The difference of tropical Indian Ocean warming, PJ-pattern, oceanic and atmospheric changes around Philippines Sea and East Asia after two types of El Nino

At the termination year of El Nino event, the tropical Indian Ocean (TIO) SST warming appears in boreal summer accompanying with anomalous anticyclone over the Philippine Sea with negative phase of Pacific-Japan (PJ) teleconnection pattern (i.e., low pressure centered east of Japan) and is related to the increase of mei-yu-baiu rainfall over East Asia. Previous studies showed that above oceanic and atmospheric process becomes dominant after the climate regime shift of 1977. It was reported that there are two types of El Nino: one is strong El Nino type having large positive SST anomalies in the central-to-eastern Pacific (e.g., 1997/98 El Nino), and the other is weak El Nino type that shows weak/medium positive SST anomalies centered at the International Date Line (or El Nino Modoki). At present it is unclear whether or not TIO SST warming and following atmospheric and oceanic variations show different feature between the two El Nino types. The purpose of this study is to explore the differences in TIO SST warming and also related climate variations in the boreal summer of the El Nino termination year between the two El Nino types after the 1977 regime shift. The composite analysis of SST shows that strong El Nino type (occurring in 1982, 1986, and 1998) shows TIO SST warming in boreal summer of El Nino termination year. On the other hand, weak type (occurring in 1991, 1994, 2002, 2004, and 2006) shows other SST anomaly pattern in IO: weak positive SST anomalies and negative SST anomalies appear in the north IO and the south IO respectively. Also, strong type shows clear negative PJ pattern and negative air temperature anomalies especially in the north Japan. Weak type does not show such tendency. In summer of the termination year of weak type El Nino events except for 2002/03 El Nino, anomalies of air-temperature in north Japan are positive or almost zero, in contrast to strong type. The present study indicates that strong type shows clear signals of TIO SST warming, PJ pattern and related climate variations in the boreal summer of El Nino termination year that were pointed out by previous studies, although the weak type shows different behaviors of atmospheric and oceanic condition after El Nino peak from the strong type.