Extended Abstract (196K)P5.6
Scale-discriminating vorticity budget for a mesoscale convective vortex
Jason C. Knievel, Colorado State Univ., Fort Collins, CO; and R. H. Johnson
Formal research of mesoscale convective vortices (MCVs) is less than two decades old. For most of that time, the sparsity of operational tropospheric soundings has limited the scope of MCV studies. Although operational soundings of temperature and dew point over the Plains, where most MCVs in the United States form, are still available only semi-daily from stations approximately 350 km apart, the recently established NOAA Profiler Network (NPN) has made available hourly soundings of wind at up to twice the spatial resolution of operational soundings from radiosondes.
The authors use data from the NPN to construct a vorticity budget for an MCV that was generated by a mesoscale convective system (MCS) in the Great Plains. Barnes analyses are employed as filters to separate observed hourly wind into two components. The first component is predominately a synoptic background flow and the second component is predominately a mesoscale perturbation on that background flow. This method allows both components of the observed wind to vary in all four dimensions. The vorticity budget is for an area centered on the MCV and depicts tendencies of vertical vorticity from horizontal advection, vertical advection, divergence, and tilting. Tendencies from these four terms are further subdivided into contributions from the synoptic background wind, the mesoscale perturbation in wind, and combinations of the two.
Results indicate that as the MCS matured, the MCV strengthened and deepened primarily from convergence of total vertical vorticity in the middle troposphere. As the MCS dissipated, the MCV weakened slightly but deepened considerably more due to tilting in the upper troposphere. The budget also reveals a few consistent sources of vertical vorticity throughout the nine hours of detailed observations of the MCV. The largest contributor to tendency from horizontal advection was advection of mesoscale vorticity by the synoptic wind. The largest contributor to tendency from vertical advection was advection of mesoscale vorticity by mesoscale vertical motion. The two largest contributors to tendency from divergence were divergence of both synoptic vorticity and mesoscale vorticity by the mesoscale wind. Finally, the two largest contributors to tendency from tilting were from horizontal gradients of mesoscale vertical motion acting on both the mesoscale vertical wind shear and the synoptic vertical wind shear.
Poster Session 5, New insights regarding mesoscale structure based on recent field experiments and new observing platforms—with Coffee Break
Wednesday, 1 August 2001, 2:30 PM-4:00 PM
Previous paper Next paper