Seasonal Variation Characteristics Of Geomagnetic Sq External And Internal Equivalent Current Systems In East-Asia And Oceania Regions

Geomagnetic data from 20 observatories in East-Asia and Oceania regions were used to investigate the seasonal variation characteristics of the external and internal Sq current systems by spherical harmonic analysis (SHA). The seasonal current models of D (northern winter) season, E (equinox) season, and J (northern summer) season have been constructed respectively, and the current parameters of these models were analyzed. The main results are obtained as follows: (1) The local time T of the northern vortex moves from local noon to prenoon from D to E to J season for both external and internal currents; meanwhile, in the southern hemisphere, the T moves from local noon to afternoon. (2) The vortex intensity J increases from local winter to equinox then to local summer. The interseasonal change rate of internal current is larger than that of external current. (3) The latitude phi of the external current vortex exhibits seasonal variation in the southern hemisphere, while in the northern hemisphere the latitude phi of the internal current vortex shows obvious seasonal changes. (4) The correlations between the internal and external currents are further analyzed. In the E season the correlation of T is the highest, and in the local summer and winter, the correlation of J is the strongest. The different seasonal behavior of the external and internal current systems is unexpected, and its mechanism remains to be identified in future study.