We classify
the atmosphere into layers, or spheres, by characteristics exhibited in the
layers.
The
troposphere is the layer from the surface to an average altitude of about 37 000
feet.
It is
characterized by an overall decrease of temperature with increasing altitude.
The height
of the troposphere varies with latitude and season.
Over the
poles it is about 20 000 feet and over the Equator the troposphere goes up
to 65 000 feet.
The
troposphere is also higher in summer than in winter.
At the top
of the troposphere is the tropopause, a thin layer marking the boundary between
the troposphere and the layer above Stratosphere.
It is characterized
by an abrupt change in temperature lapse rate.
The
Stratosphere is above the tropopause, the stratosphere is typified by
relatively small changes in temperature with height except for a warming trend
near the top.