Precipitation Increases in the Low Hills of Southern Illinois: Part 2. Field Investigation of Anomaly

Abstract

The studies described in the companion paper (Part 1) led to an intensive field study in July 1970. The field study employed networks of recording raingages, wind recorders, and hygrothermographs, along with a meteorological radar, cloud cameras, and a meteorologically-instrumented aircraft. The study occurred in an abnormally dry period with mostly air mass showers (non-frontal storm). These air mass showers were found to be enhanced partially by the moisture derived from the forested hills under low wind speed conditions. In addition, the low speed winds from the south were found to be directed by the valleys within the hills, so as to develop a convergent pattern above the hills where the atmosphere was convectively unstable.