Abstract
Abstract. In this paper we introduce a new model for the location of the auroral oval. The auroral boundaries are derived from small- and medium-scale field-aligned current (FAC) based on the high-resolution CHAMP (CHAllenging Minisatellite Payload) magnetic field observations during the years 2000–2010. The basic shape of the auroral oval is controlled by the dayside merging electric field, Em, and can be fitted well by ellipses at all levels of activity. All five ellipse parameters show a dependence on Em which can be described by quadratic functions. Optimal delay times for the merging electric field at the bow shock are 30 and 15 min for the equatorward and poleward boundaries, respectively. A comparison between our model and the British Antarctic Survey (BAS) auroral model derived from IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) optical observations has been performed. There is good agreement between the two models regarding both boundaries, and the differences show a Gaussian distribution with a width of ±2° in latitude. The difference of the equatorward boundary shows a local-time dependence, which is 1° in latitude poleward in the morning sector and 1° equatorward in the afternoon sector of the BAS model. We think the difference between the two models is caused by the appearance of auroral forms in connection with upward FACs. All information required for applying our auroral oval model (CH-Aurora-2014) is provided.
Highlights
The auroral oval is the region in the ionosphere receiving the main part of the magnetospheric particle precipitation
One important feature of the auroral oval pattern is that it approximately forms the boundary of the polar cap, inside which the magnetic field lines are open and merged with interplanetary magnetic field (IMF) lines
We choose the merging electric field derived from solar wind data for characterizing the expansion of the auroral oval and for parameterizing the model in this study
Summary
The auroral oval is the region in the ionosphere receiving the main part of the magnetospheric particle precipitation. Based on DMSP (Defense Meteorological Satellite Program) auroral photographs, there have already been some early model attempts for predicting the location of the auroral oval (Feldstein and Starkov, 1970; Holzworth and Meng, 1975; Hardy et al, 2008) and the global distribution of the electrons and ions streaming into the ionosphere (Hardy et al, 1985) These observations did not cover all the magnetic local times (MLT) well, in particular in the Southern Hemisphere. An automatic approach for detecting the boundaries of the auroral oval based on the intensity of FACs has been developed and applied by Xiong et al (2014). We make use of the derived boundary locations from the whole CHAMP mission
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