A Comparison of Quasi-Geostrophic Vertical Motion Using Various Analyses

Abstract

Three subjective and two objective analysis techniques were employed to prepare height data for a synoptic case over North America. These heights were used as input to a ten-level quasi-geostrophic model for computation of omegas (vertical velocities in pressure coordinate system) over a grid 2° latitude square. Using a subjective analysis prepared by F. Sanders as a standard, all the techniques gave synoptically acceptable patterns locating the 500-mb low center within one grid square with the intensity within ±20 m. The average height differences at each level for each technique never exceeded 11 m. One subjective and one objective technique did slightly better than the others for the height field. Comparison of the quasi-geostrophic omegas with the Sanders' values shows good agreement for all analysis techniques for the broad scale rising and sinking centers and zero lines. The 500-mb centers are located within one grid interval with the main central values generally within 10?20% of the Sanders' value. Areas enclosed by a given omega isopleth show even better agreement. Overall the subjective analysis prepared by the team of Johnson, Golden, Hudson and Cotter (JGHC) agrees best with the Sanders' results, but the results via Inman's Objective Height Analysis (HOBAN) were quite close.