9.3 A Climatology of Bow Echo Mesovortices

Wednesday, 7 November 2012: 9:00 AM
Symphony I and II (Loews Vanderbilt Hotel)
George Limpert, University of Nebraska, Lincoln, NE; and A. Houston

An important finding of the Bow Echo and MCV experiment was that the strongest and most damaging winds in bow echoes are frequently associated with embedded mesovortices. Despite the importance of mesovortices to severe weather, the current state of mesovortex forecasting and nowcasting is limited due to the short lifetimes of mesovortices and the lack of understanding of mesovortex genesis. Several conceptual models for mesovortex development in mesoscale convective systems (MCSs) have been proposed, most of which are based on the tilting of baroclinically generated horizontal vorticity in downdrafts. Tilting up (down) of vortex lines parallel to the MCS gust front by updrafts (downdrafts) results in couplets of cyclonic and anticyclonic mesovortices. Although model simulations suggest that anticyclonic mesovortices should occur frequently, though not as often as cyclonic mesovortices, only a few anticyclonic mesovortices have been documented. Trapp and Weisman (2003) found that convergence of planetary vorticity was responsible for weakening anticyclonic mesovortices, a reason that is often used to explain the lack of observed anticyclonic mesovortices. However, the modeling simulations suggested that anticyclonic mesovortices should be weaker and shorter-lived than their cyclonic counterparts and does not necessarily explain why they are almost altogether absent in observations. A radar-based climatology of bow echo mesovortices was created using 41 MCS events from 2009 and 2010. The purpose of this climatology is to test hypotheses regarding the frequency and intensity of cyclonic and anticyclonc mesovortices to draw inferences about hypotheses regarding mesovortex genesis, including which of the proposed methods for mesovortex genesis are most frequently responsible for their development. The NSSL mesocyclone detection algorithm, which is designed to detect a wide range of storm-scale circulations, was used to identify mesovortices and a tracking algorithm was created to track mesovortex detections across the domains of multiple radars. A description of the tracking algorithm and the results of the climatology will be presented.
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