Linkage Between Atmospheric Rivers and Overshooting Convection and Their Roles on UTLS Water Vapor During the North American Monsoon: Insight From DCOTSS

Abstract Overshooting convection significantly impacts the composition of the upper troposphere and lower stratosphere (UTLS), yet its linkage to Atmospheric Rivers (ARs) remains poorly understood. This study investigates how ARs modulate environmental conditions and moisture distribution associated with overshooting convection in the central and southeastern U.S. using data from the 2021–2022 DCOTSS field campaign, GridRad, and ERA5. ARs were most frequent and persistent during May and June, aligning with climatological peaks. Synoptic analysis reveals that AR size, rather than intensity, is positively correlated with overshooting convection, showing a distinct contrast between AR‐associated and non‐AR overshooting events. AR‐associated cases are primarily driven by broad frontal updrafts and large‐scale troughs with strong low‐level jets. Conversely, non‐AR events are characterized by localized, intense updrafts supported by high CAPE within anticyclonic upper jets. Although both types share the Gulf of Mexico as a low‐level moisture source, AR‐associated overshooting convection is distinguished by mid‐level inflow from Pacific westerlies and a near‐doubling of low‐level air mass transport. DCOTSS measurements highlight critical differences in moisture signatures: AR‐associated overshooting convection produces broad water vapor enhancements (∼100 ppmv) concentrated near the tropopause (340–380 K) and features more abundant lower‐level moisture (315–340 K). In contrast, non‐AR events produce narrow, geographically confined enhancements (∼50 ppmv) that penetrate deeper into the stratosphere (380–420 K). These findings demonstrate that AR‐driven moisture pathways, modulated by synoptic‐scale conditions, directly influence both the chemical composition and structural distribution of the UTLS over the North American Monsoon region.