Intra-winter atmospheric circulation changes over East Asia and North Pacific associated with ENSO in a seasonal prediction model

Abstract

Though tropical SST anomalies associated with El Nio change slowly during the mature phase of El Nio, the resultant extratropical teleconnection patterns are quite different with time. In this study, the intra-winter changes in the teleconnection pattern associated with El Nio are investigated using the NCEP reanalysis and observational data and the high-resolution seasonal prediction data. The observational analyses show that there are distinctively changes in the teleconnection pattern over the North Pacific within the winter. In the early winter (November-December) of El Nio years, there is a distinctive anomalous Kuroshio anticyclone, which is closely related to the East Asian climate. In January, in contrast, the Kuroshio anticyclone suddenly disappears and a strong cyclonic flow, which is part of the Pacific-North American (PNA) teleconnection pattern, develops. It is suggested that the intra-winter changes are controlled by the relative roles of the equatorial central Pacific (CP) and western north Pacific (WNP) precipitation anomalies on the extratropical teleconnection over the North Pacific. On the other hand, the prediction data failed to capture the observed intra-winter changes in the teleconnection pattern, though the predictive skills for tropical SST and precipitation are high. It is revealed that this model's discrepancy in the extratropical teleconnection is partly originated from the failure in predicting the relative magnitude of CP and WNP precipitation anomalies. Further analyses on the ensemble spread of the prediction data support the relative roles of CP and WNP precipitation anomalies in affecting the extratropical circulation over the North Pacific.