Large-Scale Atmospheric Circulation Patterns Associated With US Great Plains Warm Season Droughts Revealed by Self-Organizing Maps

This study uses a multivariate self-organizing map approach to diagnose precipitation anomalies over the United States' Great Plains during the warm season (April-August) and the associated anomalous large-scale atmospheric patterns, as represented by standardized anomalies of 500 hPa geopotential (Z500 '), integrated vapor transport (IVT '), and convective inhibition index (CINi '). Circulation patterns favoring dryness identified by the method are generally consistent with those shown in previous studies, but this study provides a more comprehensive and probabilistic characterization of those that favor drought over the Southern Great Plains (SGP) and the Central Great Plains (CGP) and their temporal evolutions. Six circulation types that are associated with warm season rainfall variability over the Great Plains are identified. The SGP droughts are attributable to more frequent and persistent northern low-southern high as well as dominant high circulation types and are connected to larger negative CINi '. In contrast, CGP droughts are attributable to more frequent and persistent western low-eastern high, or northern high-southern low, or dominant high patterns, and are linked to a larger negative IVT ', but not larger CINi '. Thus, these results suggest that land surface dryness and a stable atmospheric boundary layer may play a more important role over the SGP than reduced moisture transport in warm season droughts, but reduced moisture transport may play a more important role than thermodynamic stability in droughts over the CGP.