Regulation of the intraseasonal oscillation over mid-to-high latitude Eurasia on winter surface air temperature over China

Abstract

Using reanalysis and gauge data, the modulation of the intraseasonal oscillation (ISO) both in terms of its phase and amplitude originating from mid-to-high latitude Eurasia on surface air temperature (SAT) over China in boreal winter is investigated. The dominante period of the ISO at mid-to-high latitudes is 10–30 days during boreal winter. Based on an empirical orthogonal function analysis, ISO phase and amplitude over mid-to-high latitude Eurasia are defined. The phase is defined based on the ratio of the first two principal components, and the amplitude is defined as the square root of the sum of the squares of the first two principal components. During Phase 2–5 (6‒1), China is mainly controlled by intraseasonal warm (cold) anomaly air, as the quasi-barotropic ISO anticyclone (cyclone) over mid-to-high latitude gradually propagates southeastward to East Asia. In Phase 2 (Phase 6), the strongest positive (negative) anomaly appears over northern China, while in Phase 3–4 (Phase 7–8) it is over northeastern China, and Phase 5 (Phase 1) in southern China. When the ISO amplitude exceeds one standard deviation, the SAT anomaly over China is enhanced. When the amplitude is under negative one standard deviation, the anomaly over China is evidently weakened and the area passing the statistical significance test is obviously reduced. Modulated by ISO, the extremely high-temperature events over China in boreal winter tend to appear in Phase 3–5, especially in Phase 4, whilst the extremely cold events are likely to occur in Phase 6–1.