subrainband structure and dynamic characteristics in the principal rainband of typhoon hagupit 2008 abstractthe principal rainband in tropical cyclones is currently depicted as a solitary and continuous precipitation region however the airborne radar observations of the principal rainband in typhoon hagupit 2008 reveal multiple subrainband structures these subbands possess many characteristics of the squall lines with trailing stratiform in the midlatitudes and are different from those documented in previous principal rainband studies the updraft and reflectivity cores are upright and elevated the updraft is fed by a low level radial outflow from the inner side the tangential wind speed shows a clear midlevel jet on the inner side of the reflectivity core except for the structural similarities the dynamics of the subbands is also similar to the squall lines the local environment near the subbands shows little convective inhibition modest instability and vertical wind shear the temperature retrieval shows a cold pool structure in the stratiform precipitation region the estimated vertical w

inversion of seismic refraction data in planar dipping structure summary a new method is presented for the direct inversion of seismic refraction data in dipping planar structure three recording geometries each consisting of two common shot profiles are considered reversed split and roll along profiles inversion is achieved via slant stacking the common shot wavefield to obtain a delay time slowness tau p wavefield the tau p curves from two shotpoints describing the critical raypath of refracted and post critically reflected arrivals are automatically picked using coherency measurements and the two curves are jointly used to calculate velocity and dip of isovelocity lines iteratively thereby obtaining the final two dimensional velocity model this procedure has been successfully applied to synthetic seismograms calculated for a dipping structure and to field data from central california the results indicate that direct inversion of closely spaced refraction wideaperture reflection data can practically be achieved in laterally inhomogeneous structures

importance of diabatic processes on ageostrophic circulations observed during the fronts 87 experiment the impact of condensation and evaporation on real cross frontal circulations is studied using data from the fronts 87 field experiment the sawyer eliassen equation is solved numerically in its primitive equation form for one intensive observing period of fronts 87 three different schemes of parametrization of condensation heating are used comparison between diagnosed and observed ageostrophic circulations shows that latent heat release plays an important role in enhancing the ascending branch of the ageostrophic circulation ahead of the frontal zone in particular when a parametrization scheme for the low level moisture convergence is applied a cell of strong ascending motion is formed ahead of the frontal zone in good agreement with the observations further a simple parametrization of evaporative cooling below the frontal discontinuity leads to a reinforcement of downdraughts in the cold sector of the front as observed in regions where precipitation originating from the strong line convection evaporates in comparison with their adiabatic counterparts the current solutions show strong similarities with the observed circulation and indicate the predominance of diabatic effects in the frontal zone

airborne doppler radar and sounding analysis of an oceanic cold front abstract an analysis of a cold front over the eastern atlantic ocean based on airborne doppler wind syntheses and dropsonde data is presented the focus and unique aspect of this study is a segment of the front that was near the center of the cyclone the dual doppler wind synthesis of the frontal zone combined with an average dropsonde spacing of 30 km covers a total distance of 450 km in the cross frontal direction the finescale resolution and areal coverage of the dataset are believed to be unprecedented the cold front was characterized by a distinct wind shift and a strong horizontal temperature gradient the latter was most intense aloft and not at the surface in contrast to the classical paradigm of surface cold fronts the shear of the alongfront component of the wind was relatively uniform as a function of height within the frontal zone this observation is contrary to studies suggesting that frontal zones decrease in intensity above the surface the surface convergence within the frontal zon

thermodynamic recovery of the pressure and temperature fields over complex terrain using wind fields derived by multiple doppler radar synthesis abstracta new thermodynamic retrieval scheme is developed by which one can use the wind fields synthesized from multiple doppler radars to derive the three dimensional thermodynamic fields over com

non uniqueness with refraction inversion the mt bulga shear zone summary standard implementations of refraction tomography routinely use low resolution starting models tomograms obtained from these starting models can frequently fail to detect even major lateral variations in seismic velocities such as a 50 m wide low velocity shear zone at mt bulga by contrast the successful detection of the shear zone is unequivocal in tomograms generated with the generalized reciprocal method grm further improvements in resolution which facilitate the definition of additional zones with moderate reductions in seismic velocity are achieved with a novel application of the hilbert transform to the grm refractor velocity analysis algorithm however the improved resolution also requires the use of a lower average vertical seismic velocity which accommodates a velocity reversal in the weathering the lower seismic velocity is derived with the grm whereas most refraction tomography programs assume vertical velocity gradients as the default although all of the tomograms are consistent with the traveltime data the resolution of each tomogram is comparable only with that of the starting model refraction tomography rarely if ever extracts additional detail which is not apparent in the starting model it essentially smoothes unrealistic or inconsistent starting models therefore it can be concluded that the major effect of refraction tomography is largely cosmetic a comparison of the errors of tomographic inversion does not prove that a given result is either correct or even geologically reasonable this study proposes that the three tomograms generated with detailed grm time and velocity models for the optimum xy value and half the station spacing are a more useful measure of the uncertainties with refraction inversion non uniqueness is most conveniently resolved with refraction attributes derived from the digital field data before the implementation of more expensive drilling programs

simulations of the potential vorticity structure and budget of fronts 87 iop8 dropsonde observations in the cold fronts sampled during the joint british french fronts 87 experiment along the west coast of europe have shown that the dry and moist potential vorticity fields q d and q e respectively have significant anomalies on the mesoscale the processes associated with these anomalies during a 12 h period encompassing the observation time have been examined by simulating the q d and q e structures observed near the cold front of iop8 using the meteo france mesoscale peridot model and by developing and using an eulerian potential vorticity budget module high resolution dropsonde rawinsonde and doppler radar observations are used as verification of the simulated potential vorticity structures initial and boundary conditions are obtained from three different analysis systems the simulated potential vorticity structures are sensitive to the initial conditions because the analyses over the data sparse atlantic ocean vary significantly from one analysis system to another of the seven persistent mesoscale potential vorticity features identified in the observations five were simulated reasonably well using at least one of the initial analyses and examined with the potential vorticity budget the low level pre frontal positive q d anomaly along the length of the cold front is maintained through a balance between lagrangian source sink terms dominated by differential diabatic heating and vertical advection within the main frontal updraught this balance maintains the q d anomaly in a region of near zero q d tendency between areas of q d generation near the surface and q d destruction in the middle troposphere a mid tropospheric region of negative q e directly behind the surface cold front appears to be produced by a weak but persistent generation by the solenoid term in the region of strong humidity gradients along the back edge of the mid tropospheric cloud shield this position and the model evolution suggest that the solenoid created region of negative q e can lead to enhanced mid tropospheric updraughts through conditional symmetric instability or a combination of conditional symmetric instability and large scale forcing the magnitudes of regions of negative q d and q e on the anticyclonic side of the upper level jet decrease throughout the simulation due to horizontal momentum diffusion while a post frontal low level negative q e region is generated principally by temperature and moisture diffusion

the oceanic mesoscale convective system observed with airborne doppler radars on 9 february 1993 during toga coare structure evolution and budgets data collected on 9 february 1993 during the tropical ocean and global atmosphere programme coupled ocean atmosphere response experiment toga coare with the doppler radars on board the two national oceanic and atmospheric administration wp 3d and the national center for atmospheric research electra aircraft are analysed to study the structure and evolution of an equatorial oceanic mesoscale convective system mcs observations lasted more than five hours a period during which the cloud cluster characteristics changed from convective to stratiform this mesoscale system was approximately aligned along the tropospheric wind shear but it was nearly perpendicular to the low level shear series of three dimensional fields of reflectivity air velocity components retrieved pressure and temperature perturbations show similarities with previously observed convective systems over the tropical oceans in particular although the cloud top reached 18 km altitude relatively weak vertical motions and temperature perturbations resulted from a moderate convective instability in the low levels a cold front to rear flow intensified and deepened as the overall structure evolved from convective to stratiform the vertical profiles of mean horizontal divergence evolved from low level convergence in the cross line direction for the earliest analyses to mid level convergence from all directions during the later stratiform phase vertical momentum fluxes were important and led to an increase in the cross line wind shear and a decrease in the along line one analysis of radiosounding data from the nearest stations of the toga coare array shows that the period during which airborne doppler observations were conducted was characterized by relatively strong large scale ascent and apparent sources of heat moisture and momentum these diagnosed values and the mean radarderived ones agree fairly well this shows that the early convective and late stratiform phases of the mcs are equally important for the apparent sources of heat and momentum

kinematic and thermodynamic study of a shallow hailstorm sampled by the mcgill bistatic multiple doppler radar network abstract in this paper the authors examine the kinematic and thermodynamic characteristics of a shallow hailstorm sampled by the mcgill bistatic multiple doppler radar network on 26 may 1997 this storm consists of two main shallow convective cells depth less than 5 km aligned along a sw ne convective line propagating to the southeast the authors also analyze the interactions between the two cells during the life cycle of the convective line in particular it is shown that dynamic interactions play a major role in the intensification of the second cell this storm is found to evolve in a manner that shares some characteristics with both multicell and supercell storms a rotating updraft associated with a mesocyclone develops in the mature stage of the storm which is characteristic of a supercell however the lack of a vault structure on the precipitation field the relatively fast evolution of the cells and other characteristics detailed henceforth seem to indicate that this storm only shares a f

observations of mesoscale circulations within extratropical cyclones over the north atlantic ocean during erica abstract pseudo dual doppler analyses of two mesoscale circulations 20 40 km in horizontal dimensions that formed along a warm front within a rapidly deepening extratropical cyclone over the ocean are presented the circulations were analyzed using airborne doppler radar during erica experiment on rapidly intensifying cyclones over the atlantic iop intensive observing period 4 and are believed to be a type of frontal instability that has not been addressed in past theoretical studies of frontal waves and cyclones these features may be the shallow circulations that have been documented to play a role in cyclogenesis when they become coupled with an upper level baroclinic wave the present case is compared and contrasted with the only other well analyzed event during erica iop 5 a retrieval of the perturbation pressure and buoyancy fields using the kinematic wind fields is performed in order to facilitate the interpretation of the dynamic structure of these vortices in addition a set of equations

planetary and synoptic scale signatures associated with central american cold surges abstract motivated by outstanding issues from a previous case study of a midlatitude cold surge that affected mexico and central america the climatology of central american cold surges is examined in this paper an independently derived listing of 177 cold surge events is employed for which the following properties are tabulated onset date duration time between cold surge events latitude of maximum equatorward penetration min and 48 h maximum surface temperature change at merida mexico t these data show that 75 of the cold surges have durations of 2 6 days the same timescale as mobile disturbances in the westerlies also there does not appear to be any relationship between t and the duration of the event although cold surges that penetrate to low latitudes min 7 10 n have a weak tendency to persist longer than those that do not penetrate to low latitudes min 15 20 n in addition the reding data indicate that the cold surges tend to reach their most equatorward extent where

the san angelo texas supercell of 31 may 1995 visual observations and tornadogenesis abstract airborne radar analysis combined with cloud photogrammetry of a supercell that formed on 31 may 1995 near san angelo texas is presented the superposition of the doppler wind syntheses with the cloud pictures provides a unique view of the relationship between the low level mesocyclone and the developing lowered cloud base the mesocyclone accompanying the storm went through two periods of intensification the end of the first period of intensification did not lead to the formation of a tornado an occlusion downdraft formed but was primarily driven by negative buoyancy rather than a downward directed perturbation pressure gradient recent studies have suggested that cold downdrafts inhibit the formation of tornadoes the present study supports this hypothesis and provides the first quantitative view of the vertical structure of this downdraft the mesocyclone evolved through a second period of intensification that produced a weak tornado that was visually apparent from the aircraft no occlusio

convective scale downdrafts in the principal rainband of hurricane katrina 2005 abstract airborne doppler radar data collected during the hurricane rainband and intensity change experiment rainex document downdrafts in the principal rainband of hurricane katrina 2005 inner edge downdrafts ieds originating at 6 8 km altitude created a sharp reflectivity gradient along the inner boundary of the rainband low level downdrafts llds evidently driven by precipitation drag originated at 2 4 km within the heavy rain cells of each convective element the ied and lld were spatially separated by but closely associated with the updrafts within the rainband the ied was forced aloft by pressure perturbations formed in response to the adjacent buoyant updrafts once descending the air attained negative buoyancy via evaporative cooling from the rainband precipitation a convective scale tangential wind maximum tended to occur in the radial inflow at lower levels in association with the ied which enhanced the inward flux of angular momentum at lower levels convergence at the base of the

the kellerville tornado during vortex damage survey and doppler radar analyses abstract a detailed aerial and ground survey of a long track 50 km f5 tornado is presented the survey revealed that the tornado exhibited unusual nonlinear movements at two different locations one portion of the track was associated with a pronounced sinusoidal pattern while another location was characterized by a cusplike pattern for the first time high resolution dual doppler wind measurements can be used to evaluate mechanisms for such deviations from a linear tornado path the analyses of data collected with electra doppler radar eldora suggest that these departures are trochoidal marks produced as the tornado was revolving within the larger scale mesocyclone retrieved perturbation pressures indicate that the mesocyclone departed significantly from a cyclostrophically balanced state during these deviations the maximum vorticity associated with the mesocyclone at low levels was shown to be an unreliable indicator of the tornado s intensity vertical cross sections of wind vertical vorticity

structural and surface features of arc shaped radar echoes along an outer tropical cyclone rainband this study uses ground based dual doppler radar and surface observations to document the structural and surface features of the arc shaped radar echoes asres evident along an outer rainband of typhoon longwang as it approached northern taiwan on 1 october 2005 the particular aim of this study is to explore the possible distinction between the present case previously documented tropical cyclone rainbands tcrs and squall lines the dual doppler derived fields show that the leading precipitation of the studied asres exhibited a convective nature with a sharp horizontal gradient of reflectivity and a significant vertical extent theregionsbehindtheleadingconvectionwerecharacterizedbyband relativerear to frontflowatlowlevels and were associated with a broader area of stratiform precipitation the deep layer of front to rear flow extending from the surface to the upper troposphere was generally present ahead of the asres this flow appearstobeliftedupwardatandimmediatelyaheadoftheleadingedgeofthelow levelrear to frontflowto form rearward tilting updrafts these airflow patterns are similar to those of the convective region of squall lines but differ fundamentally from those of previously documented tcrs that were located closer to the inner core of cyclones the detailed analyses of surface fluctuations during the passage of one of the studied asresfurthershowanabruptpressurerise 2mb atemperaturedrop 48c andapronounceddeceleration of inflow air coincident with the leading heavy precipitation the evaluation presented suggests that the convectively generated cold pool may be important in influencing the structures and propagation of the studied asres

kinematic and moisture characteristics of a nonprecipitating cold front observed during ihop part i across front structures abstract a wide array of ground based and airborne instrumentation is used to examine the kinematic and moisture characteristics of a nonprecipitating cold front observed in west central kansas on 10 june 2002 during the international h2o project ihop this study the first of two parts is focused on describing structures in the across front dimension coarsely resolved observations from the operational network and dropsondes deployed over a 200 km distance centered on the front are combined with higher resolution observations from in situ sensors doppler radars a microwave radiometer and a differential absorption lidar that were collected across a 40 km swath that straddled a 100 km segment of the front the northeast southwest oriented cold front moved toward the southeast at 8 10 m s 1 during the morning hours but its motion slowed to less than 1 m s 1 in the afternoon in the early afternoon the cold front separated cool air with a northerly component flow of 2 4 m s 1 from a 10 km wide ban

late neogene quaternary evolution of the intermontane clusone basin southern alps italy integration of seismic and geological data in the clusone basin a large intermontane basin filled by thick late neogene quatern ary sediments in the middle val seriana southern alps two high resolution seismic profiles have been acquired in order to reconstruct the geometries of the sediments that fill the depression with a maximum thickness of more than 200 m as documented by available well data and to define their relationships with the bedrock consisting of late triassic carbonates in addition to standard seismic reflection processing a seismic refraction inversion technique has been applied the integration of geological both surface and well data and seismic data indicates a complex history of the drainage patterns of the clusone basin documenting a shift of the serio river from a palaeodrainage toward the southeast val borlezza to the present situation toward the south val seriana between the older and the present day drainages an important depositional stage occurred as documented by the thick sediments that fill the clusone basin controlling the capture of the serio river along the val seriana copyright 2004 john wiley sons ltd

retrieved pressure field and its influence on the propagation of a supercell thunderstorm an analysis of the observed propagation of the garden city supercell storm based on data collected by an airborne doppler radar is presented the environmental wind profile was characterized by a straight hodograph wind syntheses were used to retrieve the perturbation pressure fields in order to isolate the important dynamical processes controlling storm movement the pressure perturbations produced by the linear and nonlinear effects were comparable in magnitude the rightward bias in storm motion was primarily a result of the forcing produced by the vertical gradients of perturbation pressure this finding is consistent with the results based on numerical simulations the vertical gradients of the linear perturbation pressure were important in determining storm motion early in its life cycle subsequently the nonlinear effects dominated a decomposition of the nonlinear forcing into contributions from cyclostrophically balanced flow and nonlinear shear was also presented this partitioning revealed that both the forcing produced by the mesocyclone and the horizontal shear that was baroclinically produced by the gradient of buoyancy along the flanks of the updraft were important effects to consider

convective contribution to the genesis of hurricane ophelia 2005 abstract the convection occurring in the tropical depression that became hurricane ophelia 2005 was investigated just prior to tropical storm formation doppler radar showed a deep wide intense convective cell of a type that has been previously thought to occur in intensifying tropical depressions but has not heretofore been documented in detail the updraft of the cell was 10 km wide 17 km deep had updrafts of 10 20 m s 1 throughout its mid to upper levels and contained a cyclonic vorticity maximum the massive convective updraft was maintained by strong positive buoyancy which was maximum at about the 10 km level probably aided by latent heat of freezing evaporative cooling and precipitation drag occurred in the rain shower of the cell but were insufficient to produce a strong downdraft or gust front outflow to force the updraft the convective updraft was fed by a layer of strong inflow that was several kilometers deep wind induced turbulence just above the ocean surface enriched the equi

airborne doppler observations of a cold front in the vicinity of vancouver island abstract this study uses airborne doppler radar and flight level measurements from the coastal observations and simulations with topography experiment to examine the detailed mesoscale structure of an oceanic cold front upstream of vancouver island on 13 december 1993 these aircraft observations show that there were dramatic differences in frontal structure and movement between nearshore and offshore regions presumably due to the effects of blocking by the terrain the aircraft observations are considered in two parts since the behavior of the front evolved over the flight period during the early and middle portion of the flight the low level flow east of the front was out of the south southeast in the nearshore region rather than southerly as found farther offshore the nearshore segment of the front was oriented south north and appeared to be stationary the zone of orographic influence was found to extend to a region 20 km offshore and confined primarily to the lowest 1 5 km msl in distinct c

a new direction for shallow refraction seismology integrating amplitudes and traveltimes with the refraction convolution section the refraction convolution section rcs is a new method for imaging shallow seismic refraction data it is a simple and efficient approach to full trace processing which generates a time cross section similar to the familiar reflection cross section the rcs advances the interpretation of shallow seismic refraction data through the inclusion of time structure and amplitudes within a single presentation the rcs is generated by the convolution of forward and reverse shot records the convolution operation effectively adds the first arrival traveltimes of each pair of forward and reverse traces and produces a measure of the depth to the refracting interface in units of time which is equivalent to the time depth function of the generalized reciprocal method grm convolution also multiplies the amplitudes of first arrival signals to a good approximation this operation compensates for the large effects of geometrical spreading with the result that the convolved amplitude is essentially proportional to the square of the head coefficient the signal to noise s n ratios of the rcs show much less variation than those on the original shot records the head coefficient is approximately proportional to the ratio of the specific acoustic impedances in the upper layer and in the refractor the convolved amplitudes or the equivalent shot amplitude products can be useful in resolving ambiguities in the determination of wave speeds the rcs can also include a separation between each pair of forward and reverse traces in order to accommodate the offset distance in a manner similar to the xy spacing of the grm the use of finite xy values improves the resolution of lateral variations in both amplitudes and time depths the use of amplitudes with 3d data effectively improves the spatial resolution of wave speeds by almost an order of magnitude amplitudes provide a measure of refractor wave speeds at each detector whereas the analysis of traveltimes provides a measure over several detectors commonly a minimum of six the ratio of amplitudes obtained with different shot azimuths provides a detailed qualitative measure of azimuthal anisotropy and in turn of rock fabric the rcs facilitates the stacking of refraction data in a manner similar to the common midpoint methods of reflection seismology it can significantly improve s n ratios most of the data processing with the rcs as with the grm is carried out in the time domain rather than in the depth domain this is a significant advantage because the realities of undetected layers incomplete sampling of the detected layers and inappropriate sampling in the horizontal rather than the vertical direction result in traveltime data that are neither a complete an accurate nor a representative portrayal of the wave speed stratification the rcs facilitates the advancement of shallow refraction seismology through the application of current seismic reflection acquisition processing and interpretation technology

triple doppler radar analysis of the heavy rain event observed in the lago maggiore region during map iop 2b this paper presents analyses of data collected with three ground based doppler radars during the mesoscale alpine programme map intensive observation period iop 2b from 1900 utc 19 september until 1100 utc 20 september 1999 during this period the synoptic situation was characterized by the propagation of a deep upper tropospheric trough towards the alps as often observed when heavy precipitation occurs on the southern slopes of the alpine massif a frontal cloud system with embedded convective cells passed over northern italy in association with the trough moving rapidly eastwards ahead of the advancing cold front a strong south to south easterly low level flow impinged on the mountains near lago maggiore and produced copious amounts of rain 200mm at several locations an analysis of three dimensional radar derived wind and precipitation fields shows that the most intense precipitation occurred where and when the easterly component of the low to mid level flow was the strongest with however a preferential location on the southern slopes of the alps this phenomenon can be explained by enhanced confluence between the main southerly flow and an intensifying easterly flow and or more favourable orientation of the moist inflow perpendicular to the mountain slopes in addition the propagation of convective cells from the po valley toward the alps led to enhanced precipitation over the mountainous area taking advantage of the approximately two dimensional character of the event the different terms of the water budget are calculated for a series of 25 successive vertical cross sections to analyse the transformation of atmospheric moisture into surface rainfall copyright 2003 royal meteorological society

imaging refractors with the convolution section seismic refraction data are characterized by large moveouts between adjacent traces and large amplitude variations across the refraction spread the moveouts are the result of the predominantly horizontally traveling trajectories of refraction signals whereas the amplitude variations are the result of the rapid geometric spreading factor which is at least the reciprocal of the distance squared the large range of refraction amplitudes produces considerable variation in signal to noise s n ratios inversion methods which use traveltimes only employ data with a wide range of accuracies which are related to the variations in the s n ratios the time section generated by convolving forward and reverse seismic traces addresses both issues of large moveouts and large amplitude variations the addition of the phase spectra with convolution effectively adds the forward and reverse traveltimes the convolution section shows the structural features of the refractor without the moveouts related to the sourc

nonlinear refraction and reflection travel time tomography we develop a rapid nonlinear travel time tomography method that simultaneously inverts refraction and reflection travel times on a regular velocity grid for travel time and ray path calculations we apply a wave front method employing graph theory the first arrival refraction travel times are calculated on the basis of cell velocities and the later refraction and reflection travel times are computed using both cell velocities and given interfaces we solve a regularized nonlinear inverse problem a laplacian operator is applied to regularize the model parameters cell slownesses and reflector geometry so that the inverse problem is valid for a continuum the travel times are also regularized such that we invert travel time curves rather than travel time points a conjugate gradient method is applied to minimize the nonlinear objective function after obtaining a solution we perform nonlinear monte carlo inversions for uncertainty analysis and compute the posterior model covariance in numerical experiments we demonstrate that combining the first arrival refraction travel times with later reflection travel times can better reconstruct the velocity field as well as the reflector geometry this combination is particularly important for modeling crustal structures where large velocity variations occur in the upper crust we apply this approach to model the crustal structure of the california borderland using ocean bottom seismometer and land data collected during the los angeles region seismic experiment along two marine survey lines details of our image include a high velocity zone under the catalina ridge but a smooth gradient zone between catalina ridge and san clemente ridge the moho depth is about 22 km with lateral variations

the seismic refraction method a viable tool for mapping shallow targets into the 1990 s geometrical considerations show that first arrivals can be recorded from below hidden layers a certain minimum amount of data must be collected in order to resolve lateral versus vertical subsurface changes and thereby to determine the interpretation method field procedures therefore are independent of the interpretation method the optimum xy parameter in the generalized reciprocal method grm of processing refraction seismic data is significant as a quality control factor in refraction data interpretation by comparison of the optimum xy value that is recovered through velocity analysis and time depth function analysis with a value for optimum xy that is calculated from the migrated depth section the hidden layer condition can be recognized in addition to identifying the hidden layer condition on the basis of first arrivals alone the grm allows the hidden layers to be accommodated and depth precisions of less than 5 are possible

the 12 13 january 1988 narrow cold frontal rainband observed during mfdp fronts 87 part i kinematics and thermodynamics abstract the kinematic and thermodynamic structure of a narrow cold frontal rainband ncfr observed during the english french german mfdp fronts 87 experiment is presented radiosonde data indicated a very weak convective instability below 1500 m altitude and a low level jet of 30 m s 1 from ssw before the arrival of the front a cooling of about 1 c associated with an airflow of 13 m s 1 from wsw after its passage a composite of wind and reflectivity fields from 17 dual doppler radar analyses shows high reflectivity values large convergence and relatively intense vertical motions associated with this ncfr at the 1000 m altitude a mean vertical cross section perpendicular to the surface front derived from three successive high resolution dual doppler scans is used to examine the general characteristics of the air circulation a structure apparently similar to that of a density current is observed above the 2 km altitude however air flowing at a speed faster than the surface front appreciably mod

multi refractor imaging with stacked refraction convolution section multi refractor imaging is a technique for constructing a single two dimensional image of a number of refractors by stacking multiple convolved and cross correlated reversed shot records the method is most effective with high fold data that have been obtained with roll along acquisition programs because the stacking process significantly improves the signal to noise ratios the major advantage of the multi refractor imaging method is that all the data can be stacked to maximize the signal to noise ratios before the measurement of any traveltimes however the signal to noise ratios can be further increased if only those traces that have arrivals from the same refractor are used and if the correct reciprocal times or traces are employed a field case study shows that multi refractor imaging can produce a cross section similar to the familiar reflection cross section with substantially higher signal to noise ratios for the equivalent interfaces

equatorial response to northeasterly cold surges as inferred from satellite cloud imagery abstract day today convective activity in the equatorial regions 10 n 10 s and 90 180 e during december 1974 and january 1975 was estimated from noaa satellite visible imageries using simple visual techniques the daily convective estimates were composited with respect to the phase of individual cold surge episodes occurring during the two month period by decomposing the data into symmetric and anti symmetric components with respect to the equator it was shown that eastward and westward propagating cloud clusters had phase speeds 10 m s 1 and 5 m s 1 respectively and were generated near southwestern borneo following a cold surge onset the strong equatorially trapped character of the eastward moving components suggested the possibility of kelvin wave responses the eastward moving convective clusters interacted strongly with westward moving disturbances which may be identified with low order symmetric rossby waves originating from the western pacific the predominantly larger response amplitude of

refractor imaging using an automated wavefront reconstruction method the classical wavefront method for interpreting seismic refraction arrival times is implemented on a digital computer modern finite difference propagation algorithms are used to downward continue recorded refraction arrival times through a near surface hetero geneousvelocity structure two such subsurface trav eltime fields need to be reconstructed from the arrivals observed on a forward and reverse geophone spread the locus of a shallow refracting horizon is then defined by a simple imaging condition involving the reciprocal time the traveltime between source posi tions at either end of the spread refractor velocity is estimated in a subsequent step by calculating the directional derivative of the reconstructed subsurface wavefronts along the imaged interface the principle limitation of the technique arises from imprecise knowledge of the overburden velocity distribution this velocity information must be obtained from up hole times direct and reflected arrivals shallow re fractions and borehole data analysis of synthetic data examples indicates that the technique can accurately image both synclinal and anticlinal structures finally the method is tested apparently successfully on a shallow refraction data set acquired at an archeological site in western crete

extratropical forcing of convectively coupled kelvin waves during austral winter abstract observations are presented that link extratropical rossby wave disturbances excited in the southern hemisphere subtropical jet to the initiation of convectively coupled kelvin waves in the pacific intertropical convergence zone itcz during austral winter a baroclinic zonal wavenumber 6 eastward propagating rossby wave train in the subtropical jet turns northeastward in the vicinity of australia inducing upper tropospheric divergence and vertical motion fields that spread equatorward and induce cloudiness anomalies in the tropics lower tropospheric pressure surges excited from the extratropics also induce kelvin wave like geopotential height and temperature anomalies at the surface providing additional lower tropospheric convergence and vertical motion forcing the tropical outgoing longwave radiation olr and circulation fields propagate eastward in tandem with the extratropical rossby wave train at approximately 17 m s 1 kelvin wave activity in the central pacific itcz thus appears to

dynamics of a low level jet observed during the fronts 87 experiment a study of the internal dynamics of a low level jet its role on the frontal discontinuity evolution and its relevance to the organization of convection at mesoscale and small scale is presented the low level jet studied is associated with an active cold front that was observed during the french british co operative field experiment fronts 87 the originality of the present low level jet description lies in the fact that it is observed not only by means of soundings but also by means of a new tool for mesoscale meteorology observations a wind profiler stratospheric tropospheric uhf radar the high resolution of the wind profiler data in both time and height allows one to assess in precipitating as well as in clear sky areas a detailed image of the low level jet and the associated mesoscale and convective scale circulations the comparison between observations and predictions of various theories provides information on the physical mechanisms responsible for the initiation and maintenance of the observed mesoscale features the flow resulting from the presence of the low level jet produces inertial acceleration and baroclinic symmetric instability which lead to a narrow mesoscale line of sloping motions moreover the interaction of the cold surface outflow with the low level vertical shear below the jet maximum is found to be crucial in the intensification and maintenance of the observed narrow cold frontal rainband

axisymmetric potential vorticity evolution of hurricane patricia 2015 abstractoperational numerical models failed to predict the record setting rapid intensification and rapid overwater weakening of hurricane patricia 2015 in the eastern north pacific basin result

ground penetrating radar refraction imaging with stacked refraction convolution section method abstractwe have evaluated a technique initially developed for the seismic refraction imaging the stacked refraction convolution section srcs which we have properly adapted to process ground penetrating radar gpr refraction data through a mute operation the subsurface refracting signals recorded by the receiver from two reciprocal sources are selected following that a velocity analysis by means of the crosscorrelation of the refracted signals and the convolution of resulting traces is performed the refraction image in intercept times is successively derived from three main steps namely 1 the convolution of the subsurface refracted signals 2 the crosscorrelation of convolved trace with the reciprocal refracted signal and 3 the stacking of crosscorrelated traces over all source couples the technique is not only suitable for the processing of gpr data acquired with two or more reciprocal common source profiles but it is also convenient for its low acquisition cost in addition to the si

refraction traveltime and amplitude corrections for very near surface inhomogeneities the performance of refraction inversion methods that employ the principle of refraction migration whereby traveltimes are laterally migrated by the offset distance which is the horizontal separation between the point of refraction and the point of detection on the surface can be adversely affected by very near surface inhomogeneities even inhomogeneities at single receivers can limit the lateral resolution of detailed seismic velocities in the refractor the generalized reciprocal method statics smoothing method grm ssm is a smoothing rather than a deterministic method for correcting very near surface inhomogeneities of limited lateral extent it is based on the observation that there are only relatively minor differences in the time depths to the target refractor computed for a range of xy distances which is the separation between the reverse and forward traveltimes used to compute the time depth however any traveltime anomalies which originate in the near surface migrate laterally with increasing xy distance therefore an average of the time depths over a range of xy values preserves the architecture of the refractor but significantly minimizes the traveltime anomalies originating in the near surface the grm statics smoothing corrections are obtained by subtracting the average time depth values from those computed with a zero xy value in turn the corrections are subtracted from the traveltimes and the grm algorithms are then re applied to the corrected data although a single application is generally adequate for most sets of field data model studies have indicated that several applications of the grm ssm can be required with severe topographic features such as escarpments in addition very near surface inhomogeneities produce anomalous head wave amplitudes an analogous process using geometric means can largely correct amplitude anomalies furthermore the coincidence of traveltime and amplitude anomalies indicates that variations in the near surface geology rather than variations in the coupling of the receivers are a more likely source of the anomalies the application of the grm ssm together with the averaging of the refractor velocity analysis function over a range of xy values significantly minimizes the generation of artefacts and facilitates the computation of detailed seismic velocities in the refractor at each receiver these detailed seismic velocities together with the grm ssm corrected amplitude products can facilitate the computation of the ratio of the density in the bedrock to that in the weathered layer the accuracy of the computed density ratio improves where lateral variations in the seismic velocities in the weathered layer are known

airborne doppler observations of a landfalling cold front upstream of steep coastal orography abstract this study uses airborne doppler radar observations to describe the mesoscale structure and evolution of a cold frontal system as it made landfall on the mountainous coast of oregon and northern california on 1 december 1995 during the coastal observations and simulations with topography experiment this section of coastline constitutes a steep approximately two dimensional north south oriented orographic barrier the front exhibited a northeast southwest orientation and thus intersected the axis of high terrain at an acute angle the along barrier pressure gradient and low level winds increased with time along the coastal zone and reached a maximum as the front made landfall stably stratified prefrontal flow was strongly blocked by the orography resulting in a confluent transition from pervasive southwesterly winds offshore to a narrow zone of accelerated south southwesterly flow near the coast where wind speeds approached 30 m s 1 at a height of 750 m above mean sea level postfrontal flow

the garden city kansas storm during vortex 95 part i overview of the storm s life cycle and mesocyclogenesis abstract analysis of a supercell storm that produced an f1 tornado near garden city kansas is presented this event provided one of the first opportunities to synthesize data collected by a new airborne radar platform called eldora electra doppler radar developed by the national center for atmospheric research the early stages of development of the midlevel mesocyclone and the entire evolution of the low level mesocyclone are captured over a 70 min period the low level mesocyclone began as an incipient shallow circulation along a synoptic scale trough the circulation intensified and grew in depth via vortex stretching under the influence of a strong updraft as this rotation built up from the boundary layer it initially remained separate and distinct from the midlevel mesocyclone subsequently the two mesocyclones merge to produce a single column of rotation 4 5 km in diameter an occlusion downdraft develops within the mesocyclone circulation during the last passes by the storm signaling the beg

high winds generated by bow echoes part ii the relationship between the mesovortices and damaging straight line winds airborne radar analysis of a mesovortex that developed near the apex of a bow echo is presented the mesovortex was shown to play a critical role in determining the location of intense straight line wind damage at the surface the perturbation pressure gradient force in natural coordinates along the parcel path accelerated the horizontal winds however intense mesovortices modified the low level outflow and largely determined the locations where the strongest winds occurred regions of maximum winds are accounted for as a superposition of the vortex and the flow in which it is embedded the strongest winds occur on the side of the vortex where translation and rotation effects are in the same direction this model explains the observed tongue of high wind speeds that were confined to the periphery of the mesovortex the origin of the mesovortex is also examined similarities and differences of this bow echo event with recent modeling studies are presented