Pc 1 micropulsation activity and magnetospheric amplification of 0.2- to 5.0-Hz hydromagnetic waves

A model of hydromagnetic-wave (hm-wave) amplification in the magnetosphere is presented that permits a consistent interpretation of several general and specific features of Pc 1 micropulsation activity (0.2 Hz ≲ ƒ ≲ 5 Hz). It has been found that (1) micropulsations with 0.2 Hz ≲ ƒ ≲ 5 Hz originate preferentially in the magnetospheric regions of maximum amplification; (2) the complete frequency range is amplified in the plasmasphere whereas the plasma trough amplification is limited to the 0.3 Hz ≲ ƒ ≲ 1 Hz range; (3) the μ = 10–100 Mev/gauss protons amplify only the 0.2 Hz ≲ ƒ ≲ 5 Hz primary hm waves. Several properties of the μ = 10–100 Mev/gauss protons are implied on the basis of micropulsation activity. The amplification mechanism is cyclotron resonance between left-hand polarized hm waves and the energetic component of the magnetospheric proton population. Spatial and energy distributions of the magnetospheric proton population and a model of the bounded geomagnetic field that are consistent with experimental observations are utilized in the amplification model.