Satellite Derived Snowmelt in Greenland Shows Positive Anomalies for 2006
11 Jun, 2007 07:13 pm
Although it did not break any record in terms of overall extent and duration, snow melting in Greenland in 2006 followed the trend of the past recent years, confirming increasing of snowmelt extent and duration. But why scientists are so eager to know what is happening in Greenland ?
The large extension of the Greenland ice sheet and its extreme weather conditions makes ground-based monitoring difficult. Therefore, space-borne remote sensing plays a key role. The Special Sensor Microwave Imaging radiometer (SSM/I) measures the naturally emitted radiation of the Earth at microwave frequencies from an altitude of approximately 800 Km. Differently from visible data, which are limited to the surface and by the presence of sunlight, microwave data can provide information on snow sub-surface processes, as they are sensitive to internal snow layers. This property is complemented by the fact that microwave data are sensitive to snow even in presence of clouds and do not require sun illumination. SSM/I data have been collected since 1987, providing an opportunity for the analysis of long-term trends of melting extent and duration, allowing to compare the 2006 surface melting characteristics with the average trend for the previous years.
In 2006, areas along Greenland's western, southeastern and northeastern coast saw the largest number of melt days. 2006 melt extent (e.g., the number of pixels which experienced at least one day of melting) was ~ 973,000 Km2 (roughly 2.3 times the area of California), above the average value for the period 1988 – 2005 of ~ 920,000 Km2. Also, in 2006 melting lasted 10 days longer than the average for areas at high altitude (> 2200 m) in southern Greenland. 2006 ranked sixth in terms of melt extent, with 1998 showing a very similar extent. The maximum melt extent was reached in 2002 (~1,400,000 Km2, corresponding to ~ 3.5 times the surface of California ), with 2005 showing also similar values. 2006 melting index (which accounts for both spatial and temporal information, and it is defined as the melting area times the number of days) is ~ 14,000,000 Km2*day, ranking fifth. 2005, 2002 and 1998 are the top three, showing similar values (~19,000,000 Km2*day).
A multi-interdisciplinary and choral effort is ongoing within the polar science community in order to distinguish between changes related either to natural variability or to anthropogenic activities. The International Polar Year (IPY), March 2007 – 2009, will bring together scientists from different disciplines and countries. This cooperative work will combine extensive observations on ground with tools, such as remote sensing techniques and climate models, to accelerate our understanding of the ice sheets, as well as its interaction with ocean and atmospheric circulation, in a sort of a race between our knowledge and the speed at which Greenland is changing.
Tedesco, M., Snowmelt detection over the Greenland ice sheet from SSM/I brightness temperature daily variations, Geophys. Res. Lett., 34, L02504,doi:10.1029/2006GL028466, January 2007
Tedesco M., 2006 Greenland Ice Sheet Snowmelt From Spaceborne Microwave Brightness Temperatures, EOS Transactions of the American Geophysical Union Society, Volume 88, Numer 22, May 29, 2007