Abnormal quiet day variations in Indian region along 75° E meridian

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.

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…Obviously, the meaning of principal components could be different for different components of the geomagnetic field, for different stations, and for different selections of the data length. The following is a (partial) list of Sq studies in which the principal component analysis is used: Golovkov et al (1978), Rajaram (1983), Alex et al (1998), Gurubaran (2002), Yamada (2002Yamada ( , 2009), Xu and Kamide (2004), Stening et al (2005a), Chen et al (2007), Bhardwaj et al (2015), Bhattacharyya and Okpala (2015). The first principal component (added to the average daily variation) is often interpreted as the contribution of normal Sq currents.…”

Principal Component Analysis As a Tool to Extract Sq Variation from the Geomagnetic Field Observations: Conditions of Applicability

“…Later, Xu and Kamide (2004) and Chen et al (2007) revived the interest of the geomagnetic community in PCA as a useful tool that allows not only to extract regular variations of the geomagnetic eld, as Sq and SD but also to analyze seasonal and geographic variations of the phase and amplitude of the Sq and SD elds and the dependence of their intensity on the level of the solar and geomagnetic activity. Works of Wu et al (2007), De Michelis et al, (2009Michelis et al, ( , 2010, Bhardwaj et al (2015Bhardwaj et al ( , 2016 and others (see also review by Yamazaki and Maute, 2017), generally con rmed the applicability of PCA to the extraction of the regular geomagnetic eld variations observed at different latitudes, and for the time intervals of different length and corresponding to different geomagnetic activity levels. However, the results obtained for different regions/time intervals were somewhat different.…”

“…In particular, it was found that for the H (X) component for the Asian sector (Xu and Kamide, 2004;Chen et al, 2007;Wu et al, 2007;Bhardwaj et al, 2015Bhardwaj et al, , 2016 the Sq variation is ltered to the rst PC and the SD variation is ltered to the second PC. On the contrary, for the European sector (De Michelis et al, 2010) PC1 is associated with SD and PC2 is associated with Sq.…”

First results from the Swarm Dedicated Ionospheric Field Inversion chain

“…Reasons for this hemispheric asymmetry could be that: (a) Some electrical currents flow from the equatorial region into the Southern hemisphere, i.e., there is some electrical coupling between the EEJ and Sq currents in that hemisphere; (b) part of the DE3 tide or another tide contributing to the equatorial wave-4 structure leaks into the Southern hemisphere. In both cases, there seems to be the need for some coupling between EEJ and Sq currents, an issue that is still open (see, e.g., Bhardwaj et al 2015;Manoj et al 2006b, who presented the opposite view, and references therein).…”