The Synergistic Relationship between Soil Moisture and the Low-Level Jet and Its Role on the Prestorm Environment in the Southern Great Plains

Abstract

Changes in low-level moisture alter the convective parameters [e.g., convective available potential energy (CAPE), lifted index (LI), and convective inhibition (CIN)] as a result of alterations in the latent and sensible heat energy exchange. Two sources for low-level moisture exist in the southern Great Plains: 1) moisture advection by the low-level jet (LLJ) from the Gulf of Mexico and 2) evaporation and transpiration from the soils and vegetation in the region. The primary focus of this study is to examine the spatial distribution of soil moisture on a daily basis and to determine the effect it has on the convective parameters. The secondary objective is to investigate how the relationship between soil moisture and convective parameters is altered by the presence of an LLJ. The soil moisture data were obtained through newly developed procedures and advances in technology aboard the Tropical Rainfall Measuring Mission Microwave Imager. The convective parameter data were obtained through the North American Regional Reanalysis dataset. The study examined seven warm seasons (April?September) from 1998 to 2004 and found that the convective environment is more unstable (CAPE > 900 J kg?1, LI < ?2°C) but more strongly capped (CIN > 70 J kg?1) on days with an LLJ present. Spearman?s rank correlation analysis showed a less stable atmosphere with increased soil moisture, after soil moisture reached 5%, on most days. Additional analysis determined that on all synoptic-type days the probability of reaching various thresholds of convective intensity increased as soil moisture values increased. The probabilities were even greater on days with an LLJ present than on the days without an LLJ present. An examination of four days representing each synoptic-type day indicates that on the daily scale the intensity of the convective environment is closely related to the high soil moisture and the presence of an LLJ.