Seasonal variations of L equivalent current systems

Equivalent ionospheric current systems of the lunar daily geomagnetic variations during a solar active period are estimated from geomagnetic data for three seasons and the yearly average. The external current intensity ratio in summer over winter is 1.4–6.0 for the diurnal current, 1.3–3.7 for the semidiurnal current, and 1.3–4.1 for the combined current of the first four harmonics. Also, the phase of the current in local winter frequently shifts, to a large extent, relative to the yearly average current system. This anomalous behavior during solstitial months, particularly in winter, is caused by lunar tidal wind variations. It is emphasized that the L current flows mainly at the ionospheric E region which is same as for the Sq current.

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