Extended Abstract (240K)8.6
Numerical Simulations of Flanking Line Phenomena
Leigh Orf, University of North Carolina, Asheville, NC; and R. Wilhelmson
Much of the numerical research on the dynamical behavior of isolated supercell thunderstorms has focused on the main updraft/downdrafts and on the tornadic region of the storm. Exploration of flanking line behavior has remained predominately an observational exercise. However, understanding of flanking line dynamics can be important to the understanding of the overall evolution and structure of supercells.
In this study, the evolution and structure of flanking lines and the processes supporting these lines is investigated using a three-dimensional nonhydrostatic cloud model containing ice microphysics. A control simulation is integrated for five hours. This simulation develops a distinct flanking line 45 minutes into the simulation, coinciding with the development of the cold pool. The flanking line exhibits a "stair-stepped" appearance which is commonly observed in the field, and which is supported by theory. The flanking line remains a distinct feature throughout the simulation, and preliminary results indicate that convection initiated along the flanking line near the main updraft is involved in the splitting of the main supercell three hours into the integration. Regions of enhanced vertical vorticity propagate along the flanking line away from the updraft, and the processes forcing these vortices and their effect on storm morphology are investigated.
In addition to the control simulation, simulations with varied environmental soundings are investigated. Preliminary results indicate that supercell morphology is changed dramatically when a weak inversion is included above the mixed layer, and also when the amount of environmental moisture at low and mid levels is changed a fair amount. In some cases, a flanking line is not observed at all. The reasons for this will be studied in light of the fact that many supercells are associated observationally with flanking lines.
Session 8, Numerical Modeling of Severe Storms
Wednesday, 14 August 2002, 8:00 AM-10:00 AM
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