Subseasonal Predictability Sources for Three Successive Episodes of a Prolonged Extreme High Temperature Event over the Yangtze River Basin in the Summer of 2022

In the summer of 2022, the Yangtze River Basin (YRB) experienced the most intense and prolonged extreme high temperature event since 1961, featured by three successive episodes of June 18–29 (P1), July 6–17 (P2) and August 3–26 (P3). An assessment of two operational subseasonal-to-seasonal models reveals that the spatial pattern of surface air temperature (SAT) anomalies over the YRB can be predicted with lead times of 11-12 days, 8-9 days and 15-20 days for P1, P2 and P3, respectively. However, both models underestimate the intensity of maximum SAT anomalies, especially during P3. In P1 and P2, both models fail to reproduce the propagation of Eurasian transient waves at the lead time of 15 days, hindering the development of high-pressure anomalies over East Asia. In P2, additional biases in reproducing the Boreal summer intraseasonal oscillation (BSISO)-like convection anomalies promote the further northward shift of the high-pressure anomaly. These model errors result in poor simulations of local diabatic heating, which is the primary contributor to SAT anomalies over the YRB in P1 and P2. In P3, well-reproduced mid-high-latitude Eurasian transient waves and BSISO-like convection are favorable for simulating SAT anomalies over YRB. Nonetheless, the underestimation of regional adiabatic heating associated with vertical motion in P3 limits the skill in predicting the intensity of SAT anomalies over the YRB. Thus, the ability of accurately capturing the two predictability sources of both Eurasian transient waves and tropical Indo-Pacific convections is key to improve the subseasonal prediction of this prolonged extreme high temperature event over the YRB.