Le Huy Minh*, Tran Thi Lan, C. Amory -Mazaudier, R. Fleury, A. Bourdillon, J. Hu, Vu Tuan Hung, Nguyen Chien Thang, Le Truong Thanh, Nguyen Ha Thanh


This study presents the continuous GPS network in Vietnam and the results of the study on time variations of the total electron content (TEC) in the South East Asian equatorial ionization anomaly (EIA) for the 2006-2013 period. In each year we observe a semiannual pattern of TEC diurnal variation in all the stations with its maximum amplitude at the equinox. In both hemispheres, the amplitude of the crest is larger in northern spring equinox than in autumn from 2006 to 2008 (descending phase of solar cycle) and smaller in spring than in autumn from 2009 to 2011 (increasing phase of solar cycle), from 2012-2013 (maximum period of solar cycle) the amplitudes of the crests in spring and autumn are equivalent. We also observe an asymmetry between the amplitude and the position of the two crests of ionization. There is a very high level of correlation between the amplitude of the TEC at the two crests and the sunspot number is approximately equal to 0.9. During the deep solar minimum 2008-2009, the amplitude of crests of ionization becomes small during several months in summer and winter (about 20 TECu). The results show that both crests move more significantly equatorward in winter than in other seasons and there is a tendency for both crests to appear earlier in winter and later in summer. In the solar minimum years, the amplitudes of the crests are minimal; the positions of the crests are nearer the magnetic equator and the crests appear earlier than in other years.


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Equatorial ionization anomaly; Total electron content (TEC); GPS technology; Sunspot; Solar cycle

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