Seasonal evolution of S q current system at sub-auroral latitude

Abstract

The quiet-time (ΣKp ≤ 3) daily variations of the geomagnetic field at the Indian Antarctic station, Maitri (Geographic Coord.: 70.75°S, 11.73°E; Geomagnetic Coord.: 66.84°S, 56.29°E) during two consecutive years of a solar minimum are considered in order to investigate the characteristics of the solar quiet (Sq) current system. The present work reports the signatures of the south limb of the Sq current loop of the southern hemisphere over a sub-auroral station. It is observed that the seasonal variation of the Sq current strength over Maitri is strongest during the summer months and weakest during the winter months. In spite of the total darkness during the winter months, an Sq pattern is identified at Maitri. The range of the horizontal field variation in the daily Sq pattern during summer is one order higher than that during winter. An interesting feature regarding the phase of the local time variation in the seasonal pattern is found here. A sharp shift in the time of the peak Sq current to later local times (> 1 hour per month) is observed during January–February and July–August, which may correspond to the transition from the complete presence, or absence, of sunlight to partial sunlight. The differences in the incoming solar UV radiation during such transitions can cause a sudden change in the local ionospheric conductivity pattern, and can also trigger some unusual thermo-tidal activity, that might be responsible for modifying the global Sq pattern.