Sq-Field Behaviour & Daily H, D-component Variability at Sonmiani Geomagnetic Observatory, Pakistan

First results are presented on the behaviour of solar quiet-day (Sq) variations of northsouth (H) and east-west (D) component of geomagnetic field at Sonmiani geomagnetic observatory (SON) for data set 2009-2012. The hourly mean values are used to study the variation of the components and only quiet conditions are examined. It is found that variation of Sq(H) and Sq(D) is a dawn to dusk phenomenon with non zero variation at night-time and pre-sunrise hour. H-component has its maximum in equinoctial months whereas D-component attains maximum values in June solstice. Day-to-Day variability in H and D-components is observed even on quiet days which can be attributed to the variability of ionospheric conductivities and local atmospheric wind pattern. We found that monthly mean variations show diurnal variations in H-component and semi-diurnal for D-component whereas seasonal variations are found to have semi-annual pattern for H-component and annual pattern for D-component. Equinoctial asymmetry is also observed in both components with spring amplitude consistently greater than autumnal amplitude for H-component whereas for D-component spring amplitude is greater for less solar active years and autumnal amplitudes are greater for more solar active years. The amplitude of annual mean is greater for H-component than D with D-component variation consistently shown smaller amplitude for morning eastward maximum and greater amplitude for afternoon westward maximum for the study period. Diurnal variation with Semi-annual characteristics is observed for observatories in northern hemisphere for local winter and summer season whereas for observatories in southern hemisphere diurnal variation is observed for local summer season and semi-diurnal for local winter season for H-component. However, for D-component semi-diurnal variation with annual varying pattern is seen for observatories in both hemispheres. We also observed the winter anomaly at Sonmiani in D-component which could be due to the movement of Sq focus position to the lower latitudes. It is therefore concluded that the behaviour of Sq current system observed at Sonmiani agrees with previous studies carried out for this longitude sector. However, at SON we observe consistently morning and evening negative amplitudes with secondary maxima in D months. Since winter has higher possibility of occurrence of Abnormal Quiet days (AQD) it is suggested that this may be due to abnormal behaviour of Sq field at Sonmiani. Also, sea surface and ground induced current may affect the regular quiet daily variation and only detailed Sq modelling at Sonmiani could answer these observed features. ▫ Keywords—Geomagnetism, Solar Quiet (Sq) Daily Variation, Pakistani latitude, Equatorial electrojet