根据PMIP2中的4个海气耦合模式对中全新世气候的模拟结果,利用现代和中全新世两个时间段的冬季海平面气压场(SLP),分析了北大西洋海平面气压的变化情况并计算了这两个时间段的北大西洋涛动(NAO)指数。结果表明,中全新世亚速尔高压加强,冰岛低压加深,南北气压差增加,NAO强度显著增强。对中全新世北大西洋地区SLP进行经验正交函数(EOF)分析显示,4个模式均能捕捉到了NAO的主要结构。中全新世NAO处于正位相的时间较现代提高了10%~30%,其中MIROC3.2提高了29.3%;虽然NAO指数振幅变化不大,但还是能显示中全新世NAO显著强于现代,这与地质资料恢复的结果相一致。对NAO指数的多窗谱分析显示,现代NAO指数存在3~5 a的准周期变化,中全新世NAO指数存在3 a的准周期变化。NAO对中全新世亚洲地区冬季增温有重要影响。北大西洋地区中纬度海面温度(SST)的增温可能是导致中全新世NAO强度增强的一个重要因素。
The mid-Holocene(6 000 years before present) North Atlantic Oscillation(NAO) is studied from the results of four ocean-atmosphere coupled models in the Paleclimate Modeling Intercomparison Project Phase 2(PMIP2).Using winter North Atlantic sea level pressure(SLP),this paper analyze sea level pressure changes in the North Atlantic during the mid-Holocene compared to pre-industrial(1750 AD) control runs and calculate the NAO index of present and mid-Holocene.There is considerable variation in mean SLP(DJF) between 6 ka and 0 ka across models.Features common to all models include a stronger subtropical high pressure center,a deeper Icelandic low and a tendency toward an increased latitude gradient in mean SLP,and therefore a more positive NAO regime during the mid-Holocene compared to present day.The principal structural of NAO was captured well from all of the models through Empirical orthogonal function(EOF) analyses of North Atlantic sea level pressure in winter time(DJF).There is a robust cross-model change in the variance of the NAO time series.In NAO positive phase,the time lasts 10%~30% longer during the mid-Holocene,especially 29.3% longer in MIROC3.2.Although the amplitude of NAO variability show no greater during the mid-Holocene,it can still be found a more positive NAO from all models.Proxy based reconstructions of the NAO indicate a more positive NAO regime during the Mid-Holocene compared to present day.Simulated NAO variability corresponds fairly closed to proxy-based NAO reconstructions.The Multi-Taper Method of Spectrum Analysis shows that there are three-to five-year quasi-cycles in the NAO index at present and three-year quasi-cycles during the mid-Holocene.NAO plays an important role in the Asian winter warming during the mid-Holocene.The positive SST anomalies in mid-latitude North Atlantic might lead to a more positive NAO during the Mid-Holocene.