MODIS-Derived Arctic Melt Season Fog and Low Stratus over East Greenland Glaciers and the Ice Sheet

摘要

In a first attempt to quantify fog over vast snow and ice surfaces, we present the horizontaland vertical spatial extent of significant melt-season fog events over East Greenland glaciersand the Greenland ice sheet. Two established MODIS fog classification methods are adjustedfor use in Arctic glacierized regions and applied to Terra-MODIS Collection 6 Level 1B scenesand Level 2 cloud products. In a 6-step procedure, we process these products in combinationwith a digital elevation model and glacier extents to separate fog from low stratusover glaciers. The procedure was optimized using Landsat 7 and ground observations andverified with concurrent CloudSat–CALIPSO very low-level clouds. The MODIS-derived endproducts are 500-m resolution fog and low stratus mask maps over East Greenland withassociated fog statistics. Six days throughout the 2002–2007 melt season are mapped,revealing maximum fog extent in July–August covering 20,000–70,000km~2 of glacier surface.Mean fog thickness is ～200m and maximum inland extent of continuous fog ～100 km,although patches occur high on the ice sheet. Our method and results will aid in cloudchange detection and in the quantification of cloud radiative forcing and thermal effectsover snow and ice surfaces.