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

作     者：Marquis, James Richardson, Yvette Markowski, Paul Wurman, Joshua Kosiba, Karen Robinson, Paul 

作者机构：Penn State Univ Dept Meteorol 503 Walker Bldg University Pk PA 16802 USA Ctr Severe Weather Res 1945 Vassar Cir Boulder CO 80305 USA 

出 版 物：《MONTHLY WEATHER REVIEW》 (天气月评)

年 卷 期：2016年第144卷第9期

页      面：3441-3463页

核心收录：

学科分类：07[理学] 070601[理学-气象学] 0706[理学-大气科学] 

基　　金：National Science Foundation [AGS-0801035, AGS-0801041, AGS-1157646, AGS-1211132, AGS-1361237, AGS-1447268] Directorate For Geosciences Div Atmospheric & Geospace Sciences Funding Source: National Science Foundation 

主　　题：Atm/Ocean Structure/ Phenomena Downbursts Supercells Tornadoes Observational techniques and algorithms Radars/Radar observations Models and modeling Data assimilation Numerical analysis/modeling 

摘      要：Storm-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 model) all decrease as the tornado intensifies and matures. The tornado and its parent low-level mesocyclone both dissipate surrounded by a weakening rear-flank downdraft. The decreasing buoyancy of parcels within the low-level mesocyclone may partly be responsible for the weakening of the updraft surrounding the tornado and decoupling of the mid- and low-level circulation. Although the supply of horizontal vorticity generated in the forward flank of the storm increases throughout the life cycle of the tornado, it is presumably less easily tilted and stretched on the mesocyclone-scale during tornado maturity owing to the disruption of the low-level updraft/downdraft structure. Changes in radar-measured tornado intensity lag those of ensemble Kalman filter (EnKF) mesocyclone vorticity and circulation.