S.O. Ikubanni

Ionospheric foF2 morphology and response of F2 layer height over Jicamarca during different solar epochs and comparison with IRI-2012 model

Diurnal, seasonal and annual foF2 variability and the response of the F2-layer height over Jicamarca (11.9 °S, 76.8 °W, 1 °N dip) during periods of low (LSA), moderate (MSA) and high (HSA) solar activities was investigated. The relative standard deviation (VR) was used for the analysis. The F2-layer critical frequency pre-noon peak increases by a factor of 2 more than the post-noon peak as the solar activity increases. The variability coefficient (VR) is lowest during the day (7–16%) for the three solar epochs; increases during nighttime (20–26%, 14–26%, and 10–20%, respectively for the LSA, MSA and HSA years); and attained highest magnitude during sunrise (21–27%, 24–27%, and 19–30%, respectively in similar order). Two major peaks were observed in VR – the pre-sunrise peak, which is higher, and the post-sunset peak. Generally, the variability increases as the solar activity decreases. Annually, VR peaks within 23–24%, 19–24% and 15–24% for the LSA, MSA, and HSA periods, respectively. The ionospheric F2-layer height rises to the higher level with increasing solar activity. The foF2 comparison results revealed that Jicamarca is well represented on the IRI-2012 model, with an improvement on the URSI option. The importance of vertical plasma drift and photochemistry in the F2-layer was emphasized.

Ionospheric response to magnetic activity at low and mid-latitude stations

The F2-layer response to the moderate storm of 5–7 April 2010 was investigated using data from two equatorial stations (Ilorin: lat. 8.5°N, 4.5°E; Kwajalein: lat. 9°N, long. 167.2°E) and mid-latitude (San Vito: lat. 40.6°N, long. 17.8°E; Pruhonice: lat. 50°N, long. 14.6°E). Before storm commencement, enhancement, and depletion of NmF2 values were observed in the equatorial and mid-latitude stations, respectively, indicating the latitudinal dependence of the pre-storm event. All the stations with the exception of Kwajalein show positive phase in NmF2 response at the storm onset stage. Positive phase in NmF2 continues over Ilorin and appears on the daytime ionosphere of Kwajalein on 6 April, whereas negative phase suppressed the positive feature in Pruhonice and San Vito until the recovery condition. The differences in the response of F2-layer to the storm for the two equatorial stations were attributed to their longitudinal differences. On the average, both the AE and Dst indices revealed poor correlation relationship. More studies are required to ascertain this finding.

Performance evaluation of GIM-TEC assimilation of the IRI-Plas model at two equatorial stations in the American sector

Empirical models of the ionosphere, such as the International Reference Ionosphere (IRI) model, play a vital role in evaluating the environmental effect on the operation of space-based communication and navigation technologies. The IRI extended to Plasmasphere (IRI-Plas) model can be adjusted with external data to update its electron density profile while still maintaining the overall integrity of the model representations. In this paper, the performance of the total electron content (TEC) assimilation option of the IRI-Plas at two equatorial stations, Jicamarca, Peru (geographic: 12°S, 77°W, dip angle 0.8°) and Cachoeira Paulista, Brazil (Geographic: 22.7°S, 45°W, dip angle �26°), is examined during quiet and disturbed conditions. TEC, F2 layer critical frequency (foF2), and peak height (hmF2) predicted when the model is operated without external input were used as a baseline in our model evaluation. Results indicate that TEC predicted by the assimilation option generally produced smaller estimation errors compared to the “no extra input” option during quiet and disturbed conditions. Generally, the error is smaller at the equatorial trough than near the crest for both quiet and disturbed days. With assimilation option, there is a substantial improvement of storm time estimations when compared with quiet time predictions. The improvement is, however, independent on storm’s severity. Furthermore, the modeled foF2 and hmF2 are generally poor with TEC assimilation, particularly the hmF2 prediction, at the two locations during both quiet and disturbed conditions. Consequently, IRI-Plas model assimilated with TEC value only may not be sufficient where more realistic instantaneous values of peak parameters are required.

Solar eclipse induced perturbations at mid-latitude during the 21 August 2017 event

A study of the response of some ionospheric parameters and their relationship in describing the behaviour of ionospheric mechanisms during the solar eclipse of 21 August 2017 is presented. Mid-latitude stations located along the eclipse path and with data available from the Global Ionospheric radio Observatory (GIRO) database were selected. The percentage of obscuration at these stations ranges between 63 % and 100 %. A decrease in electron density during the eclipse is attributed to a reduction in solar radiation and natural gas heating. The maximum magnitude of the eclipse consistently coincided with a hmF2 increase and with a lagged maximum decrease in NmF2 at the stations investigated. The results revealed that the horizontal neutral wind flow is as a consequence of the changes in the thermospheric and diffusion processes. The unusual increase and decrease in the shape and thickness parameters during the eclipse period relative to the control days points to the perturbation caused by the solar eclipse. The relationships of the bottomside ionosphere and the F2 layer parameters with respect to the scale height are shown in the present work as viable parameters for probing the topside ionosphere during the eclipse. Furthermore, this study shows that in addition to traditional ways of analysing the thermospheric composition and neutral wind flow, proper relation of standardized NmF2 and hmF2 can be conveniently used to describe the mechanisms.

Nighttime ionospheric saturation effect estimation in the African equatorial anomaly trough: A comparison of two approaches

Using the two-segmented and the quadratic regression analyses methods, the existence of saturation effect in the ionospheric electron content has been established in published literatures. With data set that spans an 11 year period (one solar cycle) from an African low-latitude station—Ouagadougou, Burkina Faso (Geographical coordinates 12oN, 1.8oW, dip ~3oN)—and adopting the quadratic and the two-segmented regression methods, we have studied nighttime saturation effect on the critical frequency of ionospheric F2 layer (foF2) around the magnetic dip. Bothmethods revealed that saturation effect in foF2 cuts across all seasons during nighttime. This phenomenon was least at the peak of the prereversal enhancement (PRE) period and increases significantly beyond midnight. Either of the two approaches can be adopted for saturation effect studies. The advantage of the two-segmented over the quadratic is that the change point (breakpoint), which is the solar flux levelwhere saturation effects first become observable, can be determined. The effect seen around the PRE period may be attributed to the E × B drift while the effect beyond the PRE period is masked by other mechanisms.