Study of a Splitting Anvil Over Iowa on May 15, 1977, Using 3-Minute SMS and Lear Jet Pictures

摘要

A dramatic case of anvil splitting near Des Moines, Iowa was studied through the use of 3-minute SMS and Lear Jet photographs. The storm was situated in an area of vigorous upper divergence and only slight low-level convergence. The split and subsequent decay is related to a strong horizontal shear associated with a passing mesoscale wave. Many of such waves were evident in the analysis and showed a marked effect on cloud formation and dissipation. The waves were characterized by two north-south bands: a cloud (bright) band immediately followed by a cloud-free (dark) band. The 14 km band separation gives a measure of the half-wavelength of the mesoscale wave. 6,480 cloud-motion vectors were obtained using SMS pictures taken at 3 minute intervals. Most of the tracked low-level clouds are 0.7 to 2.0 mile cumulus turrets, which are likely to move with sub-cloud winds.