Processes Preventing the Development of a Significant Tornado in a Colorado Supercell on 26 May 2010

2020 ◽  
Vol 148 (5) ◽  
pp. 1753-1778
Author(s):  
Shawn S. Murdzek ◽  
Paul M. Markowski ◽  
Yvette P. Richardson ◽  
Robin L. Tanamachi
Keyword(s):  
Small Radius ◽  
Future Research ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Far Field ◽  
Streamwise Vorticity ◽  
Low Level ◽  
Precipitation Region ◽  
Negative Buoyancy

Abstract A 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 mobile radars performing dual-Doppler scans, a five-probe mobile mesonet, and a proximity sounding, factors that prevented this vortex from strengthening into a significant tornado are examined. Mobile mesonet observations indicate that portions of the supercell outflow possessed excessive negative buoyancy, likely owing in part to low boundary layer relative humidity, as indicated by a high environmental lifted condensation level. Comparisons to a tornadic supercell suggest that the Prospect Valley storm had enough far-field circulation to produce a significant tornado, but was unable to converge this circulation to a sufficiently small radius. Trajectories suggest that the weak convergence might be due to the low-level mesocyclone ingesting parcels with considerable crosswise vorticity from the near-storm environment, which has been found to contribute to less steady and weaker low-level updrafts in supercell simulations. Yet another factor that likely contributed to the weak low-level circulation was the inability of parcels rich in streamwise vorticity from the forward-flank precipitation region to reach the low-level mesocyclone, likely owing to an unfavorable pressure gradient force field. In light of these results, we suggest that future research should continue focusing on the role of internal, storm-scale processes in tornadogenesis, especially in marginal environments.

scholarly journals The Pretornadic Phase of the Goshen County, Wyoming, Supercell of 5 June 2009 Intercepted by VORTEX2. Part I: Evolution of Kinematic and Surface Thermodynamic Fields

2012 ◽  
Vol 140 (9) ◽  
pp. 2887-2915 ◽  
Author(s):  
Paul Markowski ◽  
Yvette Richardson ◽  
James Marquis ◽  
Joshua Wurman ◽  
Karen Kosiba ◽  
...  
Keyword(s):  
Potential Temperature ◽  
Radar Data ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Vertical Vorticity ◽  
Low Level ◽  
The Past ◽  
Virtual Potential Temperature ◽  
Perturbation Pressure ◽  
Negative Buoyancy

Abstract The authors analyze the pretornadic phase (2100–2148 UTC; tornadogenesis began at 2152 UTC) of the Goshen County, Wyoming, supercell of 5 June 2009 intercepted by the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2). The analysis relies on radar data from the Weather Surveillance Radar-1988 Doppler (WSR-88D) in Cheyenne, Wyoming (KCYS), and a pair of Doppler-on-Wheels (DOW) radars, mobile mesonet observations, and mobile sounding observations. The storm resembles supercells that have been observed in the past. For example, it develops a couplet of counter-rotating vortices that straddle the hook echo within the rear-flank outflow and are joined by arching vortex lines, with the cyclonic vortex becoming increasingly dominant in the time leading up to tornadogenesis. The outflow in the hook echo region, where sampled, has relatively small virtual potential temperature θυ deficits during this stage of evolution. A few kilometers upstream (north) of the location of maximum vertical vorticity, θυ is no more than 3 K colder than the warmest θυ readings in the inflow of the storm. Forward trajectories originating in the outflow within and around the low-level mesocyclone rise rapidly, implying that the upward-directed perturbation pressure gradient force exceeds the negative buoyancy. Low-level rotation intensifies in the 2142–2148 UTC period. The intensification is preceded by the formation of a descending reflectivity core (DRC), similar to others that have been documented in some supercells recently. The DRC is associated with a rapid increase in the vertical vorticity and circulation of the low-level mesocyclone.

scholarly journals The Role of Surface Drag in Mesocyclone Intensification Leading to Tornadogenesis within an Idealized Supercell Simulation

2017 ◽  
Vol 74 (9) ◽  
pp. 3055-3077 ◽  
Author(s):  
Brett Roberts ◽  
Ming Xue
Keyword(s):  
Pressure Gradient ◽  
Surface Friction ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Surface Drag ◽  
Vertical Pressure ◽  
Low Level ◽  
Physical Mechanisms ◽  
Key Factor

Abstract The idealized supercell simulations in a previous study by Roberts et al. are further analyzed to clarify the physical mechanisms leading to differences in mesocyclone intensification between an experiment with surface friction applied to the full wind (FWFRIC) and an experiment with friction applied to the environmental wind only (EnvFRIC). The low-level mesocyclone intensifies rapidly during the 3 min preceding tornadogenesis in FWFRIC, while the intensification during the same period is much weaker in EnvFRIC, which fails to produce a tornado. To quantify the mechanisms responsible for this discrepancy in mesocyclone evolution, material circuits enclosing the low-level mesocyclone are initialized and traced back in time, and circulation budgets for these circuits are analyzed. The results show that in FWFRIC, surface drag directly generates a substantial proportion of the final circulation around the mesocyclone, especially below 1 km AGL; in EnvFRIC, circulation budgets indicate the mesocyclone circulation is overwhelmingly barotropic. It is proposed that the import of near-ground, frictionally generated vorticity into the low-level mesocyclone in FWFRIC is a key factor causing the intensification and lowering of the mesocyclone toward the ground, creating a large upward vertical pressure gradient force that leads to tornadogenesis. Similar circulation analyses are also performed for circuits enclosing the tornado at its genesis stage. The frictionally generated circulation component is found to contribute more than half of the final circulation for circuits enclosing the tornado vortex below 400 m AGL, and the frictional contribution decreases monotonically with the height of the final circuit.

scholarly journals On the fine vertical structure of the low troposphere over the coastal margins of East Antarctica

2019 ◽  
Author(s):  
Étienne Vignon ◽  
Olivier Traullé ◽  
Alexis Berne
Keyword(s):  
Pressure Gradient ◽  
Vertical Structure ◽  
East Antarctica ◽  
Radiosonde Data ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Ice Shelves ◽  
Low Level ◽  
Humidity Profiles

Abstract. Eight years of high-resolution radiosonde data at nine Antarctic stations are analysed to provide the first large scale characterization of the fine scale vertical structure of the low troposphere up to 3 km of altitude over the coastal margins of East Antarctica. Radiosonde data show a large spatial variability of wind, temperature and humidity profiles, with different features between stations in katabatic regions (e.g., Dumont d'Urville and Mawson stations), stations over two ice shelves (Neumayer and Halley stations) and regions with complex orography (e.g., Mc Murdo). At Dumont d'Urville, Mawson and Davis stations, the yearly median wind speed profiles exhibit a clear low-level katabatic jet. During precipitation events, the low-level flow generally remains of continental origin and its speed is even reinforced due to the increase in the continent- ocean pressure gradient. Meanwhile, the relative humidity profiles show a dry low troposphere, suggesting the occurence of low-level sublimation of precipitation in katabatic regions but such a phenomenon does not appreciably occur over the ice-shelves near Halley and Neumayer. Although ERA-Interim and ERA5 reanalyses assimilate radiosoundings at most stations considered here, substantial – and sometimes large – low-level wind and humidity biases are revealed but ERA5 shows overall better performances. A free simulation with the regional model Polar WRF (at a 35-km resolution) over the entire continent shows too strong and too shallow near-surface jets in katabatic regions especially in winter. This may be a consequence of an understimated coastal cold air bump and associated sea-continent pressure gradient force due to the coarse 35 km resolution of the Polar WRF simulation. Beyond documenting the vertical structure of the low troposphere over coastal East-Antarctica, this study gives insights into the reliability and accuracy of two major reanalysis products in this region on the Earth and it raises the difficulty of modeling the low-level flow over the margins of the ice sheet with a state-of-the-art climate model.

scholarly journals Evolution of Low-Level Angular Momentum in the 2 June 1995 Dimmitt, Texas, Tornado Cyclone

2007 ◽  
Vol 64 (4) ◽  
pp. 1365-1378 ◽  
Author(s):  
Erik N. Rasmussen ◽  
Jerry M. Straka
Keyword(s):  
Angular Momentum ◽  
Life Cycle ◽  
Axisymmetric Flow ◽  
Tangential Velocity ◽  
Secondary Circulation ◽  
Cloud Base ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Low Level ◽  
Debris Cloud

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 with time in part of the tornado cyclone. During the transition phase, downdrafts began to occur within the tornado cyclone. The transport of angular momentum by the secondary circulation nearly was offset by eddy flux convergence of angular momentum so that the azimuthally averaged angular momentum tendency was only weakly negative at most radii. The tornado was visually impressive during this stage, featuring a 400-m diameter debris cloud extending to cloud base, while the surrounding wall cloud shrank and eroded. During the weakening phase, the funnel and debris cloud gradually shrank, and the funnel went through a rope stage prior to disappearing. The weakening phase was characterized by extensive downdrafts at all radii outside the tornado, and large-scale near-ground outflow as observed by mobile mesonet systems in a portion of the tornado cyclone. The secondary circulation acted to transport smaller angular momentum downward from aloft, and outward along the ground. All terms of the angular momentum budget became negative throughout most of the low-level (0–800-m AGL) tornado cyclone during the weakening phase. Several hypotheses for this evolution are evaluated, including changes in water loading in the tornado cyclone, cooling of the near-ground air, and the distribution of tangential velocity with height with its concomitant influence on the nonhydrostatic vertical pressure gradient force.

CFD Study on the Role of Gas Friction on the Molten Layer Shape and Melt Removal Mechanism in Laser Cutting Process of Steel

2013 ◽  
Vol 856 ◽  
pp. 220-225 ◽  
Author(s):  
Karim Kheloufi ◽  
El Hachemi Amara
Keyword(s):  
Friction Force ◽  
Laser Cutting ◽  
Cutting Process ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Central Plane ◽  
Removal Mechanism ◽  
Molten Layer ◽  
Wavy Structure

A numerical analysis of the role of the gas friction force on the shape of the melt surface in laser cutting process is carried out. The liquid film shape is analyzed in the central plane of cutting for both cases with the pressure gradient force only and for the case of gas friction force contribution. It is shown that, the gas friction force has a significant role in the formation of humps in the central kerf zone and the transition from the smooth melt ejection regime to a wavy structure characterized by humps formation.

scholarly journals Large Sensitivity of Near-Surface Vertical Vorticity Development to Heat Sink Location in Idealized Simulations of Supercell-Like Storms

2017 ◽  
Vol 74 (4) ◽  
pp. 1095-1104 ◽  
Author(s):  
Paul M. Markowski ◽  
Yvette P. Richardson
Keyword(s):  
Heat Sink ◽  
Vertical Axis ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Vertical Vorticity ◽  
Supercell Storm ◽  
History Of ◽  
Perturbation Pressure ◽  
Negative Buoyancy

Abstract In idealized numerical simulations of supercell-like “pseudostorms” generated by a heat source and sink in a vertically sheared environment, a tornado-like vortex develops if air possessing large circulation about a vertical axis at the lowest model levels can be converged. This is most likely to happen if the circulation-rich air possesses only weak negative buoyancy (the circulation-rich air has a history of descent, so typically possesses at least some negative buoyancy) and is subjected to an upward-directed vertical perturbation pressure gradient force. This paper further explores the sensitivity of the development of near-surface vertical vorticity to the horizontal position of the heat sink. Shifting the position of the heat sink by only 2–3 km can significantly influence vortex intensity by altering both the baroclinic generation of circulation and the buoyancy of circulation-rich air. Many of the changes in the pseudostorms that arise from shifting the position of the heat sink would be difficult to anticipate. The sensitivity of the pseudostorms to heat sink position probably at least partly explains the well-known sensitivity of near-surface vertical vorticity development to the microphysics parameterizations in more realistic supercell storm simulations, as well as some of the failures of actual supercells to produce tornadoes in seemingly favorable environments.

scholarly journals Subsiding Shells around Shallow Cumulus Clouds

2008 ◽  
Vol 65 (3) ◽  
pp. 1003-1018 ◽  
Author(s):  
Thijs Heus ◽  
Harm J. J. Jonker
Keyword(s):  
Detailed Comparison ◽  
Momentum Equation ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Cumulus Clouds ◽  
Responsible Mechanism ◽  
Lateral Mixing ◽  
Environmental Air ◽  
The Individual

Abstract In this study large-eddy simulations (LES) are used to gain more knowledge on the shell of subsiding air that is frequently observed around cumulus clouds. First, a detailed comparison between observational and numerical results is presented to better validate LES as a tool for studies of microscale phenomena. It is found that horizontal cloud profiles of vertical velocity, humidity, and temperature are in good agreement with observations. They show features similar to the observations, including the presence of the shell of descending air around the cloud. Second, the availability of the complete 3D dataset in LES has been exploited to examine the role of lateral mixing in the exchange of cloud and environmental air. The origin of the subsiding shell is examined by analyzing the individual terms of the vertical momentum equation. Buoyancy is found to be the driving force for this shell, and it is counteracted by the pressure-gradient force. This shows that evaporative cooling at the cloud edge, induced by lateral mixing of cloudy and environmental air, is the responsible mechanism behind the descending shell. For all clouds, and especially the smaller ones, the negative mass flux generated by the subsiding shell is significant. This suggests an important role for lateral mixing throughout the entire cloud layer. The role of the shell in these processes is further explored and described in a conceptual three-layer model of the cloud.

scholarly journals On the Orographically Generated Low-Level Easterly Jet and Severe Downslope Storms of March 2006 over the Tacheng Basin of Northwest China

2018 ◽  
Vol 146 (6) ◽  
pp. 1667-1683 ◽  
Author(s):  
Guangxing Zhang ◽  
Da-Lin Zhang ◽  
Shufang Sun
Keyword(s):  
Large Scale ◽  
Inversion Layer ◽  
Dust Storms ◽  
Frozen Soil ◽  
Gradient Force ◽  
Mountain Range ◽  
Pressure Gradient Force ◽  
Low Level ◽  
Downslope Winds ◽  
The Impact

A high-latitude low-level easterly jet (LLEJ) and downslope winds, causing severe dust storms over the Tacheng basin of northwestern China in March 2006 when the dust source regions were previously covered by snow with frozen soil, are studied in order to understand the associated meteorological conditions and the impact of complex topography on the generation of the LLEJ. Observational analyses show the development of a large-scale, geostrophically balanced, easterly flow associated with a northeastern high pressure and a southeastern low pressure system, accompanied by a westward-moving cold front with an intense inversion layer near the altitudes of mountain ridges. A high-resolution model simulation shows the generation of an LLEJ of near-typhoon strength, which peaked at about 500 m above the ground, as well as downslope windstorms with marked wave breakings and subsidence warming in the leeside surface layer, as the large-scale cold easterly flow moves through a constricting saddle pass and across a higher mountain ridge followed by a lower parallel ridge, respectively. The two different airstreams are merged to form an intense LLEJ of cold air, driven mostly by zonal pressure gradient force, and then the LLEJ moves along a zonally oriented mountain range to the north. Results indicate the importance of the lower ridge in enhancing the downslope winds associated with the higher ridge and the importance of the saddle pass in generating the LLEJ. We conclude that the intense downslope winds account for melting snow, warming and drying soils, and raising dust into the air that is then transported by the LLEJ, generated mostly through the saddle pass, into the far west of the basin.

Nocturnal Destabilization Associated with the Summertime Great Plains Low-Level Jet

2020 ◽  
Vol 148 (11) ◽  
pp. 4641-4656
Author(s):  
Thomas R. Parish ◽  
Richard D. Clark ◽  
Todd D. Sikora
Keyword(s):  
Great Plains ◽  
The United States ◽  
Temperature Gradients ◽  
Gradient Force ◽  
Wind Component ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Low Level ◽  
Temperature Advection ◽  
Low Level Jet

AbstractThe Great Plains low-level jet (LLJ) has long been associated with summertime nocturnal convection over the central Great Plains of the United States. Destabilization effects of the LLJ are examined using composite fields assembled from the North American Mesoscale Forecast System for June and July 2008–12. Of critical importance are the large isobaric temperature gradients that become established throughout the lowest 3 km of the atmosphere in response to the seasonal heating of the sloping Great Plains. Such temperature gradients provide thermal wind forcing throughout the lower atmosphere, resulting in the establishment of a background horizontal pressure gradient force at the level of the LLJ. The attendant background geostrophic wind is an essential ingredient for the development of a pronounced summertime LLJ. Inertial turning of the ageostrophic wind associated with LLJ provides a westerly wind component directed normal to the terrain-induced orientation of the isotherms. Hence, significant nocturnal low-level warm-air advection occurs, which promotes differential temperature advection within a vertical column of atmosphere between the level just above the LLJ and 500 hPa. Such differential temperature advection destabilizes the nighttime troposphere above the radiatively cooled near-surface layer on a recurring basis during warm weather months over much of the Great Plains and adjacent states to the east. This destabilization process reduces the convective inhibition of air parcels near the level of the LLJ and may be of significance in the development of elevated nocturnal convection. The 5 July 2015 case from the Plains Elevated Convection at Night field program is used to demonstrate this destabilization process.

scholarly journals Low-Level Easterly Winds Blowing through the Tsugaru Strait, Japan. Part II: Numerical Simulation of the Event on 5–10 June 2003

2012 ◽  
Vol 140 (6) ◽  
pp. 1779-1793 ◽  
Author(s):  
Teruhisa Shimada ◽  
Masahiro Sawada ◽  
Weiming Sha ◽  
Hiroshi Kawamura
Keyword(s):  
Pressure Gradient ◽  
Air Temperature ◽  
Temperature Difference ◽  
Diurnal Variations ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
The West ◽  
Low Level ◽  
Tsugaru Strait ◽  
Mutsu Bay

Abstract This paper investigates the structures of and diurnal variations in low-level easterly winds blowing through the Tsugaru Strait and Mutsu Bay on 5–10 June 2003 using a numerical weather prediction model. Cool air that accompanies prevailing easterly winds owing to the persistence of the Okhotsk high intrudes into the strait and the bay below 500 m during the nighttime and retreats during the daytime. This cool-air intrusion and retreat induce diurnal variations in the winds in the east inlet of the strait, in Mutsu Bay, and in the west exit of the strait. In the east inlet, a daytime increase in air temperature within the strait produces a large air temperature difference with the inflowing cool air, and the resulting pressure gradient force accelerates the winds. The cool air flowing into Mutsu Bay is heated over land before entering the bay during the daytime. The resulting changes in cool-air depth and in pressure gradient force strengthen the daytime winds. In the west exit, local pressure gradient force perturbations are induced by the air temperature difference between warm air over the Japan Sea and cool air within the strait, and by variations in the depth of low-level cool air. The accelerated winds in the west exit extend southwestward in close to geostrophic balance during the daytime and undergo a slight anticyclonic rotation to westerly during the nighttime owing to the dominance of the Coriolis effect.

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