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

The quiet time characteristics of equatorial electrojet (EEJ), counter electrojet (CEJ), and solar quiet (Sq) day geomagnetic field over two decades (1980–2002) are established using Principal component analysis (PCA) from equatorial (Ettaiyapuram) and off‐equatorial (Hyderabad) Magnetic Observatories, India, over sunspot cycles 21–23. The patterns of normal field shows that the diurnal amplitudes were strong during equinox compared to other seasons. The diurnal amplitudes have reduced from the 21st to the 23rd sunspot maxima following the trend of weakening of sunspot cycle. Analysis of seasonal means shows evening CEJs were more pronounced when compared to morning and afternoon in different phases of sunspot cycle. The abnormal field variations have a strong correlation with the occurrence of afternoon CEJs during solar minima; a correlation of seasonal occurrences of CEJs with phases of sunspot cycles is revealed. The first principal component (PC1) closely correlates with the observed diurnal amplitudes of EEJ and Sq, whereas the other principal components reveal the presence of abnormal variations during daylight hours at equatorial observatory. 




N. Phani Chandrasekhar and Arka Roy, Journal of Geophysical Research: Space Physics,

125, e2020JA028464.