Dipole Anomaly (DA) and Sea Ice Motion|
An atmospheric circulation anomaly-Dipole Anomaly (DA) in the Arctic atmosphere is identified to be a major dynamical forcing of winter sea ice motion, based on International Arctic Buoy Programme (IABP) dataset (1979-1998) and datasets from the National Center for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) for the period of 1960-2002. The DA corresponds to the second-leading mode of EOF of monthly mean SLP north of 70?N during winter season (Oct.óMar.), and accounts for 13% of the variance. One of its two anomalous centers stably occupied between the Kara Sea and the Laptev Sea; the other is situated within from the Canadian Archipelago through Greenland extending southeastwards to the Nordic seas. The DA can be attributed to an eastwards shift of the center of action of the North Atlantic Oscillation. Since the DA shows a strong meridionality, it becomes an important mechanism to drive both anomalous sea ice exports 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 between the Kara Sea and the Laptev Sea with concurrent positive SLP over from the Canadian Archipelago extending southeastwards to 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 from 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. During the negative phase of the DA, SLP anomalies show an opposite scenario in the Arctic Ocean and its marginal seas when compared to the positive phase, with the center of negative SLP anomalies over the Nordic seas. Correspondingly, sea ice exports decrease from the Arctic Basin flowing into the Nordic seas and the northern Barents Sea because of the strengthened Beaufort Gyre.
The finding indicates that influences of the DA on winter sea ice motion are greater than that of the winter AO, particularly in the central Arctic Basin and the north to Fram Strait, implying that effects of the DA on sea ice export out of the Arctic Basin becomes robust.
Figure 1. Spatial distributions of the first two leading EOF modes of winter monthly mean SLP (Oct.óMar.) (a) EOF1 (AO) and (b) EOF2 (DA), accounting for 61% and 13% of total variance, respectively.
Figure 2. Regression maps of monthly mean sea ice motion on (a) the monthly AO and (b) the monthly Dipole Anomaly. Unit: cm s-1
Wang, J., A. van der Baaren and L.A. Mysak, 1995, A principal component analysis of
gridded global sea-level pressure, surface air temperature and sea-ice concentration in the Arctic region, 1953-1993, C2GCR Report No. 95-4, McGill Univ., Montreal, 22 pp+figures+Fortran source programs.
Wu, B., J. Wang, J.E. Walsh, 2006. Dipole anomaly in the winter Arctic atmosphere and its
association with Arctic sea ice motion. J. Climate, 19(2), 210-225. DOI:
Watanabe, E., J. Wang, T. Sumi, and H. Hasumi, 2006. Arctic Dipole and its contribution to
sea ice exports in the last 20th century (submitted to Geophys. Res. Lett.)