Start
October 9, 2020 - 3:00 pm
End
October 9, 2020 - 4:00 pm
Categories
Convective Meteorology (Mesoscale Dynamics)Convective Meteorology (Mesoscale Dynamics) Seminar
Prediction of Tornado-Like Vortex (TLV) Embedded in the 8 May 2003 Oklahoma City Tornadic Supercell Initialized from the Sub-Kilometer Grid Spacing Analysis Produced by the Dual Resolution GSI Based EnVar Data Assimilation System
Yongming Wang
Friday, October 9th
3 pm
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Explicit forecasts of tornado-like vortex (TLV) require sub-kilometer grid spacing because of their small size. Most previous TLV prediction studies started from interpolated kilometer grid spacing initial conditions (ICs) rather than sub-kilometer grid spacing ICs. The tornadoes embedded in the 8 May 2003 Oklahoma City tornadic supercell are used to understand the impact of IC resolution on TLV predictions. Two ICs at 500-m and 2-km grid spacings are, respectively, produced through an efficient dual-resolution (DR) and a single-coarse-resolution (SCR) EnVar ingesting a 2-km ensemble. Both experiments launch 1-h forecasts at a 500-m grid spacing. Diagnostics of data assimilation (DA) cycling reveal DR produces stronger and broader rear-flank cold pools, more intense downdrafts and updrafts with finer-scales, and more hydrometeors at high altitudes through accumulated differences between two DA algorithms. Relative differences in DR, compared to SCR, include the integration from higher-resolution analyses, the update for higher-resolution backgrounds, and the propagation of ensemble perturbations along higher-resolution model trajectory. Predictions for storm morphology and cold pools are more realistic in DR than in SCR. The DR-TLV tracks match better with the observed tornado-tracks than SCR-TLV in timing of intensity variation, and in duration. Additional experiments suggest (1) the analyzed kinematic variables strongly influence the timing of intensity variation through affecting both low-level rear-flank outflow and midlevel updraft; (2) potential temperature analysis by DR extends the second track’s duration consistent with enhanced low-level stretching, delayed broadening large-scale downdraft, and (or) increased near-surface baroclinic vorticity supply; and (3) hydrometeor analyses have little impact on TLV predictions.