Regional air-sea coupled model simulation for two types of extreme heat in North China.

Extreme heat (EH) over North China (NC) is affected by both large scale circulations and local topography, and could be categorized into foehn favorable and no-foehn types. In this study, the performance of a regional coupled model in simulating EH over NC was examined. The effects of regional air-sea coupling were also investigated by comparing the results with the corresponding atmosphere-alone regional model. On foehn favorable (no-foehn) EH days, a barotropic cyclonic (anticyclonic) anomaly is located to the northeast (northwest) of NC, while anomalous northwesterlies (southeasterlies) prevail over NC in the lower troposphere. In the uncoupled simulation, barotropic anticyclonic bias occurs over China on both foehn favorable and no-foehn EH days, and the northwesterlies in the lower troposphere on foehn favorable EH days are not obvious. These biases are significantly reduced in the regional coupled simulation, especially on foehn favorable EH days with wind anomalies skill scores improving from 0.38 to 0.47, 0.47 to 0.61 and 0.38 to 0.56 for horizontal winds at 250, 500 and 850 hPa, respectively. Compared with the uncoupled simulation, the reproduction of the longitudinal position of Northwest Pacific subtropical high (NPSH) and the spatial pattern of the low-level monsoon flow over East Asia are improved in the coupled simulation. Therefore, the anticyclonic bias over China is obviously reduced, and the proportion of EH days characterized by anticyclonic anomaly is more appropriate. The improvements in the regional coupled model indicate that it is a promising choice for the future projection of EH over NC. [ABSTRACT FROM AUTHOR]