Abstract

This study identifies an atmospheric circulation anomaly-Dipole Anomaly (DA) in the arctic atmosphere, and its relationship with winter sea ice motion, based on an International Arctic Buoy Programme (IABP) dataset (1979-1998) and datasets ftom the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) for the period of 1960-2002.The DA is the second-leading mode of EOF (empirical orthogonal function) of monthly mean SLP north of 70oN during the winter season (October-March) and accounts for 13% of the variance. One of its two anomaly centers is over the Canadian Archipelago; the other is situated over northern Eurasia and the Siberian marginal seas. Due to the DA's strong meridionality, it becomes an important dynamic mechanism to drive both anomalous sea ice out of the Arctic Basin and cold air outbreaks into the Barents Sea, the Nordic seas and northern Europe. When the DA remains in its positive phase (that is, negative SLP anomalies appear in northern Eurasia and the Siberian marginal seas with the concurrent positive SLP over the northern North America and Greenland), there are large-scale changes in the intensity and character of sea ice transport in the Arctic Basin. The significant changes include a weakening of the Beaufort Gyre, an increase in sea ice export out of the Arctic Basin through Fram Strait and the northern Barents Sea, and enhanced sea ice import ftom the Laptev Sea and the East Siberian Sea into the Arctic Basin. Consequently, more sea ice appears in the Greenland and the Barents Seas during the positive phase of the DA.

A pan-Arctic Coupled Ice-Ocean Model (CIOM) was used to examine the response of sea ice motion to both the AO/NAO (Arctic OscillationINorth Atlantic Oscillation) and DA. The spatial patterns and temporal variations of sea ice are identified to be more closely related to the DA than the AO/NAO. Furthermore, the 20th century model simulations ftom a global atmosphere-sea ice-ocean model were analyzed to confirm that the DA is dynamically more important in transporting sea ice than the AO/NAO.

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