Analysis of the diurnal and semiannual variations of Dst index at different activity levels

[1] The diurnal and semiannual variations of the geomagnetic disturbances for different activity levels exhibit distinct characteristics. In this paper, the variations are analyzed for different activity levels on the basis of the Dst index. For the activity level Dst approximate to 0 nT, the disturbance variations may be the manifestation of the residual S-q-field and the Chapman-Ferraro current field. The disturbances on this level may be ascribed to the uneven distribution of the Dst stations. For the higher activity levels, the disturbances and their diurnal variations are mainly contributed by magnetic storms. The analysis shows that the diurnal variation of the disturbances for the level around -100 nT in J-months (May to August) is in reversed phase in comparison with that in D-months (January, February, November, and December). For high activity levels, the diurnal variations of disturbances may be associated with the tilt angle of the geomagnetic axis in the GSM coordinates. The effect of the disturbance fields of asymmetrical current systems may exist as a part in the diurnal variation of the Dst index. This effect is relating to the activity level concerned.Astronomy & AstrophysicsSCI(E)5ARTICLEA3null10