scholarly journals Variability of the Critical Frequency foF2 during Minimum and Maximum Phases of Solar Cycles 20 and 21: A Comparative Study between American and African Equatorial Regions

2022 ◽  
Vol 12 (01) ◽  
pp. 105-112
Author(s):  
Kaboré M’Bi ◽  
Diabaté Abidina ◽  
Ouattara Frédéric
Keyword(s):  
Comparative Study ◽  
Critical Frequency ◽  
Solar Cycles ◽  
Critical Frequency Fof2

scholarly journals Investigating the foF2 variations at the Ionospheric Observatory of Rome during different solar cycles minimums and levels of geomagnetic activity

2020 ◽  
Vol 10 ◽  
pp. 52
Author(s):  
Alessandro Ippolito ◽  
Loredana Perrone ◽  
Christina Plainaki ◽  
Claudio Cesaroni
Keyword(s):  
Geomagnetic Activity ◽  
Solar Minimum ◽  
Critical Frequency ◽  
Background Level ◽  
Solar Cycles ◽  
Physical Processes ◽  
Minimum Duration ◽  
Critical Frequency Fof2 ◽  
Definition Of ◽  
Low Activity

The variations of the hourly observations of the critical frequency foF2, recorded at the Ionospheric Observatory of Rome by the AIS-INGV ionosonde (geographic coordinates 41.82° N, 12.51° E; geomagnetic coordinates 41.69° N, 93.97° E) during the low activity periods at the turn of solar cycles 21–22, 22–23 and 23–24, are investigated. Deviations of foF2 greater than ± 15% with respect to a background level, and with a minimum duration of 3 h, are here considered anomalous. The dependence of these foF2 anomalies on geomagnetic activity has been accurately investigated. Particular attention has been paid to the last deep solar minimum 2007–2009, in comparison with the previous solar cycle minima. The lack of day-time anomalous negative variations in the critical frequency of the F2 layer, is one of the main findings of this work. Moreover, the analysis of the observed foF2 anomalies confirms the existence of two types of positive F2 layer disturbances, characterised by different morphologies and, different underlying physical processes. A detailed analysis of four specific cases allows the definition of possible scenarios for the explanation of the mechanisms behind the generation of the foF2 anomalies.

scholarly journals The impact of CMEs on the critical frequency of F2-layer ionosphere (foF2)

2019 ◽  
Vol 15 (S356) ◽  
pp. 400-402
Author(s):  
Alene Seyoum ◽  
Nat Gopalswamy ◽  
Melessew Nigussie ◽  
Nigusse Mezgebe
Keyword(s):  
Critical Frequency ◽  
Angular Width ◽  
High Latitudes ◽  
Solar Cycles ◽  
Middle Latitudes ◽  
Low Latitudes ◽  
Critical Frequency Fof2 ◽  
The Impact ◽  
Very High

AbstractThe ionospheric critical frequency (foF2) from ionosonde measurements at geographic high, middle, and low latitudes are analyzed with the occurrence of coronal mass ejections (CMEs) in long term variability of the solar cycles. We observed trends of monthly maximum foF2 values and monthly averaged values of CME parameters such as speed, angular width, mass, and kinetic energy with respect to time. The impact of CMEs on foF2 is very high at high latitudes and low at low latitudes. The time series for monthly maximum foF2 and monthly-averaged CME speed are moderately correlated at high and middle latitudes.

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

2021 ◽  
Vol 19 (8) ◽  
pp. 157-168
Author(s):  
Wafaa H.A. Zaki
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Sunspot Number ◽  
Critical Frequency ◽  
Radio Communication ◽  
Ionospheric Layer ◽  
Solar Cycle 24 ◽  
Critical Frequency Fof2 ◽  
Cycle 24 ◽  
The Impact

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.

scholarly journals IRI-2001 model predictions compared with ionospheric data observed at Brazilian low latitude stations

2006 ◽  
Vol 24 (8) ◽  
pp. 2191-2200 ◽  
Author(s):  
F. Bertoni ◽  
Y. Sahai ◽  
W. L. C. Lima ◽  
P. R. Fagundes ◽  
V. G. Pillat ◽  
...  
Keyword(s):  
Reasonable Agreement ◽  
Critical Frequency ◽  
Peak Height ◽  
Low Latitude ◽  
F Region ◽  
Model Predictions ◽  
Critical Frequency Fof2

Abstract. In this work, the F-region critical frequency (foF2) and peak height (hmF2) measured by digital ionosondes at two Brazilian low-latitude stations, namely Palmas (10.17° S, 48.20° W, dip –10.80°) and São José dos Campos (23.20° S, 45.86° W, dip –38.41°), are compared with the IRI-2001 model predictions. The comparison at the latter station shows quite a reasonable agreement for both parameters. The former station exhibits a better agreement for hmF2 than for foF2. In general, the model generates good results, although some improvements are still necessary to implement in order to obtain better simulations for equatorial ionospheric regions.

scholarly journals Performance of the IRI-2016 at the Brazilian low-latitude ionosphere over the South America Magnetic Anomaly during solar minimum

2019 ◽  
Author(s):  
Juliano Moro ◽  
Jiyao Xu ◽  
Clezio Marcos De Nardin ◽  
Laysa Cristina Araújo Resende ◽  
Régia Pereira Silva ◽  
...  
Keyword(s):  
South America ◽  
Magnetic Anomaly ◽  
Critical Frequency ◽  
Peak Height ◽  
The South ◽  
Iri Model ◽  
Radio Science ◽  
Critical Frequency Fof2 ◽  
Dip Angle ◽  
Navigation Signals

Abstract. In this work we analyse the ionograms obtained by the recent Digisonde installed in Santa Maria (29.7º S, 53.7º W, dip angle = − 37º), Brazil, to calculate the monthly averages of the F2 layer critical frequency (foF2), its peak height (hmF2), and the E-region critical frequency (foE) acquired during geomagnetically quiet days from September 2017 to August 2018. The monthly averages are compared to the 2016 version of the International Reference Ionosphere (IRI) model predictions in order to study its performance close to the center of the South America Magnetic Anomaly (SAMA), which is a region particularly important for High Frequency (HF) ground-to-satellite navigation signals. The foF2 estimated with the Consultative Committee International Radio (CCIR) and International Union of Radio Science (URSI) options predicts well throughout the year. Whereas, for hmF2, it is recommended to use the SHU-2015 option instead of the other available options (AMTB2013 and BSE-1979). The IRI-2016 model outputs for foE and the observations presented very good agreements.

scholarly journals On the relation between ionospheric parameters and sunspot number

2020 ◽  
Vol 1 ◽  
Author(s):  
Chris Hall ◽  
Magnar Gullikstad Johnsen
Keyword(s):  
Solar Activity ◽  
Change Point ◽  
Critical Frequency ◽  
Auroral Oval ◽  
Change Points ◽  
Observation Site ◽  
F Region ◽  
Critical Frequency Fof2 ◽  
E Region ◽  
The Relationship

AbstractIn a recent study, mid-latitude ionospheric parameters were compared with solar activity; it was suggested that the relationship between these, earlier assumed stable, might be changing with time (Lastovicka, 2019). Here, the information is extended to higher latitude (69.6°N, 19.2E) and further back in time. For the ionospheric F-region (viz. the critical frequency, FoF2) the same behaviour is seen with a change-point around 1996. For the ionospheric E-region (viz. the critical frequency, foE), change-points are less obvious than in the mid-latitude study, presumably owing to the observation site lying under the auroral oval.

scholarly journals The 22-year cycle in the geomagnetic 27-day recurrences reflecting on the F2-layer ionization

2004 ◽  
Vol 22 (4) ◽  
pp. 1171-1176 ◽  
Author(s):  
E. M. Apostolov ◽  
D. Altadill ◽  
M. Todorova
Keyword(s):  
Solar Cycle ◽  
Geomagnetic Activity ◽  
Activity Index ◽  
Solar Rotation ◽  
Rotation Period ◽  
Sunspot Cycle ◽  
Solar Cycles ◽  
Solar Radio Flux ◽  
Critical Frequency Fof2 ◽  
Northern And Southern Hemispheres

Abstract. Solar cycle variations of the amplitudes of the 27-day solar rotation period reflected in the geomagnetic activity index Ap, solar radio flux F10.7cm and critical frequency foF2 for mid-latitude ionosonde station Moscow from the maximum of sunspot cycle 18 to the maximum of cycle 23 are examined. The analysis shows that there are distinct enhancements of the 27-day amplitudes for foF2 and Ap in the late declining phase of each solar cycle while the amplitudes for F10.7cm decrease gradually, and the foF2 and Ap amplitude peaks are much larger for even-numbered solar cycles than for the odd ones. Additionally, we found the same even-high and odd-low pattern of foF2 for other mid-latitude ionosonde stations in Northern and Southern Hemispheres. This property suggests that there exists a 22-year cycle in the F2-layer variability coupled with the 22-year cycle in the 27-day recurrence of geomagnetic activity. Key words. Ionosphere (mid-latitude ionosphere; ionosphere- magnetosphere interactions) – Magnetospheric physics (solar wind-magnetosphere interactions)

The F-layer at sunrise

1995 ◽  
Vol 13 (4) ◽  
pp. 367-374 ◽  
Author(s):  
H. Rishbeth ◽  
B. Jenkins ◽  
R. J. Moffett
Keyword(s):  
Computational Model ◽  
Seasonal Change ◽  
Solar Zenith Angle ◽  
Critical Frequency ◽  
Diffusion Processes ◽  
Relative Importance ◽  
Production Loss ◽  
Critical Frequency Fof2 ◽  
And Diffusion ◽  
Composition Changes

Abstract. It was noticed 60 years ago that at sunrise (i) the ionospheric critical frequency foF2 increases faster in winter than in summer and (ii) the increase begins at a greater solar zenith angle in winter. It was later suggested that this "seasonal sunrise anomaly" is due to a seasonal change of atomic/molecular ratio in the neutral air in the F2-layer. This paper uses the Sheffield University plasmasphere-ionosphere computational model (SUPIM) with the MSIS thermosphere model to examine the relative importance at sunrise of production, loss and diffusion processes, and the effect of neutral air winds. The results show that both (i) and (ii) can be explained in terms of neutral composition changes.

Sign in / Sign up

Export Citation Format

Share Document