We extend previous theories of stochastic ion heating to account for the motion of ions along the magnetic field B . We derive an analytic expression for the temperature ratio T 0/T 0p in the solar wind assuming that stochastic heating is the dominant ion heating mechanism, where T 0i is the perpendicular temperature of species i and T 0p is the perpendicular proton temperature. This expression describes how T 0i/T 0p depends upon U i and βp, where U i is the average velocity along B of species i in the proton frame and βp is the ratio of the parallel proton pressure to the magnetic pressure, which we take to be ≲ 1. We compare our model with previously published measurements of alpha particles and protons from the Wind spacecraft. We find that stochastic heating offers a promising explanation for the dependence of T 0α/T 0p on U α and βp when the fractional cross helicity and Alfvén ratio at the proton-gyroradius scale have values that are broadly consistent with solar-wind measurements. We also predict how the temperatures of other ion species depend on their drift speeds.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
- solar wind
- Sun: corona