Item

Abstract

Wintertime sub-seasonal variability over the Eurasian continent is often accompanied by intense cold air outbreaks in East Asia. On interannual-to-decadal timescales, the wintertime sub-seasonal variability of surface air temperature (SAT) can be modulated by the longer timescale variability of the tropospheric seasonal mean state, which can be remotely influenced by oceanic variability in regions from the tropics to the Arctic. The objective of this study is to examine the interannual-to-decadal modulation of the wintertime sub-seasonal variability at the surface over Eurasia and East Asia. We defined sub-seasonal variability of SAT (SAT-SSV) for each year as a standard deviation of 10-60 days band-passed filtered SAT during a winter season from December through February and applied an EOF analysis to SAT-SSV derived from two sets of atmospheric reanalysis data: JRA55 and ERA-20C. Spatio-temporal structures of the two leading modes for the overlapped period correspond well with each other between the two reanalysis products. The two modes of the SAT-SSV exhibit zonally elongated patterns at different latitudes across the Eurasian continent which correspond well to horizontal gradients of the seasonal-mean SAT. The modes are also associated with seasonal mean, upper tropospheric circulation anomalies that extend circumglobally in the northern hemisphere. The seasonal mean circulation anomalies associated with the 1st mode of SAT-SSV are similar to Arctic Oscillation, whereas those associated with the 2nd mode of SAT-SSV display regional signatures of the North Atlantic Oscillation and Warm Arctic-Cold Eurasia patterns.