Diagnosing Different Evolutionary Paths for the Development of Mesoscale Convective Vortices

Open Access
- Author:
- Kirk, James Robert
- Graduate Program:
- Meteorology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 28, 2006
- Committee Members:
- John H Clark, Committee Chair/Co-Chair
Craig F Bohren, Committee Member
Hampton Nelson Shirer, Committee Member
Akhlesh Lakhtakia, Committee Member - Keywords:
- convective
phase plot
MCV
vortices
vortex
mesoscale
convection - Abstract:
- Examination of the literature regarding mesoscale convective vortices (MCVs) exposes incongruity over their origin and development. A vorticity budget analysis conclusively demonstrates that incongruous results are due, at least in part, to different MCV developmental paths. A study of the dynamics of two numerically generated MCVs for the purpose of comparing their evolution from the initial stages to maturity produced the result that the final MCV structure was achieved from different developmental paths. Each MCV was diagnosed using model output from the fifth generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model 5 (MM5). The analysis consisted of detailing the dynamics of MCV formation through diagnosis of the traditional vertical vorticity equation. The results of the study, combined with a comparison with other studies, led to the conclusion that the same mature MCV structure was produced from a variety of dynamical paths. Rewriting the traditional form of the relative vertical vorticity equation in terms of momentum advection curl produced an alternative form of the equation. The re-written equation was used to design a phase- plot depiction of evolutionary growth. When thermodynamics was included in the phase plot by correlating the path to the heating characteristics of the troposphere, the similarities and differences for MCV cases were diagnosed. The application of the phase-plot scheme to several cases showed that, for MCV formation events, there were two interconnected regions that combined to produce the vortex. The upper-middle and upper troposphere vorticity growth was governed primarily by vertical motion with heating driving the vorticity growth in the upper-middle region. The lower-middle and lower troposphere vorticity growth was governed primarily by horizontal motion with the vertical heating gradient driving the vorticity growth in the lower-middle region. In the middle troposphere, evolutionary paths were governed by the relative strengths of heating and heating gradient. Additional phase-plot and mesoscale analysis clarified the characteristics of two MCV formation modes. In some cases heating drove the complete formation of the MCV, whereas in cases with less heating, upper-level dynamics were vital to MCV formation. In total, these results helped synthesize the results of other investigators.