Recent Changes in Pan-Arctic Melt Onset from Satellite Passive Microwave Measurements
Wang, Libo1; Derksen, Chris1; Brown, Ross2; Markus, Thorsten3
1Climate Research Division, Environment Canada, CANADA; 2Climate Research Division, Ouranos, Environment Canada, CANADA; 3Cryospheric Sciences Branch, NASA Goddard Space Flight Center, UNITED STATES
A new satellite passive microwave (PMW) melt onset retrieval algorithm based on temporal variations in the differences of the brightness temperature between 19 GHz and 37 GHz is shown to be as effective as radar (e.g. QuikScat) measurements. The PMW technique shows improved melt estimates that are more closely linked to observed snow-off dates than previous studies. An integrated pan-Arctic (north of 50°N) melt onset date (MOD) dataset is produced by combining estimates on land and sea ice for the entire satellite PMW record. During the 1979-2011 period, significant trends of 2~4 days (decade)-1 to earlier MOD are mainly concentrated over the Eurasian land sector of the Arctic and a narrow band on the central Arctic sea ice (Figure 1). The latitudinally averaged MOD trends are more negative in the Eurasian Arctic than the North American Arctic, consistent with changes in spring snow cover extent observed with visible satellite data. Correlation analyses show that the inter-annual variability in MOD is significantly correlated with spring surface air temperature, with over 70% of trends in MOD congruent with warming trends in the Arctic. In contrast, the variability and change in MOD are not significantly influenced by low frequency modes of atmospheric circulation.
Figure 1. (a) Linear least squares trends (days/year), (b) the associated P values for local significance over the 1979-2011 period, and (c) Time series of latitudinally-averaged MOD in the Subarctic and Arctic zones of NA and EUR.