Meso-β Scale Perturbations of the Wind Field by Thunderstorm Cells

Abstract

Analysis of data from the high density storm-scale rawinsonde network of SESAME during the storm events on 2 May 1979 showed the existence of persistent and strong regions of tropospheric convergence and divergence which were detectable on the meso-? scale. In particular, mid- and upper-tropospheric divergence was superimposed over low-level convergence. The divergence, which had a maximum value of 4 ? 10?4 s?1, occurred well upwind (75?100 km) as well as over the tornadic cells. To the south of the storm cells, the kinematic pattern is reversed with upper-level convergence superimposed over low-level divergence. Calculations indicate a vertical motion doublet with ascent (?40 µb s?1) over the squall line and descent (+40 µb s?1) approximately 70 km south of the squall line. It is hypothesized that the above flow fields resulted from a combination of 1) blocking of tropospheric environmental flow by the storm cells, 2) anvil outflows, particularly from the tornadic cells; and 3) divergence from the exit region of the jet stream.