Three-dimensional structure and transport flux of springtime smoke aerosols over the Indochina Peninsula

Springtime smoke aerosols attributable to biomass burning on the Indochina Peninsula (ICP) are a major source of absorbing aerosols globally, and play a nonnegligible perturbing role in climate change. Using smoke extinction profiles provided by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument, and aerosol and meteorological reanalyses for the period 2007-2021, this study investigated the three-dimensional structure and transport flux of springtime smoke aerosols over the ICP. Stratified analysis revealed that CALIOP-derived peaks of smoke aerosol optical depth (SAOD) and smoke mass flux (SMF) at altitudes of 0-2 km occur over the central ICP, which is the main source region. Driven by a southwesterly jet stream and updrafts, massive amounts of smoke aerosols are transported toward the northeast of the ICP, resulting in the largest stratified SAOD and SMF observed at altitudes of 2-4 km. Over the main smoke source regions, the estimated springtime SMF was approximately 0.4 Tg accumulated through a distance of 2 latitude at altitudes of 2-4 km. Meteorological analyses indicated a path for the transport of smoke aerosols to the mid-troposphere. Smoke aerosols in the source region are first lifted thermally to the 600-hPa level. Lifting then continues to the 500-hPa level via the combined effects of topography and frequent, deep, and dry convective updrafts over the mountainous areas of the northern ICP. The smoke aerosols are subsequently transported to South China and the western Pacific owing to strong westerly winds and weak vertical motion. Further analyses demonstrated that differences in meteorological conditions between daytime and nighttime have substantial impact on the vertical structure of smoke aerosols, particularly over the northeast of ICP. Compared to daytime, enhanced updrafts and moisture transport at night favor further lifting of smoke aerosols and greater extinction intensity owing to increased hygroscopic growth.