近30年来南极海冰增长的本质特征及其影响机制

发布时间：2018-08-05 09:16

【摘要】：本文将南极海冰的变化放置在一个较为长期的环境背景中,利用未插值的原始海洋观测资料、陆地站点资料、再分析资料以及卫星反演资料对比分析了1950-1978年和1979-2011年南半球夏季南大洋SST、近地面10m风场以及海平面气压的气候趋势。进一步用ERA-I全球再分析资料分析了1979-2011年南半球中高纬度纬向风的变化,发现西风趋势呈现出非常显著的区域性特征和季节不对称性特征。我们将热带海洋SST、臭氧和温室气体作为模式的三种强迫源,利用三种强迫源的不同组合,通过CAM4大气环流模式进行了4组AMIP实验,并分别提取出各个强迫项对环流异常的贡献。为进一步探究热带海洋对近年来南极气候异常的贡献,我们通过CESM气候耦合模式设计了太平洋起搏器实验,即在海洋里加入向下的潜热通量使得赤道东太平洋的海表面温度尽可能地接近于观测,在耦合模式中强调热带海洋的作用。本文得到的主要结论有：(1)1979-2011年,除南极半岛及周围海域,南大洋海表面温度和表面气温均降低,与南极海冰的扩张相一致。相反,在1950-1978南大洋几乎为一致性的增暖。海平面气压和近地面纬向风在1979年前、后也呈现出相反的变化趋势,例如在前(后)一时间段南大洋的增温(变冷)伴随着西风的减弱(增强)和气压梯度力的降低(升高)。各个彼此独立观测的物理量间相似的时间演变特征强有力地证明了南大洋存在着年代际低频振荡的特征。(2)南半球夏季时间,中高纬度的环流异常主要是受到热带海洋和臭氧的共同作用,温室气体等外强迫对中高纬度环流异常影响微弱；而到南半球秋季时间,环流的异常信号主要集中在太平洋扇区,赤道中太平洋激发的遥相关波列将热带信号传播至太平洋扇区的中高纬度,该区域主要是受到热带海洋的遥相关影响。(3)起搏器实验模拟的SST趋势均在太平洋区域呈现出一个与Interdecadal Pacific Oscillilation (IPO)相似的分布结构,并与观测结果相同。而在南大洋,几乎所有的起搏器实验均呈现出太平洋扇区显著变冷的特征,但南大洋海温大范围变冷和南极海冰缓慢增长的特征却并不显著。尽管如此,出现在太平洋扇区的显著变冷,意味着太平洋扇区是与热带气候紧密联系的关键区域,并进一步证实了南极气候与热带海洋的联系。总之,近年来南极海冰的增长趋势是其年代际变化的一部分,绕极西风的增强通过使南大洋变冷最终导致南极海冰的增长。绕极西风的增强是热带海洋和臭氧的共同作用导致的。尽管我们在耦合模式中强调热带海洋的作用,但对南大洋海温和南极海冰的模拟能力仍较弱。
[Abstract]:In this paper, the variation of Antarctic sea ice is placed in a relatively long-term environmental background, using uninterpolated original ocean observation data, land station data, From 1950 to 1978 and from 1979 to 2011, the climate trends of the Southern Ocean SST, the 10 m wind field near the surface and the sea level pressure in the Southern Hemisphere from 1950 to 1978 and from 1979 to 2011 were compared and analyzed by reanalysis data and satellite inversion data. The variation of latitudinal winds in the Southern Hemisphere from 1979 to 2011 is analyzed by using the ERA-I global reanalysis data. It is found that the westerly wind trends show very significant regional and seasonal asymmetry characteristics. The tropical ocean, ozone and greenhouse gases are used as three forcing sources of the model. Using different combinations of the three forcing sources, four groups of AMIP experiments are carried out through the CAM4 atmospheric circulation model, and the contribution of each forcing term to the circulation anomaly is extracted respectively. In order to further explore the contribution of tropical oceans to Antarctic climate anomalies in recent years, we designed the Pacific pacemaker experiment through the CESM climate coupling model. That is to say, the downward latent heat flux in the ocean makes the sea surface temperature in the equatorial eastern Pacific as close as possible to observations, and emphasizes the role of the tropical ocean in the coupling model. The main conclusions obtained in this paper are as follows: (1) from 1979 to 2011, the surface temperature and surface temperature of the Southern Ocean Sea decreased except for the Antarctic Peninsula and the surrounding sea area, which is consistent with the expansion of Antarctic sea ice. In contrast, the Southern Ocean was almost uniformly warmer in 1950-1978. The sea level pressure and the near-surface zonal wind also showed a reverse trend before 1979, for example, the warming (cooling) of the Southern Ocean was accompanied by the weakening (strengthening) of the westerly wind and the decrease (rise) of the pressure gradient force in a period of time before (after). The similar temporal evolution characteristics among the physical quantities observed independently of each other strongly prove the existence of Interdecadal low frequency oscillation in the Southern Ocean. (2) Summer time in the Southern Hemisphere, The anomaly of circulation in middle and high latitudes is mainly affected by the interaction of tropical ocean and ozone, and the extrinsic forcing of greenhouse gases has a weak effect on the anomaly of circulation in middle and high latitudes, while in the autumn of the southern hemisphere, the anomalous signals of circulation are mainly concentrated in the Pacific sector. Teleconnective wave trains excited in the equatorial central Pacific transmit tropical signals to the mid-high latitudes of the Pacific sector. This region is mainly affected by the teleconnection of tropical ocean. (3) the SST trends simulated by pacemaker experiments all show a similar distribution structure to Interdecadal Pacific Oscillilation (IPO) in the Pacific region, and the results are the same as those observed. However, in the Southern Ocean, almost all pacemaker experiments show significant cooling in the Pacific sector, but the characteristics of large-scale cooling in the Southern Ocean and slow growth of the Antarctic sea ice are not significant. Nevertheless, the significant cooling in the Pacific sector means that the Pacific sector is a key area closely linked to the tropical climate, and further confirms the link between the Antarctic climate and the tropical ocean. In a word, the increasing trend of Antarctic sea ice in recent years is a part of its decadal variation. The increase of circumpolar westerly wind finally leads to the increase of Antarctic sea ice by cooling the Southern Ocean. The enhancement of circumpolar westerly wind is caused by the combined action of tropical ocean and ozone. Although we emphasize the role of the tropical ocean in the coupling model, the ability to simulate the southern ocean sea and Antarctic sea ice is still weak.
【学位授予单位】：中国海洋大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P731.15

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