The region of Midwestern North America from 80-95° W and 35-55° N is examined in terms of land cover and convective cloud cover during the summers of 1985 and 1989, using a combination of published land use maps and GOES visible and infrared satellite imagery, for the presence of favoured convective cloud cover over large areas (˜ 100 km scale) of homogeneous forest. Days with synoptic flow are eliminated through analysis of 500-mb winds and surface frontal activity. The resulting ‘weak flow’ days’ imagery is organized into 1° × 1° latitude/longitude cells, within which total cumulus cloud cover is manually determined. Three-hourly analysis of convective cloud cover from visible and infrared imagery shows forests in Ontario and the Appalachians to have greater convective cloud cover and the Great Lakes to have less convective cloud cover, on days without frontal activity. This pattern persists throughout the day, for both 1985 and 1989, despite differences in soil moisture (as determined from Crop Moisture and Palmer Drought Indices) and topography. The apparent associated cloud cover increase over forests for the Midwest matches well with similarly predicted patterns of cloud and precipitation from the existence of weak non-classical mesoscale circulations
展开▼
