[A-CG30] Extratropical oceans and atmosphere

[ACG30-P16] Interannual-to-decadal modulation of wintertime sub-seasonal variability over the Eurasia-East Asian sector

*Bunmei Taguchi¹, Kazuaki Nishii², Masato Mori³, Hisashi Nakamura⁴ (1.Faculty of Sustainable Design, University of Toyama, 2.Faculty of Bioresources, Mie University , 3.RIAM, University of Kyusyu, 4.RCAST, The University of Tokyo)

Keywords:teleconnection, Warm Arctic-Cold Eurasia pattern, North Atlantic Oscillation

Wintertime subseasonal variability over the Eurasian continent is often accompanied by intense cold air outbreaks in East Asia. On interannual-to-decadal timescales, the wintertime subseasonal variability of surface air temperature (SAT) can be modulated by the longer timescale variability of the tropospheric seasonal mean state. As remote influence from the Arctic to Eurasia/East Asia has been reported on the interannual time scale, it is of scientific interest and societal importance whether the low-frequency variability in teleconnection from the Arctic to East Asia could modulate the occurrence of shorter time-scale cold events over Eurasia and East Asia. The objective of this study is thus to examine the interannual-to-decadal modulation of the wintertime sub-seasonal variability at the surface over Eurasia and East Asia.

We defined subseasonal 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 SAT-SSV 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.