Author(s): Jia Wang; Xuezhi. Bai; John Bratton; Bingyi Wu; Charles H. Greene
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Abstract: Since the beginning of the satellite era (1979), record lows and highs of Arctic summer sea ice extent are found to be caused not only by dynamically-forced meridional wind advection, but also by the intensified ice/ocean albedo feedback, both of which are triggered by the Arctic atmospheric Dipole Anomaly (DA) pattern. This local, secondary mode of anomalous sea-level pressure (SLP) in the Arctic produces a strong anomalous meridional wind, which was responsible for driving more sea ice out of the Arctic Ocean from the western to the eastern Arctic into the northern Atlantic during the summers of 1995,1999,2002,2005, and 2007-2012 during its positive phase. In September of 2012, a new record minimum in Arctic sea ice extent was caused by the combined dynamic wind forcing of+DA and thermodynamic forcing, accelerating melting, and advective loss of Arctic sea ice. Sea ice extent in August 2012 exceeded the previous record low of September 2007, occurring one month earlier in the summer season. In addition, high summer sea ice extent was associated with the–DA dynamic wind forcing and+AO’s divergence effect. A new feedback mechanism for the Pacific Arctic region’s atmosphere-ice-ocean climate system is hypothesized to be responsible for the accelerating decline of Arctic summer sea ice. In this hypothesis, the DA provides an intermittent, pulse-like forcing to the system, directly driving sea ice loss by wind forcing and enhancing northward transport of warm Pacific water, and indirectly driving its loss through thermal melting associated with positive ice/ocean albedo feedback and negative ice/cloud feedback. These processes contributed to a series of summer ice minima, particularly occurring since 1995, in which the+DA was associated with accelerating the Transpolar Drift Stream and sea ice export, and amplifying the melting of sea ice.
Year: 2014