Disparity in Meiyu precipitation in the middle-lower Yangtze River basin during El Niño decay years

Abstract

Meiyu (plume rain) is a distinctive weather phenomenon during boreal early summer, known for its increased precipitation during El Niño decay years bridged through the northwest Pacific anticyclone (NWPAC). It has been widely acknowledged that super El Niño (SEN) events consistently correspond to more Meiyu. This study highlights the instability in the relationship between El Niño and Meiyu, particularly during normal El Niño (NEN) decay years, where the probability of more or less Meiyu is almost equal by statistical analysis. Using the Liang-Kleeman information flow (LIF), our findings confirm that warming in the Maritime Continent (MC) induced by SEN leads to tropical North Atlantic warming in boreal spring. This suppresses northwest Pacific convection via Kevin waves and forms the north-south dipole mode of the NWPAC (EOF2), corresponding to strong Meiyu. Moreover, it is found that subtropical North Pacific cooling induced by NEN leads to the tropical North Atlantic warming in boreal spring via Pacific North American (PNA) pattern, reinforcing the region-wide consistent mode of the NWPAC (EOF1) via Rossby waves and resulting in strong Meiyu. Conversely, warming in the tropical North Atlantic induced by NEN in boreal early summer leads to anticyclonic circulation over the east of Japan (EOF3) and weak Meiyu. The contributions of these three causal structures to the uncertainty of Meiyu are 31 %, 25.7 %, and 28.2 %, respectively. This study sheds new light on the understanding the significance of NEN for Meiyu, emphasizing the importance of its causal relationship with warming in the tropical North Atlantic.