科研之友
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摘要
Using NCEP/NCAR reanalysis (NNR) data and 13 models from phase 5 of Coupled Model Intercomparison Project (CMIP5), this study focuses on historical statistics and future change in blocking over key regions (Urals, Baikal, and Okhotsk regions) in Eurasia. The statistical characteristic using NNR data shows that short-duration and long-duration blocking highs are 75 and 25% of the total, respectively. It is also shown that frequency of blocking highs presents a decreased trend in Eurasia during 1956-2006, except blocking highs in summer in Baikal region, long-duration blocking highs in summer, and short-duration blocking highs in winter in Okhotsk region. Compared with NNR, the frequency of blocking highs is underestimated in Eurasia by CMIP5 models, except these with long-duration in the Baikal and Okhotsk regions. Most of the CMIP5 models can reproduce the historical trend of blocking highs over Eurasia during 1956-2005. In addition, projections show that the future change of long-duration blocking highs in Eurasia is not always consistent with that in the whole Northern Hemisphere. The results of the multiple models ensemble (MME) suggest that long-duration blocking highs in the Urals will significantly increase by 0.3 times/10 years (decrease by 0.22 times/10 years) under RCP4.5 (RCP8.5) in the wintertime. In the summertime, the frequency fluctuates with little change. In Okhotsk, long-duration blocking highs will increase by 0.23 times/10 years (decrease by 0.22 times/10 years) in the wintertime (summertime) under RCP4.5. Under RCP8.5, long-duration blocking high frequency will remain the same, and the decreasing trend in the wintertime and the increasing trend (0.32 times/10 years) in the summertime will even accelerate over the trends in the twentieth century.
