Things Temporal And Spatial Variation Of The Siberian Sea Ice Area Characteristics And Related Factors

Sea ice has been playing an important role in the variation of physical properties of the sea surface and the change of global climate by the dynamic and thermodynamic processes which result in a series of feedbacks in space and time. The sea ice in Arctic Ocean, as an essential part of the global climate system, the obvious changes of it's extent and thickness are interesting the scientists. East Siberian Sea (ESS), which is one of the Arctic marginal seas, has a significant impact on the climatic and environmental changes in China, and the variation of its sea ice is closely related to the atmospheric circulation system in the Northern Hemisphere and the winter monsoon in the East Asia.This thesis presents the detailed analysis of the annual and inter-annual variability and spatial distribution of the sea ice extent in ESS by using satellite remote sensing dataset, which include the sea ice concentration from the National Snow and Ice Data Center of USA and the Met Office Hadley Center of UK, and the sea surface wind velocity, the surface air temperature (SAT) and the sea level pressure (SLP) from the NCEP-NCAR. The driving mechanism of the change of the sea ice extent is also discussed in this paper.The changes of the sea ice extent in the ESS are characterized by the annual variation. Based on the control factors in the each stage, it could be divided into five stages, namely, packed ice, broken belt along the continental slope, western melting, all-sea melting and autumn freezing. We suggest that divergence of the local wind field is the primary driving element for the main characteristic the sea ice being broken firstly along the continental slope. The runoffs, especially from Indigirka River,Kolyma River,Yana River and Lena River, are the key elements for sea ice melting in the East Siberian Sea.By analyzing the variation of the sea ice cover area in the years of 1997-2005, it is shown that ice cover area increased lightly in 1997-2001 and then it declined heavily in 2002-2005. Generally speaking, the ice area presents a decreasing trend. An ice area index is defined as a quantitative standard to examine the ice condition in the year, the positive value and the negative value of which indicate the heavy ice condition and light ice condition respectively. The duration of the ice melting reflects the speed of the ice melting and freezing and correlated well with the ice area index as well as the negative accumulated temperature of the surface air temperature for the ice freezing. Since 2000, the local wind field was dominated by the southerly wind being of benefit to sea ice moving northward, which produced more ice-free area in which the water gained increasing heat energy resulting in the sea ice melted quickly in the melted stage. However, in the freezing stage, it is disadvantageous to sea ice covered whole Arctic.In recent 50 years, the sea ice concentration presented an obvious decreasing trend as a whole in ESS by 2.0% decade-1, with a stronger reduction of 3.3% decaded-1 in summer. The decreasing rates of the ice concentration rose heavily in recent 10 years. The similar trend happened in the Arctic Ocean and the Chukchi Sea. The primary period of sea ice concentration variation is 2.5 years, with the secondary period of 11.5 years, as well as the primary cycle of local SAT and SLP. The abrupt changes of the ice extent are found in ESS in 1969 and 1990, respectively, with same abrupt change in the AO index,local SAT and SLP in 1989. It shows the direct affect of the atmospheric process on the variation of the sea ice concentration.In the Arctic Ocean, the regions of the most obvious variation of the sea ice concentration are in the Greenland Sea and in the Barents Sea while it is secondary obvious region in the ESS. The most notable regions of variation of the sea ice extent are along Siberian Continent and north of the New Siberian Islands with the light change in the northern continent slope in the ESS. The spatial distribution of the local SAT is characterized by the heavy change of the SAT in the north of the New Siberian Islands and around the Wrang Island. The change of the local SLP is controlled by Arctic Oscillation which influences the variation of the sea ice extent in Arctic Ocean and drives the change of the sea ice concentration further in the ESS.