The Role of Upper-Level Coupling to the Great Plain’s Low-Level Jet Stream and Precipitation

The United States’ Great Plain’s low-level jet (LLJ) is a southerly jet that can be coupled to the large-scale cyclone-anticyclone flow pattern or uncoupled in response to various local land-atmosphere coupling mechanisms. In either case, the LLJ contributes to moisture advection from the Gulf of Mexico into the Great Plains where moisture convergence may produce precipitation or fuel mesoscale convective systems among others. Owing to the large percentage of precipitation that is associated with the LLJ and the multi-billion-dollar livestock and agricultural ventures across the Midwest, characterizing aspects of the LLJ in its current state and its response to climate change forcing is essential.

The current study utilizes the recently released Coupled ERA 20^th Century (CERA-20C) dataset from ECMWF to first develop an objective metric to differentiate those LLJs associated with synoptic-scale, cyclonically forced waves from those LLJs associated with weak upper atmospheric forcing and strong local land-atmosphere coupling. With 110 years of data from the CERA-20C dataset to analyze the LLJ, the summertime seasonal variability, multidecadal trend, and association to precipitation and drought are also investigated. In particular, the relationship between the Great Plain’s LLJ and the large-scale climate drivers, such as El-Niño Southern Oscillation, Pacific North American pattern, and the Bermuda High is investigated to determine the influence these low-frequency modes of variability have on the LLJ variability in the current climate and with climate change.