Solar daily variation at geomagnetic observatories in Pakistan

The synthesized solar daily variation for D component, S(D), at Karachi, Sonmiani, Quetta and Islamabad did not show any signs of winter anomaly for the period studied. However, S(D) variation at Karachi during winter season showed morning minimum followed by a maximum at local noon and another minimum in the afternoon. We suggest this could be the effects of Equatorial Ionospheric Anomaly (EIA) observable at the Karachi observatory only during the winter season. Similarly, much disturbed in equinoctial and summer months, S(Z) illustrated an unwavering daily variation for the winter season at the Karachi observatory for both solar cycles. We find that it is the vertical component which is more strongly correlated with the mean monthly sunspot number and F10.7 solar radio flux. An interesting result obtained at Islamabad is the semi-diurnal variation of H component with a morning maximum and afternoon minimum and the phase reversal noticed for Z component variation. Attributed to an early eastward current this is, usually, observed for stations close to the Sq focus current system.