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Journal articles on the topic 'FoF2'

Author: Grafiati

Published: 4 June 2021

Last updated: 26 July 2025

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1

Pavan Chaitanya, P., A. K. Patra, N. Balan, and S. V. B. Rao. "Ionospheric variations over Indian low latitudes close to the equator and comparison with IRI-2012." Annales Geophysicae 33, no. 8 (2015): 997–1006. http://dx.doi.org/10.5194/angeo-33-997-2015.

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Abstract. In this paper, we analyze daytime observations of the critical frequencies of the F2 (foF2) and F3 (foF3) layers based on ionosonde observations made from Indian low latitudes close to the magnetic equator and study their local time, seasonal, planetary-scale variations (including the solar rotation effect), and solar activity dependence. Given the occurrence of the F3 layer, which has remarkable local time, seasonal and solar activity dependences, variations in foF2 have been evaluated. Local time variations in foF2 and foF3 show noon "bite-out" in all seasons and in all solar activ

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2

Pham Thi Thu, H., C. Amory-Mazaudier, and M. Le Huy. "Time variations of the ionosphere at the northern tropical crest of ionization at Phu Thuy, Vietnam." Annales Geophysicae 29, no. 1 (2011): 197–207. http://dx.doi.org/10.5194/angeo-29-197-2011.

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Abstract. This study is the first which gives the climatology of the ionosphere at the northern tropical crest of ionization in the Asian sector. We use the data from Phu Thuy station, in Vietnam, through three solar cycles (20, 21 and 22), showing the complete morphology of ionosphere parameters by analyzing long term variation, solar cycle variation and geomagnetic activity effects, seasonal evolution and diurnal development. Ionospheric critical frequencies, foF2, foF1 and foE, evolve according to the 11-year sunspot cycle. Seasonal variations show that foF2 exhibits a semiannual pattern wi

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3

Danilov, A. D. "Long-term trends in the relation between daytime and nighttime values of <I>fo</I>F2." Annales Geophysicae 26, no. 5 (2008): 1199–206. http://dx.doi.org/10.5194/angeo-26-1199-2008.

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Abstract. The data from the vertical ionospheric sounding for 12 stations over the world were analyzed to find the relation between the values of foF2 for 02:00 LT and 14:00 LT of the same day. It is found that, in general, there exists a negative correlation between foF2(02) and foF2(14). The value of the correlation coefficient R(foF2) can be in some cases high enough and reach minus 0.7–0.8. The value of R(foF2) demonstrates a well pronounced seasonal variations, the highest negative values being observed at the equinox periods of the year. It is also found that R(foF2) depends on geomagnet

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4

Zhivolup, Taras, Sergii Panasenko, Olexander Koloskov, and Volodymyr Lisachenko. "Joint Ionosonde Studies of F2 Layer Critical Frequency Variations in the Ionosphere Over Kharkiv and Tromsø During Fall Equinox in Quiet and Disturbed Conditions." PHYSICS OF ATMOSPHERE AND GEOSPACE 2, no. 1 (2021): 38–49. http://dx.doi.org/10.47774/phag.02.01.2021-4.

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According to the results of joint ionosonde studies of variations in the ionospheric F2 layer critical frequency over Kharkiv and Tromsø during low solar activity for fall equinox on September 22 – 24, 2020, the features of foF2 variations in middle and low latitudes were investigated for magnetically quiet and magnetically disturbed conditions. On the magnetically quiet day of September 22, 2020, the foF2 values over Kharkiv were found to exceed the foF2 values over Tromsø for the entire time interval of joint observations 02:45 - 16:45 UT. Both over Tromsø and over Kharkiv, a rapid increase

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5

Laštovička, Jan. "Long-Term Changes in Ionospheric Climate in Terms of foF2." Atmosphere 13, no. 1 (2022): 110. http://dx.doi.org/10.3390/atmos13010110.

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There is not only space weather; there is also space climate. Space climate includes the ionospheric climate, which is affected by long-term trends in the ionosphere. One of the most important ionospheric parameters is the critical frequency of the ionospheric F2 layer, foF2, which corresponds to the maximum ionospheric electron density, NmF2. Observational data series of foF2 have been collected at some stations for as long as over 60 years and continents are relatively well covered by a network of ionosondes, instruments that measure, among others, foF2. Trends in foF2 are relatively weak. T

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6

Aristide Marie Frederic, Gyebre, Kabore Salfo, Diabate Abidina, and Ouattara Frederic. "SEASONAL EFFECT ON FOF2 VARIABILITY DURING ONE-DAY-SHOCK AT OUAGADOUGOU STATION DURING SOLAR CYCLES 20, 21 AND 22." International Journal of Advanced Research 10, no. 11 (2022): 608–16. http://dx.doi.org/10.21474/ijar01/15706.

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The seasonal effect on the F2 sublayer critical frequency of the ionosphere (foF2), during one-day-shock, at Ouagadougou station during three solar cycles (20, 21, and 22) is examined in this work. It appears that summer has an effect tending to decrease the values â€‹â€‹of foF2 in the maximum, ascending and descending phase. At solar cycle maximum, winter and autumn do not modify the foF2 amplitudes. At solar cycle minimum, winter decreases foF2 values â€‹â€‹in the morning (08:00 a.m. to 1:00 p.m.), while spring amplifies them (09:00 a.m. to 1:00 p.m.). In the ascending phase, winter, spring

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7

Zhu, Peng, Cong Xie, Chunhua Jiang, et al. "Ionospheric Behavior of foF2 over Chinese EIA Region and Its Comparison with IRI-2016." Universe 6, no. 8 (2020): 122. http://dx.doi.org/10.3390/universe6080122.

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The ionograms, which were recorded by the ionosonde located at Pu’er station (PUR, 22.7° N, 101.05° E, Dip Latitude 12.9° N) in the Southwest of China in the year of 2016, were used to study the ionospheric behavior of the ordinary critical frequency of the F2 layer (foF2) in the region of the northern equatorial ionization anomaly. To verify the performance of the International Reference Ionosphere (IRI) over the Southwest of China, a comparative study of the observed foF2 and the latest version of the International Reference Ionosphere (IRI-2016) was carried out. We found that the foF2 in eq

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8

Foppiano, A. J., and A. S. Rodger. "F-region ionospheric irregularities over King George Island and Argentine Islands – a comparative study." Antarctic Science 6, no. 3 (1994): 411–17. http://dx.doi.org/10.1017/s0954102094000623.

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Spread-F is caused by the presence of ionospheric electron concentration irregularities of scale-size of order 5 km at F-region altitudes. Estimates of spread-F in the vicinity of the maximum plasma frequency of the Flayer (foF2) have been determined at 15 min intervals from ionograms recorded over a ten day period (1–10 May 1986) both at Marsh (62.2°S, 58.9°W), King George Island, and Faraday (65.2°S, 64.3°W), Argentine Islands. The interval, at low solar activity, includes periods of quiet and disturbed geomagnetic activity. Spread-F is observed on every night at both stations. It is more fr

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9

Hafizhah, Luthfia, and Dwi Pujiastuti. "Perbandingan Anomali Frekuensi Kritis Lapisan F2 (Fof2) Ionosfer Pada Gempa Bumi Laut Dan Gempa Bumi Darat Pulau Sumatera." Jurnal Fisika Unand 10, no. 1 (2021): 41–47. http://dx.doi.org/10.25077/jfu.10.1.41-47.2021.

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Pada saat akan terjadinya gempa bumi, maka akan diikuti dengan peningkatan injeksi gas radon di daerah zona persiapan gempa. Gas radon ini akan menyebabkan perubahan terhadap lapisan ionosfer. Telah dilakukan analisis perbedaan anomali frekuensi kritis lapisan F2 ionosfer (foF2) sebelum kejadian gempa laut dan gempa darat menggunakan ionogram ionosonda FMCW (Frequency Modulation Continous Wave) untuk melihat perbedaan karakteristiknya. Terdapat 5 kejadian gempa darat dan 5 kejadian gempa laut yang dianalisis. Rentang hari pengambilan ionogram adalah 21 hari sebelum kejadian gempa bumi (analisi

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10

Liu, Yiran, Qiao Yu, Yafei Shi, Cheng Yang, and Jian Wang. "A Reconstruction Method for Ionospheric foF2 Spatial Mapping over Australia." Atmosphere 14, no. 9 (2023): 1399. http://dx.doi.org/10.3390/atmos14091399.

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To improve the accuracy of predicting the ionospheric critical frequency of the F2 layer (foF2), a reconstruction method for the spatial map of the ionospheric foF2 based on modified geomagnetic dip coordinates is proposed. Based on the strong correlation between the ionospheric foF2 and geomagnetic coordinates, the variation function of ionospheric distance is built. In the end, the spatial map of the ionospheric foF2 is predicted by solving the Kriging equation. The results show that the regional characteristics of the ionospheric foF2 analyzed by the proposed method are consistent with the

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11

Lubis, Ashar Muda, Mawaddah Mawaddah, Afrizal B., Halauddin Halauddin, and Zainal Abidin. "STUDI FREKUENSI KRITIS (foF2) PADA LAPISAN IONOSFER YANG BERHUBUNGAN DENGAN KEJADIAN GEMPA BUMI DI SEGMEN MENTAWAI TAHUN 2010-2015." Jurnal Meteorologi dan Geofisika 22, no. 2 (2021): 81. http://dx.doi.org/10.31172/jmg.v22i2.717.

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<p>Telah dilakukan kajian frekuensi kritis (foF2) lapisan F ionosfer untuk mencari apakah perubahan/anomali foF2 pada lapisan ini berhubungan dengan kejadian gempa bumi di segment Mentawai Sumatera Barat sehingga dapat digunakan sebagai prekusor gempa bumi dalam order harian. Untuk itu data ionogram pada waktu 2005-2015 yang merupakan hasil pengamatan ionosonda tipe Frequency Modulation Continous Wave (FMCW) di stasiun Kototabang, Kabupaten Agam, Sumatra barat, kemudian data aktivitas geomagnetik melalui indeks Disturbance Storm Time Index (DST) dan data aktivitas matahari <em>(&lt

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12

Seyoum, Alene, Nat Gopalswamy, Melessew Nigussie, and Nigusse Mezgebe. "The impact of CMEs on the critical frequency of F2-layer ionosphere (foF2)." Proceedings of the International Astronomical Union 15, S356 (2019): 400–402. http://dx.doi.org/10.1017/s1743921320003579.

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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 a

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13

Bremer, J. "Trends in the ionospheric E and F regions over Europe." Annales Geophysicae 16, no. 8 (1998): 986–96. http://dx.doi.org/10.1007/s00585-998-0986-9.

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Abstract. Continuous observations in the ionospheric E and F regions have been regularly carried out since the fifties of this century at many ionosonde stations. Using these data from 31 European stations long-term trends have been derived for different parameters of the ionospheric E layer (h' E, foE), F1 layer (foF1) and F2 layer (hmF2, foF2). The detected trends in the E and F1 layers (lowering of the E region height h'E; increase of the peak electron densities of the E and F1 layers, foE and foF1) are in qualitative agreement with model predictions of an increasing atmospheric greenhouse

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14

Богданов, В. В., and А. В. Павлов. "Disturbances in the F2 Layer of the Ionosphere Preceding the Onset of Earthquakes with M≥6.0 in the Kamchatka Region." Вестник КРАУНЦ. Физико-математические науки 45, no. 4 (2023): 67–80. http://dx.doi.org/10.26117/2079-6641-2023-45-4-67-80.

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В работе представлен анализ данных ежечасных измерений критической частоты F2-слоя ионосферы (foF2), произведенных за временной интервал 01.07.1968–30.06.1997 гг. на станции вертикального радиозондирования ионосферы PK553 (с. Паратунка, Камчатский край) с целью идентификации сейсмоионосферных аномалий, предшествующих наступлению землетрясений с магнитудами M≥6.0. В ходе анализа было рассмотрено 45 землетрясений соответствующих магнитуд, в зоне подготовки которых, определяемой по формуле Добровольского, находилась ионосферная станция PK553. В качестве контрольной станции была выбрана станция ве

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15

Gordiyenko, Galina, Artur Yakovets, Yurii Litvinov, and Murat Zhiganbayev. "Long-Term Changes and Trends in the F2 Layer Critical Frequency over Alma-Ata (Kazakhstan)." Atmosphere 16, no. 1 (2024): 2. https://doi.org/10.3390/atmos16010002.

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The long-term variability and trends in the F2 layer critical frequency variations over Alma-Ata [43.25 N, 77.92 E] for the period 07.1957–04.2018 are studied using near-midday, near-midnight, and hourly median foF2 values. It is shown that the foF2 and solar activity index F10.7 display regular 11-year periodicity, stable negative trend over the 60-year observation interval, and some long-term (approximately four 11-year solar cycles) oscillation. The foF2 trend dependencies on the season and time of day are studied. The critical frequency shows a good connection with solar activity for the e

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16

Pignalberi, Alessio, Marco Pietrella, and Michael Pezzopane. "Towards a Real-Time Description of the Ionosphere: A Comparison between International Reference Ionosphere (IRI) and IRI Real-Time Assimilative Mapping (IRTAM) Models." Atmosphere 12, no. 8 (2021): 1003. http://dx.doi.org/10.3390/atmos12081003.

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This paper focuses on a detailed comparison, based on the F2-layer peak characteristics foF2 and hmF2, between the International Reference Ionosphere (IRI), which is a climatological empirical model of the terrestrial ionosphere, and the IRI Real-Time Assimilative Mapping (IRTAM) procedure, which is a real-time version of IRI based on data assimilation from a global network of ionosondes. To perform such a comparison, two different kinds of datasets have been considered: (1) foF2 and hmF2 as recorded by 40 ground-based ionosondes spread all over the world from 2000 to 2019; (2) foF2 and hmF2 f

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17

Danilov, A. D. "Time and spatial variations of the foF2(night)/foF2(day) values." Advances in Space Research 43, no. 11 (2009): 1786–93. http://dx.doi.org/10.1016/j.asr.2008.08.012.

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18

Mikhailov, A. V., and D. Marin. "Geomagnetic control of the <i>fo</i>F2 long-term trends." Annales Geophysicae 18, no. 6 (2000): 653–65. http://dx.doi.org/10.1007/s00585-000-0653-2.

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Abstract. Further development of the method proposed by Danilov and Mikhailov is presented. The method is applied to reveal the foF2 long-term trends on 30 Northern Hemisphere ionosonde stations. Most of them show significant foF2 trends. A pronounced dependence of trend magnitude on geomagnetic (invariant) latitude is confirmed. Periods of negative/positive foF2 trends corresponding to the periods of long-term increasing/decreasing geomagnetic activity are revealed for the first time. Pronounced diurnal variations of the foF2 trend magnitude are found. Strong positive foF2 trends in the post-

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19

Kane, R. P., E. R. de Paula, and N. B. Trivedi. "Variations of solar EUV, UV and ionospheric foF2 related to the solar rotation period." Annales Geophysicae 13, no. 7 (1995): 717–23. http://dx.doi.org/10.1007/s00585-995-0717-4.

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Abstract. Spectral analysis of daily values of various solar indices viz. sunspot number, 10.7-cm flux, H Lyman-α and -β, specific He, Fe and Mg lines and solar X-rays was carried out for two selected intervals. During interval A (May-August 1978, 123 days) the solar indices showed a prominent periodicity near 27 days, while during interval B (January-May 1979, 151 days) the solar indices showed a prominent periodicity near 13 days. For the same intervals, foF2 (max) and foF2 (average) during 1000-1500 LT were similarly analysed for the locations Cachoeira Paulista, SP, Brazil (23°S, 45°W), an

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20

Wang, Jian, Qiao Yu, Yafei Shi, Yiran Liu, and Cheng Yang. "An Explainable Dynamic Prediction Method for Ionospheric foF2 Based on Machine Learning." Remote Sensing 15, no. 5 (2023): 1256. http://dx.doi.org/10.3390/rs15051256.

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To further improve the prediction accuracy of the critical frequency of the ionospheric F2 layer (foF2), we use the machine learning method (ML) to establish an explanatory dynamic model to predict foF2. Firstly, according to the ML modeling process, the three elements of establishing a prediction model of foF2 and four problems to be solved are determined, and the idea and concrete steps of model building are determined. Then the data collection is explained in detail, and according to the modeling process, foF2 dynamic change mapping and its parameters are determined in turn. Finally, the es

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21

Ehinlafa, O. E., G. A. Alagbe, M. J. Johnson, S. O. Ige, and J. O. Adeniyi. "Ionospheric F2-Region Characteristics of Profile Parameters at an Equatorial Station During Low Solar Activity." Nigerian Journal of Physics 32, no. 4 (2024): 73–80. http://dx.doi.org/10.62292/njp.v32i4.2023.55.

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The ionospheric characteristics of the F2 region critical frequency (foF2), peak electron density (NmF2) and the height of occurrence of electron density (hmF2), was investigated over Ilorin (lat. 8.31°N, long. 4.34°E, dip lat. 2.95o), a station along the equatorial ionization anomaly trough, during a period of low solar activity (LSA). Diurnally, foF2, NmF2 and hmF2 were found to have two characteristic peaks: pre-noon and post-noon peaks, except hmF2 that has post-sunset peak. The foF2 and NmF2 pre-noon peaks occurred around 0800–0900 LT, hmF2’s peak around 1000 LT. The post-noon peaks of fo

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22

Pietrella, M. "A short-term ionospheric forecasting empirical regional model (IFERM) to predict the critical frequency of the F2 layer during moderate, disturbed, and very disturbed geomagnetic conditions over the European area." Annales Geophysicae 30, no. 2 (2012): 343–55. http://dx.doi.org/10.5194/angeo-30-343-2012.

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Abstract. A short-term ionospheric forecasting empirical regional model (IFERM) has been developed to predict the state of the critical frequency of the F2 layer (foF2) under different geomagnetic conditions. IFERM is based on 13 short term ionospheric forecasting empirical local models (IFELM) developed to predict foF2 at 13 ionospheric observatories scattered around the European area. The forecasting procedures were developed by taking into account, hourly measurements of foF2, hourly quiet-time reference values of foF2 (foF2QT), and the hourly time-weighted accumulation series derived from

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23

Husni, Husni, Ali Warsito, and Asnawi Husin. "ANALISIS VARIASI FREKUENSI KRITIS DAN KETINGGIAN LAPISAN IONOSFER DI ATAS KUPANG." Jurnal Fisika : Fisika Sains dan Aplikasinya 2, no. 2 (2018): 85–91. http://dx.doi.org/10.35508/fisa.v2i2.549.

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ABSTRAK Variasi perubahan frekuensi kritis lapisan F2 (foF2) dan ketinggian lapisan F2 (h'F2) di atas Kupang selama tahun 2014 mengalami perubahan yang bervariasi dimana hal ini bergantung pada aktivitas matahari, semakin tinggi tingkat aktivitas matahari semakin tinggi pula tingkat variasi pada foF2 dan h'F2, sebaliknya semakin rendah tingkat aktivitas matahari semakin berkurang pula tingkat variasi foF2 dan h'F2 variasi perubahan terhadap lapisan F diindikasikan dengan penurunan dan peningkatan nilai foF2 dan h'F2. Peningkatan nilai foF2 rata-rata terjadi pada pukul 07.00 WITA mencapai

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24

Bradley, P. A., I. Stanislawska, and G. Juchnikowski. "Options for mapping foF2." Advances in Space Research 43, no. 11 (2009): 1776–79. http://dx.doi.org/10.1016/j.asr.2008.09.028.

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Pietrella, M., and L. Perrone. "A local ionospheric model for forecasting the critical frequency of the F2 layer during disturbed geomagnetic and ionospheric conditions." Annales Geophysicae 26, no. 2 (2008): 323–34. http://dx.doi.org/10.5194/angeo-26-323-2008.

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Abstract. An ionospheric forecasting empirical local model over Rome (IFELMOR) has been developed to predict the state of the critical frequency of the F2 layer (foF2) during geomagnetic storms and disturbed ionospheric conditions. Hourly measurements of foF2 obtained at the Rome observatory, hourly quiet-time values of foF2 (foF2QT), and the hourly time-weighted accumulation series derived from the geomagnetic planetary index ap (ap(τ)), were considered during the period January 1976–December 2003. Under the assumption that the ionospheric disturbance index log(foF2/foF2QT) is correlated to t

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26

Ippolito, Alessandro, Loredana Perrone, Christina Plainaki, and Claudio Cesaroni. "Investigating the foF2 variations at the Ionospheric Observatory of Rome during different solar cycles minimums and levels of geomagnetic activity." Journal of Space Weather and Space Climate 10 (2020): 52. http://dx.doi.org/10.1051/swsc/2020054.

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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

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Laštovička, J., X. Yue, and W. Wan. "Long-term trends in <I>fo</I>F2: their estimating and origin." Annales Geophysicae 26, no. 3 (2008): 593–98. http://dx.doi.org/10.5194/angeo-26-593-2008.

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Abstract. This paper deals with two problems, methods of foF2 trend determination and origin of trends in foF2, both being controversial in current literature. We found that various regression-based methods and artificial neural network-based method of Yue et al. (2006) provided comparable results within uncertainties caused mainly by various ways of removing/suppressing the dominant solar cycle effect. The role of geomagnetic activity in the observed trends in foF2 was probably substantial and might be still even rather dominant in the last quarter of the 20th century.

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Li, Xiaojun, Chen Zhou, Qiong Tang, et al. "Forecasting Ionospheric foF2 Based on Deep Learning Method." Remote Sensing 13, no. 19 (2021): 3849. http://dx.doi.org/10.3390/rs13193849.

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In this paper, a deep learning long-short-term memory (LSTM) method is applied to the forecasting of the critical frequency of the ionosphere F2 layer (foF2). Hourly values of foF2 from 10 ionospheric stations in China and Australia (based on availability) from 2006 to 2019 are used for training and verifying. While 2015 and 2019 are exclusive for verifying the forecasting accuracy. The inputs of the LSTM model are sequential data for the previous values, which include local time (LT), day number, solar zenith angle, the sunspot number (SSN), the daily F10.7 solar flux, geomagnetic the Ap and

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Ortiz de Adler, N., and A. G. Elias. "Latitudinal variation of <I>fo</I>F2 hysteresis of solar cycles 20, 21 and 22 and its application to the analysis of long-term trends." Annales Geophysicae 26, no. 5 (2008): 1269–73. http://dx.doi.org/10.5194/angeo-26-1269-2008.

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Abstract. Noon foF2 monthly median values for equinoctial months of solar cycles 20, 21 and 22, were analyzed for 37 worldwide stations. For each solar cycle and for a given Rz, the difference between foF2 in the falling branch of the cycle and the corresponding value of the rising branch is evaluated. The maximum difference, considered as the hysteresis magnitude, varies systematically with geomagnetic latitude. The pattern is similar for every cycle, with greater hysteresis magnitudes for stronger solar cycles. It is positive between 45° S and 45° N, with minimum values at equatorial latitud

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Duran, Trinidad, Bruno Santiago Zossi, Yamila Daniela Melendi, Blas Federico de Haro Barbas, Fernando Salvador Buezas, and Ana Georgina Elias. "Impact of different solar extreme ultraviolet (EUV) proxies and Ap index on hmF2 trend analysis." Annales Geophysicae 42, no. 2 (2024): 473–89. https://doi.org/10.5194/angeo-42-473-2024.

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Abstract. Long-term trend estimation in the peak height of the F2 layer, hmF2, needs the previous filtering of much stronger natural variations such as those linked to the diurnal, seasonal, and solar activity cycles. If not filtered, they need to be included in the model used to estimate the trend. The same happens with the maximum ionospheric electron density that occurs in this layer, NmF2, which is usually analyzed through the F2 layer critical frequency, foF2. While diurnal and seasonal variations can be easily managed, filtering the effects of solar activity presents more challenges, as

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Mikhailov, A. V., and D. Marin. "An interpretation of the <i>ƒo</i>F2 and <i>hm</i>F2 long-term trends in the framework of the geomagnetic control concept." Annales Geophysicae 19, no. 7 (2001): 733–48. http://dx.doi.org/10.5194/angeo-19-733-2001.

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Abstract. Earlier revealed morphological features of the foF2 and hmF2 long-term trends are interpreted in the scope of the geomagnetic control concept based on the contemporary F2-layer storm mechanisms. The F2-layer parameter trends strongly depend on the long-term varying geomagnetic activity whose effects cannot be removed from the trends using conventional indices of geomagnetic activity. Therefore, any interpretation of the foF2 and hmF2 trends should consider the geomagnetic effects as an inalienable part of the trend analysis. Periods with negative and positive foF2 and hmF2 trends cor

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Wang, Jian, Hongmei Bai, Xiangdong Huang, Yuebin Cao, Qiang Chen, and Jianguo Ma. "Simplified Regional Prediction Model of Long-Term Trend for Critical Frequency of Ionospheric F2 Region over East Asia." Applied Sciences 9, no. 16 (2019): 3219. http://dx.doi.org/10.3390/app9163219.

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To improve the accuracy of predictions and simplify the difficulty with the algorithm, a simplified empirical model is proposed in developing a long-term predictive approach in determining the ionosphere’s F2-layer critical frequency (foF2). The main distinctive features introduced in this model are: (1) Its vertical incidence sounding data, which were obtained from 18 ionosonde stations in east Asia between 1949 and 2017, used in reconstructing the model and verification; (2) the use of second-order polynomial and triangle harmonic functions, instead of linear ones, to obtain the relationship

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Danilov, A. D., and N. A. Berbeneva. "Statistical Analysis of the Critical Frequency foF2 Dependence on Various Solar Activity Indices." Геомагнетизм и аэрономия 63, no. 5 (2023): 619–29. http://dx.doi.org/10.31857/s0016794023600588.

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A description of the ionospheric F2-layer critical frequency foF2 dependence on solar activity byvarious indices (proxies) has been analyzed. The results of the vertical ionospheric sounding at the Juliusruhstation during 2 winter months (January and February), 2 equinox months (March and October), and a summermonth (June) are considered. Five solar proxies: Ly-α, MgII, Rz, F30, and F10.7 have been analyzed.The changes in foF2 are compared to the corresponding changes in 1957–1980. The determination coefficientR2 according to the Fisher F-test is used as a measure of the quality of the descrip

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Santoso, Anwar, Dadang Nurmali, Mira Juangsih, et al. "ANALISIS PENGARUH PENETRASI MEDAN LISTRIK LINTANG TINGGI KE LINTANG RENDAH TERHADAP IONOSFER SAAT BADAI GEOMAGNET (ANALYSIS OF THE ELECTRIC FIELD PENETRATION EFFECT FROM HIGH TO LOW LATITUDES ON THE IONOSPHERE DURING GEOMAGNETIC STORM)." Jurnal Sains Dirgantara 14, no. 2 (2018): 97. http://dx.doi.org/10.30536/j.jsd.2017.v14.a2368.

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The influence of geomagnetic storms on the ionosphere in the equatorial and low latitudes can be either rising or falling value of the value foF2 with the different response delay time. The difference in response is one of them allegedly influenced by the modification of Equatorial Electrojet (EEJ) generated by the penetration of high latitude electric field towards the low latitude electric field and the equator. Therefore, this paper analyzes the influence of the high latitude penetration of electric current to the low latitude electric current towards the ionosphere response to Indonesia's

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Shmelev, J. A., O. A. Maltseva, V. E. Morozov, D. I. Shilov, and S. A. Bezvytnyj. "Testing of the IRI Model by Data from Lovozero, Dickson, Tunguska, and Yakutsk Ionospheric Stations." Arctic and Antarctic Research 64, no. 1 (2018): 31–41. http://dx.doi.org/10.30758/0555-2648-2018-64-1-31-41.

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Empirical models are one of effective ways to set and predict a condition of the ionosphere. To estimate an accuracy of such setting it is necessary to test models by means of experimental data. One of most widely used models is IRI (International Reference Ionisphere), however it is insufficiently tested in the region of high latitudes. In the given article results of testing of the model IRI according to vertical sounding on Russian ionosondes, located in subauroral and high-latitude zones in March– April 2016 are presented. Feature of the period is presence of several geomagnetic disturbanc

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Fan, Jieqing, Chao Liu, Yajing Lv, Jing Han, and Jian Wang. "A Short-Term Forecast Model of foF2 Based on Elman Neural Network." Applied Sciences 9, no. 14 (2019): 2782. http://dx.doi.org/10.3390/app9142782.

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The critical frequency foF2 of the ionosphere F2 layer is one of the most important parameters of the ionosphere. Based on the Elman neural network (ENN), this paper constructs a single station forecasting model to predict foF2 one hour ahead. In order to avoid the network falling into local minimum, the model is optimized by the improved particle swarm optimization (IPSO). The input parameters used in the model include local time, seasonal information, solar cycle information and magnetic activity information. Data of the Wuhan Station from 2008 to 2016 were used to train and test the model.

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Mikhailov, A. V., D. Marin, T. Yu Leschinskaya, and M. Herraiz. "A revised approach to the ƒ<i>o</i>F2 long-term trends analysis." Annales Geophysicae 20, no. 10 (2002): 1663–75. http://dx.doi.org/10.5194/angeo-20-1663-2002.

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Abstract. A new approach to extract foF2 long-term trends, which are free to a great extent from solar and geomagnetic activity effects, has been proposed. These trends are insensitive to the phase (increasing/decreasing) of geomagnetic activity, with long-term variations being small and insignificant for such relatively short time periods. A small but significant residual foF2 trend, with the slope Kr = - 2.2 × 10-4 per year, was obtained over a 55-year period (the longest avail-able) of observations at Slough. Such small trends have no practical importance. On the other hand, negative (altho

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Apostolov, E. M., D. Altadill, and M. Todorova. "The 22-year cycle in the geomagnetic 27-day recurrences reflecting on the F2-layer ionization." Annales Geophysicae 22, no. 4 (2004): 1171–76. http://dx.doi.org/10.5194/angeo-22-1171-2004.

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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 th

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Abidina, DIABATE, SAWADOGO Wambi Emmanuel, GUIBULA Karim, and OUATTARA Frédéric. "Variation of the Critical Frequency of the Ionospheric F2 Layer during Moderate Geomagnetic Conditions: A Study Using Data from the Ouagadougou Ionosonde Station Across Solar Cycles 21 and 22." Current Journal of Applied Science and Technology 44, no. 1 (2025): 76–86. https://doi.org/10.9734/cjast/2025/v44i14477.

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This study investigates the variations in the critical frequency of the F2 layer (foF2) at the Ouagadougou ionosonde station during moderate geomagnetic activities, focusing on corotating and magnetic cloud events across the minimum and maximum phases of solar cycles 21 and 22. The analysis reveals significant perturbations in the diurnal profiles of foF2 during magnetic cloud activity at the solar minimum phase, compared to profiles observed during magnetically quiet activity. These perturbations indicate a disturbance of electrodynamic processes, including ionospheric currents and upward dri

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Nayak, C. K., D. Tiwari, K. Emperumal, and A. Bhattacharyya. "The equatorial ionospheric response over Tirunelveli to the 15 January 2010 annular solar eclipse: observations." Annales Geophysicae 30, no. 9 (2012): 1371–77. http://dx.doi.org/10.5194/angeo-30-1371-2012.

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Abstract. In this paper we present a case study of the annular solar eclipse effects on the ionization of E and F regions of equatorial ionosphere over Tirunelveli [77.8° E, 8.7° N, dip 0.4° N] by means of digital ionosonde on 15 January 2010. The maximum obscuration of the eclipse at this station was 84% and it occurred in the afternoon. The E and F1 layers of the ionosphere showed very clear decrease in their electron concentrations, whereas the F2 layer did not show appreciable changes. A reduction of 30% was observed in the foF1 during the maximum phase of the eclipse. During the beginning

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Araujo-Pradere, E. A., B. Lazo Olazábal, and R. Meléndez Venancio. "The ionospheric F region over El Cerillo, Mexico on magnetically quiet conditions." Geofísica Internacional 35, no. 4 (1996): 425–31. http://dx.doi.org/10.22201/igeof.00167169p.1996.35.4.536.

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Este trabajo describe el comportamiento de las capas F1 y F2 ionosféricas sobre El Cerillo, México, a partir de datos de foF1 y foF2, seleccionados bajo condiciones magneto-tranquilas. Encontramos que la capa F1, en periodos de baja actividad solar, tiene un comportamiento semejante a la capa E. En alta actividad solar, los máximos de foF1 aparecen cerca de los equinoccios y los mínimos cerca de los solsticios. Esto es un preámbulo del claro efecto semianual que se observa en la capa F2. La capa F2 tranquila, en general, presenta el mismo comportamiento que el descrito por diversos autores, ob

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Rush, C. M. "URSI foF2 model maps (1988)." Planetary and Space Science 40, no. 4 (1992): 546–47. http://dx.doi.org/10.1016/0032-0633(92)90181-m.

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Matuura. "ISS-b foF2 maps (1981)." Planetary and Space Science 40, no. 4 (1992): 547. http://dx.doi.org/10.1016/0032-0633(92)90182-n.

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Klimenko, Maxim V., Vladimir V. Klimenko, Irina E. Zakharenkova, et al. "Similarity and differences in morphology and mechanisms of the <i>fo</i>F2 and TEC disturbances during the geomagnetic storms on 26–30 September 2011." Annales Geophysicae 35, no. 4 (2017): 923–38. http://dx.doi.org/10.5194/angeo-35-923-2017.

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Abstract. This study presents an analysis of the ground-based observations and model simulations of ionospheric electron density disturbances at three longitudinal sectors (eastern European, Siberian and American) during geomagnetic storms that occurred on 26–30 September 2011. We use the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) to reveal the main mechanisms influencing the storm-time behavior of the total electron content (TEC) and the ionospheric F2 peak critical frequency (foF2) during different phases of geomagnetic storms. During the storm's

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Zaki, Wafaa H. A. "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." NeuroQuantology 19, no. 8 (2021): 157–68. http://dx.doi.org/10.14704/nq.2021.19.8.nq21128.

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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 o

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Zhang, Bingbing, Zhengtao Wang, Yi Shen, Wang Li, Feng Xu, and Xiaoxiao Li. "Evaluation of foF2 and hmF2 Parameters of IRI-2016 Model in Different Latitudes over China under High and Low Solar Activity Years." Remote Sensing 14, no. 4 (2022): 860. http://dx.doi.org/10.3390/rs14040860.

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The height of the peak electron density (hmF2) and the critical frequency of the F2 layer (foF2) are very important in the research of ionospheric electrodynamics and high frequency (HF) wireless communication. In the article, we validated the hmF2/foF2 model values of the latest version of the International Reference Ionosphere (IRI-2016) with observations from three ionosonde stations which belong to low, middle, and high latitudes (i.e., Sanya, Beijing and Mohe) over China during a high solar activity year (2014, F10.7 = 145.9 sfu) and a low solar activity year (2016, F10.7 = 88.7 sfu). Amo

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Ouattara, F., C. Amory-Mazaudier, R. Fleury, P. Lassudrie Duchesne, P. Vila, and M. Petitdidier. "West African equatorial ionospheric parameters climatology based on Ouagadougou ionosonde station data from June 1966 to February 1998." Annales Geophysicae 27, no. 6 (2009): 2503–14. http://dx.doi.org/10.5194/angeo-27-2503-2009.

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Abstract. This study is the first which gives the climatology of West African equatorial ionosphere by using Ouagadougou station through three solar cycles. It has permitted to show the complete morphology of ionosphere parameters by analyzing yearly variation, solar cycle and geomagnetic activity, seasonal evolution and diurnal development. This work shows that almost all ionospheric parameters have 11-year solar cycle evolution. Seasonal variation shows that only foF2 exhibits annual, winter and semiannual anomaly. foF2 seasonal variation has permitted us to identify and characterize solar e

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Mielich, J., and J. Bremer. "Long-term trends in the ionospheric F2 region with different solar activity indices." Annales Geophysicae 31, no. 2 (2013): 291–303. http://dx.doi.org/10.5194/angeo-31-291-2013.

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Abstract. A new comprehensive data collection by Damboldt and Suessmann (2012a) with monthly foF2 and M(3000)F2 median values is an excellent basis for the derivation of long-term trends in the ionospheric F2 region. Ionospheric trends have been derived only for stations with data series of at least 22 years (124 stations with foF2 data and 113 stations with M(3000)F2 data) using a twofold regression analysis depending on solar and geomagnetic activity. Three main results have been derived: Firstly, it could be shown that the solar 10.7 cm radio flux F10.7 is a better index for the description

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Maltseva, O., T. Nikitenko, and A. Kharakhashyan. "On the global model of the ionospheric equivalent slab thickness." Journal of Physics: Conference Series 2388, no. 1 (2022): 012066. http://dx.doi.org/10.1088/1742-6596/2388/1/012066.

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Abstract The equivalent slab thickness τ of the ionosphere links two of its parameters: the critical frequency foF2 and the total electron content TEC and, as a consequence, allows the determination of foF2 using TEC. Interest in the parameter τ has recently increased, as evidenced by a publication in Space Science Reviews 2022, 218:37, 1-65, which provides a historical overview of τ research, presents features of τ behavior in different regions of the globe under different solar activity conditions, and indicates directions for further research. This led to the following objectives for this p

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Bi, Cheng, Peng Ren, Ting Yin, Zheng Xiang, and Yang Zhang. "Modeling and Forecasting Ionospheric foF2 Variation in the Low Latitude Region during Low and High Solar Activity Years." Remote Sensing 14, no. 21 (2022): 5418. http://dx.doi.org/10.3390/rs14215418.

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Prediction of ionospheric parameters, such as ionospheric F2 layer critical frequency (foF2) at low latitude regions is of significant interest in understanding ionospheric variation effects on high-frequency communication and global navigation satellite system. Currently, deep learning algorithms have made a striking accomplishment in capturing ionospheric variability. In this paper, we use the state-of-the-art hybrid neural network combined with a quantile mechanism to predict foF2 parameter variations under low and high solar activity years (solar cycle-24) and space weather events. The hyb

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