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A Scale-Discriminating Vorticity Budget for a Mesoscale Vortex in a Midlatitude, Continental Mesoscale Convective System

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  • 1 National Center for Atmospheric Research, Boulder, and Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado
  • | 2 Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado
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Abstract

The authors employ data from the NOAA Wind Profiler Network to present a scale-discriminating vorticity budget for a mesoscale convective vortex (MCV) that was generated by a mesoscale convective system (MCS) in Oklahoma and Kansas on 1 August 1996.

A spatial bandpass filter was used to divide observed wind into mesoscale and synoptic components. Then the authors sought sources and sinks of vorticity in those two components over 9 h of the MCV's lifetime.

The vorticity budget reveals that both the mesoscale and synoptic winds supplied significant vorticity to the MCV. The vortex's origin could not be proved, but data weakly suggest that tilting may have been mostly responsible. Convergence of absolute vorticity by the mesoscale wind was the reason the MCV grew deeper and stronger as the MCS weakened. Finally, tilting of synoptic and mesoscale vorticity by gradients in mesoscale vertical motion was responsible for a secondary deepening of the MCV as the MCS dissipated.

The budget suggests that, if the MCV of 1 August 1996 is representative, completely realistic simulations of MCVs should include planetary vorticity and a plausible, three-dimensionally heterogeneous synoptic wind.

Corresponding author address: Dr. Jason Knievel, NCAR, P.O. Box 3000, Boulder, CO 80307-3000. Email: knievel@ucar.edu

Abstract

The authors employ data from the NOAA Wind Profiler Network to present a scale-discriminating vorticity budget for a mesoscale convective vortex (MCV) that was generated by a mesoscale convective system (MCS) in Oklahoma and Kansas on 1 August 1996.

A spatial bandpass filter was used to divide observed wind into mesoscale and synoptic components. Then the authors sought sources and sinks of vorticity in those two components over 9 h of the MCV's lifetime.

The vorticity budget reveals that both the mesoscale and synoptic winds supplied significant vorticity to the MCV. The vortex's origin could not be proved, but data weakly suggest that tilting may have been mostly responsible. Convergence of absolute vorticity by the mesoscale wind was the reason the MCV grew deeper and stronger as the MCS weakened. Finally, tilting of synoptic and mesoscale vorticity by gradients in mesoscale vertical motion was responsible for a secondary deepening of the MCV as the MCS dissipated.

The budget suggests that, if the MCV of 1 August 1996 is representative, completely realistic simulations of MCVs should include planetary vorticity and a plausible, three-dimensionally heterogeneous synoptic wind.

Corresponding author address: Dr. Jason Knievel, NCAR, P.O. Box 3000, Boulder, CO 80307-3000. Email: knievel@ucar.edu

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