Enhanced Spring Frontal Precipitation in Southern China Induced by Anthropogenic Aerosol Mitigation

Abstract

Synoptic fronts are frequent weather systems over East Asia and closely associated with rainfall, especially in spring when frontal activities contribute to most of the precipitation. Aerosols have been considered as an important factor in modulating regional precipitation, and recently the pronounced decreasing trend is observed in China, which could potentially affect frontal precipitation (FP). However, the fast‐response mechanism of how anthropogenic aerosols decline influences FP is not fully explored. Particularly how FP changed after the marked aerosols reduction due to China's stringent air pollution policies has not been well investigated and understood. In this study, we used an objective front identification method to quantify FP across China. During the past two decades, a significant intensification of springtime FP was observed over southern China whereas a weak decrease in northern China, coinciding with the timeline of emission reductions. Model simulations reproduce similar FP variations, accompanied by increased front frequency and precipitation in the south and concurrent decreases in the north. Further analysis suggests decreased aerosols trigger stronger convergence updraft over southern China by changing temperature gradients, thus enhancing atmospheric moisture and favoring FP formation. With further emission reductions under China's carbon neutrality pledge, the contrasting patterns of FP intensity and front frequency driven by stronger temperature gradients are expected to intensify. Therefore, FP over the south will continue to increase while it will decrease over the north in the near future. This work would help understand the influence of air pollution control on regional climate from a synoptic process perspective.