ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-28-883-2010 Comparison of the open-closed field line boundary location inferred using IMAGE-FUV SI12 images and EISCAT radar observations Hubert B. 1 Aikio A. T. 2 Amm O. 3 Pitkänen T. 2 Kauristie K. 3 Milan S. E. 4 Cowley S. W. H. 4 Gérard J.-C. 1 Laboratory for Planetary and Atmospheric Physics, University of Liège, Liège, Belgium Department of Physics, University of Oulu, Oulu, Finland Space Physics Group, Finnish Meteorological Institute, Helsinki, Finland Department of Physics and Astronomy, University of Leicester, Leicester, UK 01 04 2010 28 4 883 892 Copyright: © 2010 B. Hubert et al. 2010 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/28/883/2010/angeo-28-883-2010.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/28/883/2010/angeo-28-883-2010.pdf

We compare the location of the polar cap boundary (PCB) determined using two different techniques, and use them as proxies for the open-closed field line boundary (OCB). Electron temperatures from observations of the EISCAT radar facility are used to estimate the latitude of the PCB along the meridian of the EISCAT VHF beam. The second method utilizes global images of proton aurora obtained by the IMAGE satellite FUV SI12 instrument. These methods are applied to three different intervals. In two events, the agreement between the methods is good and the mean of the difference is within the resolution of the observations. In a third event, the PCB estimated from EISCAT data is located several degrees poleward of that obtained from the IMAGE FUV SI12 instrument. Comparison of the reconnection electric field estimated from the two methods shows that high-resolution measurements both in time and space are needed to capture the variations in reconnection electric field during substorm expansion. In addition to the two techniques introduced above to determine the PCB location, we also use a search for the location of the reversal of the east-west component of the equivalent current known as the magnetic convection reversal boundary (MCRB). The MCRB from the MIRACLE magnetometer chain mainly follows the motion of the polar cap boundary during different substorm phases, but differences arise near the Harang discontinuity.

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