Equivalent current systems for the annual and semiannual S_q variations observed along the 210°MM CPMN stations

We analyzed ground magnetometer data for the 10 International Quiet Days during 1996-2007. The data were obtained from 19 stations along 210°magnetic meridian (MM) of the Circum-pan Pacific Magnetometer Network (CPMN) covering both the Northern Hemisphere and Southern Hemisphere. From the daily variations of the geomagnetic field, we deduced the latitude-local time (LAT-LT) diagram of the equivalent S_q current system, which can be regarded as the superposition of the following three current systems: Sq_o, Sq ₁, and Sq₂. The Sq₀, Sq₁, and Sq₂ current systems are equivalent current systems for the yearly average, annual variation, and semiannual variation of the S_q field, respectively. We have examined temporal and spatial features of these current systems. The principal features are as follows: (1) The total current intensities of the Sq₁ and Sq₂ current systems are about 35% and 15% of that of the Sq₀ current system, respectively. (2) The Sq₀ and Sq₂ current systems have a dayside vortex in each hemisphere, while the Sq₁ current system has a single vortex centered at the equatorial region in the morning sector (∼1000 LT).