第二届未来大气科学论坛

More than half of winter extreme precipitation days in the southern Philippines occurred in La Niña years during 1996-2022. Present study investigates atmospheric circulation patterns and synoptic systems leading to the occurrence of those extreme precipitations. It is found that La Niña winter extreme precipitation in the southern Philippines tends to occur when the East Asian winter monsoon is stronger. Extreme precipitation in the southern Philippines is caused by three synoptic systems: westward moving tropical cyclones and tropical depressions (TCs/TDs) generated in the Philippine Sea, northeasterly cold surges (CSs) originating from the mid-latitude East Asia, and local vortices (LVs). Those synoptic systems act individually or in combination in causing extreme precipitation in the southern Philippines. They are associated with different atmospheric circulation patterns. TCs/TDs play the role when anomalous upper-level divergence over the tropical central Pacific is located northward and the westward steering flows are present over the Philippine Sea, favorable for the westward move of TCs/TDs generated in the Philippine Sea. CSs play the role when the East Asian trough is intensified and the East Asian westerly jet stream is enhanced, which is favorable for the occurrence and southward move of the CSs. LVs play the role when anomalous downward motion over the tropical central Pacific is located southward and anomalous lower-level convergence over the southern Philippines is shifted southward, favorable for the formation of LVs.
 

Extreme precipitation; southern Philippines; La Niña winters; tropical cyclones/depressions; northeasterly cold surges; local vortices