Two Distinct Modes of Tropical Convection Structure and Associated Climate Variability Over East Asia/Korea in January

Abstract

AbstractTwo distinct modes of convection variability over the tropical Indo‐Pacific during January and the associated climate variability over East Asia, especially in Korea, are identified. The first mode (empirical orthogonal functions [EOF1]) exhibits a zonal dipole structure of suppressed convection over the Maritime Continent and enhanced convection over the tropical central Pacific, which represents a typical El Niño response. The second mode (EOF2) is a tripole pattern showing suppressed convection over the eastern Indian Ocean and east of the dateline, and enhanced convection over the tropical western Pacific. The temporal variation of EOF2 exhibits a distinctive positive trend and stronger amplitude after the early 2000s. During the positive phase of EOF2, the sea surface temperature (SST) anomaly pattern displays central Pacific (CP) El Niño, and the associated atmospheric circulation pattern is characterized by a high‐pressure anomaly that directly affects Korea and induces warm and dry conditions. Of the winter months, these distinctive features of EOF2 are particularly evident in January. This study attempts to identify a possible mechanism for the relatively unfamiliar convection structure of EOF2. Enhanced Madden‐Julian Oscillation (MJO) activity over the tropical western Pacific, namely, phases 5, 6, and 7, plays a crucial role in driving the positive phase of the EOF2 convection structure. The recent CP type El Niño, which does not accompany the cold SST anomaly and suppressed convection over the Maritime Continent, may provide favorable conditions for the frequent occurrence of MJO phases 5, 6, and 7.