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.

SUMMARY. The constant B-ovala estimated from the Tsyganenko and Usmanov magnetic field model for fields corresponding to the equatorward border of the auroral oval are displaced by 2 .5 degrees of latitude towards the nightside of the earth (i.e. 5 °closer to the magnetic pole on the dayside as compared to the night side). This is somewhat leas than the offset fuund in several auroral oval studies, which show a displacement of about 4.0 degrees. The present field model ia rather insensitive to the variation of the parameters of the model. The center of the oval changes less than 0.5 degrees when vary ing the parameters corresponding to quiet magnetospheric conditions in the model. Calculations have also been carried out for parameters corresponding to disturbed magnetospheric conditions and the ovals are found to be concent ric with those calculated for quiet conditions. However, as pointed out by Tsyganenko (private communication) it is possible that an addition of a thin sheet current in the tail or an asymmetric ring current, will increase the offset. Both these currents may be physically significlent and should be included in the model. It should also be pointed out that the electric field has been neglected, which will have largest influence on particles of low magnetic moment. The main conclusion from this study is that a considerable improvement in ordering of auroral data can be achieved, if a magnetic field model is used that includes external currents. The field model is estimated from "average" conditions which means that it is likely to represent only periods between substorms properly. It is also possible that future magnetic field models will include additional current systems which will improve t h fit with auroral observations. R E F E R E N C E S : Tsyganenko N.A., Usmanov A.V. Determination of the magnetospheric current system parameters and development of experimental geomagnetic field models based on data from IMP and HEOS satellites. - Planet.Space Sci., 30, 985- 998, 1982. Gustafsson G. On the orientation of auroral arcs. - Planet.Space Sci.. 15, 277-294, 1967. Gustafsson G., Feldstein Y.I., Shevnina N.F. The auroral orientation curves for the IQSY. - Planet.Space Sci., 17, 1657-1666, 1969. Peldstein Y.I., Starkov G.V, Dynamics of auroral belt and polar geomag netic disturbances. - Planet.Space Sci., 15, 209, 1967. Whalen J.A. A quantitative description of the spatial distribution and dynamics of the energy flux in the continuous aurora. - J.Geophys.Res. . 88 7155-7169, 1983. ' Shepherd G.G. Dayside cleft aurora and its ionospheric effects. - Rev Geophys. 17, 2017,'1979. 104