Abstract
The studies on the hydromagnetic interactions of the ionic exosphere with the geomagnetic field are reviewed. Considering the various hydromagnetic interactions, it is shown that the geomagnetic dipole field and the earth's atmosphere are confined within the cavity with the radius of the about from six to ten earth's radii, and hydromagnetics in the outer atmosphere are reduced to the electrodynamics for the thin transition layer between the interplanetary gas and the earth's exosphere.
