bioturbation influence on reservoir quality a case study from the cretaceous ben nevis formation jeanne d arc basin offshore newfoundland canada the delineation ben nevis l 55 well located in the hebron ben nevis field offshore newfoundland targeted the cretaceous ben nevis formation in the petroleum rich jeanne d arc basin this case study focuses on the bioturbated net pay horizons and assesses the importance of animal sediment interactions in controlling the porosity and permeability of sandstone reservoir intervals our data reveal that bioturbation can either reduce permeability and porosity by as much as approximately 33 or enhance it by up to 600 dependent on burrow type and behavior of the trace making organism the net pay interval in the cored interval of ben nevis l 55 is characterized by ophiomorpha dominated ichnofabrics the action of bioturbators can be classified in terms of sediment mixing sediment cleaning sediment packing and pipe work building strategies bioturbation has the potential to 1 increase isotropy or uniformity of grain size by destroying sedimentary laminae through burrow homogenization or 2 decrease isotropy by selectively sorting grains into burrow lining and fill by grain size and through creation of open burrow systems filled with later sediments of differing character to the host sediment the petrophysical characteristics of the reservoir facies are highly dependent on trace fossil morphology presence or absence of burrow linings nature of burrow fills burrow size and bioturbation intensity mudstone rich facies and ichnofabrics containing mudstone filled and or lined burrows e g ophiomorpha and clusters of chondrites have the net effect of permeability reduction in contrast permeability enhancement is documented from muddy sandstone facies with clean sand filled burrows e g thalassinoides and clean sandstones with burrow mottled or diffuse to massive textures

parametric representation of the primary hurricane vortex part i observations and evaluation of the holland 1980 model although numerical models are essential to hurricane forecasting many other applications require only statistical depiction of the wind distribution in holland s 1980 parametric profile radius of maximum wind maximum wind and a measure of the profile width describe the radial variation of the axisymmetric wind variants of the holland profile are used to predict insurance underwriting risk ocean response and storm surge inundation since these calculations guide high stakes financial and emergency managment decisions it is logical to test them against observations the hurricane research division s flight level database archives observations were obtained by noaa and u s air force reserve aircraft the data considered here are winds and geopotential heights observed during 606 lower and midtropospheric flights into atlantic and eastern pacific tropical cyclones during 1977 2000 the 493 profiles that meet quality control criteria are seasonally geographically representative least squares fits of the holland model to these data provide evaluation of the parameters distributions and critical examination of the profile s realism individual fitted profiles differ from the observations in a consistent pattern the areas of strong winds in the eyewall and of nearly calm winds at the vortex center are too wide beyond 2 or 3 times the eye radius the wind decreases too rapidly with distance from the center although the average bias in fitted profiles is 1ms 21 the root mean square error is 4 2 m s 21 5 2 m s21 for independent data maximum winds estimated from the fitted holland profile height wind relation average 2 5 m s 21 too strong with an rms error of 6 5 m s 21 the pattern of too strong wind spread over too much real estate exaggerates the occurrence of winds stronger than 50 m s 21 by 50

the governing dynamics of the secondary eyewall formation of typhoon sinlaku 2008 abstractthrough successful convection permitting simulations of typhoon sinlaku 2008 using a high resolution nonhydrostatic model this study examines the role of peripheral convection in the storm s secondary eyewall formation sef and its eyewall replacement cycle erc the study demonstrates that before sef the simulated storm intensifies via an expansion of the tangential winds and an increase in the boundary layer inflow which are accompanied by peripheral convective cells outside the primary eyewall these convective cells which initially formed in the outer rainbands under favorable environmental conditions and move in an inward spiral play a crucial role in the formation of the secondary eyewall it is hypothesized that sef and erc ultimately arise from the convective heating released from the inward moving rainbands the balanced response in the transverse circulation and the unbalanced dynamics in the atmospheric boundary layer along with the positive feedback between these processes

the impact of horizontal grid spacing on the microphysical and kinematic structures of strong tropical cyclones simulated with the wrf arw model abstract using the advanced weather research and forecasting numerical model the impact of horizontal grid spacing on the microphysical and kinematic structure of a numerically simulated tropical cyclone tc and their relationship to storm intensity was investigated with a set of five numerical simulations using input data for the case of hurricane rita 2005 the horizontal grid spacing of the parent domain was systematically changed such that the horizontal grid spacing of the inner nest varied from 1 to 5 km by an increment of 1 km this while keeping geographical dimensions of the domains identical within this small range of horizontal grid spacing the morphology of the simulated storms and the evolution of the kinematic and microphysics field showed noteworthy differences as grid spacing increased the model produced a wider more tilted eyewall a larger radius of maximum winds and higher amplitude low wavenumber eyewall asymmetries the coarser resolution simulations also produced larger v

an analysis of hurricane opal s forecast track errors using quasigeostrophic potential vorticity inversion abstract hurricane opal s landfall in october 1995 forms the basis of a serious hurricane forecast problem the potential for hurricane conditions over land with insufficient warning time official national hurricane center nhc a division of the tropical prediction center forecasts predicted landfall and passage inland over the eastern united states at a later time than observed because of underestimation of the northward component of the steering flow by the national centers for environmental prediction s ncep operational models and other hurricane track models the goal of this paper is to isolate the cause of the poor forecast of meridional storm motion in ncep s early eta model by using quasigeostrophic potential vorticity qgpv inversion qgpv inversion permits decomposition of the steering flow into contributions from different synoptic scale features the inversion procedure is applied to the eta analysis and 48 h eta forecast valid at 1200 utc 5 october 1995 analyses from the european centre

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

numerical study of a typhoon with a large eye model simulation and verification abstract typhoon winnie 1997 was the fourth supertyphoon in the western north pacific in 1997 in its mature stage an outer eyewall consisting of deep convection with a diameter of 370 km was observed by satellite and radar within this unusually large outer eyewall existed an inner eyewall which consisted of a ring of shallow clouds with a diameter of 50 km in this study typhoon winnie is simulated using a nested grid version of the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 with an inner grid length of 9 km the model reproduces an outer cloud eyewall with a diameter of 350 km the simulated radar reflectivity and hourly precipitation are verified with satellite microwave infrared and cloud brightness temperature images analysis of the model results indicates that the large outer eyewall in many ways possesses the structure of a typical hurricane eyewall this includes strong tangential winds and radial inflow out

multiscale interactions in the life cycle of a tropical cyclone simulated in a global cloud system resolving model part ii system scale and mesoscale processes abstract the life cycle of tropical storm isobel was simulated reasonably well in the nonhydrostatic icosahedral atmospheric model nicam a global cloud system resolving model the evolution of the large scale circulation and the storm scale structure change was discussed in part i both the mesoscale and system scale processes in the life cycle of the simulated isobel are documented in this paper in the preconditioned favorable environment over the java sea mesoscale convective vortices model mcvs developed in the mesoscale convective systems mcss and convective towers with cyclonic potential vorticity pv anomalies throughout the troposphere model vortical hot towers vhts appeared in the model mcvs multiple model vhts strengthened cyclonic pv in the interior of the model mcv and led to the formation of an upright monolithic pv core at the center of the concentric mcv primary vortex enhancement as the monolithic pv core with a warm core developed near the circulation center the intensif

a modeling study of typhoon nari 2001 at landfall 2 structural changes and terrain induced asymmetries 1 in this study a series of model output diagnoses using the cloud resolving simulations of typhoon nari 2001 with or without taiwan topography is performed to gain insight into the landfall characteristics of the storm as it moves across taiwan island various kinematic and precipitation features prior to and after landfall are examined with a focus on the dynamic effects of taiwan s high topography upon the generation of nari s asymmetric structures results show that tangential winds weaken whereas the low level inflows and midlevel outflows increase after landfall due to the increased friction and terrain blocking meanwhile the eye wall updrafts exhibit more cellular structures and tend to tilt more outward with height over the high topography however nari s primary and secondary circulations are stronger in the presence of terrain than those without terrain the radii of the maximum winds and the eye wall updrafts could contract further after landfall with more pronounced contraction occurring in the portion of the eye wall where more terrain retardation and blocking are present in particular the high topography allows the elevated low equivalent potential temperature e air over the rugged terrain to intrude into the inner core region causing the breakdown of the eye wall it is concluded that the interaction of nari s circulations with the elevated low e air combined with topographical effects accounts for most of the asymmetrical structures after landfall

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

structure of the eye and eyewall of hurricane hugo 1989 on 15 september 1989 one of noaa s wp 3d research aircraft n42rf lower aircraft la penetrated the eyewall of hurricane hugo the aircraft had an engine fail in severe turbulence while passing the radius of maximum wind and before entering the eye at 450 m altitude after the aircraft returned to controlled flight within the 7 km radius eye it gained altitude gradually as it orbited in the eye observations taken during this period provide an updated model of the inner core structure of an intense hurricane and suggest that la penetrated an intense cyclonic vorticity maximum adjacent to the strongest convection in the eyewall eyewall vorticity maximum evm this evm was distinct from the vortex scale cyclonic circulation observed to orbit within the eye three times during the 1 h that la circled in the eye at the time hugo had been deepening rapidly for 12 h the maximum flight level tangential wind was 89 m s 1 at a radius of 12 5 km however the primary vortex peak tangential wind derived from a 100 s filter of the flight level data was estimated to be 70 m s 1 also at 12 5 km radius the primary vortex tangential wind was in approximate gradient wind balance was characterized by a peak in angular velocity just inside the radius of maximum wind and had an annular vorticity structure slightly interior to the angular velocity maximum the evm along the aircraft s track was roughly 1 km in diameter with a peak cyclonic vorticity of 1 25 10 1 s 1 the larger circulation center with a diameter 15 km was observed within the eye and exhibited an average orbital period of 19 min this period is about the same as that of the angular velocity maximum of the axisymmetric mean vortex and is in reasonable agreement with recent theoretical and model predictions of a persistent trochoidal wobble of circulation centers in mature hurricane like vortices this study is the first with in situ documentation of these vortical entities which were recently hypothesized to be elements of a lower tropospheric eye eyewall mixing mechanism that supports strong storms

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

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

prediction and diagnosis of the motion and rapid intensification of typhoon sinlaku during tropical cyclone structure experiment 2008 tcs08 abstractthe impact of initial structure on storm evolution is examined for the case of a tropical storm entering rapid intensification at the onset of rapid intensification satellite cloud signatures suggest that the structural organization of typhoon sinlaku 2008 was dominated by a primary band of convection present at outer radii the development of the eyewall subsequently occurred within this band of deep convection numerical forecasts of sinlaku are initialized at 15 and 5 km resolution using a broad range of vortex scales at a time when the storm was still weak and its structure not clearly defined evidence is presented that beta propagation played a key role in changing the storm s motion under weak environmental steering it is found that the track forecast improves over the period when beta propagation is prominent if the vortex is initialized with a large radius of maximum wind rmw corresponding with the primary outer cloud band the initial vortex structure is also suggested to play a

rapid filamentation zone in a numerically simulated tropical cyclone abstract in a recent study rozoff et al proposed a possible mechanism to explain the formation and maintenance of the weak echo annulus or moat outside of the primary eyewall of a tropical cyclone observed in radar images by this mechanism the moat is determined to be a region of the strain dominated flow outside of the radius of maximum wind in which essentially all fields are filamented and deep convection is hypothesized to be highly distorted and even suppressed this strain dominated region is defined as the rapid filamentation zone wherein the filamentation time is shorter than the overturning time of deep convection an attempt has been made in this study to test the hypothesis in a full physics tropical cyclone model under idealized conditions and to extend the concept to the study of the inner core dynamics of tropical cyclones the foci of this paper are the evolution of the rapid filamentation zone during the storm intensification the potential roles of rapid filamentation in the organiz

the role of sedimentation history and lithology on fluid flow and reactions in off axis hydrothermal systems a perspective from the troodos ophiolite abstract off axis hydrothermal systems are thought to carry globally significant chemical fluxes but different ocean crust sections show widely differing extents of alteration making the quantification of these fluxes complex with the aim of better understanding the origin of this diversity in alteration extent we have studied two sections of the lava pile in the troodos ophiolite with distinct sedimentation history and volcanic architecture the akaki section is dominated by pillow lavas and the oldest sediments overlying the crust are 20 myr younger than the ophiolite here there is a 300 m thick zone at the top of the lavas that is enriched in co2 and alkali elements and has high 87sr 86sr and 7li these features indicate extensive chemical exchange with seawater in contrast to the akaki area the onophrious section is dominated by sheet flows and the oldest sediments are of the same age as the ophiolite here the co2 and alkali element enriched zone is much thinner

the variability and predictability of axisymmetric hurricanes in statistical equilibrium abstractthe variability and predictability of axisymmetric hurricanes are determined from a 500 day numerical simulation of a tropical cyclone in statistical equilibrium by design the solution is independent of the initial conditions and environmental variability which isolates the intrinsic axisymmetric hurricane variability variability near the radius of maximum wind is dominated by two patterns one associated primarily with radial shifts of the maximum wind and one primarily with intensity change at the time mean radius of maximum wind these patterns are linked to convective bands that originate more than 100 km from the storm center and propagate inward bands approaching the storm produce eyewall replacement cycles with an increase in storm intensity as the secondary eyewall contracts radially inward a dominant time period of 4 8 days is found for the convective bands which is hypothesized to be determined by the time scale over which subsidence from previous bands suppresses convection a

mechanisms for the generation of mesoscale vorticity features in tropical cyclone rainbands a high resolution tropical cyclone model with explicit cloud microphysics has been used to investigate the dynamics and energetics of tropical cyclone rainbands analysis of the vorticity interactions that occur within the simulated rainbands demonstrates that couplets of cyclonic anticyclonic mesovortices can be produced in outer bands the primary source of this vorticity is the upward tilting of system generated horizontal vorticity by diabatic heating gradients the vertical heating gradient in the stratiform cloud also creates a potential vorticity pv dipole that accelerates the tangential flow and develops a midlevel jet the strength of the jet is enhanced by the vortex pair that is oriented radially across the rainband the fourier decomposition of the absolute vorticity field shows two counterpropagating vortex rossby waves associated with the rainband the wave located on the inner side of the band transports energy toward the vortex center the outer wave is made up of high wavenumbers and uses the vorticity gradients generated by the rainband the results support the hypothesis that the heating profile in the stratiform regions of rainbands generates cyclonic pv across the freezing level which develops a midlevel jet this mechanism creates a vorticity gradient that enables the propagation of vortex rossby waves that could allow the rainbands to interact with the mean flow and potentially influence the evolution of the storm by contributing to the symmetric component of vorticity and the development of secondary eyewalls

an estimation of turbulent characteristics in the low level region of intense hurricanes allen 1980 and hugo 1989 this study analyzes the flight level data collected by research aircraft that penetrated the eyewalls of category 5 hurricane hugo 1989 and category 4 hurricane allen 1980 between 1 km and the sea surface estimates of turbulent momentum flux turbulent kinetic energy tke and vertical eddy diffusivity are obtained before and during the eyewall penetrations spatial scales of turbulent eddies are determined through a spectral analysis the turbulence parameters estimated for the eyewall penetration leg are found to be nearly an order of magnitude larger than those for the leg outside the eyewall at similar altitudes in the low level intense eyewall region the horizontal length scale of the dominant turbulent eddies is found to be between 500 and 3000 m and the corresponding vertical length scale is approximately 100 m the results suggest also that it is unwise to include eyewall vorticity maxima evm in the turbulence parameter estimation because the evms are likely to be quasi two dimensional vortex structures that are embedded within the three dimensional turbulence on the inside edge of the eyewall this studyis afirstattempt at estimatingthe characteristics of turbulent flow in the low leveltroposphereof an intense eyewall using in situ aircraft observations the authors believe that the results can offer useful guidance in numerical weather prediction efforts aimed at improving the forecast of hurricane intensity because of the small sample size analyzed in this study further analyses of the turbulent characteristics in the high wind region of hurricanes are imperative

how does the boundary layer contribute to eyewall replacement cycles in axisymmetric tropical cyclones abstractthree diagnostic models of the axisymmetric tropical cyclone boundary layer with different levels of approximation are applied to the problem of tropical cyclones with concentric eyewalls the outer eyewall is shown to have an inherently stronger frictional updraft than the inner because it is in an environment of lower vorticity similarly a relatively weak local enhancement of the radial vorticity gradient outside the primary radius of maximum winds can produce a significant frictional updraft even if there is no outer wind maximum based on these results it is proposed that the boundary layer contributes to the formation of outer eyewalls through a positive feedback among the local enhancement of the radial vorticity gradient the frictional updraft and convection the friction induced secondary circulation associated with the inner eyewall is shown to weaken as the outer wind maximum strengthens and or contracts so boundary layer processes will contribute along with the heating induced

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

comments on convectively generated potential vorticity in rainbands and formation of the secondary eyewall in hurricane rita of 2005 abstractin a previous paper judt and chen propose that secondary eyewall formation can be the result of the accumulation of convectively generated potential vorticity in the rainbands they argue that secondary potential vorticity maxima precede the development of the secondary wind maximum and conclude that vortex rossby waves do not contribute to the formation of the secondary eyewall amidst examination of their thought provoking study some questions arose regarding their methodology interpretation and portrayal of previous literature here the authors inquire about aspects of the methodology for diagnosing vortex rossby waves and assessing their impact on their simulation inaccuracies in the literature review are noted and further analysis of existing three dimensional full physics numerical hurricane integrations that exhibit canonical secondary eyewalls are encouraged

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

rapid development of the tropical cyclone warm core this paper presents a simple theoretical argument to isolate the conditions under which a tropical cyclone can rapidly develop a warm core thermal structure and subsequently approach a steady state the theoretical argument is based on the balanced vortex model and in particular on the associated transverse circulation equation and the geopotential tendency equation these second order partial differential equations contain the diabatic forcing and three spatially varying coefficients the static stability a the baroclinity b and the inertial stability c thus the transverse circulation and the temperature tendency in a tropical vortex depend not only on the diabatic forcing but also on the spatial distributions of a b and c experience shows that the large radial variations of c are typically the most important effect under certain simplifying assumptions as to the vertical structure of the diabatic forcing and the spatial variability of a b and c the transverse circulation equation and the geopotential tendency equation can be solved via separation of variables the resultingradialstructureequationsretainthedynamicallyimportantradialvariationofcandcanbe solvedin terms of green s functions these analytical solutions show that the vortex response to a delta function in the diabatic heating depends critically on whether the heating occurs in the low inertial stability region outside the radius of maximum wind or in the high inertial stability region inside the radius of maximum wind this resultsuggeststhatrapidintensification isfavoredforstormsthathaveat leastsome oftheeyewallconvection inside the radius of maximum wind the development of an eye partially removes diabatic heating from the high inertial stability region of the storm center however rapid intensification may continue if the eyewall heating continues to become more efficient as the warm core matures and static stability increases over the inner core conditions there become less favorable for deep upright convection and the storm tends to approach a steady state

reply to comments on convectively generated potential vorticity in rainbands and formation of the secondary eyewall in hurricane rita of 2005 terwey et al 2013 hereafter t13 have posted a few questions regarding the analysis of vortex rossby waves vrws and the role of vrws in secondary eyewall formation in judt and chen 2010 hereafter jc10 one of the main complaints in t13 is about a point made in jc10 that a numerical simulation of eyewall replacement and related intensity change shown in terwey and montgomery 2008 hereafter tm08 is unphysical and inconsistent with observations we welcome the opportunity to respond to the questions raised by t13 and will further demonstrate the aforementioned inconsistency between the model simulation of tm08 and observations by willoughby et al 1982 and more recently bell et al 2012

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

reexamining the near core radial structure of the tropical cyclone primary circulation implications for vortex resiliency abstract recent theoretical studies based on vortex rossby wave vrw dynamics have established the importance of the radial structure of the primary circulation in the response of tropical cyclone tc like vortices to ambient vertical wind shear linear vrw theory suggests in particular that the degree of broadness of the primary circulation in the near core region beyond the radius of maximum wind strongly influences whether a tilted tc vortex will realign and resist vertical shear or tilt over and shear apart fully nonlinear numerical simulations have verified that the vortex resiliency is indeed sensitive to the initial radial structure of the idealized vortex this raises the question of how well the true nature of a tc s primary circulation is represented by idealized vortices that are commonly used in some theoretical studies in this paper the swirling wind structure of tcs is reexamined by utilizing flight level observations collected from atlantic and eastern pacific storms during 1977 2

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

the kinematic structure of a hurricane with sea level pressure less than 900 mb abstract a national oceanic and atmospheric administration aircraft recorded the first doppler radar data in a tropical cyclone with a minimum sea level pressure mslp 50 m s 1 extended to 12 km higher than has been reported in previous hurricanes the inner eyewall contained weak

tropical cyclone kinematic structure retrieved from single doppler radar observations part iii evolution and structures of typhoon alex 1987 abstract this paper is the third of a series that focuses on the applications of the ground based velocity track display gbvtd technique and the gbvtd simplex center finding algorithm developed in the previous two papers to a real tropical cyclone tc the evolution and structure of typhoon alex 1987 including full tangential winds mean radial winds one component of the mean flow and their derived axisymmetric angular momentum and perturbation pressure fields are reconstructed from 16 volume scans 6 5 h of data with a 2 h gap from the civil aeronautic administration caa doppler radar while typhoon alex moved across the mountainous area in northern taiwan this analysis retrieves a plausible and physically consistent three dimensional primary circulation of a landfalling tc using a single ground based doppler radar highly asymmetric wind structures were resolved by the gbvtd technique where the maximum relative tangential wind at z 2 km evolved from 52 m s 1 before landfall to less than

on the secondary eyewall formation of hurricane edouard 2014 abstracta first observationally based estimation of departures from gradient wind balance during secondary eyewall formation is presented the study is based on the atlantic hurricane edouard 2014 this storm was observed during the national aeronautics and space administration s nasa hurricane and severe storm sentinel hs3 experiment a field campaign conducted in collaboration with the national oceanic and atmospheric administration noaa a total of 135 dropsondes are analyzed in two separate time periods one named the secondary eyewall formation period and the other one referred to as the decaying double eyewalled storm period during the secondary eyewall formation period a time when the storm was observed to have only one eyewall the diagnosed agradient force has a secondary maximum that coincides with the radial location of the secondary eyewall observed in the second period of study the maximum spinup tendency of the radial influx of absolute vertical vorticity is within the boundary la

a piecewise potential vorticity inversion algorithm and its application to hurricane inner core anomalies in this study a piecewise potential vorticity pv inversion algorithm for an arbitrary number of pv pieces is developed by extending wang and zhang s pv inversion scheme and then the nonlinear responses to various types and magnitudes of axisymmetric pv anomalies pvas in hurricane vortices are investigated results show that the upper and lower level pvas in the eye help enhance cyclonic flows in the eyewall but with weak vertical interactions between them the balanced flows corresponding to the pvas in the eyewall appear to account for a substantial portion of the warm core and the minimum pressure in the eye however the lower level pva in the eye inversionlayer is more effective in contributing to the hurricane intensitythan that at the upper levels results also show that the radius of the balanced response of pvas is more sensitive tothemeanvortexintensitythantheverticalpenetration theweakerthemeanvortexintensity thelargerthe radius of the influence will be similar behaviors are also observed for the quasi balanced secondary circulations thatis givenadiabaticheatingprofilein theeyewall theweakerthebackgroundvortexor thepvas the stronger the secondary circulations will be it is found that the development of an outer eyewall or spiral rainbands could be inimical to the inner eyewall in several ways such as by 1 adding an anticyclonic flow inside to offset the cyclonic rotation of the inner eyewall 2 enhancing a ring of a lower pressure zone underneath to broaden the inner core lower pressureregion 3 inducingan inward outward radialflowoutside inside in thepbl upperlevel to block the energy supply to outflow of the inner eyewall and 4 generating subsidence between the two eyewalls to suppress the development of deep convection in the inner eyewall

eye excess energy and the rapid intensification of hurricane lili 2002 abstract over 4 5 days noaa and u s air force personnel in reconnaissance aircraft deployed 44 global positioning system dropwindsondes gps sondes in the eye of hurricane lili 2002 the vertical profiles derived from these gps sondes were used to determine the evolution of the height of the inversion presence and height of the hub cloud the height of the lifted condensation layer and the depth of the mixed layer as lili deepened underwent rapid intensification ri and eventually rapid decay the lower portion of the eye moistened and the lapse rate became moist adiabatic the inversion layer rose as lili intensified and then quickly fell over 1500 m at the beginning of ri comparison of the equivalent potential temperature e of the eye with that in the eyewall revealed that like many other hurricanes the eye was a reservoir for the warmest e the authors define a variable called eye excess energy that is a function of the difference in e between the eye and the eyewall and the depth over

long lived concentric eyewalls in typhoon soulik 2013 abstractthe authors report on western north pacific typhoon soulik 2013 which had two anomalously long lived concentric eyewall ce episodes as identified from microwave satellite data radar data and total precipitable water data the first period was 25 h long and occurred while soulik was at category 4 intensity the second period was 34 h long and occurred when soulik was at category 2 intensity a large moat and outer eyewall width were present in both ce periods and there was a significant contraction of the inner eyewall radius from the first period to the second period the typhoon intensity decrease was partially due to encountering unfavorable environmental conditions of low ocean heat content and dry air even though inner eyewall contraction would generally support intensification the t vmax diagram where t is the brightness temperature and vmax is the best track estimated intensity is used to analyze the time sequence of the intensity and convective activity the convective activity

vertical structure of tropical cyclones with concentric eyewalls as seen by the trmm precipitation radar ten years of data from the tropical rainfall measurement mission satellite s precipitation radar are analyzed to determinethe typical vertical structure of the concentric eyewalls of tropical cyclones undergoing eyewall replacement the vertical structure of the secondary outer eyewall is different from the primary inner eyewall and also different from the eyewall of single eyewall storms the upper troposphere portions of the outer eyewalls are like the rainbands from which they evolve their lower tropospheric portions are more intense and more uniform than rainbands of single eyewall storms suggesting that these secondary eyewalls are forming from rainbands undergoing axisymmetrization and building from below the inner concentric eyewalls are more strongly affected by shear than are the eyewalls of single eyewall storms while the outer eyewalls are relativelyunaffectedby shear which suggeststhe outereyewall is amplifyingthe shearinduced asymmetry of the inner eyewall

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

a multiscale numerical study of hurricane andrew 1992 part ii kinematics and inner core structures despite considerable research understanding of the temporal evolution of the inner core structures of hurricanes is very limited owing to the lack of continuous high resolution observational data of a storm in this study the results of a 72 h explicit simulation of hurricane andrew 1992 with a grid size of 6 km are examined to explore the inner core axisymmetric and asymmetric structures of the storm during its rapid deepening stage based on the simulation a conceptual model of the axisymmetric structures of the storm is proposed most of the proposed structures confirm previous observations the main ingredients include a main inflow outflow in the boundary layer upper troposphere with little radial flow in between a divergent slantwise ascent in the eyewall a penetrative dry downdraft at the inner edge of the eyewall and a general weak subsiding motion in the eye with typical warming drying above an inversion located near an altitude of about 2 3 km the storm deepens as the axes of these features contract it is found that the inversion divides the eye of the hurricane vertically into two parts with a deep layer of warm dry air above and a shallow pool of warm moist air below the air aloft descends at an average rate of 5c m s 21 and has a residency time of several days in contrast the warm moist pool consists of air from the main inflow and penetrative downdrafts offset somewhat by the air streaming in a returning outflow into the eyewall in the lowest 2 km it is subject to the influence of the upward heat and moisture fluxes over the underlying warm ocean the warm moist pool appears to play an important role in supplying high ue air for deep convective development in the eyewall the penetrative downdraft is dry and originates from the return inflow in the upper troposphere and it is driven by sublimative evaporative cooling under the influence of the asymmetric radial inflow of dry cold air in the midtroposphere it penetrates to the bottom of the eye azimuthally downshear with a width often greater than 100 km in a radially narrow zone along the slantwise inner edge of the eyewall it is further shown that all the meteorological fields are highly asymmetric whereas the storm scale flow features a source sink couplet in the boundary layer and dual gyres aloft the inner core structures exhibit alternative radial inflow and outflow and a series of inhomogeneous updrafts and downdrafts all the fields tilt more or less with height radially outward and azimuthally downshear furthermore pronounced fluctuations of air motion are found in both the eye and the eyewall sometimes a deep layer of upward motion appears at the center of the eye all these features contribute to the trochoidal oscillation of the storm track and movement the main steering appears to be located at the midtroposphere 4 5 km and the deep layer mean winds represent well the movement of the hurricane

concentric eye walls secondary wind maxima and the evolution of the hurricane vortex abstract research aircraft observations in recent hurricanes support the model of shapiro and willoughby 1982 for the tropical cyclone s response to circularly symmetric convective heat sources convective rings in both nature and the numerical model the tangential wind commonly increases rapidly just inside the radius of maximum wind and decreases inside the eye near the central axis of the vortex thus both secondary outer wind maxima and eyewall wind maxima often contract as they intensify this response is independent of the horizontal spatial scale of the maximum an outer maximum is frequently observed to constrict about a pre existing eye and replace it this chain of events often coincides with a weakening or at least a pause in intensification of the vortex as a whole the concentric eye phenomenon is a common but by no means universal feature of tropical cyclones it is most frequently observed in intense highly symmetric systems

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 role of polygonal eyewalls in rapid intensification of typhoon megi 2010 abstracthigh resolution numerical experiments for typhoon megi 2010 in the western north pacific are conducted using the advanced research version of the weather research and forecasting wrf mo

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

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

outer rainbands driven secondary eyewall formation of tropical cyclones abstractsecondary eyewall formation sef could be considered as the aggregation of a convective ring coupling with a tangential wind maximum outside the primary eyewall of a tropical cyclone tc

some dynamical aspects of tropical cyclone concentric eyewalls the intensification of tropical cyclones is often interrupted by an eyewall replacement cycle a process in which an outer eyewall forms contracts and replaces an inner eyewall the radial distributions of inertial stability and diabatic heating change during such events impacting the transverse circulation to examine the effects of such changes an analytical solution of the transverse circulation equation associated with a balanced vortex model is derived using a parameterization that distinguishes five radial regions subdividing the domain by each region s values of inertial stability and diabatic heating these regions define the eye inner eyewall moat outer eyewall and far field in mature concentric eyewall situations the solutions do not support the hypothesis that the inner eyewall collapses as a direct result of subsidence from the outer eyewall however the results suggest subsidence and warming temperatures in the moat are governed by enhanced inertial stability associated with a strengthening outer eyewall the model solutions also illustrate how the diabatic heating in the inner eyewall imbedded in a region of high inertial stability induces larger temperature tendencies than the diabatic heating in the outer eyewall which borders the far field region of low inertial stability thus as the inner eyewall dies the storm temporarily loses its ability to produce an intense localized warm region this ability is restored during the contraction and intensification of the outer eyewall these results provide a partial dynamical explanation of how an eyewall replacement cycle can act as a temporary brake on tropical cyclone intensification copyright 2008 royal meteorological society

secondary eyewall formation and concentric eyewall replacement in association with increased low level inner core diabatic cooling abstractthe role of increased diabatic cooling in secondary eyewall formation sef and eyewall replacement cycle erc is examined using idealized numerical simulation the experiment with the low

on the interaction of tropical cyclone scale vortices ii discrete vortex patches the interaction of vortex patches in relation to the observed scales and features reported in part i of this paper is investigated it is found that the initial approach of compound vortices such as tropical cyclones arises from distortion of their weaker outer vorticity fields care needs to be taken in applying simple concepts such as the propagation of each vortex on the gradient of its neighbour for similar vortices the initial interaction consists of mutual orbit and approach with only minor fluctuations in shape once the vortices approach to within a critical separation distance rapid merger occurs a simplified expression for this critical distance is derived and it indicates that binary tropical cyclones must approach to within 150 300 km before merger of the cores can occur when vortices have substantial differences in size or intensity the smaller weaker system shears into the outer circulation of the other and no core merger occurs it is suggested that this is typical of the interaction between tropical cyclones and both the monsoon trough and embedded mesoscale convective complexes the motion of interacting vortices consists largely of a mutual orbit which scales according to their relative sizes and intensities an important finding however is that higher frequency meanders may develop this indicates that a tropical cyclone interacting with a monsoonal shear zone may develop internal asymmetries and a trochoidal oscillations as a direct result of such interaction further weak mesoscale vortices within the cyclone circulation may continue to cause a track meander long after they have been sheared beyond the resolving capacity of atmospheric observations

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

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

structure and formation of an annular hurricane simulated in a fully compressible nonhydrostatic model tcm4 abstract the structure and formation of an annular hurricane simulated in a fully compressible nonhydrostatic tropical cyclone model tcm4 are analyzed the model is initialized with an axisymmetric vortex on an f plane in a quiescent environment and thus the transition from the nonannular hurricane to the annular hurricane is attributed to the internal dynamics the simulated annular hurricane has all characteristics of those recently documented by knaff et al from satellite observations quasi axisymmetric structure large eye and wide eyewall high intensity and suppressed major spiral rainbands a striking feature of the simulated annular hurricane is its large outward tilt of the wide eyewall which is critical to the quasi steady high intensity and is responsible for the maintenance of the large size of the eye and eyewall of the storm although the annular hurricane has a quasi axisymmetric structure marked low wavenumber asymmetries exist in the eyewall region the formation of the simulated a

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

on the distribution of subsidence in the hurricane eye two hurricane eye features that have yet to be adequately explained are the clear air moat that forms at the outer edge of the eye and the hub cloud that forms near the circulation centre to investigate whether these features can be explained by the spatial distribution of the subsidence field we have derived an analytical solution of the sawyer eliassen transverse circulation equation for a three region approximation with an unforced central eye region of intermediate or high inertial stability a diabatically forced eyewall region of high inertial stability and an unforced far field of low inertial stability this analytical solution isolates the conditions under which the subsidence is concentrated near the edge of the eye the crucial parameter is the dimensionless dynamical radius of the eye defined as the physical radius of the eye divided by the characteristic rossby length in the eye when this dimensionless dynamical radius is less than 0 6 there is less than 10 horizontal variation in the subsidence rate across the eye when it is greater than 1 8 the subsidence rate at the edge of the eye is more than twice as strong as at the centre of the eye when subsidence is concentrated at the edge of the eye the largest temperature anomalies occur near there rather than at the vortex centre this warm ring structure as opposed to a warm core structure is often observed in the lower troposphere of intense hurricanes copyright 2007 royal meteorological society

single doppler radar observation of the concentric eyewall in typhoon saomai 2006 near landfall 1 landfalling typhoon saomai 2006 was observed by the cinrad wsr 98d radar on the southeast coast of china this study documents the formation and evolution of a concentric eyewall episode using the axisymmetric circulation derived from the ground based velocity track display technique saomai s outer eyewall formed after reaching its peak intensity 5 hours before landfall updraft tangential wind maximum and shallow low level inflow coincided with the high reflectivity and voriticity ring in both inner and outer eyewalls surrounding a moat region characterized by weak downward motion and lower reflectivity the subsidence and rain free moat region between the two eyewalls was filled with rain and upward motion prior to landfall indicating a breakdown in the outer eyewall which was a barrier to radial inflow meanwhile the outer vorticity maximum flattened and the central pressure dropped 9 hpa the eyewall replacement cycle didn t complete probably due to the landfall

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

secondary eyewall formation and eyewall replacement cycles in a simulated hurricane effect of the net radial force in the hurricane boundary layer abstractmultiple secondary eyewall formations sefs and eyewall replacement cycles ercs are simulated with the fifth generation pennsylvania state university psu national center for atmospheric research ncar mesoscale model mm5 at horizontal grid spacing of 0 67 km the simulated hurricane is initialized from a weak synthetic vortex in a quiescent environment on an f plane after spinup and rapid intensification the hurricane enters a mature phase during which the intensity change is relatively slow convective clouds then organize into a ring with a secondary tangential wind maximum at radii beyond the hurricane s primary eyewall this secondary eyewall se then contracts and strengthens the primary eyewall weakens and is eventually replaced by the se the hurricane grows in size and the radius of maximum wind rmw increases as similar ercs repeat 5 times during the simulation two existing hypotheses on sef are evaluated using the simulation output then model diagnostics are used to revea

revisiting the relationship between eyewall contraction and intensification abstractin the widely accepted convective ring model of tropical cyclone intensification the intensification of the maximum winds and the contraction of the radius of maximum winds rmw occur simultaneously this study shows that in idealized numerical simulations contraction and intensification commence at the same time but that contraction ceases long before peak intensity is achieved the rate of contraction decreases with increasing initial size while the rate of intensification does not vary systematically with initial size utilizing a diagnostic expression for the rate of contraction it is shown that contraction is halted in association with a rapid increase in the sharpness of the tangential wind profile near the rmw and is not due to changes in the radial gradient of the tangential wind tendency it is shown that a number of real storms exhibit a relationship between contraction and intensification that is similar to what is seen in the idealized simulations in particular the statistical

a new parametric tropical cyclone tangential wind profile model abstracta new parametric tropical cyclone tc wind profile model is presented for depicting representative surface pressure profiles corresponding to multiple maxima wind profiles that exhibit single dual and triple maximum concentric eyewall wind peaks associated with the primary inner secondary first outer and tertiary second outer complete rings of enhanced radar reflectivity one profile employs five key parameters tangential velocity maximum radius of the maximum and three different shape velocity parameters related to the shape of the profile after tailoring the model for tc applications a gradient wind is computed from a cyclostrophic wind formulated in terms of the cyclostrophic rossby number a pressure via cyclostrophic balance was partitioned into separate pressure components that corresponded to multiple maxima cyclostrophic wind profiles in order to quantitatively evaluate the significant fluctuations in central pressure deficits the model tc intensity in terms of varying

polygonal eyewalls asymmetric eye contraction and potential vorticity mixing in hurricanes hurricane eyewalls are often observed to be nearly circular structures but they are occasionally observed to take on distinctly polygonal shapes the shapes range from triangles to hexagons and while they are often incomplete straight line segments can be identified other observations implicate the existence of intense mesovortices within or near the eye region is there a relation between polygonal eyewalls and hurricane mesovortices are these phenomena just curiosities of the hurricane s inner core circulation or are they snapshots of an intrinsic mixing process within or near the eye that serves to determine the circulation and thermal structure of the eye as a first step toward understanding the asymmetric vorticity dynamics of the hurricane s eye and eyewall region these issues are examined within the framework of an unforced barotropic nondivergent model polygonal eyewalls are shown to form as a result of barotropic instability near the radius of maximum winds after reviewing linear theory simulations with a high resolution pseudospectral numerical model are presented to follow the instabilities into their nonlinear regime when the instabilities grow to finite amplitude the vorticity of the eyewall region pools into discrete areas creating the appearance of polygonal eyewalls the circulations associated with these pools of vorticity suggest a connection to hurricane mesovortices at later times the vorticity is ultimately rearranged into a nearly monopolar circular vortex while the evolution of the finescale vorticity field is sensitive to the initial condition the macroscopic end states are found to be similar in fact the gross characteristics of the numerically simulated end states are predicted analytically using a generalization of the minimum enstrophy hypothesis in an effort to remove some of the weaknesses of the minimum enstrophy approach a maximum entropy argument developed previously for rectilinear shear flows is extended to the vortex problem and end state solutions in the limiting case of tertiary mixing are obtained implications of these ideas for real hurricanes are discussed

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