Location of Pc 1–2 waves relative to the magnetopause

Abstract. 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 occurrence P_wav is large (> 0.15) between L = 7–12, peaking at L = 8–10 (P_wav ~ 0.25). When the L-value is normalized to the magnetopause position L_mp, however, the highest probabilities of Pc 1 wave occurrence are close to the magnetopause, with P_wav ~0.25 for L_norm = L/L_mp = 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.

Key words. Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma waves and instabilities)