A Two-Dimensional Numerical Sensitivity Study of the Great Plains Low-Level Jet

Abstract

Observations have shown the existence of a diurnal oscillation of the wind profile in the springtime boundary layer of the central United States called the Great Plains low-level jet. This low-level jet is a mesoscale phenomenon that is not easily predicted by larger-scale numerical forecast models, which lack adequate resolution of the boundary layer. It has been postulated that this nocturnal jet can act as a triggering mechanism in the development of localized convective precipitation. If the mechanisms that cause this low-level jet are better understood and modeled, more accurate short-range local forecasts of these convective events could be made. The dominant forcing mechanisms in the development of the Great Plains low-level jet are the coupled frictional and thermal oscillations in the planetary boundary layer. In this study, a two-dimensional planetary boundary-layer model linked with a soil hydrology system is used to determine the sensitivity of the low-level jet to perturbations in the thermal and frictional forces caused by various surface characteristics. This research provides a theoretical analysis of how the thermal and frictional forces are modified by secondary effects such as variation of slope, latitude, soil type, and soil moisture content and distribution. Typical springtime synoptic conditions are used to initialize the forecast model. The magnitude and structure of the simulated low-level jet is very sensitive to small variations in surface slope and soil moisture content and distribution. The jet is affected by variations in latitude and soil type, but relatively large changes in these parameters are necessary to significantly alter the wind profile.