Atmosphere Summary

Section Coordinator: James Overland

NOAA Pacific Marine Environmental Laboratory, Seattle, WA, USA

December 3, 2012

Extended high pressure over southern Greenland (left) caused anomalously high air temperatures (right) and extensive melting at the surface of the ice sheet (see essay on Greenland Ice Sheet). Large version available from NOAA Climate.gov.

October 2011 through August 2012 was a departure from typical atmospheric conditions of recent years (2003-2010) in that warm temperature anomalies were relatively small over the central Arctic relative to the late 20th Century. Similarly, cloud cover in 2012 was average compared to the period 2001-2010. Stratospheric ozone concentrations during spring 2012 were also within normal ranges and considerably lower than those in spring 2011, when unprecedented chemical ozone losses occurred. Air sampling sites in the Arctic continue to measure rising greenhouse gas concentrations from worldwide human sources, and indicate that there is, as yet, no direct atmospheric evidence that Arctic emissions of CH₄ or the net balance of C from CO₂ are changing.

Notable weather activity in fall 2011 and winter 2012 occurred in the sub-Arctic due to a strong positive North Atlantic Oscillation (NAO) Index, which promoted westerly winds in the northern North Atlantic Ocean region and warm temperatures in western Eurasia and the Kara Sea. Further east, in the Siberian sub-Arctic, unusually cold winter conditions caused many fatalities. Though 2012 saw a new record summer minimum sea ice extent for the satellite period starting in 1979, the atmospheric forcing conditions were very different than those during the previous record retreat of 2007. In 2012, southerly winds in early June and a major storm in August in the East Siberian and Chukchi seas enhanced sea ice retreat, whereas a persistent warm and windy pattern was responsible for more rapid sea ice melt than normal in 2007. Also noteworthy in 2012 was NAO-related high sea level pressure over Greenland in early summer, a feature of the last six years that has promoted greater than expected mass loss from Greenland and Canadian Arctic glaciers and reduced snow cover in North America.

Photograph of the "Big House" at Summit, Greenland, where the SUV-150B UV spectroradiometer of the NSF Arctic Observing Network is located. Courtesy of Germar Bernhard.