East Asian Monsoon Forcing and North Atlantic Subtropical High
Modulation of Summer Great Plains Low-level Jet
Abstract
Dynamic influences on summertime seasonal United States rainfall
variability are not well understood. A major cause of moisture transport
is the Great Plains low-level jet (LLJ). Using observations and a dry
atmospheric general circulation model, this study explored the distinct
and combined impacts of two prominent atmospheric teleconnections - the
East Asian monsoon (EAM) and North Atlantic subtropical high (NASH) - on
the Great Plains LLJ in the summer. Separately, a strong EAM and strong
western NASH are linked to a strengthened LLJ and positive rainfall
anomalies in the Plains/ Midwest. Overall, NASH variability is more
important for considering the LLJ impacts, but strong EAM events amplify
western NASH-related Great Plains LLJ strengthening and associated
rainfall signals. This occurs when the EAM-forced Rossby wave pattern
over North America constructively interferes with low-level wind field,
providing upper-level support for the LLJ and increasing mid- to
upper-level divergence.