Roles of intra-seasonal oscillations in the sub-seasonal prediction of the long-lasting compound heatwave over southern China in 2010

Abstract Sub-seasonal prediction of regional compound heatwaves and their predictability sources remain unclear. In this study, the underlying mechanisms for the long-lasting compound heatwave over southern China during 1-18 July 2010, and the major sources of its sub-seasonal prediction skill are identified. The results show that both the development and decay of this compound heatwave are mainly dominated by atmospheric processes (i.e., adiabatic heating associated with anticyclonic circulation), whereas land-atmosphere coupling processes play an important role in sustaining the heatwave. A further analysis indicates that by inducing anomalous anticyclonic circulations over southern China, the tropical intra-seasonal oscillations with periods of 30-60 days and 10-30 days facilitate the occurrence and maintenance of the heatwave during its entire and second half periods, respectively. The NCEP Climate Forecast System version 2 shows a low skill in predicting the 2010 compound heatwave over southern China when the lead time is longer than 2 pentads, which is largely attributed to the model's bias in representing the intensity and phase of intra-seasonal oscillations.