2003年与1999年楚科奇海海冰的差异及其发生原因

DIFFERENCES OF SEA ICE DISTRIBUTION IN CHUKCHI SEA AND THEIR DYNAMIC MECHANISM IN 1999 AND 2003

我国在1999年和2003年进行了两次北极考察,这两年海冰的冰情差别很大,分别对应冰情较重和较轻的年份。本文利用卫星遥感资料对1999年和2003年的海冰分布状况及其差异进行了全面的分析,并利用气温和风场资料深入研究形成这种差异的动力学原因。结果表明, 2003年的海冰冰情与1999年相比要轻很多,海冰面积在春季融冰季节和秋季冻结季节显著减小。2003年春季,来自白令海的海水提早半个月进入楚科奇海,导致海冰大范围融化。但是,到了夏季,海冰的面积减少过程停滞下来。而秋季楚科奇海封冻过程比1999年晚半个月。以上这些特征形成了2003年与1999年海冰的显著差异。研究结果表明, 2003年春季和秋季的气温比1999年要明显增高,最大月平均温差接近18°C,显著的高温为海冰融化的加剧和冻结的推迟提供了热量。直接影响海冰分布的是海面风场,两年风场的差异产生了来自白令海的太平洋入流的差异,对春季海冰融化的提前、夏季入流的减弱和秋季冻结过程的推迟起到关键的作用。季节性气象要素的年际差异可以归因于整个北极的AO系统变化, 2003年AO指数是正值, 1999年为负值,成为楚科奇海局地海冰变化的气候背景。

In this paper,the difference of Chukchi Sea ice distribution in 1999 and 2003 is studied by using the satellite remote sensing data form NSIDC.The results showed that the total sea ice in 2003 was obviously lighter than that in 1999.Sea ice cover was decreased in the spring and autumn of 2003. The sea water coming from Bering Sea passed the Bering Strait and entered into the Chukchi Sea half month earlier than that in 1999,which caused the sea ice melt seriously. However, the increase process of sea ice area was slowed down in July and August of 2003, and the ice area was close to that of 1999. In the autumn, the sea ice freezing process was postponed greatly, at least half month. The difference can better explain the heavy ice we met in 1999 expedition and the moderate ice status in 2003 expedition. The most important reason for lighter ice in 2003 is the higher air temperature (SAT).The SAT in 2003 spring and autumn were much higher than that in 1999, and the highest SAT difference record is about 18°C in coastal area of Alaska. The notable warmer weather provides the extra heat to decrease sea ice in 2003.Another factor acting on Chukchi Sea ice is the difference in wind field between the two years.The water flux from Pacific is greatly affected by the local wind field in both Chukchi Sea and Bering Sea.In 1999, the wind went against the entering of Pacific water in spring,whereas wind in 2003 spring is benefit to the entering.The southern wind occurred in both first few days of November 2003,caused the delay in sea ice freezing in autumn.The disagreement of the meteorologic factors in both years could be attributed to the difference in AO index,a larger scale process. AO index is positive in 2003 and negative in 1999, which determined in great extent the different pattern in both years.