buoyancy and shear characteristics of hurricane tornado environments abstract detailed composite profiles of temperature moisture and wind are constructed for tornado environments in tropical cyclones that affected the united states during the period 1948 86 winds are composited in components radial and tangential to the tropical cyclone center at observation time guided by observed patterns of tornado occurrence composites are constructed for a variety of different stratifications of the data including proximity to tornadoes position relative to the cyclone center time of day time after cyclone landfall cyclone translation speed and location of landfall the composites are also compared to composite soundings from great plains tornado environments a variety of sounding parameters am examined to see which are most closely related to the patterns of tornado distribution lower tropospheric vertical shears are generally stronger in the tropical cyclone tornado environments than on the great plains vertical shear and helicity parameters along with 700 hpa wind s

a numerical study of the effect of island terrain on tropical cyclones abstract a triply nested movable mesh model was used to study the behavior of tropical cyclones encountering island mountain ranges the integration domain consisted of a 37 wide and 45 long channel with an innermost mesh resolution of 1 6 the storms used for this study were embedded in easterly flows of 5 and 10 m s 1 initially realistic distributions of island topography at 1 6 resolution were inserted into the model domain for the region of the caribbean including the islands of cuba hispaniola and puerto rico the island of taiwan and the region of luzon in the northern philippines it was found that the islands affected the basic flow as well as the wind field directly associated with the storm system the combination of these effects caused changes in the track and translational speed of the storm in particular in the case of the 5 m s 1 easterly flow the storm accelerated and veered to the north well before reaching taiwan for the other island distributions the northward deflecti

an analysis of the landfall of hurricane nora 1997 abstract the changes to the motion and structure of the eastern pacific tropical cyclone nora 1997 during landfall are investigated nora developed south of the mexican coast intensified into a hurricane and made landfall over northwestern mexico and the southwestern united states in this study the authors document the evolution of the structure of nora from a variety of sources observations derived from satellite imagery show the approach of the hurricane to the baja california peninsula and the development of a localized area of mesoscale convection that intensified while moving over the gulf of california the propagation of this convective system became the dominant feature of the landfall and provided heavy precipitation over a region confined to western arizona numerical simulations with the pennsylvania state university national center for atmospheric research mesoscale model version 5 are used to examine the details of the evolution of the observed area of convection over the gulf simulat

effects of vertical wind shear on the intensity and structure of numerically simulated hurricanes a series of numerical simulations of tropical cyclones in idealized large scale environments is performed to examine the effects of vertical wind shear on the structure and intensity of hurricanes the simulations are performed using the nonhydrostatic pennsylvania state university national center for atmospheric research fifth generation mesoscale model using a 5 km fine mesh and fully explicit representation of moist processes when large scale vertical shears are applied to mature tropical cyclones the storms quickly develop wavenumber one asymmetries with upward motion and rainfall concentrated on the left side of the shear vector looking downshear in agreement with earlier studies the asymmetries develop due to the storm s response to imbalances caused by the shear the storms in shear weaken with time and eventually reach an approximate steady state intensity that is well below their theoretical maximum potential intensity as expected the magnitude of the weakening increases with increasing shear all of the storms experience time lags between the imposition of the large scale shear and the resulting rise in the minimum central pressure while the lag is at most a few hours when the storm is placed in very strong 15 m s21 shear storms in weaker shears experience much longer lag times with th e5ms 21 shear case showing no signs of weakening until more than 36 h after the shear is applied these lags suggest that the storm intensity is to some degree predictable from observations of largescale shear changes in all cases both the development of the asymmetries in core structure and the subsequent weakening of the storm occur before any resolvable tilt of the storm s vertical axis occurs it is hypothesized that the weakening of the storm occurs via the following sequence of events first the shear causes the structure of the eyewall region to become highly asymmetric throughout the depth of the storm second the asymmetries in the upper troposphere where the storm circulation is weaker become sufficiently strong that air with high values of potential vorticity and equivalent potential temperature are mixed outward rather than into the eye this allows the shear to ventilate the eye resulting in a loss of the warm core at upper levels which causes the central pressure to rise weakening the entire storm the maximum potential vorticity becomes concentrated in saturated portions of the eyewall cloud aloft rather than in the eye third the asymmetric features at upper levels are advected by the shear causing the upper portions of the vortex to tilt approximately downshear the storm weakens from the top down reaching an approximate steady state intensity when the ventilated layer can descend no farther due to the increasing strength and stability of the vortex at lower levels

the effect of vertical shear on tropical cyclone intensity change abstract the effect of vertical shear on tropical cyclone intensity change is usually explained in terms of ventilation where heat and moisture at upper levels are advected away from the low level circulation which inhibits development a simple two layer diagnostic balance model is used to provide an alternate explanation of the effect of shear when the upper layer wind in the vortex environment differs from that in the lower layer the potential vorticity pv pattern associated with the vortex circulation becomes tilted in the vertical the balanced mass field associated with the tilted pv pattern requires an increased midlevel temperature perturbation near the vortex center it is hypothesized that this midlevel warming reduces the convective activity and inhibits the storm development previous studies have shown that diabatic heating near the storm center acts to reduce the vertical tilt of the vortex circulation these studies have also shown that there is an adiabatic process that acts to redu

the transition of the hurricane frederic boundary layer wind field from the open gulf of mexico to landfall abstract numerous aircraft ship buoy and land nation data were composited with respect to the center of hurricane frederic for two time periods a 24 h period corresponding to the storm s position in the open gulf of mexico on 12 september 1979 and an 8 h period corresponding to the landfall of frederic near 0400 gmt on 13 september comparison of wind analyses for the two periods indicated a rotation of maximum inflow angles from the southeast to northeast quadrants and a strong frictional decrease of wind speed over land them and other features of the landfall analysis were compared with a model landfall study by moss and jones 1978 the landfall composite wind field was compared with the fujita damage vector analysis to determine the damage time interval and mean wind speed range damage vector directions were found to be well correlated with the surface streamlines with the most severe damage being associated with frederic s northern eyewall ten meter level wind speed data over water vo and

orographic influences on rainfall and track deflection associated with the passage of a tropical cyclone abstract in this study a nonhydrostatic mesoscale model coupled ocean atmosphere mesoscale prediction system coamps was adopted to simulate supertyphoon bilis 2000 and investigate the dynamics of orographic rain and track deflection accompanying the storm as it passes the central mountain range cmr of taiwan both the storm track and its associated orographic rainfall distribution are well predicted by the numerical model the intensity of the storm is underpredicted resulting in a discontinuous track due to the lack of specifying a bogus vortex at the time of model initialization cyclonic curvature of the storm track over the island topography track as well as major circulation features are similar to previous studies of landfalling typhoons affecting taiwan the model overpredicts the total amount of accumulated rainfall generalization of the flux model proposed in a 2001 study by lin and coauthors is used to help predict and understand the observed rainfall distribution by calculating bo

interaction of typhoons with the taiwan orography part ii continuous and discontinuous tracks across the island abstract numerical model simulations of west moving tropical cyclones approaching and crossing the taiwan orography are shown to contain many of the observed surface features vortices tend to track continuously around the northern end of the island due to the deflection of the deep layer mean flow and the vortex circulation is modified less because the higher winds to the right of the center do not have a strong interaction with the barrier discontinuous tracks predominate for vortices approaching the central southern portions of the taiwan orography severe distortions of the inner core circulation occur and the surface pressure and surface wind centers become decoupled and may be dissipated at different rates numerical sensitivity studies demonstrate that more intense and rapidly moving vortices are more like to cross directly over the barrier and thus maintain a continuous track in one special case of a weak but fast moving vortex approaching the southern end the model simulates the existence of

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

the effects of complex terrain on severe landfalling tropical cyclone larry 2006 over northeast australia abstract the interaction between complex terrain and a landfalling tropical cyclone tc over northeastern australia is investigated using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 severe tc larry in march 2006 made landfall over an area of steep coastal orography and caused extensive damage the damage pattern suggested that the mountainous terrain had a large influence on the tc wind field with highly variable damage across relatively small distances the major aims in this study were to reproduce the observed features of tc larry including track intensity speed of movement size decay rate and the three dimensional wind field using realistic high resolution terrain data and a nested grid with a horizontal spacing of 1 km for the finest domain referred to as ctrl and to assess how the above parameters change when the terrain height is set to zero notopog the tc track for ctrl including the timing and locat

modeling the effects of land sea roughness contrast on tropical cyclone winds abstract the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 is used to simulate tropical cyclone tc wind distribution near landfall on an f plane at 15 n the effects of the different surface roughness between the land and sea on the wind asymmetry is examined under a strong constraint of a dry atmosphere and time invariant axisymmetric mass fields the winds are found to adjust toward a steady state for prelandfall 50 100 and 150 km offshore landfall and postlandfall 50 100 and 150 km inland tc positions the tc core is asymmetric even when it lies completely offshore or inland the surface 10 m wind asymmetry at the core for pre post landfall position is apparently related to the acceleration deceleration of the flow that has just moved over the sea land as a response to the sudden change of surface friction for prelandfall tc positions the resulted strong surface inflow to the left and front left relative

numerical simulation of typhoon gladys 1994 and its interaction with taiwan terrain using the gfdl hurricane model abstract numerical integrations using the geophysical fluid dynamics laboratory gfdl hurricane model were performed to study the evolution of typhoon gladys 1994 and its interaction with the taiwan terrain consistent with most previous studies the taiwan topography results in the deceleration of gladys s translation speed and southward deviation as it approaches taiwan on the other hand gladys accelerates northwestward while passing taiwan which is likely to be related to the moist processes and differs from the track pattern in the dry model of lin et al although the gfdl hurricane model forecast underestimates gladys s intensity the model can capture the evolution of gladys s intensity especially its weakening during landfall which is primarily due to the cutoff of the water vapor supply in the boundary layer as gladys approached the taiwan terrain other mesoscale phenomena including the pattern of heavy precipitation and the formation of secondary lows are well simulated by the model

finescale spiral band features within a numerical simulation of hurricane opal 1995 abstract one of the most recognizable features associated with a well organized tropical system are spiral rainbands these quasi stationary rainbands often extend hundreds of kilometers from the storm center and have been well described in the literature observational studies have since identified additional banding structures including outward propagating small scale spiral bands these rainbands may have considerable implications for core type tornadoes local wind maxima associated with downburst damage swaths as well as a role in overall hurricane dynamics as such here a numerical simulation of hurricane opal 1995 is examined with unprecedented resolution necessary to capture these small scale spiral bands opal was an intense landfalling hurricane that demonstrated small scale spiral banding features analogous to those observational studies the scale and characteristics of the simulated bands are consistent with observed small scale spiral banding of intense hurricanes a varietal of kelvi

the petrogenesis of a platiniferous dunite pipe in the bushveld complex infiltration metasomatism by a chloride solution the driekop dunite pipe crosscuts part of the noritic layered sequence of the upper critical zone in the eastern bushveld complex the central orebody of the pipe contains platinum group minerals base metal sulfides magnetite and iron rich olivine the country rock forms a collapse structure around the pipe with the layered sequence becoming almost vertical near the contact with the pipe it is proposed that a high temperature chloride solution flowed through irregular channel ways along a structural weakness near the axis of the pipe and reacted with the noritic host rocks leading ultimately to the formation of dunite reaction fronts advanced at different rates outward from the channelways and produced a sequence of metasomatic zones characteristics of infiltration metasomatism that are evident in the pipe include the movement of material over large distances in predominantly one direction the formation of a monomineralic rock the occurrence of a marginal zone that is enriched by displaced components and plateaus in the compositions of mineral solid solutions the reactions responsible for the major changes in the bulk composition of the host rocks were desilication of orthopyroxene to produce olivine and dissolution of plagioclase the 67 percent volume loss accompanying these reactions can account for the structural collapse of the critical zone around the pipe some olivine in the pipe is too fayalitic to have been produced by simple desilication of host rock orthopyroxene the enrichment of olivine in iron can take place bymg 2 sio 4 2fecl sub 2 sub aq fe 2 sio 4 2mgcl sub 2 sub aq forsterite fayalite aqueous chloride complexes are also believed to have played an important role in the transport and precipitation of the platinum group elements the base metals and other cations interdependent chemical reactions involving a chloride solution olivine magnetite and the platinum group elements can account for the preferential association of the ore with iron rich olivine infiltration metasomatism by a high temperature chloride solution may have an important bearing on the interpretation of other features of the bushveld complex

interaction of typhoons with the taiwan orography part i upstream track deflections abstract a combined observational and numerical modeling approach is used to study the upstream track deflections of westward moving tropical cyclones approaching the mountainous terrain of taiwan although the standard deviations are large the mean track deflections are larger and have a different orientation for storms approaching the southern end of the island from those approaching the northern end the deflections tend to be larger for weaker and slower moving storms two distinct regions of upstream track deflections that are detected in the observations are explored in a sensitivity study with a 45 km horizontal resolution and 16 layer numerical model as the outer circulation of the tropical cyclone begins to interact with the mountain barrier the zonal decelerations and southward track deflections are explained by an enhanced blocking and deflection of the environmental flow advecting the cyclone the larger effect for southern approaching storms compared to northern storms is because the stron

why rolls are prevalent in the hurricane boundary layer recent remote sensing observations show that the hurricane boundary layer flow although energetic is not a region of homogeneous turbulence in fact the observations convincingly demonstrate that a large fraction of the turbulent flow in the regions away from the deep convective rainbands is highly organized into intense horizontal roll vortices that are approximately aligned with the mean wind and span the depth of the boundary layer these observations show that rolls strongly increase the flux of momentum between the underlying surface and the main body of the storm compared to an equivalent hurricane boundary layer flow without rolls the linear and nonlinear dynamics of hurricane boundary layer roll formation are outlined and it is shown why rolls are in fact the expected basic hurricane boundary layer state the model presented here explains the hurricane roll features currently documented in field programs and makes predictions that can be tested in future experiments the primary effects of rolls on the boundary layer fluxes are inherently nonlocal and nongradient and hence cannot be captured by standard downgradient turbulence parameterizations used in hurricane simulations however the nonlinear theory is the proper starting point for developing boundary layer parameterizations that include roll modification of the turbulent fluxes

a high resolution simulation of asymmetries in severe southern hemisphere tropical cyclone larry 2006 abstract advances in observations theory and modeling have revealed that inner core asymmetries are a common feature of tropical cyclones tcs in this study the inner core asymmetries of a severe southern hemisphere tropical cyclone tc larry 2006 are investigated using the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 and the kepert wang boundary layer model the mm5 simulated tc exhibited significant asymmetries in the inner core region including rainfall distribution surface convergence and low level vertical motion the near core environment was characterized by very low environmental vertical shear and consequently the tc vortex had almost no vertical tilt it was found that prior to landfall the rainfall asymmetry was very pronounced with precipitation maxima consistently to the right of the westward direction of motion persistent maxima in low level convergence and vertical motion formed ahead of the translating tc resul

laser oxygen isotope analysis of weathering goethite from the lateritic profile of yaou french guiana paleoweathering and paleoclimatic implications abstract oxygen isotopic compositions of weathering goethite pseudomorphs after pyrite in the lateritic profile of yaou french guiana were measured by laser fluorination the laterite at yaou is composed of a 25 m thick saprolite overlain by a 3 m thick latosol petrographic observations indicate that the pseudomorphic replacement of pyrite by goethite occurs at or near the weathering front and is complete the goethite pseudomorphs are essentially devoid of al and are progressively dissolved and partially replaced by a microcrystalline plasma of kaolinite and goethite in the upper horizons latosol of the profile the laser technique used in this study permitted the determination of the 18 o value of individual grains of goethite and the investigation of grain to grain variation within a single sample horizon as well as vertical variation with depth in the latosol the goethite 18 o values range from 0 8 to 3 2 and exhibit significant grain to grain and vertical variation this most likely reflects undetected intragrain contamination with microcrystalline kaolinite in the saprolite the goethite 18 o values are consistent ranging from 1 0 to 1 8 between 3 and 18 m depth and from 2 5 to 3 3 between 23 m depth and the weathering front at 28 m oxygen isotope compositions of present groundwater soil water and rainfall at yaou were also measured and compared with calculated isotopic compositions for goethite forming waters goethite pseudomorphs in the lower part of the saprolite are in isotopic equilibrium with present groundwater indicating that they may be forming today or that they formed in the recent past under climatic conditions similar to present conditions in contrast goethite pseudomorphs found higher in the profile are not in isotopic equilibrium with present water but with a water depleted in 18 o by 1 50 relative to present groundwater it is suggested that these low 18 o pseudomorphs are probably older and formed under different paleoclimatic conditions at a time when climatic regimes were possibly more monsoonal than today this is in agreement with models of climatic evolution derived from pedological considerations the results of this study suggest that goethite pseudomorphs in ancient saprolites may preserve their original o isotopic composition acquired at the weathering front and may therefore be used as indicators of changes in weathering climatic conditions during the evolution of a profile

high precision u th dating of storm transported coral blocks on frankland islands northern great barrier reef australia abstract high energy storm transported coral blocks are widespread on the reef flats of the great barrier reef gbr australia and have the potential to be used as proxies for reconstructing past storm cyclone events prior to historical or instrumental records in this study samples from 42 individual transported coral blocks were collected from the inshore frankland islands northern gbr for high precision mc icpms u th dating with their surface mortality ages recording the timing of individual storms or cyclones responsible for their uplift from their original growth position the dated mortality ages were found to match well with known historical storm cyclone events in the last century with 80 of them falling within episodes of increased storm activity 1910 1915 1945 1950 1955 1960 1975 1990 1995 2000 ad captured by instrumental historic records confirming that transported coral blocks on inshore reefs can be used as proxies for past storm cyclone occurrences using this approach this study also identified 17 additional storm cyclone events that occurred before european settlement in the 1850s including three oldest events at 758 4 3 7 777 9 4 9 and 985 2 4 8 ad respectively our results despite still preliminary suggest that the storm cyclone activity in this region tends to broadly correlate with the positive modes of the pacific decadal oscillation pdo during the last millennium in addition there appears to be a decreasing age trend from the shore to the reef edge from 758 4 3 7 ad to 1988 3 1 6 ad which can be attributed to sea level fall and or reef island progradation over the last 2000 years

effects of vertical wind shear and storm motion on tropical cyclone rainfall asymmetries deduced from trmm abstract vertical wind shear and storm motion are two of the most important factors contributing to rainfall asymmetries in tropical cyclones tcs global tc rainfall structure in terms of azimuthal distribution and asymmetries relative to storm motion has been previously described using the tropical rainfall measuring mission microwave imager rainfall estimates the mean tc rainfall distribution and the wavenumber 1 asymmetry vary with storm intensity and geographical location among the six oceanic basins this study uses a similar approach to investigate the relationship between the structure of tc rainfall and the environmental flow by computing the rainfall asymmetry relative to the vertical wind shear the environmental vertical wind shear is defined as the difference between the mean wind vectors of the 200 and 850 hpa levels over an outer region extending from the radius of 200 800 km around the storm center the wavenumber 1 maximum rainfall asymmetry is downshear left right in the northern

re os isotope and pd ru variations in chromitites from the critical zone bushveld complex south africa abstract rhenium osmium isotope measurements of selected chromitites from the critical zone of the bushveld igneous complex reveal that a significant component of radiogenic os was present in the magma when it formed 2 06 ga ago measured 187 os 188 os ratios increase with stratigraphic height and individual layers have similar values across the complex initial 187 os 188 os ratios for chromitites from the western bushveld decrease from 0 140 at the lg to 0 129 at the mg2 chromitite increasing to 0 153 at the ug2 chromitite the inflection at mg2 mg3 is the boundary between the lower and upper critical zone consistent with previous mineralogical and geochemical studies indicating a shift in magma composition at this point chromite separates have os values of 12 35 at 2 06 ga and are too radiogenic for a purely mantle derivation assimilation of 5 mafic granulitic lower crust in a tholeiitic parent magma can explain the radiogenic values pd ru ratios for the intergranular and chromite separate components of each layer differ by orders of magnitude but relative shifts from layer to layer are similar combined with the re os data the results suggest that pge were concentrated into chromitites by magmatic or early deuteric processes that were specific to each layer post layering upward mobilization of pge by hydrothermal processes probably did not play a significant role in pge enrichment

orographic influence on a drifting cyclone abstract in this study a primitive equation numerical model is adopted to investigate the orographic influence on a drifting cyclone over an idealized topography similar to that of taiwan for a cyclone propagating from the east and impinging on the central portion of the mountain a northerly surface jet tends to form upstream of the mountain between the primary cyclone and the mountain due to blocking and channeling effects two pressure ridges and one trough are also produced when the cyclone approaches the mountain the low level vorticity and low pressure centers decelerate and turn southward upstream of the mountain due to orographic blocking at the same time the upstream low level vorticity is blocked by the mountain the abrupt increase of surface vorticity and the contraction of cyclone scale on the lee side are explained by the generation of new potential vorticity pv due to wave breaking associated with the severe downslope wind and hydraulic jump the generation of this new pv is evidenc

the influence of large scale topography on barotropic vortex motion abstract the motion of a barotropic vortex in the vicinity of a large scale topographic feature is examined through numerical integration of the shallow water equations in an equatorial beta plane channel the topographic parameters are chosen to represent the sierra madre mountains of mexico the motion of the vortex is affected through modification of the asymmetric circulation by vortex stretching associated with divergence of the horizontal velocity field as the air flows across the mountain a vortex that approaches the topography from the east is accelerated and deflected toward the south and a vortex initially west of the mountain recurves and moves toward the cut this motion is in contrast to the northwestward motion of a vortex over level terrain the vortex motion is also compared to the direction of the imposed potential vorticity gradient the topographic effects described in this paper may be important in forecasting hurricane motion in the eastern north pacific and western gulf of mexico

changes in the low level kinematic and thermodynamic structure of hurricane alicia 1983 at landfall abstract aircraft land station and buoy data were composited with respect to the center of hurricane alicia 1983 for three 8 h periods corresponding to prelandfall in the open gulf of mexico landfall in the galveston area and postlandfall in the vicinity of houston comparison of the wind analyses before during and after landfall emphasizes the land sea frictional asymmetry at landfall in addition other asymmetries in the surface wind field and differences between the flight level and the surface wind fields are revealed the asymmetric structure of the surface wind field may be interpreted as having resulted from the combined effects of land sea roughness differences background environmental flow and storm translation the land sea frictional difference acted to oppose the mean vortex flow over land and reinforce it over water the southwest background environmental flow acted nearly parallel to the coastline producing surface inflow on the left side and outflow on the right side while the

a numerical study of the effect of a mountain range on a landfalling tropical cyclone abstract a triply nested movable mesh model was used to study the effects of a mountain range on a landfalling tropical cyclone embedded in an easterly flow of 10 m s 1 the integration domain consisted of a 37 wide and 45 long channel with an innermost mesh resolution of 1 6 an idealized mountain range with maximum height of 958 meters was placed parallel to the shoreline the mountain range which spanned 19 in the north south direction and 5 in the east west direction was centered in the middle of the channel results obtained were compared with a previous landfall simulation performed without the effect of the mountain range included in particular comparison was made of the total storm rainfall maximum wind distribution and storm decay rate it was found that the storm filled much more rapidly in the simulation run with the mountain included the mountain range affected the decay rate through reduction in the supply of latent and kinetic energy into the storm circulation during as well

a comparison of numerical simulations of hydrostatic flow over mountains with observations abstract numerical solutions of a hydrostatic mesoscale model for stratified flow over topography are compared with analytical results and observational data the numerical model was found to reproduce well phase and amplitude of linear and nonlinear waves provided by analytical models the model was effective in simulating observed chinook associated with an intense mountain wave in a nonchinook case the model was successful in reproducing main features of the observed velocity distribution associated with an elevated region of blocking the observed and simulated momentum flux profiles are almost identical the comparisons of the model results with observations and analytical results demonstrate the overall ability of the model to realistically simulate mountain wave flow in a series of numerical experiments we have investigated how far the steepness of the waves depends on stratospheric wind structure and on orography our simulations suggest that there is a bifurcation line between the linear and no

investigation of turbulent momentum flux in the typhoon boundary layer turbulent momentum flux in the typhoon boundary layer was measured at a turbulent flux tower in southeast china using an eddy covariance technique during the passage of typhoons fanapi and megi in 2010 the anemometers were mounted on the cantilever bracket at the height of 26 6 m 42 4 m 60 4 m and 82 9 m the momentum flux in the typhoon boundary layer decreased with increasing height during the two typhoon passages the decrease was nearly linear during the passage of the typhoon fanapi however in the boundary layer of the typhoon megi the momentum flux at 26 6 m height was much greater than that at 42 4 m height the cospectra of wind components showed that the enhanced flux at the bottom of the boundary layer was caused by small scale turbulence with frequency in the range of 0 1 1 hz and can be explained by the turbulent energy accumulation of small scale turbulence this article is protected by copyright all rights reserved

the dynamics of boundary layer jets within the tropical cyclone core part ii nonlinear enhancement abstract observations of wind profiles within the tropical cyclone boundary layer until recently have been quite rare however the recent spate of observations from the gps dropsonde have confirmed that a low level wind speed maximum is a common feature of the tropical cyclone boundary layer in part i a mechanism for producing such a maximum was proposed whereby strong inward advection of angular momentum generates the supergradient flow the processes that maintain the necessary inflow against the outward acceleration due to gradient wind imbalance were identified as being i vertical diffusion ii vertical advection and iii horizontal advection and a linear analytical model of the boundary layer flow in a translating tropical cyclone was presented and used to diagnose the properties of the jet and the near surface flow a significant shortcoming was that the jet was too weak which was argued to be due to the neglect of vertical advection here a high resolution dry hydrostatic numerical

high resolution simulation of tropical storm ivan 2004 in the southern appalachians role of planetary boundary layer schemes and cumulus parametrization the weather research and forecasting wrf model was used to simulate the evolution of tropical storm ivan 2004 in the southeast united states using both the yonsei university ysu and mellor yamada janjic myj boundary layer parametrizations in contrast to tropical cyclone tc simulations over the ocean the effect of the surface layer becomes secondary for a dissipating hurricane along its terrestrial track although these two schemes can reproduce ivan reasonably well our results suggest that the mixing properties for damped mechanical turbulent conditions weakly stable are strongly underestimated by both parametrizations this underestimation impacts the thermodynamic properties of the storm leading to significant differences in the storm areal extent and the simulated precipitation fields suggestions for further improvements are provided an evaluation of the impact of using or not using a convective parametrization specifically the kain fritsch kf scheme at 3 km grid spacing shows marginal impact on storm coverage intensity and precipitation except for the presence of widespread light rainfall in the piedmont east of the mountains when the kf is employed analysis of the thermal structure of the simulated storm indicates that in the inner storm region the kf is either not activated or primarily produces parametrized shallow convection as a result the net heating tendency associated with adiabatic and diabatic processes is almost unaltered inside the storm together with a nearly equivalent surface momentum sink leading to similar storm areal extent and intensity light rainfall to the east of the mountains can be due to the trigger mechanism of kf which depends on boundary layer convergence forcing parametrized deep convection near the coast where surface roughness changes enhance convergence

dynamics of track deflection associated with the passage of tropical cyclones over a mesoscale mountain abstract in this study the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 was used to simulate supertyphoon bilis in 2000 and typhoon toraji in 2001 in order to investigate the dynamics of track deflection caused by the central mountain range cmr of taiwan the mm5 predicted the track of each storm reasonably well bilis was stronger and had a relatively faster forward motion which helped make the track continuous as it crossed the cmr the use of a bogus vortex in the initialization process helped produce a storm closer to the observed strength bilis is a classic example of a typhoon crossing taiwan with a continuous track for comparison typhoon toraji a typical typhoon having a discontinuous track was also studied toraji was weaker and had a relatively slower forward speed which prevented the original low center from crossing over the cmr and forced more air parcels to go around the northern tip of the cmr as a r

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

effects of terrain on the surface structure of typhoons over taiwan abstract the island of taiwan is situated in the main path of western north pacific typhoons its dominant central mountain range cmr with a hoizontal scale comparable to the radius of a typhoon often produces significant distortions in the typhoon circulation a 20 year dataset from 22 surface stations is used to describe the effects of the taiwan terrain on the surface structure of typhoons empirical orthogonal function analysis on the pressure field is used to identify the primary structure modes the first mode is a uniform sign anomaly pattern portraying the decrease in pressure as a typhoon is approaching the second mode represents the strong terrain induced west east pressure gradient that is normal to the main axis of the cmr the third mode results mainly from the west cast pressure gradient arising from the relative location of the typhoon center to the east or west of taiwan but it also contains a weak south north pressure gradient that can he attributed to the terrain a regression tech

control parameters for the influence of a mesoscale mountain range on cyclone track continuity and deflection abstract in this study prospective control parameters are identified for diagnosing the continuity and deflection of cyclone tracks across a mesoscale mountain range based on idealized simulations of a westward moving cyclone it was found that the cyclone track becomes a discontinuous continuous track and the cyclone experiences more less deflection with a combination of small large values of vmax nh u nh r ly u flx and vmax fr and large small value of h lx the symbols are defined as follows vmax the maximum tangential wind n the brunt vaisala frequency h the mountain height u the basic wind speed r the radius of vmax f the coriolis parameter and lx and ly the horizontal scales of the mountain in x and y directions respectively a conceptual model is proposed to explain track deflection and continuity for a westward moving cyclone encountering idealized topography representative of the central mountain range of taiwan with weak orographic blocking a cyclone crosses over the mount

application of the 187re 187os system to black shale geochronometry the decay of 187re to 187os provides a tool for determining depositional ages of black shales re and os concentrations and os isotopic compositions of whole rock samples of the bakken shale a mississippian devonian boundary black shale yield a whole rock isochron with an age of 354 49 ma this age is in agreement with the accepted age of the bakken shale 360 ma the initial 187os186os ratio of the isochron is 6 2 3 3 this value is indistinguishable from the 187os186os ratios observed in modern black sea sediments the concentration of common os in bakken shale samples is strongly correlated with total nitrogen indicating that a large fraction of the os in these samples is associated with a hydrogenous component which overwhelms any os supplied to the sediment in association with detrital material or cosmic dust the dominance of the hydrogenous component imparts a relatively homogeneous initial 187os186os ratio to the sediment at the time of deposition the degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity the pattern of scatter is consistent with postdepositional mobilization of re and or os on a small spatial scale we suggest that this mobilization may be a consequence of petroleum formation and migration in the bakken shale

an observational case for the prevalence of roll vortices in the hurricane boundary layer abstract doppler velocity data from weather surveillance radar 1988 doppler wsr 88d radars during four hurricane landfalls are analyzed to investigate the presence of organized vortices in the hurricane boundary layer hbl the wavelength depth magnitude and track of velocity anomalies were compiled through analysis of doppler velocity data the analysis reveals alternating bands of enhanced and reduced azimuthal winds closely aligned with the mean wind direction resulting statistics provide compelling evidence for the presence of organized secondary circulations or boundary layer rolls across significant areas during four hurricane landfalls the results confirm previous observations of the presence of rolls in the hbl a potential limitation of the study presented here is the resolution of the wsr 88d data in particular analysis of higher resolution data e g from the doppler on wheels is needed to confirm that data aliasing has not unduly impacted the statistics reported here momentum flux

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