Impacts of recent El Nino Modoki on dry/wet conditions in the Pacific rim during boreal summer

Present work uses 1979-2005 monthly observational data to study the impacts of El Nino Modoki on dry/wet conditions in the Pacific rim during boreal summer. The El Nino Modoki phenomenon is characterized by the anomalously warm central equatorial Pacific flanked by anomalously cool regions in both west and east. Such zonal SST gradients result in anomalous two-cell Walker Circulation over the tropical Pacific, with a wet region in the central Pacific. There are two mid-tropospheric wave trains passing over the extratropical and subtropical North Pacific. They contain a positive phase of a Pacific-Japan pattern in the northwestern Pacific, and a positive phase of a summertime Pacific-North American pattern in the northeastern Pacific/North America region. The western North Pacific summer monsoon is enhanced, while the East Asian summer monsoon is weakened. In the South Pacific, there is a basin-wide low in the mid-latitude with enhanced Australian high and the eastern South Pacific subtropical high. Such an atmospheric circulation pattern favors a dry rim surrounding the wet central tropical Pacific. The El Nino Modoki and its climate impacts are very different from those of El Nino. Possible geographical regions for dry/wet conditions influenced by El Nino Modoki and El Nino are compared. The two phenomena also have very different temporal features. El Nino Modoki has a large decadal background while El Nino is predominated by interannual variability. Mixing-up the two different phenomena may increase the difficulty in understanding their mechanisms, climate impacts, and uncertainty in their predictions.