Convection Initiation along Soil Moisture Boundaries in the Southern Great Plains

Abstract

Boundaries between two dissimilar air masses have been shown to be the focus region for convection initiation. One feature that has been shown to create these boundaries, as well as mesoscale circulation patterns conducive for convection, is soil moisture heterogeneities. These relationships have been validated in modeling studies, short-term field campaigns, and reanalysis of severe weather events. This study examines the role of soil moisture on convection initiation by using observational data over 7 yr (1998?2004) in the southern Great Plains. A key component to this research is the recently developed daily soil moisture product from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). The locations of convection initiation, based on the Weather Surveillance Radar-1988 Doppler (WSR-88D) data, were compared to volumetric soil moisture values and volumetric soil moisture gradient values. The locations of convection initiation were also examined based on synoptic-type day. On synoptically benign days, increased soil moisture and soil moisture gradient values were associated with decreased convection initiation, to a point. After soil moisture reached 15% (25%) on days with (without) a low-level jet, the likelihood of convection initiation increased. On synoptically primed days, the probabilities of convection initiation were more variable throughout the range of soil moisture values, indicating that the synoptically primed conditions may reduce the influence of soil moisture heterogeneities. Results indicate that a critical value in soil moisture and soil moisture gradient may exist that alters the mesoscale effect of changes in soil moisture on convection initiation, particularly on days that would be classified as synoptically benign.