The role of acoustic gravity waves in the generation of spread-F and ionospheric scintillation |
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| Affiliation: | 1. Space Weather Laboratory, Department of Physics and Astronomy, George Mason University, Fairfax, VA, USA;2. Space Sciences Laboratory, University of California at Berkeley, Berkeley, USA;3. Atmospheric Oceanic and Space Sciences, University of Michigan, Ann Arbor, USA;1. State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China;2. China-Brazil Joint Laboratory for Space Weather, Chinese Academy of Sciences, São Jose dos Campos, Brazil;3. School of Physics and Electronics Engineering, Hainan Normal University, Haikou 571158, China;1. Faculty of Math. and Computer Sci., Amirkabir University of Technology (Tehran Polytechnic), 15914 Tehran, Iran;2. Dipartimento di Matematica e Informatica U. Dini, Università degli Studi di Firenze, viale Morgagni 67/a, 50134 Firenze, Italy;3. Dipartimento di Matematica F. Enriques, Università degli Studi di Milano, via Saldini 50, 20133 Milano, Italy;4. Departament de Matemàtiques, Facultat de Matemàtiques, Universitat de València, 46100 Burjassot, València, Spain;1. College of Geomatics, Xi’an University of Science and Technology, Xi’an 710054, China;2. State Key Laboratory of Geodesy and Earth’s Dynamics, Wuhan 430077, China;3. School of Geodesy and Geomatics, Wuhan University, Wuhan 430079, China;4. Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, Wuhan University, Wuhan 430079, China;1. Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China;2. Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, West Beijing Road, Nanjing, JiangSu 210008, China |
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| Abstract: | In the aggregate, acoustic gravity waves in the F-region constitute a spectrum of geophysical noise extending from the frequencies involved in diurnal variations up to the Brunt-Väisälä buoyancy frequency. They drive a roughly uniform power spectrum of travelling ionospheric disturbances (TIDs) with vertical scales of the order of the atmospheric scale height H and with horizontal scales extending from the radius of the Earth down to H. It has been known since the 1950s that this permits multiple normals onto the F-region from an ionosonde, thereby creating the multiple-trace type of spread F on ionograms. At shorter scales the spectrum of TIDs decreases in strength and, below the mean free path of the neutral atmosphere, creates a spectrum of plasma turbulence aligned along the Earth's magnetic field. Progressively shorter scales are responsible for phase scintillation, for amplitude scintillation and for blur-type spread F on ionograms. A weak extension of the spectrum to scales less than the ion gyroradius is responsible for spread F and transequatorial propagation in the VHF band. Under evening conditions in equatorial regions a band of TIDs with wavelengths of the order of 600 km can, at times, have a phase velocity that matches the drift velocity of the plasma (Röttger 1978). This band of TIDs is then amplified until it breaks (Klostermeyer 1978). The associated explosive increase in plasma turbulence creates the plume phenomenon discovered by Woodmn and La Hoz (1976). |
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