The Influence of the North Atlantic Subtropical High on Atmospheric Rivers Over the Eastern United States

Atmospheric rivers (ARs) are a major mechanism for water vapor transport throughout the latitudes with many connections to heavy precipitation events and a myriad of atmospheric phenomena. Eastern United States ARs (EUSARs) have been found to supply moisture to extreme precipitation events over the southeastern United States, as well as interact with tropical moisture exports (TMEs) amongst other hydrological events, posing a significant threat of severe flooding amongst other risk factors. The North Atlantic Subtropical High (NASH), a semi-permanent anticyclone over the subtropical North Atlantic Ocean basin, exhibits a westward expansion and increase in intensity that research has shown has a significant impact on precipitation in the southeastern US and directly contributes to increased precipitation variability over the region. This study utilizes the ERA5 Reanalysis dataset from which integrated water vapor transfer (IVT) was calculated to apply four separate atmospheric river detection tools (ARDTs) with thresholds for IVT magnitude and length. Geopotential heights at 850 hPa were derived from the ERA5 hourly geopotential at that pressure level to identify the strength and position of the NASH using the location of the 1560 gpm isoheight. The hypothesis for this study is that the intensity of the NASH and the westward migration of its western ridge has the potential to influence the behavior of EUSARs by imposing enhanced southerly flow and moisture from the tropics to the mid-latitudes resulting in more intense ARs.