Climate Research News

Two papers on the role of winds and atmospheric circulations in Arctic sea ice losses, one of which is ‘in press,’ have been published in GRL:

Summer Retreat of Arctic Sea Ice: Role of Winds, by Ogi et al (in press)

The Abstract states:

The unprecedented retreat of first-year ice during summer 2007 was enhanced by strong poleward drift over the western Arctic induced by anomalously high sea-level pressure (SLP) over the Beaufort Sea that persisted throughout much of the summer. Comparison of the tracks of drifting buoys with monthly mean SLP charts shows a substantial Ekman drift. By means of linear regression analysis it is shown that Ekman drift during summer has played an important role in regulating annual minimum Arctic sea-ice extent in prior years as well. In combination, the preconditioning by events in prior years, as represented by an index of May multi-year ice, and current atmospheric conditions, as represented by an index of July-August-September SLP anomalies over the Arctic basin account for ~60% of the year-to-year variance of September sea ice extent since 1979.

In the Discussion the authors state:

We have shown that summertime SLP anomalies over the Arctic are as important as preconditioning by events in prior years in determining the variations in September Sea Ice Extent (SIE) from one year to the next, and our analysis suggests that they are even more important than preconditioning in determining how September SIE will change relative to conditions observed during the previous year.

The six summers that exhibited highest values of the SLP index (1995, 1998, 1999, 2005, 2007 and 2008) were all in the last half of the record. September SIE reached record lows in three of these years (1995, 2005, and 2007), and it nearly tied the record in 2008. Yet it is clear from Fig. 4c that the precipitous decline in September SIE in recent years is mainly due to the cumulative loss of multi-year ice: summertime SLP anomalies have played an important role in setting the timing of record lows, but the long term trend is mainly due to preconditioning.

The second paper is entitled, ‘Recent radical shifts of atmospheric circulations and rapid changes in Arctic climate system,’ by Zhang et al

The Abstract states:

Arctic climate system change has accelerated tremendously since the beginning of this century, and a strikingly extreme sea-ice loss occurred in summer 2007. However, the greenhouse-gas-emissions forcing has only increased gradually and the driving role in Arctic climate change of the positively-polarized Arctic/North Atlantic Oscillation (AO/NAO) trend has substantially weakened. Although various contributing factors have been examined, the fundamental physical process, which orchestrates these contributors to drive the acceleration and the latest extreme event, remains unknown. We report on drastic, systematic spatial changes in atmospheric circulations, showing a sudden jump from the conventional tri-polar AO/NAO to an unprecedented dipolar leading pattern, following accelerated northeastward shifts of the AO/NAO centers of action. These shifts provide an accelerating impetus for the recent rapid Arctic climate system changes, perhaps shedding light on recent arguments about a tipping point of global-warming-forced climate change in the Arctic. The radical spatial shift is a precursor to the observed extreme change event, demonstrating skilful information for future prediction.

November 26th, 2008 | Tags: Arctic, Climate Change, Sea Ice | Category: News | Subscribe to comments | Leave a comment | Trackback URL