Roles of the Tropical/Extratropical Intraseasonal Oscillations on Generating the Heat Wave Over Yangtze River Valley: A Numerical Study

Yangtze River Valley (YRV) is the core region for the occurrence of heat wave (HW) in China. HW over YRV has been reported to be associated with intraseasonal oscillations (ISOs) from tropical/extratropical regions. However, the specific roles of these ISOs on the generation of HW cannot be separated in the observational analysis. This study identified the impact of ISOs from tropic/extratropic on the period of HW development through partial lateral forcing (PLF) experiments using the Weather Research and Forecasting model for a typical ISO‐related HW event over YRV in 2012. The observations show that a remarkable eastward/westward extension of South Asian high/western North Pacific subtropical high accompanied the HW occurrence. Accordingly, this anomalous strong high pressure produced the HW through horizontal warm advection and adiabatic heating, which was related to a lower‐level westward propagating meridional dipole anomaly and an upper‐level eastward migrating wave train from the extratropical region. The PLF experiments confirmed that this HW event was caused by the propagation of intraseasonal perturbations from the surrounding regions. The tropical westward propagating meridional dipole anomaly directly generated a lower‐level anomalous anticyclone in the early period of HW development, whereas extratropical intraseasonal forcing primarily contributed to the eastward extension of the South Asian high in the late, which jointly established the strong high pressure and caused the HW. The PLF experiments also indicate plausible tropical–extratropical interaction of intraseasonal perturbations over YRV. Improving the prediction skills of the tropical/extratropical ISOs may facilitate the subseasonal forecast of the local HW events.