Robust Estimates of Spatiotemporal Variations in the Auroral Boundaries Derived From Global UV Imaging

Abstract

The aurora often appears as an approximately oval shape surrounding the magnetic poles, and is a visible manifestation of the intricate coupling between the Earth's upper atmosphere and the near‐Earth space environment. While the average size of the auroral oval increases with geomagnetic activity, the instantaneous shape and size of the aurora is highly dynamic. The identification of auroral boundaries holds significant value in space physics, as it serves to define and differentiate regions within the magnetosphere connected to the aurora by magnetic field lines. In this work, we demonstrate a new method to estimate the spatiotemporal variations of the poleward and equatorward boundaries in global UV images. We apply our method, which is robust against outliers and occasional bad data, to 2.5 years of UV imagery from the Imager for Magnetopause‐to‐Aurora Global Exploration satellite. The resulting data set is compared to recently published boundaries based on the same images (Chisham et al., 2022, https://doi.org/10.1029/2022JA030622), and shown to give consistent results on average. Our data set reveals a root mean square boundary normal velocity of 149 m/s for the poleward boundary and 96 m/s for the equatorward boundary and the velocities are shown to be stronger on the nightside than on the dayside. Interestingly, our findings demonstrate an absence of correlation between the amount of open magnetic flux and the amount of flux enclosed within the auroral oval.

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

“…Given the OCB latitude (θ b ) as a function of MLT (ϕ) and time, the following analytic expressions provide the OCB velocity components normal to the OCB, u θ and u ϕ (Hatch, 2023;Ohma et al, 2024): Journal of Geophysical Research: Space Physics 10.1029/2024JA032599…”