Hodograph Variability within Analytically Modeled, Synoptic-Scale, Baroclinic Systems

Abstract

Although the relationship between the behavior of convective storms and their environmental vertical wind shear has been examined using proximity soundings and idealized numerical modeling experiments, the manner in which the vertical shear profiles, as visualized by hodographs, is regulated by the larger-scale baroclinic wave structure has not been considered in detail. To examine this synoptic-scale dependence, a relatively simple, analytic model for baroclinic systems in midlatitudes having exact solutions for a frictionless, quasigeostrophic atmosphere is employed. The analytical model consists of a checkerboard of high and low pressure areas at 1000 mb, hydrostatically modulated above by a mean meridional temperature gradient and a checkerboard of warm and cold centers at 1000 mb. Aloft, the model atmosphere consists of a zonally oriented wave train. This approach allows a systematic examination of the dependence of hodographs on the following five synoptic-scale parameters included in the model: 1) mean meridional temperature gradient, 2) system wavelength, 3) phase lag between the height and temperature fields at 1000 mb, 4) magnitude of the temperature perturbation associated with the checkerboard of warm and cold centers at 1000 mb, and 5) magnitude of the 1000-mb height perturbation. It is seen that the phase lag between the height and temperature fields and the system wavelength have the greatest quantitative influence on the relative contribution of the ageostrophic wind component to the total wind. These two parameters are associated with significant clockwise curvature with height in the hodograph of the total wind, particularly if the deep-layer ageostrophic wind shear is oriented perpendicular and to the right of the geostrophic shear. Hodograph curvature, however, is not ubiquitous in the model, and despite the model's simplicity, likely speaks to the importance of features departing from the model, mesoscale variability, and boundary layer friction in enhancing hodograph curvature.