A modeling study of the dryline

Abstract

Results of a modeling study of the 24 May 1989 dryline are presented. A non hydrostatic, two-dimensional version of the CSU-RAMS is used to deduce the impact of east-west variability of soil moisture and vegetation on convective boundary layer evolution and dryline formation. The effects of the initial moisture and wind fields and the impact of the Coriolis force on the model results are also examined. Model output is compared with special airborne and sounding observations of the 24 May dryline. Several findings of an earlier observational study of the 24 May dryline are supported in the present study. The modeled drylines are broadly comparable to the observed dryline with respect to the following properties: 1) width, 10 km; 2) strong horizontal moisture and virtual potential temperature gradients, >4 g kg-1/10 km and 2 K/10 km; 3) strong horizontal convergence, updraft, W-E shear of N-S wind component, 8 × 10-4 s-1, 1 m s-1, 10 m s-1/10 km, respectively; 4) bulges of moisture and N-S wind component above the surface dryline location (due to combination of vertical mixing and vertical advection); and 5) elevated moist layer east of the dryline during late afternoon (due to eastward advection of the moisture bulge). -Authors