Impact of preceding winter sea surface temperature on the spring smoke aerosol dipole over the Indochina Peninsula

Smoke aerosols from biomass burning (BB) in the Indochina Peninsula (ICP) constitute a globally significant source of absorptive aerosols, substantially impacting regional climate and air quality. Over the past four decades, the second dominant mode of spring smoke aerosol distribution over the ICP has exhibited a characteristic north-south dipole pattern. To investigate its driving mechanisms, this study analyzes smoke aerosols and meteorological variables using climate statistics (1980–2024), with a focus on interactions among sea surface temperature (SST), atmospheric circulation, and smoke absorptive aerosol optical depth (SAAOD). Results demonstrate high sensitivity of the SAAOD dipole to meteorological conditions: positive SAAOD anomalies in the northern ICP correspond to decreased humidity, elevated temperatures, and reduced precipitation, while negative anomalies in the southern ICP correlate with increased humidity, enhanced upward motion, and greater precipitation. Singular value decomposition (SVD) analysis reveals a significant correlation (correlation coefficient = 0.41) between the interannual variability of the SAAOD dipole and preceding winter SST anomalies in the Arabian Sea (AS), Bay of Bengal (BOB), and South China Sea (SCS). Mechanistically, warm SST anomalies in these regions drive anomalously strong equatorial westerlies, triggering a coupled cyclone system spanning the BOB and SCS. Convergence of BOB-derived westerly moisture and SCS-derived easterly moisture over the southern ICP fuels intense convection and high precipitation, suppressing BB. Moreover, warm SST anomalies induce a meridional overturning circulation, causing downdrafts over the northern ICP. The anomalous cyclone over the SCS enhances transport of dry continental northeasterlies to the northern ICP. These winds warm the leeward slopes of the Yungui Plateau, generating localized hot, dry conditions conducive to BB.