Evaluation of the Sq Magnetic Field Variation Calculated by GAIA

Magnetic variations calculated by the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) are compared with those observed at global magnetic observatory network in geomagnetic calm days in order to evaluate accuracy of the ionospheric current system calculated by GAIA. The calculated Y-component magnetic variations can reproduce more than 50% of the observed variations at more than half observatories treated. In particular, GAIA can reproduce more than 75% of the observed Y-component variations in the equinox. Whereas, there is tendency of low correlation of the waveform between the calculated and observed variations in the winter season. Next, GAIA reproduces so well of the X-component variations at the low-latitude observatories. Low correlation between the calculated and observed X-component variations at middle-latitude observatories seems to be caused by inaccurate determination of the position of the ionospheric Sq current vortex. Last, although the calculated Z-component variations does not so well reproduce the observed ones compared with other component, GAIA can reproduce more than 50% of the observed Z-component variation at about half observatories in general. Calculated amplitude of the horizontal magnetic variations (X- and Y-components) exhibit smaller than the observed one, whereas that of the vertical variation (Z-component) is larger than the observed one. This tendency is roughly explained by the induction effect of the Earth that is not considered in GAIA. Thus, GAIA considerably well reproduces the pure ionospheric current system that is not affected by the solid Earth.