Day-to-day variability in the occurrence characteristics of Sq focus during d-months and its association with diurnal changes in the Declination component

Abstract

Scrutiny of the geomagnetic observations of the Declination component 'D' from equatorial and low-latitude locations in the Indian longitude revealed anomalous variations during d-months. Examination of the Quiet day (Ap≤7) variations in the Declination component (Y in nT = H sin D) and Horizontal component (H ) during the d-months (November, December, January, February) of the low solar activity year 1977 revealed the salient features associated with the day-to-day changes observed in Sq current system over the latitude chain in the Indo-Russian longitude. Diurnal variations in the east-west component Y and north-south component H were used to depict the effect of changes in the Sq current pattern for a selected set of Quiet days, which are classified into normal and abnormal days based on the trend in the variation of the Declination component. Normal days designated in the study clearly showed the expected pattern of variation in Y (eastward-directed field) in the morning hours and westward-directed field in the afternoon hours, and diurnal variation of H simultaneously showed the presence of northern Sq focus within the low-latitude range. In contrast, the abnormal days projected by the variation in Y and H on certain days of d-months showed an almost complete absence of the focus formation within the expected latitude extent. Day-to-day variability characteristics of the Declination component discussed in the study are illustrated in relation to modifications in the expected Sq current system by the invasion of the prevalent southern hemisphere current whorl to the northern hemisphere during the winter months. Some of the anomalous changes observed in the day-to-day variation in the latitudinal pattern of Y and H components are also interpreted as suggesting an influence of high-latitude magnetospheric current systems on certain quiet days.