impact of bedrock surface topography on spatial distribution of quaternary sediments and on the flow pattern of late weichselian glaciers on the east european craton russian plain this paper presents the first high quality maps of the bedrock surface topography and the quaternary sediment distribution for the late weichselian glaciation area on the east european craton eec and the reasoning behind the estimated sediment distribution geographic information system gis based three dimensional model of the bedrock surface topography the current digital terrain model dtm and the ice flow pattern of the last glaciation provided the main source data for the analyses and interpretations in the current continental area of the western eec which was covered by the last scandinavian ice sheet sis the bedrock lies overwhelmingly 85 above the contemporary sea level with an average altitude of 54 m above sea level the topography of the bedrock surface is very well reflected in the current topography and an 80 m difference in the ice bed surface altitudes results in the topographic focusing of the ice flow and thus all late weichselian ice streams were accommodated to the depressions in the subglacial surface such depressions are characterised by a thin 10 m layer of sediment with one till bed just 50 m upslope from the bottom of the depressions the thickness of the sediment increases two to threefold and comprises five or more till layers indicating relief enhancement through subsequent glaciations the average calculated thickness of the quaternary deposits in the study area was 49 m and the total volume of sediments was 20 280 km3

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

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

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

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

a new ice thickness and bed data set for the greenland ice sheet 1 measurement data reduction and errors ice thickness data collected between 1993 and 1999 using a coherent ice penetrating radar system developed at the university of kansas have been combined with data collected by the technical university of denmark in the 1970s to produce a new ice thickness grid for greenland crossover analysis was used to assess the relative accuracy of the two data sets and they were weighted accordingly and interpolated onto a regular 5 km spacing grid using a kriging interpolation procedure a high resolution land ice mask was used to help constrain the interpolation of the ice thickness data near the ice sheet margins where in the past the relative errors have been largest the ice thickness grid was combined with a new digital elevation model of the ice sheet and surrounding rock outcrops to produce a new bed elevation data set for the whole of greenland the ice thickness grid was compared with the currently available data set differences in the center of the ice sheet where the ice is thickest were of the order of a few percent near the margins however large differences of as much as a factor of 10 were found the total volume of ice contained in the ice sheet was reestimated and found to have a value of 2 93 x 10 6 km 3 the ice thickness grid was used to calculate the spatial pattern of gravitational driving stress over the ice sheet anomalous patterns of stress were found in areas that appeared to be associated with areas of rapid flow

dependence of tropical cyclone intensification on the boundary layer representation in a numerical model we present idealized numerical model experiments to investigate the dependence of tropical cyclone intensification and in particular the kinematic structure of the tropical cyclone boundary layer on the boundary layer parametrization in the model the study is motivated by recent findings highlighting the important dynamical role of the boundary layer in tropical cyclone intensification the calculations are carried out using the pennsylvania state university national center for atmospheric research fifth generation mesoscale model mm5 predictions using one of five available schemes are compared not only between themselves but where possible with recent observational analyses of boundary layer structure at this stage the study falls short of being able to advocate the use of a particular scheme although certain shortcomings of individual schemes are identified the current inability to determine the optimum scheme has implications for the predictability of tropical cyclone intensification copyright 2010 royal meteorological society

structure of the eye and eyewall of hurricane hugo 1989 on 15 september 1989 one of noaa s wp 3d research aircraft n42rf lower aircraft la penetrated the eyewall of hurricane hugo the aircraft had an engine fail in severe turbulence while passing the radius of maximum wind and before entering the eye at 450 m altitude after the aircraft returned to controlled flight within the 7 km radius eye it gained altitude gradually as it orbited in the eye observations taken during this period provide an updated model of the inner core structure of an intense hurricane and suggest that la penetrated an intense cyclonic vorticity maximum adjacent to the strongest convection in the eyewall eyewall vorticity maximum evm this evm was distinct from the vortex scale cyclonic circulation observed to orbit within the eye three times during the 1 h that la circled in the eye at the time hugo had been deepening rapidly for 12 h the maximum flight level tangential wind was 89 m s 1 at a radius of 12 5 km however the primary vortex peak tangential wind derived from a 100 s filter of the flight level data was estimated to be 70 m s 1 also at 12 5 km radius the primary vortex tangential wind was in approximate gradient wind balance was characterized by a peak in angular velocity just inside the radius of maximum wind and had an annular vorticity structure slightly interior to the angular velocity maximum the evm along the aircraft s track was roughly 1 km in diameter with a peak cyclonic vorticity of 1 25 10 1 s 1 the larger circulation center with a diameter 15 km was observed within the eye and exhibited an average orbital period of 19 min this period is about the same as that of the angular velocity maximum of the axisymmetric mean vortex and is in reasonable agreement with recent theoretical and model predictions of a persistent trochoidal wobble of circulation centers in mature hurricane like vortices this study is the first with in situ documentation of these vortical entities which were recently hypothesized to be elements of a lower tropospheric eye eyewall mixing mechanism that supports strong storms

a comparison of balance velocities measured velocities and thermomechanically modelled velocities for the greenland ice sheet balance velocities for the greenland ice sheet have been calculated from a new digital elevation model accumulation rates compilation and anexisting ice thickness grid using a fully two dimensional finite difference scheme the pattern of velocities over the ice sheet is presentedand compared with velocities derived from synthetic aperture radar interferometry for part of northern greenland and a limited number ofgps data this comparison indicated that the balance velocity scheme and boundary conditions used here provide a remarkably goodrepresantation of the dynamics of the ice sheet inland from the margins it is suggested therefore that these balance velocity data couldprovide a valuable method of constraining a numerical ice sheet model the balance velocities were compared with the diagnostic velocityfield calculated from several different configurations of a numerical ice sheet model the general pattern of flow agrees well the detail however is quite different for example the large greater than 300 km ice stream in the north east is not generated by the numerical modeland much of the detailed flow pattern is completely lost due to the limited model resolution and limitations in the model physics

channelized bottom melting and stability of floating ice shelves 1 the floating ice shelf in front of petermann glacier in northwest greenland experiences massive bottom melting that removes 80 of its ice before calving into the arctic ocean detailed surveys of the ice shelf reveal the presence of 1 2 km wide 200 400 m deep sub ice shelf channels aligned with the flow direction and spaced by 5 km we attribute their formation to the bottom melting of ice from warm ocean waters underneath drilling at the center of one of channel only 8 m above sea level confirms the presence of ice shelf melt water in the channel these deep incisions in ice shelf thickness imply a vulnerability to mechanical break up and climate warming of ice shelves that has not been considered previously

intensity and inner core structure of typhoon haiyan 2013 near landfall doppler radar analysis abstractthe intensity and inner core structure of an extremely intense tropical cyclone typhoon haiyan 2013 were examined using real time ground based doppler radar products from the guiuan radar over the period of about 2 5 h immediately before the storm approached guiuan in eastern samar philippines haiyan s wind fields from 2 to 6 km altitude were retrieved by the ground based velocity track display gbvtd technique from the doppler velocity data the gbvtd retrieved maximum wind speed reached 101 m s 1 at 4 km altitude on the right side of the track the relatively fast forward speed of haiyan about 11 m s 1 increased maximum wind speed on the right hand side of the storm azimuthal mean tangential wind increased with height from 2 to 5 km and a local maximum of 86 m s 1 occurred at 5 km altitude the central pressure was estimated as 906 hpa with an uncertainty of 4 hpa by using the gbvtd retrieved tangential wind and by assuming gradient wind balance the radius of maximum radar reflecti

deeply incised submarine glacial valleys beneath the greenland ice sheet the bed topography beneath the greenland ice sheet controls the flow of ice and its discharge into the ocean a combination of sparse radar soundings of ice thickness and high resolution ice motion data suggest that many submarine ice covered valleys extend significantly deeper below sea level and farther inland than thought

eemian interglacial reconstructed from a greenland folded ice core efforts to extract a greenland ice core with a complete record of the eemian interglacial 130 000 to 115 000 years ago have until now been unsuccessful the response of the greenland ice sheet to the warmer than present climate of the eemian has thus remained unclear here we present the new north greenland eemian ice drilling neem ice core and show only a modest ice sheet response to the strong warming in the early eemian we reconstructed the eemian record from folded ice using globally homogeneous parameters known from dated greenland and antarctic ice core records on the basis of water stable isotopes neem surface temperatures after the onset of the eemian 126 000 years ago peaked at 8 4 degrees celsius above the mean of the past millennium followed by a gradual cooling that was probably driven by the decreasing summer insolation between 128 000 and 122 000 years ago the thickness of the northwest greenland ice sheet decreased by 400 250 metres reaching surface elevations 122 000 years ago of 130 300 metres lower than the present extensive surface melt occurred at the neem site during the eemian a phenomenon witnessed when melt layers formed again at neem during the exceptional heat of july 2012 with additional warming surface melt might become more common in the future

coherent radar ice thickness measurements over the greenland ice sheet we developed two 150 mhz coherent radar depth sounders for ice thickness measurements over the greenland ice sheet we developed one of these using connectorized components and the other using radio frequency integrated circuits rfics both systems are designed to use pulse compression techniques and coherent integration to obtain the high sensitivity required to measure the thickness of more than 4 km of cold ice we used these systems to collect radar data over the interior and margins of the ice sheet and several outlet glaciers we operated both radar systems on the nasa p 3b aircraft equipped with gps receivers radar data are tagged with gps derived location information and are collected in conjunction with laser altimeter measurements we have reduced all data collected since 1993 and derived ice thickness along all flight lines flown in support of program for regional climate assessment parca investigations and the north greenland ice core project radar echograms and derived ice thickness data are placed on a server at the university of kansas http tornado rsl ukans edu greenlanddata htm for easy access by the scientific community we obtained good ice thickness information with an accuracy of 10 m over 90 of the flight lines flown as a part of the parca initiative in this paper we provide a brief description of the system along with samples of data over the interior along the 2000 m contour line in the south and from a few selected outlet glaciers

transition of the hurricane boundary layer during the landfall of hurricane irene 2011 abstractthe hurricane boundary layer hbl has been observed in great detail through aircraft investigations of tropical cyclones over the open ocean but the coastal transition of the hbl has been

on the characteristic height scales of the hurricane boundary layer in this study data from 794 gps dropsondes deployed by research aircraft in 13 hurricanes are analyzed to studythecharacteristicheightscalesofthehurricaneboundarylayer theheightscalesaredefinedinavariety of ways the height of the maximum total wind speed the inflow layer depth and the mixed layer depth the height of the maximumwind speed and the inflow layerdepth are referred to asthe dynamical boundarylayer heights while the mixed layer depth is referred to as the thermodynamical boundary layer height the data analyses show that there is a clear separation of the thermodynamical and dynamical boundary layer heights consistent with previous studies on the boundary layer structure in individual storms the dynamical boundary layer height is found to decrease with decreasing radius to the storm center the thermodynamic boundary layer height which is much shallower than the dynamical boundary layer height is also found to decrease with decreasing radius to the storm center the results also suggest that using the traditional critical richardson number method to determine the boundary layer height may not accurately reproduce the height scale of the hurricane boundary layer these different height scales reveal the complexity of the hurricane boundary layer structure that should be captured in hurricane model simulations

effects of parameterized boundary layer structure on hurricane rapid intensification in shear abstractthis study investigates the role of the parameterized boundary layer structure in hurricane intensity change using two retrospective hwrf forecasts of hurricane earl 2010 in which the ver

an improved coherent radar depth sounder the university of kansas developed a coherent radar depth sounder during the 1980s this system was originally developed for glacial ice thickness measurements in the antarctic during the field tests in the antarctic and greenland we found the system performance to be less than optimum the field tests in greenland were performed in 1993 as a part of the nasa program for arctic climate assessment parca we redesigned and rebuilt this system to improve the performance the radar uses pulse compression and coherent signal processing to obtain high sensitivity and fine along track resolution it operates at a center frequency of 150 mhz with a radio frequency bandwidth of about 17 mhz which gives a range resolution of about 5 m in ice we have been operating it from a nasa p 3 aircraft for collecting ice thickness data in conjunction with laser surface elevation measurements over the greenland ice sheet during the last 4 years we have demonstrated that this radar can measure the thickness of more than 3 km of cold ice and can obtain ice thickness information over outlet glaciers and ice margins in this paper we provide a brief survey of radar sounding of glacial ice followed by a description of the system and subsystem design and performance we also show sample results from the field experiments over the greenland ice sheet and its outlet glacicrs

a new ice thickness and bed data set for the greenland ice sheet 2 relationship between dynamics and basal topography new data sets of bed and surface elevation have been combined with balance velocities bed topography and radar reflectivity to investigate the relationship between ice flow and bed conditions it has been found that the bed topography affects the local driving stresses and initiates the onset of streaming flow in specific areas where there are large undulations this onset region only appears significantly inland in three areas the northeast greenland ice stream kangerdlugssuaq gletscher and a region in the southwest associated with abnormally low driving stresses and an apparently unnamed but active glacier bed reflectance values below the northeast ice stream suggest that basal melting could be occurring along its length and it seems likely therefore that the enhanced flow observed inland from the onset of streaming may be due in part to basal sliding

numerical modeling of iceberg capsizing responsible for glacial earthquakes the capsizing of icebergs calved from marine terminating glaciers generate horizontal forces on the glacier front producing long period seismic signals referred to as glacial earthquakes these forces can be estimated by broadband seismic inversion but their interpretation in terms of magnitude and waveform variability is not straightforward we present a numerical model for fluid drag that can be used to study buoyancy driven iceberg capsize dynamics and the generated contact forces on a calving face using the finite element approach we investigate the sensitivity of the force to drag effects iceberg geometry calving style and initial buoyancy we show that there is no simple relationship between force amplitude and iceberg volume and similar force magnitudes can be reached for different iceberg sizes the force history and spectral content varies with the iceberg attributes the iceberg aspect ratio primarily controls the capsize dynamics the force shape and force frequency whereas the iceberg height has a stronger impact on the force magnitude iceberg hydrostatic imbalance generates contact forces with specific frequency peaks that explain the variability in glacial earthquake dominant frequency for similar icebergs top out and bottom out events have significantly different capsize dynamics leading to larger top out forces especially for thin icebergs for realistic iceberg dimensions we find contact force magnitudes that range between 5 6 1011 and 2 1014 kg m consistent with seismic observations this study provides a useful framework for interpreting glacial earthquake sources and estimating the ice mass loss from coupled analysis of seismic signals and modeling results

an estimation of turbulent characteristics in the low level region of intense hurricanes allen 1980 and hugo 1989 this study analyzes the flight level data collected by research aircraft that penetrated the eyewalls of category 5 hurricane hugo 1989 and category 4 hurricane allen 1980 between 1 km and the sea surface estimates of turbulent momentum flux turbulent kinetic energy tke and vertical eddy diffusivity are obtained before and during the eyewall penetrations spatial scales of turbulent eddies are determined through a spectral analysis the turbulence parameters estimated for the eyewall penetration leg are found to be nearly an order of magnitude larger than those for the leg outside the eyewall at similar altitudes in the low level intense eyewall region the horizontal length scale of the dominant turbulent eddies is found to be between 500 and 3000 m and the corresponding vertical length scale is approximately 100 m the results suggest also that it is unwise to include eyewall vorticity maxima evm in the turbulence parameter estimation because the evms are likely to be quasi two dimensional vortex structures that are embedded within the three dimensional turbulence on the inside edge of the eyewall this studyis afirstattempt at estimatingthe characteristics of turbulent flow in the low leveltroposphereof an intense eyewall using in situ aircraft observations the authors believe that the results can offer useful guidance in numerical weather prediction efforts aimed at improving the forecast of hurricane intensity because of the small sample size analyzed in this study further analyses of the turbulent characteristics in the high wind region of hurricanes are imperative

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

observed hurricane wind speed asymmetries and relationships to motion and environmental shear abstractwavenumber 1 wind speed asymmetries in 35 hurricanes are quantified in terms of their amplitude and phase based on aircraft observations from 128 individual flights between 1998 and 2011 the impacts of motion and 850 200 mb environmental vertical shear are examined separately to estimate the resulting asymmetric structures at the sea surface and standard 700 mb reconnaissance flight level the surface asymmetry amplitude is on average around 50 smaller than found at flight level and while the asymmetry amplitude grows in proportion to storm translation speed at the flight level no significant growth at the surface is observed contrary to conventional assumption however a significant upwind storm motion relative phase rotation is found at the surface as translation speed increases while the flight level phase remains fairly constant after removing the estimated impact of storm motion on the asymmetry a significant residual shear direction relative asymmetry is found particularly at the

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

steady state characteristics of the greenland ice sheet under different climates the greenland ice sheet is modelled to simulate its extent and volume in warmer climates and also to find out whether the ice sheet would re form on theice free bedrock under present climatic conditions the ice sheet model is a three dimensional thermo mechanical model with a fine resolution grid thebedrock surface beneath the ice sheet was mapped using radio echo sounding measurements by the electromagnetic institute copenhagen the modelexperiments show that increased temperature will result in ice margin retreat but the ice sheet is relatively stable it takes a rather high temperature rise of atleast 6ic for the ice sheet to disappear completely which indicates that the ice sheet probably survived the last interglacial also it appears that the greenlandice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re form on the bare bedrock under the present or evenslightly warmer climatic conditions

hurricane sea surface inflow angle and an observation based parametric model abstractthis study presents an analysis of near surface 10 m inflow angles using wind vector data from over 1600 quality controlled global positioning system dropwindsondes deployed by aircraft on 187 flights into 18 hurricanes the mean inflow angle in hurricanes is found to be 22 6 2 2 95 confidence composite analysis results indicate little dependence of storm relative axisymmetric inflow angle on local surface wind speed and a weak but statistically significant dependence on the radial distance from the storm center a small but statistically significant dependence of the axisymmetric inflow angle on storm intensity is also found especially well outside the eyewall by compositing observations according to radial and azimuthal location relative to storm motion direction significant inflow angle asymmetries are found to depend on storm motion speed although a large amount of unexplained variability remains generally the largest storm relative inflow angles 50 are found in the fas

radio echo sounding and ice volume estimates of western nordenskiold land glaciers svalbard as part of ongoing work to obtain a reliable estimate of the total ice volume of svalbard glaciers and their potential contribution to sea level rise we present here volume calculations with detailed error estimates for ten glaciers on western nordenskiold land central spitsbergen svalbard the volume estimates are based upon a dense net of gpr retrieved ice thickness data collected over several field campaigns spanning the period 1999 2012 the total area and volume of the ensemble are 116 06 4 53 km 2 and 10 439 0 373 km 3 respectively while the individual areas volumes and average ice thickness lie within 2 6 50 4 km 2 0 08 5 54 km 3 and 29 108 m respectively volume area scaling relationships overestimate the total volume of these glaciers by up to 35 with respect to our calculation on the basis of the pattern of scattering in the radargrams we also analyse the hydrothermal structure of these glaciers nine of the ten are polythermal while only one is entirely cold

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

prediction experiments of hurricane gloria 1985 using a multiply nested movable mesh model abstract the prediction capability of the gfdl triply nested movable mesh model with finest grid resolution of degree was investigated using several case studies of hurricane gloria 1985 during the period that the storm approached and moved up the east coast of the united states the initial conditions for these experiments were interpolated from an nmc t80 global analysis at 0000 utc 25 september and 1200 utc 22 september the integrations starting from 0000 utc 25 september were run 72 h while those starting on 1200 utc 22 september were run 132 h the lateral boundary conditions were obtained from either an integration of the nmc t80 forecast model or the t80 global analysis or were fixed to the initial value the model s predicted track of gloria for each integration was compared against the best track determined by the national hurricane center nhc for the case starting from 0000 utc 25 september using a forecasted boundary condition the model successfully forecasted significant acceler

forward modeling of ice topography on mars to infer basal shear stress conditions 1 understanding the history of ice caps on mars could reveal important information about martian geologic and climatic history to do this an ice reconstruction model is needed that operates over complex topography and can be constrained with a limited number of free parameters in this study we developed a threshold sliding model for ice cap morphology based on the classic model of nye later incorporated into the models of reeh and colleagues we have updated the nye reeh model with a new numerical algorithm although the model was originally developed to model perfectly plastic deformation it is applicable to any ice body that deforms when a threshold basal shear stress is exceeded the model requires three inputs a digital elevation model of bed topography a mask grid that defines the position of the ice terminus and a function defining the threshold basal shear stress to test the robustness of the model the morphology of the greenland ice sheet is reconstructed using an empirical equation between threshold basal shear stress and ice surface slope the model is then used to reconstruct the morphology of ice draping impact craters on the margins of the south polar layered deposits using an inferred constant basal shear stress of 0 6 bar for the majority of the examples this inferred basal shear stress value is almost 1 3 of the average basal shear stress calculated for the greenland ice sheet what causes this lower basal shear stress value on mars is unclear but could involve the strain weakening behavior of ice

why is the tropical cyclone boundary layer not well mixed abstractplausible diagnostics for the top of the tropical cyclone boundary layer include i the top of the layer of strong frictional inflow and ii the top of the well mixed layer that is the layer over which potential temperature is approximately constant observations show that these two candidate definitions give markedly different results in practice with the inflow layer being roughly twice the depth of the layer of nearly constant here the authors will present an analysis of the thermodynamics of the tropical cyclone boundary layer derived from an axisymmetric model the authors show that the marked dry static stability in the upper part of the inflow layer is due largely to diabatic effects the radial wind varies strongly with height and therefore so does radial advection of this process also stabilizes the boundary layer but to a lesser degree than diabatic effects the authors also show that this differential radial advection contributes to the observed superadiabatic layer ad

observation and analysis of ice flow in the largest greenland ice stream we have applied satellite radar interferometry methods to map the velocity field of the recently discovered northeast greenland ice stream we have used these data in conjunction with ice thickness and accumulation data to determine that the ice stream is in balance within the measurement errors we used control methods to invert a finite element model of ice sheet flow constrained by the data to infer the ice stream s basal shear stress distribution our results reveal that flow in a section of the downstream end has much in common with the streaming flow of the ross ice streams of west antarctica e g a weak bed and fast flow in the presence of low driving stresses for several hundred kilometers along the middle of the ice stream the basal shear stress balances the driving stress in the upstream area where the ice stream is first visible in the velocity data the bed appears to be weak which may contribute to the initiation of the ice stream

greenland ice sheet surface melt and its relation to daily atmospheric conditions abstractmelt area is one of the most reliably monitored variables associated with surface conditions over the full greenland ice sheet gris surface melt is also an important indicator of surface mass balance and has potential relevance to the ice sheet s global sea level contribution melt events are known to be spatially heterogeneous and have varying time scales to understand the forcing mechanisms it is necessary to examine the relation between the existing conditions and melt area on the time scales that melt is observed here we conduct a regression analysis of atmospheric reanalysis variables including sea level pressure near surface winds and components of the surface energy budget with surface melt the regression analysis finds spatial heterogeneity in the associated atmospheric circulation conditions for basins in the southern gris there is an association between melt area and high pressure located south of the denmark strait which allows for southerly flow over the western half of th

aircraft observations of tropical cyclone boundary layer turbulence over the south china sea abstractthere have been no high frequency aircraft observations of tropical cyclone tc eyewall boundary layer turbulence since two flights into atlantic hurricanes in the 1980s we present an ana

simulation and parameterization of the turbulent transport in the hurricane boundary layer by large eddies 1 hurricane boundary layer hbl processes especially the structure of the coherent large eddy circulations lecs and their induced vertical transport are not well understood this paper introduces a large eddy simulation les framework in a weather hindcasting mode developed from a multiple scale nested weather research and forecasting wrf model using the wrf les this study investigated the structure of the hbl lecs and the associated vertical transport during the landfall of hurricane ivan 2004 the simulation shows that the hbl lecs exist in a mean stable environment and consist of well defined updraft and downdraft statistically the hbl lecs are only slightly skewed with the updrafts and downdrafts relatively evenly distributed spatially the inversion base basically envelopes the upper boundary of lecs the trough in between two adjacent lecs is where most entrainment takes place whereas the crest of the lecs is where boundary layer air detrains out of the hbl in such a way lecs directly connect the surface the hbl and the main body of a hurricane vortex and enhance the exchange of energy moisture and momentum between them it is found that the current boundary layer schemes significantly underestimate the resolved turbulent fluxes due to the fact that the effects of lecs have not been included in the parameterizations on the basis of the statistical structure of lecs simulated by the wrf les this paper proposes a conceptual updraft downdraft model that can potentially be implemented in weather forecasting models to parameterize the fluxes induced by the hbl lec transport

a new high resolution digital elevation model of greenland fully validated with airborne laser altimeter data a new digital elevation model of the greenland ice sheet and surrounding rock outcrops has been produced at 1 km postings from a comprehensive suite of satellite remote sensing and cartographic data sets height data over the ice sheet were mainly from ers 1 and geosat radar altimetry these data were corrected for a slope dependent bias that had been identified in a previous study the radar altimetry was supplemented with stereophotogrammetric data sets synthetic aperture radar interferometry and digitized cartographic maps over regions of bare rock and where gaps in the satellite altimeter coverage existed the data were interpolated onto a regular grid with a spacing of 1 km the accuracy of the resultant digital elevation model over the ice sheet was assessed using independent and spatially extensive measurements from an airborne laser altimeter that had an accuracy of between 10 and 12 cm in a comparison with the laser altimetry the digital elevation model was found to have a slope dependent accuracy ranging from 1 04 1 98 m to 0 06 14 33 m over the ice sheet for a slope range of 0 0 1 0 the mean accuracy over the whole ice sheet was 0 33 6 97 m over the bare rock areas the accuracy ranged from 20 to 200 m dependent on the data source available the new digital elevation model was used as an input data set for a positive degree day model of ablation the new elevation model was found to reduce ablation by only 2 compared with using an older 2 5 km resolution model which suggests that resolution induced errors in estimating ablation are no longer important

a photograph of a wavenumber 2 asymmetry in the eye of hurricane erin a photograph of a wavenumber 2 asymmetry in the eye of hurricane erin taken during a noaa wp 3d research flight during the fourth convection and moisture experiment camex 4 field program on 10 september 2001 is described the photograph of the cloud structure within the eye is evaluated using airborne and satellite remote sensing observations and a possible explanation for the asymmetry is presented

spiral rainbands in a numerical simulation of hurricane bill 2009 part i structures and comparisons to observations abstractthis study examines spiral rainbands in a numerical simulation of hurricane bill 2009 this paper the first part of the study evaluates the structures of spiral rainbands and compares them to previous observations four types of spiral rainbands are identified principal secondary distant and inner rainbands principal rainbands tend to be stationary relative to the storm center while secondary rainbands are more transient and move around the storm center both principal and secondary rainbands are tilted radially outward with height and have many of the commonly observed kinematic features such as overturning secondary circulation and enhanced tangential velocity on their radially outward sides principal rainbands are bounded by very dry air on their radially outward sides distant rainbands are radially inward tilting convective features that have dense cold pools near the surface inner rainbands are made of shallow convection that appears to have originated from near the eyewall dif

a multiscale numerical study of hurricane andrew 1992 part ii kinematics and inner core structures despite considerable research understanding of the temporal evolution of the inner core structures of hurricanes is very limited owing to the lack of continuous high resolution observational data of a storm in this study the results of a 72 h explicit simulation of hurricane andrew 1992 with a grid size of 6 km are examined to explore the inner core axisymmetric and asymmetric structures of the storm during its rapid deepening stage based on the simulation a conceptual model of the axisymmetric structures of the storm is proposed most of the proposed structures confirm previous observations the main ingredients include a main inflow outflow in the boundary layer upper troposphere with little radial flow in between a divergent slantwise ascent in the eyewall a penetrative dry downdraft at the inner edge of the eyewall and a general weak subsiding motion in the eye with typical warming drying above an inversion located near an altitude of about 2 3 km the storm deepens as the axes of these features contract it is found that the inversion divides the eye of the hurricane vertically into two parts with a deep layer of warm dry air above and a shallow pool of warm moist air below the air aloft descends at an average rate of 5c m s 21 and has a residency time of several days in contrast the warm moist pool consists of air from the main inflow and penetrative downdrafts offset somewhat by the air streaming in a returning outflow into the eyewall in the lowest 2 km it is subject to the influence of the upward heat and moisture fluxes over the underlying warm ocean the warm moist pool appears to play an important role in supplying high ue air for deep convective development in the eyewall the penetrative downdraft is dry and originates from the return inflow in the upper troposphere and it is driven by sublimative evaporative cooling under the influence of the asymmetric radial inflow of dry cold air in the midtroposphere it penetrates to the bottom of the eye azimuthally downshear with a width often greater than 100 km in a radially narrow zone along the slantwise inner edge of the eyewall it is further shown that all the meteorological fields are highly asymmetric whereas the storm scale flow features a source sink couplet in the boundary layer and dual gyres aloft the inner core structures exhibit alternative radial inflow and outflow and a series of inhomogeneous updrafts and downdrafts all the fields tilt more or less with height radially outward and azimuthally downshear furthermore pronounced fluctuations of air motion are found in both the eye and the eyewall sometimes a deep layer of upward motion appears at the center of the eye all these features contribute to the trochoidal oscillation of the storm track and movement the main steering appears to be located at the midtroposphere 4 5 km and the deep layer mean winds represent well the movement of the hurricane

observational estimates of the horizontal eddy diffusivity and mixing length in the low level region of intense hurricanes this study examines further the characteristics of turbulent flow in the low level region of intense hurricanes using in situ aircraft observations the data analyzed here are the flight level data collected by research aircraft that penetrated the eyewalls of category 5 hurricane hugo 1989 category 4 hurricane allen 1980 and category 5 hurricane david 1979 between 1 km and the sea surface estimates of horizontal eddy momentum flux horizontal eddy diffusivity and horizontal mixing length are obtained it is found that the horizontal momentum flux and horizontal diffusivity increase with increasing wind speed the horizontal mixing length increases slightly with wind speed also but the mixing length is not significantly dependent on the wind speed the magnitude of the horizontal momentum flux is found to be comparable to that of the vertical momentum flux indicating that horizontal mixing by turbulence becomes nonnegligible in the hurricane boundary layer especially in the eyewall region within the context of simple k theory the results suggest that the average horizontal eddy diffusivity and mixing length are approximately 1500 m 2 s 21 and 750 m respectively at about 500 m in the eyewall region corresponding to the mean wind speed of approximately 52 m s 21 it is recalled also that the mixing length is a virtual scale in numerical models and is quantitatively smaller than the energy containing scale of turbulent eddies the distinction between these two scales is a useful reminder for the modeling community on the representation of small scale turbulence in hurricanes

history of the greenland ice sheet paleoclimatic insights abstract paleoclimatic records show that the greenland ice sheet consistently has lost mass in response to warming and grown in response to cooling such changes have occurred even at times of slow or zero sea level change so changing sea level cannot have been the cause of at least some of the ice sheet changes in contrast there are no documented major ice sheet changes that occurred independent of temperature changes moreover snowfall has increased when the climate warmed but the ice sheet lost mass nonetheless increased accumulation in the ice sheet s center has not been sufficient to counteract increased melting and flow near the edges most documented forcings and ice sheet responses spanned periods of several thousand years but limited data also show rapid response to rapid forcings in particular regions near the ice margin have responded within decades however major changes of central regions of the ice sheet are thought to require centuries to millennia the paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur the evidence suggests nearly total ice sheet loss may result from warming of more than a few degrees above mean 20th century values but this threshold is poorly defined perhaps as little as 2 c or more than 7 c paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming or changes may have been induced by factors other than temperature without having been recorded

sedimentary molybdenum cycling in the aftermath of seawater inflow to the intermittently euxinic gotland deep central baltic sea abstract molybdenum mo concentrations and isotope compositions in sediments and shales are commonly used as proxies for anoxic and sulfidic i e euxinic conditions in the water column of paleo marine systems a basic assumption underlying this practice is that the proxy signal extracted from the geological record is controlled by long term order of decades to millennia mo scavenging in the euxinic water column rather than mo deposition during brief episodes or events order of weeks to months to test whether this assumption is viable we studied the biogeochemical cycling of mo and its isotopes in sediments of the intermittently euxinic gotland deep in the central baltic sea here multiannual to decadal periods of euxinia are occasionally interrupted by inflow events during which well oxygenated water from the north sea penetrates into the basin during these events manganese mn oxyhydr oxide minerals are precipitated in the water column which are known to scavenge mo we present sediment and pore water mo and mo isotope data for sediment cores which were taken before and after a series of inflow events between 2014 and 2016 after seawater inflow pore water mo concentrations in anoxic surface sediments exceed the salinity normalized concentration by more than two orders of magnitude and coincide with transient peaks of dissolved mn a fraction of the mo liberated into the pore water is transported by diffusion in a downward direction and sequestered by organic matter within the sulfidic zone of the sediment diffusive flux calculations as well as a mass balance that is based on the sedimentary mo isotope composition suggest that about equal proportions of the mo accumulating in the basin are delivered by mn oxyhydr oxide minerals during inflow events and mo scavenging with hydrogen sulfide during euxinic periods since the anoxic surface sediment where mo is released from mn oxyhydr oxides are separated by several centimeters from the deeper sulfidic layers where mo is removed the solid phase record of mo concentration and isotope composition would be misinterpreted if steady state mo accumulation was assumed based on our observations in the gotland deep we argue that short term redox fluctuations need to be considered when interpreting mo based paleo records

spectral characteristics of turbulence in the hurricane boundary layer over the ocean between the outer rain bands spectra and cospectra of wind velocity potential temperature and humidity have been analysed using data collected in the atmospheric boundary layer in hurricanes fabian 2003 and isabel 2003 during the coupled boundary layer air sea transfer cblast hurricane experiment the spectra and cospectra are normalized following the surface layer scaling methods according to similarity theory it is found that the cblast data gathered in the mixed layer between the outer rain bands below 400 m can be grouped into well defined curves for spectra of wind velocity potential temperature and humidity and for cospectra of momentum and humidity flux however the cospectra of sensible heat flux do not exhibit well defined universal shape the cblast universal shape spectra and cospectra generally resemble the shapes of those from previous studies but shift to higher frequencies that correspond to smaller wavelengths of turbulent eddies that contain most of the energy this work highlights the structural difference between the hurricane boundary layer and the standard atmospheric boundary layer over land and ocean copyright 2010 royal meteorological society

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

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

effects of horizontal diffusion on tropical cyclone intensity change and structure in idealized three dimensional numerical simulations abstractthis study examines the effects of horizontal diffusion on tropical cyclone tc intensity change and structure using idealized simulations of the hurricane weather research and forecasting model hwrf a series of sensitivity experiments were conducted with varying horizontal mixing lengths lh but kept the vertical diffusion coefficient and other physical parameterizations unchanged the results show that both simulated maximum intensity and intensity change are sensitive to the lh used in the parameterization of the horizontal turbulent flux in particular for lh less than the model s horizontal resolution the results also show that simulated storm structures such as storm size kinematic boundary layer height and eyewall slope are sensitive to lh as well however lh has little impact on the magnitude of the surface inflow angle and thermodynamic mixed layer height angular momentum budget analyses indicate that the effect of lh is to mainly spin down a tc vortex both mean and eddy adve

comments on symmetric and asymmetric structures of hurricane boundary layer in coupled atmosphere wave ocean models and observations abstract in a recent paper lee and chen 2012 hereafter lc12 presented numerical simulations of symmetric and asymmetric hurricane boundary layer structures in a fully coupled atmosphere wave ocean model and used these simulations to compare aspects of the boundary layer structure against an analysis of observations one of their main conclusions was that the azimuthally averaged inflow layer tends to misrepresent the overall inflow structure in tropical cyclones especially the asymmetric structure p 3593 another main conclusion was that the complicated asymmetric three dimensional boundary layer structures attributed by them to be due in part to the air sea and wind wave coupling make it difficult to parameterize the atmosphere wave ocean coupling effects without a fully coupled model p 3593 after careful examination of their study we have a number of questions regarding their methodology their interpretations including their interpretations of previous literature and their conclusions specifically we inquire about aspects of the methodology for defining the dynamical boundary layer depth the selection of the boundary layer scheme and we question the conclusions inferred in addition to the foregoing concerns inaccuracies in their literature review are noted and inconsistencies between their conclusions and reported results are identified for many decades physical processes across the air sea interface and within the atmospheric boundary layer have been known to be essential for the development and maintenance of a tropical cyclone ooyama 1969 emanuel 1986 1995 smith et al 2009 smith and montgomery 2010 bryan and rotunno 2009 bryan 2012 however the boundary layer is the least observed part of a storm in particular its turbulence structure with the advent of the global positioning system gps dropsonde hock and franklin 1999 the mean boundary layer structure has been progressively studied

high resolution ice thickness mapping in south greenland airborne radar sounding is difficult in south greenland because of the presence of englacial water which prevents the signal from reaching the bed data coverage remains suboptimal for traditional methods of ice thickness and bed mapping that rely on geostatistical techniques such as kriging because important features are missing here we apply two alternative approaches of high resolution 300 m ice thickness mapping that are based on the conservation of mass to two regions of south greenland 1 qooqqup sermia and kiattuut sermiat and 2 ikertivaq these two algorithms solve optimization problems for which the conservation of mass is either enforced as a hard constraint or as a soft constraint for the first region very few measurements are available but there is no gap in ice motion data whereas for ikertivaq more ice thickness measurements are available but there are gaps in ice motion data we show that mass conservation algorithms can be used as validation tools for radar sounding we also show that it is preferable to apply mass conservation as a hard constraint rather than a soft constraint as it better preserves elongated features such as glacial valleys and ridges

observed boundary layer wind structure and balance in the hurricane core part i hurricane georges abstract the gps dropsonde allows observations at unprecedentedly high horizontal and vertical resolution and of very high accuracy within the tropical cyclone boundary layer these data are used to document the boundary layer wind field of the core of hurricane georges 1998 when it was close to its maximum intensity the spatial variability of the boundary layer wind structure is found to agree very well with the theoretical predictions in the works of kepert and wang in particular the ratio of the near surface wind speed to that above the boundary layer is found to increase inward toward the radius of maximum winds and to be larger to the left of the track than to the right while the low level wind maximum is both more marked and at lower altitude on the left of the storm track than on the right however the expected supergradient flow in the upper boundary layer is not found with the winds being diagnosed as close to gradient balance the tropical cyclone boundary layer model of kepert and wan

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

calibrating a glaciological model of the greenland ice sheet from the last glacial maximum to present day using field observations of relative sea level and ice extent we constrain a three dimensional thermomechanical model of greenland ice sheet gris evolution from the last glacial maximum lgm 21 ka bp to the present day using primarily observations of relative sea level rsl as well as field data on past ice extent our new model huy2 fits a majority of the observations and is characterised by a number of key features i the ice sheet had an excess volume relative to present of 4 1 m ice equivalent sea level at the lgm which increased to reach a maximum value of 4 6 m at 16 5 ka bp ii retreat from the continental shelf was not continuous around the entire margin as there was a younger dryas readvance in some areas the final episode of marine retreat was rapid and relatively late c 12 ka bp leaving the ice sheet land based by 10 ka bp iii in response to the holocene thermal maximum htm the ice margin retreated behind its present day position by up to 80 km in the southwest 20 km in the south and 80 km in a small area of the northeast as a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka bp which corresponds to a deficit volume relative to present of 0 17 m ice equivalent sea level our results suggest that remaining discrepancies between the model and the observations are likely associated with non greenland ice load differences between modelled and observed present day ice elevation around the margin lateral variations in earth structure and or the pattern of ice margin retreat

reconciling the ice 6g_c reconstruction of glacial chronology with ice sheet dynamics the cases of greenland and antarctica we describe a theoretical and numerical framework that has been developed to investigate the compatibility of the ice 6g c reconstruction of the glaciation histories of the greenland and antarctic ice sheets with the latest understanding of ice physics the ice 6g c reconstruction has been produced solely on the basis of the theory of the glacial isostatic adjustment gia process and it has remained an issue as to whether such reconstructions of the time dependent thickness variations of grounded continental ice sheets were compatible with physics based ice mechanical considerations our analyses focus on the evolution over the last glacial cycle of these extent ice sheet complexes and demonstrate that the gia inferred models are entirely consistent with such considerations when uncertainties in net mass balance history are taken fully into account

structure and formation of an annular hurricane simulated in a fully compressible nonhydrostatic model tcm4 abstract the structure and formation of an annular hurricane simulated in a fully compressible nonhydrostatic tropical cyclone model tcm4 are analyzed the model is initialized with an axisymmetric vortex on an f plane in a quiescent environment and thus the transition from the nonannular hurricane to the annular hurricane is attributed to the internal dynamics the simulated annular hurricane has all characteristics of those recently documented by knaff et al from satellite observations quasi axisymmetric structure large eye and wide eyewall high intensity and suppressed major spiral rainbands a striking feature of the simulated annular hurricane is its large outward tilt of the wide eyewall which is critical to the quasi steady high intensity and is responsible for the maintenance of the large size of the eye and eyewall of the storm although the annular hurricane has a quasi axisymmetric structure marked low wavenumber asymmetries exist in the eyewall region the formation of the simulated a

on the distribution of subsidence in the hurricane eye two hurricane eye features that have yet to be adequately explained are the clear air moat that forms at the outer edge of the eye and the hub cloud that forms near the circulation centre to investigate whether these features can be explained by the spatial distribution of the subsidence field we have derived an analytical solution of the sawyer eliassen transverse circulation equation for a three region approximation with an unforced central eye region of intermediate or high inertial stability a diabatically forced eyewall region of high inertial stability and an unforced far field of low inertial stability this analytical solution isolates the conditions under which the subsidence is concentrated near the edge of the eye the crucial parameter is the dimensionless dynamical radius of the eye defined as the physical radius of the eye divided by the characteristic rossby length in the eye when this dimensionless dynamical radius is less than 0 6 there is less than 10 horizontal variation in the subsidence rate across the eye when it is greater than 1 8 the subsidence rate at the edge of the eye is more than twice as strong as at the centre of the eye when subsidence is concentrated at the edge of the eye the largest temperature anomalies occur near there rather than at the vortex centre this warm ring structure as opposed to a warm core structure is often observed in the lower troposphere of intense hurricanes copyright 2007 royal meteorological society

height dependent transition from 3 d to 2 d turbulence in the hurricane boundary layer received 7 february 2013 revised 6 march 2013 accepted 7 march 2013 1 here we show from in situ aircraft measurements in the hurricane boundary layer a height dependent transition of the flow from 3 d to 2 d turbulence this marks a fundamental change in the energy dynamics of the hurricane boundary layer due to the fact that in 3 d energy flows downscale from larger to smaller scales whereas in 2 d it flows upscale from smaller to larger scales these results represent the first measurement of the 2 d upscale energy flux in the atmosphere and also the first to characterize the transition from 3 d to 2 d it is shown that the large scale parent vortex may gain energy directly from small scales in tropical cyclones citation byrne d and j a zhang 2013 height dependent transition from 3 d to 2 d turbulence in the hurricane boundary layer geophys res lett 40 doi 10 1002 grl 50335

numerical simulations of the genesis of hurricane diana 1984 part ii sensitivity of track and intensity prediction abstract the authors examine numerous simulations that probe the dynamics governing the intensification and track of tropical cyclone diana 1984 simulated in part i the development process is fundamentally dependent on a preexisting upper tropospheric trough ridge couplet this couplet focuses mesoscale vertical motion that in turn produces lower tropospheric potential vorticity pv anomalies which form the seed for the tropical storm removal of this trough ridge couplet from the initial conditions eliminates cyclogenesis the simulated rate of development of diana in the prehurricane phase depends principally on choices of cumulus parameterization boundary layer treatment sea surface temperature and grid spacing simulations with cumulus schemes that allow more grid scale precipitation on the 9 km grid exhibit unrealistic grid scale overturning and slower intensification primarily due to production of cyclonic vorticity anomalies at large radii use of an innermost nest with 3 km grid spacing

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

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

multiplatform observations of boundary layer structure in the outer rainbands of landfalling typhoons this paper analyzes data collected from a new set of observational platforms in the coastal area of china which consist of a mobile observation system meteorological tower automatic weather station and doppler radars to investigate the mean and turbulent boundary layer structure and evolution during the landfall of typhoons an example of these data is provided from typhoon morakot 2009 vertical profiles of wind velocities and thermodynamic parameters from the observed data allow us to identify different boundary layer structures during and after landfall these structures sampled in regions of the outer core are stratified into periods where convection is occurring termed convective and periods where convection has recently 2 h occurred termed postconvective data analyses show that the thermodynamic mixed layer depth and inflow layer depth are higher during the convective period than the postconvective period the mixed layer depth is found to be within the strong inflow layer but the height of the maximum tangential wind speed is above the inflow layer during both periods contrary to recent observational studies of the boundary layer structure of tropical cyclones over water high frequency wind data show that momentum flux turbulent kinetic energy tke and integral length scales of wind velocities are all much larger during the convective period than the postconvective period the results suggest that convective downdrafts may play an important role in modulating turbulent flux tke vertical mixing and boundary layer recovery processes