A Quantitative Analysis of the Uncertainties on Reconnection Electric Field Estimates Using Ionospheric Measurements

Calculating the magnetic flux transfer across the open-closed boundary (OCB) per unit time and distance-the reconnection electric field-is an important means of remotely monitoring magnetospheric dynamics. Ground-based measurements of plasma convection velocities together with velocities of the OCB are commonly used to infer reconnection rates. However, this approach is limited by spatial coverage and often lacks robust uncertainty quantification. In this paper, we assimilate Super Dual Auroral Radar Network convection measurements, ground magnetometer data, and estimates of the conductance derived from the Imager for Magnetopause-to-Aurora Global Exploration satellite imagers, using the Local mapping of polar ionospheric electrodynamics (Lompe) framework over a region in North America. We present a new method to assess various contributions to uncertainties in the derived reconnection electric fields, including a novel approach to estimate uncertainties in conductance from global auroral imaging. Our method is demonstrated on a substorm event with an associated pseudobreakup during a period of favorable observational coverage. In this case study, the uncertainties in the reconnection electric field are similar to 5-10 mV/m at the peak of substorm expansion, roughly 15% of the peak reconnection electric field. We find that the main contributor to the reconnection electric field estimates after substorm onset is the OCB motion, whereas during the pseudobreakup the main contributor is ionospheric plasma convection. The solar wind is a stream of particles and magnetic field flowing away from the Sun. Under certain orientations of the solar wind magnetic field, magnetic reconnection can occur between the magnetic fields of the solar wind and Earth. Magnetic reconnection is the process by which oppositely directed magnetic field lines "break," then merge into a new configuration. Magnetic reconnection is the primary process responsible for coupling the solar wind energy to the Earth's magnetic field, and is ultimately the principal driver of space weather. In the Earth's magnetosphere, reconnection is associated with topological changes at both dayside and nightside, where stored magnetic energy is released through a global reconfiguration of the magnetosphere which is referred to as magnetospheric substorms. We can remotely monitor this reconnection from the ground by studying the transfer of magnetic flux across the boundary between open and closed magnetic field lines. In this study, we combined data from ground-based radars, ground magnetometers, and space-based auroral imaging to monitor the reconnection rate across the entire nightside auroral oval for a full substorm event. We additionally derived uncertainties in this reconnection rate stemming from uncertainties in the ionospheric velocities, the ionospheric conductances, and the open-closed boundary motion. We estimate Hall and Pedersen conductance uncertainties using global auroral satellite images from Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) for an isolated substorm We calculate uncertainties in ionospheric reconnection electric fields related to conductance, open-closed boundary (OCB) motion, and convection We find that the main contributor to the reconnection electric field estimates after onset is the OCB motion