Quantifying Non‐Maxwellian Properties of Ion Populations During Reconnection at Earth's Magnetopause

Abstract We investigate ion velocity‐space features within the exhaust of magnetopause reconnection using a global hybrid‐Vlasov simulation. The Hermite transform and Gaussian Mixture Model (GMM) are applied to quantify the complexity of velocity‐space structures that arise during the mixing of magnetospheric and magnetosheath ion populations. Using the Hermite transform, we calculated the enstrophy metric to quantify available free energy. From the GMM multi‐beam decomposition we obtained pseudothermal energy. We find that pseudothermal energy appeared due directed beam motion accounts for nearly half of the apparent thermal energy within the exhaust. The enstrophy evolves similarly to the pseudothermal energy estimate selected via the optimal number of Gaussian components. These results revise ion energy partitioning during magnetopause reconnection and suggest an approach for defining thermal energy in non‐Maxwellian plasmas.