the vertical structure of a tornado near happy texas on 5 may 2002 high resolution mobile w band doppler radar observations abstract a mobile w band doppler radar scanned at close range portions of a tornado near happy texas on 5 may 2002 simultaneous boresighted video images were also recorded which facilitated correlating the radar observed features of the tornado with its visual features range height indicators rhis of radar reflectivity and doppler velocity were collected that detail with high spatial resolution aspects of the vertical structure of the tornado near the ground most of the rhis showed a column of a weak echo hole from about 60 m above the ground up to the top of the domain at 800 1000 m above the ground the hole was roughly 40 broader about 100 m above the ground as it was above resulting in a characteristic pear shaped vertical cross section of reflectivity in this tornado the condensation funnel was much narrower than the width of the weak echo hole the visible debris cloud near the ground was approximately just as wide as the hole above 150 m the mean depth of the debris cloud was arou

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

a similarity theory for unsaturated downdrafts within clouds abstract recent observations of cumulus clouds strongly support the hypothesis of squires 1958 that much of the mixing within such clouds is associated with downward propagating currents initiated near their tops a similarity theory is here proposed to describe the properties of such currents the use of similarity is defended on the basis of the observed and predicted scale of the downdrafts the theory suggests that downward propagating unsaturated thermals are pervasive throughout all but the largest convective clouds and that quasi steady unsaturated downdraft plumes may exist in the lower portions of cumulonimbi in addition to providing a reasonable explanation for the microstructure of and liquid water distribution within cumulus clouds the theory appears to account for certain severe convective phenomena including down bursts a new but related cloud instability is proposed to account for the occurrence of mamma

centrifuging of hydrometeors and debris in tornadoes radar reflectivity patterns and wind measurement errors high resolution doppler radar observations of tornadoes reveal a distinctive tornado scale signature with the following properties a reflectivity minimum aloft inside the tornado core described previously as an eye a high reflectivity tube aloft that is slightly wider than the tornado core and a tapering of this high reflectivity tube near the ground the results of simple one dimensional and two dimensional models demonstrate how these characteristics develop important processes in the models include centrifugal ejection of hydrometeors and or debris by the rotating flow and recycling of some objects by the nearsurface inflow and updraft doppler radars sample the motion of objects within the tornado rather than the actual airflow since objects move at different speeds and along different trajectories than the air error is introduced into kinematic analyses of tornadoes based on radar observations in a steady axisymmetric tornado objects move outward relative to the air and move more slowly than the air in the tangential direction in addition the vertical air relative speed of an object is less than it is in still air the differences between air motion and object motion are greater for objects with greater characteristic fall speeds i e larger denser objects and can have magnitudes of tens of meters per second estimates of these differences for specified object and tornado characteristics can be obtained from an approximation of the one dimensional model doppler on wheels observations of the 30 may 1998 spencer south dakota tornado demonstrate how the apparent tornado structure can change when the radar scatterer type changes when the spencer tornado entered the town and started lofting debris changes occurred in the doppler velocity and reflectivity fields that are consistent with an increase in mean scatterer size

low level mesovortices within squall lines and bow echoes part i overview and dependence on environmental shear this two part study proposes fundamental explanations of the genesis structure and implications of lowlevel meso g scale vortices within quasi linear convective systems qlcss such as squall lines and bow echoes such mesovortices are observed frequently at times in association with tornadoes idealized simulations are used herein to study the structure and evolution of meso g scale surface vortices within qlcss and their dependence on the environmental vertical wind shear within such simulations significant cyclonic surface vortices are readily produced when the unidirectional shear magnitude is 20 m s 21 or greater over a 0 2 5 or 0 5 km agl layer as similarly found in observations of qlcss these surface vortices form primarily north of the apex of the individual embedded bowing segments as well as north of the apex of the larger scale bow shaped system they generally develop first near the surface but can build upward to 6 8 km agl vortex longevity can be several hours far longer than individual convective cells within the qlcs during this time vortex merger and upscale growth is common it is also noted that such mesoscale vortices may be responsible for the production of extensive areas of extreme straight line wind damage as has also been observed with some qlcss surface vortices are also produced for weaker shears but remain shallow weak and short lived although similar in size and strength to mesocyclones associated with supercell storms and also sometimes producing similar hooklike structures in the rain field it is also shown that the present vortices are quite distinct structurally and dynamically most critically such vortices are not associated with long lived rotating updrafts at midlevels and the associated strong dynamically forced vertical accelerations as occur within supercell mesocyclones

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

clouds in tropical cyclones abstract clouds within the inner regions of tropical cyclones are unlike those anywhere else in the atmosphere convective clouds contributing to cyclogenesis have rotational and deep intense updrafts but tend to have relatively weak downdrafts within the eyes of mature tropical cyclones stratus clouds top a boundary layer capped by subsidence an outward sloping eyewall cloud is controlled by adjustment of the vortex toward gradient wind balance which is maintained by a slantwise current transporting boundary layer air upward in a nearly conditionally symmetric neutral state this balance is intermittently upset by buoyancy arising from high moist static energy air entering the base of the eyewall because of the radial influx of low level air from the far environment supergradient wind in the eyewall zone and or small scale intense subvortices the latter contain strong erect updrafts graupel particles and large raindrops produced in the eyewall fall out relatively quickly while ice splinters left

deformation of biotite and muscovite tem microstructure and deformation model abstract growth and deformation defects have been observed in 1m and 2m 1 biotites and 2m 1 muscovites using transmission electron microscope tem techniques these have been related to optical observations in deformed biotite the dislocation density increases as the strain increases the density of stacking faults also increases with strain the spatial ordering of stacking faults decreases as the strain increases in muscovites selected from the same areas as the biotites stacking fault and dislocation densities show little or no variation with deformation the different responses of biotite and muscovite to deformation are explained in part by the physical and chemical differences between 1m biotite and 2m 1 muscovite there is strong evidence in both the biotites and muscovites that stacking faults may be result of deformation as well as a crystal growth process the grain size of the deformed mica aggregates is reduced by the nucleation of new micas there is also evidence for a grain size reduction mechanism segmentation in biotites this mechanism appears to achieve the same result as recovery recrystallization mechanisms but not by the same method segmentation may be a mechanism which is favoured in strongly anisotropic minerals with a limited number of slip systems a model is proposed that attempts to correlate response of the biotite to deformation the deformation is synchronous with and post dates the nucleation of the new metamorphic micas

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

a finescale radar examination of the tornadic debris signature and weak echo reflectivity band associated with a large violent tornado abstracthigh resolution data of the tornadic debris signature tds and weak echo reflectivity band wrb associated with a large violent tornado on 24 may 2011 in central oklahoma are examined using a rapid scan x band polarimetric mobile doppler radar various characteristics of these features and their evolution are examined over time intervals of 20 s or less the formation of the tds debris fallout and inhomogeneities in the tds structure are analyzed from volumetric and single elevation observations constant radius vertical cross sections of doppler velocity reflectivity and copolar cross correlation coefficient are compared at various times during the tornado s life cycle from them it is found that the weak echo column wec is considerably narrower than the tds and the wec is confined to the strong gradient of doppler velocities in the tornado s core the tds of the mature tornado extends radially outward bound approximately by the 40 m s 1 radial isodop rapid scan near surface data w

damaging surface wind mechanisms within the 10 june 2003 saint louis bow echo during bamex abstract detailed radar and damage survey analyses of a severe bow echo event that occurred on 10 june 2003 during the bow echo and mesoscale convective vortex mcv experiment are presented a bow echo formed just east of saint louis missouri and produced a continuous straight line wind damage swath approximately 8 km in width and 50 km in length along with five f0 f1 tornadoes careful superposition of the damage survey analysis and weather surveillance radar 1988 doppler wsr 88d data from saint charles missouri klsx showed that the primary straight line wind damage swath was not collocated with the bow echo apex as has been suggested in previous studies rather the primary damage swath was found north of the bow apex collocated with a low level vortex that formed on the leading edge of the bow echo much of the primary damage swath appeared to have been created by the low level vortex moreover most of the surface straight line wind damage was generated during the early stages of bow echo mo

the multiple vortex structure of the el reno oklahoma tornado on 31 may 2013 abstractthis study documents the formation and evolution of secondary vortices associated within a large violent tornado in oklahoma based on data from a close range mobile polarimetric rapid s

simulation of a progressive derecho using composite initial conditions abstract this study focuses on the progressive derecho a widespread convectively induced windstorm produced by a mesoscale convective system that often occurs within a relatively benign synoptic scale environment sounding data from 12 progressive derechos which occurred in weakly forced large scale environments are composited in order to examine important large scale features in the preconvective environment this analysis captures many features that are common in warm season derecho environments such as an upper level wind maximum a relatively dry midtroposphere and low level warm advection initial and boundary conditions for the pennsylvania state university national center for atmospheric research fifth generation mesoscale model mm5 are created using this analysis a three dimensional horizontally nonhomogeneous explicitly resolved simulation of a progressive derecho is produced and compared to previous more idealized simulations of similar convective systems that have been used to expla

models of ice melting and edifice growth at the onset of subglacial basaltic eruptions 1 models of the early stages of basaltic eruptions beneath temperate glaciers are presented that consider the evolving sizes of volcanic edifices emplaced within subglacial cavities the cavity size reflects the competing effects of enlargement by melting and closure by downward ductile deformation of the ice roof which occurs when the cavity pressure is less than glaciostatic due to meltwater drainage eruptions of basaltic magma from fissures and point sources are considered which form either hemicylindrical or hemispherical cavities the rate of roof closure can therefore be estimated using nye s law the cavity size edifice size and depth of meltwater above the edifice are predicted by the model and are used to identify two potential eruption mechanisms explosive and intrusive when the cavity is considerably larger than the edifice hydroclastic fragmentation is possible via explosive eruptions with deposition of tephra by eruptionfed aqueous density currents when the edifice completely fills the cavity rising magma is likely to quench within waterlogged tephra in a predominantly intrusive manner the models were run for a range of magma discharge rates ice thicknesses and cavity pressures relevant to subglacial volcanism in iceland explosive eruptions occur at high magma discharge rates when there is insufficient time for significant roof closure the models correctly predict the style of historic and pleistocene subglacial fissure eruptions in iceland and are used to explain the contrasting sedimentology of basaltic and rhyolitic tuyas the models also point to new ways of unraveling the complex coupling between eruption mechanisms and glacier response during subglacial eruptions

radar and damage analysis of severe bow echoes observed during bamex abstract this study examines damaging wind production by bow shaped convective systems commonly referred to as bow echoes recent idealized numerical simulations suggest that in addition to descending rear inflow at the bow echo apex low level mesovortices within bow echoes can induce damaging straight line surface winds in light of these findings detailed aerial and ground surveys of wind damage were conducted immediately following five bow echo events observed during the bow echo and mesoscale convective vortex mcv experiment bamex field phase these damage locations were overlaid directly onto weather surveillance radar 1988 doppler wsr 88d images to i elucidate where damaging surface winds occurred within the bow shaped convective system in proximity to the apex north of the apex etc and then ii explain the existence of these winds in the context of the possible damaging wind mechanisms the results of this study provide clear observational evidence that low level mesovortices wit

tornadoes and downbursts in the context of generalized planetary scales abstract in order to cover a wide range of horizontal dimensions of airflow the author proposes a series of five scales maso meso miso to be read as my so moso and muso arranged in the order of the vowels a e 1 o u the dimensions decrease by two orders of magnitude per scale beginning with the planet s equator length chosen to be the maximum dimension of masoscale for each planet mesoscale highs and lows were described on the basis of mesoanalyses while sub mesoscale disturbances were depicted by cataloging over 20 000 photographs of wind effects taken from low flying aircraft during the past 15 years various motion thus classified into these scales led to a conclusion that extreme winds induced by thunderstorms are associated with misoscale and mososcale airflow spawned by the parent mesoscale disturbances

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

observational analysis of the 27 may 1997 central texas tornadic event part ii tornadoes abstract the 27 may 1997 central texas tornadic event has been investigated in a two part observational study as demonstrated in part i the 1d environment associated with this event was unfavorable for significant f2 tornadoes yet the storm complex produced at least six significant tornadoes including one rated f5 the jarrell texas tornado the purpose of this article is to examine the spatiotemporal interrelationships between tornadoes preexisting boundaries antecedent low level mesocyclones convective cells and midlevel mesocyclones it is shown that each of the six observed tornadoes that produced greater than f0 damage formed along the storm generated gust front not along preexisting boundaries half of these tornadoes formed on the distorted gust front the portion of the storm generated gust front whose orientation was deformed largely by the horizontal shear across the cold front the remaining three tornadoes developed at the gust front cusp the persistent gust front inflection l

mobile doppler radar observations of a tornado in a supercell near bassett nebraska on 5 june 1999 part i tornadogenesis abstract this two part paper details an analysis of high resolution wind and reflectivity data collected by a mobile w band doppler radar the dataset captures the near surface life history of a tornado in a supercell in north central nebraska on 5 june 1999 the formation of the tornado vortex near the ground is described from a sequence of sector scans ranging from 30 s intervals prior to tornadogenesis to 10 15 s intervals during much of the lifetime of the tornado cyclonic vortices of 100 200 m width were found along a bow shaped line of enhanced radar reflectivity at what appears to have been the leading edge of a rear flank gust front at the time of tornadogenesis one of these vortices was located just ahead of the nose of the bow shaped radar echo and a jet which were embedded within a larger scale cyclone at other times small scale cyclonic vortices coexisted with the tornado along an arc shaped line extending to its north and northeast but did not appear to interact with the tornado the

radar characteristics of storms in the sydney area abstract the characteristics of radar echoes for 12 thunderstorm days in the vicinity of sydney australia in the summer of 1995 96 have been examined using an objective methodology for storm identification and tracking the spatial distribution of identified storms shows a maximum in frequency and intensity along the east side of the mountains that lie inland from the coast characteristics such as storm volume area and height are shown to have a lognormal frequency distribution reflectivity also has a skewed frequency distribution with a prevalence of lower reflectivity storms both the maximum reflectivity and storm height are shown to be correlated with the logarithm of storm volume although small storms predominate the bulk of precipitation flux comes from the relatively few large scale storms it is also shown that storms generally move or propagate in a direction slightly to the left of the mass weighted mean wind for the surface to 300 hpa layer at a speed slightly less than the mean speed

microbursts a hazard for aircraft microbursts are believed to have been responsible for several aircraft accidents in recent years we report here laboratory experiments which show that when a descending column of dense fluid reaches the ground and begins to spread out horizontally an intense vortex with a horizontal axis forms at the leading edge of the outflowing air the intensity of this vortex results from the increase in vorticity due to the rapid stretching of the length of the leading edge the properties of such a horizontal vortex with its associated updrafts and downdrafts are consistent with those found in microbursts which are a severe hazard to aircraft when taking off or landing