Springtime Onset of Isolated Convection in the Central and Eastern United States

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Christopher M Jarrett (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: In the southeast United States (SE US), precipitation is present year-round though with a variety of distinct regimes. Convection organized as isolated precipitation features (IPF), typically isolated afternoon thunderstorms, has a strong annual cycle and accounts for nearly 40% of the total rain during summer. When extracted from the annual precipitation cycle, the seasonal evolution of IPF rain in the SE US is reminiscent of the summer monsoon in other parts of the world. Close examination of this hidden monsoon-like regime of summer thunderstorms may guide our understanding of how subtropical precipitation regimes change as the Earth warms. Recent studies for the SE US have shown that onset of the IPF summer precipitation regime is abrupt, occurring over a few weeks in May. The spatial range of IPF onset across the US is not known. This work (1) extends the analysis to a nine-year temporal period (2003-2011), (2) expands the spatial extent into the Central Plains and northeast US, and (3) determines onset within an array of box regions of 4o x 4o and 2o x 2o in size, while using a new hourly radar dataset. The impact of different array size and rain threshold on the timing and geographic pattern of onset was examined. Results show that for the nine-year average, IPF onset is generally centered geographically on the SE US, but also extends into the mid-Atlantic region and the lower Mississippi River valley. The 4o x 4o box array using the climatological average IPF rain for the SE US as a threshold performed well for the IPF onset analysis. On average, IPF onset begins at the end of April (pentad 24) in south Florida and continues across the southeastern coastal plain into early and mid-May (pentads 27-28). Onset progresses northward and westward in early June (pentads 31-32), with the latest onset in eastern Ohio and the Texas Gulf Coast by mid-late June (pentads 35-36). These results support the hypothesis the springtime increase in moisture and instability from the seasonal the seasonal establishment of the North Atlantic subtropical high is mainly limited to the SE US and is responsible for conditions leading to IPF onset.

Additional Information

Publication

Thesis

Language: English

Date: 2023

Subjects

Geography

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