cape in tropical cyclones abstractconvective available potential energy cape and the vertical distribution of buoyancy were calculated for more than 2000 dropsonde soundings collected by the noaa gulfstream iv aircraft calculations were done with and without the effects of condensate loading entrainment and the latent heat of fusion cape showed larger values downshear than upshear within 400 km of the center consistent with the observed variation of convective intensity the larger downshear cape arose from i higher surface specific humidity ii lower midtropospheric temperature and for entraining cape iii larger free tropospheric relative humidity reversible cape had only one half the magnitude of pseudoadiabatic cape as shown previously reversible cape with fusion closely resembled pseudoadiabatic cape without fusion entrainment had the most dramatic impact entraining cape was consistent with the observed radial distribution of convective intensity displaying the largest values downshear at inner radii with

development of inverted metamorphic isograds in the western metamorphic belt juneau alaska an inverted metamorphic gradient is preserved in the western metamorphic belt near juneau alaska the western metamorphic belt is part of the coast plutonic metamorphic complex of western canada and southeastern alaska that developed as a result of tectonic overlap and or compressional thickening of crustal rocks during collision of the alexander and stikine terranes detailed mapping of pelitic single mineral isograds systematic changes in mineral assemblages and silicate geothermometry indicate that thermal peak metamorphic conditions increase structurally upward over a distance of about 8 km peak temperatures of metamorphism increase progressively from about 530 c for the garnet zone to about 705 c for the upper kyanite biotite zone silicate geobarometry suggests that the thermal peak metamorphism occurred under pressures of 9 11 kbar the metamorphic isograds are in general parallel to the tonalite sill that is regionally continuous along the east side of the western metamorphic belt although truncation of the isograds north of juneau indicates that the sill intrusion continued after the isograds were established our preferred interpretation of the cause of the inverted gradient is that it formed during compression of a thickened wedge of relatively wet and cool rocks in response to heat flow associated with the formation and emplacement of the tonalite sill magma garnet rim compositions and widespread growth of chlorite suggest partial re equilibration of the schists under pressures of 5 6 kbar during uplift in response to final emplacement and crystallization of the tonalite sill the combined results of this study with previous studies elsewhere in the western metamorphic belt indicate that high t high p metamorphism associated with the collision of the alexander and stikine terranes was a long lived event extending from about 98 ma to about 67 ma

on the sensitivity of tropical cyclone intensification under upper level trough forcing this study is part of the efforts undertaken to resolve the bad trough good trough issue for tropical cyclone tc intensity changes and to improve the prediction of these challenging events sensitivity experiments are run at 8 km resolution with vortex bogusing to extend the previous analysis of a real case of tc trough interaction dora in 2007 the initial position and intensity of the tc are modified leaving the trough unchanged to describe a realistic environment simulations are designed to analyze the sensitivity of tc prediction to both the variety of tc trough configurations and the current uncertainty in model analysis of tc intensity and position results show that tc intensification under upper level forcing is greater for stronger vortices the timing and geometry of the interaction between the two cyclonic potential vorticity anomalies associated with the cutoff low and the tc also play a major role in storm intensification the intensification rate increases when the tc initially located 12 northwest of the trough is displaced 1 closer by allowing a gradual deformation and equatorward tilting of the trough both scenarios foster an extended inflow channel of cyclonic vorticity at midlevels toward the vortex inner core conversely unfavorable interaction is found for vortices displaced 3 or 4 east or northeast variations in environmental forcing relative to the reference simulation illustrate that the relationship between intensity change and the 850 200 hpa wind shear is not systematic and that the 200 hpa divergence 335 350 k mean potential vorticity or 200 hpa relative eddy momentum fluxes may be better predictors of tc intensification during tc trough interactions

rapid weakening of tropical cyclones in monsoon gyres over the tropical western north pacific abstractas one major source of forecasting errors in tropical cyclone intensity rapid weakening of tropical cyclones an intensity reduction of 20 kt or more over a 24 h period over the tropical open ocean can result from the interaction between tropical cyclones and monsoon gyres this study aims to examine rapid weakening events occurring in monsoon gyres in the tropical western north pacific wnp basin during may october 2000 2014 although only less than one third of rapid weakening events happened in the tropical wnp basin south of 25 n more than 40 of them were associated with monsoon gyres about 85 of rapid weakening events in monsoon gyres occurred in september and october the rapid weakening events associated with monsoon gyres are usually observed near the center of monsoon gyres when tropical cyclone tracks make a sudden northward turn the gyres can enlarge the outer size of tropical cyclones and tend to induce prolonged rapid weakening events with an average duration of 33 2 h the la

on the influences of vertical wind shear on symmetric tropical cyclone structure derived from amsu abstract axisymmetric temperatures and gradient balanced winds associated with tropical cyclones derived from the advanced microwave sounding unit are stratified by the 24 h averaged vector difference of the horizontal wind between 200 and 850 hpa or vertical wind shear using 186 total cases that are limited to tropical cyclones with intensities greater than 33 m s 1 or mature and are located over sea surface temperatures greater than 26 4 c vertical wind shear based composites are created results show that as the vertical wind shear increased the upper level warm core structure associated with the tropical cyclone descended resulting in a shallower balanced vortex these observationally based results are presented in the context of recent mesoscale modeling results of the effect of shear on tropical cyclone structure

the structure and evolution of hurricane elena 1985 part i symmetric intensification one of the most complete aircraft reconnaissance and ground based radar datasets of a single tropical cyclone was recorded in hurricane elena 1985 as it made a slow 3 day anticyclonic loop in the gulf of mexico eighty eight radial legs and 47 vertical incidence scans were collected aboard noaa wp 3d aircraft and 1142 ground based radar scans were made of elena s eyewall and inner rainbands as the storm intensified from a disorganized category 2 to an intense category 3 hurricane this large amount of continuously collected data made it possible to examine changes that occurred in elena s inner core symmetric structure as the storm intensified on the first day of study elena was under the influence of vertical wind shear from an upper tropospheric trough to the west the storm was disorganized with no discernable eyewall and nearly steady values of tangential wind and relative vorticity early on the second day of study a near superposition and constructive interference occurred between the trough and elena coincident with upward vertical velocities and the radial gradient of reflectivity becoming concentrated around the 30 km radius once an inner wind maximum and eyewall developed the radius of maximum winds contracted and a sharp localized vorticity maximum emerged with much lower values on either side this potentially unstable vorticity profile was accompanied by a maximum in equivalent potential temperature in the eyewall deeper and stronger inflow out to 24 km from the eyewall and mean outflow toward the eyewall from the eye within 6 12 h intensification came to an end and elena began to slowly weaken vorticity and equivalent potential temperature at 850 hpa showed indications of prior mixing between the eye and eyewall during the weakening stage an outflow jet developed at the eyewall radius a strong 850 hpa updraft accompanied the outflow jet yet convection was less active aloft than before this feature appeared to represent a shallow outward sloping updraft channel associated with the spindown of the storm

life of a six hour hurricane hurricane claudette developed from a weak vortex in 6 h as deep convection shifted from downshear into the vortex center despite ambient vertical wind shear exceeding 10 m s 1 six hours later it weakened to a tropical storm and 12 h after the hurricane stage a circulation center could not be found at 850 hpa by aircraft reconnaissance at hurricane strength the vortex contained classic structure seen in intensifying hurricanes with the exception of 7 12 c dewpoint depressions in the lower troposphere upshear of the center these extended from the 100 km radius to immediately adjacent to the eyewall where equivalent potential temperature gradients reached 6 k km 1 the dry air was not present prior to intensification suggesting that it was associated with vertical shear induced subsidence upshear of the developing storm it is argued that weakening of the vortex was driven by cooling associated with the mixing of dry air into the core and subsequent evaporation and cold downdrafts evidence suggests that this mixing might have been enhanced by eyewall instabilities after the period of rapid deepening the existence of a fragile small but genuinely hurricane strength vortex at the surface for 6 h presents difficult problems for forecasters such a temporary hurricane in strongly sheared flow might require a different warning protocol than longer lasting hurricane vortices in weaker shear

large intensity changes in tropical cyclones a case study of supertyphoon flo during tcm 90 abstract a unique dataset recorded during the rapid intensification and rapid decay of typhoon flo is analyzed to isolate associated environmental conditions and key physical processes this case occurred during the tropical cyclone motion tcm 90 field experiment with enhanced observations especially in the upper troposphere beyond about 300 km these data have been analyzed with a four dimensional data assimilation technique and a multiquadric interpolation technique while both the ocean thermal structure and vertical wind shear are favorable they do not explain the rapid intensification or the rapid decay a preconditioning phase is defined in which several interrelated factors combine to create favorable conditions i a cyclonic wind burst occurs at 200 mb ii vertical wind shear between 300 and 150 mb decreases 35 iii the warm core is displaced upward and iv 200 mb outflow becomes larger in the 400 1200 km radial band while a layer of inflow develops below this outflow these condit

numerical study on the development of asymmetric convection and vertical wind shear during tropical cyclone landfall idealized simulations on an f plane of tropical cyclone tc landfall under a quiescent environment in the southern hemisphere are performed to investigate the effects of land sea surface contrast on precipitation in the control simulation with realistic roughness and moisture over land to the south of the tc the simulated vortex moves toward land due to a land induced steering flow the abrupt decrease increase of tangential wind at the surface leads to convergence divergence on the onshore offshore flow side enhanced convergence at the top of the planetary boundary layer is found on both onshore and offshore sides and is caused by advection from the surface and the enhanced offshore radial wind the boundary layer top convergence pattern is consistent with the rainfall distribution vertical wind shear develops during the landfall process associated with the low and upper level asymmetric flows across the model domain the wavenumber 1 like low level asymmetric flow is introduced by an asymmetric geopotential height field that is generated by the large area of frictionally induced convergence on the onshore side and divergence on the offshore side the upper level asymmetric flow is attributed to asymmetric convection and associated diabatic heating after landfall most rainfall is found in the down shear right quadrant which is consistent with previous studies that focused on the effect of environmental shear although the existence of feedback from the vertical wind shear to rainfall remains an open question the relation between maximum rainfall and vertical wind shear is robust especially when the shear magnitude is large after landfall

assessing the influence of upper tropospheric troughs on tropical cyclone intensification rates after genesis abstractthe role of upper tropospheric troughs on the intensification rate of newly formed tropical cyclones tcs is analyzed this study focuses on tcs forming in the presence of upper tropospheric troughs in the north atlantic basin between 1980 and 2014 tcs were binned into three groups based upon the 24 h intensification rate starting at the time of genesis rapid tc genesis rtcg slow tc genesis stcg and neutral tc genesis ntcg composite analysis shows rtcg events are characterized by amplified upper tropospheric flow with the largest upshear displacement between the tc and trough of the three groups rtcg events are associated with greater quasigeostrophic qg ascent in upshear quadrants of the tc forced by differential vorticity advection by the thermal wind especially around the time of genesis this pattern of qg ascent closely matches the rtcg composite of infrared brightness temperatures conversely ntcg events are associated with an upper tropospheric trough that is closest to the

reintensification and eyewall formation in strong shear a case study of typhoon noul 2015 abstractstrong vertical wind shear produces asymmetries in the eyewall structure of a tropical cyclone tc and is generally a hostile environment for tc intensification typhoon noul 2015 howev

paleobotanical evidence for ecosystem disruption at the cretaceous tertiary boundary from wood mountain saskatchewan canada a continuous subsurface cretaceous tertiary boundary section including the boundary clay within an 87 cm thick lignite has been recovered from a core hole near wood mountain saskatchewan canad

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

extratropical transition of southwest pacific tropical cyclones part ii midlatitude circulation characteristics abstract this second of two papers on extratropical transition et over the southwest pacific ocean focuses on the variability of et a climatology of et onset based on a previously described objective technique shows that et commences 15 of latitude nearer the equator on average than similar cases from the northern hemisphere characteristic midlatitude circulation patterns accompanying et near 30 s are identified by means of empirical orthogonal function eof analysis of 50 storms the first eigenvector pattern explaining nearly half the circulation variability expresses relaxed and enhanced pressure gradients south of the storm that define composites similar to cradled and captured classifications previously described for the southeast indian ocean the second eof distinguishes redeveloping from weakening storms reintensifying storms were located beneath strong cyclonic vorticity advection cva near the equatorward entrance region of an upper jet whereas the upper jet was well to the west of

the paleogeographic significance of aquilapollenites occurrence in pakistan abstract the occurrence of the genus aquilapollenites in upper cretaceous and neogene sediments of northwestern pakistan is reported here aquilapollenites amplus aquilapollenites reductus and aquilapollenites sp occur in the maastrichtian palynomorph assemblage from an outcrop sample of the mir ali section northern waziristan aquilapollenites medeis in the neogene murgha faqir zai formation of the pishin basin balochistan is considered a reworked cretaceous specimen the upper cretaceous sediments of the asian plate on the tethys margin are considered to be the source of aquilapollenites spp in these samples

dynamical and physical processes leading to tropical cyclone intensification under upper level trough forcing abstractthe rapid intensification of tropical cyclone tc dora 2007 southwest indian ocean under upper level trough forcing is investigated tc trough interaction is simulated using a limited area operational numerical weather prediction model the interaction between the storm and the trough involves a coupled evolution of vertical wind shear and binary vortex interaction in the horizontal and vertical dimensions the three dimensional potential vorticity structure associated with the trough undergoes strong deformation as it approaches the storm potential vorticity pv is advected toward the tropical cyclone core over a thick layer from 200 to 500 hpa while the tc upper level flow turns cyclonic from the continuous import of angular momentum it is found that vortex intensification first occurs inside the eyewall and results from pv superposition in the thick aforementioned layer the main pathway to further storm intensification is associated with secondary eyewall formation triggered by external

external influences on hurricane intensity part iii potential vorticity structure abstract the interaction of hurricane elena 1985 with a baroclinic wave was reexamined using both potential vorticity pv and a formulation for eliassen palm fluxes in cylindrical coordinates the hurricane began to deepen rapidly as a narrow upper level positive pv anomaly became nearly superposed over the low level center the intensification appeared to represent an evaporation wind feedback activated by constructive interference of the pv anomalies enhanced convection associated with this process eroded the upper pv anomaly and prevented it from crossing the hurricane and reversing the intensification the eliassen palm flux divergence showed that maximum eddy activity remained in the upper troposphere prior to the reintensification this activity was produced in part because the action of the outflow anticyclone of the hurricane contributed to synoptic scale wave breaking the upper level pv anomaly that approached the center was much narrower in extent than the original synoptic scale trough th

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

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

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

on hurricane outflow structure abstract flow fields from the model of wu and emanuel are presented it is demonstrated that the interaction of background shear with a uniform source of low potential vorticity air at the storm top can produce many of the observed characteristics of hurricane outflow including outflow jets our model is compared to other extant models of hurricane outflow

relationship between the track and structural evolution of hurricane sandy 2012 using a regional ensemble abstractan ensemble of 72 weather research and forecasting wrf model simulations is evaluated to examine the relationship between the track of hurricane sandy 2012 and its structural evolution

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

a composite study of the interactions between tropical cyclones and upper tropospheric troughs abstract the objective of this study is to understand how interactions with upper tropospheric troughs affect the intensity of tropical cyclones the study includes all named atlantic tropical cyclones between 1985 and 1996 to minimize other factors affecting intensity change times when storms are over subcritical sea surface temperatures 26 c or near landfall are removed from the sample a trough interaction is defined to occur when the eddy momentum flux convergence calculated over a 300 600 km radial range is greater than 10 m s 1 day 1 the trough interaction cases are separated into four composites i favorable superposition tropical cyclone intensifies with an upper tropospheric potential vorticity pv maximum within 400 km of the tropical cyclone center ii unfavorable superposition iii favorable distant interaction upper pv maximum between 400 and 1000 km from the tropical cyclone center and iv unfavorable distant interaction for comparison two additional composites are cre

low level kinematic thermodynamic and reflectivity fields associated with hurricane bonnie 1998 at landfall during 11 h on 26 august 1998 two noaa wp 3d aircraft deployed 85 global positioning system gps dropwindsondes within 2 of latitude of the circulation center of hurricane bonnie as it made landfall in north carolina about 75 of the sondes successfully collected data which were used to create a series of storm relative horizontal maps of kinematic and thermodynamic variables from 10 m to 2 km reflectivity fields were analyzed from the weather surveillance radar 1988 dopplers wsr 88ds located at wilmington and morehead city north carolina and the tail and lower fuselage radars aboard the wp 3ds gps sonde performance and deployment spacing is adequate to identify several aspects of the vortex these include 1 warm dry stable air in the offshore flow that results in reduced equivalent potential temperatures entering the southern portion of the eyewall 2 cooler air collocated with the upwelled water in the right rear quadrant and under the eyewall and 3 an atypical radial wind pattern with strong inflow southwest of the circulation center and outflow northeast of the center the strongly asymmetric structure found at 10 m becomes much more homogeneous by 2 km altitude no intense rainbands developed over land in the onshore flow nor did the bands in the onshore flow undergo any significant changes once they made landfall beyond the eyewall the offshore flow contained much less precipitation than the onshore portion of the storm characteristics beyond the eyewall appear to have been modulated by the proximity to land but hurricane intensity did not vary the authors infer that the lower energy content of the inflow was offset by the contraction of the eyewall

tropical storm formation in a baroclinic environment abstract an analysis is presented of the large scale conditions associated with the initial development of tropical storm diana september 1984 in a baroclinic environment ordinary extratropical wave cyclogenesis began along an old frontal boundary east of florida after 0000 utc 7 september and culminated in tropical cyclogenesis 48 h later water vapor satellite imagery showed that the initial cyclogenesis and incipient tropical storm formation was nearly indistinguishable from a classical midlatitude development cyclogenesis occurred in three stages a large scale cold trough and associated frontal system crossed the atlantic coast while a small potential vorticity maximum aloft fractured off the main trough and stalled over central florida in the first stage as the main trough sheared off eastward cyclogenesis began along the southwestern end of the stalled frontal zone east of florida anticyclogenesis to the north in the wake of the shearing trough allowed a surge of cooler and drier air to flo

north atlantic extratropical rossby wave breaking during the warm season wave life cycle and role of diabatic heating abstractthis study investigates the life cycle of anticyclonic rossby wave breaking during the extended warm season july october over the north atlantic basin it was found that upper tropospheric breaking waves are coupled with lower level perturbations and can be traced back to a wave train that extends from the north pacific the overturning of potential vorticity pv contours during wave breaking is associated with the rapid development of an upper level ridge which occurs along the east coast of north america and over a warm and moist airstream the ridge development is investigated using the pv budget analysis and trajectory analysis the pv budget analysis suggests that the horizontal advection of pv by the perturbed flow dictates the movement and the later decay of the ridge the ridge amplification opposed by the horizontal advection of pv is driven by the vertical advection and the diabatic production of pv both of which are connected to diabatic heating the vital role of diabatic heatin

idealized tropical cyclone responses to the height and depth of environmental vertical wind shear abstractthree sets of idealized cloud resolving simulations are performed to investigate the sensitivity of tropical cyclone tc structure and intensity to the height and depth of environmental vertical wind shear in the first two sets of simulations shear height and depth are varied independently in the third set orthogonal polynomial expansions are used to facilitate a joint sensitivity analysis despite all simulations having the same westerly deep layer 200 850 hpa shear of 10 m s 1 different intensity and structural evolutions are observed suggesting the deep layer shear alone may not be sufficient for understanding or predicting the impact of vertical wind shear on tcs in general vertical wind shear that is shallower and lower in the troposphere is more destructive to model tcs because it tilts the tc vortex farther into the downshear left quadrant the vortices that tilt the most are unable to precess upshear and realign resulting in their failure to intensify shear height appears to

the role of synoptic scale flow during tropical cyclogenesis over the north atlantic ocean abstract the synoptic scale flow during tropical cyclogenesis and cyclolysis over the north atlantic ocean is investigated using compositing methods genesis and lysis are defined using the national hurricane center nhc now known as the tropical prediction center best track data genesis lysis occurs when nhc first last identifies and tracks a tropical depression in the final best track dataset storm centered composites are created with the analysis of the tropical oceanic lower level atoll 900 hpa and 200 hpa winds for june november produced by nhc for the years 1975 93 results show that significant regional differences exist in 200 hpa flow during genesis across the atlantic basin composites of genesis in the western part of the basin show a 200 hpa trough ridge located to the west east of the atoll disturbance in the eastern half of the basin composites of genesis show a sprawling 200 hpa ridge centered northeast of the atoll disturbance the major axis of this elliptically shaped 20

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

the convective evolution and rapid intensification of hurricane earl 2010 abstractthe relationship between an inner core r 100 km lightning outbreak and the subsequent rapid intensification ri of hurricane earl 2010 is examined using lightning strikes recorded by the world wide lightning location network wwlln and in situ observations from various aircraft missions moderate 8 4 m s 1 northeasterly deep layer 850 200 hpa vertical wind shear caused by outflow from hurricane danielle existed over earl at the beginning of a prolonged period of ri over 70 of the lightning strikes within a 500 km radius occurred downshear with a preference toward downshear right in the outer rainbands in agreement with previous studies the location of inner core strikes in earl differed markedly from previous studies the inner core lightning activity precessed from left of shear to upshear an extremely rare event beginning just prior to the onset of ri diagnosis of the vortex tilt midway through the lightning precession showed this convection was occurring downtilt in the ups

rossby wave packets on the midlatitude waveguide a review abstractrossby wave packets rwps are rossby waves for which the amplitude has a local maximum and decays to smaller values at larger distances this review focuses on upper tropospheric transient rwps along the midlatitude jet stream their central characteristic is the propagation in the zonal direction as well as the transfer of wave energy from one individual trough or ridge to its downstream neighbor a process called downstream development these rwps sometimes act as long range precursors to extreme weather and presumably have an influence on the predictability of midlatitude weather systems the paper reviews research progress in this area with an emphasis on developments during the last 15 years the current state of knowledge is summarized including a discussion of the rwp life cycle as well as rossby waveguides recent progress in the dynamical understanding of rwps has been based in part on the development of diagnostic methods these methods include algorithms to identify and track rwps

hurricane juan 2003 part i a diagnostic and compositing life cycle study abstract a detailed analysis of the complex life cycle of hurricane juan in 2003 is undertaken to elucidate the structures and forcings that prevailed over the period leading up to the hurricane s landfall in halifax nova scotia canada despite the presence of easterly wave precursors hurricane juan s initial development is shown to occur in a baroclinic environment beneath a low latitude potential vorticity streamer this feature interacts with a lower level shear line as the incipient vortex begins to effectively focus ascent and convection the system undergoes a slow tropical transition over a period of several days as the deep layer shear over the developing storm decreases the hurricane is repeatedly perturbed by subsynoptic scale waves traveling along the leading edge of a large upstream trough however hurricane juan maintains its tropical structure despite its relatively high formation latitude 28 n and its northward trajectory the unusual persistence of the storm s tropical nature as i

on the dynamics of tropical cyclone and trough interactions abstractthe interaction between a tropical cyclone tc and an upper level trough is simulated in an idealized framework using coupled ocean atmosphere mesoscale prediction system coamps for trop

high resolution leaf fossil record spanning the cretaceous tertiary boundary theories that explain the extinctions characterizing the cretaceous tertiary k t boundary1 3 need to be tested by analyses of thoroughly sampled biotas palynological studies are the primary means for stratigraphic placement of the terrestrial boundary and for estimates of plant extinction4 12 but have not been combined with quantitative analyses of fossil leaves megaflora megafloral studies complement palynology by representing local floras with assemblages capable of high taxonomic resolution13 but have previously lacked the sample size and stratigraphic spacing needed to resolve latest cretaceous floral history5 14 18 we have now combined megafloral data from a 100 m thick composite k t boundary section in north dakota with detailed palynological analysis here the boundary is marked by a 30 palynofloral extinction coincident with iridium and shocked mineral anomalies and lies 2 m above the highest dinosaur remains the megaflora undergoes a 79 turnover across the boundary and smaller changes 17 and 25 m below it this pattern is consistent with latest cretaceous climatic warming preceding a bolide impact

external influences on hurricane intensity part i outflow layer eddy angular momentum fluxes abstract outflow layer winds were objectively analyzed every 12 h for 6 days during the life cycle of hurricane elena 1985 a high correlation was found between angular momentum fluxes by azimuthal eddies at large radii and central pressure changes in the storm 27 33 h later momentum flux by eddies exceeded that by the azimuthal mean outside the 800 km radius while vortex spinup by the eddies reached instantaneous magnitudes as large as 25 m s 1 day outflow maxima and minima repeatedly appeared more than 1000 km from the hurricane center and tracked inward with time the results provide evidence of significant environmental control on the behavior of the storm after reaching hurricane strength elena experienced a major secondary intensification associated with a large inward cyclonic eddy momentum flux produced by the passage of a middle latitude trough north of the hurricane an outflow maximum appeared radially inside of the eddy momentum source consistent with balanced vortex theory and tracke

rapid intensification of a sheared tropical storm abstract a weak tropical storm gabrielle in 2001 experienced a 22 hpa pressure fall in less than 3 h in the presence of 13 m s 1 ambient vertical wind shear a convective cell developed downshear left of the center and moved cyclonically and inward to the 17 km radius during the period of rapid intensification this cell had one of the most intense 85 ghz scattering signatures ever observed by the tropical rainfall measuring mission trmm the cell developed at the downwind end of a band in the storm core maximum vorticity in the cell exceeded 2 5 10 2 s 1 the cell structure broadly resembled that of a vortical hot tower rather than a supercell at the time of minimum central pressure the storm consisted of a strong vortex adjacent to the cell with a radius of maximum winds of about 10 km that exhibited almost no tilt in the vertical this was surrounded by a broader vortex that tilted approximately left of the ambient shear vector in a similar direction as the broad precipitation shield this st

the extratropical transition of tropical cyclones part i cyclone evolution and direct impacts abstractextratropical transition et is the process by which a tropical cyclone upon encountering a baroclinic environment and reduced sea surface temperature at higher latitudes transforms into an extratropical cyclone this process is influenced by and influences phenomena from the tropics to the midlatitudes and from the meso to the planetary scales to extents that vary between individual events motivated in part by recent high impact and or extensively observed events such as north atlantic hurricane sandy in 2012 and western north pacific typhoon sinlaku in 2008 this review details advances in understanding and predicting et since the publication of an earlier review in 2003 methods for diagnosing et in reanalysis observational and model forecast datasets are discussed new climatologies for the eastern north pacific and southwest indian oceans are presented alongside updates to western north pacific and north atlantic ocean climatologies advances in understanding and in some cases mode

subtropical cyclones over the southwestern south atlantic climatological aspects and case study abstracthurricane catarina 2004 and subtropical storm anita 2010 called attention to the development of subtropical cyclones scs over the south atlantic basin besides strong and organized storms a large number of weaker shallower cyclones with both extratropical and tropical characteristics form in the region impacting the south american coast the main focus of this study is to simulate a climatology of subtropical cyclones and their synoptic pattern over the south atlantic proposing a broader definition of these systems in addition a case study is presented to discuss the main characteristics of one weak sc the interim ecmwf re analysis era interim and ncep ncar reanalysis are used to construct the 33 yr 1979 2011 climatology and a comparison between them is established both reanalyses show good agreement in the scs intensity geographical distribution and seasonal variability but the interannual variability is poorly correlated anomaly composites for austral summer show that sub

sequential palynological changes across the composite cretaceous tertiary k t boundary claystone and contiguous strata western canada and montana u s a the boundary claystone in the western canada basin is composed of three intimately associated layers with a regional distribution a basal brownish grey hackly claystone a middle brownish black sa

secondary circulation of tropical cyclones in vertical wind shear lagrangian diagnostic and pathways of environmental interaction abstractthis study introduces a lagrangian diagnostic of the secondary circulation of tropical cyclones tcs here defined by those trajectories that contribute to latent heat release in the region of high inertial stability of the tc core this definition accounts for prominent asymmetries and transient flow features trajectories are mapped from the three dimensional physical space to the two dimensional entropy temperature space the mass flux vector in this space subsumes the thermodynamic characteristics of the secondary circulation the lagrangian diagnostic is then employed to further analyze the impact of vertical wind shear on tcs in previously published idealized numerical experiments one focus of this analysis is the classification and quantitative depiction of different pathways of environmental interaction based on thermodynamic properties of trajectories at initial and end times confirming results from previous work vertical shear significantly increases the intrusion of low equivalent

garnet chloritoid equilibria in eclogitic pelitic rocks from the sesia zone western alps their bearing on phase relations in high pressure metapelites abstract a detailed study of garnet chloritoid micaschists fom the sesia zone western alps is used to constrain phase relations in high pressure hp metapelitic rocks in addition to quartz phengite paragonite and rutile the micaschists display two distinct parageneses namely garnet chloritoid chlorite and garnet chloritoid kyanite talc has never been observed garnet and chloritoid are more magnesian when chlorite is present instead of kyanite the distinction of the two equilibria results from different bulk rock chemistries not from p t conditions or redox state estimated p t conditions for the eclogitic metamorphism are 550 600 c 15 18 kbar the presence of primary chlorite in association with garnet and chloritoid leads us to construct two possible afm topologies for the sesia metapelites the paper describes a kfmash multisystem for hp pelitic rocks which extends the grid of harte hudson 1979 towards higher pressures and adds the phase talc observed parageneses in hp metapelites are consistent with predicted phase relations critical associations are gt ctd chl and gt ctd ky at relatively low temperatures and gl chl ky and gt tc ky at relatively high temperatures

heat sources of cretaceous metamorphism in the eastern alps a discussion abstract the alpine orogenic cycle is characterised by a series of early metamorphic events that occurred in the cretaceous the eoalpine events a collection of data on peak metamorphic conditions pt paths and on relationships between structure and metamorphism for these events in the eastern alps shows that 1 eoalpine metamorphism occurred largely simultaneously with pervasive deformation 2 the eoalpine thermal peak was reached near the pressure peak 3 lower grade structurally higher rocks reached their metamorphic peak earlier than higher grade structurally lower rocks and there is a wide spread of metamorphic ages 4 low grade metamorphic conditions are probably more perturbed than high grade conditions and 5 there is a conspicuous regional distribution of metamorphic grade with amphibolite and eclogite facies metamorphism occurring predominantly in two regions located symmetrically west and east of the tauern window possible heating mechanisms are discussed that can satisfy these observations and a review of previous thermal models is provided it is shown that models which rely on conductive heat transfer cannot account for all of these observations in order to assess other heat sources the effects of shear heating are evaluated here with simple model calculations and a straightforward comparison of length and time scales of dissipative heat production the results suggest that shear heat episodically released during the stacking of the austroalpine nappe pile may be a significant contributor to the observed thermal perturbation

rapid intensification of a sheared fast moving hurricane over the gulf stream abstracthurricane irene 1999 rapidly intensified from 65 to 95 kt 33 4 to 48 9 m s 1 in 18 h during the rapid intensification ri period the northeastward storm motion increased from 10 to 18 m s 1 the ambient southwesterly vertical wind shear increased from 6 7 to 10 13 m s 1 and the downshear tilt of the inner core vortex increased the azimuthal wavenumber 1 asymmetric convection that developed was consistent with a superposition of shear induced and storm motion induced forcing for vertical motion downshear and ahead of the center although the diabatic heating remained strongly asymmetric it was of sufficient intensity to dramatically increase the azimuthally averaged heating this heating occurred almost entirely inside the radius of maximum winds a region known to favor rapid warm core development and spinup of the vortex it is hypothesized that asymmetric forcing from the large vertical wind shear and rapid storm motion were responsible for ri an unanswered question is what determin

the metamorphic evolution of garnet cordierite sillimanite gneisses of the gruf complex eastern pennine alps metapelitic gneisses occuring as lenses and bands within the migmatites of the gruf complex in the eastern pennine alps contain various combinations of the minerals quartz biotite cordierite garnet sillimanite plagioclase k feldspar spinel orthopyroxene anthophyllite and muscovite the most common rock type is represented by a darkschistosebiotiterichcordierite garnet sillimanite gneiss a consistent pressure temperature range of 3 4 kb and 600 650 c has been calculated for the last metamorphic equilibration from six geological thermobarometers

synoptic and frontal scale influences on tropical transition events in the atlantic basin part i a six case survey abstract the process by which a baroclinic vertically sheared extratropical cyclone is transformed into a warm core vertically stacked tropical cyclone is known as tropical transition six recent tropical transitions of strong extratropical precursors in the subtropical north atlantic are compared to better understand the manner by which some of the canonical structures and dynamical processes of extratropical cyclones serve to precondition the cyclone for transition all six transitions resulted from the interaction between a surface baroclinic zone and an upper level trough during the extratropical cyclogenesis of each storm a period of intense near surface frontogenesis along a bent back warm front occurred to the northwest of each sea level pressure minimum within the resultant circulation diabatic redistribution of potential vorticity pv promoted the growth of a low level pv maximum near the western end of the warm front concurrently the upper level pv anomaly associated with each trough w

the alpine geodynamic evolution of penninic nappes in the eastern central alps the eastern central alps consist of several pennine nappes with different tectonometamorphic histories the tectonically uppermost units oceanic avers bundnerschiefer continental suretta and tambo nappes oceanic vals bundnerschiefer show cretaceous early tertiary w directed thrusting with associated blueschist facies metamorphism related to subduction of the pennine units beneath the austroalpine continental crust this event caused eclogite facies metamorphism in the underlying continental adula nappe the gross effect was crustal thickening the tectonically lower continental simano nappe is devoid of any imprint from this event in the course of continent continent collision high t metamorphism and n directed movements occurred both affected the whole nappe pile more or less continuously from amphibolite to greenschist facies conditions crustal thinning commenced during the regional temperature peak a final phase is related to differential uplift under retrograde p t conditions further thinning of the crust was accommodated by e to ne directed extensional deformation

the present day simulation and twenty first century projection of the climatology of extratropical transition in the north atlantic abstractthis study explores the simulations and twenty first century projections of extratropical transition et of tropical cyclones tcs in the north atlantic with a newly developed global climate model the forecast oriented low ocean resolution flor version of the geophysical fluid dynamics laboratory gfdl coupled model version 2 5 cm2 5 flor exhibits good skill in simulating present day et properties e g cyclone phase space parameters a version of flor in which sea surface temperature sst biases are artificially corrected through flux adjustment flor fa shows much improved simulation of et activity e g annual et number this result is largely attributable to better simulation of basinwide tc activity which is strongly dependent on larger scale climate simulation flor fa is also used to explore changes of et activity in the twenty first century under the representative concentration pathway rcp 4 5 scenario a contrasting pattern is found in which regional tc density increas

a technique for diagnosing three dimensional ageostrophic circulations in baroclinic disturbances on limited area domains abstract the methodology developed by keyser et al for representing and diagnosing three dimensional vertical circulations in baroclinic disturbances using a two dimensional vector streamfunction referred to as the psi vector is restricted to f plane channel model geometry the vertical circulation described by the psi vector consists of the irrotational or divergent part of the ageostrophic wind and the vertical velocity a key property of the psi vector is that its projections onto arbitrarily oriented orthogonal vertical planes yield independent vertical circulations allowing separation of a three dimensional vertical circulation into two two dimensional components and thus objective assessment of the extent to which a three dimensional vertical circulation is oriented in a preferred direction here the methodology for determining the psi vector is modified to be suitable for real data applications the modifications consists of reformulating the diagnostic equations to apply to conformal map pr

the effects of vertical wind shear on the distribution of convection in tropical cyclones abstract the influence of vertical wind shear on the azimuthal distribution of cloud to ground lightning in tropical cyclones was examined using flash locations from the national lightning detection network the study covers 35 atlantic basin tropical cyclones from 1985 99 while they were over land and within 400 km of the coast over water a strong correlation was found between the azimuthal distribution of flashes and the direction of the vertical wind shear in the environment when the magnitude of the vertical shear exceeded 5 m s 1 more than 90 of flashes occurred downshear in both the storm core defined as the inner 100 km and the outer band region r 100 300 km a slight preference for downshear left occurred in the storm core and a strong preference for downshear right in the outer rainbands the results were valid both over land and water and for depression storm and hurricane stages it is argued that in convectively active tropical cyclones deep divergent circulations oppose the ver

biodiversity changes in cretaceous palynofloras of eastern asia and western north america abstract palynology has great potential for providing comparative data and interpretations about changes in biodiversity during the cretaceous period this is especially true for both eastern asia and western north america because of strong floristic similarities that existed between these regions during cretaceous time also because palynomorphs of terrestrial origin can be deposited in offshore as well as terrestrial environments significant potential exists for marine to continental palynostratigraphic correlations in both regions palynological biostratigraphy can improve the geologic dating of changes in biodiversity during the early cretaceous eastern asia and western north america lay within the cerebropollenites palynofloral province a circumpolar phytogeographic zone characterized by distinctive palynological assemblages during most of the late cretaceous these regions lay within the palynofloristically unique aquilapollenites province which was more restricted geographically than the cerebropollenites province the most important development during cretaceous time that is reflected in palynological assemblages was the rise of the angiosperms as the numerically and ecologically dominant forms of vegetation the most striking short term palynofloral event in the two regions was the sudden disappearance of species of aquilapollenites and associated genera at the cretaceous tertiary k t boundary both of these occurrences produced major changes in biodiversity in the terrestrial realm geologic research in international geological correlation program project 434 can benefit from applications of palynostratigraphy palynologic research within project 434 could include development of a comprehensive palynostratigraphic zonation for the cretaceous the definition of regional palynostratigraphic datums and investigation of the record of floral change at the k t boundary

synoptic scale disturbances with circular symmetry abstract ate balanced flow structure of various classic synopitc scale disturbances is reviewed using the invertibility principle for isentropic potential vorticity ipv distributions complete solutions are shown for cold and warm core structures of various types the basic model imagines the tropopause to be the interface between the lower potential vorticity of the troposphere and the approximately six fold larger value typical of the lower stratosphere the sensitivity of the structure of the potential temperature variation along the tropopause and at the surface is described results are presented in diagrammatic form to allow easy diagnosis of the vortex structure from synoptic data available at perhaps only a few levels the point is made that upper air ipv and surface potential temperature distributions are often the most crucial in accounting for the balanced flow structure

a numerical study of the outflow layer of tropical cyclones abstract the structure and dynamics of the outflow layer of tropical cyclones are studied using a three dimensional numerical model weak and strong tropical cyclones are produced by the numerical model when starting from idealized initial vortices embedded in mean hurricane soundings the quasi steady state outflow layers of both the weak and strong tropical cyclones have similar characteristics 1 the circulations are mainly anticyclonic except for a small region of cyclonic flow near the center and highly asymmetric about the center 2 the outflow layer is dominated by a narrow but elongated outflow jet which contributes up to 50 of the angular momentum transport and 3 the air particles in the outflow jet mostly originate from the lower level following in up and out trajectories we found that there are secondary circulations around the outflow jet very much like those associated with midlatitude westerly jet streaks in the jet entrance region the secondary circulation is thermally direct

extreme helicity and intense convective towers in hurricane bonnie abstract helicity was calculated in hurricane bonnie 1998 using tropospheric deep dropsonde soundings from the nasa convection and moisture experiment large helicity existed downshear of the storm center with respect to the ambient vertical wind shear it was associated with veering semicircular hodographs created by strong vortex scale radial vertical flow induced by the shear the most extreme values of helicity among the largest ever reported in the literature occurred in the vicinity of deep convective cells in the downshear left quadrant these cells reached as high as 17 5 km and displayed the temporal and spatial scales of supercells convective available potential energy cape averaged 861 j kg 1 downshear but only about one third as large upshear the soundings nearest the deep cells were evaluated using two empirical supercell parameters that make use of cape helicity and or shear these parameters supported the possible existence of supercells as a consequence of the exceptional hel

quasi biweekly oscillations of the south asian monsoon and its co evolution in the upper and lower troposphere the upper tropospheric quasi biweekly oscillation uqbw of the south asian monsoon is studied using the potential vorticity field on the 370 k isentrope the uqbw is shown to be a common occurrence in the upper troposphere during the monsoon and its typical evolution is described we suggest that the uqbw is a phenomenon of both the middle and tropical latitudes owing its existence to the presence of the planetary scale upper tropospheric monsoon anticyclone the uqbw is first identified as rossby waves originating in the northern flank of the monsoon anticyclone these rossby waves break when reaching the pacific ocean and their associated cyclonic pv anomalies move southward to the east of asia and then westward across the indian ocean and africa advected by the monsoon anticyclone a strong correlation or co evolution between the uqbw and quasi biweekly oscillations in the lower troposphere qbw is also found in particular analysis of vertically integrated horizontal moisture transport 850 hpa geopotential and outgoing long wave radiation show that the uqbw is usually observed at the same time as and co evolves with the lower tropospheric qbw over south asia we discuss the nature of the uqbw and its possible physical link with the qbw

the dynamics of the enso atlantic hurricane teleconnection enso related changes to the north african asian jet affect atlantic basin tropical cyclogenesis abstract the nature of the teleconnection linking enso variability with atlantic basin tropical storm formation is investigated solutions of the linearized barotropic vorticity equation forced with august october el nino event divergence produce upper tropospheric vorticity anomalies over the sahel and at the mouth of the north african asian naa jet over the tropical atlantic these responses are similar in magnitude and orientation to observed enso vorticity variability for this region further investigation reveals that the vorticity anomalies over the subtropical atlantic develop primarily in response to very low wavenumber westward propagating stationary rossby waves excited by el nino related convective activity over the equatorial pacific ocean however the dynamics of this teleconnection change as the atlantic basin hurricane season progresses in august and september the response is dominated by the westward propagating stationary rossby waves that alter vorticity within the naa jet and to it

tropical cyclone formation in a sheared environment a case study abstract the development of hurricane danny 1997 from depression to hurricane was examined using cloud to ground lightning data reconnaissance aircraft data and satellite imagery vertical wind shear between 850 and 200 hpa of 5 11 m s 1 produced persistent downshear convective outbreaks that became progressively more intense and closer to the center during the development early in the period the storm intensified steadily in the presence of this downshear convection during the last and most intense outbreak a second vortex appeared to develop within the convection evidence is presented that the new downshear vortex became the dominant vortex and absorbed the original based on these events it is hypothesized that the presence of moderate vertical wind shear accelerated the early development process equivalent potential temperature fields within 500 m of the surface were examined only well after the period of vortex interaction did the characteristic mature tropical cyclone radial profile of eq

asymmetric distribution of convection associated with tropical cyclones making landfall along the south china coast this study examines the convection distribution associated with 18 tcs that made landfall along the south china coast during 1995 and 2005 cloud top temperatures from high resolution satellite imageries of the geosynchronous meteorological satellite 5 are used as proxy of strong convection it is found that convection tends to be enhanced on the western side of the tc as it makes landfall in 10 of the cases in agreement with the conclusion of some previous studies four cases have stronger convection on the eastern side this deviation from the general rule appears to be related to the tcs being more slow moving or their interaction of the tc with another land surface prior to its making landfall along the south china coast for the remaining cases in which no significant asymmetries in convection can be identified the vertical wind shear appears to enhance convection on the east side

the unusual behavior and precipitation pattern associated with tropical storm ignacio 1997 a case study of eastern north pacific tropical storm ignacio 1997 which brought rainfall to the southwestern united states as a tropical cyclone and to the northwestern united states as an extratropical cyclone is presented this tropical cyclone formed from a region of disturbed weather rather than a tropical wave outside the typical eastern north pacific genesis region and intensified into a tropical storm coincident with the passage of an upper tropospheric trough moisture transported from ignacio along an outflow jet associated with the trough resulted in precipitation in mexico and the southwestern united states as ignacio moved north and away from the trough this tropical cyclone weakened and eventually underwent extratropical transition over the open ocean in contrast to climatological eastern north pacific tropical cyclone behavior ignaciothenstrengthenedasanextratropicalcycloneduetofavorablebaroclinicconditionsandthe passage of another upper tropospheric trough before making landfall on the northern coast of california bringing rain to the northwestern united states ignacio s remnant moisture eventually merged into a slowmoving midlatitude low pressure system that developed after interacting with the extratropical remnant of hurricane guillermo

alpine metamorphism of pelitic schists in the nufenen pass area lepontine alps the effects of tertiary alpine metamorphism on pelitic mesozoic cover rocks have been studied along a cross section in the central lepontine alps in the nufenen pass area switzerland greenschist facies to amphibolite facies conditions are indicated by the formation of the index minerals chloritoid garnet staurolite and kyanite in pelitic rocks regional metamorphism reached maximum conditions during the interkinematic period between a main alpine penetrative d2 and a late alpine d3 crenulation type deformation phase or synchronous with the late alpine deformation based on afm phase relationships four different metamorphic zones can be distinguished 1 chloritoid zone 2 staurolite chlorite zone 3 staurolite biotite zone and 4 kyanite zone the isograds that separate these zones can be modelled by univariant reactions in the kfmash system the conditions of metamorphism calculated from geological ther mobarometers for the maximum post d2 por phyroblast stage are from north to south 500 c at 5 6 kbar and 600 c at 7 8 kbar detailed thermobarometry of garnet por phyroblasts with complex textures suggests that maximum temperature was reached later than maximum pressure early garnet growth occurred along a prograde p t path post d2 rims grew with increasing temperature but decreasing pressure and finally post d3 garnet formed along a retrograde p t path it may be concluded from the calculated pressure and temperature difference over a short distance 3 km across the mapped area that the isogradic surfaces of the post d2 metamorphism are steeply oriented the data also suggest that isobaric and isothermal surfaces are parallel much of the observed metamorphic pattern can be explained as the result of a significant post d2 differential uplift of the hot pennine area relative to the helvetic area along a tectonic contact zone the closely spaced isograds isotherms in the north may then be interpreted as a thermal effect owing to the emplacement of the hot pennine rocks against the got thard massif with its cover whereas in the pennine metasediments post d2 porphyroblast formation can be related to the decompression path which was steep enough for dehydration reactions to proceed it is also remarkable that late kyanite porphyroblasts probably formed with decreasing pressure the interpretation given here for the nufenen pass area may also apply to the luk manier pass area where similar metamorphic patterns have been reported by fox 1975 the formation of the northern steep belt as denned by milnes 1974b and the associated late alpine fold zones may therefore have significantly modified the metamorphic pattern of the helvetic penninic contact zone

a new geobarometer for the assemblage biotite muscovite chlorite quartz the equilibrium thermodynamics of the reaction 4kmga1si40 o oh mg5a1 si30 o oh muscovlte chlorite muscovite biotite ka13si 0 oh 3kmg3aisi 0 0 oh 7si0 4h o quartz fluid can be formulated as a geobarometer thermo dynamic data for the mg a1 celadonite end member of muscovite is derived from the reversed mineral equilibria experiments of velde i 965 using the calculation method of powell 1978 giving afh 1298 5823 5 kj s 1298 0 3060kjk v 1298 13 8kjkbar

tectonic controls of metamorphic field gradients abstract we investigate the effects of horizontal variations in tectonic factors heat production and rate amount and duration of erosion on the magnitudes and gradients of pressure p temperature t and cooling ages observed in mountain belts horizontal gradients of p t and cooling ages are largely controlled by two dimensionless parameters 1 the horizontal length scale over which erosion erosion rate or erosion duration varies and 2 the peclet number pe which describes the relative rates of advection and diffusion of heat in contrast the magnitudes of observed p and t depend strongly on the degree of thickening and original burial depth as well as pe and since horizontal heat conduction can usually be ignored do not depend strongly on p and t gradients generally increase with decreasing and pe for calculations in which either but not both erosion rate or erosion duration is horizontally constant p and t gradients are moderate in magnitude and increase in the direction of increasing total erosion in contrast calculations with horizontally constant total erosion but varying erosion rate and erosion duration show small temperature and pressure gradients pressures and temperatures can increase in the same or in opposite directions depending on the magnitude of calculations with horizontally varying crustal heat production show small but non zero temperature gradients and negligible pressure gradients these results indicate that knowledge of temperature pressure and cooling age gradients in individual mountain belts can constrain fundamental quantities such as magnitude and horizontal gradient of the exhumation rate and the average shear strain rate occurring during exhumation on the basis of their metamorphic field gradients most mountain belts can be divided into one of three groups the first and largest group shows strongly positive p and t gradients precambrian orogenic areas comprise the second group and have small t gradients

mesoscale aspects of the downshear reformation of a tropical cyclone the downshear reformation of tropical storm gabrielle 2001 was investigated using radar reflectivity and lightning data that were nearly continuous in time as well as frequent aircraft reconnaissance flights initially the storm was a marginal tropical storm in an environment with strong 850 200 hpa vertical wind shear of 12 13 m s 1 and an approaching upper tropospheric trough both the observed outflow and an adiabatic balance model calculation showed that the radial vertical circulation increased with time as the trough approached convection was highly asymmetric with almost all radar return located in one quadrant left of downshear in the storm reconnaissance data show that an intense mesovortex formed downshear of the original center this vortex was located just south of rather than within a strong downshear left lightning outbreak consistent with tilting of the horizontal vorticity associated with the vertical wind shear the downshear mesovortex contained a 972 hpa minimum central pressure 20 hpa lower than minimum pressure in the original vortex just 3 h earlier the mesovortex became the new center of the storm but weakened somewhat prior to landfall it is argued that dry air carried around the storm from the region of upshear subsidence as well as the direct effects of the shear prevented the reformed vortex from continuing to intensify despite the subsequent weakening of the reformed center it reached land with greater intensity than the original center it is argued that this intensification process was set into motion by the vertical wind shear in the presence of an environment with upward motion forced by the upper tropospheric trough in addition the new center formed much closer to the coast and made landfall much earlier than predicted such vertical shear induced intensity and track fluctuations are important to understand especially in storms approaching the coast

end cretaceous devastation of terrestrial flora in the boreal far east a continuous marine sedimentary sequence spanning the cretaceous tertiary k t boundary has been identified in eastern hokkaido japan on the basis of planktonic foraminifera the k t boundary is marked by a 6 10 cm thick layer of pyrite rich fossil poor greyish black claystone1 which is lithologically similar to the well known boundary clay of the classical european k t boundary sections2 4 we show here that terrestrial palyno morphs from the hokkaido section record sudden changes in the floristic composition precisely at the base of the boundary claystone layer in particular both angiosperm and gymnosperm pollen abundances decline markedly and these changes are accompanied by an abrupt rise in the proportion of fern spores return to the original moderate level of fern dominance occurs within a few centimetres above the boundary layer a sharp increase of fern spores has also been reported at the palynologically defined k t boundary in the western interior of north america5 which coincides with the top of an iridium rich clay layer6 7 the possibly synchronous occurrence of analogous floral changes at these widely separated regions implies a devastation of the land flora which although geologically brief was intercontinental in scope and which was probably caused by a major catastrophic event such as the impact of a massive meteorite7

idealized numerical simulations of hurricane trough interaction abstract a three dimensional nonhydrostatic fine resolution model with explicitly resolved convective processes is used to investigate the evolution of a a hurricane in two sheared flows and b a hurricane interacting with four different upper level lows the negative impact of vertical shear on hurricane intensification is confirmed the hurricanes display asymmetries that are most pronounced in higher shear flow in both shear cases the hurricane asymmetries seem to be related to a single upper tropospheric outflow jet forcing convective activity below its right entrance region weak subsidence is confined to only part of the eye less eye subsidence leads to less inner core warming and hence a smaller fall in central surface pressure a hurricane in zero flow control displays subsidence in the entire eye leading to a symmetric storm with a deep strong warm core temperature anomaly and lower central surface pressure in the weak shear and control cases the radius of maximum wind rmw cont

a diagnostic study of the intensity of three tropical cyclones in the australian region part i a synopsis of observed features of tropical cyclone kathy 1984 abstract objective streamline analyses and digitized high resolution ir satellite cloud data have been used to examine in detail the changes in the environmental circulation and in the cloud structure that took place in and around tropical cyclone kathy 1984 when it started to intensify and during its intensification and dissipation stages the change of low level circulation around tropical cyclone kathy was measured by the change in the angle of inflow 4 at a radius of 4 latitude from the cyclone center when kathy started to intensify 4 increased suddenly from 20 to 42 5 in the northerly airstream to the north and northeast of the depression and decreased to 0 to the south of the depression at that stage the low level circulation around the depression appeared as a giant swirl that started some 600 km to the north and northeast of the depression and spiraled inward toward its center while trade air which is usually cool dry and stable did not enter the cyclonic circulation the angle

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