Wave activity in front of high-β Earth bow shocks

Abstract. Earth's bow shock in high β (ratio of thermal to magnetic pressure) solar wind environment is relatively rare phenomenon. However such a plasma object may be of interest for astrophysics. We survey statistics of high-β (β > 10) shock observations by near-Earth spacecraft since 1995. Typical solar wind parameters related with high β are: low speed, high density and very low IMF 1–2 nT. These conditions are usually quite transient and need to be verified immediately upstream of the observed shock crossings. About a hundred crossings were initially identified mostly with quazi-perpendicular geometry and high Mach number. In this report 22 Cluster project crossings are studied with spacecraft separation within 30–200 km. Observed shock front structure is different from that for quaziperpendicular supercritical shocks with β = 1. There is no well defined ramp. Dominating magnetic waves have frequency 0.1–0.5 Hz (in some events 1–2 Hz). Polarization has no stable phase and is closer to linear. In some cases it is possible to determine wavelength at 0.1–0.5 Hz of the order of 200–900 km.