a critique of emanuel s hurricane model and potential intensity theory we present a critique of emanuel s steady state hurricane model which is a precursor to his theory for hurricane potential intensity pi we show that a major deficiency of the theory is the tacit assumption of gradient wind balance in the boundary layer a layer that owes its existence to gradient wind imbalance in the radial momentum equation if a more complete boundary layer formulation is included using the gradient wind profiles obtained from emanuel s theory the tangential wind speed in the boundary layer becomes supergradient invalidating the assumption of gradient wind balance we show that the degree to which the tangential wind is supergradient depends on the assumed boundary layer depth the full boundary layer solutions require a knowledge of the tangential wind profile above the boundary layer in the outer region where there is subsidence into the layer and they depend on the breadth of this profile this effect is not considered in emanuel s theory we argue that a more complete theory for the steady state hurricane would require the radial pressure gradient above the boundary layer to be prescribed or determined independently of the boundary layer the issues raised herein highlight a fundamental problem with emanuel s theory for pi since that theory makes the same assumptions as in the steady state hurricane model our current findings together with recent studies examining intense hurricanes suggest a way forward towards a more consistent theory for hurricane pi copyright 2008 royal meteorological society

directional wind wave coupling in fully coupled atmosphere wave ocean models results from cblast hurricane abstractthe extreme high winds intense rainfall large ocean waves and copious sea spray in hurricanes push the surface exchange parameters for temperature water vapor and momentum into untested regimes the coupled boundary layer air sea transfer cblast hurricane program is aimed at developing improved coupling parameterizations using the observations collected during the cblast hurricane field program for the next generation hurricane research prediction models hurricane induced surface waves that determine the surface stress are highly asymmetric which can affect storm structure and intensity significantly much of the stress is supported by waves in the wavelength range of 0 1 10 m which is the unresolved spectral tail in present wave models a directional wind wave coupling method is developed to include effects of directionality of the wind and waves in hurricanes the surface stress vector is calculated using the two dimensional wave spectra from a wave model with an added short wave s

isotopic variation in rhythmically bedded chalks paleotemperature variation in the upper cretaceous detailed sampling at 2 cm intervals of a rhythmically bedded chalk marl sequence in southeast england has revealed a cyclic variation in oxygen isotopic composition of the carbonate component these changes are most consistent with paleotemperature fluctuations of up to 4 5 c contrary to some recent models chalk horizons are interpreted to reflect periods of warmer temperature and higher primary productivity than those responsible for marl deposition the effects of different faunal content diagenesis and variations in the water chemistry can all be discounted

upper ocean thermal structure and the western north pacific category 5 typhoons part i ocean features and the category 5 typhoons intensification abstract category 5 cyclones are the most intense and devastating cyclones on earth with increasing observations of category 5 cyclones such as hurricane katrina 2005 rita 2005 mitch 1998 and supertyphoon maemi 2003 found to intensify on warm ocean features i e regions of positive sea surface height anomalies detected by satellite altimeters there is great interest in investigating the role ocean features play in the intensification of category 5 cyclones based on 13 yr of satellite altimetry data in situ and climatological upper ocean thermal structure data best track typhoon data of the u s joint typhoon warning center together with an ocean mixed layer model 30 western north pacific category 5 typhoons that occurred during the typhoon season from 1993 to 2005 are systematically examined in this study two different types of situations are found the first type is the situation found in the western north pacific south eddy zone sez 21 26 n 127 170 e and the kuroshio 21 30

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

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

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

supercells and mesocyclones in outer rainbands of hurricane katrina 2005 1 this study documents and describes supercells embedded within the outer rainbands of hurricane katrina 2005 radar reflectivity and velocity data collected on 29 august 2005 by weather surveillance radar 1988 doppler radars were used to track the supercells radar analysis indicates that the supercells were characterized by heavy precipitation collocated with band relative mesocylonic circulations containing strong vorticity and a wind speed enhancement to their northeast atmospheric soundings and dual doppler derived shear suggest that environmental conditions were comparable to those in previous hurricane spawned supercell studies twenty three storms from 0300 0900 utc were tracked and single and dual doppler radar analyses were used to examine characteristics such as shear and rotational velocity remarkably the majority of the supercells formed over the gulf of mexico rather than over land which contrasts with previous studies furthermore the ground relative wind speeds of these potentially tornadic mesocyclones in the outer rainbands could have been category 4 intensity despite sustained winds in katrina s eyewall only reaching category 3 at landfall

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

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

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

an ocean coupling potential intensity index for tropical cyclones american geophysical union 2013 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in geophysical research letters 40 2013 1878 1882 doi 10 1002 grl 50091

tropical cyclone eye thermodynamics in intense tropical cyclones sea level pressures at the center are 50 100 hpa lower than outside the vortex but only 10 30 hpa of the total pressure fall occurs inside the eye between the eyewall and the center warming by dry subsidence accounts for this fraction of the total hydrostatic pressure fall convection in the eyewall causes the warming by doing work on the eye to force the thermally indirect subsidence soundings inside hurricane eyes show warm and dry air aloft separated by an inversion from cloudy air below dewpoint depressions at the inversion level typically 850 500 hpa are 10 30 k rather than the 100 k that would occur if the air descended from tropopause level without dilution by the surrounding cloud the observed temperature and dewpoint distribution above the inversion can however be derived by 100 hpa of undilute dry subsidence from an initial sounding that is somewhat more stable than a moist adiabat it is hypothesized that the air above the inversion has remained in the eye since it was enclosed when the eyewall formed and that it has subsided at most a few kilometers the cause of the subsidence is the enclosed air s being drawn downward toward the inversion level as the air below it flows outward into the eyewall shrinkage of the eye s volume is more than adequate to supply the volume lost as dry air is incorporated into the eyewall or converted to moist air by turbulent mixing across the eye boundary the moist air below the inversion is in thermodynamic contact with the sea surface its moisture derives from evaporation of seawater inside the eye frictional inflow of moist air under the eyewall and from moist downdrafts induced as condensate mixes into the eye the moist air s residence time in the eye is much shorter than that of the dry air above the inversion the height of the inversion is determined by the balance between evaporation inflow and inward mixing on one hand and loss to the eyewall updrafts on the other

western north pacific typhoons with concentric eyewalls abstract this study examines the intensity change and moat dynamics of typhoons with concentric eyewalls using passive microwave data and best track data in the western north pacific between 1997 and 2006 of the 225 typhoons examined 55 typhoons and 62 cases with concentric eyewalls have been identified the data indicate that approximately 57 of category 4 and 72 of category 5 typhoons possessed concentric eyewalls at some point during their lifetime while major typhoons are most likely to form concentric eyewalls the formation of the concentric structure may not be necessarily at the lifetime maximum intensity approximately one third of concentric eyewall cases are formed at the time of maximum intensity the moat is known to be heavily influenced by the subsidence forced by the two eyewalls rozoff et al proposed that the rapid filamentation dynamics may also contribute to the organization of the moat this paper examines the possibility of rapid filamentation dynamics by devising a filamentati

hurricane intensity and eyewall replacement observations made during the historic 2005 hurricane season document a case of eyewall replacement clouds outside the hurricane eyewall coalesce to form a new eyewall at a greater radius from the storm center and the old eyewall dies the winds in the new eyewall are initially weaker than those in the original eyewall but as the new eyewall contracts the storm reintensifies understanding this replacement mechanism is vital to forecasting variations in hurricane intensity processes in the moat region between the new and old eyewall have been particularly unclear aircraft data now show that the moat becomes dynamically similar to the eye and thus is converted into a region inimical to survival of the inner eyewall we suggest that targeting aircraft to key parts of the storm to gain crucial input to high resolution numerical models can lead to improvements in forecasting hurricane intensity

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

u series and radiocarbon dates on mollusc shells from the uppermost layer of the archaeological site of khb 1 ra s al khabbah oman the archaeological site of khb 1 oman has been investigated in order to improve the chronological knowledge of the site which is dated to the beginning of the fourth millennium b c on the basis of the archaeological context mollusc shells of the genus anadara coming from the uppermost layers of the site have been dated using two different methods radiocarbon and u series technique the results of the two techniques date the last occupational phase of the site from the end of the fourth millennium b c to the beginning of the third millennium b c

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 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