A tropical Pacific convection ENSO index suitable for measuring the impact of ENSO on the East Asian winter monsoon

The current El Ni & ntilde;o-Southern Oscillation (ENSO) indices are defined based on the sea surface temperature anomalies (SSTAs) in different regions of the equatorial Pacific. Considering that the impact of ENSO on the large-scale atmospheric circulation is mainly through the release of latent heat associated with convection anomalies, we found a zonal dipole distribution of convection anomalies expressed by outgoing long wave radiation anomalies (OLRAs) over the central-western tropical Pacific, which links well with both the ENSO and the East Asian winter monsoon (EAWM). A new index (ITC) based on the anomalous tropical Pacific convection dipole is thus defined to measure ENSO and its impact on EAWM. It is illustrated that the new index ITC can well represent ENSO events. Detailed comparisons are made for the differences in the connections of each ENSO index with the EAWM indices, precipitation and atmospheric circulation over East Asia in winter. It is demonstrated that the ITC is more closely related to the EAWM and can better depict the impact of ENSO on the precipitation and atmospheric circulation over East Asia than the ENSO indices defined by SSTAs.The new ENSO index ITC can act as a single representative among the numerous existing ENSO indices in understanding, monitoring and predicting the impact of ENSO on the EAWM, eliminating the uncertainty and inconvenience that numerous existing ENSO indices defined by SSTAs may have caused.