scholarly journals Dual-Doppler and Single-Doppler Analysis of a Tornadic Storm Undergoing Mergers and Repeated Tornadogenesis

2007 ◽  
Vol 135 (3) ◽  
pp. 736-758 ◽  
Author(s):  
Joshua Wurman ◽  
Yvette Richardson ◽  
Curtis Alexander ◽  
Stephen Weygandt ◽  
Peng Fei Zhang
Keyword(s):  
Current Analysis ◽  
Convective Storm ◽  
Wind Fields ◽  
Front Structure ◽  
Supercell Storm ◽  
Intensity Parameters ◽  
Tornadic Storms ◽  
First Time ◽  
Vector Wind ◽  
Gust Front

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 second time to form the tornado. The initial tornadogenesis was coincident with the merger of the main supercell and a much smaller convective storm. This tornado, which was always surrounded by substantial precipitation originating from both storms, began to dissipate just a few minutes after genesis, and the rotation both aloft and near the surface weakened substantially. A second storm merger, with a much larger and supercellular storm, was coincident with a reintensification of the mesocyclone aloft, a new hook echo development, and the genesis of a short-lived tornado. After the dissipation of this second tornado, the merger disrupted the structure of the supercell storm, the hook echo was absorbed, and the mesocyclone dissipated. The current analysis suggests a process in which storm mergers may, in sequence, aid tornadogenesis by enhancing surface convergence, or through another mechanism, but subsequently disrupt the tornado’s parent supercell perhaps by cooling the inflow air, with the result being short-lived tornadoes.

scholarly journals Dual-Doppler Analysis of Winds and Vorticity Budget Terms near a Tornado

2007 ◽  
Vol 135 (6) ◽  
pp. 2392-2405 ◽  
Author(s):  
Joshua Wurman ◽  
Yvette Richardson ◽  
Curtis Alexander ◽  
Stephen Weygandt ◽  
Peng Fei Zhang
Keyword(s):  
Three Dimensional ◽  
Wind Fields ◽  
Vertical Vorticity ◽  
Model Predictions ◽  
Vorticity Budget ◽  
Vorticity Generation ◽  
Tornadic Storms ◽  
First Time ◽  
Vector Wind ◽  
Single Set

Abstract Three-dimensional dual-Doppler observations with unprecedented finescale spatial and temporal resolution are used to characterize the vector wind field and vorticity generation terms in and near a weak, short-lived tornado. The beam widths of the two Doppler on Wheels (DOW) mobile radars, at the range of the tornado, are 250 m with gate lengths of 75 m, resulting in a resolution of less than 107 m3. One of the DOWs collected data during the 240 s prior to the formation of the tornado, enabling examination of the genesis process. A single set of volumetric scans suitable for dual-Doppler analyses were completed by both DOWs, permitting the calculation of vertical and horizontal vorticity, divergence, and stretching and tilting terms in the vorticity budget of the large but weak tornado and its surroundings, but no local tendency terms. Analyses of the dual-Doppler vector wind fields document, for the first time in a supercellular tornado, revealed several structures expected to be associated with tornadoes, including the tilting of horizontal vorticity into the vertical near the tornado, and stretching of vertical vorticity in the region of the tornado. The analyses are compared to conceptual and computer models of tornadic storms, confirming the existence of various phenomena and processes, although some model predictions, particularly those concerning the distribution of horizontal vorticity, could not be verified through these analyses. The observed magnitudes of stretching of vertical vorticity and tilting of horizontal vorticity are consistent with those necessary for generating the observed vorticity near the tornado.

Impacts of Assimilating Measurements of Different State Variables with a Simulated Supercell Storm and Three-Dimensional Variational Method

2013 ◽  
Vol 141 (8) ◽  
pp. 2759-2777 ◽  
Author(s):  
Guoqing Ge ◽  
Jidong Gao ◽  
Ming Xue
Keyword(s):  
Potential Temperature ◽  
Three Dimensional ◽  
Horizontal Wind ◽  
Cold Pool ◽  
State Variables ◽  
Wind Fields ◽  
Simulation Experiments ◽  
Supercell Storm ◽  
The Impact ◽  
Analysis Quality

Abstract This paper investigates the impacts of assimilating measurements of different state variables, which can be potentially available from various observational platforms, on the cycled analysis and short-range forecast of supercell thunderstorms by performing a set of observing system simulation experiments (OSSEs) using a storm-scale three-dimensional variational data assimilation (3DVAR) method. The control experiments assimilate measurements every 5 min for 90 min. It is found that the assimilation of horizontal wind can reconstruct the storm structure rather accurately. The assimilation of vertical velocity , potential temperature , or water vapor can partially rebuild the thermodynamic and precipitation fields but poorly retrieves the wind fields. The assimilation of rainwater mixing ratio can build up the precipitation fields together with a reasonable cold pool but is unable to properly recover the wind fields. Overall, data have the greatest impact, while have the second largest impact. The impact of is the smallest. The impact of assimilation frequency is examined by comparing results using 1-, 5-, or 10-min assimilation intervals. When is assimilated every 5 or 10 min, the analysis quality can be further improved by the incorporation of additional types of observations. When are assimilated every minute, the benefit from additional types of observations is negligible, except for . It is also found that for , , and measurements, more frequent assimilation leads to more accurate analyses. For and , a 1-min assimilation interval does not produce a better analysis than a 5-min interval.

scholarly journals Multi-static spatial and angular studies of polar mesospheric summer echoes combining MAARSY and KAIRA

2018 ◽  
Author(s):  
Jorge L. Chau ◽  
Derek McKay ◽  
Juha P. Vierinen ◽  
Cesar La Hoz ◽  
Thomas Ulich ◽  
...  
Keyword(s):  
Direct Evidence ◽  
Middle Atmosphere ◽  
Lower Sensitivity ◽  
Wind Fields ◽  
Receiver Array ◽  
Schmidt Numbers ◽  
Summer Echoes ◽  
Imaging Receiver ◽  
Highly Correlated ◽  
First Time

Abstract. Polar mesospheric summer echoes (PMSEs) have been long associated with Noctilucent clouds (NLCs). For large ice particles sizes and relatively high ice densities, PMSE and NLCs have been shown to be highly correlated at 3-m Bragg wavelengths and are known to be good tracers of the atmospheric wind dynamics. Combining the Middle Atmosphere ALOMAR Radar System (MAARSY) and the Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA), i.e., monostatic and bistatic observations, we show for the first time direct evidence of limited-volume PMSE structures drifting more than 90 km almost unchanged. These structures are shown to have widths of 5–15 km and are separated by 20–60 kms, consistent with structures due to atmospheric waves previously observed in NLCs from the ground and from space. Given the lower sensitivity of KAIRA, the observed features are attributed to echoes from regions with high Schmidt numbers that provide a large radar cross-section. The bistatic geometry allows us to determine an upper value for the angular sensitivity of PMSE echoes at meter scales. We find no evidence for strong aspect sensitivity for PMSE echoes, which is consistent with recent observations using radar imaging approaches. Our results indicate that multi-static all-sky interferometric radar observations of PMSE could be a powerful tool for studying mesospheric wind-fields within large geographic areas.

scholarly journals C-Band Dual-Doppler Retrievals in Complex Terrain: Improving the Knowledge of Severe Storm Dynamics in Catalonia

2020 ◽  
Vol 12 (18) ◽  
pp. 2930 ◽  
Author(s):  
Anna del Moral ◽  
Tammy M. Weckwerth ◽  
Tomeu Rigo ◽  
Michael M. Bell ◽  
María Carmen Llasat
Keyword(s):  
Complex Terrain ◽  
Prediction Models ◽  
Weather Prediction ◽  
Warning System ◽  
Wind Fields ◽  
Severe Thunderstorm ◽  
Radar Network ◽  
Storm Dynamics ◽  
Storm Cells ◽  
First Time

Convective activity in Catalonia (northeastern Spain) mainly occurs during summer and autumn, with severe weather occurring 33 days per year on average. In some cases, the storms have unexpected propagation characteristics, likely due to a combination of the complex topography and the thunderstorms’ propagation mechanisms. Partly due to the local nature of the events, numerical weather prediction models are not able to accurately nowcast the complex mesoscale mechanisms (i.e., local influence of topography). This directly impacts the retrieved position and motion of the storms, and consequently, the likely associated storm severity. Although a successful warning system based on lightning and radar observations has been developed, there remains a lack of knowledge of storm dynamics that could lead to forecast improvements. The present study explores the capabilities of the radar network at the Meteorological Service of Catalonia to retrieve dual-Doppler wind fields to study the dynamics of Catalan thunderstorms. A severe thunderstorm that splits and a tornado-producing supercell that is channeled through a valley are used to demonstrate the capabilities of an advanced open source technique that retrieves dynamical variables from C-band operational radars in complex terrain. For the first time in the Iberian Peninsula, complete 3D storm-relative winds are obtained, providing information about the internal dynamics of the storms. This aids in the analyses of the interaction between different storm cells within a system and/or the interaction of the cells with the local topography.

scholarly journals A Numerical Study of the 6 May 2012 Tsukuba City Supercell Tornado. Part I: Vorticity Sources of Low-Level and Midlevel Mesocyclones

2016 ◽  
Vol 144 (3) ◽  
pp. 1069-1092 ◽  
Author(s):  
Wataru Mashiko
Keyword(s):  
Numerical Study ◽  
Streamwise Vorticity ◽  
Retrograde Motion ◽  
Low Level ◽  
Vortex Lines ◽  
Supercell Storm ◽  
Nested Grids ◽  
Generation Mechanisms ◽  
Eastern Japan ◽  
Gust Front

Abstract On 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 hydrometeors (hereafter hook echo). Most of the circulation for the circuit surrounding the midlevel mesocyclone was conserved, although the baroclinity associated with positive buoyancy within the storm led to an up-and-down trend. The circulation of the material circuit encircling the low-level mesocyclone showed a gradual increase caused by baroclinity along the forward-flank gust front. Friction also had a positive net effect on the circulation. In contrast, most of the negative circulation of the low-level mesoanticyclone was rapidly acquired owing to baroclinity around the tip of the hook echo. Just after tornadogenesis, the low-level mesocyclone intensified significantly and developed upward, which caused retrograde motion of the midlevel mesocyclone.

Simulated Changes in Storm Morphology Associated with a Sea-Breeze Air Mass

2020 ◽  
Author(s):  
Joshua Hartigan ◽  
Robert A. Warren ◽  
Joshua S. Soderholm ◽  
Harald Richter
Keyword(s):  
Front Propagation ◽  
Sea Breeze ◽  
Wind Fields ◽  
Air Mass ◽  
Convective Storms ◽  
Low Level ◽  
Environmental Air ◽  
Homogeneous Environment ◽  
Gust Front

AbstractThe central east coast of Australia is frequently impacted by large hail and damaging winds associated with severe convective storms, with individual events recording damages exceeding AU$1 billion. These storms present a significant challenge for forecasting due to their development in seemingly marginal environments. They often have been observed to intensify upon approaching the coast, with case studies and climatological analyses indicating that interactions with the sea breeze are key to this process. The relative importance of the additional lifting and vorticity along the sea-breeze front compared to the change to a cooler, moister air mass with stronger low-level shear behind the front has yet to be investigated. Here, the role of the sea-breeze air mass is isolated using idealized numerical simulations of storms developing in a horizontally homogeneous environment. The base-state substitution (BSS) modeling technique is utilized to introduce the sea-breeze air mass following initial storm development. Compared to a simulation without BSS, the storm is longer lived and more intense, ultimately developing supercell characteristics including increased updraft rotation, deviant motion to the left of the mean wind vector, and a strong reflectivity gradient on the inflow edge. Separately simulating the changes in the thermodynamic and wind fields reveals that the enhanced storm longevity and intensity are primarily due to the latter. The change in the low-level environmental winds slows gust front propagation, allowing the storm to continue to ingest warm, potentially buoyant environmental air. At the same time, increased low-level shear promotes the development of persistent updraft rotation causing the storm to transition from a multicell to a supercell.

scholarly journals High-Resolution Dual-Doppler Analyses of the 29 May 2001 Kress, Texas, Cyclic Supercell

2006 ◽  
Vol 134 (11) ◽  
pp. 3125-3148 ◽  
Author(s):  
Jeffrey R. Beck ◽  
John L. Schroeder ◽  
Joshua M. Wurman
Keyword(s):  
Conceptual Models ◽  
Striking Similarity ◽  
Airborne Radar ◽  
Surface Boundary ◽  
Synthesis Time ◽  
Low Level ◽  
Time Period ◽  
Tornadic Storms ◽  
Gust Front ◽  
Observation Period

Abstract On 29 May 2001, Doppler on Wheels radars collected data on a supercell near Kress, Texas. The supercellular storm, cyclic in nature, produced multiple mesocyclones throughout its lifetime. Dual-Doppler syntheses were conducted using a grid spacing of 100 m, resulting in the highest-resolution observational analysis of a cyclic supercell to date. In addition, collection of data from ground-based radar allowed for the analysis of near-ground features irresolvable with airborne radar, providing another advantage over previous studies. The syntheses revealed a number of evolving low-level mesocyclones over the observation period of 900 s. While nontornadic during the synthesis period, the supercell exhibited evidence of strong (vertical vorticity greater than 10−2 s−1) low-level circulation with classic cyclic structure and multiple tornadoes beginning 3600 s later. A comparison between the current results, conceptual models, and previous lower-resolution analyses is presented. A striking similarity exists between the cyclic evolution of the Kress storm during the synthesis time period and other previous cyclic conceptual models. However, differences did exist between the Kress storm and previously studied tornadic storms. Analysis showed that the rear-flank downdraft provided the only surface boundary associated with low-level mesocyclogenesis. Other characteristics, including forward-flank gust front structure and the orientation of low-level horizontal vorticity, also differed. In addition, there was a general lack of surface convergence associated with the forward-flank reflectivity gradient, yet convergence associated with the forward-flank gust front increased with height. Finally, a large component of crosswise horizontal vorticity was found to exist throughout the supercell environment, within both the inflow and outflow. Incorporating these differences, an attempt was made to identify possible mechanisms responsible for the lack of tornadogenesis during the synthesis time period.

Comparison of AI-based approaches for statistical downscaling of surface wind fields in the North Atlantic

2021 ◽  
Author(s):  
Vadim Rezvov ◽  
Mikhail Krinitskiy ◽  
Alexander Gavrikov ◽  
Sergey Gulev
Keyword(s):  
Wind Speed ◽  
Statistical Downscaling ◽  
North Atlantic ◽  
Surface Wind ◽  
Surface Winds ◽  
Wind Fields ◽  
The North ◽  
The North Atlantic ◽  
Vector Wind ◽  
Resolution Data

<p>Surface winds — both wind speed and vector wind components — are fields of fundamental climatic importance. The character of surface winds greatly influences (and is influenced by) surface exchanges of momentum, energy, and matter. These wind fields are of interest in their own right, particularly concerning the characterization of wind power density and wind extremes. Surface winds are influenced by small-scale features such as local topography and thermal contrasts. That is why accurate high-resolution prediction of near‐surface wind fields is a topic of central interest in various fields of science and industry. Statistical downscaling is the way for inferring information on physical quantities at a local scale from available low‐resolution data. It is one of the ways to avoid costly high‐resolution simulations. Statistical downscaling connects variability of various scales using statistical prediction models. This approach is fundamentally data-driven and can only be applied in locations where observations have been taken for a sufficiently long time to establish the statistical relationship. Our study considered statistical downscaling of surface winds (both wind speed and vector wind components) in the North Atlantic. Deep learning methods are among the most outstanding examples of state‐of‐the‐art machine learning techniques that allow approximating sophisticated nonlinear functions. In our study, we applied various approaches involving artificial neural networks for statistical downscaling of near‐surface wind vector fields. We used ERA-Interim reanalysis as low-resolution data and RAS-NAAD dynamical downscaling product (14km grid resolution) as a high-resolution target. We compared statistical downscaling results to those obtained with bilinear/bicubic interpolation with respect to downscaling quality. We investigated how network complexity affects downscaling performance. We will demonstrate the preliminary results of the comparison and propose the outlook for further development of our methods.</p><p>This work was undertaken with financial support by the Russian Science Foundation grant № 17-77-20112-P.</p>

Fine gust front structure observed by coherent Doppler lidar at Lanzhou Airport (103°49$^{\prime}$′E, 36°03$^{\prime}$′N)

2020 ◽  
Vol 59 (9) ◽  
pp. 2686
Author(s):  
Yuli Han ◽  
Jie Liu ◽  
Dongsong Sun ◽  
Fei Han ◽  
Anran Zhou ◽  
...  
Keyword(s):  
Doppler Lidar ◽  
Front Structure ◽  
Coherent Doppler Lidar ◽  
Gust Front

Nanometer-Scale Shock-Front Structure in Metals

1988 ◽  
Vol 141 ◽  
Author(s):  
Paul A. Taylor ◽  
Brian W. Dodson
Keyword(s):  
Shock Wave ◽  
Molecular Dynamics ◽  
Shock Front ◽  
Nanometer Scale ◽  
Many Body ◽  
Front Structure ◽  
Atomic Interactions ◽  
The Many ◽  
First Time ◽  
Structural Instabilities

AbstractMolecular dynamics shock wave simulations have been performed, which for the first time include a realistic many-body description of the atomic interactions. The structural instabilities observed in the shock-front structure are dramatically influenced by the many-body effects of these atomic interactions.

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