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The snow cover map shows the fraction of an area covered by snow on a monthly basis. Measurements were made by the MODIS sensor on NASA’s Terra satellite. Gray indicates land areas with no snow, darkest blue represents minimal snow cover, and solid white indicates 100 percent snow cover. Because MODIS relies on visible light to assess snow cover, the sensor cannot collect data over the highest latitudes of the Northern Hemisphere during winter when no sunlight reaches the polar region.
The carbon monoxide maps show the monthly averages of carbon monoxide at an altitude of about 12,000 feet, based on data from the MOPITT sensor on NASA’s Terra satellite. Concentrations of carbon monoxide are expressed in parts per billion by volume (ppbv). A concentration of 1 ppbv means that for every billion molecules of gas in the measured volume, one of them is a carbon monoxide molecule. Yellow areas have little or no carbon monoxide, while progressively higher concentrations are shown in orange and red.
View, download, or analyze more of these data from NASA Earth Observations (NEO):