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Roles of the Intraseasonal Oscillations on Generating the Heat Wave over Yangtze River Valley: Numerical Study and Extended–range Prediction
亓欣
北京师范大学
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 firstly identified the impact of ISOs from tropic/extra-tropic on the period of HW development through partial lateral forcing (PLF) experiments using the WRF model for a typical ISO-related HW event over YRV in 2012. 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 SAH in the late, which jointly established the strong high pressure and caused the HW. Subsequently, the extended-range prediction skill of the HW event was evaluated based on the ECMWF subseasonal reforecast database, and further unravels the close link between the ISO and extended-range prediction of the event. With a two-week lead time, this HW event failed to occur in the reforecast because the predicted surface temperature was significantly underestimated. More detailed analysis demonstrated that the biases for both the intensity and the location of the warming region were primarily attributable to the inaccurate extratropical intraseasonal traveling signals, which indicated that accurately capturing the extratropical intraseasonal signal from the Eurasian continent is indispensable for extended-range prediction of East Asian extreme HW events.