Quiet Time Variation of Ionosphere Parameters near Equator

In recent, ionosphere has been intensively investigated by analyzing data variability and or improving
existing models for now casting and or forecasting reasons. Therefore, the investigation of f2 layer
critical frequency (fof2) parameter by means of the 2012 version of iri (international reference
ionosphere) model and tiegcm (thermosphere ionosphere electrodynamics general circulation model)
is required. The present study appreciates the estimation of TIEGCM (Thermosphere Ionosphere
Electrodynamics General Circulation Model) and that of the 2012 version of IRI in African Equatorial
Ionisation Anomaly (EIA) region through the diurnal variation of F2 layer critical frequency (foF2). The
comparison made between data and theoretical values carried out from TIEGCM and IRI-2012 during
solar cycle minimum and maximum phases and under quiet time condition over seasons. Data
concern solar cycle 22 foF2 data of Ouagadougou station (Lat: 12.4° N; Long: 358.5°E, dip: 1.43°N
for 2013) provided by Télécom Bretagne. Quiet time condition is determined by Aa inferior or equal to
20 nT and solar cycle maximum, and minimum phases correspond to sunspot number Rz superior to
100 and Rz inferior to 20, respectively. Seasons are estimated by considering December as winter
month, March as spring month, June as summer month and September as autumn month. Models
predictions are better during solar maximum than during solar minimum and strongly dependent on
pre-sunrise and post-sunset periods. The seasonal Hourly quiet time foF2 is given by the arithmetic
mean values of the five quietest day hourly values. Data profiles show noon bite out a profile with
more and less pronounced morning or afternoon peak in equinox and that during solar maximum and
that also in solar minimum except during solstice where the profile fairly is dome or plateau. During
solar minimum, both models present a more or less pronounced afternoon peak with more or less
deep trough between 1000 LT and 1400 LT. During solar maximum, in general, TIEGCM shows
afternoon peak and IRI-2012 present plateau profile. This result exhibits the non-well estimation of the
dynamic process of this region. Model accuracy is highlighted by the Mean Relative Error (MRE)
values. These values show a better prediction for IRI-2012 except in September for both solar cycle
phases involved. The non-good prediction of TIEGCM is observed in December during solar minimum
and in June during solar maximum. This study shows that running IRI model enables to show that
foF2 time variations present “reversed profiles” on minimum and “plateau profile” on maximum solar
cycle phases. It also shows winter anomaly on foF2 profiles. These different conclusions have been
previously found by other authors. This work also reports winter anomaly on foF2 parameter. The
closed link between foF2 and TEC time variations is carried out. (Winter anomaly on TEC). The study
shows Total electron contents effects on critical frequency of radio waves in the ionosphere layer.