GEOMAGNETIC DIPOLE INTENSITY DECREASE DURING LAST DECADE

In the last decade, according to the International Geomagnetic Reference Field 2000 (IGRF-2000) and IGRF-2005 models, geomagnetic field weakens with the rate 11-15 nT/year. In this paper we assume that the external source, namely the ionospheric current system controlled by solar activity, contributes to the model. If so, we show - this source provides more than a half to the observed weakening. As the quantitative indicators of solar activity we use the index F10.7, solar wind speed V and the Z-component of interplanetary magnetic field (Bz). Basic data for the model are taken from the CHAMP satellite for May 2001 - December 2005 period. In the analysis, we exclude the trend associated with solar activity from the three main coefficients of the spherical harmonic expansion of the magnetic field and show - the remained weakening is 4-8 nT/year only.