum horizontal wind speed between 1000 and 1500 m in height with occasional evidence of a secondary horizontal wind maximum near 3500 5000 m storm relative wind components are calculated and radial wind profiles show a mean transition from radial inflow at low levels to radial outflow around 2500 3000 m altitude the radial inflow maximum is around 500 m while maximum outflow is more variable these profile characteristics are consistent with previous wind observations in rainbands over land and water changes in wind structure within one 4 h period are examined with changes seen linked to the environmental influence on

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

the evolution of hurricane humberto 2001 abstractin 2001 the national oceanic and atmospheric administration and the national aeronautical and space administration marshaled their resources to sample hurricane humberto for 3 successive days during the fourth convection and moisture experiment camex 4 humberto developed from a tropical storm into a category 2 hurricane despite the deep layer vertical shear of the environmental horizontal wind vws increasing markedly on the second and third days of sampling as exhibited in earlier studies the eyewall convection developed an azimuthal wavenumber 1 n 1 asymmetry as the vws increased horizontal divergence and vertical stability within 100 km of the eye exhibited persistent relationships to the vws vector the warm core evolved in an unexpected way the warm anomaly was initially located in the lower troposphere and built upward as the storm intensified the maximum temperature anomaly remained in the lower troposphere on all 3 days while the development of the upper tropospheric warm anom

on the use of two dimensional incompressible flow to study secondary eyewall formation in tropical cyclones abstract previous studies have offered hypotheses for the mechanisms that lead to secondary eyewall formation in tropical cyclones by using two dimensional incompressible flow those studies represented the convection induced vorticity field as either large but weak vortices that are the same sign as the tropical cyclone core or as purely asymmetric vorticity perturbations that are an order of magnitude weaker than the core however both observations and full physics simulations of tropical cyclones indicate that the convection induced vorticity field should also include clusters of small vorticity dipoles whose magnitude is comparable to that of the high vorticity core results of numerical simulations indicate that the interaction between the tropical cyclone core vortex and the convection induced small vorticity dipoles of considerable strength in two dimensional flow does not lead to coherent concentric vorticity ring formation the axisymmetrization process under the simplification of two dimensiona

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

convective scale downdrafts in the principal rainband of hurricane katrina 2005 abstract airborne doppler radar data collected during the hurricane rainband and intensity change experiment rainex document downdrafts in the principal rainband of hurricane katrina 2005 inner edge downdrafts ieds originating at 6 8 km altitude created a sharp reflectivity gradient along the inner boundary of the rainband low level downdrafts llds evidently driven by precipitation drag originated at 2 4 km within the heavy rain cells of each convective element the ied and lld were spatially separated by but closely associated with the updrafts within the rainband the ied was forced aloft by pressure perturbations formed in response to the adjacent buoyant updrafts once descending the air attained negative buoyancy via evaporative cooling from the rainband precipitation a convective scale tangential wind maximum tended to occur in the radial inflow at lower levels in association with the ied which enhanced the inward flux of angular momentum at lower levels convergence at the base of the

transition of the hurricane boundary layer during the landfall of hurricane irene 2011 abstractthe hurricane boundary layer hbl has been observed in great detail through aircraft investigations of tropical cyclones over the open ocean but the coastal transition of the hbl has been

a preliminary morphology of precipitation systems in tropical northern australia a preliminary morphology of convective systems observed in the vicinity of darwin australia is presented several types of tropical convection during monsoonal and break season flow are identified using specific examples and compared with a range of systems observed worldwide in the general context of the bulk richardson number a significant spectrum of convective activity ranging from low shear and low convective available potential energy cape to high shear and moderate to high cape typical of mid latitude severe storms is identified significant differences between monsoonal flow and break season systems are apparent the formation of convective lines perpendicular to the low level shear and the apparent balance between advancing shallow cold pools and the shear are ubiquitous features convective scale downdraughts and mesoscale descent appear to be responsible for redistribution of 700 mb momentum to the planetary boundary layer pel the motion of the break season squall lines appears to result from an equilibrium between the cold pool and the undisturbed environmental pel flow deviations from this balance are hypothesized to result in the observed propagating and non propagating or slow moving modes examples of these modes are given showing the classical continuous development of new cells in a balanced state along the leading edge of long lived squalls and in the propagating case the discontinuous development of new cells on the cold pool ahead of the squall

structural and surface features of arc shaped radar echoes along an outer tropical cyclone rainband this study uses ground based dual doppler radar and surface observations to document the structural and surface features of the arc shaped radar echoes asres evident along an outer rainband of typhoon longwang as it approached northern taiwan on 1 october 2005 the particular aim of this study is to explore the possible distinction between the present case previously documented tropical cyclone rainbands tcrs and squall lines the dual doppler derived fields show that the leading precipitation of the studied asres exhibited a convective nature with a sharp horizontal gradient of reflectivity and a significant vertical extent theregionsbehindtheleadingconvectionwerecharacterizedbyband relativerear to frontflowatlowlevels and were associated with a broader area of stratiform precipitation the deep layer of front to rear flow extending from the surface to the upper troposphere was generally present ahead of the asres this flow appearstobeliftedupwardatandimmediatelyaheadoftheleadingedgeofthelow levelrear to frontflowto form rearward tilting updrafts these airflow patterns are similar to those of the convective region of squall lines but differ fundamentally from those of previously documented tcrs that were located closer to the inner core of cyclones the detailed analyses of surface fluctuations during the passage of one of the studied asresfurthershowanabruptpressurerise 2mb atemperaturedrop 48c andapronounceddeceleration of inflow air coincident with the leading heavy precipitation the evaluation presented suggests that the convectively generated cold pool may be important in influencing the structures and propagation of the studied asres

asymmetric hurricane boundary layer structure from dropsonde composites in relation to the environmental vertical wind shear this study investigates the asymmetric structure of the hurricane boundary layer in relation to the environmentalverticalwind shearin theinner core region data from1878 gps dropsondesdeployed by research aircraft in 19 hurricanes are analyzed in a composite framework kinematic structure analyses based on doppler radar data from 75 flights are compared with the dropsonde composites shear relative quadrantmeancomposite analysesshow that boththekinematicandthermodynamic boundarylayerheight scalestend to decrease with decreasing radius consistent with previous axisymmetric analyses there is still a clear separation between the kinematic and thermodynamic boundary layer heights both the thermodynamic mixed layer and height of maximum tangential wind speed are within the inflow layer the inflow layer depth is found to be deeper in quadrants downshear with the downshear right dr quadrant being the deepest the mixed layer depth and height of maximum tangential wind speed are alike at the eyewall but are deeper outside in quadrants left of the shear the results also suggest that air parcels acquire equivalent potential temperature ue from surface fluxes as they rotate through the upshear right ur quadrant from the upshear left ul quadrant convection is triggered in the dr quadrant in the presence of asymmetric mesoscale lifting coincident with a maximum in ue energy is then released by latent heating in the downshear left dl quadrant convective downdrafts bring down cool and dry air to the surface and lower ue again in the dl and ul quadrants this cycling process may be directly tied to shear induced asymmetry of convection in hurricanes

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 boundary layer dynamics of tropical cyclone rainbands abstractspiral bands are ubiquitous features in tropical cyclones and significantly affect boundary layer thermodynamics yet knowledge of their boundary layer dynamics is lacking prompted by rece

the effect of vertical wind shear on radiative convective equilibrium states abstract using a three dimensional cloud ensemble model a systematic exploration is undertaken of radiative convective equilibrium states as a function of the structure and magnitude of an imposed background flow with vertical shear in such simulations mesoscale organization appears naturally independent of the particulars of the initial condition as the magnitude of an imposed low level shear increases the convection becomes increasingly organized in lines or arcs propagating broadly downshear as predicted by earlier work when the shear is very strong the convection tends to organize into lines at an angle to the shear such that the line normal component is not far from its theoretical optimal value midlevel shear favors shear parallel lines but if it occurs in conjunction with sufficiently strong low level shear the convection can become very strongly organized into lines or arcs generally orthogonal to the low level shear optimal organization occurs when the depth of the shear layer is c

concentric eyewall asymmetries in hurricane gonzalo 2014 observed by airborne radar abstracttwo eyewall replacement cycles were observed in hurricane gonzalo by the noaa p3 tail ta radar and the recently developed nasa high altitude imaging wind and rain airborne profiler hiwrap radar these observations captured detailed precipitation and kinematic features of gonzalo s concentric eyewalls both before and after the outer eyewall s winds became the vortex maximum winds the data were analyzed relative to the deep layer environmental wind shear vector during the beginning eyewall replacement cycle stages the inner and outer eyewalls exhibited different asymmetries the inner eyewall asymmetry exhibited significant low level inflow updrafts and positive tangential acceleration in the downshear quadrants consistent with observational and theoretical studies the outer eyewall asymmetry exhibited these features in the left of shear quadrants further downwind from those of the inner eyewall it is suggested that the low level inflow occurring at the outer but not at the inner eyewal

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

low level kinematic thermodynamic and reflectivity fields associated with hurricane bonnie 1998 at landfall during 11 h on 26 august 1998 two noaa wp 3d aircraft deployed 85 global positioning system gps dropwindsondes within 2 of latitude of the circulation center of hurricane bonnie as it made landfall in north carolina about 75 of the sondes successfully collected data which were used to create a series of storm relative horizontal maps of kinematic and thermodynamic variables from 10 m to 2 km reflectivity fields were analyzed from the weather surveillance radar 1988 dopplers wsr 88ds located at wilmington and morehead city north carolina and the tail and lower fuselage radars aboard the wp 3ds gps sonde performance and deployment spacing is adequate to identify several aspects of the vortex these include 1 warm dry stable air in the offshore flow that results in reduced equivalent potential temperatures entering the southern portion of the eyewall 2 cooler air collocated with the upwelled water in the right rear quadrant and under the eyewall and 3 an atypical radial wind pattern with strong inflow southwest of the circulation center and outflow northeast of the center the strongly asymmetric structure found at 10 m becomes much more homogeneous by 2 km altitude no intense rainbands developed over land in the onshore flow nor did the bands in the onshore flow undergo any significant changes once they made landfall beyond the eyewall the offshore flow contained much less precipitation than the onshore portion of the storm characteristics beyond the eyewall appear to have been modulated by the proximity to land but hurricane intensity did not vary the authors infer that the lower energy content of the inflow was offset by the contraction of the eyewall

tracking a long lasting outer tropical cyclone rainband origin and convective transformation abstractthis study used radar and surface observations to track a long lasting outer tropical cyclone rainband tcr of typhoon jangmi 2008 over a considerable period of time 10 h from its for

convectively generated potential vorticity in rainbands and formation of the secondary eyewall in hurricane rita of 2005 abstracteyewall replacements in mature tropical cyclones usually cause intensity fluctuations one reason for eyewall replacements remaining a forecasting challenge is the lack of understanding of how secondary eyewalls form this study uses high resolution full physics model forecast fields of hurricanes katrina and rita 2005 to better understand potential vorticity pv generation in the rainbands and the role that convectively generated pv played in the formation of a secondary eyewall in hurricane rita previous studies have focused on dynamic processes in the inner core and or the effects of certain specified pv distributions however the initial development of a concentric pv ring in the rainband region has not been fully addressed katrina and rita were extensively observed by three research aircraft during the hurricane rainband and intensity change experiment rainex which was designed to study the interaction of the rainbands and the inner core rita developed a secondary eyewall and went

mesoscale and convective structure of a hurricane rainband abstract the mesoscale thermodynamic kinematic and radar structure of a hurricane floyd rainband observed on 7 september 1981 is presented data are from 26 aircraft passes through the rainband from 150 to 6400 m a composite technique which presents rainband structure as a function of distance from the storm circulation center reveals inflow from the outer edge of the band and a partial barrier to this flow below 3 km in the direction parallel to rainband orientation radar reveals cellular reflectivity structure on the upwind and central portions of the rainband the frequency of cellular precipitation decreases in favor of stratiform precipitation further downwind as the band spirals gradually towards the eyewall in the radial direction a decrease of 12 k in e is observed across the rainband in the subcloud layer convective scale up and downdrafts that are associated with cellular reflectivity structure are hypothesized to be responsible for the thermodynamic modification of the cloud and subc

kinematic structure of convective scale elements in the rainbands of hurricanes katrina and rita 2005 1 airborne doppler radar data collected during the hurricane rainband and intensity change experiment rainex show the convective scale air motions embedded in the principal rainbands of hurricanes katrina and rita these embedded convective cells have overturning updrafts and low level downdrafts originating at 2 4 km that enter the rainband on its radially outward side and cross over each other within the rainband as well as a strong downdraft emanating from upper levels 6 km on the radially inward side these vertical motion structures repeat from one convective cell to another along each rainband the resulting net vertical mass transport is upward in the upwind portion of the band and greatest in the middle sector of the principal rainband where the updraft motions contribute generally to an increase of potential vorticity below the 3 4 km level because the convective cells in the middle sector are systematically located radially just inside the secondary horizontal wind maximum shwm the local increase in vorticity implied by the convective mass transport is manifest locally as an increase in the strength of the shwm at midlevels 4 km the overturning updrafts of the convective cells tilt stretch and vertically transport vorticity such that the convergence of the vertical flux of vorticity strengthens the vorticity anomaly associated with the shwm this process could strengthen the shwm by several meters per second per hour and may explain how high wave number convective scale features can influence a low wave number feature such as the principal rainband and subsequently influence the primary vortex

convective contribution to the genesis of hurricane ophelia 2005 abstract the convection occurring in the tropical depression that became hurricane ophelia 2005 was investigated just prior to tropical storm formation doppler radar showed a deep wide intense convective cell of a type that has been previously thought to occur in intensifying tropical depressions but has not heretofore been documented in detail the updraft of the cell was 10 km wide 17 km deep had updrafts of 10 20 m s 1 throughout its mid to upper levels and contained a cyclonic vorticity maximum the massive convective updraft was maintained by strong positive buoyancy which was maximum at about the 10 km level probably aided by latent heat of freezing evaporative cooling and precipitation drag occurred in the rain shower of the cell but were insufficient to produce a strong downdraft or gust front outflow to force the updraft the convective updraft was fed by a layer of strong inflow that was several kilometers deep wind induced turbulence just above the ocean surface enriched the equi

clouds in tropical cyclones abstract clouds within the inner regions of tropical cyclones are unlike those anywhere else in the atmosphere convective clouds contributing to cyclogenesis have rotational and deep intense updrafts but tend to have relatively weak downdrafts within the eyes of mature tropical cyclones stratus clouds top a boundary layer capped by subsidence an outward sloping eyewall cloud is controlled by adjustment of the vortex toward gradient wind balance which is maintained by a slantwise current transporting boundary layer air upward in a nearly conditionally symmetric neutral state this balance is intermittently upset by buoyancy arising from high moist static energy air entering the base of the eyewall because of the radial influx of low level air from the far environment supergradient wind in the eyewall zone and or small scale intense subvortices the latter contain strong erect updrafts graupel particles and large raindrops produced in the eyewall fall out relatively quickly while ice splinters left

intensity and structure changes during hurricane eyewall replacement cycles abstracta flight level aircraft dataset consisting of 79 atlantic basin hurricanes from 1977 to 2007 was used to develop an unprecedented climatology of inner core intensity and structure changes associated with eyewall replacement cycles ercs during an erc the inner core structure was found to undergo dramatic changes that result in an intensity oscillation and rapid broadening of the wind field concentrated temporal sampling by reconnaissance aircraft in 14 of the 79 hurricanes captured virtually the entire evolution of 24 erc events the analysis of this large dataset extends the phenomenological paradigm of ercs described in previous observational case studies by identifying and exploring three distinct phases of ercs intensification weakening and reintensification in general hurricanes intensify sometimes rapidly when outer wind maxima are first encountered by aircraft the mean locations of the inner and outer wind maximum at the start of an erc are 35 and 106 km from storm center respe

thermodynamic and kinematic influences on precipitation symmetry in sheared tropical cyclones bertha and cristobal 2014 abstractprior studies have shown an association between symmetrically distributed precipitation and tropical cyclone tc intensification although environmental vertical wind shear typically forces an asymmetric precipitation distribution in tcs the magnitude of this asymmetry can exhibit considerable variability even among tcs that experience similar shear magnitudes this observational study examines the thermodynamic and kinematic influences on precipitation symmetry in two such cases bertha and cristobal 2014 consistent with the impact of the shear both tcs exhibited a tilted vortex as well as a pronounced azimuthal asymmetry with the maximum precipitation occurring in the downshear left quadrant however bertha was characterized by more symmetrically distributed precipitation and relatively modest vertical motions while cristobal was characterized by more azimuthally confined precipitation and much more vigorous vertical motions observations showed three potential hindrances to precipitat

global electrodynamics observed during the initial and main phases of the july 1991 magnetic storm data acquired by seven fortuitously positioned satellites in the interplanetary medium the magnetosphere and the topside ionosphere as well as from numerous ground magnetometers have allowed us to follow the evolution of global currents and electric fields during the geomagnetic storm on july 8 9 1991 an interplanetary disturbance collided with the magnetosphere at 1636 ut on july 8th compressing the magnetopause inside of geostationary orbit for about 3 hours as observed by magnetometers on two goes satellites the resulting storm developed in four segments with a 7 hour lull separating the initial and main phases the initial phase was characterized by 1 an extensive dp 2 current system that produced an ae perturbation of 3500 nt with reporting stations on the dayside 2 a twenty fold increase in auroral electron fluxes and 3 the immediate appearance of electric fields in the inner magnetosphere the main phase intensification and earthward movement of the ring current are associated with southward turnings of the interplanetary magnetic field imf and a polar cap potential increase above 200 kv a significant fraction of the ring current growth was observed prior to the first of several substorms that occurred during the main and recovery phases the beginning of recovery was characterized by a diminution of the southward imf component the cross polar cap potential and magnetospheric electric fields it was also marked by a substorm onset considering the timing of dst modulations relative to substorm occurrence we conclude that during this magnetic storm the electric fields responsible for ring current transport energization were mostly associated with the dp 2 current system finally in the evening sector penetration electric fields of the initial and main phases led to the formation of upward moving equatorial plasma bubbles that were detected by two dmsp satellites in the topside ionosphere

buoyancy of convective vertical motions in the inner core of intense hurricanes part ii case studies abstract this is the second of two papers on the buoyancy of convective vertical motions in the inner core of intense hurricanes this paper uses extensive airborne radar dropwindsonde and flight level observations in hurricanes guillermo 1997 and georges 1998 to illustrate typical azimuthal distribution of buoyant convection and demonstrate that the low level eye can be an important source region for buoyant eyewall convection in both hurricanes eyewall vertical velocity and radar reflectivity are asymmetric and exhibit persistent relationships with the direction of the environmental vertical wind shear mesoscale vertical motions exhibit a wavenumber 1 structure with maximum ascent downshear and weak descent upshear the mesoscale reflectivity maxima are located left of shear buoyant eyewall updraft cores and transient convective scale reflectivity cells are predominantly downshear and left of shear most eyewall downdraft cores that transport significant mass downward are located upshear nega

spiral rainbands in a numerical simulation of hurricane bill 2009 part i structures and comparisons to observations abstractthis study examines spiral rainbands in a numerical simulation of hurricane bill 2009 this paper the first part of the study evaluates the structures of spiral rainbands and compares them to previous observations four types of spiral rainbands are identified principal secondary distant and inner rainbands principal rainbands tend to be stationary relative to the storm center while secondary rainbands are more transient and move around the storm center both principal and secondary rainbands are tilted radially outward with height and have many of the commonly observed kinematic features such as overturning secondary circulation and enhanced tangential velocity on their radially outward sides principal rainbands are bounded by very dry air on their radially outward sides distant rainbands are radially inward tilting convective features that have dense cold pools near the surface inner rainbands are made of shallow convection that appears to have originated from near the eyewall dif

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

inner core strength of atlantic tropical cyclones abstract the evolution of the wind field beyond the radius of maximum winds is studied for 18 atlantic tropical cyclones tcs with 989 research and reconnaissance flight legs inner core strength defined as the storm relative mean tangential wind from 65 to 140 km from the circulation center for a given flight leg is shown to be linearly correlated with tropical cyclone intensity inner core strengthening coincides with deepening but as a hurricane decays the inner core may exhibit a wider range of behavior during an eyewall replacement cycle inner core strength and intensity become out of phase inner core strength tends to be axisymmetric as no quadrant maintains a higher inner core strength than the other quadrants for more than a day increases of inner core strength occur throughout the entire 65 140 km radial distance and thus are not due to the higher winds found in rainbands alone the authors speculate that inner core strength being relatively close to the circulation center responds ef

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

surface pressure features of landfalling typhoon rainbands and their possible causes abstract this study uses temporally high resolution surface observations doppler radar and micro rain radar to document the finescale features of the two landfalling rainbands associated with typhoon longwang 2005 as they passed over northern taiwan the present case allows a unique opportunity to investigate well defined convectively active tropical cyclone rainbands over land in particular the surface pressure fluctuations observed during the passage of the two rainbands and their possible causes are explored the rainbands were predominantly convective in nature with embedded stratiform precipitation outside their inner outer edge analyses of surface observations show similar surface pressure fluctuations during the rainband s passage low high pressure with relatively strong weak cross band flow and warmer colder temperature was located inside the outer inner edge maximum minimum pressure perturbations were observed to be 1 5 1 mb with smaller magnitudes 0 4 mb outside th

from concentric eyewall to annular hurricane a numerical study with the cloud resolved wrf model 1 observations show that concentric eyewalls may lead to the formation of an annular hurricane ah but available radar and satellite images provide very limited information by using the cloud resolved weather research and forecasting wrf model the transformation from a non ah to an ah through a concentric eyewall replacement cycle is simulated under a resting environment the simulated hurricane experiences three distinct stages the formation of a secondary eyewall the eyewall replacement and the formation of an ah the simulated eyewall succession and accompanying intensity change are qualitatively consistent with observations the bottom up mixing of the elevated pv in the concentric eyewalls leads to the formation of an ah the time of the transition from concentric eyewalls to the ah is less than 24 hours suggesting that the concentric eyewall replacement is an efficient route to ah formation the results demonstrate potential capability of the wrf model to predict concentric eyewall cycles the formation of ahs and associated intensity changes

structural changes of an outer tropical cyclone rain band encountering the topography of northern taiwan this study utilized ground based doppler radar observations to document the detailed structures of an outer tropical cyclone rainband tcr of typhoon longwang 2005 as the rainband passed over the topography of northern taiwan on 1 october 2005 the tcr was oriented northeast southwest and was roughly parallel to the mountain barrier with a higher lower terrain height in its southern northern landfalling segment during the pre landfall stage the tcr was characterized by convective precipitation on its inner side where the front to rear flow met with the rear to front flow to lift air upward with overturning updraft like signatures significant relatively minor changes in the tcr s structures were evident in the southern northern landfalling segment during the landfalling stage in particular the southern landfalling segment exhibited a much stronger front to rear flow that passed through the region of the rainband resulting in the absence of low level organized convergence and a relatively disorganized nature of precipitation this structural change was shown to be closely related to a significant decrease in the cross barrier flow due to the orographic blocking that occurred as easterly ambient winds encountered local high mountains in the vicinity of the rainband segment as the tcr propagated over the western side of the major topography the low level rear to front flow reappeared due to the collapse of low level orographic blocking and the convergence between the front to rear flow and the rear to front flow tended to rebuild a well organized convective circulation along the rainband results from this case study provide insight into processes that contribute to rapid structural changes in a landfalling tcr over mountainous regions

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

buoyancy of convective vertical motions in the inner core of intense hurricanes part i general statistics abstract the buoyancy of hurricane convective vertical motions is studied using aircraft data from 175 radial legs collected in 14 intense hurricanes at four altitudes ranging from 1 5 to 5 5 km the data of each leg are initially filtered to separate convective scale features from background mesoscale structure convective vertical motion events called cores are identified using the criteria that the convective scale vertical velocity must exceed 1 0 m s 1 for at least 0 5 km a total of 620 updraft cores and 570 downdraft cores are included in the dataset total buoyancy is calculated from convective scale virtual potential temperature pressure and liquid water content using the mesoscale structure as the reference state core properties are summarized for the eyewall and rainband regions at each altitude characteristics of core average convective vertical velocity maximum convective vertical velocity and diameter are consistent with previous studies of hurricane convection most cores are superi

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

reflectivity ice scattering and lightning characteristics of hurricane eyewalls and rainbands part i quantitative description abstract covering december 1997 through december 1998 261 overpasses of 45 hurricanes by the tropical rainfall measuring mission trmm satellite are used to document the observed radar reflectivity values passive microwave ice scattering magnitudes and total lightning cloud to ground plus in cloud these parameters are interpreted as describing convective vigor or intensity with greater reflectivities particularly aloft greater ice scattering lower 85 and 37 ghz brightness temperatures and increased lightning frequency indicating more intense convection for each parameter the full distribution of values observed during the trmm satellite s first year is presented for specific regions properties of three regions of the hurricane eyewall inner rainband and outer rainband are treated separately and compared to other tropical oceanic and tropical continental precipitation systems reflectivity profiles and ice scattering signatures are found to be fairly similar for both hurricane and non

vortex rossby waves in a numerically simulated tropical cyclone part ii the role in tropical cyclone structure and intensity changes abstract in part i the author analyzed the asymmetric structure in the inner core of a numerically simulated tropical cyclone and found that the asymmetry near the eyewall in the mid lower troposphere is dominated by wavenumber 1 and 2 vortex rossby waves these waves are found to be well coupled with asymmetries in eyewall convection and thus may play an important role in the life cycle of a tropical cyclone in this paper analyses are extended to include the role of these vortex rossby waves in tropical cyclone structure and intensity changes the waves are found to transport angular momentum from the eyewall to the eye accelerating tangential winds in the eye at the expense of decelerating the tangential wind in the eyewall and thus they play an important role in the inner core dynamics of the tropical cyclone convection in the eyewall is enhanced between the downstream trough and upstream ridge in the vortex rossby waves but suppressed between the downstream ridge and upstream trough this close

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

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

surface cold pools in the outer rainbands of tropical storm hanna 2008 near landfall surface mesonet observations were used to document the structure of prominent cold pools associated with twoconvectiveouterrainbandsoftropicalstormhannaon5september2008 thedevelopingrainbandswere located 400 kmnorth ofthestormcenterastheycrossedthecarolinacoastlineandpassedover themesonet the combination of moderate cape moderate low level cross band vertical shear and dry midlevel air provided an environment supportive of surface cold pool formation and long lived quasi linear convection both rainbands exhibited multiple outward tilting convective cells and discrete line segments centered within a narrow zone of nearly continuous stratiform precipitation the mesonet observations provided a unique along and cross band perspective of discrete cold pools situated beneath andbehind the convection portions of each rainband prominentcold pools extended 40 80 km behind the rainband s leading edge and exhibited maximum potential temperature mixing ratio and equivalentpotentialtemperaturedeficitsof2 4 k 1 2 g kg 21 and4 10 k respectively inthecross banddirection convergence of storm relative inflow along the cold pool leading edge was coincident with a modest high pressure anomaly while inflow divergence prevailed through the cold pool and rainfall maxima several cold pools expanded along band while being advected downband by the prevailing cyclonic flow cold pool wakes were observed more than 50 km behind the rainband leading edge and up to 20 km downband from intense convection variations in cold pool intensitywerenotwell correlated with convectiveintensity rainfallrate or the degree of midlevel dryness implications of prominent cold pools on tropical cyclone convection size and intensity are discussed

the axisymmetric and asymmetric aspects of the secondary eyewall formation in a numerically simulated tropical cyclone under idealized conditions on an f plane abstractthe axisymmetric and asymmetric aspects of the secondary eyewall formation sef in a numerically simulated tropical cyclone tc under idealized conditions were analyzed consistent with p

spiral rainbands in a numerical simulation of hurricane bill 2009 part ii propagation of inner rainbands abstractthis is the second part of a study that examines spiral rainbands in a numerical simulation of hurricane bill 2009 this paper evaluates whether the propagation of inner rainbands in the hurricane bill simulation is consistent with previously proposed hypotheses results indicate that the propagation of inner rainbands is not consistent with gravity waves vortex rossby waves or squall lines an alternative hypothesis is offered arguing that inner rainbands are simply convective clouds that are advected by the rapidly rotating tropical cyclone wind field while being deformed into spiral shapes a summary and a discussion of the results of both parts i and ii are provided

kinematics and microphysics of convection in the outer rainband of typhoon nida 2016 revealed by polarimetric radar abstractthis study analyzes the microphysics of convective cells in an outer rainband of typhoon nida 2016 using data collected by a newly upgraded operational polarimetric radar in china the li

multiscale analysis of tropical cyclone kinematic structure from airborne doppler radar composites abstractthe multiscale inner core structure of mature tropical cyclones is presented via the use of composites of airborne doppler radar analyses the structure of the axisymmetric vortex and the convective and turbulent scale properties within this axisymmetric framework are shown to be consistent with many previous studies focusing on individual cases or using different airborne data sources on the vortex scale these structures include the primary and secondary circulations eyewall slope decay of the tangential wind with height low level inflow layer and region of enhanced outflow radial variation of convective and stratiform reflectivity eyewall vorticity and divergence fields and rainband signatures in the radial wind vertical velocity vorticity and divergence composite mean and variance fields statistics of convective scale fields and how they vary as a function of proximity to the radius of maximum wind show that the inner eyewall edge is associated with stronger updrafts and higher refl

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