Arctic Oscillation Was a Precursor Signal of Compound Cold–Wet Events in the Yangtze River Basin During the 2023/24 Winter

ABSTRACT During the boreal winter of 2023/24, persistent precipitation with cold‐air outbreaks over the Yangtze River basin (YRB) resulted in severe compound cold–wet events, causing disastrous impacts on local transportation and agriculture. The subseasonal causes of these persistent extreme events remain unclear. Our findings revealed that the phase of the surface air temperature (SAT) intraseasonal oscillation (ISO) preceded the counterpart of precipitation by 4–5 days, indicating its dominant role in regulating precipitation anomalies over the YRB. SAT anomalies can be attributed to Rossby wave trains originating from the Arctic and midlatitude North Atlantic. The 10–30‐day ISO of the Arctic Oscillation (AO) index leads SAT and precipitation anomalies in the YRB by 3–8 days, serving as a precursor signal of these anomalies. Historical analyses show that since 1979/80, when winter AO index exhibited strong 10–30‐day ISO, both ISO of SAT and AO anomalies have undergone sign reversals during wet and dry processes. Following the peak of wet (dry) ISO events, colder (warmer) SAT anomalies enhanced the likelihood of compound cold–wet (warm–dry) events. Therefore, the 10–30‐day AO can be considered a valuable precursor signal for subseasonal predictions for compound events in the YRB during the boreal winter.