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

A. Ohma,K. M. Laundal,M. Madelaire,S. M. Hatch, S. Gasparini,J. P. Reistad, S. J. Walker, M. Decotte

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS(2024)

Univ Bergen

Cited 2|Views7
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, ), 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. We present a method to create spatiotemporal models of auroral boundaries based on global UV images We present distributions of boundary locations and velocities based on images from Imager for Magnetopause-to-Aurora Global Exploration FUV from 2000 to 2002 We examine how the spatial extent of the aurora and its rate of change relate to other geophysical quantities
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Key words
aurora,open-closed boundary,auroral boundaries,polar cap,global aurora
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