Interannual variability of surface air temperature over indochina peninsula during summer monsoon onset

Previous studies suggest that interannual variability of surface air temperature (SAT) over India peaks in June, a month later than its climatology, which is due to the significant year-to-year variability of abrupt summer monsoon onset. However, April is the hottest month over Indochina Peninsula (ICP), and SAT variability is much larger in April than summer monsoon season which starts in mid-May. The first empirical orthogonal function (EOF) mode of daily-mean SAT evolution over ICP from 1 April to 20 May on the interannual timescale captures 49.6% of total variance, and tends to occur during post-ENSO spring with significant intraseasonal modulations. During post-El Niño April-May, persistent positive SAT anomalies over ICP are associated with anomalous north Indian Ocean warming and tropical Indo-northwestern (TNW) Pacific cooling, which induce a low-level anomalous anticyclonic circulation (AAC) over the TNW Pacific region through coupled ocean-atmosphere feedbacks. The easterly wind anomalies on the southern flank of the AAC induce anomalous warming over ICP by delaying the onset of local monsoonal rainfall. On the intraseasonal timescale, the onset process of ICP summer monsoon is modulated by both 10-20-day and 30-80-day oscillations. At the positive phase of EOF1, the dry spells of both 30-80-day (phase 3 & 4) and 10-20-day (phase 1) are much stronger than the climatology, with consistent easterly wind anomalies over ICP as part of the TNW Pacific AAC, contributing to 9 days late of ICP summer monsoon onset. These results provide important implications for the prediction of both SAT and summer monsoon onset over ICP.