balanced contribution to the intensification of a tropical cyclone simulated in tcm4 outer core spinup process abstract the balanced contribution to the intensification of a tropical cyclone simulated in the three dimensional nonhydrostatic full physics tropical cyclone model version 4 tcm4 in particular the spinup of the outer core circulation is investigated by solving the sawyer eliassen equation and by computing terms in the azimuthal mean tangential wind tendency equation results demonstrate that the azimuthal mean secondary circulation radial and vertical circulation and the spinup of the midtropospheric outer core circulation in the simulated tropical cyclone are well captured by balance dynamics the midtropospheric inflow develops in response to diabatic heating in mid upper tropospheric stratiform anvil clouds outside the eyewall in active spiral rainbands and transports absolute angular momentum inward to spin up the outer core circulation although the azimuthal mean diabatic heating rate in the eyewall is the largest its contribution to radial winds and thus the spinup of outer core circul

repeated eyewall replacement cycles in hurricane frances 2004 abstracthurricane frances 2004 represented an unusual event that produced three consecutive overlapping eyewall replacement cycles ercs their evolution followed some aspects of the typical erc

on the height of the warm core in tropical cyclones abstractthe warm core structure of tropical cyclones is examined in idealized simulations using the weather research and forecasting wrf model the maximum perturbation temperature in a control simulation occurs in the midtroposphere 5 6 km in contrast to the upper tropospheric 10 km warm core that is widely believed to be typical this conventional view is reassessed and found to be largely based on three case studies and it is argued that the typical warm core structure is actually not well known in the control simulation the height of the warm core is nearly constant over a wide range of intensities from additional simulations in which either the size of the initial vortex or the microphysics parameterization is varied it is shown that the warm core is generally found at 4 8 km a secondary maximum often develops near 13 14 km but is almost always weaker than the primary warm core it is demonstrated that microwave remote sensing instruments are of insufficient resolution to detect this

reverse age relations of talc and tremolite deduced from reaction textures in metamorphosed siliceous dolomites of the southern damara orogen namibia the regional metamorphosed siliceous dolomites of the southern damara orogen namibia show a distinct talc bearing zone on the lower metamorphic grade side and a distinct tremolite bearing zone on the higher metamorphic grade side separated by the occurrence of the fivemineral assemblage i tremolite talc calcite dolomite quartz

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

rapid filamentation zones in intense tropical cyclones intense tropical cyclones often possess relatively little convection around their cores in radar composites this surrounding region is usually echo free or contains light stratiform precipitation while subsidence is typically quite pronounced in this region it is not the only mechanism suppressing convection another possible mechanism leading to weak echo moats is presented in this paper the basic idea is that the strain dominated flow surrounding an intense vortex core creates an unfavorable environment for sustained deep moist convection strain dominated regions of a tropical cyclone can be distinguished from rotationdominated regions by the sign of s 2 s 2 2 where s1 ux y and s2 x uy are the rates of strain and x uy is the relative vorticity within the radius of maximum tangential wind the flow tends to be rotation dominated 2 s 2 s 2 so that coherent structures such as mesovortices can survive for long periods of time outside the radius of maximum tangential wind the flow tends to be strain dominated s 2 s 2 2 resulting in filaments of anomalous vorticity in the regions of strain dominated flow the filamentation time is defined as fil 2 s 2 s 2 2 1 2 in a tropical cyclone an approximately 30 kmwide annular region can exist just outside the radius of maximum tangential wind where fil is less than 30 min and even as small as 5 min this region is defined as the rapid filamentation zone since the time scale for deep moist convective overturning is approximately 30 min deep convection can be significantly distorted and even suppressed in the rapid filamentation zone a nondivergent barotropic model illustrates the effects of rapid filamentation zones in category 1 5 hurricanes and demonstrates the evolution of such zones during binary vortex interaction and mesovortex formation from a thin annular ring of enhanced vorticity

evaluation of planetary boundary layer parameterizations in tropical cyclones by comparison of in situ observations and high resolution simulations of hurricane isabel 2003 part ii inner core boundary layer and eyewall structure this is the second of a two part study of the representation of the planetary boundary layer pbl in highresolutionweatherresearchandforecastmodel wrf simulationsofhurricaneisabel 2003 theyonsei university ysu pbl parameterization and the mellor yamada janjic myj pbl parameterization are evaluated by direct comparison to in situ data obtained by research aircraft the numerical model simulation design details of the pbl schemes and the representation of the boundary layer in the outer core were presented in part i this part presents a detailed study of the inner core pbl including its axisymmetric and asymmetric structures and comparisons to analyses of dropsonde data from previous studies although neither pbl scheme was designed specifically for hurricane conditions their simulated boundary layers are reasonably good representations of the observed boundary layer both schemes reproduce certain unique features of the hurricane boundary layer such as the separate depths of the well mixed layer and the inflow layer and the pronounced wind speed maxima near the top of the inflow layer modification of the original ysu and myj schemes to have ocean roughness lengths more in agreement with recent studies considerably improves the results of both schemes even with these improvements the myj consistently produces larger frictional tendencies in the boundary layer than the ysu scheme leading to a stronger lowlevel inflow and a stronger azimuthal wind maximum at the top of the boundary layer for both schemes differences in the low level asymmetries between the simulated and observed wind fields appear to be related to eyewall asymmetries forced by environmental wind shear the effects of varying horizontal and vertical resolutions are also considered increasing the vertical resolution in the pbl results in minor improvements in the inner core structures increasing the horizontal resolution around the eyewall also leads to improved boundary layers as well as an improvement of the vertical structure of the inner core wind field a summary and discussion of the results of both parts i and ii is provided

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

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

revisiting the balanced and unbalanced aspects of tropical cyclone intensification abstractthe balanced and unbalanced aspects of tropical cyclone tc intensification are revisited with the balanced contribution diagnosed with the outputs from a full physics model simulation of a tc using the sawyer eliassen se equation the results show that the balanced dynamics can well capture the secondary circulation in the full physics model simulation even in the inner core region in the boundary layer the balanced dynamics can largely explain the intensification of the simulated tc the unbalanced dynamics mainly acts to prevent the boundary layer agradient flow in the inner core region from further intensification although surface friction can enhance the boundary layer inflow and make the inflow penetrate more inward into the eye region contributing to the eyewall contraction the net dynamical effect of surface friction on tc intensification is negative the sensitivity of the balanced solution to the procedure used to ensure the ellipticity condition for the se equation is also examine

growth and deformation mechanisms of talc along a natural fault a micro nanostructural investigation this paper documents the occurrence of large amounts of talc within a continental normal fault the talc in reaction is deformation enhanced and occurs by the interaction between dolostones and silica rich hydrothermal fluids in the high strain foliated fault core talc forms an interconnected network of oriented 001 lamellae 200 300 nm thick locally associated with minor tremolite fibres up to 300 nm in diameter the talc structure is affected by several strain induced defects among which 001 interlayer delamination that produces talc sublamellae down to 10 30 nm thick micro nanostructural observations definitely point to a predominant deformation mechanism of 001 frictional sliding further enhanced by pervasive delamination that gives rise to an almost infinite number of possible sliding surfaces these effects have fundamental implications in fault mechanics resulting in significant fault weakening

effect of peripheral convection on tropical cyclone formation abstract the effect of peripheral convection on the formation and intensification of tropical cyclones has been studied earlier with diagnostic models and with prognostic models that do not resolve convection in this paper a prognostic axisymmetric model with explicit convection is used to study the effect of peripheral convection on tropical cyclone formation from a weak mesoscale vortex peripheral convection becomes stronger in the model if downdrafts extinguish deep convection in the core of the mesoscale vortex the subsequent concentration of convection in the core of the vortex and the onset of rapid intensification of the vortex occur simultaneously in model experiments relative humidity in the midtroposphere reaches a value of 90 within 100 km from the center of the vortex before the onset of rapid intensification occurs decreasing the sea surface fluxes of sensible and latent heat artificially in the outer region of the vortex decreases the amount of outer convection in the model this re

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

improved global maps and 54 year history of wind work on ocean inertial motions 1 the global distribution and 54 year time dependence of the energy flux from the wind to near inertial motions is computed by driving a slab mixed layer model with ncep ncar reanalysis winds improving upon previous estimates alford 2001 watanabe and hibiya 2002 the slab model is solved spectrally with frequency dependent damping the resulting solutions are more physically sensible than the previous and more skillful at high latitudes where the inertial frequency approaches the 4 daily sampling of the reanalysis winds this enables alford s calculation whose domain was limited to 50 to be extended to the poles the high latitude reliability is demonstrated by direct comparison with a high resolution regional model remo in the ne atlantic the total power input 0 47 tw has increased by 25 since 1948 paralleling observed increases in extratropical cyclone frequency and intensity if believable the trend may have important consequences for modulation of the meridional overturning circulation

a numerical investigation of the eyewall evolution in a landfalling typhoon abstract an interesting eyewall evolution occurred in typhoon zeb 1998 when it devastated luzon the eyewall of zeb contracted before landfall and broke down and weakened after landfall then a much larger new eyewall formed and strengthened as it left luzon and reentered the ocean the fifth generation pennsylvania state university ncar mesoscale model mm5 with four nested domains was used to perform numerical experiments to understand the effects of terrain and land surface variation on the observed eyewall evolution results show that the presence of luzon plays a critical role in the observed eyewall evolution quite different from the conventional concentric eyewall replacement the eyewall replacement that occurred in typhoon zeb was triggered by the mesoscale landmass and terrain variation with a horizontal scale similar to the core of the typhoon in typhoon zeb the original eyewall contracted and broke down because of enhanced surface friction after landfall the outer eyewall was triggered

textural and isotopic development of marble assemblages during the barrovian style m2 metamorphic event naxos greece a detailed petrological analysis of the marble assemblages observed within the m2 metamorphic complex on naxos is presented two distinct periods of mineral growth are documented the first is associated with prograde m2 metamorphism and the second with retrograde m2 metamorphism occurring during ductile extensional thinning of the complex the textural and miner alogical characteristics and the carbon and oxygen isotope compositions of each generation are described and the p t xco2 conditions at which these two mineral generations were stable and the compositions of the fluids present during metamorphism are characterised whereas the low variance and stable isotope compositions of prograde siliceous dolomite assemblages are consistent with internally buffered fluid evolution the retrograde mineral generation is shown to have grown as a result of the infiltration of a water rich fluid phase that transported silica al2o3 na2o and feo into the host rocks this observation together with the stable isotope compositions of the retrograde calcite and the fact that occurrences of veins of this type are limited to marbles in the highest grade areas t 600 c of the metamorphic complex suggests that the fluids responsible for vein formation were generated during the crystallisation of melts as the metamorphic complex cooled from peak temperatures the existence of this second generation of minerals has significant implications for previous studies of heat transport by fluid flow on naxos because many of the unusually low 18o compositions of pelites at high grades may be ascribable to the effects of interaction with retrograde m2 fluids rather than with prograde fluids

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

vortex rossby waves in a numerically simulated tropical cyclone part i overall structure potential vorticity and kinetic energy budgets abstract the asymmetric structure in the inner core of a numerically simulated tropical cyclone is analyzed in this study the simulated tropical cyclone is found to be highly asymmetric in the inner core in the mid lower troposphere the asymmetry in the core is dominated by azimuthal wavenumber 1 and wavenumber 2 vortex rossby waves these waves propagate azimuthally upwind against the azimuthal mean cyclonic tangential flow around the eyewall and thus have a much longer cyclonic rotation period by a factor of 2 than the period of a parcel moving with the cyclonic mean tangential flow around the circumference they also propagate outward against the boundary layer inflow of the azimuthal mean cyclone the waves are only visible within a radius of about 60 km from the cyclone center beyond this distance the radial gradient of potential vorticity pv of the azimuthal mean cyclone is too weak to support the vortex rossby waves although the divergent motion remains strong the geopotential height an

boundary layer structure and dynamics in outer hurricane rainbands part i mesoscale rainfall and kinematic structure abstract results of hurricane boundary layer experiments conducted in outer rainbands of hurricanes josephine 1984 and earl 1986 are presented comparisons of precipitation and kinematic structures in these storms and in hurricane floyd 1981 indicate that principal rainbands have common characteristic mesoscale and convective scale features in the boundary layer the two dimensional mesoscale structure suggests that these rainbands are made up of a linear aggregate of cellular reflectivity elements on the inner upshear side of the band and stratiform rain on the outer downshear side the bands are oriented perpendicular to the shear above the boundary layer and cells move downband at about 85 of the density weighted mean wind speed of the 0 2 6 km layer the boundary layer wind field is strongly influenced by the rainband with alongband and crossband wind maxima located on the outer side of the band axis and minima 4 8 km to the inner side maximum crossband convergence and cyclonic shear vor

evolution of the warm core structure during the eyewall replacement cycle in a numerically simulated tropical cyclone abstractthis study examines the evolution of the warm core structure during the secondary eyewall formation sef and the subsequent eyewall replacement cycle erc in a numerically simulated tropi

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

evaluation of planetary boundary layer parameterizations in tropical cyclones by comparison of in situ observations and high resolution simulations of hurricane isabel 2003 part i initialization maximum winds and the outer core boundary layer in this study thefirst of two parts the planetary boundarylayer pbl depicted in high resolution weather research and forecast model wrf simulations of hurricane isabel 2003 is studied and evaluated by direct comparisons with in situ data obtained during the coupled boundary layer and air sea transfer experiment cblast in particular two boundary layer schemes are evaluated the yonsei university ysu parameterization and the mellor yamada janjic myj parameterization investigation of these schemes is useful since they are available for use with wrf are both widely used and are based on entirely different methods for simulating the pbl in this first part the model domains and initialization are described for additional realism of the low level thermodynamic environment a simple mixed layer ocean model is used to simulate ocean cooling the ysu and myj schemes are discussed along with some modifications standard measures of the accuracy of the hurricane simulations such as track maximum surface wind speed and minimum surface pressure are describedforavarietyofparameterchoicesandforthetwoparameterizations theeffectsontrackandintensity of increased horizontal and vertical resolutions are also shown a modification of the original ysu and myj schemes to have ocean roughness lengths more in agreement with recent studies considerably improves the results of both schemes instantaneous wind maximaon the innermost grid with 1 33 kmresolutionare shown to be an accurate representation of the simulated 1 min sustained winds thesimulatedboundarylayersareevaluatedby directcomparison ofthepblassimulatedandasobserved by in situ data from the cblast experiment in the outer core region of the storm the two pbl schemes and their modifiedcounterparts reproduce the observed pbl remarkably well comparisonsare also made to the observed vertical fluxes of momentum heat and moisture in part ii the detailed comparisons of the intensities and structures of the simulated and observed innercore boundary layers are presented and the reasons for the differences are discussed

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

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

miniature supercells in an offshore outer rainband of hurricane ivan 2004 abstract airborne doppler radar observations are used to document the structure of three miniature supercells embedded in an outer rainband of hurricane ivan on 15 september 2004 the cells were located more than 100 km offshore beyond the doppler range of coastal radars the combination of large cape large vertical wind shear and moderate cell relative helicity with an apparent midlevel dry air intrusion provided an offshore environment supporting rotating storms each shallow cell contained a 5 7 km diameter mesocyclonic updraft with midlevel updraft and vorticity maxima that exceeded 6 m s 1 and 0 008 s 1 respectively such offshore structures are consistent with miniature supercells observed onshore in association with tropical cyclone tornado outbreaks the strong updrafts resulted from a combination of kinematic convergence thermal instability and shear induced vertical perturbation pressure gradients mesocyclone production largely resulted from the tilting and subsequent stretching of low l

understanding the vertical structure of potential vorticity in tropical depressions author s murthy vs boos wr abstract 2019 royal meteorological society potential vorticity pv has been used to understand the intensification and motion of a variety of tropical vortices here atmospheric reanalyses and idealized models are used to understand how the vertical structures of moist convective heating and adiabatic advection jointly shape the vertical structures of pv in tropical depressions observationally based estimates reveal a top heavy pv structure in tropical depressions contrasting with bottom heavy structures of absolute vorticity and diabatic pv generation these distinct vertical structures are reproduced in an axisymmetric model which employs the weak temperature gradient approximation for conceptual simplicity and is forced by stratiform and deep convective heating when applied in isolation the stratiform and deep convective heatings produce pv maxima at 500 hpa and near the surface respectively when these two heatings are applied simultaneously interactions between the stratiform and deep convective modes enhance the adiabatic advective tendencies produced by the transverse circulation making the pv distribution more top heavy in the lower and middle troposphere radial advection also greatly reduces the radius of the pv structure relative to that of the imposed heating consistent with structures in observed tropical depressions the implications of these differences in radial structures for using the flux form of the relevant conservation equations e g for pv substance or absolute vorticity are discussed

metamorphic evolution of the assemblage tremolite talc calcite dolomite quartz within a sample of siliceous dolomite from the southern damara orogen namibia magnesian calcite temperatures of calcites formed during metamorphic reactions and fluorine distribution between oh bearing minerals have been measured for the assemblage ie180 1 within a sample of siliceous dolomite from the southern damara orogen two groups of temperatures were found a group with higher temperatures in the range 583 to 545 c for reaction sites where tremolite was formed and a second group with lower temperatures from 522 to 476 c for reaction sites where talc has grown from special reaction textures it is evident that the reaction sites of the higher temperature group related with temolite is older whereas talc has grown after the formation of tremolite with decreasing temperature the transition from the tremolite stability field to the talc stability field occurred at a temperature between the two temperature groups each measured magnesian calcite temperature can be assigned to a microscopic fluid vein which connects single reaction sites either with tremolite or with talc single microveins developed at different times because the prevailing temperature during the formation of individual fluid veins and the connected reaction sites are different the mineral associations and the reaction textures of the sample were formed within a period of time necessary for cooling the rock at least from about 580 to 480 c the textural relations after the successive reaction processes appear to be the result of a single univariant reaction distribution of fluorine between tremolite phlogopite pairs and tremolite talc pairs show that the fluorine content of the tremolite may be inherited in the latter case a plausible p t path is outlined explaining the evolution of assemblages in dolomites and metapelites of the same area which contain staurolite and kyanite the first appearance of staurolite and kyanite in the field is situated on the lower grade side of the zone containing assemblage i the conversation of the present field occurrence of assemblage i is due to the fading of fluid infiltration into the dolomites

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

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

metamorphic response and crustal architecture in a classic collisional orogen the damara belt namibia abstract the damara belt is a well exposed mid crustal section through a collisional orogen of cambrian age that closed the khomas ocean basin between passive margins on the congo and kalahari cratons collision resulted in a bi vergent orogen with a distinct paired metamorphic pattern of foreland vergent high p low t orogenic margins and a broad high grade low p high t orogen core spatial and temporal patterns of the metamorphic response to collision have been characterized for all parts of the belt using a large dataset n 240 of internally consistent quantitative pt determinations evolution of mineral parageneses and semi quantitative p t paths metamorphic mapping and quantitative metamorphic field gradients integration with deformation history structural profiles metamorphic chronology magmatic history and stratigraphy constrains a dynamic model of crustal architecture during peak metamorphic events the pattern of zonal metamorphic response is demarcated by three major metamorphic discontinuities md with steep pressure gradients inferring crustal scale structures that accommodated lateral exhumation of crustal wedges discontinuities are confirmed by deformation features in the field and metamorphic mineral growth indicates that vertical flattening at the peak of metamorphism progressing through ductile to brittle extensional structures crustal wedges along the orogenic margins experienced steep clockwise p t paths with peak pt conditions terminated by isothermal decompression during rapid exhumation in isostatic response to deep burial metamorphic chronology and over printing metamorphic fabrics constrain a sequence of foreland propagating out wedging of crustal thrust wedges that resulted in telescoping of the orogenic margins peak metamorphism at a geothermal gradient of 20 25 c km and 8 9 kb in the southern zone wedge i was attained between 517 530 ma followed by south directed out wedging at the uis pass suture accommodated by relative extension md1 at high structural levels near the boundary with the high grade orogen core out wedging of the southern zone further buried the southern margin zone wedge ii in the footwall below the uis pass suture peak metamorphism at 17 c km and 9 5 11 5 kb in the southern margin zone was attained at 517 4 ma and followed by out wedging on basal thrusts accommodated by vertical flattening and extensional reactivation of the uis pass suture md2 peak metamorphism at 17 c km and 10 5 kb in a high p low t crustal wedge in the northern margin wedge iii occurred at 510 4 ma peak metamorphism in this wedge was terminated by isothermal decompression during north directed thrusting accommodated by extension at higher structural levels near the high grade orogen core md3 granulite facies metamorphism in the high grade orogen core which formed the upper plate to the deeper thrust wedges occurred at significantly lower pressures 4 3 6 0 kb higher t depth ratios 38 47 c km and low p t clockwise p t paths indicating only moderate burial and protracted high grade conditions metamorphic chronology confirms high grade conditions 540 505 ma persisted beyond isostatic adjustment of the high p low t orogenic margins high heat flow conditions and long thermal lag are best explained by lithospheric breakoff during collision in contrast to the high p low t margins that experienced lateral exhumation in a convergent system the high grade orogen core was exhumed vertically as a broad core complex during extensional collapse of the orogen peak metamorphic conditions in the central part of the orogen core record higher pressures than marginal lower grade zones to both the north and south indicating vertical exhumation as a broad massif this post peak vertical exhumation of the central core occurred after 505 ma was accommodated by brittle extensional detachments at high stratigraphic levels with km scale omission of crustal section

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

impacts of evaporation of rainwater on tropical cyclone structure and intensity a revisit abstractthe impact of evaporation of rainwater on tropical cyclone tc intensity and structure is revisited in this study evaporative cooling can result in strong downdrafts and produce low equivalent potential temperature air in the inflow boundary layer particularly in the region outside the eyewall significantly suppressing eyewall convection and reducing the final intensity of a tc different from earlier findings results from this study show that outer rainbands still form but are short lived in the absence of evaporation evaporation of rainwater is shown to facilitate the formation of outer rainbands indirectly by reducing the cooling due to melting of ice particles outside the inner core not by the cold pool dynamics as previously believed only exclusion of evaporation in the eyewall region or the rapid filamentation zone has a very weak effect on the inner core size change of a tc whereas how evaporation in the outer core affects the inner core size depends on how active the inner rainba

a multiscale numerical study of hurricane andrew 1992 part i explicit simulation and verification abstract in this study the inner core structures of hurricane andrew 1992 are explicitly simulated using an improved version of the penn state ncar nonhydrostatic two way interactive movable triply nested grid mesoscale model mm5 a modified betts miller cumulus parameterization scheme and an explicit microphysics scheme were used simultaneously to simulate the evolution of the larger scale flows over the coarser mesh domains the intense storm itself is explicitly resolved over the finest mesh domain using a grid size of 6 km and an explicit microphysics package containing prognostic equations for cloud water ice rainwater snow and graupel the model is initialized with the national centers for environmental prediction analysis enhanced by a modified moisture field a model generated tropical storm like vortex was also incorporated a 72 h integration was made which covers the stages from the storm s initial deepening to a near category 5 hurricane intensity and the landfall over florida as

evaluation of an e e and three other boundary layer parameterization schemes in the wrf model over the southeast pacific and the southern great plains abstractto accurately simulate the atmospheric state within the planetary boundary layer pbl by pbl parameterization scheme in different regions with their dominant weather climate regimes is imp

reply to comment by f feser et al on improved global maps and 54 year history of wind work on ocean inertial motions 1 in their comment feser et al 2003 argue that the ncep reanalysis surface winds used by alford 2003 henceforth a03 are artificially high at high frequencies due to temporal aliasing this possibility is investigated here by direct comparison with buoy winds in the northeastern atlantic as in a previous more extensive buoy comparison in the pacific alford 2001 henceforth a01 no evidence for aliasing of ncep winds is found

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

a study on the synoptic dynamical characteristics of compact tropical cyclones in the western north pacific abstractthis study focuses on the synoptic and dynamical characteristic of compact and incompact tropical cyclones tcs in the western north pacific to identify the distinct mechanisms related to the development and maintenance of these two categories of tcs the weather research and forecasting model wrf is used to simulate the compact typhoon yutu 2007 and the incompact typhoon manyi 2007 simulation results of yutu show that the wind speed increases primarily in the inner core region where strong relative vorticity and high inertial stability is also located comparatively the inertial stability for typhoon manyi is much weaker which makes it more susceptible to influences from external low level forcing diagnoses of the numerical simulations as well as examination of the synoptic environments that embed the two tcs suggest that compact tcs mainly develop through internal dynamics whereas incompact tcs are usually driven by external forcing several sets of sensitivity experiments are desi

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 numerical study of typhoon megi 2010 part i rapid intensification abstracttyphoon megi 15w was the most powerful and longest lived tropical cyclone tc over the western north pacific during 2010 while it shared many common features of tcs that crossed luzon island in the northern philippines megi experienced unique intensity and structural changes which were reproduced reasonably well in a simulation using the advanced research weather research and forecasting model arw wrf with both dynamical initialization and large scale spectral nudging in this paper processes responsible for the rapid intensification ri of the modeled megi before it made landfall over luzon island were analyzed the results show that megi experienced ri over the warm ocean with high ocean heat content and decreasing environmental vertical shear the onset of ri was triggered by convective bursts cbs which penetrate into the upper troposphere leading to the upper tropospheric warming and the formation of the upper level warm core in turn cbs with their roots inside of the eyewall in

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