Synergistic effects of El Niño and the Aleutian Low on spring zonal displacement of WNPSH and associated near-surface temperatures over the Indochina Peninsula

The Indochina Peninsula, located between China and the South Asian subcontinent, serves as a convergence zone for the South Asian monsoon, the East Asian monsoon, and the South China Sea monsoon. Our study reveals that the interannual variability of spring near-surface temperature in the Indochina Peninsula is influenced by the westward extension of the western North Pacific subtropical high (WNPSH). Specifically, the westward extension of the WNPSH leads to a decrease in the low cloud cover over the Indochina Peninsula, resulting in radiation warming and thus an increase in the near-surface temperature. Furthermore, this westward extension of the latter is modulated synergistically by El Niño and the Aleutian Low. El Niño reduces rainfall near the Philippine Sea by weakening the Walker circulation, which acts as a cooling forcing and triggers an anticyclonic anomaly on its northwest side. This contributes to the westward motion of the WNPSH. In addition, the Aleutian Low promotes this westward shift of the WNPSH through a southwesterly flow at its periphery. Further results indicate that there is an 87.5% probability for the WNPSH to move westward with a synergistic modulation by El Niño and the Aleutian Low, compared to 50% without such modulation. Based on these findings, we have developed a prediction model for predicting potential (westernmost point of the WNPSH) of spring near-surface temperature in the Indochina Peninsula using January Niño3.4 index and Aleutian Low index. The correlation coefficient between hindcasting potential during spring from 2014 to 2023 using this model and observations is 0.67.