- Physics and Astronomy; Earth and Planetary Sciences; Appearance probability; AMPTE/IRM satellite; Magnetometry; Geomagnetic field; Magnetosphere; Growth rate; Satellite observation; Ion cyclotron wave; Electromagnetic wave; Magnetopause; Pc 2 micropulsation; Pc 1 micropulsation; Probabilité apparition; Satellite AMPTE/IRM; Physical Sciences and Mathematics; Physics; Plasma and Beam Physics
Spacecraft-borne and ground-based magnetometers frequently detect magnetospheric micropulsations in the period range 0.2-10 s, termed Pc 1-2, and attributed to electromagnetic ion cyclotron waves driven by temperature anisotropy (T> T). Previous surveys of Pc 1 occurrence locations have been limited to L ≤ 9. We present AMPTE/IRM observations of the distribution of Pc 1 waves out to the magnetopause, for a limited region of MLT = 10-14. The probability of wave occurence Pis large (> 0.15) between L = 7-12, peaking at L = 8-10 (P∼ 0.25). When the L-value is normalized to the magnetopause position L, however, the highest probabilities of Pc 1 wave occurence are close to the magnetopause, with P∼ 0.25 for LΞ L/L= 0.8-1.0. These results are consistent with increased convective growth rate at large L and with the greater effect of magnetosphere compression close to the magnetopause. On the other hand, we only directly observe magnetic field compression for at most about 25% of the wave events.