The Relationship Between the Structure of Low-Level Jets and Precipitation Extremes

The relationship between low level jets (LLJs) and precipitation extremes (e.g., drought and flooding) in the southern Great Plains Region is investigated. Structures of the LLJs regarding locations, types, orientations and their affects on precipitation are examined. The Hydrological Years 2006 (a drought year) and 2007 (a flood year) are studied and compared in terms of the distribution, frequency, and characteristics of LLJs and associated precipitation. NCEP North American Regional Reanalysis (NARR), NASA Modern Era Retrospective Analysis for Research and Applications (MERRA), NOAA wind profiler data, and NASA TRMM satellite data products are used. Statistics are calculated for various quantities to relate when and how the LLJs will lead to heavy precipitation events. Composite maps for LLJ periods, centered on the LLJ core, are produced to study the specific effect of LLJs on the surrounding environment.

It is found that LLJs are more likely to produce heavy precipitation when their source regions are from the Gulf area, when the jets are stronger, or when they occur further south. More importantly, it is found that LLJs influence precipitation production and distribution. Specifically, they lead to a local precipitation maximum, which is located downwind of the jet core. Detailed results will be reported during the conference.