Study On The Variation Of Arctic Sea Ice And Its Effect On Global Climate

Arctic region is one of the most important parts that contribute to the global climate system. As a cold source of the global climate, changes of Arctic through the movements of atmosphere, ocean, and sea ice can directly or indirectly influence the global-scale atmospheric, oceanic circulations and the variations of global climate, which is thought to be one of the factors driving changes of global climate and environment. It is known that, much more changes of the climate system have occurred in the Arctic region than any other areas for the past 30 years, thus, Arctic region is usually used as an indicator of global warming. Sea ice, as an important component in Arctic region, its variation is closely related to the Arctic climate change, and interacts with other factors of the climate system by different kinds of feedbacks.In this study, monthly averaged SSM/I(Special Sensor Microwave/Imager) sea ice concentration data(1978.10-2002.9,25x25km) and NCEP reanalysis data(1978-2002) are used to analyze the temporal and spatial variations of sea ice in different Arctic areas by using methods of EOF and synthesis data analysis. For the years of which time coefficients of the first-mode ice spatial distribution in north Pacific and north Atlantic are higher than +0.5 or lower than -0.5 respectively, we did the synthetic analysis and the results of atmospheric circulation and sea surface temperature anomaly were studied. In order to study the influence of sea ice variation on global climate, NASA GISS ModelE atmospheric circulation model were employed. Two cases were modeled, the first one used 10-year sea ice extent trend in Arctic ocean as the forcing and the second used 10-year sea ice extent trend in north Pacific as the forcing. According to the model results, we analyzed the responses and its mechanisms of atmospheric circulation and air temperature and compared the results of those two cases. Moreover, the responses of air temperature in China were also studied here.The main conclusions from this study can be drawn as:1) Sea ice in Arctic region has obviously seasonal, interannual and interdecadal variation. It is decreasing rapidly in all, and the decreasing trend is more obvious in summer than that in winter. In summer, Sea ice decrease in inner part of Arctic ocean can not be resumed in a short time.2) The main spatial distribution of Arctic sea ice from EOF analysis in north Pacific part is that the ice area anomalies in Okhotsk is out of phase with that of Bering sea and the time coefficient keeps positive since 1989, which means this mode is the principal pattern how sea ice distributes after 1990s.3) For the reverse phase of the same mode, atmospheric circulation and air temperature of have the obvious opposite phase structure; when the first mode of sea ice distribution in north pacific has the positive phase, positive air temperature anomaly occurs in the Northeast, North and Mongolia with the highest response in northeast China, while the other areas of China remain negative; when the first mode of sea ice distribution in north Atlantic has the positive phase, the temperature anomaly keeps negative all over China. Comparison results between the positive phase of first mode in north Pacific and north Atlantic, show that temperature in the northeast China are opposite, and the atmospheric response in north Pacific is much stronger than that in north Atlantic.4) Model result shows that variations of Arctic sea ice can influence surface heat exchange in local areas by negative feedback mechanism:heat exchange increases with decreasing sea ice extent in Okhotsk and Barents sea; heat exchange decreases with increasing sea ice extent in baring sea.5) Variations of sea ice in Arctic effect on the atmospheric circulation and air temperature in middle and high latitude region strongly. Atrend will intensify AO and the westerly belt, which impairs the south-north heat exchange in high latitude region; Ptrend will destroy AO, impairs Arctic vortices and westerly belt, thus intensify the south-north heat exchange. In winter, variation of Arctic sea ice can influence the air temperature in China:Atrend leads to strong positive temperature response in northeast and strong negative temperature response in most other areas of China, while Ptrend can cause positive response in the east area of China with much weaker intensity.And the response in East and Southwest are reverse for the two trends.China, locating in the middle and high latitude areas of north hemisphere, is influenced by the cold air from Arctic region every year. Study on the mechanisms how variations of Arctic sea ice will influence the climate in China is sure to be very useful for the weather forecast, especially for now when the positive phase of north Pacific sea ice first mode is relating to the positive temperature anomaly in northeast, and north areas of China.