- Meteorological Society of Japan
- 気象集誌. 第2輯 (ISSN:00261165)
- pp.2019-054, (Released:2019-07-05)
Based on the monthly outgoing longwave radiation (OLR) data from 1979 to 2013, a significant correlation of convective activity over the western Pacific warm pool between June and August is detected while there are no significant correlations between June and July and between July and August. The analysis results indicate that consistent anomalies in June and August usually occur during the years with strong warm pool convection. Moreover, two prerequisites are necessary for this consistent anomaly, i.e., a higher sea surface temperature (SST) over the warm pool during the preceding spring and a relatively weak El Niño and Southern Oscillation (ENSO). An analysis based on the selected typical years indicates that convection in June tends to enhance when the warm pool SST is higher in the spring. The enhanced convection, in turn, reduces the solar insolation and local SST and consequently suppresses convection in July. In contrast to June, the local SST tends to increase due to the suppressed convection in July. Accordingly, the warm pool convection in August is subsequently enhanced again. In this process, the local air-sea interaction plays a major role in regulating SST anomalies from June to August and forming the consistent warm pool convection anomalies in June and August. There are additional complications in understanding intraseasonal variation in the warm pool convection from June to August as related to the ENSO forcing. During strong El Niño decaying years (e.g., 1998), the warm pool convection is suppressed with consistent positive OLR anomalies from June to August, implying that the El Niño forcing contributes to the significant positive correlation of convective activity between June and August. During moderate El Niño decaying years (e.g., 2007), however, the convection anomaly in June is opposite to that in August. In general, the local air-sea interaction effect plays an essential role in the significant correlation of convective activity between June and August, though this correlation also depends on the intensity of the El Niño forcing.