Location of Pc 1–2 waves relative to the magnetopause

• Main Authors: R. E. Denton, J. LaBelle, X. Zhu
• Format: Article
• Language: English
• Published: Copernicus Publications 2002-11-01
• Series: Annales Geophysicae
• Online Access: https://www.ann-geophys.net/20/1763/2002/angeo-20-1763-2002.pdf
• ISSN: 0992-7689; 1432-0576

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 (<i>T</i><font face="Symbol" >_^</font> &gt; T <font face="Symbol" >_||</font>). Previous surveys of Pc 1 occurrence locations have been limited to L <u>&lt;</u>&nbsp; 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 <i>P</i>_wav is large (&gt; 0.15) between <i>L</i> = 7–12, peaking at <i>L</i> = 8–10 (<i>P</i>_wav ~ 0.25). When the <i>L</i>-value is normalized to the magnetopause position <i>L</i>_mp, however, the highest probabilities of Pc 1 wave occurrence are close to the magnetopause, with <i>P</i>_wav ~0.25 for <i>L</i>_norm <u>=</u> <i>L/L</i>_mp = 0.8–1.0. These results are consistent with increased convective growth rate at large <i>L</i> 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.<br><br><b>Key words. </b>Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma waves and instabilities)