analysis of a nontornadic storm during vortex 95 abstract analysis of a supercell storm that did not produce a tornado near hays kansas is presented a well defined midlevel mesocyclone was apparent throughout most of the storm s life cycle numerous shallow circulations were observed along the rear flank gust front during the data collection period six of these circulations strengthened into intense low level mesocyclones each of these mesocyclones failed to produce a tornado the strongest low level mesocyclone referred to as vortex 4 underwent a life cycle that was consistent with other tornadic mesocyclones documented in the literature these results illustrate that the presence of a long lived mesocyclone at low levels is not sufficient for tornadogenesis to occur the kinematic structure of the low level mesocyclone that did not produce a tornado is compared with a tornadic mesocyclone from another storm in order to understand the characteristic differences between these circulations the results lead to the conclusion that the presence of

inversion migration tomography seismic inversion broadly enough defined is equivalent to doing migration and reflection tomography simultaneously diffraction tomography and inversion work best when sources and receivers surround the region of interest as in medical imaging applications theoretical studies have shown that high vertical wavenumber velocity perturbations are resolved by inverting surface seismic reflection data but the low vertical wavenumbers must be obtained using a separate step such as velocity analysis or reflection tomography i propose that a nonlinear iterative inversion that updates a varying background velocity obtains all wavenumbers that are resolvable separately by migration and tomography the background velocity must contain reflectors to provide data on both upward and downward transmission paths through the earth and hence the low wavenumbers by considering the downward transmission paths to be between surface sources and buried image geophones and the upward transmission paths to be between surfa

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

buoyancy and pressure perturbations derived from dual doppler radar observations of the planetary boundary layer applications for matching models with observations abstract the technique developed by gal chen in 1978 is used to derive vertical velocities buoyancy and pressure perturbations from dual doppler radar observations of the planetary boundary layer pbl several approaches to verification are pursued they include a scan to scan temporal continuity of the derived fields b an objective test to find out how well the derived pressure perturbations balance the dynamical equations c comparison of dual doppler derived horizontally averaged fluxes of heat versus in situ measurements and other data sets and d a noteworthy improvement in the quality of the retrieved pressure when tendencies are included previous studies indicate that in order for the method to be viable the radars have to resolve the pbl with at least ten vertical levels one such event occurred on 27 september 1978 during project phoenix conducted at the boulder atmospheric observatory bao 300 m tower an inversion above a shallow boundary layer of height around 800 m was eroded

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

an analysis of cold season supercell storms using the synthetic dual doppler technique abstractcold season tornadic outbreaks occur with regularity in the southeastern united states however detailed analyses of parent supercell storms in the cold season environment often low cape high shear are scarce this is often because storms do not always move close enough to radars for a comprehensive single doppler analysis and significant topography or trees in the southeast make it difficult for mobile radars to operate thus limiting dual doppler coverage however during the super tuesday tornado outbreak of 5 6 february 2008 two tornadic supercell storms passed within 30 40 km of the weather surveillance radar 1988 doppler wsr 88d sites in memphis and nashville tennessee knqa and kohx respectively the relative steadiness of these storms during passage along with the large motion vector from the southwest at 20 25 m s 1 allowed the application of a synthetic dual doppler sdd analysis as such a detailed analysis of these storms was completed including examinations of low lev

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

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

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

development and forcing of the rear inflow jet in a rapidly developing and decaying squall line during bamex abstract this study examines the development structure and forcing of the rear inflow jet rij through the life cycle of a small short lived squall line over north central kansas on 29 june 2003 the analyses were developed from airborne quad doppler tail radar data from the noaa and nrl p 3 aircraft obtained over a 2 h period encompassing the formation development and decay of the squall line during the bow echo and mesoscale convective vortex experiment bamex the strengthening of the system relative rear inflow to 17 m s 1 was concurrent with the formation of a bow echo an increased dynamic pressure gradient beneath the rearward tilted updraft and two counterrotating vortices at either end of the bow the later weakening of the rij to 8 m s 1 was concurrent with the weakening of the bow a decreased dynamic pressure gradient at midlevels behind the bow and the weakening and spreading of the vortices in a modeling study weisman quantified the forcing mechanisms responsible for the developm

observations of convection initiation failure from the 12 june 2002 ihop deployment abstract observations of the development of cumulus convection which reached depths of several kilometers but failed to develop into sustained precipitating cumulonimbus clouds an event the authors term convection initiation failure are presented from the 12 june 2002 international h2o project ihop case the investigation relies heavily on remote and in situ data obtained by mobile truck borne doppler radars mobile mesonets mobile soundings and stereo cloud photogrammetry data collection was focused in northwestern oklahoma near the intersection of an outflow boundary and dryline thunderstorms developed along the dryline during the late afternoon approximately 40 km east of the domain intensively observed by the ground based observing systems farther west within the region of dense observations analyzed herein cumulus congestus clouds formed along an outflow boundary multiple doppler wind syntheses revealed that the boundary layer vertical velocity field was dominated by thermals rather t

crustal structure of mexico and surrounding regions from seismic ambient noise tomography summary using continuous seismic data from newly available broadband stations in mexico and central america we have obtained group and phase velocity maps of fundamental mode rayleigh wave for the region these new maps have been calculated for periods between 8 and 60 s from cross correlations of seismic ambient noise between 100 broadband stations and stacked for 30 months from 2006 to 2008 the tomographic inversion of the obtained dispersion measurements has been carried out on a 1 1 grid resulting in maps with resolution better than 250 km in the well sampled regions of the model for short periods 8 16 s dispersion maps show good correlation with surface structural features low velocity anomalies correlate with sedimentary basins around the gulf of mexico and colorado embayment high velocity anomalies at short periods correlate with mountain ranges and regions of thin extended crust such as the gulf of california both the lowest and highest group velocity anomalies at these periods reach values of up to 15 per cent for periods between 25 and 40 s velocity anomalies are related to variations in crustal thickness and temperature the most prominent low velocity anomaly correlates with thick crust and high mantle temperatures associated with the trans mexican volcanic belt and the central american volcanic arc the most remarkable features for longer periods 40 60 s are the differences between high velocity anomalies beneath the mayan block the gulf of mexico and the cratonic part of the united states and low velocity anomalies beneath the chortis block and northern mexico the long wavelength features of our model agree well with previous global and continental scale studies however because of the increased station density of the data set used we are able to obtain reliable dispersion maps for shorter periods and to image smaller scale features

assimilation impact of high temporal resolution volume scans on quantitative precipitation forecasts in a severe storm evidence from nudging data assimilation experiments with a thermodynamic retrieval method

structure and evolution of the 22 february 1993 toga coare squall line aircraft observations of precipitation circulation and surface energy fluxes abstract this study documents the precipitation and kinematic structure of a mature eastward propagating oceanic squall line system observed by instrumented aircraft during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare doppler radar and low level in situ observations are used to show the evolution of the convection from an initially linear nnw sse oriented convective line to a highly bow shaped structure with an embedded low to midlevel counterclockwise rotating vortex on its northern flank in addition to previously documented features of squall lines such as highly upshear tilted convection on its leading edge a channel of strong front to rear flow that ascended with height over a rear inflow that descended toward the convective line and a pronounced low level cold pool apparently fed from convective and mesoscale downdrafts from the convective line rearward the observations of this system showed distinct multiple maxima in updraft strength with

shear instability wave along a snowband instability structure evolution and energetics derived from dual doppler radar data abstract this article presents a detailed analysis of a meso scale 17 km wavelength shear instability wave along a snowband using a series of dual doppler radar data the wave developed along a low level shear line that formed under the strain wind field caused by an adjacent mesoscale vortex the horizontal wind shear across the line was largest at lower levels and the eddy component horizontal winds and the retrieved pressure anomaly showed a bottom intensified structure as well the resultant vertical pressure gradient force was found to be responsible for the enhancement of alternating updrafts and downdrafts that were subsequently related to the formation of the reflectivity core gap structure of the wave eddy kinetic energy eke budgets of the evolving disturbance were investigated using time series of retrieved kinematic and thermodynamic data the wave grew at an approximately constant growth rate for about 40 min from its onset the eke in this quasi linear growth period was primarily gen

wind and temperature retrievals in the 17 may 1981 arcadia oklahoma supercell ensemble kalman filter experiments abstract the feasibility of using an ensemble kalman filter enkf to retrieve the wind and temperature fields in an isolated convective storm has been tested by applying the technique to observations of the 17 may 1981 arcadia oklahoma tornadic supercell radial velocity and reflectivity observations from a single radar were assimilated into a nonhydrostatic anelastic numerical model initialized with an idealized horizontally homogeneous base state the assimilation results were compared to observations from another doppler radar the results of dual doppler wind syntheses and in situ measurements from an instrumented tower observation errors make it more difficult to assess enkf performance than in previous storm scale enkf experiments that employed synthetic observations and a perfect model nevertheless the comparisons in this case indicate that the locations of the main updraft and mesocyclone in the arcadia storm were determined rather accurately especially at midlevels the magnitudes of v

two dimensional velocity models from wide angle seismic data by wavefield inversion summary modern wide angle surveys are often multi fold and multi channel with densely sampled source and receiver spacings such closely spaced data are potentially amenable to multi channel techniques involving wavefield propagation methods such as those commonly used in reflection data processing however the wide angle configuration requires techniques capable of handling very general wave types including those not commonly used in reflection seismology this is a situation analogous to that faced in cross borehole seismics where similar wave types are also recorded in a real cross borehole example we compare pre stack migration traveltime tomography and wavefield inversion we find that wavefield inversion produces images that are quantitative in velocity as are the tomograms but are of significantly higher resolution the wavefield inversion results have a resolution comparable to that of the qualitative pre stack migration images we seek to extend this novel development to the larger scale problem of crustal imaging an essential element of the approach we adopt is its formulation entirely within the temporal frequency domain this has three principal advantages 1 we can choose to decimate the data by selecting only a limited number of frequency components to invert thus making inversion of data from large numbers of source positions feasible 2 we can mitigate the notorious non linearity of the seismic inverse problem by progressing from low frequency components in the data to high frequency components and 3 we can include in the model any arbitrary frequency dependence of inelastic attenuation factors q and indeed solve for the spatial distribution of q an initial synthetic test with an anomaly located within the middle crust yields a velocity image with the correct structural features of the anomaly and the correct magnitude of velocity anomaly this is related to the fact that the reconstruction is obtained from forward scattered waves under these conditions the method thus behaves much like tomography a second test with a deeper more extensive anomaly yields an image with the correct velocity polarity and the correct location but with a deficiency in low and high wavenumbers in this case this is because the reconstruction is obtained from backscattered waves under these conditions the method behaves not like tomography but like migration a more extensive test based on a large wide angle survey in south eastern california and western arizona demonstrates a real potential for high resolution imaging of crustal structures although our results are limited by the acoustic approximation and by the relatively low frequencies that we can model today the images are sufficiently encouraging to warrant future research the problem of local minima in the objective function is the most significant practical problem with our method but we propose that appropriate layer stripping methods can handle this problem

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

multiple doppler radar observations of the evolution of vorticity extrema in a convective boundary layer abstract overdetermined dual doppler wind syntheses are used to document the evolution structure and dynamics of vertical vorticity extrema observed in a convective boundary layer during the 12 june 2002 international h2o project ihop mission discrete vertical vorticity extrema having horizontal scales of 1 2 km can be observed continuously for periods exceeding an hour the evolution of the vorticity field is characterized by complex interactions among vorticity extrema and between the vertical vorticity and vertical velocity fields the most prominent vorticity maxima have amplitudes of approximately 0 01 s 1 and are associated with retrieved pressure deficits of order 0 1 mb the vorticity extrema weaken with height and tilt in the presence of vertical wind shear advection and propagation both contribute substantially to the motion of the vorticity extrema amplifications of vertical vorticity are closely linked to the intensification of updrafts both stretching and tilting can contribute signi

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