The Impact of Sunspots Number on Critical Frequencies foF2 for the IONOSPHERIC Layer-F2 Over Erbil Station During the Down Phase of Solar Cycle 24

The ionosphere layer (F2) is known as the most important layer for High frequency (Hf) radio communication because it is a permanent layer and excited during the day and night so it is able to reflect the frequencies at night and day due to its high critical frequency, and this layer is affected by daily and monthly solar activity. In this study the characteristics and behavior of F2 layer during Solar cycle 24 were studied, the effect of Sunspots number (Ri) on the critical frequency (foF2), were investigated for the years (2015, 2016, 2017, 2018, 2019, 2020) which represents the down phase of the solar cycle 24 over Erbil station (36° N, 44° E) by finding the critical frequency (foF2) values, the layer’ s impression times are determined for the days of solstice as well as equinox, where the solar activity was examined for the days of the winter and summer solstice and the days of the spring and autumn equinoxes for a period of 24 hours by applied the International Reference Ionosphere model IRI (2016). The output data for foF2 were verified by using the IRI-Ne- Quick option by specifying the time, date and Sunspot number parameters. Statistical analysis was caried out through the application of the Minitab (version 2018) in order to find the correlation between the critical frequency (foF2) of Ionospheric layer F2 and Sunspot number. It was concluded that the correlation is strong and positive, this indicate that critical frequency (foF2) increase with increasing Sunspots number (Ri) for solar cycle 24.

Behavior of electron density in the ionosphere over Norilsk during the period of declining solar activity

We report the results of approximation of electron density Ne array obtained with a digisonde at the high-latitude station Norilsk (69.40° N, 88.10° E) during years of declining solar activity (2003–2006). The calculations are made using the author's semi-empirical model with new coefficients calculated specifically for the station Norilsk. We obtain altitudinal changes of annual variations in daily Ne at heights of the ionospheric layer F1 (120–200 km). Approximation of experimental data describes Ne quite satisfactorily at these heights. Nevertheless, there are periods with quite pronounced deviations of model values from the experiment. The presence of significant geomagnetic disturbances during these periods is probably one of the reasons for such deviations.

Behavior of electron density in the ionosphere over Norilsk during the period of declining solar activity

We report the results of approximation of electron density Ne array obtained with a digisonde at the high-latitude station Norilsk (69.40° N, 88.10° E) during years of declining solar activity (2003–2006). The calculations are made using the author's semi-empirical model with new coefficients calculated specifically for the station Norilsk. We obtain altitudinal changes of annual variations in daily Ne at heights of the ionospheric layer F1 (120–200 km). Approximation of experimental data describes Ne quite satisfactorily at these heights. Nevertheless, there are periods with quite pronounced deviations of model values from the experiment. The presence of significant geomagnetic disturbances during these periods is probably one of the reasons for such deviations.

Alternative Approach for Tsunami Early Warning Indicated by Gravity Wave Effects on Ionosphere

The rapid displacement of the ocean floor during large ocean earthquakes or volcanic eruptions causes the propagation of tsunami waves on the surface of the ocean, and consequently internal gravity waves (IGWs) in the atmosphere. IGWs pierce through the troposphere and into the ionospheric layer. In addition to transferring energy to the ionosphere, they cause significant variations in ionospheric parameters, so they have considerable effects on the propagation of radio waves through this dispersive medium. In this study, double-frequency measurements of the Global Positioning System (GPS) and ionosonde data were used to determine the ionospheric disturbances and irregularities in response to the tsunami induced by the 2011 Tohoku earthquake. The critical frequency of the F2 layer (foF2) data obtained from the ionosonde data also showed clear disturbances that were consistent with the GPS observations. IGWs and tsunami waves have similar propagation properties, and IGWs were detected about 25 min faster than tsunami waves in GPS ground stations at the United States west coast, located about 7900 km away from the tsunami’s epicenter. As IGWs have a high vertical propagation velocity, and propagate obliquely into the atmosphere, IGWs can also be used for tsunami early warning. To further investigate the spatial variation in ionospheric electron density (IED), ionospheric profiles from FORMOSAT-3/COSMIC (F3/C) satellites were investigated for both reference and observation periods. During the tsunami, the reduction in IED started from 200 km and continued up to 272 km altitude. The minimum observed reduction was 2.68 × 105 el/cm3, which has happened at 222 km altitude. The IED increased up to 767 km altitude continuously, such that the maximum increase was 3.77 × 105 el/cm3 at 355 km altitude.

THE ATMOSPHERE BELOW 200 km OVER NORILSK AT SOLAR MINIMUM AND MAXIMUM

We have obtained seasonal variations in relative values of the main thermospheric gas components [O]/[N₂] and [O₂]/[O] during solar maximum. We have used our method and measurements made with the Norilsk digisonde (69.4° N, 88.1° E) at heights of the ionospheric layer F1 (120–200 km) in quiet and disturbed geomagnetic conditions. We have compared [O]/[N₂] and [O₂]/[O] ratios during solar maximum with the corresponding values for the long period of solar minimum (2007–2009) in Norilsk. The relative content of atomic oxygen particles has been found to increase during solar maximum by more than 35 % in winter and autumn on quiet and disturbed days. In spring and summer, the atmosphere is enriched with molecular oxygen particles by 20 % both on quiet and disturbed days of solar maximum as compared to the conditions of solar minimum.

INVERSION OF BACKSCATTER IONOGRAMS INTO QUASI-PARABOLIC IONOSPHERIC LAYER PARAMETERS

We present an inversion scheme of the backscatter signal leading edge into parameters of the quasi-parabolic electron density profile, which is based on the comparison of experimental and calculated minimum delays of scattered signals with corresponding distance to the skip zone border. Input parameters are frequency dependences of minimum group path of signal propagation, derived from processing and interpreting backscatter ionograms. For a fixed sounding frequency, the ionospheric parameter pair — the critical frequency and height of the F2-layer maximum — is defined as the intersection point of two curves representing solutions of minimization problems for discrepancy functionals of the minimum group path and the range to the skip zone border. Determining the ionospheric parameters by this inversion scheme on the sounding frequency grid allows us to construct a two-dimensional distribution of electron density in the direction of backscatter sounding.

THE ATMOSPHERE BELOW 200 km OVER NORILSK AT SOLAR MINIMUM AND MAXIMUM

We have obtained seasonal variations in relative values of the main thermospheric gas components [O]/[N₂] and [O₂]/[O] during solar maximum. We have used our method and measurements made with the Norilsk digisonde (69.4° N, 88.1° E) at heights of the ionospheric layer F1 (120–200 km) in quiet and disturbed geomagnetic conditions. We have compared [O]/[N₂] and [O₂]/[O] ratios during solar maximum with the corresponding values for the long period of solar minimum (2007–2009) in Norilsk. The relative content of atomic oxygen particles has been found to increase during solar maximum by more than 35 % in winter and autumn on quiet and disturbed days. In spring and summer, the atmosphere is enriched with molecular oxygen particles by 20 % both on quiet and disturbed days of solar maximum as compared to the conditions of solar minimum.

INVERSION OF BACKSCATTER IONOGRAMS INTO QUASI-PARABOLIC IONOSPHERIC LAYER PARAMETERS

We present an inversion scheme of the backscatter signal leading edge into parameters of the quasi-parabolic electron density profile, which is based on the comparison of experimental and calculated minimum delays of scattered signals with corresponding distance to the skip zone border. Input parameters are frequency dependences of minimum group path of signal propagation, derived from processing and interpreting backscatter ionograms. For a fixed sounding frequency, the ionospheric parameter pair — the critical frequency and height of the F2-layer maximum — is defined as the intersection point of two curves representing solutions of minimization problems for discrepancy functionals of the minimum group path and the range to the skip zone border. Determining the ionospheric parameters by this inversion scheme on the sounding frequency grid allows us to construct a two-dimensional distribution of electron density in the direction of backscatter sounding.