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

formation of di and trioctahedral smectite as evidence for paleoclimatic changes in southern and central peninsular india abstract di and trioctahedral smectites in saprolites developed on precambrian gneiss and gondwana sediments in southern and central peninsular india indicate a climatic change from tropical humid to semi arid during the plio pleistocene transition period well crystallised dioctahedral smectite was the first weathering product of peninsular gneiss and was subsequently transformed to kaolinite in ferruginous soils formed in a pre pliocene tropical humid climate when the humid climate terminated both these clay minerals were preserved to the present silt and clay size trioctahedral smectite i e low charge vermiculite in these saprolites is regarded as the alteration product of biotite formed in arid climate since the plio pleistocene transition period we conclude that the ferruginous soils on peninsular gneiss and gondwana sediments are relict paleosols but are polygenetic because of their subsequent alterations

on assessing local conditional symmetric instability from atmospheric soundings abstract the standard parcel method of assessing the susceptibility of the atmosphere to moist convection using tephigrams is extended to account for the centrifugal as well as the gravitational potential energy of the displaced air parcel this leads to a measure of the stability of the moist baroclinic atmosphere to finite slantwise reversible displacements of a two dimensional air parcel such a measure differs from previously derived measures of conditional symmetric instability which have considered only infinitesimal displacements in saturated atmospheres it is demonstrated that the combined gravitational and centrifugal potential of a two dimensional air parcel or tube can be assessed by displacing the tube slantwise along a surface of constant angular momentum and that this combined potential energy can be estimated using a single atmospheric sounding several examples of the application of this technique are presented in the context of a case study of apparent slantwise convection the result

warm cores eyewall slopes and intensities of tropical cyclones simulated by a 7 km mesh global nonhydrostatic model abstractbased on the data of a 1 yr simulation by a global nonhydrostatic model with 7 km horizontal grid spacing the relationships among warm core structures eyewall slopes and the intensities of tropical cyclones tcs were investigated the results showed that stronger tcs generally have warm core maxima at higher levels as their intensities increase it was also found that the height of a warm core maximum ascends descends as the tc intensifies decays to clarify how the height and amplitude of warm core maxima are related to tc intensity the vortex structures of tcs were investigated by gradually introducing simplifications of the thermal wind balance it was established that warm core structures can be reconstructed using only the tangential wind field within the inner core region and the ambient temperature profile a relationship between tc intensity and eyewall slope was investigated by introducing a parameter that characterizes the shape of eyewalls and can be evaluated from satellite m

low richardson number in the tropical cyclone outflow layer abstractdropsondes from the noaa g iv aircraft were used to examine the presence of low bulk richardson numbers rb in tropical cyclones at least one 400 m layer above z 7 5 km exhibited rb 1 in 96 of the sondes and rb 0 25 in 35 of the sondes the latter represent almost certain turbulence sondes from major hurricane ivan 2004 were examined in detail turbulent layers fell into three broad groups the first was found below cloud base near the edge of the central dense overcast cdo where relative humidity fell below 40 near zero static stability existed within the turbulent layer with stability and shear maxima above it this structure strongly resembled that seen previously from sublimation of precipitation beneath cloud base the second type of turbulent layer was located within cdo clouds in the upper troposphere and was due almost entirely to near zero static stability this most likely arose as a result of cooling via longwave flux divergence below cdo top the third type of turbulent

evaluation of the assumptions in the steady state tropical cyclone self stratified outflow using three dimensional convection allowing simulations abstractthe criteria and assumptions that were used to derive the steady state tropical cyclone intensity and structure theory of emanuel and rotunno are assessed using three dimensional convection

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

heightened hurricane surge risk in northwest florida revealed from climatological hydrodynamic modeling and paleorecord reconstruction historical tropical cyclone tc and storm surge records are often too limited to quantify the risk to local populations paleohurricane sediment records uncover long term tc activity but interpreting these records can be difficult and can introduce significant uncertainties here we compare and combine climatological hydrodynamic modeling including a method to account for storm size uncertainty historical observations and paleohurricane records to investigate local surge risk using apalachee bay in northwest florida as an example the modeling reveals relatively high risk with 100 year 500 year and worst case surges estimated to be about 6 3 m 8 3 m and 11 3 m respectively at bald point a paleorecord site and about 7 4 m 9 7 m and 13 3 m respectively at st marks the head of the bay supporting the inference from paleorecords that apalachee bay has frequently suffered severe inundation for thousands of years both the synthetic database and paleorecords contain a much higher frequency of extreme events than the historical record the mean return period of surges greater than 5 m is about 40 years based on synthetic modeling and paleoreconstruction whereas it is about 400 years based on historical storm analysis apalachee bay surge risk is determined by storms of broad characteristics varies spatially over the area and is affected by coastally trapped kelvin waves all of which are important features to consider when accessing the risk and interpreting paleohurricane records in particular neglecting size uncertainty may induce great underestimation in surge risk as the size distribution is positively skewed while the most extreme surges were generated by the uppermost storm intensities medium intensity storms categories 1 3 can produce large to extreme surges due to their larger inner core sizes for apalachee bay the storms that induced localized barrier breaching and limited sediment transport overwash regime surge between 3 and 5 m are most likely to be category 2 or 3 storms and the storms that inundated the entire barrier and deposited significantly more coarse materials inundation regime surge 5 m are most likely to be category 3 or 4 storms

self stratification of tropical cyclone outflow part ii implications for storm intensification tropical cyclones intensify and are maintained by surface enthalpy fluxes that result from the thermodynamics disequilibrium that exists between the tropical oceans and atmosphere while this general result has beenknownfor at least a half century the detailednatureof feedbacksbetweenthermodynamic anddynamic processes in tropical cyclones remains poorly understood in particular the spatial relationship between surface fluxes and the radial entropy distribution apparently does not act to amplify the entropy gradient and therefore the surface winds in previous work this problem was addressed by accounting for the radial distribution of convective fluxes of entropy out of the boundary layer this led to the conclusion that a radial gradient of such convective fluxes is necessary for intensification part i showed that the assumption of constant outflow temperature is incorrect and argued that the thermal stratification of the outflow is set by small scale turbulence that limits the richardson number the assumption of richardson number criticality of the outflow allows one to derive an equation for the variation of outflow temperature with angular momentum this in turn leads to predictions of vortex structure and intensity that agree well with tropical cyclones simulated using a full physics axisymmetric model here it is shown that the variation of outflow temperature with angular momentum also permits the vortex to intensify with time even in the absence of radial gradients of entrainment into the boundary layer an equation is derived for the rate of intensity change and compared to simple models and to simulations using a full physics model

evolution of the upper tropospheric outflow in hurricanes iselle and julio 2014 in the navy global environmental model navgem analyses and in satellite and dropsonde observations upper tropospheric outflow was examined during the life cycles of two hurricanes in the eastern and central pacific ocean the outflow from hurricanes iselle and julio was evaluated using analyses from the navy global environmental model navgem which were very highly correlated with satellite atmospheric motion vector amv and noaa g iv dropsonde observations a synoptic overview provided the environmental context for the lifecycles of both tropical cyclones tcs then the outflow magnitude and direction within 6 radial degrees of each tc center were analyzed in relation to tc intensity the synoptic environment and inertial stability with the following results in both iselle and julio the azimuthally averaged outflow magnitude was maximized initially more than 4 radial degrees from the center and that maximum moved steadily inward during a 4 day intensification period and reached a position radially inward of 2 degrees within 6 h of the time of maximum surface winds furthermore the direction of the outflow in both tcs was related to the evolution of the large scale upper tropospheric flow pattern particularly the phasing of subtropical jet ridges and troughs moving eastward north of both tcs finally outflow channels were consistently bounded by regions of lowest highest values of inertial stability counterclockwise clockwise from the maximum outflow azimuth a pattern that persisted throughout the life cycles of both storms regardless of intensity environmental flow and the number and direction of outflow channels present

self stratification of tropical cyclone outflow part i implications for storm structure extant theoretical work on the steady state structure and intensity of idealized axisymmetric tropical cyclones relies on the assumption that isentropic surfaces in the storm outflow match those of the unperturbed environment at large distances from the storm s core these isentropic surfaces generally lie just above the tropopause wheretheverticaltemperaturestructureisapproximatelyisothermal soithas beenassumedthat the absolute temperature of the outflow is nearly constant here it is shown that this assumption is not justified at least when applied to storms simulated by a convection resolving axisymmetric numerical model in whichmuchofthe outflowoccursbelowtheambienttropopauseanddevelopsits ownstratification unrelated to that of the unperturbed environment the authors propose that this stratification is set in the storm s core by the requirement that the richardson number remain near its critical value for the onset of small scale turbulence this ansatz is tested by calculating the richardson number in numerically simulated storms and then showing that the assumption of constant richardson number determines the variation of the outflow temperature with angular momentum or entropy and thereby sets the low level radial structure of the storm outside its radius of maximum surface winds part ii will show that allowing the outflow temperature to vary also allows one to discard an empirical factor that was introduced in previous work on the intensification of tropical cyclones

tropical cyclones in rotating radiative convective equilibrium with coupled sst abstracttropical cyclones are studied under the idealized framework of rotating radiative convective equilibrium achieved in a large doubly periodic f plane by coupling the column physics of a global atmospheric model to rotating hydrostatic dynamics unlike previous studies that prescribe uniform sea surface temperature sst over the domain ssts are now predicted by coupling the atmosphere to a simple slab ocean model with coupling ssts under the eyewall region of tropical cyclones tcs become cooler than the environment however the domain still fills up with multiple long lived tcs in all cases examined including at the limit of the very small depth of the slab the cooling of ssts under the eyewall increases as the depth of the slab ocean layer decreases but levels off at roughly 6 5 k as the depth approaches zero at the eyewall the storm interior is decoupled from the cooler surface and moist entropy is no longer well mixed along the angular momentum surface in the boundary layer tc intens

low probability of tropical cyclones on ocean planets in the habitable zones of m dwarfs abstract the genesis potential index gpi of tropical cyclones tc on ocean planets in the habitable zones of m dwarfs is analyzed based on 3d gcm simulations we found that gpi on these planets are smaller than those in tc basins on the earth mainly because of slow rotation of such planets gpi s on exoplanets with eccentric orbits are strong function of time with values generally greater than those on circular orbits future high resolution models are needed to better understand whether tcs could form on ocean exoplanets and what their potential intensities and distributions might be

a model for the complete radial structure of the tropical cyclone wind field part ii wind field variability abstractpart i of this work developed a simple physical model for the complete radial structure of the low level azimuthal wind field in a tropical cyclone that compared well with observations however wind field variability in the model is tied principally to its external parameters given by the maximum wind speed and the radius of maximum wind the latter of which lacks a credible independent physical model for its variability here the authors explore the modes of variability that arise from the alternative specification of the model which takes the outer radius in lieu of the radius of maximum wind nondimensionalization of the model reveals two theoretical modes of structural variability in absolute angular momentum that are shown to closely match observations these two modes correspond to three modes of wind field variability associated with variations in intensity outer storm size and latitude these wind field modes are demonstrated to mirror the dominant modes of variability found in nature

a preliminary electron probe study of microchemical variations in desert varnish in western new south wales australia examination of desert varnish samples from australia by electron microprobe and energy dispersive spectrometry has shown that gross layering of iron and manganese enrichments is variable surface upper varnish may be similar to lower varnish or be relatively enriched in either iron or manganese when viewed in sections cut parallel to the varnished surface microlaminations with high manganese content up to 30 per cent were sometimes found in concentrically zoned patterns around grains dorn et al 1986 have proposed that chemical changes occur with increasing varnish age in this study the possibility of such changes was examined at the within varnish scale by comparing near surface and deeper upper and lower portions of the same varnishes variations in elemental ratios k ca ti at this scale were shown to be largely unsystematic suggesting either that samples were unrepresentative that element inputs to varnish have varied over time that the varnish was too young for differentiation by weathering into an upper and lower layer that varnish cover formed rapidly and at one time or that existing varnish cover represents the coalescence of numerous individual patches of varnish each of which formed over a relatively short period

determining key model parameters of rapidly intensifying hurricane guillermo 1997 using the ensemble kalman filter abstractin this work the authors determine key model parameters for rapidly intensifying hurricane guillermo 1997 using the ensemble kalman filter enkf the approach is to utilize the enkf as a tool only to estimate the parameter values of the model for a particular dataset the assimilation is performed using dual doppler radar observations obtained during the period of rapid intensification of hurricane guillermo a unique aspect of guillermo was that during the period of radar observations strong convective bursts attributable to wind shear formed primarily within the eastern semicircle of the eyewall to reproduce this observed structure within a hurricane model background wind shear of some magnitude must be specified and turbulence and surface parameters appropriately specified so that the impact of the shear on the simulated hurricane vortex can be realized to identify the complex nonlinear interactions induced by changes in these parameters an ensemble of model simulations have been condu

rock engraving chronologies and accelerator mass spectrometry radiocarbon age of desert varnish abstract it has been proposed that the minimum age of rock engravings can be established from dating organic carbon associated with desert varnish a naturally occurring coating on rocks in arid regions in this study five radiocarbon ages were obtained from organic carbon in previously undated varnishes from the pilbara western australia four varnish samples were scraped from dull black coatings and one from patchy shiny black varnish all radiocarbon ages were younger than 2800 years bp ages were younger at the rock varnish interface than in overlying varnish a reversal of expected stratigraphic relations these results highlighted a number of difficulties associated with the interpretation of varnish radiocarbon ages including the potential absence of a link between organic carbon age and varnish deposition age linkages are complicated by the time transgressive nature of varnish formation its weathering over time and the probable mixed ages of dated organic carbon engraving chronologies based solely on radiocarbon ages of varnish should be treated with extreme caution

slab and height resolving models of the tropical cyclone boundary layer part i comparing the simulations diagnostic models of the tropical cyclone boundary layer have important practical uses including engineering design and climatological risk assessment studies and as components of tropical cyclone potential intensity models a widely used class of such models has been slab models in which the governing equations are depth averaged here a slab model is compared with one that fully resolves height and it is shown that the vertical averaging leads to substantial differences in the simulations the slab model produces excessively strong inflow and too great a departure of the boundary layer mean winds from gradient balance in moving storms the slab models produce much too strong a motion induced asymmetry and can support an asymmetric analogue of the quasi inertial oscillation previously noted in axisymmetric slab models given the considerable impact of the vertical averaging in slab models on the simulated flow in the tropical cyclone boundary layer it is difficult to recommend their further use for applications where quantitative accuracy is important other applications will require care to ensure that the results are not unduly affected by the depth averaging part ii of this article presents a detailed analysis of the reasons for the differences between depth averaged and height resolving simulations of the tropical cyclone boundary layer 2010 published by john wiley sons ltd

a quikscat climatology of tropical cyclone size 1 quikscat data of near surface wind vectors for the years 1999 2008 are used to create a climatology of tropical cyclone tc size defined as the radius of vanishing winds the azimuthally averaged radius of 12 ms 1 wind r12 is calculated for a subset of tcs n 2154 whose centers of circulation were clearly identifiable via subjective analysis of the quikscat analyzed wind field the outer radius r0 is determined from r12 using an outer wind structure model that assumes no deep convection beyond r12 the global median values of r12 and r0 are 197 km and 423 km respectively with statistically significant variation across ocean basins the global distribution of r12 is found to be approximately log normal the distribution of r0 is quantitatively much closer to log normal and the improvement in fit between r12 and r0 is attributed to the combined effect of the nature of the model employed and the paired distributions of r12 and f moreover the normalization employed by dean et al 2009 is found to weaken rather than improve the log normal fit finally within a given storm both r12 and r0 tend to expand very slowly with time early in the storm lifecycle and then becomes quasi constant though significant variance exists across storms

observed tropical cyclone size revisited abstractthis work revisits the statistics of observed tropical cyclone outer size in the context of recent advances in our theoretical understanding of the storm wind field the authors create a new dataset of the radius of 12 m s 1 winds based on a recently updated version of the quikscat ocean wind vector database and apply an improved analytical outer wind model to estimate the outer radius of vanishing wind the dataset is then applied to analyze the statistical distributions of the two size metrics as well as their dependence on environmental parameters with a specific focus on testing recently identified parameters possessing credible theoretical relationships with tropical cyclone size the ratio of the potential intensity to the coriolis parameter is found to perform poorly in explaining variation of size with the possible exception of its upper bound the latter of which is in line with existing theory the rotating radiative convective equilibrium scaling of khairoutdinov and emanuel is also f

inertial waves in axisymmetric tropical cyclones abstractthe heat engine model of tropical cyclones describes a thermally direct overturning circulation outflowing air slowly subsides as radiative cooling to space balances adiabatic warming a p

ambiguities in direct dating of rock surfaces using radiocarbon measurements an attempt was made to date rock surfaces with accelerator mass spectrometry ams radiocarbon measurements of rock varnishes or rock weathering rinds in two case studies samples pretreated in the laboratory of dr ronald dorn prior to ams analysis have been found to contain significant quantities of carbon rich materials of two distinct classes type i material resembles bituminous coal whereas type ii material resembles pyrolized wood charcoal fragments in samples where these type i and type ii materials were separated and ams radiocarbon dated they were found to have widely differing radiocarbon ages in these cases the measurement of the radiocarbon age of the entire sample would yield results that are at best ambiguous neither type i nor type ii materials were found in comparable samples that were independently prepared

toward understanding the dynamics of spinup in emanuel s tropical cyclone model abstractwe seek to understand the mechanism of vortex spinup in emanuel s 2012 axisymmetric theory for tropical cyclone intensification in physical coordinates starting from first principles it i

the impact of gradient wind imbalance on potential intensity of tropical cyclones in an unbalanced slab boundary layer model the assumption of gradient wind balance is customarily made so as to derive the theoretical upper bound intensity of a mature tropical cyclone emanuel s theory of hurricane potential intensity e pi makes use of this assumption whereas more recent studies by bryan and rotunno demonstrate that the effect of unbalanced flow can result in maximum winds that are well in excess of e pi superintensity the existence of supergradient winds has been verified in a slab boundary layer model developed by smith here the authors apply the slab boundary layer model within the framework of classical e pi theory to investigate the sensitivity of supergradient winds to the radius of maximum gradient wind rmgw and four nondimensional model parameters the authors find that the rossby number the drag coefficient and the modified rankine decayparameterallhaveaconsiderableinfluenceonthestrengthoftheunbalancedflow incontrast theratio of surface exchange coefficients has little noticeable effect on superintensity the inclusion of horizontal momentum diffusion leads to a weaker superintensity but the qualitative features of the model remain similar to furtherelucidatethesefindings theauthorsusetheboundarylayermodeltoexaminethemodified e pi theoryproposedby emanueland rotunno theyassumea constantrichardsonnumberforthe outflow the boundary layer model driven by the modified e pi solution depends on just three model parameters rather than the four parameters used in the classical e pi framework despite this apparent advantage the resultsobtainedintheframeworkofthemodifiede piarelessrealisticthanthosecomputedwiththeclassical e pi approach

dramatic inner core tropopause variability during the rapid intensification of hurricane patricia 2015 abstractdropsondes with horizontal spacing as small as 4 km were released from the stratosphere in rapidly intensifying hurricane patricia 2015 during the office of naval research tropical cyclone intensity experiment these observations provide cross sections of unprecedented resolution through the inner core of a hurricane on 21 october patricia exhibited a strong tropopause inversion layer til across its entire circulation with a maximum magnitude of 5 1 k 100 m 1 this inversion weakened between 21 and 22 october as potential temperature increased by up to 16 k just below the tropopause and decreased by up to 14 k in the lower stratosphere between 22 and 23 october the til over the eye weakened further allowing the tropopause to rise by 1 km meanwhile over patricia s secondary eyewall the til restrengthened and bulged upward by about 700 m into what was previously the lower stratosphere these observations support many aspects of recent modeling studies including eyewall penetration i

an analysis of the observed low level structure of rapidly intensifying and mature hurricane earl 2010 abstract we examine dynamic and thermodynamic aspects of atlantic hurricane earl 2010 during its intensification and mature phases over four days of intensive measurements during this period earl underwent an episode of rapid intensification maturity secondary eyewall replacement re intensification and the early part of its decline the observations are used to appraise elements of a new model for tropical cyclone intensification the results affirm the conventional vortex interior and boundary layer spin up mechanisms that form dynamical elements of the azimuthally averaged view of the new intensification model the average maximum tangential winds beneath the eyewall are found to exceed the gradient wind by between 20 and 60 the results suggest also that the gradient wind balance approximation in the low level vortex interior above the strong inflow layer may not be as accurate in the inner core region of a tropical cyclone during its intensification as has been widely held an analysis of the low level thermodynamic structure affirms the radial increase of moist equivalent potential temperature e with decreasing radius during the intensification process a necessary ingredient of the new model for maintaining convective instability in the presence of a warming upper troposphere an unanticipated finding is the discovery of an unmixed boundary layer in terms of e within several hundred kilometres of the vortex centre in the inner core region this finding is not consistent with the axisymmetric eruption of the boundary layer into the eyewall unless there are non conservative eddy processes acting to modify the entropy of ascending air

tropopause evolution in a rapidly intensifying tropical cyclone a static stability budget analysis in an idealized axisymmetric framework abstractupper level static stability n2 variations can influence the evolution of the transverse circulation and potential vorticity in intensifying tropical cyclones tcs this paper examines t

an air sea interaction theory for tropical cyclones part ii evolutionary study using a nonhydrostatic axisymmetric numerical model abstract in part i of this study an analytical model for a steady state tropical cyclone is constructed on the assumption that boundary layer air parcels are conditionally neutral to displacements along the angular momentum surfaces of the hurricane vortex the reversible thermodynamics implied by this assumption allows the mature storm to be thought of as a simple carnot engine acquiring heat at the high temperature ocean surface and losing heat near the low temperature tropopause although the oceanic heat source is universally recognized as the sine qua non for the mature hurricane there is also wide acceptance of conditional instability of the second kind cisk which makes no specific reference to surface heat fluxes as the formative mechanism this ambivalence is seen in that all numerical simulation studies find it essential to have transfer from the ocean surface yet all start from a conditionally unstable atmosphere the hypothesis put forward in part i based on the steady state theory is t