This is the fourth layer of the atmosphere.
It is located above the mesosphere.
This layer spreads upto the height of 400 kms from the surface of the earth.
The width of this layer is about 300 kms.
The temperature starts increasing again with increasing height in this layer.
Electrically charged currents flows in the air in this sphere.
Radio waves are reflected back on the earth from this sphere and due to this radio broadcasting has become possible.