Atmospheric studies satellites were some of the very first satellites launched into space. They generally have pretty low Earth orbits so that they can study the Earth's atmosphere.
Alouette, the first satellite launched by Canada, was also the world's first atmospheric studies satellite. The purpose of Alouette was to study the Earth's ionosphere (a charged layer of the atmosphere). Canadian scientists were trying to learn more about the aurora borealis, or northern lights - disturbances of the ionosphere in the atmosphere which create brilliant lights in the northern skies at night, but disturb radio communications.
A more recent example of a satellite studying the atmosphere is NASA's Polar satellite.