A New Approach to Study Stochastic Heating in the Solar Wind with Implications for Parker Solar Probe and Solar Orbiter

The solar wind undergoes significant heating as it propagates away from the Sun, however the exact mechanisms heating the plasma are not yet fully understood. Identifying the physical mechanisms responsible for this heating is fundamentally important to describe the solar corona and solar wind. Parker Solar Probe and Solar Orbiter will provide a wealth of data from an unexplored region to quantify the heating contribution of proposed mechanisms including stochastic heating as a function of the heliocentric distance. As a preparation for these upcoming missions we study stochastic heating at 1 AU. Stochastic heating occurs when the motion of ions becomes chaotic as the amplitude of electromagnetic field fluctuations at scales comparable to the ion gyroscale exceed a critical value. Under these conditions, the magnetic moment of ions is not conserved, allowing for diffusion across magnetic fields, consequently leading to perpendicular heating of the ions. We analyze over a decade of Wind observations using previously proposed techniques and show that the nature of stochastic heating in various subsets of the solar wind is in qualitatively good agreement with predictions, focusing on the critical amplitude of magnetic fluctuations where stochastic heating starts operating. In the second part of this study, we repeat the analysis using a new approach and we demonstrate that our technique yields results, which are in excellent agreement with predictions and rely on fewer assumptions than previous methods. Our technique allows us to study in detail how the turbulent energy is partitioned between ions and electrons. This novel analysis will be useful for studying data from Parker Solar Probe and Solar Orbiter to determine what mechanisms heat the solar wind.