El Niño Modoki and its possible teleconnection

TL;DR: In this article, the authors found that anomalous warming events different from conventional El Nino events occur in the central equatorial Pacific, where a horseshoe pattern is flanked by a colder sea surface temperature anomaly (SSTA) on both sides along the equator.

Abstract: [1] Using observed data sets mainly for the period 1979–2005, we find that anomalous warming events different from conventional El Nino events occur in the central equatorial Pacific. This unique warming in the central equatorial Pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly (SSTA) on both sides along the equator. empirical orthogonal function (EOF) analysis of monthly tropical Pacific SSTA shows that these events are represented by the second mode that explains 12% of the variance. Since a majority of such events are not part of El Nino evolution, the phenomenon is named as El Nino Modoki (pseudo-El Nino) (“Modoki” is a classical Japanese word, which means “a similar but different thing”). The El Nino Modoki involves ocean-atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution, analogous to the Southern Oscillation in the case of El Nino. Hence the total entity is named as El Nino–Southern Oscillation (ENSO) Modoki. The ENSO Modoki events significantly influence the temperature and precipitation over many parts of the globe. Depending on the season, the impacts over regions such as the Far East including Japan, New Zealand, western coast of United States, etc., are opposite to those of the conventional ENSO. The difference maps between the two periods of 1979–2004 and 1958–1978 for various oceanic/atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline. This appears to be a cause of more frequent and persistent occurrence of the ENSO Modoki event during recent decades.