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Quantitative Characteristics of Equatorial Ionization Gradient Above 150 km at Low Solar Activity
Author(s) -
Adebesin B. O.,
Adeniyi J. O.,
Oladipo O. A.,
Olawepo A. O.,
Adimula I. A.
Publication year - 2018
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/2018rs006560
Subject(s) - sunrise , sunset , noon , solstice , equinox , solar maximum , atmospheric sciences , altitude (triangle) , daytime , solar minimum , tec , ionogram , ionosphere , ionization , environmental science , physics , geodesy , geology , mathematics , solar cycle , latitude , electron density , solar wind , geometry , electron , optics , astronomy , ion , quantum mechanics , magnetic field
The electron ionization gradient (d N/ d h ) characteristics were quantitatively presented using data from Ilorin (8.50°N, 4.68°E) Digisonde during low solar activity. Ionogram inversion using calculated average representative profile program was employed in obtaining the profile data. Results were presented for both the minimum and maximum gradient positions above the 150‐km altitude. The daily hours were classified into four segments. Our result revealed that at sunset/postsunset and nighttime hours, the ionization magnitude at the point of maximum gradient during the equinoxes is twice the value in solstices. This feature of the higher ratio in the equinox is less distinct at sunrise/presunrise and noon/postnoon hours and not pronounced at all hours of the minimum gradient position. The time of occurrence of the maximum gradient for the sunrise/prenoon, noon/postnoon, and nighttime hours, respectively, are 07 LT, 17 LT, and 23 LT for all seasons. For this same diurnal segments at the point of minimum gradient, it is 05 LT, 12 LT, and 04 LT, respectively. The height ( h dN ) at which the highest gradient was reached is ≈310 km, occurring during the sunset/postsunset hours for both the maximum and minimum gradient positions. The lowest (≈235 km) was reached during the sunrise/prenoon hours. h dN at the position of maximum ionization is lower than the real height ( h m F 2 ) across all seasons. The percentage difference in d N/ d h magnitude at the position of maximum and minimum gradients is lowest at noon/postnoon period and highest at sunrise/prenoon hours. The various physical processes involved were discussed. We established an inverse relationship between the pattern of d N/ d h and vertical drift velocity.