Abstract:
The present study mainly focuses on the anomalous characteristics observed in some abnormal quiet day (AQD)
variations of the north–south (H) and east–west (D) components of geomagnetic field at 11 Indian stations for the
years 2004, 2005, and 2009 during low solar activity period for summer and winter months. In this study, during
some quiet days, horizontal component (H) at stations situated near equator to the Sq focus latitudes has shown
double peak structure, exhibiting maximum in the forenoon and afternoon hours. Correspondingly, declination
component (D) over the low latitudes has shown features outside the normal trend, i.e., westward-directed field in
the morning hours and eastward-directed field in the afternoon hours and shows negative bay-type of variations.
The technique of principal component analysis (PCA) has been applied to the data sets for presenting a
quantitative estimate of the influence of day-to-day variability in the Sq current system on normal (NQD) and
abnormal quiet (AQD) days. AQDs observed at the Indian stations are reflected in the second principal component
PC-2. Anomalous changes in day-to-day variations (H and D) are interpreted as an influence of high latitude
magnetospheric current systems as well as due to single current vortex (SCV) located in the ionosphere whose
focus lie between 10° and 15° N geomagnetic latitude for the northern hemisphere winter AQDs.
