HIERARCHY OF MESOSCALE FLOW ASSUMPTIONS AND EQUATIONS

The present research proposes a standard nomenclature for mesoscale me teorological concepts and integrates existing concepts of atmospheric space scales, flow assumptions, governing equations, and resulting mot ions into a hierarchy useful in categorization of mesoscale models. Ne w dynamically based mesoscale time- and space-scale boundaries are pro posed, consistent with the importance of the Coriolis force. In the pr oposed flow-class classification, the starting point is the complete ( no approximations) set of mesoscale equations for non-Boussinesq flows . In the subsequent scale analysis, the deep and shallow Boussinesq fl ow divisions of Dutton and Fichtl are kept, as is the shallow-flow sub divisions of Mahrt. In addition, the scale analysis approach of Mahrt is extended to deep Boussinesq motions. Limits of applicability of eac h derived flow-class equation set (with respect to atmospheric phenome na that can be simulated) are also discussed. The proposed hierarchy o f atmospheric motions is organized into hydrostatic versus nonhydrosta tic Bow types and then into non-Boussinesq, deep, and shallow Boussine sq motions, Criteria used to differentiate each resulting flow class a re discussed, while resulting governing thermodynamic and dynamic equa tions for each motion type are given. Separate graphical representatio ns during stable and unstable conditions of the spatial limits of each Boussinesq mesoscale flow subclass are constructed from order of magn itude estimates for the various length and flow-class separation crite ria. A summary of the consensus in the literature concerning the equat ion sets necessary to reproduce characteristics associated with specif ic atmospheric flow phenomena is given. Comparative modeling studies a re required to test the quantitative aspects of many of the ideas put forth in this paper.