Growing season convective systems in the US Corn Belt in relation to land use-land cover and synoptic patterns

Abstract

Localized short-period studies suggest that differences in surface heat uxes between croplands and remnant forest of the U.S. Corn Belt-the dominant Land Use-Land Cover (LULC) types-in uence convective cloud formation in the warm season, primarily around crop-forest boundaries. However, an investigation on climatic timescales is needed to help improve understanding of convective climate in relation to LULC. We use spatial cluster analysis to compare convective systems (CS) from the International Satellite Cloud Climatology Project's Deep Convection Tracking Database to a cropland LULC database for the summer growing seasons (May 1-September 30) of 1999-2007. Spatial-temporal patterns of CS are analyzed with respect to sub-season phenology and LULC type from the National Land Cover Database, and synoptic pressure patterns. The ndings indicate two statistically signi cant clusters of Corn Belt CS; one over the central croplands and the other around crop-forest boundaries in the southeastern area. The clustering of CS, while varying in frequency, remain spatially consistent across sub-seasons and synoptic type. These results suggest a consistent in uence of LULC on CS in the Corn Belt that is modulated by synoptic type to either suppress (e.g., via synoptic-scale subsidence) or enhance (via mid-tropospheric upward vertical motion) the frequency of convective clouds and cloud systems. These LULC related CS clusters are likely the result of Non-Classical Mesoscale Circulations resulting from spatial heterogeneities in the surface energy budget and surface roughness between cropland and remnant forests. This study's results will help inform future modelling projects required to determine these hypothesized LULC-synoptic mechanisms.