Influences of Northern Hemisphere Sea-Ice Change on Atmospheric Circulation
Abstract:Evidence from both observations and model results suggests a link between changes in the Arctic sea ice conditions and atmospheric circulation in the NH mid latitudes with its possible impacts on severe winters and extreme weather events. This study investigates underlying mechanisms for this Arctic-midlatitudes climate connection based on numerical experiments using a high-top AGCM. We compare and evaluate results from two sets of perpetual simulations (60yrs run each), one with an annual cycle of sea ice conditions from the period of 1979-1983 and the other from the 2005-2009 period while other variables and parameters including SST and GHGs are fixed.
Results from the numerical experiments show that the Arctic sea ice reduction leads to cold winters in the mid-latitude land areas centered in Siberia, Europe and the North America. The winter (DJF) mean temperature at 850 hPa averaged over the mid-latitude continents decreases by about 0.4 K associated due solely to sea ice reduction.
The analysis based on a wave-activity flux indicates that this cooling is due to low-level cold advection. In early winter negative geopotential height anomalies over Siberia and the North America develop as a stationary Rossby wave response to anomalous turbulent surface heat fluxes associated with the sea-ice reduction in the Barents and Kala Seas. As winter progresses further wave propagation acts to intensify positive geopotential height anomalies over the high Arctic, which eventually leads to cold advections in the lower troposphere. In addition, we identify a pathway via the stratosphere which appears to aid this intensification of positive geopotential height anomalies.
Observations in general support a similar relationship. For example, on interannual timescale there is a significant positive relationship between the September NH SIE time series and surface temperatures in continental regions.
Our results have significant implications that sea ice can be used as a basis for mid-range prediction and that underlying mechanisms can be in part understood within the framework of the Rossby wave propagation and wave-mean interaction theory.