How do the Pacific and Atlantic Oceans synergize to modulate Southeastern United States Precipitation Variability?

Abstract: This study explores the mechanisms behind anomalous positive and negative rainfall events in the southeastern United States (SEUS), emphasizing the interplay between upper-level large-scale atmospheric teleconnections and the lower-level North Atlantic Subtropical High (NASH). Through a novel conditional weather regime analysis of geopotential height at both lower and upper levels across the Pacific-North America-Atlantic region, we identify distinct clusters representing persistent and recurring circulation patterns originating from the Pacific and Atlantic Oceans. Our analysis of lower-level conditional weather regimes reveals two distinct phases of the NASH that influence rainfall patterns in the SEUS region. In one phase, the weakening and eastward shift of the NASH's northern boundary reduces the central low-level jet, enhances cyclonic circulation, and increases rainfall in the SEUS. In the other phase, the excessive latent heating associated with enhanced SEUS rainfall triggers a wave train pattern that strengthens the intensity of NASH. Conversely, the opposite conditions apply during anomalous negative rainfall events. Additionally, the upper-level conditional weather regime indicates that large-scale dynamics of East Asian summer monsoons trigger the Rossby wave patterns, contributing considerably to the variability in SEUS rainfall from the upper levels. Therefore, our research highlights the crucial role of global atmospheric teleconnections at upper and lower levels in shaping SEUS precipitation patterns.