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Principal components of quiet time temporal variability of equatorial and low‐latitude geomagnetic fields
Author(s) -
Bhattacharyya Archana,
Okpala Kingsley C.
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja021673
Subject(s) - solstice , equatorial electrojet , equator , earth's magnetic field , electrojet , latitude , morning , atmospheric sciences , southern hemisphere , longitude , amplitude , flux (metallurgy) , climatology , diurnal temperature variation , geology , geodesy , physics , magnetic field , astronomy , materials science , quantum mechanics , metallurgy
Diurnal variations of the horizontal component of the geomagnetic field Δ H on International Quiet days of 1999–2012, measured hourly at two stations in the same longitude zone in the Northern Hemisphere, near and away from the dip equator, have been subjected to principal component analysis. This technique is also applied to the difference Δ H EEJ of Δ H at these two stations, which is attributed to the equatorial electrojet (EEJ). The first three principal components, PC1–PC3, account for 91–96% of the variances in the data. Maximum contribution to the quiet day variations in Δ H around its peak in the morning hours at both the stations, and in the EEJ, comes from the day‐to‐day variation of the amplitude of PC1. Patterns of day‐to‐day variations of PC1 amplitudes for the equatorial station and the EEJ are essentially semiannual modulated by solar EUV flux, superimposed on a longer timescale solar EUV flux‐dependent trend. Contributions from PC2 and to a lesser extent from PC3 are seen to be responsible for the absence of semiannual variations in Δ H in the afternoon hours at the equatorial station. Distribution of amplitudes of PC2 and PC3 for Δ H EEJ for weak electrojet days shows seasonal features in accordance with greater occurrence of afternoon (morning) counter electrojet during June (December) solstice. During the extended solar minimum, PC3 amplitudes for Δ H at the equatorial station and for the EEJ display annual variation. Possible sources for these seasonal features in the variations of equatorial Δ H are discussed.