Data Mining Inspired Localized Resistivity in Global MHD Simulations of the Magnetosphere

Abstract

Recent advances in reconstructing Earth's magnetic field and associated currents by utilizing data mining of in situ magnetometer observations in the magnetosphere based on geomagnetic indices and solar wind parameters have proven remarkably accurate at reproducing observed ion diffusion regions. We investigate the effect of placing regions of localized resistivity in global simulations of the magnetosphere at specific locations inspired by the data mining results for the substorm occurring on 6 July 2017. When explicit resistivity is included, the simulation forms an x‐line at the same time and location as the Magnetospheric Multiscale Mission observation of an ion diffusion region at 15:35 UT on that day. Without this explicit resistivity, reconnection forms later in the substorm and far too close to Earth (≳−15RE), a common problem with global simulations of Earth's magnetosphere. A consequence of reconnection taking place farther down the tail due to localized resistivity is that the reconnection outflows transport magnetic flux Earthward and thus prevent the current sheet from thinning enough for reconnection to take place nearer Earth. As these flows rebound tailward from the inner magnetosphere, they can temporarily and locally (in the dawn‐dusk direction) stretch the magnetic field allowing for small scale x‐lines to form in the near Earth region. Due to the narrow cross‐tail extent of these x‐lines (≲5RE) and their short lifespan (≲5 min), they would be difficult to observe with in situ measurements. Future work will explore time‐dependent resistivity using 5 min cadence data mining reconstructions.

Global Magnetic Reconnection During Sustained Sub‐Alfvénic Solar Wind Driving

“…More generally, it is also not known how different solar wind parameters will effect the topology of closing reconnection during sub‐Alfvénic solar wind driving. Furthermore, localized resistivity inspired by data mining of observed reconnection locations has been shown to suppress reconnection closer to the Earth (Arnold et al., 2023), which could be an important factor when the tail current sheet retreats toward Earth during the transition from super‐to sub‐Alfvénic solar wind.…”

The complexity of the day-side X-line during southward interplanetary magnetic field

“…Ouellette et al (2010) used GAMERA and found during northward IMF that the reconnection location was not the same as OpenGGCM simulations using an explicit constant resistivity (Dorelli et al, 2007). Explicit resistivity is an available option for the GAMERA simulations, as Arnold et al (2023) used a data-inferred resistivity to incite reconnection in empirically-specified locations. But, a reason to favor the numerical resistivity for this study is that the highest resolution in these simulations is ∼600 km, approaching ion kinetic scales at the magnetopause [∼200 km (Burch et al, 2016a)].…”