Compared to the size of the Earth , the atmosphere is a thin shell. The part of the atmosphere we know best — the troposphere — is an even thinner shell, only 12 kilometers (7.5 miles) thick. It is in the troposphere that all weather occurs; it is only here that life exists.
Water is a minor, but very important constituent of the Earth's atmosphere. This image, taken by an instrument onboard the Upper Atmosphere Research Satellite, shows water vapor content over the Pacific Ocean during the El Niño event of October, 1997. Red indicates high water content and blue is low. High atmospheric moisture corresponds to warmer water. The data show a shift in humidity (and warm water) to the east Pacific. The result was that the heavy rainfall that usually stays west toward Indonesia instead hit the west coast of North America.
This true color perspective of Hurricane Irene was produced from an image taken by the GOES-13 satellite on August 27, 2011 at 10:10 am EDT. Satellite observations are invaluable for tracking the paths of tropical storms and other weather systems. For a current track of hurricanes and storms visit the National Weather Service's National Hurricane Center: http://www.nhc.noaa.gov/.