Quantitative Characteristics of Equatorial Ionization Gradient Above 150 km at Low Solar Activity

Abstract

The electron ionization gradient (dN/dh) 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 (hdN) 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. hdN at the position of maximum ionization is lower than the real height (hmF2) across all seasons. The percentage difference in dN/dh 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 dN/dh and vertical drift velocity.

Pattern of Ionization Gradient, Solar Quiet Magnetic Element, and F2‐Layer Bottomside Thickness Parameter at African Equatorial Location

“…The result obtained by Adebesin, Adeniyi, Oladipo, et al (2018) had prompted the present work. What happened at some specific local time of the day relative to the ionization gradient phenomenon is yet to be fully explored in the African ionospheric sector.…”

“…Hardly has the ionization gradient (dN/dh) been employed in specifying ionospheric electrodynamics. However, with the result obtained by Adebesin, Adeniyi, Oladipo, et al (2018), in which dN/dh was used to explain the pattern and morphology of the E × B drift velocity, Vz (dN/dh increases as Vz decreases), and establish a connection with production, recombination, and diffusion processes; it is worthwhile to consider dN/dh as an alternative parameter in the description of ionospheric electrodynamics. Consequently, the relationship between dN/dh, B 0 , and Sq (B H ) had been presented, together with their dependence on solar activity.…”

“…It is also anticipated that the pattern of dN/dh in this work (especially at specific hours) will be a good alternative to study plasma dynamics, and even relating to the zonal electric field (using the Sq current as a proxy parameter), that may eventually affect ionospheric altitude. An explicit information on the importance of using ionization gradient is well highlighted in the work of Adebesin, Adeniyi, Oladipo, et al (2018). The choice of the study year (2010, low solar activity period) is also to assist in specifying near quiet ionospheric electrodynamics condition.…”

“…However, none of these studies had explained the ionospheric processes involved using the dN / dh concept. The more recent work by Adebesin, Adeniyi, Oladipo, et al () was the first to quantitatively describe the characteristics of dN / dh at an African equatorial latitude in the dynamic description of the ionosphere, especially during periods of maximum and minimum ionization positions. The authors presented their results for both the maximum and minimum gradient points, and establish an inverse relationship between the pattern of dN / dh and vertical plasma drift, besides obtaining the average height during when the maximum (310 km) and minimum (235 km) gradient magnitudes were attained.…”

“…What happened at some specific local time of the day relative to the ionization gradient phenomenon is yet to be fully explored in the African ionospheric sector. For this reason, same Digisonde Portable sounder (DPS‐4.2 version) data used to obtain the ionization gradient for the same study period (2010) and location (Ilorin, in the African equatorial sector) similar to Adebesin, Adeniyi, Oladipo, et al () was employed in the present work, but this time, with emphasis on four specific diurnal hours. In addition, the data of the F 2 ‐layer bottomside thickness parameter ( B 0 ) obtained from the same digisonde and the horizontal magnetic component data from the magnetometer (Magnetic Data Acquisition System (MAGDAS)) collocated at the same station had been included in the present study.…”