Структура и динамика полярных токовых систем : материалы международного симпозиума «Полярные геомагнитные явления», 25-31 мая, Суздаль, СССР / Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т. – Апатиты : [б. и.], 1988.

G.Gustafsson, N.E.Papitashvili, V.O.Papitashvili AM IMPROVED MAGNETIC COORDINATE SYSTEM FOR AURORAL OVAL STUDIES ABSTRACT. Moat studies related to auroral phenomena are carried out using magnetic coordinates that are baaed on the internal magnetic field of the earth. Models, including external currents, are available representing the magnetic field at auroral oval latitudes rather well, at leaat during quiet conditions. A new coordinate system has been defined that ia based on such a field model. A considerable improvement ia obtained in the ordering of auroral data in this coordinate system which includes both diurnal and seaaonal dependence on the magnetic field. INTRODUCTION. Many auroral oval phenomena are caused by particle drifting in the nearly east-west direction in the magnetosphere, and many auroral structures in the auroral oval are therefore approximately east-west aligned. In particular, long auroral arcs,- as well as the statistical pattern of auro ral arcs (so called auroral orientation curves, Gustafsson,1967) are east- west oriented at auroral oval latitudes. There ax'e also several auroral feat ures that are drifting in the east-west direction. As auroral phenomena are mainly caused by precipitation of particles drifting in the magnetic- and electric fields, it is expected that suitable models of the fields should order auroral data to a high degree. Data from auroral observations are usually ordered, in magnetic time and magnetic latitude coordinates based on the internal field of the earth, which has no seasonal or magnetic activity dependence. The result is an oval shaped pattern that has the center displaced by several degrees of latitude towards the night side. The purpose of this report is to examine the importance of adding the external magnetic field of the Earth to the internal magnetic field model, when organizing the auroral data. METHOD. The internal magnetic field is distorted beyond about four earth radii by currents in the distant magnetosphere. The main sources are m a g n e t o pause currents, ring current, cross tail currents and field aligned currents. The magnetic field model by Tayganenko and Usmanov (1982) that includes these currents has been used here. This model is modular and it is easy to find the contribution from the different current systems. Particles mirroring near the magnetic equator drift on surface of cons tant magnetic field, around the earth if the electric field is neglected. In the field model these drift paths represent lines of constant magnetic field in the equatorial plane, with slightly varying distance from the earth for different local times. The field model used has only one minimum, when a certain field line is followed from one hemisphere to the other across the magnetic equator, in the latitude range corresponding to the auroral oval. The magnetic equator has been defined from this minimum. The lines of constant I02