Origin of Enhanced Warm Pool Convection in June over the Western Pacific and Its Importance to Prediction

This study focuses on the enhanced warm pool convection in June over the western Pacific based on the observed outgoing longwave radiation (OLR) data and other reanalysis datasets during 1979–2018. The composite results indicate that a higher sea surface temperature (SST) in the preceding spring due to La Niña events provides a thermal condition for the enhanced warm pool convection in June. Furthermore, the warm pool convection in June is dynamically forced by atmospheric perturbation, especially strengthened tropical westerlies. The enhanced convection in June may also affect the convection anomaly from July to August through local air–sea interactions, which results in a considerable intraseasonal variation for the warm pool convection. Thus, convection in June is important for the prediction of the monthly convection anomaly in the succeeding months. A selected example in June 1984 further indicates that the development of the warm pool convection is excited by the enhanced tropical westerly. Moreover, there is a definite lead–lag relationship between the tropical westerly and the warm pool convection. In contrast, although the warm pool SST is higher in spring due to a strong La Niña in 1989, the warm pool convection in June is not developed due to a weak tropical westerly. Consequently, the intraseasonal variation during summertime was not much greater. Therefore, the combined effects of a higher SST in spring and a strong atmospheric perturbation play important roles in enhancing the warm pool convection in June. On the other hand, the enhanced convection is not antisymmetric to the suppressed convection in the warm pool because the latter is also affected by some other factors such as El Niño.