This paper aims to establish a comparison between both geomagnetic activity classification methods on foF2 diurnal variation over solar cycle phases. It concerns first a comparison of geomagnetic activity occurrences according to both classification methods; and second the geomagnetic effect on foF2 diurnal variation profiles as defined for the equatorial latitudes. The occurrences of the different disturbed geomagnetic activities (recurrent activity (RA), shock activity (SA) and fluctuant activity (FA)) according to both classifications (ancient classification (AC) and new classification (NC)) have been studied at Dakar ionosonde station (Lat: 14.8°N; Long: 342.6°E). Regarding both classifications, the RA occurs more during the decreasing phase. And it’s observed that the RA occurs the most during the increasing phase for the AC and during the minimum phase for the NC. The maximum gap of occurrence ( ) between both classifications is ᆟ.1% (for the negative value which is observed during the increasing phase) and +16.74% (for the positive one which is observed during the decreasing phase). The occurrence of the SA in relation with both classifications is the lowest during the minimum phase and the maximum occurrence is observed during the maximum and decreasing phases, for the AC, with a value close to 37% and for the NC at the maximum phase with a percentage of 54.47%. The maximum gap of occurrence () between both classifications is ᆥ.85% (for the negative value which is observed at maximum phase) and +13.53% (for the positive one which is observed during the decreasing phase). For both classifications, the FA occurs the least during the minimum phase and the most during the maximum phase for the AC and at maximum and decreasing phases with percentage values of occurrence of roughly 37% for the NC. The maximum gap of occurrence () between both classifications is ᆞ% (for the negative value which is observed during the decreasing phase) and +20.11% (for the positive one which is observed during the maximum phase). foF2 diurnal profiles throughout solar cycle phases concerning the AC and the NC have been compared. The FA diurnal profiles don’t present a difference. The RA and the SA present a difference during minimum and increasing phases and the least at maximum and decreasing phases.
The irradiation of the Earth space environment by the magnetized plasma propagating from the Sun induced a continuous global magnetic disturbance, namely geomagnetic storms [
This Sun-Earth interaction is characterized by four geomagnetic events identified by [
Zerbo et al. [
Several papers (e.g. [
The outline of the paper is as follows: Section 2 concerns materials and methods, Section 3 is devoted to results and discussions, and the conclusion and research perspectives end the paper as its fourth section.
For the present paper, data involved are: 1) foF2 values carried out at Dakar station. This station operated from 1950 to December 1996. The involved data interval for our study is 1976-1995 and concerned Solar Cycle 21 (SC 21) and Solar Cycle 22 (SC 22); 2) Zurich sunspot number (Rz), from OMNI data set http://omniweb.gsfc.nasa.gov/form/dx1.html. For the influence of solar cycle phase and 3) Mayaud [
Solar cycle phases are determined by using the criteria given by [
Based on the strong correlation between geomagnetic index Aa (obtained from the following website: http://isgi.unistra.fr/data_download.php) and solar wind velocity established by [
It’s important to note that, this Legrand and Simon’s classification or ancient classification (AC) clearly classify only 60% of the geomagnetic activity [
The pixel diagram presents the variation of the geomagnetic activity by solar rotation, also called Bartels rotation [
This paper aims to study the difference of foF2 time variation, throughout solar cycle phases for a given disturbed activity for the both geomagnetic activity classifications. The data analysis will be done through two ways: 1) The analysis of the recurrence of the different geomagnetic activities according to the both methods of classification over solar cycle phases in one case and seasons in another case; 2) The profiles obtained are analyzed in comparison with the five standard profiles established by [
Firstly, the analysis of the occurrence of the geomagnetic activities is done by: 1) comparing the occurrence of the different geomagnetic activities in relation with the both classification by using the Equation (1);
Δ occ = GA occ / AC − GA occ / NC (1)
where Δ occ is the gap of the occurrence of the concerning geomagnetic activity classes.
GA occ / AC is the occurrence of the concerning geomagnetic activity class in relation with the ancient classification
GA occ / NC is the occurrence of the concerning geomagnetic activity class in relation with the new classification
And 2) putting error bars in data graphs. We can note that error bar is obtained by using the Equation (2);
σ = V (2)
where V is the variance defined by V = 1 N ∑ i = 1 N ( x i − x ¯ ) 2 with x ¯ mean value and N the total number of observations for a particular dataset.
Secondly, the foF2 profiles (see
during daytime and Dome profile or D profile characterized by a single maximum around noon.
This morphological analysis of the profiles will reveal the difference between the equatorial ionosphere characteristics highlighted by the profiles obtained by the both classification methods. In fact those profiles express respectively a signature of a high electrojet, an important afternoon conter-electrojet, a moderate electrojet, a weak electrojet and an absence of electrojet. In addition [
In a third time, the quantitative analysis based on the appreciation of the difference between foF2 values of the ancient classification and those from the new one will be made through the relative deviation of foF2 defined by:
σ foF2 = foF2 AC − foF2 NC foF2 NC × 100 (3)
where foF2 AC and foF2 NC are the foF2 from the ancient geomagnetic activity classification and the new one respectively. Δ foF2 is the relative deviation with the following appreciation:
σ foF2 > 10 % the ancient classification overestimates the new standard classification value;
σ foF2 < − 10 % the ancient classification underestimates the new standard classification value;
− 10 % < σ foF2 < 10 % both classifications are in agreement.
throughout solar cycle phases (panels “a” and “b”). The panels “a” and “b” concern the ancient classification (AC) and the new classification (NC) respectively.
For each solar cycle phase of both classifications, the diagram columns represent respectively the fluctuant, the recurrent, the shock and the very quiet activities. For the occurrence of the FA (FAocc) over solar cycle phases, we have for the AC, 5.23%; 10.10%; 57.14% and 27.53% and for the NC, 8.21%; 17.24%; 37.03% and 37.52, respectively for the minimum, the increasing, the maximum and the decreasing solar phases. Therefore, the FA occurs more during the maximum phase for AC and they occur more during maximum and decreasing phases with a value of occurrence roughly equal to 37% for the NC. Otherwise, for both classifications the FA occurs the least during the minimum phase. The maximum negative gap between both classifications occurrences is observed during the decreasing phase with a value of Δ occ = − 9.99 % and the maximum positive occurrence is observed during the maximum phase with a value of Δ occ = + 20.11 % . Besides, for maximum phase, the FA’s occurrence of the AC is greater than that of the NC; and we observe the opposite for the other solar cycle phases.
For the RA, we have for the AC, 8.0%; 2.29%; 19.43% and 70.29% and for the NC 9.88%; 14.20%; 22.38% and 53.55% respectively for the minimum, the increasing, the maximum and the decreasing solar phases. Therefore, the RA occurs more during the decreasing phase for both classifications. Otherwise, they occur the least during the minimum phase for the NC and the increasing phase for the AC. The AC’s configuration is in good agreement with Legrand and Simon’s [
In the case of the SA, we have for the AC, 8.32%; 7.79%; 36.62% and 37.27% and for the NC, 5.53%; 16.26%; 54.47% and 23.74% respectively for the minimum, the increasing, the maximum and the decreasing solar phases. Therefore, the SA occurs more during the maximum and the decreasing phases with a value of occurrence roughly equal to 37% and the less during increasing and minimum phase with a value of occurrence roughly equal to 8% for the AC. For the NC, it occurs the most during the maximum phase and the least during solar minimum. The maximum negative gap between both classification occurrences is observed at maximum phase with a value Δ occ = − 17.85 % and the maximum positive gap of the occurrence is observed in decreasing phase with a value Δ occ = + 8.53 % . Besides, for the decreasing phase with a value Δ occ = + 8.53 % , the SA’s occurrence of the AC is greater than that of the NC. This observation is the same for the minimum phase. We observe the opposite for the increasing and maximum solar cycle phases.
Figures 4-6 show the foF2 profiles during fluctuant activity (FA), recurrent activity (RA) and shock activity (SA) respectively. The panels “a”, “b”, “c” and “d” present the graph of the minimum, increasing, maximum and decreasing solar cycle phases respectively.
Panel “c” shows that during the maximum phase, both curves show a “P” profile for both classifications. Therefore, the RA is characterised by a weak electrojet in the E layer of the ionosphere during the maximum phase considering both classifications. Otherwise, we observe that the two graphs are overlapped during all the daytime; but both curves are different at 0600 LT and between 2000 LT to 2400 LT with respect to error bars shown in NC graph. Both curves showed a night time peak, with a peak of 12 MHz observed at 2100 LT (for the curve of AC) upper that of the NC (peak of 10 MHz observed at 2200 LT). The right column of this panel highlights this observation. In fact, the σ foF2 curve shows values within ±10% between 0000 LT to 0500 LT and 0700 LT to 2000 LT. The maximum positive σ foF2 value is observed at 2100 LT with a value equal to +18.80% and the maximum negative value, observed at 0600 LT, is fairly equal to −13.27%.
At the increasing phase (panel “b”) we observe a high difference between the two curves. The NC curve shows an “R” profile while the AC profile shows a B profile with a trough around 1300 LT. Therefore, during increasing phase, the RA shows an important afternoon conter-electrojet for the NC while it is characterized by an intense electrojet for the AC. Otherwise, we observe that the AC graph is almost over that of the NC, except between 0500 LT to 0600 LT and at 1600 LT. We observe that the two graphs are nearly overlapped between 1300 LT to 1600 LT; but both curves are different between 1800 LT to 0300 LT, 0500 LT to 0600 LT and 0800 LT to 1100 LT with respect to error bars shown in NC graph. The right column of this panel highlights this observation. In fact, the σ foF2 graph shows values within ±10% at 0700 LT, at 0400 LT and between 1200 LT to 1700 LT. The maximum positive σ foF2 value is observed at 0100 LT with a value equal to +93.55% and the maximum negative value, observed at 0500 LT, is equal to −26.10%.
Panel “b” presents an “R” profile for both classifications graphs; but that of the AC is coupled with a trough observed at 1400 LT. Therefore, at solar increasing phase, the SA of the NC classification is characterized by an intense afternoon conter-electrojet while the one of the AC is characterized by a couple of an intense afternoon conter-electrojet and a late high electrojet, signature of a trough observed at 1400 LT. Otherwise, we observe a difference between both classification’s curves between 2000 LT to 2300 LT with respect to error bars shown in NC graph; but for the remaining daily time the two profiles are closely in a good agreement. The right column of this panel highlights this observation. In fact, the σ foF2 curve shows values within ±10% between 2000 LT 2300 LT. The maximum positive σ foF2 value is observed at 2100 LT with a value equal to +26.51% and the maximum negative value, observed at 0500 LT, is equal to −9.84%.
At maximum phase (panel “c”), for both classifications graphs, the SA profile is characterized by “P” profile which is a signature of a weak electrojet. We observe that the two curves are overlapped during all the daily time with respect to error bars shown in NC graph. The right column of this panel highlights this observation. In fact, the σ foF2 curve shows values within ±10% during all the daily time. Otherwise, we observe at 3.1) that the maximum negative gap between both classification occurrences for SA is observed at maximum phase with a value Δ occ = − 17.85 % . Therefore the Cloud Shock Activity CSA occurs more during solar maximum like have been found by [
Panel “d” presents an “R” profile for both classifications graphs. Therefore, at solar decreasing phase, the both classification’s SA are characterized by an intense afternoon conter-electrojet. We observe that the two curves are overlapped during all the daily time. The right column of this panel highlights this observation. In fact, the σ foF2 curve shows values within ±10% during all the daily time. Otherwise, we observe at 3.1) that the maximum positive gap between both classification occurrences for SA is observed at decreasing phase with a value Δ occ = + 13.53 % . Therefore, we can make the assumption that the high occurrence of cloud shock activity (CSA) doesn’t impact the electrodynamics of the ionosphere E layer.
This paper shows that both classifications geomagnetic classes, at Dakar station, are different in terms of occurrences throughout solar cycle phases. It emerges that, for the RA, the higher the occurrences between two classes for a given phase are different, the more the profiles show difference and also the physical interpretation of the electrodynamics in the ionosphere layer. But the SA profiles of both classifications are closely similar during maximum and decreasing phase. In general, the AC and NC curves show different profiles during minimum and increasing phases for the RA and the SA. The FA profiles don’t depend on the classification method at all.
The authors thank Brest Telecom of Bretagne for providing Dakar ionosonde data. Many thanks to ISGI data center for providing data center.
The authors declare no conflicts of interest regarding the publication of this paper.
Sandwidi, S.A., Gnabahou, D.A. and Ouattara, F. (2020) Comparative Study of the Geomagnetic Activity Effect on foF2 Variation as Defined by the Two Classification Methods at Dakar Station over Solar Cycle Phases. International Journal of Geosciences, 11, 501-517. https://doi.org/10.4236/ijg.2020.118026