global scatterometer observations of the structure of tropical cyclone wind fields abstracta very large database containing 24 years of scatterometer passes is analyzed to investigate the surface wind fields within tropical cyclones the analysis confirms the left right asymmetry of the wind field with the strongest winds directly to the right of the tropical cyclone center northern hemisphere at values greater than 2 times the radius to maximum winds the asymmetry is approximately equal to the storm velocity of forward movement observed wind inflow angle i e storm motion not subtracted is shown to vary both radially and azimuthally within the tropical cyclone the smallest observed wind inflow angles are found in the left front quadrant with the largest values in the right rear quadrant as the velocity of forward movement increases and the central pressure decreases observed inflow angles ahead of the storm decrease and those behind the storm increase in the right rear quadrant the observed inflow angle increases with radius from the storm center in all other quadrants the observed inflow angle is approximately constant as a function of radial distance

parametric representation of the primary hurricane vortex part i observations and evaluation of the holland 1980 model although numerical models are essential to hurricane forecasting many other applications require only statistical depiction of the wind distribution in holland s 1980 parametric profile radius of maximum wind maximum wind and a measure of the profile width describe the radial variation of the axisymmetric wind variants of the holland profile are used to predict insurance underwriting risk ocean response and storm surge inundation since these calculations guide high stakes financial and emergency managment decisions it is logical to test them against observations the hurricane research division s flight level database archives observations were obtained by noaa and u s air force reserve aircraft the data considered here are winds and geopotential heights observed during 606 lower and midtropospheric flights into atlantic and eastern pacific tropical cyclones during 1977 2000 the 493 profiles that meet quality control criteria are seasonally geographically representative least squares fits of the holland model to these data provide evaluation of the parameters distributions and critical examination of the profile s realism individual fitted profiles differ from the observations in a consistent pattern the areas of strong winds in the eyewall and of nearly calm winds at the vortex center are too wide beyond 2 or 3 times the eye radius the wind decreases too rapidly with distance from the center although the average bias in fitted profiles is 1ms 21 the root mean square error is 4 2 m s 21 5 2 m s21 for independent data maximum winds estimated from the fitted holland profile height wind relation average 2 5 m s 21 too strong with an rms error of 6 5 m s 21 the pattern of too strong wind spread over too much real estate exaggerates the occurrence of winds stronger than 50 m s 21 by 50

field experiments in a fractured clay till 2 solute and colloid transport a field tracer experiment was conducted in a lateral flow field in the weathered and highly fractured upper 6 m of a 40 m thick clay rich till plain in southwestern ontario in the upper 3 m where fractures are closely spaced 5 m d simulations with a discrete fracture porous matrix flow and transport model which used the cubic law for flow in fractures showed that diffusion of the solutes but not the much larger colloids into the matrix pore water between fractures is sufficient to cause the observed difference in solute and colloid transport rates transport derived and hydraulic conductivity derived fracture aperture values were similar within a factor of 3 and falling mainly within a range of 5 40 m in the upper 3 m the solute tracers were evenly distributed between pore water in the fractures and the matrix and as a result solute transport can be closely approximated with an equivalent porous medium epm approach below this depth fractures are more widely spaced 0 13 to 1 m with concentration peaks tending to occur near visible fractures and solute transport cannot be adequately described with an epm approach

relationship between cyclone tracks anticyclone tracks and baroclinic waveguides abstract this study presents observational results concerning the structure and evolution of high frequency fluctuations with periods shorter than 6 days in the geopotential height field the results are based on a statistical analysis of 1000 500 and 250 mb height fields derived from twice daily nmc final analyses over the northern hemisphere for the 20 winters 1964 65 through 1983 84 the disturbances assume the form of waves elongated in the meridional direction with a mean wavelength of 4000 km a westward tilt with height and a mean eastward phase propagation of 12 1 5 m s 1 these results support an interpretation in terms of finite amplitude baroclinic waves whose structure and evolution varies with geographical location over the continents and especially along the eastern slopes of the rockies and the tibetan plateau the waves show marked departures in structure and evolution from those over the oceans in particular we find evidence of a systematic influence of the terrain in steering the

fitting parametric vortices to aliased doppler velocities scanned from hurricanes abstractan alias robust least squares method that produces less errors than established methods is developed to produce reference radial velocities for automatically correcting raw aliased doppler velocities scanned from hurricanes this method estimates the maximum tangential velocity vm and its radial distance rm from the hurricane vortex center by fitting a parametric vortex model directly to raw aliased velocities at and around each selected vertical level in this method aliasing caused zigzag discontinuities in the relationship between the observed and true radial velocities are formulated into the cost function by applying an alias operator to the entire analysis minus observation term to ensure the cost function to be smooth and concave around the global minimum simulated radar velocity observations are used to examine the cost function geometry around the global minimum in the space of control parameters vm rm the results show that the global minimum point can estimate the true vm rm app

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

the spatial distribution of ocean waves in tropical cyclones the spatial structure of both the wind and wave fields within tropical cyclones is investigated using two large databases the first of these was compiled from global overpasses of tropical cyclones by satellite altimeters the second dataset consists of an extensive collection of north american buoy measurements during the passage of tropical cyclones hurricanes the combined datasets confirm the vortex structure of the tropical cyclone wind field with the strongest winds to the right northern hemisphere of the storm the wave field largely mirrors the wind field but with greater right left asymmetry that results from the extended fetch to the right of the translating tropical cyclone the extensive in situ buoy database confirms previous studies indicating that the one dimensional spectra are generally unimodal the directional spectra are however directionally skewed consisting of remotely generated waves radiating out from the center of the storm and locally generated wind sea the one dimensional wave spectra have many similarities to fetch limited cases although for a given peak frequency the spectra contain less energy than for a fetch limited case this result is consistent with the fact that much of the wave field is dominated by remotely generated waves

trapped waves in the edge region of stratospheric polar vortices 1 a global distribution and seasonal variability of short period 2 days disturbances in the lower and middle stratosphere are investigated using 6 hourly european centre for medium range weather forecasts reanalysis data over 15 years 1979 1993 two dimensional spectral analysis and a recently developed lagrangian mean diagnostic are used for the analysis it is shown that the short period disturbances are most active around the polar night jet in each winter hemisphere they have a wavelike structure in the longitudinal direction with typical zonal wavelengths of 1 700 2 000 km i e zonal wave number 10 12 and a latitudinally evanescent structure with a half width of about 1 500 km suggesting that they are waves trapped in the edge region of the polar vortex where the latitudinal gradient of isentropic potential vorticity is maximized the trapped waves have a nearly barotropic structure over a depth greater than 10 km because the polar vortex in the northern hemisphere is much deformed and not symmetric around the pole dynamical characteristics of the trapped waves in the southern hemisphere alone are investigated by applying a lag correlation analysis to the reanalysis data the characteristics of trapped waves are fairly dependent on the state of the polar vortex such as zonal wind speed and its vertical shear they have a significant westward intrinsic phase velocity from june through october when the polar vortex is most stable this indicates that the trapped waves during this period have their own dynamics contrary to the filaments being passively advected by the large scale flow

the retrieval of asymmetric tropical cyclone structures using doppler radar simulations and observations with the extended gbvtd technique abstract the ground based velocity track display gbvtd technique is extended to two doppler radars to retrieve the structure of a tropical cyclone s tc s circulation with this extension it is found that the asymmetric part of the tc radial wind component can be derived up to its angular wavenumber 1 structure and the accuracy of the retrieved tc tangential wind component can be further improved although two radar systems are used a comparison with the traditional dual doppler synthesis indicates that this extended gbvtd egbvtd approach is able to estimate more of the tc circulation when there are missing data previous research along with this study reveals that the existence of strong asymmetric radial flows can degrade the quality of the gbvtd derived wind fields when a tc is observed by one radar it is suggested that the gbvtd method be applied to tcs over a flat surface e g the ocean where the assumption of relatively smaller asymmetric radial winds than asymmetric tangential winds is

seasonal variations in the southern hemisphere storm tracks and jet streams as revealed in a reanalysis dataset abstract regional characteristics of the climatological seasonal variations in southern hemisphere sh storm tracks are examined based on a reanalysis dataset when differences in vertical structure between the subpolar and subtropical jet streams spj and stj respectively are considered the regional characteristics can be interpreted reasonably well from a potential vorticity perspective of baroclinic eddy growth and downstream development of a baroclinic wave packet eddy activity in the upper and lower tropospheres is strongest in the core region of the spj over the eastern south atlantic and indian ocean throughout the year even in austral winter when the intense stj forms over the indian ocean and south pacific showing its eddy driven nature the spj accompanies the strong surface westerlies along a well defined baroclinic zone above an intense oceanic frontal zone in this core region of the storm track low level eddy activity is strongly correlated with the local near surface baroclinicity

influence of tropical cyclones on sea surface temperature seasonal cycle and ocean heat transport recent studies suggested that tropical cyclones tcs contribute significantly to the meridional oceanic heat transport by injecting heat into the subsurface through mixing here we estimate the long term oceanic impact of tcs by inserting realistic wind vortices along observed tcs tracks in a 1 2 resolution ocean general circulation model over the 1978 2007 period warming of tcs cold wakes results in a positive heat flux into the ocean oceanic heat uptake ohu of 480 tw consistent with most recent estimates however 2 5 of this ohu only compensates the heat extraction by the tcs winds during their passage another 2 5 of this ohu is injected in the seasonal thermocline and hence released back to the atmosphere during the following winter because of zonal compensations and equatorward transport only one tenth of the ohu is actually exported poleward 46 tw resulting in a marginal maximum contribution of tcs to the poleward ocean heat transport other usually neglected tc related processes however impact the ocean mean state the residual ekman pumping associated with tcs results in a sea level drop rise in the core northern and southern flanks of tc basins that expand westward into the whole basin as a result of planetary wave propagation more importantly tc induced mixing and air sea fluxes cool the surface in tc basins during summer while the re emergence of subsurface warm anomalies warms it during winter this leads to a 10 reduction of the sea surface temperature seasonal cycle within tcs basins which may impact the climate system

blueprint for a coupled model of sedimentology hydrology and hydrogeology in streambeds the streambed constitutes the physical interface between the surface and the subsurface of a stream across all spatial scales surface water groundwater interactions are controlled by the physical properties of the streambed streambed properties such as topography or hydraulic conductivity are continuously altered through erosion and sedimentation processes recent studies from the fields of ecology hydrogeology and sedimentology provide field evidence that sedimentological processes themselves can be heavily influenced by surface water groundwater interactions giving rise to complex feedback mechanisms between sedimentology hydrology and hydrogeology more explicitly surface water groundwater exchanges play a significant role in the deposition of fine sediments which in turn modify the hydraulic properties of the streambed we explore these feedback mechanisms and critically review the extent of current interaction between the different disciplines we identify opportunities to improve current modeling practices for example hydrogeological models treat the streambed as a static rather than a dynamic entity while sedimentological models do not account for critical catchment processes such as surface water groundwater exchange a blueprint for a new modeling framework is proposed that bridges the conceptual gaps between sedimentology hydrogeology and hydrology specifically this blueprint 1 fully integrates surface subsurface flows with erosion transport and deposition of sediments and 2 accounts for the dynamic changes in surface elevation and hydraulic conductivity of the streambed the opportunities for new research within the coupled framework are discussed

how does the boundary layer contribute to eyewall replacement cycles in axisymmetric tropical cyclones abstractthree diagnostic models of the axisymmetric tropical cyclone boundary layer with different levels of approximation are applied to the problem of tropical cyclones with concentric eyewalls the outer eyewall is shown to have an inherently stronger frictional updraft than the inner because it is in an environment of lower vorticity similarly a relatively weak local enhancement of the radial vorticity gradient outside the primary radius of maximum winds can produce a significant frictional updraft even if there is no outer wind maximum based on these results it is proposed that the boundary layer contributes to the formation of outer eyewalls through a positive feedback among the local enhancement of the radial vorticity gradient the frictional updraft and convection the friction induced secondary circulation associated with the inner eyewall is shown to weaken as the outer wind maximum strengthens and or contracts so boundary layer processes will contribute along with the heating induced

a diagnostic study of jet streaks kinematic signatures and relationship to coherent tropopause disturbances abstract a diagnostic study is conducted of the kinematics and evolution of upper level jet streaks representative of three of the four phases in the shapiro conceptual model of a jet streak progressing through a synoptic scale baroclinic wave over north america the three phases selected for consideration apply to those segments of the wave pattern where jet streaks are relatively straight the 1200 utc 2 december 1991 case trough over ridge considers a strong jet streak located over eastern north america and constitutes the bulk of the study the other two cases which also concern jet streaks over north america are from 0000 utc 11 november 1995 northwesterly flow and 0000 utc 28 october 1995 southwesterly flow kinematic signatures consistent with the classic four quadrant conceptual model for a straight jet streak are evident in all three cases although flow curvature and thermal advection lead to significant departures from this conceptual model the position of the jet streak within the s

on the warm core of a tropical cyclone formed near the tropopause abstracton the basis of numerical results of a three dimensional model diagnosed using balance dynamics a mechanism by which the upper level warm core of tropical cyclones tcs forms is proposed the numerical results reveal that an upper level warm core develops when tcs intensify just prior to reaching the mature stage potential temperature budget analysis reveals that for the tendency of potential temperature the azimuthal mean component of advection is dominant at the upper level of the eye at the mature stage sawyer eliassen diagnosis shows that tendencies due to forced flow by diabatic heating and diffusion of tangential wind are dominant in the eye and are negatively correlated to each other the distributions of the diabatic heating in the simulated tc are not peculiar therefore it is unlikely that the heating distribution itself is the primary cause of the flow from the lower stratosphere the analyses of forced circulations of idealized vortices show that the upper level subsidence is enh

soil erosion via preferential flow to drainage systems in clay soils runoff measurements from artificially levelled land showed that rates of particle erosion to the drainage system was even higher than that from surface runoff this effect was increased by tillage whilst no tillage reduced the losses significantly the field site soil type was a silty clay loam artificial levelling at the site had exposed an unstable subsoil susceptible to cracking soil structures with macropores and cracks were examined to find out more about water and particle transport via preferential flow pathways a field profile description of soil structure and ct scanning of monoliths from the plough layer subsoil and backfill showed different density patterns and structural properties the backfill consisted of clods and open voids with direct contact to the drainpipes the soil down to 50 cm was cracked both vertically and horizontally and some cracks were leading into the backfill cracks of up to 10 mm width were found indicating that transport of particles through them was possible the measured field hydraulic conductivities varied over 3 orders of magnitude indicative of a preferential flow network infiltration with dye tracer visually demonstrated rapid flow of water through cracks leading directly to the drainage system with a hydraulic conductivity of 9 9 10 4 m s 1 in the soil and 5 8 10 3 m s 1 in the backfill these results indicate that particles can be eroded from the plough layer and transported both laterally and vertically through macropores and cracks into the backfill and then directly to drain pipes

life history of mobile troughs in the upper westerlies abstract increasing evidence indicates that surface cyclogenesis is predominantly a response to the approach of a preexisting trough at upper levels a question then arises about the origin of the upper level predecessor as an initial approach to this question mobile troughs in the major band of westerlies were crudely tracked in daily northern hemispheric 500 mb analysis during nine recent cold seasons these troughs were identified only in the 552 dam height contour between 8 and 15 of them were present on a given day study of a particular cold season showed a median duration of 12 days and a mode of 5 days average zonal phase speed was 13 m s 1 locations or origin and termination of individual troughs were distributed over all longitudes but births greatly exceeded deaths over and east of the rocky mountains in north america and the highlands of central asia trough terminations dominated over the eastern portions of the oceans within the quasi steady planetary waves origins and terminations o

characteristics of the southern hemisphere winter storm track with filtered and unfiltered data abstract the structure and evolution of the fluctuations in synoptic scales in the southern hemisphere sh during winter are discussed using six years of european centre for medium range weather forecasts analyses it is shown that patterns from unfiltered meridional wind series in the sh display all the features needed to represent the synoptic scale waves typical periods and wavelengths are similar to those observed in the northern hemisphere 4 days 4000 km although over the pacific ocean they can be as high as 7 8 days and 4700 km respectively as in the northern hemisphere tilts are not geographically fixed but change with the stage of the evolution of the wave the phase speed of the waves agrees with the low level winds in extensive areas of the middle latitudes and ranges from 12 m s 1 in the indian ocean to 6 m s 1 in the pacific ocean the estimated group velocities achieve maximum values of about 38 m s 1 also in the indian ocean and agree with the upper level maximum winds in accor

reexamining the near core radial structure of the tropical cyclone primary circulation implications for vortex resiliency abstract recent theoretical studies based on vortex rossby wave vrw dynamics have established the importance of the radial structure of the primary circulation in the response of tropical cyclone tc like vortices to ambient vertical wind shear linear vrw theory suggests in particular that the degree of broadness of the primary circulation in the near core region beyond the radius of maximum wind strongly influences whether a tilted tc vortex will realign and resist vertical shear or tilt over and shear apart fully nonlinear numerical simulations have verified that the vortex resiliency is indeed sensitive to the initial radial structure of the idealized vortex this raises the question of how well the true nature of a tc s primary circulation is represented by idealized vortices that are commonly used in some theoretical studies in this paper the swirling wind structure of tcs is reexamined by utilizing flight level observations collected from atlantic and eastern pacific storms during 1977 2

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

shesed a physically based distributed erosion and sediment yield component for the she hydrological modelling system abstract shesed is introduced as a physically based spatially distributed erosion and sediment yield component for the existing she hydrological modelling system for use at the catchment scale for hillslopes represented spatially by the she grid square network shesed simulates soil erosion by raindrop impact leaf drip and sheet overland flow without rilling and the transport of the eroded material by overland flow for channels the component simulates the erosion of bed material and the downstream transport of this material together with that supplied by overland flow in the channel sediment routing procedure it is assumed that the flow can carry any available load of fine sediments less than 0 062 mm in diameter but for coarser sediments the load is limited by the calculated capacity transport rate of the flow the channel component also allows for bed armouring application of shesed to rainfall induced sediment yield events at two agricultural catchments areas 5 1 and 6 4 ha in iowa shows generally good reproduction of the observed temporal variations in sediment yield application to a 3 3 km reach of the east fork river wyoming for a 37 day period shows good reproduction of observed sediment discharge magnitudes but some discrepancy in the timing of the simulated sediment discharge peak

sediment detachment and transport processes associated with internal erosion of soil pipes subsurface flow can be an important process in gully erosion through its impact on decreasing soil cohesion and erosion resistance as soil water content or pressure increases and more directly by the effects of seepage forces on particle detachment and piping the development of perched water tables in duplex soils fosters lateral flow that can result in seepage at the surface of hillslopes and or formation of soil pipes by internal erosion of lateral preferential flow paths continued internal erosion of soil pipes can lead to gullies dam and levee failures however the processes involved in particle and aggregate detachment from soil pipe walls and transport processes within soil pipes have not been well studied or documented this paper reviews the limited research on sediment detachment and transport in macropores and soil pipes and applies the knowledge learned from the much more extensive studies conducted on streams and industrial pipes to hydrogeologic conditions of soil pipes knowledge gaps are identified and recommendations are made for future research on sediment detachment and transport in soil pipes

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

reexamining the vertical structure of tangential winds in tropical cyclones observations and theory a few commonly held beliefs regarding the vertical structure of tropical cyclones drawn from prior studies bothobservationalandtheoretical areexaminedinthisstudy oneofthesebeliefsisthattheoutwardslopeof the radius of maximumwinds rmw is a function of the size of the rmw another belief is that the outward slope of the rmw is also a function of the intensity of the storm specifically shea and gray found that the rmw becomes increasingly vertical with increasing intensity and decreasing radius the third belief evaluated here is that the rmw is a surface of constant absolute angular momentum m these three conventional wisdoms of vertical structure are revisited with a dataset of three dimensional doppler wind analyses comprising seven hurricanes on 17 different days azimuthal mean tangential winds are calculated for each storm andtheslopesofthermwandmsurfacesareobjectivelydetermined theoutwardslopeofthermw is shown to increase with radius which supports prior studies in contrast to prior results no relationship is found between the slope of the rmw and intensity it is shown that the rmw is indeed closely approximated by an m surface for the majority of storms however there is a small but systematic tendency for m to decrease upward along the rmw utilizing emanuel s analytical hurricane model a new equation is derived for the slope of the rmw in radius pressure space this predicts a linear increase of slope with radius and essentiallyno dependence of slope on intensity an exactly analogous equationcan be derivedin log pressure height coordinates and a numerical solution yields the same conclusions in geometric height coordinates these conclusions are further supported by the results of simulations utilizing emanuel s simple timedependent axisymmetric hurricane model as both the model and the analytical theory are governed by the dual constraints of thermal wind balance and slantwise moist neutrality it is demonstrated that it is these two assumptionsthat requirethe slope of the rmw to be a functionof its size but not of the intensityof the storm finally it is shown that within the context of emanuel s theory the rmw must very closely approximate an m surface through most of the depth of the vortex

psem_2d a physically based model of erosion processes at the plot scale 1 this paper presents the development and first applications of the plot soil erosion model 2d psem 2d infiltration is computed using a green and ampt model overland flow is computed using the depth averaged two dimensional unsteady flow equations saint venant equations and soil erosion is computed by combining the equation of mass conservation of sediment and a detachment transport coupling model for erosion by runoff a shear stress approach is used to determine the transport capacity the formation of a covering cohesionless layer as a result of depositing sediment and action of rainfall impact before runoff is considered the erosion processes involved are rainfall and runoff detachment of original soil rainfall redetachment and overland flow entrainment of sediment from the deposited layer and deposition the model uses a single representative particle size complex rainfall events on natural slopes can be simulated the accuracy of the predictions for erosion of planar surfaces is tested by comparison with observed data obtained from experiments and with an analytical solution good agreement between the calculated results and measured data was found a sensitivity analysis was also performed limitations related to the description of overland flow on plane soil surface are pointed out finally an application to a nonplanar natural surface of 75 m2 illustrated the distribution of erosion and sedimentation over the plot

evaluating a multiclass net deposition equation in overland flow conditions 1 the movement of sediment and related pollutants in overland flow from the point of erosion to a stream normally occurs through a series of deposition zones here we present the evaluation of a new multiclass model of sediment transport through these zones this model simulates size selective net deposition as a result of simultaneous deposition by settling and nonselective reentrainment of previously deposited sediment hairsine et al 2002 sander et al 2002 multiclass sediment deposition models provide a useful basis for simulating off site effects of soil erosion but information on the grain size composition of deposited and exported sediment is crucial for calibrating and evaluating such models therefore the multiclass sediment deposition model was tested using detailed experimental data information on the amount of sediment deposition on the grain size distribution of the deposited and exported sediment and on the spatial pattern of the deposits was collected during sediment deposition experiments calibration of the multiclass model using one part of these data was performed by adjusting the fraction of stream power available for sediment reentrainment by minimizing errors between both simulated and observed total outflow sediment concentration and grain size distribution of the exported sediment evaluation was conducted using the other part of the data over a wide range of conditions the evaluation shows that the deposition equation is capable of reasonably simulating the observed size selectivity of the deposition process however the model is not capable of simulating correctly the spatial pattern of the deposited sediment because of simplifications used in the hydraulic model

tropical cyclone kinematic structure retrieved from single doppler radar observations part i interpretation of doppler velocity patterns and the gbvtd technique abstract deducing the three dimensional primary circulation of landfalling tropical cyclones tcs from single ground based doppler radar data remains a difficult task the evolution and structure of landfalling tcs and their interactions with terrain are left uncharted due to the lack of dual doppler radar observations existing ground based single doppler radar tc algorithms provide only qualitative information on axisymmetric tc center location and intensity in order to improve understanding of the wind structures of landfalling tcs using the widely available wsr 88d data along the u s coastal region a single ground based radar tc wind retrieval technique the ground based velocity track display gbvtd technique is developed part i of this paper presents 1 single doppler velocity patterns of analytic asymmetric tcs 2 derivation of the gbvtd technique and 3 evaluation of the gbvtd retrieved winds using analytic tcs the doppler velocity patterns of asymmetric tcs display more complex structu

an amplification mechanism of medium scale tropopausal waves abstract the mechanism for the amplification of medium scale tropopausal waves with horizontal wavelengths of 2000 3000 km and wave periods of 1 2 days that are basically neutral is investigated using a three dimensional wave activity flux distinctive upward wave activity fluxes are found in the midtroposphere 400 hpa upstream of the region where the medium scale waves are dominant that is where the horizontal components of the wave activity flux are large these upward fluxes converge in the upper troposphere 300 hpa this convergence is a major source of medium scale waves producing large values of the horizontal components of the wave activity flux in the active regions examination of the spatial structure of the heat flux shows that the upward fluxes are due to occasional baroclinic interactions between upper level medium scale waves and lower tropospheric disturbances with the same temporal scales the seasonal and geophysical variations of the waves depend mostly on the amount of baroclin

doppler radar observations of dust devils in texas abstract analyses of a dust devil dataset collected in northwest texas are presented the data were collected just above the ground at close range with a mobile w band 3 mm wavelength doppler radar having an azimuthal radial resolution of 3 5 m 30 m at the range of the dust devils most dust devils appeared as quasi circular rings of relatively high radar reflectivity four dust devil vortices were probed three of which were cyclonic and one anticyclonic documentation was obtained of a pair of adjacent cyclonic vortices rotating cyclonically around each other approximate radial profiles of azimuthal and radial wind components and of radar reflectivity are detailed and discussed the diameters of the core of the dust devils ranged from 30 to 130 m the latter diameters are much wider than that of typical dust devils in a homogeneous environment the widest vortex was cyclonic and exhibited evidence of a two cell structure i e sinking motion near the center and rising motion just outside the ra

parametric representation of the primary hurricane vortex part ii a new family of sectionally continuous profiles abstract for applications such as windstorm underwriting or storm surge forecasting hurricane wind profiles are often approximated by continuous functions that are zero at the vortex center increase to a maximum in the eyewall and then decrease asymptotically to zero far from the center comparisons between the most commonly used functions and aircraft observations reveal systematic errors although winds near the peak are too strong they decrease too rapidly with distance away from the peak pressure wind relations for these profiles typically overestimate maximum winds a promising alternative is a family of sectionally continuous profiles in which the wind increases as a power of radius inside the eye and decays exponentially outside the eye after a smooth polynomial transition across the eyewall based upon a sample of 493 observed profiles the mean exponent for the power law is 0 79 and the mean decay length is 243 km the database actually contains 606 aircraft sorties but 113 of these failed

two distinct regimes in the kinematic and thermodynamic structure of the hurricane eye and eyewall abstract using aircraft flight level data the present work demonstrates that the kinematic and thermodynamic distributions within the eye and eyewall of strong hurricanes are observed to evolve between two distinct regimes in the first regime angular velocity is greatest within the eyewall and relatively depressed within the eye in the second regime radial profiles of angular velocity are nearly monotonic with maxima found at the eye center considering sequential profiles within individual hurricanes the authors find that the evolution of the kinematic distribution is often marked by a transition from the first regime to the second the transition can occur in less than 1 h also noted during the transition are dramatic changes in the thermodynamic structure of the hurricane prior to the transition regime 1 the eye is typically very warm and dry and the equivalent potential temperature is often elevated within the eyewall and relatively depressed within the eye after the transition regime 2

a diagnostic study of waves on the tropopause the spatial structure and phase velocity of tropopause disturbances localized around the subpolar jet in the southern hemisphere are investigated using 6 hourly european centre for medium range weather forecasts reanalysis data covering 15 yr 1979 93 the phase velocity and phase structure of the tropopause disturbances are in good agreement with those of an edge wave vertically trapped at the tropopause however the vertical distribution of the ratio of potential to kinetic energy exhibits maxima above and below the tropopause and a minimum around the tropopause in contradiction to edge wave theory for which the ratio is unity throughout the troposphere and stratosphere this difference in vertical structure between the observed tropopause disturbances and edge wave theory is attributed to the effects of a finite depth tropopause together with the next order corrections in rossby number to quasigeostrophic dynamics

the 30 may 1998 spencer south dakota storm part ii comparison of observed damage and radar derived winds in the tornadoes abstract a violent supercell tornado passed through the town of spencer south dakota on the evening of 30 may 1998 producing large gradients in damage severity the tornado was rated at f4 intensity by damage survey teams a doppler on wheels dow mobile radar followed this tornado and observed the tornado at ranges between 1 7 and 8 0 km during various stages of the tornado s life the dow was deployed less than 4 0 km from the town of spencer between 0134 and 0145 utc and during this time period the tornado passed through spencer and peak doppler velocity measurements exceeded 100 m s 1 data gathered from the dow during this time period contained high spatial resolution sample volumes of approximately 34 m 34 m 37 m along with frequent volume updates every 45 50 s the high resolution doppler velocity data gathered from low level elevation scans when sample volumes are between 20 and 40 m agl are compared to extensive ground and aerial damage surveys performed by the national weather servic

global characteristics of medium scale tropopausal waves observed in ecmwf operational data global characteristics and seasonal variation of medium scale zonal wavelengths of 2000 3000 km waves observed around the midlatitude tropopause are examined using 6 hourly european centre for medium range weather forecasts operational data over four years 1990 93 covering both hemispheres medium scale waves and synoptic scale waves are extracted using time filters and their characteristics are compared hovmoller diagrams indicate the existence of medium scale waves in the southern hemisphere as well as in the northern hemisphere the zonal wavelengths of medium scale waves are slightly larger in the southern hemisphere than in the northern hemisphere medium scale waves are mostly active in three regions the north atlantic in winter dec jan feb the north pacific in spring mar apr may mam and the south indian ocean in autumn mam these regions are roughly corresponding to and slightly downstream of storm tracks where synoptic waves are dominant significant differences in seasonal variation of the intensity between the two kinds of waves are also found the maximum of wave amplitudes is seen around the tropopause at latitudes slightly higher than the jet stream axis where the meridional gradient of the quasigeostrophic potential vorticity qpv is maximized the positive large qpv gradient is attributed to the atmospheric structure around the midlatitude tropopause that is located in vertical westerly shear of the jet stream this fact suggests that the medium scale waves are waves trapped around the midlatitude tropopause

modelling soil erosion in a clayey subsurface drained agricultural field with a three dimensional flush model summary soil erosion is an important environmental issue in agricultural areas of northern europe where clayey soils are prevalent clayey soils are routinely subsurface drained to accelerate drainage which creates an additional discharge route for suspended sediment previously assessment of the sediment load from clayey fields has been difficult because process based models were only able to simulate sediment loads via surface runoff a new distributed process based erosion model was developed and incorporated into the flush modelling system to fulfil this void the model facilitates simulation of spatially distributed soil erosion on the field surface and sediment loads via surface runoff and subsurface drainflow soil erosion on the field surface is simulated with the two dimensional sediment continuity equation coupled with hydraulic and rain drop splash erosion sediment settling and transport capacity processes subsurface sediment transport in macropores is described with the three dimensional advection dispersion equation the model was applied to a clayey subdrained field section 3 6 ha in southern finland the results demonstrated the capability of the model to simulate soil erosion and sediment transport in terms of the match between the measured 2669 kg ha 1 and modelled 2196 kg ha 1 sediment loads via surface runoff and the measured 2937 kg ha 1 and modelled 2245 kg ha 1 loads via drainflow during the validation period of 7 months the model sensitivity analysis pointed out the importance of the flow model parameters in simulation of soil erosion through their control on the division of total runoff into surface runoff and drainflow components the key parameters in the erosion model were those that affected hydraulic and splash erosion rates the model application in the experimental field suggested that both hydraulic and splash erosion were the factors behind the sediment losses during the growing season and early autumn whereas high sediment loads in late autumn were caused by hydraulic erosion due to overland flow in tilled soil

a diagnostic equation for tendency of lapse rate tropopause heights and its application abstractthe tropopause is the boundary between the troposphere and stratosphere and is normally defined by the temperature lapse rate previous studies have noted that synoptic scale and planetary

a new parametric tropical cyclone tangential wind profile model abstracta new parametric tropical cyclone tc wind profile model is presented for depicting representative surface pressure profiles corresponding to multiple maxima wind profiles that exhibit single dual and triple maximum concentric eyewall wind peaks associated with the primary inner secondary first outer and tertiary second outer complete rings of enhanced radar reflectivity one profile employs five key parameters tangential velocity maximum radius of the maximum and three different shape velocity parameters related to the shape of the profile after tailoring the model for tc applications a gradient wind is computed from a cyclostrophic wind formulated in terms of the cyclostrophic rossby number a pressure via cyclostrophic balance was partitioned into separate pressure components that corresponded to multiple maxima cyclostrophic wind profiles in order to quantitatively evaluate the significant fluctuations in central pressure deficits the model tc intensity in terms of varying

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

a method for retrieving mean horizontal wind profiles from single doppler radar observations contaminated by aliasing the velocity azimuth display vad technique was designed to estimate the areal mean vertical profile of the horizontal wind above a ground based doppler radar the method uses radial velocity observations under the assumption of a linear wind field though it encounters difficulty when the observations are contaminated by velocity ambiguities large noise and when viable data exist only over a restricted azimuthal range the method suggested in this paper uses gradients of radial velocity rather than only the velocity itself to derive wind profiles and thus is termed the gradient velocity azimuth display gvad technique both the vad and gvad methods are tested first on simulated data to examine their sensitivity to different type of errors in radial velocity the retrieved mean wind profiles are shown to be insensitive to random errors in radial velocity even at large amplitude however the vad method is very sensitive to systematic errors caused by velocity ambiguities the experiments indicate t

balanced asymmetries of waves on the tropopause tropopause disturbances have long been recognized as important features for extratropical weather since they produce organized vertical motion in the troposphere observations of cyclonic tropopause disturbances show localized depressions of the tropopause with stratospheric values of potential vorticity extending to lower altitudes anticyclonic disturbances are associated with comparatively smaller upward deflections of the tropopause analytical solutions for nonlinear interfacial wave motions are derived for an intermediate balanced dynamics based on small rossby number asymptotics beyond quasigeostrophy traveling edge wave solutions reveal realistic asymmetries such that cyclones are associated with greater deflections of the interface as well as larger anomalies in pressure and vertical motion compared to anticyclones

observed cyclone anticyclone tropopause vortex asymmetries relatively little is known about coherent vortices near the extratropical tropopause even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues through an objective census of observed tropopause vortices the authors test a hypothesis regarding vortex merger asymmetry where cyclone pairs are repelled and anticyclone pairs are attracted by divergent flow due to frontogenesis emphasis is placed on arctic vortices where jet stream influences are weaker in order to facilitate comparisons with earlier idealized numerical simulations results show that arctic cyclones are more numerous persistent and stronger than arctic anticyclones an average of 15 cyclonic vortices and 11 anticyclonic vortices are observed per month with maximum frequency of occurrence for cyclones anticyclones during winter summer there are are about 47 more cyclones than anticyclones that survive at least 4 days and for longer lifetimes 1 day survival probabilities are nearly constant at 65 for cyclones and 55 for anticyclones mean tropopause potential temperature amplitude is 13 k for cyclones and 11 k for anticyclones with cyclones exhibiting a greater tail toward larger values an analysis of close proximity vortex pairs reveals divergence between cyclones and convergence between anticyclones this result agrees qualitatively with previous idealized numerical simulations although it is unclear to what extent the divergent circulations regulate vortex asymmetries