Authors: J. Walters (University of Arizona), K. G. Klein (University of Arizona), B. D. G. Chandran (University of New Hampshire), M. L. Stevens (Harvard Smithsonian Center for Astrophysics), D. Verscharen (University College London), E. R. Lichko (University of Arizona)

Due to the low collisionality in space plasmas, velocity distribution functions (VDFs) observed in the solar wind are complex and contain structures that cannot be fully represented by combinations of a few hot, drifting bi-Maxwellian distributions. As we typically model the behavior of plasma waves in the solar wind assuming VDFs that are represented by such simplified bi-Maxwellian fits, we may be ignoring microinstabilities triggered by these non-equilibrium features or neglecting their impact on suppressing or enhancing waves predicted by simpler models. Microinstabilities are important to the processes that transfer energy at large MHD scales and dissipate them at smaller kinetic scales in collisionless plasmas, so a good understanding of their behavior using observed solar wind proton distributions is valuable. In this work, we investigate how deviations from a two-component bi-Maxwellian VDF affect the onset and evolution of parallel-propagating microinstabilities associated with solar wind protons. We use the Arbitrary Linear Plasma Solver (ALPS) numerical dispersion solver to find the real frequencies, growth or damping rates, and wave eigenfunctions of the Alfvén and fast waves using proton VDFs extracted from Wind spacecraft observations. We compare this wave behavior to that obtained by applying the same procedure to a core-and-beam bi-Maxwellian fit of the Wind proton distributions. We find several significant differences in the plasma waves obtained for the data and bi-Maxwellian fit, including both the presence and suppression of instabilities in the data compared to the model. By application of the quasi-linear diffusion operator to our model and data VDFs, we pinpoint resonantly interacting regions in velocity space where differences between the model and data VDF are seen to significantly affect the plasma wave behavior.