The leading interannual variability modes of winter surface air temperature over Southeast Asia

The present study analyzes the leading interannual variability modes of Southeast Asian surface air temperature (SAT) during boreal winter. The first Empirical Orthogonal Function (EOF1) mode displays same-sign SAT anomalies over Southeast Asia, with a center around the north Indo-China Peninsula and south China. The second EOF (EOF2) shows a dipole SAT anomaly pattern between the Indo-China Peninsula and south China. Surface heat flux change may not be able to explain SAT variation related to the EOF1, but explain partly the SAT change associated with the EOF2. Atmospheric anomalies play a crucial role in the SAT variations via wind-induced temperature advection. Specifically, for the EOF1, marked northerly anomalies appear over the Southeast Asia, which bring colder air from higher latitude and contribute to negative SAT anomalies. Change in the intensity of Arctic Oscillation, Siberian High and La Nina like sea surface temperature (SST) anomalies over the tropical central-eastern Pacific play a key role in forming the northerly anomalies related to the EOF1. For the EOF2, at the lower troposphere, a pair of anomalous cyclones appears over the tropical north and south Indian Ocean, together with southwesterly wind anomalies extending from the Indian Ocean to the Indo-China Peninsula, which favor positive SAT anomalies there. Formation of the twin cyclones is likely to be a Gill type Rossby wave response of the tropical Indian Ocean SST warming. At the upper troposphere, two wave trains, one originated from the Arctic region and another from the Mediterranean Sea, contribute collectively to the atmospheric circulation anomalies over Southeast Asia related to the EOF2.