Decadal Regime Shift Of Arctic Sea Ice And Corresponding Effects On Extreme Low Temperature

Based on daily surface air temperature dataset from NCEP/NCAR (NationalCenters for Environmental Prediction/National Center for Atmospheric Research)from1979to2012over mid-high latitudes of the Northern Hemisphere andatmospheric model simulations (GCM ECHAM5), it is found that the decreasingtrend of Arctic SIE showed a remarkably decadal regime shift. Mutations occur in1997, sea ice loss is slower and inter-annual oscillations are significant during1979to1996; while during1997to2012, the loss is accelerated and inter-annual oscillationsare less significant. However, after2007the oscillation increases sharply.In the context of the decadal transformation of the Arctic sea ice, extreme lowtemperature are studied for different grids. For the study area covers a vast area andtemperature has a regional distribution, we define extreme low temperature thresholdby using the percentage method. It is concluded that there is a significant regionalcharacteristics in frequency of extreme low temperature over mid-high latitudes of theNorthern Hemisphere. During1979to1996, regions where extreme low temperaturehave significant tendency distribute separately. The whole tendency shows a spatialdistribution of hemispheric seesaw. While, during1997to2012, the tendency ofextreme low temperature appears a north-south oscillation between the Arctic andmid-latitude regions. There appears a significant increase in extreme low temperatureover mid-latitudes of Eurasia; a decrease over Barents sea.In order to reveal the impact mechanism of extreme low temperature, regressionanalysis is used to analyze related atmospheric circulations associated with twoperiods. It is showed that the North Atlantic Oscillation is closely related withfrequency of extreme low temperature during1979to1996. When the North AtlanticOscillation in its positive phase, cold air gathers in the polar regions and is not easilymoves to mid-latitude. Then prevailing wind in Europe is west wind, and thereappears a warmer winter, which are consistent with previous researches. In certain extent this explains the North Atlantic Oscillation may lead to the pattern of frequencyof extreme low temperature during1979to1996. Conversely, during1997to2012,there appears a spatial pattern of out-of-phase oscillation between the Arctic andmid-latitude of Northern Hemispheres. In the role of the Siberian high pressure,anticyclonic system will send north wind and north-east wind towards mid-latitude,which will lead to abnormal cold over high-latitude Eurasia. This means that theSiberian high pressure largely impacts the pattern of frequency, and explain the reasonwhy frequency of extreme low temperature has an out phase oscillation betweenArctic and mid-latitudes.We use modal simulations to reveal how Arctic sea ice impacts patterns ofextreme low temperature. In both two model results, the patterns of extreme lowtemperature are greatly influenced by surface air temperature. Comparing two modelrelated surface level pressure field, we can find surface level pressure anomaly centerexpands its scope and strengthen its amplitude. There clearly appears a strengthenSiberian High. Similarly, the model simulation results are consistent with that fromNCEP dataset, which both have a strengthen Siberian High in common. And thesurface level pressure center has moved towards south. As we have known thestrengthen Siberian High can greatly influence east Asia climate. Under the control ofSiberian High, cold air easily moves towards south, which could lead to cold anomalyover mid-latitudes of Eurasia.