[A-CG43] Multi-scale ocean-atmosphere interaction in the tropics

[ACG43-04] Different ENSO Teleconnections over East Asia in Early and Late Winter and Possible Mechanismes

*WEN CHEN^1,2,3, Xiadong An^1,2,3, TIANJIAO MA^1,2,3,4 (1.Yunnan University, Kunming 650091, China, 2.Yunnan Joint International Laboratory of Monsoon and Extreme Climate Disasters, Yunnan University, Kunming 650091, China, 3.Yunnan Key Laboratory of Meteorological Disasters and Climate Resources in the Greater Mekong Subregion, Yunnan University, Kunming 650091, China, 4.RCAST, The University of Tokyo)

Keywords:East Asian winter climate, ENSO teleconnection, Causal inference, Siberian snow, PCMCI, Liang-Kleeman information flow

The El Nino–Southern Oscillation (ENSO) teleconnections over East Asia display inconsistency between early and late winter, yet the underling physical mechanisms remain unclear. During early winter, ENSO is associated with a Rossby wave train emanating from the tropical Indian Ocean toward East Asia (denoted as tIO-EA). By using partial regression analysis and numerical experiments, we identify that the formation of tIO-EA wave train is closely related to precipitation anomalies in the tropical eastern Indian Ocean and western Pacific (denoted as eIO/wP). The response of eIO/wP precipitation to ENSO is stronger in early winter than in late winter. This can be attributed to the stronger anomalous Walker circulation over the Indian Ocean, which in turn is caused by higher climatological SST and stronger mean precipitation state in the Indian Ocean during early winter. Additionally, employing causal inference analysis, including Liang-Kleeman information flow and PCMCI causal discovery, our study reveals a stable information flow from ENSO to the upper tropospheric atmospheric circulation (250 hPa) over southern East Asia. Building on this, we explore the reason behind the differences in ENSO teleconnections during early and late winter. Findings indicate that Siberian snow water equivalent acts as a ‘land bridge’, storing ENSO signals from early to late winter, which are then released via an ‘atmospheric bridge’ in late winter. Specifically, reduced snow water equivalent from early to late winter facilitates lower surface temperatures in late winter, serving as a cooling source to initiate an ENSO-related wave train over Eurasia. This leads to an inconsistent ENSO teleconnection in late winter, contrasting with early winter, and vice versa.