IJG  Vol.9 No.9 , September 2018
Electron Bulk Surface Density Effect on Critical Frequency in the F2-Layer
ABSTRACT
Ionosphere layer is the atmosphere region which reflects radio waves for telecommunication. The density in particles in this layer influences the quality of communication. This study deals with the effects of Total Electron Contents (TEC) on the critical frequency of radio waves in the F2-layer. Total Electron Contents parameter symbolizes electron bulk surface density in ionosphere layer. Above critical frequency value in F2 layer (foF2), radio waves pass through ionosphere. The knowledge of this value enables to calibrate transmission frequencies. In this study, we consider TEC effects on foF2 under quiet time conditions during the maximum and the minimum of solar cycle 22, at Ouagadougou station, in West Africa. The study also considers the effects of seasons and the hourly variability of TEC and foF2. This work shows winter anomaly on foF2 and TEC on minimum and maximum of solar cycle phase respectively. Running International Reference Ionosphere (IRI) model enables to carry out the effects of TEC on foF2 by use of their monthly average values. This leads to a new approach to calibrate radio transmitters.

1. Introduction

Many models have been developed to investigate ionosphere layer [1] - [13] . The goal of each model is to get the best approach of the ionosphere and carry out the different parameters of this layer. In this study, we use International Reference Ionosphere (IRI) model to get the Total Electron Contents (TEC) and the Critical frequency in the F2-layer (foF2) at Ouagadougou station, characterized by 12.4˚N and 358.5˚E. Ouagadougou is located in West Africa. IRI is an empirical model of the ionosphere. The model uses data sources and provides different parameters of the ionosphere for a given location. The 2012-version of the model is used in this work to get TEC and foF2 parameters. The Total Electron Contents parameter symbolizes the electron bulk surface density in ionosphere layer. This study considers only quiet time conditions [14] . The five quietest days of the minimum and the maximum of solar cycle 22 are considered to characterize the monthly behavior of the parameters. TEC and foF2 profiles are obtained at different seasons, using the given values of the parameters by running IRI model.

2. Study Assumptions

The study is based on the four characteristic months of the four seasons in selected year. For solar cycle 22, the minimum and the maximum phases are respectively 1985 and 1990 [15] . Each characteristic month in the maximum and the minimum of solar cycle 22 is characterized by the five quietest days.

Running IRI model under its 2012-version enables to carry out TEC and foF2 parameters for a given station. Ouagadougou is closed to the Greenwich Meridian and the Equator. Because of this position, local time at Ouagadougou is given by GMT hour. The hourly values of TEC and foF2 for the five quietest days given by running IRI model under its 2012-version are used to calculate TECmean and foF2mean values respectively, which are the monthly average values of these parameters.

3. Results and Discussion

Figure 1 shows Total electron contents and Critical frequency in F2-layer time profiles during minimum phase (1985) of solar cycle 22. TEC time variation is shown on the primary Y axis while foF2 time variation is shown on the secondary Y axis. Panels (a) and (b) are TEC and foF2 seasonal profiles on equinox while panels (c) and (d) represent TEC and foF2 seasonal profiles on solstice. foF2 time variations reproduce mainly “reversed profiles” previously found by [16] .

Figure 2 presents Total electron contents and Critical frequency in F2-layer time profiles during maximum phase (1990) of solar cycle 22. On this figure, TEC and foF2 time variations are shown respectively on the primary and the secondary Y axis. Panels (a’) and (b’) are TEC and foF2 seasonal profiles on equinox and panels (c’) and (d’) represent TEC and foF2 seasonal profiles on solstice. foF2 time variation reproduce “plateau profiles” on maximum solar cycle phase (1990).

On each phase of solar cycle 22, foF2 values on winter are superior to that on summer. This expresses winter anomaly already found by other authors [17] . This study also shows winter anomaly on TEC profiles during solar maximum

Figure 1. TEC and foF2 profiles during minimum solar cycle phase.

and minimum. This is a new contribution found in this study by running IRI-2012. In Figure 1 and Figure 2, TEC and foF2 time variations present similar trend. The conclusion carried out from this remark is that TEC time variations reproduce “reversed profile” on solar minimum and “plateau profile” on solar maximum.

On each panel of Figure 1 or Figure 2, the knowledge of Total electron contents parameter is determined by a given point on TEC time profile. The vertical line from this point to the X axis intersects foF2 time variation at a unique point. This intersection point between the vertical line and foF2 time variation gives foF2 value. This value is the Critical frequency in F2-layer. This method of determining critical frequency in F2-layer value by help of TEC enables to calibrate radio transmitters in telecommunication.

TECmean and foF2mean values can be expressed by the following equations:

TEC mean = i = 0 i = n 1 T E C i n (1)

and

foF 2 mean = i = 0 i = n 1 foF 2 i n (2)

where TECmean and foF2mean are the mean values of these parameters respectively for each month, n the number of terms (n = 25). TECi and foF2i are the values of TEC and foF2 respectively at i time.

Figure 2. TEC and foF2 profiles during maximum solar cycle phase.

Table 1 presents TECmean and foF2mean values for different months during the minimum and the maximum of solar cycle 22.

Table 1 presents the values of TECmean and foF2mean and the seasonal effect on these parameters. TECmean values on March, June, September and December during solar maximum are almost three times more than that on solar minimum respectively. For foF2mean, the values on solar maximum are almost one and half more than that on solar minimum respectively.

Figure 3 presents the trend of TECmean and foF2mean on maximum and minimum during solar cycle 22 obtained with the values in Table 1.

Figure 3 presents the trend of TECmean and foF2mean. A decrease of TECmean is followed by a decrease of foF2mean and conversely. In fact, it is as though the electron bulk surface density, expressed by Total electron contents parameter, is responsible of Critical frequency of F2-layer behavior. Thus, when TEC value increases, radiowaves need to get high values to pass through the F2-layer. Figure 3 shows winter anomaly on foF2mean and TECmean.

4. Conclusion

This study highlights that solar maximum TEC and foF2 parameters given by running IRI-2012 are always superior to that of solar minimum. These results have been already found with Thermosphere-Ionosphere General Circulation Model (TIEGCM) developed at High Altitude Observatory (HAO) of National Center for Atmospheric Research (NCAR) and used by [18] . On minimum

Table 1. TECmean and foF2mean values.

Figure 3. Trend of TECmean and foF2mean.

phase, TEC mean × 10 16 ( m 2 ) [ 9.9864 , 13.6256 ] and foF 2 mean ( MHz ) [ 5.660824 , 7.0736 ] while on maximum phase, TEC mean × 10 16 ( m 2 ) [ 34.8608 , 46.1072 ] and foF2 mean ( MHz ) [ 8.877976 , 10.587448 ] . Running IRI model under its 2012 version reproduces “reversed profiles” on minimum and “plateau profile” on maximum solar cycle phases on foF2 time profiles. It also reproduces winter anomaly on foF2 profiles. These different conclusions have been previously found by other authors. The closed link between foF2 and TEC time variations is carried out. Winter anomaly on TEC parameter during both solar minimum and maximum is a new contribution carried out from this study. The study shows total electron contents effect on critical frequency of radio waves in the ionosphere layer. It brings a new approach to calibrate radio transmitter for telecommunication using total electron contents value according to the season. This approach for radio waves calibration differs from the usual method using time zone adjustment of transmitters.

Cite this paper
Nanéma, E. , Ouédraogo, I. , Zoundi, C. and Ouattara, F. (2018) Electron Bulk Surface Density Effect on Critical Frequency in the F2-Layer. International Journal of Geosciences, 9, 572-578. doi: 10.4236/ijg.2018.99033.
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