The afternoon counter-electrojet current system along the 75°E meridian during the IEEY

Abstract

In the present study, the technique of principal component analysis (PCA) is applied to analyze the hourly mean values of geomagnetic field components D, H, and Z along an Indo-Russian chain of stations during the International Equatorial Electrojet Year (IEEY) from January 1992 to June 1993. This technique (PCA) is found to be suitable for separating the normal electrojet (NEJ) and counter-electrojet (CEJ) variations, and the first two principal components (PCs) are able to describe the characteristics of NEJ-and CEJ-related field variations. It is found that the first principal component (PC-1) for H, D, and Z varies as a function of time with latitude and depicts the well-known Sq variations, whereas PC-2(H) does not show any variations at all latitudes during NEJ days. On CEJ days, PC-2(H) shows a large negative excursion at equatorial stations (KAN to BAN). The NEJ-and CEJ-related current systems are determined by combining the hourly inequalities in D and H. PC-1 brings out a well-defined anticlockwise loop for NEJ days, with its focus near the dip latitude (~35°N), and a clockwise loop for CEJ days with a well-defined focus near the dip latitude (~20°N) around noon local time. The CEJ-related current system is marked by intense westward current flow in the equatorial belt and is shown to close its path by forming a clockwise loop extending from the dip equator to midlatitudes. Comparison with a numerically simulated current system, caused by various tidal modes, emphasizes the significance of antisymmetric semidiurnal tidal modes in the generation of CEJ events.

Re‐Visiting EEJ and CEJ Occurrences Pattern Under the Influence of Sq Variations of Both Hemispheres

“…The method of extraction of principal components is described in detail by Yamazaki and Maute (2017). Earlier studies on PC analysis of EEJ and Sq can be found in (Alex et al., 1998; Bhardwaj & Subba Rao, 2017; Bhattacharyya & Okpala, 2015; Faynberg, 1975; Gurubaran, 2002; Gurubaran et al., 2016; Rajaram, 1980; Vertlib & Wagner, 1970).…”

On the Occurrence of Afternoon Counter Electrojet Over Indian Longitudes During June Solstice in Solar Minimum

“…Bhattacharyya and Okpala (2015) applied a similar analysis to quiet time geomagnetic field variations between 1999 and 2012 and reported that second and third harmonics contribute to the occurrence of CEJ events. In recent investigation, Bhardwaj and Subba Rao (2017) showed that the higher harmonics are associated with clockwise current system in afternoon. Therefore, the studies by Bhattacharyya and Okpala (2015) can also be taken to produce clockwise current cell in the afternoon.…”

Imprints of Sunspot Cycles on Normal and Abnormal Geomagnetic Fields: Case Study From Equatorial and Low‐Latitude Sites of India

“…PCA is used in this study, which is based on singular‐value decomposition and has been extensively used to extract the principal components from a group of data samples and to separate the contributions from different physical processes. The nature of quiet time diurnal variation and the abnormal variation in the geomagnetic field are separated using PCA and the daily variation is expressed as a summation of a few Eigen modes (Alex et al, 1998; Bhardwaj & Subba Rao, 2017; Bhattacharyya & Okpala, 2015; Faynberg, 1975; Gurubaran, 2002; Gurubaran et al, 2016; Rajaram, 1980; Vertlib & Wagner, 1970). The above researchers extensively elucidated the methodology of PCA and hence not discussed here.…”

“…equatorial electrojet for the years 1993-2011 using Tirunelveli/Trivandrum-Alibag pair and has reported that the CEJ occurrences were found to be larger during minimum solar years and has a high correlation with enhanced tides, (v) Bhardwaj and Subba Rao (2017) discussed the quiet time current loops on normal and abnormal days in January 1992 to June 1993 along the Indo-Russian chain of stations. This study brought out the information on anticlockwise pattern for normal electrojet days with its focus near the dip latitude and a clockwise pattern for abnormal electrojet days with a well-defined focus near the dip latitude around noon local time.…”

“…By using principal component analysis (PCA), many researchers disclosed the nature of quiet time diurnal variation and provided insights on equatorial and low‐latitude ionosphere in the Indian region: (i) Rajaram (1983) determined the Sq focus and the relation between the Sq focal latitude and electrojet strength for the Indian geomagnetic stations along 75°E using 10 quiet days in vernal equinox of 1976, (ii) Alex et al (1998) discussed the quiet day characteristics of diurnal, occurrence of noontime and afternoon CEJs using Trivandrum‐Alibag pair for the months June and July 1985–1987 and examined the abnormal field variations on the days of weak electrojet, (iii) Bhattacharyya and Okpala (2015) discussed the diurnal variations of horizontal field during quiet days at two observatories: Tirunelveli and Alibag, for the years 1999–2012, which provided valuable inputs toward the semiannual, annual, and seasonal features of the first three principal components and the possible sources for the seasonal variation, (iv) Gurubaran et al (2016) demonstrated the role of atmospheric tides in the quiet time variabilities of equatorial electrojet for the years 1993–2011 using Tirunelveli/Trivandrum‐Alibag pair and has reported that the CEJ occurrences were found to be larger during minimum solar years and has a high correlation with enhanced tides, (v) Bhardwaj and Subba Rao (2017) discussed the quiet time current loops on normal and abnormal days in January 1992 to June 1993 along the Indo‐Russian chain of stations. This study brought out the information on anticlockwise pattern for normal electrojet days with its focus near the dip latitude and a clockwise pattern for abnormal electrojet days with a well‐defined focus near the dip latitude around noon local time.…”