Mechanisms of the subseasonal influences of Scandinavian events on winter surface air temperature over Eastern China

Abstract

Based on the daily Japanese 55-year Reanalysis dataset from 1958 to 2020, this study reveals that positive-phase Scandinavian (SCA) teleconnection events can cause significant negative surface air temperature (SAT) anomaly over the whole eastern China from 6 to 12 days after the peak day of SCA events. Clearly, the timing of this significant impact exceeds the e-folding timescale of approximately 6 days of SCA events by approximately one week. During the first stage (from peak day to 6 days after peak day), the vertical coupling between the upper and lower tropospheric circulation anomalies over Eurasian continent facilitates the accumulation of cold air masses from the higher latitude to the north of the Tibetan Plateau, which becomes a precursory signal of persistent negative SAT anomaly affecting eastern China. During the second stage (from 7 to 12 days after peak day), the diabatic heating anomaly caused by precipitation anomaly becomes an important factor in the persistence of the negative SAT anomaly over eastern China. Firstly, the persistent negative diabatic heating anomaly near Lake Baikal before day 12 is conducive to the maintenance of anomalously enhanced Siberian High over eastern China. Secondly, corresponding to the gradually southward movement of the positive precipitation anomaly over East Asia, significant negative diabatic heating anomaly gradually substitutes the positive diabatic heating anomaly over East Asia, which is also favorable for the maintenance of the local anticyclonic anomaly. Eventually, the sustained anticyclonic anomaly can induce the persistent negative SAT anomaly over eastern China.