The Impact of Crop Areas in Northeast Colorado on Midsummer Mesoscale Thermal Circulations

Abstract

The present study provides a preliminary evaluation of mesoscale circulations forced by surface gradients of heating arising from irrigated areas adjacent to dry land, utilizing a combination of satellite, observational, and modeling approaches. The irrigated crop areas of northeast Colorado were chosen for the study. For the cases studied satellite surface infrared temperature data indicated a typical temperature contrast of approximately 10 K at noon, between the irrigated area and the adjacent dry land. Surface observations and aircraft measurements within the lower region of the atmospheric boundary layer indicated, in general, a significant temperature contrast and moisture difference, thereby implying a potential thermally driven circulation. The anticipated thermally induced flows, however, were reflected in the measurements only by modest changes in the wind speed and wind direction across the contrast location. It is suggested that the daytime, elevated, terrain-forced flow in the area, and the synoptic flow, combined to mask to varying degrees the thermally induced circulation due to the irrigated land-dry land area effect. Numerical model simulations which were carried out over the studied area support this hypothesis. In addition, the impact of the irrigated areas on the moisture within the boundary layer, as well as on potential convective cloud developments is discussed.