Authors: Niranjana Shankarappa (University of Arizona), Kristopher Klein (University of Arizona), Mihailo Martinovic (University of Arizona)

Solar wind heating and acceleration is a long-standing problem in space plasma physics. Turbulent dissipation via Landau and cyclotron damping are plausible mechanisms whose presence is supported by spacecraft observations. In our initial work, we applied a simple 1D cascade model (Howes et al. 2008) that dissipates via Landau damping to Parker Solar Probe (PSP) observations of thermal plasma and electromagnetic fields from encounters 1 and 2. We demonstrated the feasibility of Landau damping to heat solar wind protons in the higher plasma beta regions leading to higher parallel temperatures.
We observed and quantified the energy in waves with frequencies comparable to the ion cyclotron frequency, which are consistent with parallel propagating Ion Cyclotron Waves (ICWs) and/or Fast Magnetosonic waves (FMs). Such waves arise in ~41 percent of the selected intervals. As cyclotron damping of ICWs onto protons is expected to be a significant source of enhanced anisotropic heating close to the Sun (e.g. Hollweg & Isenberg 2002), in this work we account for the dissipation of these ion-scale waves. Because the polarization in the plasma rest frame can’t be uniquely determined using single spacecraft observations alone, we evaluate the limiting magnitudes of dissipation rates of ICWs and FMs using the hot plasma linear dispersion solver, PLUME. We identify the frequency in the spacecraft frame at which the waves are observed using PSP magnetic field data. The local plasma parameters are input to PLUME obtaining doppler shifted frequencies for both ICWs and FMs. We then estimate the damping rates at the observed frequency band for ICWs and FMs propagating along either direction of the magnetic field. Using the estimated energy in these waves, we estimate the proton heating rates and compare them to our previous estimates for Landau damping.