Two Types of El Nio-related Southern Oscillation and Their Different Impacts on Global Land Precipitation

The contrast between the eastern and central Pacific (EP- and CP-) El Nio is observed in the different responses of zonal and vertical circulation in the tropics. To measure the different responses of the atmospheric circulation to the two types of El Ni, an eastern and a central Pacific southern oscillation index (EP- and CP-SOI) are defined based on the air-sea coupled relationship between eddy sea level pressure and sea surface temperature. Analyses suggest that while the EP-SOI exhibits variability on an interannual (27-yr) time scale, decadal (1015-yr) variations in the CP-SOI are more dominant; both are strongly coupled with their respective EP- and CP-El Nio patterns. Composite analysis suggests that, during EP-ENSO, the Walker circulation exhibits a dipole structure in the lower-level (850 hPa) and upper-level (200 hPa) velocity potential anomalies and exhibits a signal cell over the Pacific. In the case of CP-ENSO, however, the Walker circulation shows a tripole structure and exhibits double cells over the Pacific. In addition, the two types of ENSO events show opposite impacts on global land precipitation in the boreal winter and spring seasons. For example, seasonal precipitation across mainland China exhibits an opposite relationship with the EP- and CP-ENSO during winter and spring, but the rainfall over the lower reaches of the Yangtze River and South China shows an opposite relationship during the rest of the seasons. Therefore, the different relationships between rainfall and EP- and CP-ENSO should be carefully considered when predicting seasonal rainfall in the East Asian monsoon regions.