Characteristics, Mechanisms, and Rainfall Impacts of Warm‐Season Boundary‐Layer Jets in the Dongting‐Poyang Lake Region, South of the Middle Reach of the Yangtze River, China

Boundary‐layer (BL) jets (BLJs) exhibit significant diurnal variations and can strongly influence precipitation. The Dongting‐Poyang Lake region of China experiences frequent BLJs and heavy rainfall, yet systematic studies remain limited. This study investigates southerly and northeasterly BLJs (SBLJs and NEBLJs) in the region, focusing on their spatiotemporal distributions, formation, and precipitation impacts. SBLJs occur most frequently in summer, characterized by strong, deep south–southwesterly flows with warm advection. SBLJs peak around 02:00 Beijing Time (BJT) and weaken after sunrise as the mixed BL develops, with a typical duration of 1–9 hr. NEBLJs occur mainly in spring and fall, featuring strong but shallow northeasterly flows. NEBLJs peak around 22:00 BJT, show weaker diurnal variability, with a higher proportion of long‐duration cases persisting into daytime. Daily‐mean BLJ winds depend on synoptic patterns, while nocturnal intensification is dominated by BL inertial oscillations. Daytime mixing weakens BL winds, and reduced nighttime friction enables inertial oscillations to strengthen BL flows. Differences in seasons, thermodynamic conditions, and BL depth modulate inertial oscillation phases. This causes NEBLJs to peak ∼4 hr earlier than SBLJs. SBLJ‐associated precipitation concentrates at the jet exit region and peaks during pre‐dawn to early morning. Nocturnal BLJ strengthening enhances moisture flux and convergence to favor rainfall, while daytime deviation winds suppress precipitation. NEBLJ precipitation occurs at the jet exit during pre‐dawn to early morning and on its left side in early evening. Of these, exit‐region rainfall results from moisture transport by BL northerly and overlying southerly, combined with terrain‐induced lift.