Subtropical SST improved the understanding of the subseasonal reversal of surface air temperature in winter over the mid-high latitudes of Asia

The mid-high latitudes of Asia are cold air gathering places and dust source areas, whose subseasonal reversal of surface air temperature (SAT) between early winter (December 1 to January 14) and late winter (January 15 to February 28) could trigger extreme temperature at mid-low latitudes. Based on the observed interannual variation of SAT over mid-high latitudes of Asia (SAT(MH-A)) in early and late winter after detrending from 1979 to 2021, the across-latitude linkage between the SAT(MH-A) subseasonal reversal and subtropical sea surface temperature (SST) was revealed. The southern Indian Ocean SST anomalies caused the Ural high weakened through meridional circulations and led to a warm SAT(MH-A) in early winter, but had little effect on SAT(MH-A) in later winter. Whereas the North Atlantic SST anomalies enhanced the cold air intrusion in late winter by exciting Rossby wave to strengthen the Ural blocking, while the SAT(MH-A) in early winter was largely unresponsive. The SST factors in Indian Ocean and North Atlantic primarily impacted the SAT(MH-A) in early and late winter respectively. Their synergies effectively modulated the subseasonal reversal, which was conducive to improving the explanation and prediction for the SAT(MH-A )subseasonal reversal. Especially in the winter of 2020/21 and 2021/22, the mean prediction bias was only 0.03 C-degrees and 0.20 C-degrees in early and late winter contributed by the two SST factors. Moreover, the improved prediction ability on the subseasonal scale was also helpful for the accurate predictions of SAT(MH-A) on winter-mean scale. Findings of this study also have the potential to be applied to more accurately predict temperature extremes in mid-low latitudes.