Delayed effects of large-scale cold surge on winter heavy rainfall in southern China

Abstract

In winter, large-scale cold surges usually invade southern China and cause heavy rainfall in that region. They provide the baroclinic instability and dynamic conditions favorable for the formation of heavy rainfall. Through examining an extreme wintertime heavy rainfall event in southern China, this study demonstrates that a large amount of moisture transportation that originates from the tropical region can be driven by the northern cold surges. Results show that a strong cold surge invade southern China 4 days prior to the heavy rainfall. The residual cold airmass of the cold surge provides an important convergent lifting slope for the formation of heavy rainfall as well as determines its location. The moisture for the heavy rainfall is provided by the southerly flow along the western part of the Philippine Sea anticyclone that owes to the cold surge. As the cold surge intrudes into the Philippine Sea, decreases in temperature and humidity are expected in the lower troposphere, enhancing large-scale downdrafts and sea level pressure and eventually triggering an anticyclone. The Philippine Sea anticyclone reaches its strongest 4 days after the cold surge and activates the low-level moisture pooling in the region of interest. The findings suggest that the large-scale cold surge indirectly stimulates the wintertime heavy rainfall in southern China by a delayed effect of moisture pooling through forming the Philippine Sea anticyclone.