Changes in the East Asian Winter Monsoon under the AOGCM Global Warming Simulations

The East Asian winter monsoon (EAWM) consists of strong cold air outbreak along the climatological Aleutian low and the strong Siberian High over the Eurasian continent. It is the strongest wind system in the boreal winter. The effect of global warming on the EAWM is studied using 20 state-of-the-art Atmosphere-Ocean coupled General Ciirculation Models. In the previous study, Hori and Ueda (2006) showed that a systematic weakening of the winter monsoon coincides with the weakening of the East Asian jet and the northern shift in the location of the Aleutian low. Such change is governed not only by the effect of the warming effect of the Eurasian continent which leads to a much gradual East-West gradient over the Siberian high and the Aleutian low, but also by the change in tropical SST and convection which drives the so-called local Hadley circulation and thus has an strong influence on the strength of the local jet stream. Another strong factor in this system is the phase of the north Pacific SST, which is dominated by the Pacific Decadal Oscillation (PDO). It is shown that climate models either has strong ties with the tropical SST forcing which indirectly forces the PDO signature, or is more biased towards the influence of the tropical maritime continent. This intricate interactive system poses great challenge in the reliability of future projections in this region.