Conditions for neglecting ion motion for radio waves in a plasma

The conditions for ignoring the ion motion for radio waves in a partially ionized plasma are deduced from macroscopic equations by comparing the terms in the generalized Ohm´s law. The conditions under which Ohm´s law becomes uncoupled from the momentum transfer equation are distinguished for the three characteristic height intervals in the ionosphere. The conditions for neglecting ion motion in each region are discussed.