Suppression of winter heavy precipitation in Southeastern China by the Kuroshio warm current

Abstract

The possible effects of the Kuroshio current and associated sea surface temperature (SST) fronts on Southeastern China winter precipitation are examined using twin simulations of a regional atmospheric model. When the SST frontal features in the forcing data are artificially weakened, the simulated rainfall over Southeastern China, particularly heavy rainfall, is found to increase by a statistically significant amount, compared to the simulations with the observed SST fronts. This difference is attributed to an anomalous regional overturning circulation that interferes with the onshore moisture transport. With the presence of stronger frontal SSTs, an anomalous ascending motion is anchored along the warm current, with a descending branch to its western side, forming a circulation cell that strides across the coasts of Southern China. In days of heavy rainfall over the Southeastern China, the regional atmospheric circulation tunnels oceanic moisture onto land across the coasts, serving as the primary water vapor source for the precipitation. This process is weakened by the anomalous regional overturning circulation in that the imbalance between low-level offshore and upper-level onshore flux drains the land of moisture, and the up-lifted moisture import aloft creates unfavorable condition for land precipitation.