Seasonal variation of the Sq focus position during 2006-2010

In the present paper, the perception of the seasonal variation of the Sq focus position is re-examined during low solar activity period (2006-2010). Equivalent current vectors are plotted for each geomagnetic quiet day (Ap ⩽ 5), using diurnal variations of H and D components measured at the magnetic observatories located in a narrow longitudinal belt of the Indo-Russian region. On the formation of well-defined Sq current loop, the information about the Sq focus is extracted by identifying a pair of neighboring stations with opposite zonal currents and nearby local times with opposite meridional currents. Thus, the method employed here is different from the methods used in earlier studies. Prominent seasonal variations in the Sq focus latitude, as well as in the local time of Sq focus, are observed. It is observed that the Sq focus is located at ∼30 deg in March equinox, but it moves to lower latitudes in the month of September. In winter, it shows large variability and also the formation of clear Sq current loop is less frequent. The local time of Sq focus is at ∼12 LT in March and shifts to ∼10 LT during September. It is clearly evident from the present analysis that the March and September equinoxes behave differently. The dominance of DE3 and semidiurnal waves in the September equinox could be the reason for the observed disparity.