Typhoon has a close relationship with sea surface temperature (SST). On the other hand, the most significant signal for the interannual variation of SST is the El Niño-Southern Oscillation (ENSO) phenomenon. Therefore, the SST data were used to identify two types of El Niño in this study first: east Central-Pacific El Niño (CP El Niño) and Eastern-Pacific El Niño (EP El Niño). Then, we will exam the influence of ENSO on the typhoon genesis location and typhoon track in terms of streamlines and geopotential high analysis at multi-levels.
First, we use combined regression–EOF analysis on SST data to help distinguish CP El Niño and EP El Niño modes. Based upon these two El Niño classifications, the mutual relationship between typhoon and ENSO is analyzed. The analysis time period for Northern Hemisphere is from June to September, while the Southern Hemisphere is from November to February. Using the first mode time series from combined regression–EOF analysis as an index together with its one standard deviation as a criterion, we are able to identify the cases either belong to El Niño or La Niña category. Finally, there are four type category determined: CP El Niño, CP La Nin ̃a, EP El Niño and EP La Niña.
Based upon the composite analysis, it is found that the sequential order of the averaged location for typhoon genesis in the Northwestern Pacific from west to east is CP El Niño, EP El Niño, EP La Niña, and CP La Niña. Meanwhile, the order in the Southwestern Pacific is EP El Niño, CP El Niño, EP La Niña, and CP La Niña. Due to their asymmetric summer SST distribution for Northern and Southern Hemispheres, it is better to exam the distinct features among ENSO episodes in separate Hemispheres although the anomalous SST distributions between them do not show much difference. It appears that the sequential locations order for both the lower level monsoon trough and upper level high pressure together with the high SST region are following that of typhoon genesis accordingly.
In regard to typhoon track issue, we might only focus on the Northwestern Pacific simply because there is no significant steering flow and less typhoon numbers for the Southwestern Pacific. Let us split the typhoons into two types: straight-moving typhoon and recurving typhoon, and then construct their composite mean typhoon tracks, respectively. It turns out that the sequential order from west to east for the typhoon track in both moving types are not only the same with each other but also similar to that of genesis location. The order still are CP El Niño, EP El Niño, EP La Niña, and CP La Niña. Interestingly, the composite contour line of 5880 gpm, generated from 500 hPa geopotential high during each typhoon’s lifetime, also exhibits the same order as that of typhoon track.||en_US|