Changes in melt season characteristics on Devon Ice Cap, Canada, and their association with the Arctic atmospheric circulation

Abstract

Using June-August surface meteorological measurements for 2004-10 we found that the duration of the summer melt season at elevations of 1800, 1300 and 1000ma.s.l. on Devon Ice Cap, Canada, increased at a rate of 3.4 (p < 0.1; weak significance), 6.1 (p < 0.01) and 8.8 (p < 0.05) days a-1, respectively. The calculated surface melt rate at 1300ma.s.l. increased from 74 to 133cmw.e. a-1 between 2007 and 2010. These changes are linked to two types of change in the Arctic atmospheric circulation. Strengthening of the 500 hPa ridge over the Arctic in June-July resulted in increases in both the advection of warm air into the region and the occurrence of cloud-free conditions over the ice cap, causing the available melt energy to increase by 4-24% relative to June-July 2007-10 mean conditions. More frequent southwesterly low-pressure systems in August after 2004 accounted for a 12-38% increase in available melt energy relative to the August 2007-10 daily mean due to advection of warm air into the Arctic, reduced incoming shortwave radiation and increased net longwave radiation. This delayed the timing of freeze-up by an average of 5.5 days a-1 (p < 0.05) at the three sites over 2004-10. © 2013 Publishing Technology.