Change of the wintertime SSTA variability over the west pacific after the mid-1980s: Effect of the increasing el niño modoki

Abstract

From 1949 to 2010, the EOF 1 of sea surface temperature anomalies (SSTA) over the West Pacific (WP) in the boreal winter shows a clear increase during the 1980s, which is associated with the increase in global SSTA. It is found that the characteristics of WP SSTA are different since the mid-1980s. Before the mid-1980s, the first EOF presents a dipole pattern associated with El Niño. After the mid-1980s, EOF1 of WP SSTA captures a uniform SSTA variability over WP and is related to El Niño Modoki. Meanwhile, the dipole SSTA pattern captured by EOF2 is associated with the canonical El Niño. The generation of these two different SSTA patterns might be attributed to the different atmospheric responses to El Niño and El Niño Modoki. The impact of El Niño Modoki over the WP SSTA is significantly enhanced along with the increased occurrences of El Niño Modoki. The increasing intensity of WP SSTA variability has a similar period with that of El Niño Modoki. During El Niño Modoki, the central Pacific SSTA has a leading impact on the development of the WP SSTA by a Rossby wave response. July(0) to October(0) is suggested as a crucial period for the development ofWP SSTA during El NiñoModoki. The increasedwind speed and evaporation might be responsible for the formation ofWP SSTA. After the negative SSTA established, the suppressed convectionwould counteract the impact of evaporation anomaly and prevent the decreasing of WP SSTA.