Structures of the circumpolar currents and their interannual variations

南极海洋在全球气候系统中发挥着重要作用，因为世界上所有的海洋都通过它联系在一起。日本在南大洋的活动相对较多，日本破冰船上的海洋观测和Syowa站的海平面观测资料有20多年的积累。这项调查的目的是利用这些资料阐明绕极洋流的结构及其季节和年际变化。研究了洋流边界的洋锋结构，分析了洋锋位置的年际变化。结果揭示了几个长期变化。但详细分析表明，有些变化应解释为船舶航向逐年变化引起的空间变化或锋面结构的变化，而不是年际变化。为了验证得到的海平面年际变化的性质，分析了Syowa站海平面的季节变化和年际变化。结果表明，冬至海平面最高，盛夏最低。这种季节变化的幅度年复一年地变化很大。这种现象只能通过包括盐度在内的海洋变化来解释。现阶段海况与地平面变化的关系尚不清楚，但研究结果表明，海平面变化提供了较好的海洋变化信息。并对冰盖的季节和年际变化进行了研究。

The Antarctic ocean plays important role in the global climate system as all of the worlds oceans are connected through it. The Japanese activities in the southern oceans are relatively high.There are accumulation over 20 years period of the data from oceanographic observations conducted on board of Japanese icebreakers and from sea level observation at Syowa Station. The purpose of this investigation is to clarify the structures of the circumpolar currents and their seasonal and interannual variations by using these data. The structures of the oceanic fronts which give boundaries of currents were investigated, and the interannual variations of their positions were analyzed. The results reveal several long-term variations. But the detailed analysis shows that some of them should be interpreted as the spatial variation due to the change of ship course year by year or as the change of frontal structure rather than as the interannual variation. In order to check the nature of obtained ling-term variations, seasonal and interannual change of sea level at Syowa Station were analyzed. It is found that the sea level is highest in mid-winter and lowest in mid-summer. The amplitude of this seasonal variation is very variable year by year. This phenomenon would be explained only by oceanic change including its salinity. The relation between oceanic condition and gee level change is not clear in the present stage, but the results indicate that sea level change gives good information on oceanic variabilities. The seasonal and interannual change of the ice cover were also investigated.