numerical simulations of radiative cooling beneath the anvils of supercell thunderstorms abstract numerical simulations of supercell thunderstorms that include parameterized radiative transfer and surface fluxes are performed using the advanced regional prediction system arps to investigate the effects of anvil shadows on the near storm environment if the simulated storm is nearly stationary the maximum low level air temperature deficits within the shadows are about 2 k which is roughly half the cooling found in some previous observations it is shown that the extinction of downwelling shortwave radiation by the anvil cloud creates a differential in the flux of downwelling shortwave radiation between the sun and the shade that is at least an order of magnitude greater than the differential of any other term in either the surface radiation or the surface energy budgets the loss of strong solar heating of the model surface within the shaded regions leads to a reduction of surface temperatures and stabilization of the model surface layer beneath the anvil the reduction in vertical mixing

dryline on 19 june 2002 during ihop part i airborne doppler and leandre ii analyses of the thin line structure and convection initiation the evolution and finescale structure of a dryline that initiated a line of thunderstorms is presented both the along line variability and mean vertical structure were examined using data collected by an airborne doppler radar and a water vapor differential absorption lidar dial the initiation of convection appeared to result from the diurnally induced easterly flow in the maritime air east of the dryline that typically develops late in the day this flow increased the low level convergence and allowed rising parcels of air to reach the level of free convection the along line variability was largely attributed to numerous misocyclones distorting the thin line of radar reflectivity by advecting dry moist air across the dryline south north of the misocyclone the misocyclones also influenced the location of the updrafts with most of the peak values positioned north of the circulations as a result these updrafts were fortuitously positioned in regions of high mixing ratio where the first convective cells initiated

polarimetric and dual doppler radar observations of the lipscomb county texas supercell thunderstorm on 23 may 2002 abstract polarimetric and dual doppler observations of a supercell observed by the national center for atmospheric research ncar s band polarimetric spol radar two doppler on wheels dow radars and the greek xpol radar on 23 may 2002 during the international h2o project ihop are presented the polarimetric radar observations began as the storm organized into a supercell and continued for over an hour while the storm was in its mature phase the hydrometeor distribution within the mature storm was retrieved using a fuzzy logic hydrometeor classification algorithm the dual doppler radar observations began around the time that the polarimetric radar observations concluded and they covered the end of the mature phase and much of the dissipation phase of the storm the dual doppler wind syntheses are used to evaluate the importance of the forward flank outflow in augmenting the horizontal vorticity field near the storm above 400 m in this case having a relatively weak low level mesocyclone the pa

observation of the seismic nucleation phase in the ridgecrest california earthquake sequence near source observations of five m 3 8 5 2 earthquakes near ridgecrest california are consistent with the presence of a seismic nucleation phase these earthquakes start abruptly but then slow or stop before rapidly growing again toward their maximum rate of moment release deconvolution of instrument and path effects by empirical green s functions demonstrates that the initial complexity at the start of the earthquake is a source effect the rapid growth of the p wave arrival at the start of the seismic nucleation phase supports the conclusion of mori and kanamori 1996 that these earthquakes begin without a magnitude scaled slow initial phase of the type observed by iio 1992 1995

structure and evolution of the 22 february 1993 toga coare squall line organization mechanisms inferred from numerical simulation abstract mechanisms responsible for meso and convective scale organization within a large tropical squall line that occurred on 22 february 1993 during the tropical ocean global atmosphere coupled ocean atmosphere response experiment are investigated using a three dimensional numerical cloud model the squall line occurred in an environment typical of fast moving tropical squall lines characterized by moderate convective available potential energy and moderate to strong vertical shear beneath a low level jet with weak reverse vertical shear above a well simulated aspect of the observed squall line is the evolution of a portion of its leading convective zone from a quasi linear to a three dimensional bow shaped structure over a 2 h period this transition is accompanied by the development of both a prominent mesoscale vortex along the northern edge of the 40 60 km long bow shaped feature and elongated bands of weaker reflectivity situated rearward and oriented transverse to the leading edge within enha

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

vorticity evolution leading to tornadogenesis and tornadogenesis failure in simulated supercells abstracta three dimensional idealized cloud model was used to study the storm scale differences between simulated supercells that produce tornado like vortices and those that do not each simulation was initialized with a different rapid update cycle version 2 ruc 2 sounding that was associated with tornadic and nontornadic supercells in nature the focus is an analysis of vorticity along backward integrated trajectories leading up to tornadogenesis 19 simulations and tornadogenesis failure 14 simulations in so doing the differences between the nontornadic and tornadic cases can be explored in relation to their associated environmental sounding backward integrated trajectories seeded in the near surface circulation indicate that the largest differences in vertical vorticity production between the tornadic and nontornadic simulations occur in parcels that descend to the surface from aloft i e descending thus the results from this study support the hypothesis that descending air in the rear

the pretornadic phase of the goshen county wyoming supercell of 5 june 2009 intercepted by vortex2 part ii intensification of low level rotation abstractthe dynamical processes responsible for the intensification of low level rotation prior to tornadogenesis are investigated in the goshen county wyoming supercell of 5 june 2009 intercepted by the second verification of the origins of rotation in tornadoes experiment vortex2 the circulation of material circuits that converge upon the low level mesocyclone is principally acquired along the southern periphery of the forward flank precipitation region which is a corridor characterized by a horizontal buoyancy gradient thus much of the circulation appears to have been baroclinically generated the descending reflectivity core drc documented in part i of this paper has an important modulating influence on the circulation of the material circuits a circuit that converges upon the low level mesocyclone center prior to the drc s arrival at low levels approximately the arrival of the 55 dbz reflectivity isosurface in this case loses some of its previously acquired circulation during the final f

evolution of low level angular momentum in the 2 june 1995 dimmitt texas tornado cyclone abstract the life cycle of the 2 june 1995 dimmitt texas tornado cyclone observed during the verification of the origins of rotation in tornadoes experiment vortex is described the tornado cyclone here is defined as a significantly axisymmetric flow larger than the visible tornado and characterized by increasing angular momentum with increasing radius its life cycle included three phases with somewhat differing evolution of angular momentum herein called intensifying transition and weakening during the intensifying stage the funnel and debris cloud gradually increased in size the azimuthally averaged secondary circulation of the larger scale tornado cyclone as determined using high resolution single doppler data obtained by a mobile radar was primarily inward and upward consistent with the presence of a wall cloud outside the tornado the azimuthally averaged angular momentum increased monotonically away from the tornado so inward advection allowed the angular momentum to increase slowly

the lagrange tornado during vortex2 part i photogrammetric analysis of the tornado combined with single doppler radar data abstractthis study presents a single doppler radar analysis combined with cloud photography of the lagrange wyoming tornado on 5 june 2009 in an attempt to relate the radar observed hook echo weak echo hole weh and rotational couplet to the visual characteristics of the tornado the tornado was rated ef2 the circulation at low levels went through two intensification periods based on azimuthal shear measurements the first intensification was followed by the appearance of a brief funnel cloud the second intensification was coincident with the appearance of a second funnel cloud that remained in contact with the ground until the tornado dissipated a deep weh rapidly formed within the hook echo after damaging wind was identified at the ground and before the appearance of a funnel cloud the echo pattern through the hook echo on 5 june undergoes a dramatic evolution initially the minimum radar reflectivities are near the surface 15 dbz and the weh does not suggest a tapered structure near the gro

supercell low level mesocyclones in simulations with a sheared convective boundary layer abstractsimulations of supercell thunderstorms in a sheared convective boundary layer cbl characterized by quasi two dimensional rolls are compared with simulations having horizontally homogeneous environments the effects of boundary layer convection on the general characteristics and the low level mesocyclones of the simulated supercells are investigated for rolls oriented either perpendicular or parallel to storm motion as well as with and without the effects of cloud shading bulk measures of storm strength are not greatly affected by the presence of rolls in the near storm environment though boundary layer convection diminishes with time under the anvil shadow of the supercells when cloud shading is allowed simulations without cloud shading suggest that rolls affect the morphology and evolution of supercell low level mesocyclones initially cbl vertical vorticity perturbations are enhanced along the supercell outflow boundary resulting in nonnegligible near ground vertical vorticity regardles

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

a study of the tornadic region within a supercell thunderstorm abstract the transition of a supercell thunderstorm into its tornadic phase is investigated through high resolution numerical cloud model simulations initiated within the interior portion of a previously simulated mature supercell storm with the enhanced grid resolution the low level cyclonic vorticity increases dramatically and the gust front rapidly occludes as small scale downdrafts develop in the vicinity of the low level center of circulation as the occlusion progresses a ring of high vorticity air surrounds the circulation center and could be conducive to multiple vortex tornado formation numerous features of the simulated transition bear resemblance to those observed in tornadic storms in the model simulation the large low level vorticity is generated through the tilting and intense stretching of air from the inflow side of the storm this vertical vorticity is derived from the horizontal vorticity of the environmental shear and also from horizontal vorticity generated solenoidally as low l

impacts of lapse rates on low level rotation in idealized storms abstractadiabatic lapse rates appear to be a common feature in the lower troposphere on tornado days this article reviews physical reasons why lapse rates may influence surface vortex intensification and reports on numerical simulations designed to study the key processes in the idealized numerical model an initial mesocyclone like vortex and nonvarying convection like heat source are used in different environmental stability profiles the scales of interest in these simulations typify those of a parent supercell and the developing circulations constitute direct responses to the imposed heating downward parcel displacements are needed for surface vortex development in environments with no preexisting surface vorticity in the simulations under neutral stratification there is strong heating induced subsidence anchored near the storm edge whereas under stable stratification there are instead gravity waves that propagate away to the far field in addition under weak or neutral low level stratification

airborne doppler radar analysis of supercells during cops 91 abstract on 26 may 1991 noaa p 3 airborne doppler radar data were collected near two tornadic supercells in the southern plains during the cooperative oklahoma profiler studies cops 91 field program the 3 cm radar mounted in the tail of the aircraft was operated using the fore aft scanning technique fast both storms were sampled just minutes after each had produced a tornado the cops 91 storms are the first tornadic supercells to be sampled extensively by airborne doppler radar using the fast methodology pseudo dual doppler analyses of a dissipating storm in southwest kansas show no remaining low level circulation even though the storm had just produced a tornado the analyses of a storm in northwest oklahoma reveal better defined features in the wind field near the surface in contrast to what has been previously observed in post tornadic supercells the cyclonic vorticity in both storms was greater aloft than at low levels the 26 may 1991 storms provide further evidence that supercells often

an assessment of low level baroclinity and vorticity within a simulated supercell abstractidealized supercell modeling has provided a wealth of information regarding the evolution and dynamics within supercell thunderstorms however discrepancies in conceptual models exist including uncertainty regarding the existence placement and forcing of low level boundaries in these storms as well as their importance in low level vorticity development this study offers analysis of the origins of low level boundaries and vertical vorticity within the low level mesocyclone of a simulated supercell low level boundary location shares similarities with previous modeling studies however the development and evolution of these boundaries differ from previous conceptual models the rear flank gust front develops first whereas the formation of a boundary extending north of the mesocyclone undergoes numerous iterations caused by competing outflow and inflow before a steady state boundary is produced a third boundary extending northeast of the mesocyclone is produced through evaporative cooling of

the bowdle south dakota cyclic tornadic supercell of 22 may 2010 surface analysis of rear flank downdraft evolution and multiple internal surges abstractmobile mesonet sampling in the hook echo rear flank downdraft rfd region of a tornadic supercell near bowdle south dakota provided the opportunity to examine rfd thermodynamic and kinematic attributes and evolution focused analysis of the fifth low level mesocyclone cycle that produced two significant tornadoes including a violent tornado revealed four rfd internal surge rfdis events rfdiss appeared to influence tornado development intensity and demise by altering the thermodynamic and kinematic character of the rfd region bounding the pretornadic and tornadic circulations significant tornadoes developed and matured when the rfd modulated by internal surges was kinematically strong only weakly negatively buoyant and very potentially buoyant in contrast the demise of the bowdle tornado was concurrent with a much cooler rfdis that replaced more buoyant and far more potentially buoyant rfd air near the tornado this surge also likely contributed to a displacement of the tornado from

linear and nonlinear propagation of supercell storms abstract a nonlinear formula for updraft motion in supercell storms is derived from petterssen s formula for the motion of systems and the vertical equation of motion and tested on form preserving disturbances at each level continuous propagation of an updraft maximum is determined largely by the horizontal gradient of the nonhydrostatic vertical pressure gradient force nhvpgf at the updraft center the nhvpgf is deduced from the formal solution of the poisson equation for nonhydrostatic pressure in anelastic flow subject to homogeneous neumann boundary conditions at the ground and top boundary recourse also is made to published fields of partitioned vertical pressure gradient force updraft motion is partitioned into parts forced by horizontal gradients of hydrostatic pressure linear interaction between the environmental shear and updraft and nonlinear dynamical effects the dynamics of supercell storms for nearly straight and highly curved hodographs are found to be different nonlinear rotation

dynamic multi scale modes of severe storm structure detected in mobile doppler radar data by entropy field decomposition abstractthe detection of complex spatially and temporally varying coherent structures in data from highly nonlinear and non gaussian systems is a challenging problem in a wide range of scientific d

the 8 june 1995 mclean texas storm part ii cyclic tornado formation maintenance and dissipation abstract on 8 june 1995 scientists participating in the verification of the origins of rotation in tornadoes experiment vortex collected a unique dataset with the electra doppler radar eldora the eldora observations document the sequential life cycles of storm scale circulations associated with three large tornadoes in a supercell thunderstorm near mclean texas a qualitative description of the evolution of the storm was provided in part i of this paper during the first stage of development of each storm scale circulation interaction of the updraft with the environmental low level horizontal vorticity produced a vorticity column that increased in intensity with height as the vortex matured vorticity increased greatly at low levels i e below 2 km agl and exceeded that aloft each tornadic vortex was located near the rear side of the updraft where the surrounding low level horizontal vorticity was modified locally most likely by weak baroclinity within the storm tilting of low level horizo

numerical simulation of tornadogenesis in a high precipitation supercell part i storm evolution and transition into a bow echo abstract a nested grid primitive equation model rams version 3b was used to simulate a high precipitation hp supercell which produced two weak tornadoes six telescoping nested grids allowed atmospheric flows ranging from the synoptic scale down to the tornadic scale to be represented in the simulation all convection in the simulation was initiated with resolved vertical motion and subsequent condensation latent heating from the model microphysics no warm bubbles or cumulus parameterizations were used part i of this study focuses on the simulated storm evolution and its transition into a bow echo the simulation initially produced a classic supercell that developed at the intersection between a stationary front and an outflow boundary as the simulation progressed additional storms developed and interacted with the main storm to produce a single supercell this storm had many characteristics of an hp supercell and eventually evolved into a bow echo with a rotating comma head structure an analysi

storm relative helicity revealed from polarimetric radar measurements the dual polarization radar variables are especially sensitive to the microphysical processes of melting and size sorting of precipitation particles in deep convective storms polarimetric measurements of such processes can provide information about the airflow in and around the storm that may be used to elucidate storm behavior and evolution size sorting mechanisms include differential sedimentation vertical transport strong rotation and wind shear in particular winds that veer with increasing height typical of supercell environments cause size sorting that is manifested as an enhancement of differential reflectivity zdr along the right or inflow edge of the forward flank downdraft precipitation echo which has been called the zdr arc signature in some cases this shear profile can be augmented by the storm inflow it is argued that the magnitude of this enhancement is related to the low level storm relative environmental helicity srh in the storm inflow to test this hypothesis a simple numerical model is constructed that calculates trajectories for raindrops based on their individual sizes which allows size sorting to occur the modeling results indicate a strong positive correlation between the maximum zdr in the arc signature and the low level srh regardless of the initial drop size distribution aloft additional observational evidence in support of the conceptual model is presented potential changes in the zdr arc signature as the supercell evolves and the low level mesocyclone occludes are described

long term morphological changes in simulated supercells following mergers with nascent supercells in directionally varying shear abstractmergers involving supercells remain a challenge for severe thunderstorm forecasting in this study mergers between supercells and ordinary cells e g cells forming in a similar environment but too young to be fully developed supercells are investigated a series of numerical experiments are performed using an idealized homogenous environment supportive of cyclonically rotating right moving supercells warm bubbles are introduced at different times resulting in two storms of different maturity their placement is used to control the location of the merger and the relative maturity of the second storm simplified conceptual models for the long term outcomes of mergers are developed in the simplest mode of merger outflow from the new cell cuts off inflow to the original if the new cell s cold pool is not sufficiently strong to cut off the inflow to the original cell the minimum separation of the updraft maxima during the merger becomes a key controlling factor in the outcome if it is less

a comparison of near surface buoyancy and baroclinity across three vortex2 supercell intercepts abstractobservations obtained during the second verification of the origin of rotation in tornadoes experiment vortex2 are analyzed for three supercell intercepts these intercepts used a fleet of deployable sticknet probes complemented by mobile radars and a mobile mesonet to map state quantities over the expanse of target storms two of the deployments occurred for different stages of a supercell storm near and east of dumas texas on 18 may 2010 a comparison of the thermodynamic and kinematic characteristics of the storm provides a possible explanation for why one phase was weakly tornadic and the other nontornadic the weakly tornadic phase features a stronger horizontal virtual temperature gradient antiparallel to the forward flank reflectivity gradient and perpendicular to the near surface flow direction suggesting that air parcels could acquire more significant baroclinic vorticity as they approach the low level mesocyclone the strongly tornadic 10 may 2010 case near seminole oklahoma fea

the garden city kansas storm during vortex 95 part ii the wall cloud and tornado abstract on 16 may 1995 a supercell storm produced an f1 tornado near garden city kansas during vortex verification of the origins of rotation in tornadoes experiment this event provided the first opportunity to synthesize data collected by a new airborne radar platform called eldora electra doppler radar developed by the national center for atmospheric research the evolution of the low and midlevel mesocyclone was presented in a companion paper in this paper the sequence of events that triggered tornadogenesis within the mesocyclone circulation is shown the occlusion downdraft documented in part i appears to promote vortex breakdown resulting in the generation of multiple vorticity centers it is one of these centers that intensifies into the garden city tornado the structural relationship between the observed wall cloud and the radar reflectivity associated with the developing hook echo and the kinematic wind field is also presented although the wall cloud appears to be uniform there

a numerical study of the 6 may 2012 tsukuba city supercell tornado part i vorticity sources of low level and midlevel mesocyclones abstracton 6 may 2012 an f3 supercell tornado one of the most destructive tornadoes ever recorded in japan hit tsukuba city in eastern japan and caused severe damage to clarify the generation mechanisms of the tornadic storm and tornado high resolution numerical simulations were conducted under realistic environmental conditions using triply nested grids the innermost simulation with a 50 m mesh successfully reproduced the tsukuba city tornadic supercell storm in this study the first of a two part study the vorticity sources responsible for mesocyclogenesis prior to tornadogenesis were investigated by analyzing vortex lines and the evolution of circulation of the mesocyclones vortex lines that passed through the midlevel mesocyclone 4 km height originated from the environmental streamwise vorticity whereas the low level mesocyclone and low level mesoanticyclone were connected by several arching vortex lines over the rear flank downdraft associated with the hook shaped distribution of hydromet

tornado producing mini supercells associated with typhoon 9019 on the night of 19 september 1990 nine mini supercell storms were observed over the kanto plain of japan in the northeast quadrant of typhoon 9019 three storms out of nine spawned a tornado the characteristics of the storms and tornadoes were studied by means of a single doppler radar conventional radars surface meteorological observations and damage surveys the mini supercell storms exhibited characteristics similar to typical supercell storms over the great plains of the united states such as hook echo bounded weak echo region slower movement relative to the mean wind long lives and rightward deviation of the storm motion relative to the mean wind shear was observed they also displayed several differences from typical supercell storms with respect to the following points 1 horizontal scale of the mesocyclone was smaller and 2 vertical vorticity was confined to lower levels less than 5 km above ground level these similarities and differences correspond with those observed for miniature supercells in hurricane danny s environment the storm environment for these mini supercells was characterized by modest convective available potential energy about 1600 j kg21 and strong low level wind shear with veering the storm updrafts likely tilted the ambient horizontal vorticity associated with the strong low level wind shear to generate mesocyclonic vertical vorticity two of the tornadoes were spawned by mini supercell storms moving along a preexisting surface boundary that was accompanied by significant convergence vertical vorticity and horizontal gradients of temperature an estimation of vertical vorticity near the ground in the boundary suggests a possibility that preexisting vertical vorticity contributed to supercell evolution resulting in tornadogenesis

low level mesocyclonic concentration by nonaxisymmetric transport part i supercell and mesocyclone evolution an idealized simulation of a supercell using the regional atmospheric modeling system rams was able to produce a low level mesocyclone near the intersection of the forward and rear flank downdrafts the creation of the low level mesocyclone is similar to previous studies after 3600 s the low level mesocyclone underwent a period of rapid intensification during which its form changed from an elongated patch to a compact center this transition was also accompanied by a sudden decrease in pressure to 12 mb below that of the neighboring flow and was found to occur even in the absence of nested grids it is shown that the stage of strong intensification does not begin aloft as in the dynamic pipe effect and then descend to the surface rather the vortex is initiated near the surface and then builds upward the process is completed in 5 min and the final vortex can be clearly distinguished from the larger scale mesocyclone at the cloud base the reduction of pressure can be explained as a consequence of the evacuation of mass in the horizontal convergence equation this is in contrast to axisymmetric models of vortex intensification which generally rely on the evacuation of mass in the vertical divergence equation in the latter cases a positive horizontal convergence tendency is what initiates the concentrated vortex however nondivergent models prove that vorticity concentration can occur in the absence of any horizontal convergence here the concentration is associated with a negative horizontal convergence tendency

processes preventing the development of a significant tornado in a colorado supercell on 26 may 2010 abstracta supercell produced a nearly tornadic vortex during an intercept by the second verification of the origins of rotation in tornadoes experiment on 26 may 2010 using observations from two m

miniature supercells in an offshore outer rainband of hurricane ivan 2004 abstract airborne doppler radar observations are used to document the structure of three miniature supercells embedded in an outer rainband of hurricane ivan on 15 september 2004 the cells were located more than 100 km offshore beyond the doppler range of coastal radars the combination of large cape large vertical wind shear and moderate cell relative helicity with an apparent midlevel dry air intrusion provided an offshore environment supporting rotating storms each shallow cell contained a 5 7 km diameter mesocyclonic updraft with midlevel updraft and vorticity maxima that exceeded 6 m s 1 and 0 008 s 1 respectively such offshore structures are consistent with miniature supercells observed onshore in association with tropical cyclone tornado outbreaks the strong updrafts resulted from a combination of kinematic convergence thermal instability and shear induced vertical perturbation pressure gradients mesocyclone production largely resulted from the tilting and subsequent stretching of low l

doppler radar observations of anticyclonic tornadoes in cyclonically rotating right moving supercells abstractsupercells dominated by mesocyclones which tend to propagate to the right of the tropospheric pressure weighted mean wind on rare occasions produce anticyclonic tornadoes at the trailing end of the rear flank gust front more frequently mesoanticyclones are found at this location most of which do not spawn any tornadoes in this paper four cases are discussed in which the formation of anticyclonic tornadoes was documented in the plains by mobile or fixed site doppler radars these brief case studies include the analysis of doppler radar data for tornadoes at the following dates and locations 1 24 april 2006 near el reno oklahoma 2 23 may 2008 near ellis kansas 3 18 march 2012 near willow oklahoma and 4 31 may 2013 near el reno oklahoma three of these tornadoes were also documented photographically in all of these cases a strong mesocyclone i e vortex signature characterized by azimuthal shear in excess of 5 10 3 s 1 or a 20 m s 1 change in doppler velocity over 5 km

the impact of spatial variations of low level stability on the life cycle of a simulated supercell storm abstract this study reports on the dynamical evolution of simulated long lived right moving supercell storms in a high cape strongly sheared mesoscale environment which initiate in a weakly capped region and subsequently move into a cold boundary layer bl and inversion region before dissipating the storm simulations realistically approximate the main morphological features and evolution of the 22 may 1981 binger oklahoma supercell storm by employing time varying inflow lateral boundary conditions for the storm relative moving grid which in turn are prescribed from a parent fixed steady state mesoscale analysis to approximate the observed inversion region to the east of the dryline on that day a series of full life cycle storm simulations have been performed in which the magnitude of boundary layer coldness and the convective inhibition are varied to examine the ability of the storm to regenerate and sustain its main updraft as it moves into environments with increasing convective stability the

the structure and evolution of a numerically simulated high precipitation supercell thunderstorm the structure and evolution of a high precipitation hp supercell thunderstorm is investigated using a threedimensional nonhydrostatic cloud scale numerical model tass the model is initialized with a sounding taken from a mesoscale modeling study of the environment that produced the 28 november 1988 raleigh tornadic thunderstorm tass produces a long lived convective system that compares favorably with the observed raleigh tornadic thunderstorm the simulated storm evolves from a multicell type storm to a multiple updraft supercell storm the storm complex resembles a hybrid multicell supercell thunderstorm and is consistent with the conceptual model of cool season strong dynamic hp supercells that are characterized by shallow mesocyclones the origin of rotation in this type of storm is often in the lowest levels interactions between various cells in the simulated convective system are responsible for the transition to a supercellular structure an intense low level updraft core forms on the southwest flank of the simulated storm and moves over a region that is rich in vertical vorticity the stretching of this preexisting vertical vorticity in the storm s lowest levels is the most important vertical vorticity production mechanism during the initial stages of the main updraft s development interactions with an extensive cold pool created by the storm complex are also important in producing vertical vorticity as the main updraft grows overall the development of vorticity associated with the main updraft appears similar to nonsupercellular tornadic storms however classic supercell signatures are seen early in the simulation associated with other updrafts e g formation of vortex couplet due to tilting of ambient horizontal vorticity storm splitting etc and are deemed important in the storm s supercell stage rotation is sustained in the lowest levels of the storm despite large amounts of precipitation located near and within the main mesocyclone pulsating downdrafts periodically invigorate the storm and the gust front never occludes thus allowing the main updraft to persist for a prolonged period of time the storm s intensity is also maintained by frequent updraft mergers

hook echoes and rear flank downdrafts a review abstract nearly 50 years of observations of hook echoes and their associated rear flank downdrafts rfds are reviewed relevant theoretical and numerical simulation results also are discussed for over 20 years the hook echo and rfd have been hypothesized to be critical in the tornadogenesis process yet direct observations within hook echoes and rfds have been relatively scarce furthermore the role of the hook echo and rfd in tornadogenesis remains poorly understood despite many strong similarities between simulated and observed storms some possibly important observations within hook echoes and rfds have not been reproduced in three dimensional numerical models

dynamical influences of anvil shading on simulated supercell thunderstorms abstractnumerical simulations of supercell thunderstorms including parameterized radiative transfer and surface fluxes are performed using the advanced regional prediction system arps model to investigate how low level air temperature deficits within anvil shadows affect the simulated storms the maximum temperature deficits within the modeled cloud shadows are 1 5 2 0 k which is only about half that previously observed within the shadows the loss of strong solar heating cools and stabilizes the near surface layer which suppresses vertical mixing and modifies the near surface vertical wind shear in a case of a stationary storm the enhanced easterly shear present beneath the anvil leads to a thinning of the outflow layer and corresponding acceleration of the rear flank gust front far ahead of the overlying updraft weakening the low level mesocyclone it is further shown that the direct absorption and emission of radiation by clouds does not significantly affect the simulated supercells varying th

observations of wall cloud formation in supercell thunderstorms during vortex2 abstractthis study presents an integrated analysis of dual doppler cloud photogrammetry surface mobile mesonet and sounding data to examine wall cloud formation in two supercells observed during the verification of the origins of rotation in tornadoes experiment ii vortex2 one of the wall clouds contained significant rotation and spawned an enhanced fujita ef2 tornado while the other was clearly displaced horizontally from the mesocyclone and exhibited little rotation at the time of data collection backward parcel trajectories show that the majority of the air entering the wall cloud base originates in the forward flank region a small fraction of the parcels enter the wall cloud base from the inflow some rear flank downdraft parcels descend into the strongly rotating wall cloud for both wall clouds much of the observed wall cloud lowering is attributed to evaporatively cooled parcels in the forward flank region being ingested into the low level updraft additional wall cloud base lowering is

numerical simulation of tornadogenesis in an outer rainband minisupercell of typhoon shanshan on 17 september 2006 abstract on 17 september 2006 three tornadoes occurred along the east coast of kyusyu island in western japan during the passage of an outer rainband in the right front quadrant of typhoon shanshan to clarify the structure of the tornado producing storms and the mechanism of tornadogenesis quadruply nested numerical simulations were performed using a nonhydrostatic model with an innermost horizontal grid spacing of 50 m several simulated convective storms in the outermost rainband exhibited characteristics of a minisupercell one storm had a strong rotating updraft of more than 30 m s 1 and a large vertical vorticity exceeding 0 06 s 1 this storm spawned a tornado when the low level mesocyclone intensified the tornado was generated on the rear flank gust front near the mesocyclone center when a secondary rear flank downdraft rfd surge advanced cyclonically around the low level mesocyclone and overtook the rear flank gust front at its left front edge backward trajectories and vorticity budget anal

influence of hydrodynamic energy on holocene reef flat accretion great barrier reef the response of platform reefs to sea level stabilization over the past 6 ka is well established for the great barrier reef gbr with reefs typically accreting laterally from windward to leeward however these observations are based on few cores spread across reef zones and may not accurately reflect a reef s true accretional response to the holocene stillstand we present a new record of reef accretion based on 49 u th ages from heron and one tree reefs in conjunction with re analyzed data from 14 reefs across the gbr we demonstrate that hydrodynamic energy is the main driver of accretional direction exposed reefs accreted primarily lagoon ward while protected reefs accreted seawards contrary to the traditional growth model in the gbr lateral accretion rates varied from 86 3 m ka 42 4 m ka on the exposed one tree windward reef and 68 35 m ka 15 7 m ka on the protected leeward heron reef suggesting that wind wave energy is not a dominant control on lateral accretion rates this represents the most comprehensive statement of lateral accretion direction and rates from the mid outer platform reefs of the gbr confirming great variability in reef flat growth both within and between reef margins over the last 6 ka and highlighting the need for closely spaced transects

kinematic observations of misocyclones along boundaries during ihop during the international h2o project mobile radars collected high resolution data of several 0 5 2 kmwide vertically oriented vortices or misocyclones along at least five mesoscale airmass boundaries this study analyzes the properties of the misocyclones in three of these datasets 3 10 and 19 june 2002 to verify findings from finescale numerical models and other past observations of misocyclones and to further the understanding of the role that they play in the initiation of deep moist convection and nonsupercell tornadoes misocyclones inflect or disjoint the swath of low level convergence along each boundary to varying degrees depending on the size of their circulations when several relatively large misocyclones are next to each other the shape of low level convergence along each boundary is arranged into a staircase pattern mergers of misocyclones are an important process in the evolution of the vorticity field as a population of small vortices consolidates into a smaller number of larger ones additionally merging misocyclones may affect the mixing of thermodynamic fields in their vicinity when the merger axis is perpendicular to the boundary misocyclones interact with linear and cellular structures in the planetary boundary layers pbls of the air masses adjacent to each boundary cyclonic low level vertical vorticity generated by both types of structures makes contact with each boundary and sometimes is incorporated into preexisting misocyclones intersections of either type of pbl structure with the boundary result in strengthened pockets of low level convergence and typically strengthened misocyclones

tornado maintenance investigated with high resolution dual doppler and enkf analysis abstractdual doppler wind synthesis and ensemble kalman filter analyses produced by assimilating doppler on wheels velocity data collected in four tornadic supercells are examined in order to further understand the maintenance of tornadoes although tornado scale features are not resolved in these analyses larger scale processes involved with tornado maintenance are well represented the longest lived tornado is maintained underneath the midlevel updraft within a zone of low level horizontal convergence along a rear flank gust front for a considerable time and dissipates when horizontally displaced from the midlevel updraft the shortest lived tornado resides in a similar zone of low level convergence briefly but dissipates underneath the location of the midlevel updraft when the updraft becomes tilted and low level convergence is displaced several kilometers from the tornado this suggests that a location beneath the midlevel updraft is not always a sufficient condition for tornado maintenance particu

a numerical study of the 6 may 2012 tsukuba city supercell tornado part ii mechanisms of tornadogenesis abstractin part i the vorticity sources of midlevel and low level mesocyclones in the 6 may 2012 tsukuba city japan tornadic supercell were investigated by using high resolution simulation results with a 50 m horizontal grid spacing in part ii the analyses are extended to the mechanisms of tornadogenesis the tornado was generated at the leading edge of a rear flank downdraft rfd outflow surge backward trajectory and vortex line analyses revealed that the rfd outflow surge was a triggering factor for tornadogenesis and that horizontal vorticity around the strong rfd outflow region was ingested into the tornado to identify the vorticity source of the tornado the evolution of circulation along a material circuit surrounding the tornado was investigated owing to baroclinity at the tip of a hook shaped distribution of hydrometeors hereafter hook echo the circulation increased rapidly from a negative value when the core of the hydrometeors was descending about 10 min prior to tornadogenesis ana

an investigation of the goshen county wyoming tornadic supercell of 5 june 2009 using enkf assimilation of mobile mesonet and radar observations collected during vortex2 part ii mesocyclone scale processes affecting tornado formation maintenance and decay abstractstorm scale and mesocyclone scale processes occurring contemporaneously with a tornado in the goshen county wyoming supercell observed on 5 june 2009 during the second verification of the origins of rotation in tornadoes experiment vortex2 are examined using ensemble analyses produced by assimilating mobile radar and in situ observations into a high resolution convection resolving model this paper focuses on understanding the evolution of the vertical structure of the storm the outflow buoyancy and processes affecting the vertical vorticity and circulation within the mesocyclone that correspond to changes in observed tornado intensity tornadogenesis occurs when the low level mesocyclone is least negatively buoyant relative to the environment possesses its largest circulation and is collocated with the largest azimuthally averaged convergence during the analysis period the average buoyancy circulation and convergence within the near surface mesocyclone on spatial scales resolved by the

dual doppler and single doppler analysis of a tornadic storm undergoing mergers and repeated tornadogenesis abstract dual doppler observations with unprecedented finescale spatial and temporal resolution are used to characterize the vector wind field in and near a tornado occurring near kiefer oklahoma on 26 may 1997 analyses of the dual doppler vector wind fields document in detail for the first time several structures associated with the tornado a proximate updraft region a rear flank downdraft wrapping around the tornado a double gust front structure occluding near the tornado and a region of enhanced vorticity separated from the tornado that may have been associated with cyclic tornadogenesis the analyses are compared to conceptual and computer models of tornadic storms a subsequent tornadogenesis was observed with radar every 18 s providing a finescale temporal view of the genesis process the genesis process was complex and the evolution of tornado intensity parameters was not monotonic in time low level rotation contracted and intensified then broadened then contracted and intensified a se

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

variations in supercell morphology part i observations of the role of upper level storm relative flow abstract it is hypothesized that the precipitation intensity beneath a supercell updraft is strongly influenced by the amount of hydrometeors that are reingested into the updraft after being transported away in the divergent upper level flow of the anvil this paper presents the results of a climatological analysis of soundings associated with three types of isolated supercells having distinctive precipitation distributions the so called classic low precipitation lp and high precipitation hp storms it is shown that storm relative flow at 9 10 km above the ground is strongest in the environments of lp storms and relatively weak in the environments of hp storms with classic storms occurring in environments with intermediate magnitudes of upper storm relative flow it is plausible that comparatively strong flow in the anvil bearing levels of lp storms transports hydrometeors far enough from the updraft that they are relatively unlikely to be reingested into the updraft leading to greatly diminishe

using the translation speed and vertical structure of gust fronts to infer buoyancy deficits within thunderstorm outflow abstractthis study investigates whether the thermodynamics of supercell rear flank outflow can be inferred from the propagation speed and vertical structure of the rear flank gust front to quantif

finescale doppler radar observation of a tornado and low level misocyclones within a winter storm in the japan sea coastal region abstract life histories of low level misocyclones one of which corresponded to a tornado vortex within a winter storm in the japan sea coastal region on 1 december 2007 were observed from close range by x band doppler radar of the east japan railway company continuous plan position indicator ppi observations at 30 s intervals at the low elevation angle revealed at least four cyclonic misocyclones within the head of the comma shaped echo of the vortical disturbance under winter monsoon conditions the meso scale vortical disturbance developed within the weak frontal zone at the leading edge of cold air outbreaks high resolution observation of misocyclones revealed the detailed structures of these misocyclones and their temporal evolution as the parent storm evolved a low level convergence line was observed at the edge of the easternmost misocyclone this convergence line was considered to be important for the initiation and development of the misocyclones and the tornado through vortex stretching