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

north atlantic hurricanes 1977 99 surface hurricane force wind radii abstract the hurricane research division noaa amol hrd flight level data archive of 1977 99 north atlantic hurricanes is used to create radial profiles of earth relative surface wind speeds radii of hurricane force winds are determined directly from these generated profiles the distributions of hurricane force wind radii stratified by minimum central pressure and quadrant relative to the direction of storm motion indicate marked variability among storms however a model which uses storm parameters to predict the radius of hurricane force winds in a given quadrant of a hurricane does seem feasible roughly three quarters of the variance in the hurricane force wind radii of minimal hurricanes and about one half of the variance in the hurricane force wind radii of major hurricanes is explained by parameters of the storm enough to make a predictive model of significant value in addition cumulative two dimensional probability distributions of hurricane force wind radii may have some utility for hurr

the boundary layer winds in hurricanes danielle 1998 and isabel 2003 abstract this paper describes the boundary layer wind structure and dynamics of hurricanes danielle 1998 and isabel 2003 based on the analysis of high resolution global positioning system dropwindsonde data and simulation of the flow by a three dimensional boundary layer model produced by kepert and wang the observations show that the hurricane boundary layer has a complex three dimensional structure with large variability over small distances the analysis emphasizes three aspects the degree of gradient wind balance the radially varying depth of the boundary layer and the strength of the near surface wind speed relative to that at a higher level each aspect is compared both with results obtained in a simulation of the individual storm by kepert and wang s model and with theoretical predictions the observations show that the boundary layer depth decreases toward the center of the storm consistent with theoretical arguments the strongest azimuthal winds occur near the top of but still within

effects of vertical eddy diffusivity parameterization on the evolution of landfalling hurricanes abstractas a result of rapid changes in surface conditions when a landfalling hurricane moves from ocean to land interactions between the hurricane and surface heat and moisture fluxes become essential components of its evolution and dissipation with a research version of the hurricane weather research and forecasting model hwrf this study examines the effects of the vertical eddy diffusivity in the boundary layer on the evolution of three landfalling hurricanes dennis katrina and rita in 2005 specifically the parameterization scheme of eddy diffusivity for momentum km is adjusted with the modification of the mixed layer velocity scale in hwrf for both stable and unstable conditions results show that the change in the km parameter leads to improved simulations of hurricane track intensity and quantitative precipitation against observations during and after landfall compared to the simulations with the original km further diagnosis shows that compared to original km the modified km produces

observations of the structure and evolution of surface and flight level wind asymmetries in hurricane rita 2005 1 knowledge of the magnitude and distribution of surface winds including the structure of azimuthal asymmetries in the wind field are important factors for tropical cyclone forecasting with its ability to remotely measure surface wind speeds the stepped frequency microwave radiometer sfmr has assumed a prominent role for the operational tropical cyclone forecasting community an example of this instrument s utility is presented here where concurrent measurements of aircraft flight level and sfmr surface winds are used to document the wind field evolution over three days in hurricane rita 2005 the amplitude and azimuthal location phase of the wavenumber 1 asymmetry in the storm relative winds varied at both levels over time the peak was found to the right of storm track at both levels on the first day by the third day the peak in flight level storm relative winds remained to the right of storm track but it shifted to left of storm track at the surface resulting in a 60 degree shift between the surface and flight level and azimuthal variations in the ratio of surface to flight level winds the asymmetric differences between the surface and flight level maximum wind radii also varied indicating a vortex whose tilt was increasing

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

asymmetric structures in a simulated landfalling hurricane abstract highly asymmetric structures in a landfalling hurricane can lead to the formation of heavy rains wind gusts and tornados at prefered locations relative to the center of the hurricane in this study the development of asymmetric structures in an explicitly simulated idealized hurricane during landfall was investigated it was found that the boundary layer friction and its associated convection produce a low level positive potential vorticity pv band ahead of the hurricane the interaction between the pv band and the eyewall pv ring leads to a temporary weakening and reintensifying cycle asymmetric structures arise from the near discontinuity of the surface friction and the latent heat flux the breaking of the eyewall in the rear quadrants is favorable for the intrusion of the low moist entropy air into the core consequently pv increases significantly in the core in and just above the boundary layer due to the stabilization after the hurricane makes landfall the diabatic heating in the

topographic effects on the seismic response of steep slopes a frequency domain parametric study using generalized consistent transmitting boundaries has been performed to evaluate the significance of topographic effects on the seismic response of steep slopes the results show that the peak amplification of motion at the crest of a slope occurs at a normalized frequency h 0 2 where h is the slope height and is the wavelength of the motion the importance of the natural site frequency is illustrated by the analysis of a stepped layer over a half space it was found that the natural frequency of the region behind the crest can dominate the response relative to the topographic effect for the conditions studied moreover the effect of topography can be handled separately from the amplification due to the natural frequency of the deposit behind the crest of the slope this concept of separating the amplification caused by topography from that caused by the natural frequency is advantageous to the development of a simplified method to estimate topographic effects

a note on the representation of steric sea level in models that conserve volume rather than mass this note discusses the representation of steric sea level in ocean circulation models changes in steric sea level are caused when changes in the density of the water column imply an expansion or contraction of the column models usually make the boussinesq approximation and conserve volume rather than mass and so do not properly represent expansion or contraction this means that although expansion contraction is included in the equation of state it is not accounted for by the model dynamics in this note we examine the equation governing the time evolution of the sea level displacement it is shown that requiring conservation of mass rather than volume introduces a new term to this equation a simple example is used to show the relationship of the new term to the surface buoyancy flux the equilibrium response to the new term has two parts one part consists of the goldsbrough and stommel gyres for which in the ocean interior vortex stretching due to the local expansion contraction of the water column is balanced by changes in planetary vorticity the other part corresponds to the inverse barometer the effect is to adjust sea level by a globally uniform but timevarying factor determined by the net expansion contraction of the global ocean since this correction is globally uniform it has no dynamical significance both the goldsbrough stommel gyres and the inverse barometer solution are missing from models as currently formulated this does not represent a serious error however if comparison is made with observations of sea level model calculated sea level should be adjusted by a globally uniform time varying factor determined by the net expansion contraction of the global ocean this would be important for assessing the likely rise in sea level in response to global warming

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

polarimetric radar observations of the persistently asymmetric structure of tropical cyclone ingrid abstract tropical cyclone ingrid had a distinctly asymmetric reflectivity structure with an offshore maximum as it passed parallel to and over an extended coastline near a polarimetric weather radar located near darwin northern australia for the first time in a tropical cyclone polarimetric weather radar microphysical analyses are used to identify extensive graupel and rain hail mixtures in the eyewall the overall microphysical structure was similar to that seen in some other asymmetric storms that have been sampled by research aircraft both environmental shear and the land sea interface contributed significantly to the asymmetry but their relative contributions were not determined the storm also underwent very rapid changes in tangential wind speed as it moved over a narrow region of open ocean between a peninsula and the tiwi islands the time scale for changes of 10 m s 1 was of the order of 1 h there were also two distinct types of rainbands observed large scale principal bands with embedded d

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

what drives 20th century polar motion abstract astrometric and geodetic measurements show that the mean position of earth s spin axis drifted through the solid crust toward labrador canada at an average speed of 10 5 0 9 cm yr during the 20th century understanding the origins of this secular polar motion spm has significance for modeling the global climate as it provides a link to ice mass balance and sea level rise a perplexing issue however is that while glacial isostatic adjustment gia models satisfactorily explain the direction of spm the associated prediction of the amplitude is insufficient our bayesian gia analysis with constraints from relative sea level and vertical land motion data reveals that this process only accounts for 33 18 of the observed spm amplitude this shortfall motivates a more broadly scoped reassessment of spm drivers to address this we assemble a complete reconstruction of earth s surface mass transport derived from recent advancements in modeling the global 20th century cryospheric hydrologic oceanic and seismogenic mass exchange the summed signals nonetheless cannot fully reconcile the observed spm even when considering the error statistics of each driver we investigate an additional excitation source changes in earth s inertia tensor caused by mantle convection sophisticated models have recently been advanced in tectonic plate reconstructions in conjunction with geoid and seismic tomographic models here we use these models to compute new estimates of spm while the convection driven spm has considerable uncertainty the average direction of 283 recent models aligns with the residual spm within 2 7 14 8 significantly reducing the gap between observation and prediction we assert that one key mechanism for driving 20th century spm is long term mass movement due to mantle convection

the dynamics of boundary layer jets within the tropical cyclone core part i linear theory abstract observations of wind profiles within the tropical cyclone boundary layer have until recently been quite rare the recent massive increase in observations due to the operational implementation of the global positioning system dropwindsonde has emphasised that a low level wind speed maximum is a common feature of the tropical cyclone boundary layer here is proposed a mechanism for producing such a maximum whereby strong inward advection of angular momentum generates the supergradient flow the processes that maintain the necessary inflow against the outward acceleration resulting from gradient wind imbalance are identified as being i vertical diffusion ii vertical advection and iii horizontal advection two complementary tools are used to diagnose the properties and dynamics of the jet the first presented here is a linear analytical model of the boundary layer flow in a translating tropical cyclone it is an extension of the classical ekman boundary layer model as well as of earlier w

displacement field and fault model for the september 7 1999 athens earthquake inferred from ers2 satellite radar interferometry on september 7 1999 a moderate mw 5 9 normal faulting earthquake occurred in the northwest of athens hellas causing heavy damages and casualties using interferometric combinations of ers2 sar images we analyzed the coseismic deformation field two fringes are observed south of the fill mountain up to the coastline of the elefsis gulf they correspond to 56 mm increase in slant range modeling the earthquake as a dislocation in an elastic half space we inverted the interferometric data to assess the fault location and geometry and the amplitude of the coseismic slip the model suggests 300 mm slip on an 18 km long blind fault composed of two pieces the intersection of the fault plane with the earth surface is located in the fill mountain with a n 120 o orientation

consideration of ocean tides in an ogcm and impacts on subseasonal to decadal polar motion excitation ocean induced changes of earth s rotation are attributed either to tides or to variations of the general circulation analogously numerical world ocean models can still be divided into ocean general circulation and tidal models although a neglect of nonlinear interactions in favor of a linear superimposition of both components of motion is questionable by means of a simultaneous simulation of the ocean s circulation and tides we estimate the importance of two oceanic effects with respect to excitation of polar motion nonlinearities between circulation and long period tides and the circulation induced potential due to loading and self attraction of a baroclinic ocean comparing the linear superimposition of separate model simulations with the simultaneous calculation of circulation and tides it turns out that these second order effects contribute about 8 to ocean induced changes in earth s orientation

a numerical study of the effects of land proximity and changes in sea surface temperature on hurricane tracks a three layer shallow water model with a convection parametrization is used to study the track deflections of slow moving hurricanes on a plane as they approach straight coastlines of different orientations with respect to north or as they cross to a cooler or warmer body of water in the landfall experiments the land surface is level and is characterized by an abrupt increase of the drag coefficient and zero evaporation the tracks of a 72 h integration on a plane are compared with an ocean control experiment it is found that the divergent flow in the boundary layer in regions of offshore winds is responsible for the observed track deflections in this region middle layer air descends into the boundary layer and increases the positive potential vorticity anomaly in the middle layer in the case of land conditions to the west of the vortex the maximum potential vorticity anomaly extends less to the north of the vortex centre and results in a more southerly track than in the ocean control case if land conditions are specified in the north the positive potential vorticityasymmetry maximum extends more to the north west and results in a northward deflection of the track on the other hand land conditions to the north west of the initial vortex centre do not significantly change the location of the asymmetry and therefore the track deflection is small the magnitude of the track deflections as well as the drift speed increases when the roughness of the land is increased it is significant that track deflections commence about 20 h before landfall reaching a value of about 150 km at the time of landfall compared with landfalling hurricanes track deflections of model hurricanes which drift into a region of different sea surface temperature sst are smaller and are a result of intensity changes of the vortex circulation the maximum wind speed at the time of landfall increases if a region of higher sst is located adjacent to the coastline

reanalysis of ancient eclipse astronomic and geodetic data a possible route to resolving the enigma of global sea level rise predictions of the earth s response to the ice age appear to simultaneously reconcile a set of astronomical geodetic and ancient eclipse observations related to changes in rotation thus ruling out ice melting as a major contributor to 20th century sea level rise we demonstrate that the reconciliation disappears when an improved theory of rotational stability is applied furthermore our reanalysis of longer satellite records renders previous estimates of the secular change in rotation rate suspect the updated ice age predictions and observations permit an anomalous 20th century ice flux of 1 mm yr equivalent sea level rise thus the full suite of earth rotation observations are consistent with a connection between climatic warming and recent melting of ice reservoirs

long term polar motion excited by ocean thermal expansion 1 ocean warming is commonly considered unable to excite significant long term trends in polar motion here however we argue that this assumption needs to be revised we demonstrate that steric sea level rise leads to a distinct pattern of horizontal mass redistribution within ocean basins and hence to ocean bottom pressure changes that alter earth s inertia tensor on decadal and longer time scales based on earth system model simulations we estimate that ocean warming leads to polar motion of 0 15 to 0 20 milliarcseconds per one millimeter of thermal sea level rise this is equivalent to a polar motion rate of about 0 47 milliarcseconds per year towards 155w to 160w for current projections of steric sea level rise during the 21st century the proposed polar motion signal is therefore not negligible in comparison to other decadal and secular signals and should be accounted for in the interpretation of polar motion observations citation landerer f w j h jungclaus and j marotzke 2009 long term polar motion excited by ocean thermal expansion geophys res lett 36 l17603

the effect of a river delta and coastal roughness variation on a landfalling tropical cyclone 1 numerical simulations on an f plane are performed using the weather research forecasting wrf model to study how the presence of a river delta and variations in coastal roughness might affect the motion and the structure of a tropical cyclone tc near landfall in each delta experiment an idealized triangular shaped delta pointing to the west with length 150 km and a river mouth size of 100 km is inserted along the coastline the surface roughness and the moisture availability of the delta vary among the delta experiments and the surface properties are uniform in the rest of the land area in another set of experiments where there is no delta the roughness of a whole land area has different values along the north south oriented coast results suggest that the tc in the control experiment ctrl with no delta or roughness variation along the coast is weaker than all the delta cases during a certain period before landfall moisture supply from the delta appears to have an effect on sustaining the approaching tc despite the relatively small scale of the delta tracks of the tcs in the roughness variation experiments deviate from that of the ctrl the roughness variation along the coast apparently affects the convergence patterns higher roughness induces stronger convergence and hence increases the vertical advection term in the potential vorticity tendency distribution over the rougher area hence a tc tends to move toward a region with higher roughness

effects of polar ice on the earth s rotation and gravitational potential summary gridded values of net surface accumulation rates for the antarctic and greenland ice sheets are used to estimate the contributions these two regions make to the earth s gravity and rotation the ice discharge from both ice sheets is adjusted so that the estimates of sea level contribution from both ice sheets fall within limits for present mass balance suggested by the committee on glaciology 1985 these sea level contributions are for antarctica 0 6 0 6 mm yr minus 1 and for greenland 0 1 0 4 mm yr 1 the contributions to the low order zonal harmonic coefficients of the earth s gravitational potential from antarctica are found to be between two and 10 times larger than the uncertainties of the zonal harmonics derived from satellite solutions for greenland the coefficients are within an order of magnitude of the uncertainties of the satellite solutions these results are not definitive they are presented to demonstrate that the ice sheets contribute to gravity in amounts that are within the limits of detection by satellite ranging methods the secular trends in the x and y components of observed polar motion excitation agree in magnitude and sign with the antarctic contributions for a model where the interior regions on the ice sheet undergo a net thinning and the coastal regions thicken for this model the boundary between the interior and coastal regions is set at the contour of constant accumulation of 0 28 m yr 1 water equivalent and the magnitude of the thickness change is set equal to the local accumulation rate the contributions from greenland to the secular trends in polar motion excitation and length of day are either smaller than or of opposite sign to the observed effects and are found to be smaller than those of antarctica the limited information on mass balance and ice discharge including calving of ice and refreezing of melt water for both ice sheets and the lack of measured data for land based water storage makes the results presented here highly speculative in addition the inelastic response of the earth to changes in surface mass loading is not considered here this delayed response can reduce the magnitude of the effects presented here by as much as 15 per cent if the loading is a linear trend spanning 100 yr and the correction can be larger for longer histories of loading see wahr et al 1992 these results suggest very approximate upper and lower limits for both inter annual and secular contributions of polar ice mass balance to earth rotation and gravity these limits are useful where they fall within the range of detectability using satellites

astrometric and space geodetic observations of polar wander optical astrometric measurements of star positions taken during the past century have been recently re reduced using the final hipparcos star catalog in order to determine variations in the mean location of the earth s rotation pole with respect to the earth s crust this newly available polar motion series which is the longest homogeneous polar motion series currently available allows the drift in the pole path to be newly estimated during the 1900 0 to 1992 0 span of the smoothed hipparcos polar motion series the earth s rotation pole is observed to drift at a mean linear rate of 3 51 0 01 milliarcseconds year mas yr towards 79 2 0 2 w longitude this new estimate for the observed trend in the pole path which can be considered to be the present day expression of true polar wander is nearly the same as that estimated in previous studies using the homogeneous ils polar motion series

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

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

effects of local soil conditions on the topographic aggravation of seismic motion parametric investigation and recorded field evidence from the 1999 athens earthquake during the 1999 athens earthquake the town of adames located on the eastern side of the kifissos river canyon experienced unexpectedly heavy damage despite the particular geometry of the slope that caused significant motion amplification topography effects alone cannot explain the uneven damage distribution within a 300 m zone parallel to the canyon s crest which is characterized by a rather uniform structural quality in this article we illustrate the important role of soil stratigraphy and material heterogeneity on the topographic aggravation of surface ground motion for this purpose we first conduct an extensive time domain parametric study using idealized stratified profiles and gaussian stochastic fields to characterize the spatial distribution of soil properties and using ricker wavelets to describe the seismic input motion the results show that both topography and local soil conditions significantly affect the spatial variability of seismic motion we next perform elastic two dimensional wave propagation analyses based on available local geotechnical and seismological data and validate our results by comparison with aftershock recordings

surface cold pools in the outer rainbands of tropical storm hanna 2008 near landfall surface mesonet observations were used to document the structure of prominent cold pools associated with twoconvectiveouterrainbandsoftropicalstormhannaon5september2008 thedevelopingrainbandswere located 400 kmnorth ofthestormcenterastheycrossedthecarolinacoastlineandpassedover themesonet the combination of moderate cape moderate low level cross band vertical shear and dry midlevel air provided an environment supportive of surface cold pool formation and long lived quasi linear convection both rainbands exhibited multiple outward tilting convective cells and discrete line segments centered within a narrow zone of nearly continuous stratiform precipitation the mesonet observations provided a unique along and cross band perspective of discrete cold pools situated beneath andbehind the convection portions of each rainband prominentcold pools extended 40 80 km behind the rainband s leading edge and exhibited maximum potential temperature mixing ratio and equivalentpotentialtemperaturedeficitsof2 4 k 1 2 g kg 21 and4 10 k respectively inthecross banddirection convergence of storm relative inflow along the cold pool leading edge was coincident with a modest high pressure anomaly while inflow divergence prevailed through the cold pool and rainfall maxima several cold pools expanded along band while being advected downband by the prevailing cyclonic flow cold pool wakes were observed more than 50 km behind the rainband leading edge and up to 20 km downband from intense convection variations in cold pool intensitywerenotwell correlated with convectiveintensity rainfallrate or the degree of midlevel dryness implications of prominent cold pools on tropical cyclone convection size and intensity are discussed

a high resolution prediction study of two typhoons at landfall abstract the landfall on the china coast of two typhoons has been studied using both observational diagnostics and a 30 km 19 level prediction system the typhoons vary in size and in the amount of rainfall they produced after landfall use is made of a synthetic typhoon insertion scheme and the relatively dense observational network around china to provide objective analyses the authors illustrate that in the forecast model as the typhoon s outer circulation impinges on the china coast an outer cloud band develops offshore parallel to the coast extending cyclonically north and east during this time the inner circulation weakens as the outer cloud band strengthens the center of the circulation approaches it from the east and there is a short term intensification of both the inner region vertical motion and vorticity following landfall rapid dissipation of the core occurs using detailed diagnostics from the model integration the changing thermal structure of the forecast vortex is illustrated

oceanic signals in observed motions of the earth s pole of rotation motion of the earth s pole of rotation relative to its crust commonly referred to as polar motion can be excited by a variety of geophysical mechanisms1 in particular changes in atmospheric wind and mass fields have been linked to polar motion over a wide range of timescales but substantial discrepancies remain between the atmospheric and geodetic observations1 2 3 4 here we present results from a nearly global ocean model which indicate that oceanic circulation and mass field variability play important roles in the excitation of seasonal to fortnightly polar motion the joint oceanic and atmospheric excitation provides a better agreement with the observed polar motion than atmospheric excitation alone geodetic measurements may therefore be used to provide a global consistency check on the quality of simulated large scale oceanic fields

twentieth century sea level an enigma changes in sea level relative to the moving crust are associated with changes in ocean volume mostly thermal expansion and in ocean mass melting and continental storage t steric t eustatic t recent compilations of global ocean temperatures by levitus and coworkers are in accord with coupled ocean atmosphere modeling of greenhouse warming they yield an increase in 20th century ocean heat content by 2 1023 j compared to 0 1 1023 j of atmospheric storage which corresponds to greenhouse 2000 3 cm the greenhouse related rate is accelerating with a present value greenhouse 2000 6 cm century tide records going back to the 19th century show no measurable acceleration throughout the late 19th and first half of the 20th century we take historic 18 cm century the intergovernmental panel on climate change attributes about 6 cm century to melting and other eustatic processes leaving a residual of 12 cm of 20th century rise to be accounted for the levitus compilation has virtually foreclosed the attribution of the residual rise to ocean warming notwithstanding our ignorance of the abyssal and southern oceans the historic rise started too early has too linear a trend and is too large melting of polar ice sheets at the upper limit of the intergovernmental panel on climate change estimates could close the gap but severe limits are imposed by the observed perturbations in earth rotation among possible resolutions of the enigma are a substantial reduction from traditional estimates including ours of 1 5 2 mm y global sea level rise a substantial increase in the estimates of 20th century ocean heat storage and a substantial change in the interpretation of the astronomic record