1.2 The Recent Arctic Warm Period: the change in the dominate patterns?

Monday, 18 May 2009: 9:00 AM
Capitol Ballroom AB (Madison Concourse Hotel)
Muyin Wang, University of Washington, Seattle,, WA; and J. E. Overland

Arctic winter, spring and autumn surface air temperature (SAT) anomalies and associated sea level pressure (SLP) fields have decidedly different spatial patterns at the beginning of the 21st century (2000-2008) than for most of the 20th century; we suggest calling this major new pattern Arctic Warm Period (AW) (other names can be meridional pattern or the Dipole mode). The climate patterns in the 20th century was dominated by the two major modes of variability, identified as the Arctic Oscillation/Northern Annular Mode (AO/NAM) and the Pacific North American-like (PNA*) pattern. The predominately zonal winds associated with the positive phases of these patterns contribute to warm anomalies in the Arctic primarily over their respective eastern and western hemisphere LAND areas, as in 1977-1988 and 1989-1995. In contrast, SAT in winter (DJF) and spring (MAM) for 2000-2008 show an Arctic-wide SAT anomaly of greater than +1.0° C and regional hot spots over the central Arctic of greater than +3.0° C. The AW pattern is also showing up during the summer sea ice loss of 2007 and in autumn warming events following major sea ice loss. Unlike the AO and PNA*, anomalous geostrophic winds for 2000-2008 often tended to blow toward the central Arctic, a meridional wind circulation pattern. In spring 2000-2005 these anomalous winds were from the Bering Sea toward the North Pole, while in 2006-2008 they were mostly from the eastern Barents Sea. These meridional flow patterns favors heat transport to the central Arctic, which contributed to the accelerated reduction of sea ice. It appears that rather than the AO and AW being random patterns of variability, the AW is now more favored as a result of anthropogenic forcing and the loss of summer sea ice. The AW is a clear example of Arctic sea ice loss impacting tropospheric air temperatures and the larger-scale atmospheric general circulation.
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