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Source article

Journal of Climate

Published By

Dr. Dick van der Wateren

Tags

Climatology, Climate and Earth System Modeling, Asian monsoon, Arctic Oscillation


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Global warming makes E Asia winter weather more predictable

24.01.2012, Age: 2521 days

The East Asian winter weather is largely influenced by the Siberian High - the most intense high pressure system on the earth. Scientists from U.S. and Taiwan found that in the past three decades the intensity of the Siberian High tended to reverse between early and middle winter, so that a mild November was often followed by a cold December and January and vice versa. Their analysis showed that this reversal is related to the multi-decadal variation of the Arctic Oscillation (AO), which changed its phase from negative/cold to positive/warm in the late 1970s.

News item submitted by COSIS Member Chih-Pei Chang

During the positive phase the upper troposphere circumpolar flow is more zonal, which makes the occurrence of strong north-south oriented pressure ridges ("blockings") over the Pacific and Ural regions less frequent, to less than once a month. These blocking ridges provide important forcing to supply energy to the Siberian High. When they are strong in November, they are more often weak in December and January. Thus during the positive AO phase a strong Siberian High in early winter is followed by a weak one in middle winter. The reverse is also true.

Several climate model studies predict more positive AO patterns with increased greenhouse gas forcing, which implies that global warming may have the unexpected "benefit" of improving the predictability of middle winter weather in Asia based on the condition in early winter.

The study is led by Chih-Pei Chang, a Naval Postgraduate School professor conducting research at National Taiwan University, and Mong-Ming Lu of Taiwan's Central Weather Bureau. Their paper is being published in Journal of Climate.

Abstract

Current skill in the seasonal prediction of the Asian monsoon falls rapidly north of 40°N, where the Siberian High (SH) is a prominent manifestation of the East Asian winter monsoon (EAWM). Variations in the SH are closely related to winter weather over a large latitudinal span from North Asia to the equator. Here we show that during the three recent decades the SH had an intraseasonal variation that tended to be seasonally-synchronized, which produced an out-of-phase relationship between November and December-January. This implies a special intraseasonal predictability that did not exist in the two previous decades. If this relationship continues, the EAWM will be the only known major circulation system whose intensity can be predicted to reverse from the previous month. We hypothesize that this predictability is related to the reduced frequency of blocking events during the positive phase of the Arctic Oscillation (AO). While this suggests the predictability may diminish if the AO phase is reversed, it may become more prevalent in the future if the prediction of more frequent positive AO-like patterns in a warming world forced by greenhouse gases is borne out.


C.-P. Chang and M. M. Lu, 2012. Intraseasonal predictability of Siberian High and East Asian winter monsoon in recent decades. Journal of Climate. Link to article.


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