Northern Hemisphere Sea Ice Variability And Its Relationship With Climate Factors

In the past few decades, sea ice in the Arctic declined rapidly. And there was an accelerating rate of reducing in the annual average sea ice coverage. In2007and2012, September minimum sea ice extent in summer successively reached the lowest value since there were satellite data records. The total sea ice concentration in Arctic decreased. Melt ponds formed near Arctic polar area in summer. There was also a decline in the age of Arctic sea ice. Perennial sea ice coverage decreased, while seasonal sea ice coverage was increasing. The seasonal change of sea ice aggravated. Sea ice is an important part of the Arctic ocean system, and it also plays an important role in the global climate system. Sea ice affects the solar radiation and the exchange of heat and dynamic energy between ocean and atmosphere. Sea ice has an interaction between ocean and atmosphere in different temporal and spatial scales. Studying the variability of Arctic sea ice is of great significance to global climate, ecosystem and human activities.This thesis used the SMMR, SSMI and SSMIS daily sea ice concentration products of1979-2013from the National Snow and Ice Data Center, surface air temperature of NCEP/NCAR reanalysis data and AO, NAO, ENSO indexes to analyze the variability of Northern Hemisphere sea ice concentration, sea ice extent as well as sea ice area in the monthly, multi-year monthly, seasonal and yearly average temporal scales. There was also a discussion of the perennial and seasonal sea ice trends among the35years. And the relationship between Northern Hemisphere sea ice and climate factors was preliminarily discussed here.Northern Hemisphere sea ice concentration declined during the past35years. There was an obvious change in sea ice concentration, especially from2007to2012. The high value area significantly decreased, while the low value area extended to Arctic pole. Northern Hemisphere sea ice concentration peaked in March, and reached the minimum in September. It showed a periodical temporal and spatial difference from the lower and higher latitudes. The regular growth and melting process of sea ice was quite evident in seasonal and annual average scales.The whole Northern Hemisphere sea ice extent and sea ice area were under reduction. Their decline rates were respectively-55.5x106km2a-1and-53.0x106km2a-1annually. Both of them had almost the same change trends in different time scales. The only difference was that sea ice area was relatively smaller than sea ice extent. The Northern Hemisphere perennial ice was mainly distributed in the core region of Arctic Ocean. Its coverage kept shrinking in35years, and it was even sharp in2007. As perennial ice declined, the coverage of seasonal ice gradually occupied most area of Arctic Ocean core region.Characters of sea ice extent, sea ice area, perennial ice and seasonal ice were different in Northern Hemisphere as a whole and in the nine Arctic regions. In addition, the trend of each sea ice area was not alike with the corresponding sea ice extent as well. After comparison, it was found that the seas which affected the whole Northern Hemisphere most were Arctic Ocean core region, Kara and the Barents seas. Their sea ice changes directly influenced the overall characteristics of the Northern Hemisphere sea ice.Correlation coefficients R between Arctic annual average sea ice extent, sea ice area and annual average surface air temperature were as high as0.94. They had very strong negative correlation relationship with each other. Using annual average sea ice extent and sea ice area to do correlation analysis with winter standardization AO and the NAO indexes, the seas which had significant correlations were the Gulf of St. Lawrence, Baffin Bay/Labrador Sea and Hudson Bay. Correlation coefficients between Northern Hemisphere annual average sea ice extent, sea ice area and winter standardization AO passed95%confidence test. And the correlation coefficients with winter standardization NAO passed99%confidence test. In the correlation analysis between ENSO and annual average sea ice extent, it was found that generally during the ENSO El Nino (Warm events) years, sea ice extent increased. On the contrary, it reduced in the ENSO La Nina (Cold events) years.