Daily surface temperatures in June-August 2012 have peaked more than 5 C (~9 F) warmer for the whole ice sheet than the 2000-2009 daily averages according to my analysis of ice surface temperatures from daily NASA MODIS MOD11 satellite derived Land Surface Temperature (LST) retrievals. Over the highest elevations, surface temperatures were nearly 10 C (~18 F) warmer than in the 2000′s decade, leading to an area of ice sheet surface melting, unprecedented in the satellite observational record beginning in 1978.
To a first approximation, when ice sheet temperature increases, its reflectivity decreases (Box et al. 2012). After a low temperatures 10-13 August, 2012 the surface reflectivity of sunlight (a.k.a. albedo) increased from the accumulation of fresh bright snow (Fig. 2). Then as surface temperatures rose again, above one standard deviation of the 2000-2009 average, the ice sheet albedo again dropped 18-23 August, 2012 below previous observations (since 2000), especially at the intermediate elevations of 1000-1500 m where melting in all likelihood remains active this year. As reported by Marco Tedesco, 2012 melting is already setting the record since the late 1950s, and with this late melt season albedo drop and high surface temperature anomaly, this “Goliath” melt has got to be growing.
The daily albedo anomaly map (Fig. 3) indicates widespread low reflectivity, especially at the ice sheet periphery where surface elevations are lower, the atmosphere is warmer, and melting persists. Positive reflectivity anomalies over the northwest ice sheet suggest the return and persistence of fresh snow.
About the surface temperature data
Land surface temperature MODIS thermal infrared observations enable retrieval of land surface temperature (LST) under cloud-free conditions at 1 km horizontal resolution. The MODIS MOD11A1 data product is based on daily averaged LST retrievals from swath data and a split-window algorithm using MODIS thermal bands 31 (11 μm) and 32 (12 μm) (Wan et al., 2002). These data have a RMS error 1 deg. C in comparison with independent in-situ observations (Wan et al., 2008), with higher RMS errors found over Greenland (Hall et al., 2008a; Hall et al., 2008b; Koenig and Hall, 2010).
- Box, J. E., Fettweis, X., Stroeve, J. C., Tedesco, M., Hall, D. K., and Steffen, K.: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839, doi:10.5194/tc-6-821-2012, 2012. open access
- Hall, D. K., Williams Jr., R. S., Luthcke, S. B., and Digirolamo, N. E.: Greenland ice sheet surface temperature, melt and mass loss: 2000–2006, J. Glaciol., 54, 81–93, doi:10.3189/002214308784409170, 2008a.
- Hall, D. K. J. E. Box, K. Casey, S. J. Hook, C. A. Shuman, K. Steffen, Comparison of satellite-derived and in-situ observations of ice and snow surface temperatures over Greenland, Remote Sensing of Environment, 2008b
- Koenig, L. S., and D. K. Hall, 2010: Comparison of satellite, thermochron and station temperatures at Summit, Greenland, during the winter of 2008/09. J. Glaciol., 56, 735–741.
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