The features and a possible mechanism of semiannual variation in the peak electron density of the low latitude F2 layer |
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| Institution: | 1. CAS Key Laboratory of Geospace Environment, Department of Geophysics & Planetary Sciences, University of Science & Technology of China, Hefei, Anhui 230026, China;2. Mengcheng National Geophysical Observatory, School of Earth & Space Sciences, University of Science & Technology of China, Hefei, Anhui 230026, China;3. Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science & Technology of China, Hefei, Anhui 230026, China;4. State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190, China;5. Key Laboratory of Ionospheric Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China;6. Jülich Supercomputing Centre, Forschungszentrum Jülich, Jülich, Germany;1. National Institute of Meteorology and Hydrology, Bulgarian Academy of Sciences, 66 Tsarigradsko Shose Blvd., 1784 Sofia, Bulgaria;2. Faculty of Physics, Sofia University “St. Klement Ohridski”, 5 James Bourchier Blvd., 1164 Sofia, Bulgaria;1. Key Laboratory of Meteorological Disaster, Ministry of Education(KLME), Joint International Research Laboratory of Climate and Environment Change(ILCEC), Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing, 210044, China;2. Jiangxi Leadership Team Office of Weather Modification, Nanchang, 330096, China;1. Space Physics Laboratory, Vikram Sarabhai Space Centre, ISRO, Trivandrum 695022, India;2. Instituto Nacional de Pesquisas Espaciais, C.P. 515, São José dos Campos, SP, Brazil;1. Department of Atmospheric Physics, St. Petersburg State University, St. Petersburg, Russia;2. Institute for Meteorology, University of Leipzig, Leipzig, Germany |
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| Abstract: | Ionospheric data observed in 30 stations located in 3 longitude sectors (East Asia/Australia Sector, Europe/Africa Sector and America/East Pacific Ocean Sector) during 1974–1986 are used to analyse the characteristics of semiannual variation in the peak electron density of F2 layer (NmF2). The results indicate that the semiannual variation of NmF2 mainly presents in daytime. In nighttime, except in the region of geomagnetic equator between the two crests of ionospheric equatorial anomaly, NmF2 has no obvious semiannual variation. In the high latitude region, only in solar maxima years and in daytime, there are obvious semiannual variations of NmF2. The amplitude distribution of the semiannual variation of daytime NmF2 with latitude has a “double-humped structure”, which is very similar to the ionospheric equatorial anomaly. There is asymmetry between the Southern and the Northern Hemispheres of the profile of the amplitude of semiannual variation of NmF2 and longitudinal difference. A new possible mechanism of semiannual variation of NmF2 is put forward in this paper. The semiannual variation of the diurnal tide in the lower thermosphere induces the semiannual variation of the amplitude of the equatorial electrojet. This causes the semiannual variation of the amplitude of ionospheric equatorial anomaly through fountain effect. This process induces the semiannual variation of the low latitude NmF2. |
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