Nature of Stochastic Ion Heating in the Solar Wind: Testing the Dependence on Plasma Beta and Turbulence Amplitude

摘要: The solar wind undergoes significant heating as it propagates away from the Sun; exact mechanisms responsible for this are not yet fully understood. We present first time a statistical test one of proposed mechanisms, stochastic ion heating. use amplitude magnetic field fluctuations near proton gyroscale proxy ratio velocity to perpendicular (with respect field) thermal speed, defined $\epsilon_p$. Enhanced temperatures observed when $\epsilon_p$ is larger than critical value ($\sim 0.019 - 0.025$). This enhancement strongly depends on plasma beta ($\beta_{||p}$); $\beta_{||p} \ll 1$ only temperature $T_{\perp}$ increases, while \sim increased parallel and both observed. For smaller no $T_p$ minor increases in $T_{\parallel}$ measured. change across threshold agreement with model Chandran et al. (2010). find that $\epsilon_p > \epsilon_{\rm crit}$ 76\% studied periods implying may operate most at 1 AU.