Record-breaking summer rainfall in the Asia-Pacific region attributed to the strongest Asian westerly jet related to aerosol reduction during COVID-19

The Asia-Pacific region suffered record rainfall in summer 2020, which was accompanied by the strongest Asian subtropical westerly jet (ASWJ) of the past four decades. Meanwhile, the COVID-19 pandemic spread rapidly around the world, resulting in an abrupt reduction in emissions in East Asia. Here, we investigate whether the enhanced ASWJ induced by plummeting aerosols contributed to the record-breaking rainfall. The results show that tropospheric warming in Southeast Asia, in particular southern China, due to local aerosol reduction, acted to increase the meridional temperature gradients in the mid-lower troposphere, which supported a strong ASWJ in the upper troposphere via the thermal wind balance. The latter enhanced divergence in the upper troposphere over the Asia-Pacific region, which provided a favorable ascending motion for the record rainfall that took place there. Therefore, against a background of carbon neutrality (i.e. the reduction in aerosols), our results imply more strong summer rainfall in the Asia-Pacific region.