Variability of the ionosphere |
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| Affiliation: | 1. George Mason University, Space Weather Laboratory, Department of Physics and Astronomy, Fairfax, USA;2. Akdeniz University, Department of Space Sciences and Technologies, Turkey;3. Univ. Nacl. Tucuman, Fac. Ciencias Exactas and Tecnol., Dept. Fis., Argentina;4. Kandilli Observatory and Earthquake Research Institute, Bogazici University, Turkey;5. Big Bear Solar Observatory, Big Bear City, CA, USA;6. Korea Astronomy and Space Science Institute, Daejeon, South Korea;7. Université de la Cote d’Azur, OCA, 77, Grasse, France;1. Instituto Nacional de Pesquisas Espaciais (INPE), Av. de Astronautas, 1758, Jd da Granja, São José dos Campos, São Paulo 12227-010, Brazil;2. Instituto de Pesquisa e Desenvolvimento (IP&D), Universidade do Vale do Paraíba (UNIVAP), Av. Shishima Hifumi, 2911, São José dos Campos, São Paulo 12444-000, Brazil;3. Nagoya University, 3-13 Honohara, Toyokawa, Aichi 442-8507, Japan;1. Dep. of Electrical Engineering, University of Brasilia (UnB), 70910-900 Brasília, Brazil;2. The Abdus Salam International Centre for Theoretical Physics (ICTP), Strada Costiera 11, 34151 Trieste, Italy;1. ACSE, University of Sheffield, Sheffield S1 3JD, UK;2. DAE, INPE, Sao Jose dos Campos, Brazil;3. Applied Mathematics, University of Sheffield, Sheffield S10 2TN, UK;1. Utah State University, Logan, UT, 87545, USA;2. University of Colorado at Boulder, Boulder, CO, 80302, USA;3. Delft University of Technology, Delft, The Netherlands;4. National Centre for Space Studies (CNES), Toulouse, France |
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| Abstract: | Hourly foF2 data from over 100 ionosonde stations during 1967–89 are examined to quantify F-region ionospheric variability, and to assess to what degree the observed variability may be attributed to various sources, i.e., solar ionizing flux, meteorological influences, and changing solar wind conditions. Our findings are as follows. Under quiet geomagnetic conditions (Kp<1), the 1-σ (σ is the standard deviation) variability of Nmax about the mean is approx. ±25–35% at ‘high frequencies’ (periods of a few hours to 1–2 days) and approx. ±15–20% at ‘low frequencies’ (periods approx. 2–30 days), at all latitudes. These values provide a reasonable average estimate of ionospheric variability mainly due to “meteorological influences” at these frequencies. Changes in Nmax due to variations in solar photon flux, are, on the average, small in comparison at these frequencies. Under quiet conditions for high-frequency oscillations, Nmax is most variable at anomaly peak latitudes. This may reflect the sensitivity of anomaly peak densities to day-to-day variations in F-region winds and electric fields driven by the E-region wind dynamo. Ionospheric variability increases with magnetic activity at all latitudes and for both low and high frequency ranges, and the slopes of all curves increase with latitude. Thus, the responsiveness of the ionosphere to increased magnetic activity increases as one progresses from lower to higher latitudes. For the 25% most disturbed conditions (Kp>4), the average 1-σ variability of Nmax about the mean ranges from approx. ±35% (equator) to approx. ±45% (anomaly peak) to approx. ±55% (high-latitudes) for high frequencies, and from approx. ±25% (equator) to approx. ±45% (high-latitudes) at low frequencies. Some estimates are also provided on Nmax variability connected with annual, semiannual and 11-year solar cycle variations. |
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