Magnetic reconnection is a highly dynamic process that excites a wide variety of kinetic waves and instabilities. Transverse current sheet instabilities such as the lower-hybrid drift and secondary drift-kink instabilities in particular have been shown by kinetic simulations to modify the reconnection and introduce significant turbulence and mixing to the reconnection layer. Past studies using the ten-moment fluid model to capture important kinetic physics such as the electron inertia and full representation of the pressure tensor proved advantageous to a two-fluid representation of reconnection, but the model struggled when using a local relaxation closure for the heat flux to replicate the current sheet instabilities and subsequent mixing seen in kinetic simulations. This work uses the \texttt{Gkeyll} software framework to perform simulations of asymmetric reconnection based on the 16 October 2015 MMS crossing of a diffusion region, the Burch event. An improved gradient-based heat flux closure is implemented, showing significant improvement in secondary kinetic instabilities that grow in the current sheet. These instabilities generate turbulence which leads to growth of secondary magnetic islands and flux ropes.
The planetary magnetosphere plays a key role in the shielding of the Earth from the energetic solar wind. Improved modeling of the coupling between the Earth's magnetosphere and the solar wind is of great importance, particularly in understanding and predicting the space weather events which can impact technological infrastructure (Baker et al., 2004). One frequent phenomenon that occurs within the magnetosphere is magnetic reconnection. The primary locations at which reconnection occur are dayside near the heliopause, and nightside in the magnetosphere tail. In dayside reconnection regions where the solar wind magnetic fields stream in the opposite direction of the dipole field, reconnection occurs frequently and results in energy transfer from the solar wind into the magnetosphere (Paschmann et al., 1979). The Magnetospheric Multiscale (MMS) mission has provided access to high-resolution in situ measurements of the of the dissipation region where this energy transfer occurs. The first such set of measurements was the 16 October 2015 crossing (Burch et al., 2016), referred to hereafter as the Burch event. This data is an invaluable resource to simulation frameworks as it provides an opportunity to test the fidelity of the physics being captured by the underlying models.
Traditional modeling of the magnetosphere has relied predominantly on a confluence of magnetohydrodynamics (MHD), hybrid kinetic, and particle-in-cell methods, each with strengths and limitations. MHD, while reproducing global dynamics surprisingly well, fails near the dissipation region since magnetospheric plasmas are typically collisionless (Hesse et al., 2011). Resistive Hall MHD does better in the reconnection boundarylayers (Birn et al., 2001;Liu et al., 2025), but the assumption of scalar pressure is flawed since the pressure tensor and electron inertia have been found to be important, theoretically as well as observationally (Liu et al., 2025). Hybrid kinetic models typically evolve the Vlasov equation for ions but use fluid electrons due to how restrictive electron kinetic scales are to resolve. This approach has similar issues to expanded MHD methods, failing to capture important electron dynamics contained within the full pressure tensor. More sophisticated electron models have been utilized on top of existing hybrid kinetic frameworks (Omelchenko & Karimabadi, 2012;Omelchenko, Roytershteyn, et al., 2021;Omelchenko, Chen, & Ng, 2021), assuming the magnetic field evolution comes from the hybrid kinetic simulation (Battarbee et al., 2021;Ganse et al., 2023).
MHD and more recently with improved algorithms and computational power, hybrid kinetic, have been used extensively for global modeling of planetary magnetospheres (Lavraud & Borovsky, 2008;Pokhotelov et al., 2013;Palmroth et al., 2018;Burkholder et al., 2024). An alternative approach to global magnetosphere modeling which seeks to add the missing electron physics is multi-moment multifluid models. This approach has been applied to a variety of systems, including Ganymede (Wang et al., 2018), Mercury (Dong et al., 2019), and Earth (Wang et al., 2020). The addition of the full pressure tensor evolution allows for improved physics fidelity of reconnection simulations, comparing favorably to kinetic simulations for key metrics such as the Ohm’s Law (Wang et al., 2015) and scaling of the reconnection rate with island size (Ng et al., 2015). Higher moment multifluid models allow for great improvements in capturing kinetic physics over MHD models, especially in regions where electron inertia and pressure agyrotropy drive electron demagnetization. The focus of this work is the ten-moment model introduced by Wang et al. (2015), which retains finite mass and includes the evolution of the full pressure tensor.
Simulations of magnetic reconnection which retain finite electron inertia have revealed a number of instabilities which grow in the reconnection region and influence the reconnection properties (Graham et al., 2025). Fluid and hybrid simulations often struggle to replicate all of these phenomena due to lacking the aforementioned electron dynamics. Past multifluid simulations performed by TenBarge et al. ( 2019) using the Gkeyll software framework were capable of replicating many of the important features of the MMS data and kinetic simulations, but there were several prominent features which were not captured by the model. The most notable of these is the growth of the lower-hybrid drift instability (LHDI) in the transverse direction along the current sheet (Yoon et al., 2002;Roytershteyn et al., 2012). LHDI is predicted by kinetic simulations to grow rapidly during reconnection, and to lead to increased turbulence and mixing of electrons between the layers (Le et al., 2017). The limiting factor to the effectiveness of this previous work was the use of an overly simplistic heat flux closure for reconnection. The approximation, based on the work of Hammett and Perkins (1990), took
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