资源环境科技发展态势分析平台

The impacts of different types of El Nino-Southern Oscillation (ENSO) on the interannual negative correlation (seesaw) between the Somali cross-equatorial flow (CEF) and the Maritime Continent (MC) CEF during boreal summer (June-August) are investigated using the ECMWF twentieth-century reanalysis (ERA-20C) dataset and numerical experiments with a global atmospheric model [ the Met Office Unified Model global atmosphere, version 6 (UM-GA6)]. The results suggest that ENSO plays a prominent role in governing the CEF-seesaw relation. A high positive correlation (0.86) exists between the MC CEF and Nino-3.4 index and also in the case of eastern Pacific (EP) El Nino, central Pacific (CP) El Nino, EP La Nina, and CP La Nina events. In contrast, a negative correlation (20.35) exists between the Somali CEF and Nino-3.4 index, and this negative relation is significant only in the EP El Nino years. Further, the variation of the MC CEF is highly correlated with the local north-south sea surface temperature (SST) gradient, while the variation of the Somali CEF displays little relation with the local SST gradient. The Somali CEF may be remotely influenced by ENSO. The model results confirm that the EP El Nino plays a major role in causing the weakened Somali CEF via modifying the Walker cell. However, the impact of the EP El Nino on the Somali CEF differs with different seasonal background. It is also found that the interannual CEF seesaw displays a multidecadal change before and after the 1950s, which is linked with the multidecadal strengthening of the intensity of the EP ENSO.