Infrared sensors on satellites measure water vapor
in a layer of the atmosphere about 6-10 km above Earth's
surface. At this altitude, strong currents such as jet
streams control the movement of weather systems. Jet
streams show up as elongated dark regions bordered by
lighter regions in the images. Dark areas have little
water vapor (dry air), while white areas represent moist
weather systems. This animation shows water vapor images
recorded every 6 hours over a period of four days.
! Click the image to see the animation.