Authors: William Ryan (West Virginia University), Paul Cassak (West Virginia University), Haoming Liang (University of Maryland, College Park; NASA GSFC), Ida Svenningsson (Uppsala University, Sweden; Swedish Institute of Space Physics, Uppsala, Sweden) Giulia Cozzani (University of Helsinki, Finland)

In the solar wind, electron temperature anisotropies drive the generation of whistler waves (e.g., Huang et al., ApJ, 861:29, 2018). The conditions for the whistler anisotropy instability to occur have been well studied (e.g., Gary and Wang, JGR, 101, 10749, 1996). Recently, an analytical expression quantifying changes from local thermodynamic equilibrium (LTE) was derived based on an entropic approach (Cassak et al., PRL, 130, 085201, 2023). An effective power density describing changes to the non-Maxwellianity of the phase space density was derived and named the Higher-ORrder Non-Equilibrium Terms (HORNET) power density (Barbhuiya et al., PRE, 109, 015205, 2024). During the whistler anisotropy instability, the phase space density isotropizes, so it should have negative values of HORNET. In this study, we investigate the whistler anisotropy instability in the context of the entropic approach to non-LTE dynamics. We perform 2.5D simulations of the whistler anisotropy instability. We show that the whistler anisotropy instability produces an appreciable negative HORNET signal and quantify its parametric dependence. For future work, we will assess the feasibility of applying the HORNET diagnostic to Magnetospheric Multiscale (MMS) data of the whistler anisotropy instability in the magnetosheath that are well-resolved by MMS satellites.