Impacts of Two East Asian Atmospheric Circulation Modes on Black Carbon Aerosol Over the Tibetan Plateau in Winter

Abstract

Light-absorbing particles over the Tibetan Plateau (TP) can accelerate glacial retreat, thus causing a series of serious environmental and social problems. Previous studies mainly focus on seasonal transport of aerosols over the TP, while the potential factors influencing the subseasonal variation in airborne black carbon (BC) are almost ignored. In this study, the Weather Research and Forecasting coupled with chemistry (WRF-Chem) model and multiple observations are used to investigate the impacts of East Asian atmospheric circulation on BC aerosol over the TP in winter. Results show that the weakness of westerly wind over northern TP, acceleration of westerly wind over southern TP, and eastward shift of East Asia major trough are responsible for the high BC concentration over east slope of the TP. In this circumstance, more BC from northern India can be transported to eastern TP and the south slopes of the TP by the enhanced westerly wind. The intensified southwesterly wind over eastern TP brings more BC from the Sichuan Basin to northeastern TP. The BC can also penetrate to eastern TP in planetary boundary layer. Subsequently, the weakened westerly wind over northern TP and positive anomalous updrafts over east slope of the TP support the accumulation and uplift of BC. Another circulation mode is opposite to the pattern above and results in low BC concentration over the TP. These two circulation modes are possibly associated with the low-level meridional temperature anomaly over East Asia, which modulates the upper level atmospheric circulation through the transient eddy feedback.