Alfvén waves as a source of lower‐hybrid activity in the ring current region

A coupling mechanism between lower‐hybrid waves and low‐frequency electromagnetic activity in the Earth's ring current region is analyzed. In the ring current region the observed amplitudes of Alfvén and/or fast magnetosonic waves, as a rule, do not exceed the threshold of flux instability of lower‐hybrid waves in an electromagnetic field of a low‐frequency wave. Even for these conditions, however, a mechanism of parametric generation of lower‐hybrid waves from low‐frequency Alfvén or fast magnetosonic waves is possible, and this theory is presented. In the studied case, lower‐hybrid waves are saturated because of induced scattering with plasma electrons. For typical plasma and low‐frequency wave parameters in the Earth's ring current region the saturation level of lower‐hybrid waves, excited by the proposed mechanism, is in good agreement with experimental data.