Land-surface-atmosphere interactions associated with deep convection in Illinois

Geostationary operational environmental satellite (GOES East) imagery are used to investigate a possible spatial clustering of free convective cloud masses along land-cover-type boundaries in the state of Illinois on days with weak synoptic-scale flow. Soil moisture data and a surface cover-type classification system are employed to identify likely cloud formation zones las a function of non-classical mesoscale circulations (NCMCs)) forced by heterogeneous surface fluxes of sensible and latent heat. The emphasis of this research is on documenting the existence of convective cloud clusters and determining locations where they would be expected to occur if land-surface-atmosphere forcing were involved. This research shows that a statistically significant spatial clustering of free convective cloud masses does exist, and that these clusters occur along land-cover-type and soil-order boundaries. The three most conspicuous locations for both the initiation and vertical enhancement of convective clouds are along: (i) the agricultural and mixed forest-agricultural boundary that extends west-east from near St. Louis, Missouri, to Terre Haute, Indiana; (ii) along the urban/suburban Chicago metropolitan area and agricultural boundary in northeast Illinois; and (iii) along the agricultural and agricultural-mixed forest boundary along the Illinois River in east-central Illinois. It is also apparent from composite rawinsonde soundings that a majority of free convective cloud masses develop along land-cover-type boundaries on weak synoptic-scale flow days when planetary boundary layer moisture levels are large. This provides further support for the proposal that non-classical mesoscale circulations (NCMCs) provide the mass convergence necessary to force moist air parcels to the level of free convection along land-cover-type boundaries. These results also suggest that human-modification of the Earth's surface may play a significant role in local-scale climate change. (C) 1998 Royal Meteorological Society.