Self-Reformation of the Quasi-Perpendicular Shock: CLUSTER Observations

Abstract

Among several mechanisms issued from simulation and theoretical studies proposed to account for the nonstationarity of quasi-perpendicular supercritical shocks, one process-the so-called self-reformation-driven by the accumulation of reflected ions in the foot has been intensively analyzed with simulations. Present results based on experimental CLUSTER mission clearly evidence signatures of this self-reformation process for the terrestrial bow shock. The study based on magnetic field measurements includes two parts: (i) a detailed analysis of one typical shock crossing for almost perpendicular shock directions where the risk of pollution by other nonstationarity mechanisms is minimal. A special attention is drawn on appropriate treatment of data to avoid any wrong interpretation. One key result is that the ramp width can reach a very narrow value covering a few electron inertial lengths only; (ii) a statistical analysis allows relating the signatures of this nonstationarity with different plasma conditions and shock regimes. Present results are discussed in comparison with previous simulation works.