Observations of vertical wind shear heterogeneity in convective boundary layers

Dual-Doppler wind syntheses from mobile radar observations obtained during the International H₂O Project document some of the spatial variability of vertical wind profiles in convective boundary layers. Much of the variability of popular forecasting parameters such as vertical wind shear magnitude and storm-relative helicity is thought to result from pressure and temperature gradients associated with mesoscale boundaries (e.g., drylines, outflow boundaries, fronts). These analyses also reveal substantial heterogeneity even in the absence of obvious mesoscale wind shifts - in regions many might have classified as "horizontally homogeneous" with respect to these parameters in the past. This heterogeneity is closely linked to kinematic perturbations associated with boundary layer convection. When a mean wind is present, the large spatial variability implies significant temporal variability in the vertical wind profiles observed at fixed locations, with the temporal variability increasing with mean wind speed. Significant differences also can arise between true hodographs and "pseudohodographs" obtained from rawinsondes that are advected horizontally as they ascend. Some possible implications of the observed heterogeneity with respect to forecasting and simulating convective storms also are discussed.