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Annual and semiannual variations in the height of the ionospheric F2-layer

Annual and semiannual variations in the height of the ionospheric F2-layer
Annual and semiannual variations in the height of the ionospheric F2-layer
Ionosonde data from sixteen stations are used to study the semiannual and annual variations in the height of the ionospheric F2-peak, hmF2. The semiannual variation, which peaks shortly after equinox, has an amplitude of about 8 km at an average level of solar activity (10.7 cm flux = 140 units), both at noon and midnight. The annual variation has an amplitude of about 11 km at northern midlatitudes, peaking in early summer; and is larger at southern stations, where it peaks in late summer. Both annual and semiannual amplitudes increase with increasing solar activity by day, but not at night. The semiannual variation in hmF2 is unrelated to the semiannual variation of the peak electron density NmF2, and is not reproduced by the CTIP and TIME-GCM computational models of the quiet-day thermosphere and ionosphere. The semiannual variation in hmF2 is approximately "isobaric", in that its amplitude corresponds quite well to the semiannual variation in the height of fixed pressure-levels in the thermosphere, as represented by the MSIS empirical model. The annual variation is not "isobaric". The annual mean of hmF2 increases with solar 10.7 cm flux, both by night and by day, on average by about 0.45 km/flux unit, rather smaller than the corresponding increase of height of constant pressure-levels in the MSIS model. The discrepancy may be due to solar-cycle variations of thermospheric winds. Although geomagnetic activity, which affects thermospheric density and temperature and therefore hmF2 also, is greatest at the equinoxes, this seems to account for less than half the semiannual variation of hmF2. The rest may be due to a semiannual variation of tidal and wave energy transmitted to the thermosphere from lower levels in the atmosphere.
Atmospheric composition and structure (thermosphere - composition and chemistry) - Ionosphere (mid-latitude ionosphere)
0992-7689
285-299
Rishbeth, H.
fb69f152-f92f-4579-95b2-532898a077d1
Sedgemore-Schulthess, K.J.F
e0f58fd7-a4e7-4fea-8d14-b0388827dccc
Ulich, Th.
9f0c5895-1a6e-47e6-9909-220f5b359ef5
Rishbeth, H.
fb69f152-f92f-4579-95b2-532898a077d1
Sedgemore-Schulthess, K.J.F
e0f58fd7-a4e7-4fea-8d14-b0388827dccc
Ulich, Th.
9f0c5895-1a6e-47e6-9909-220f5b359ef5

Rishbeth, H., Sedgemore-Schulthess, K.J.F and Ulich, Th. (2000) Annual and semiannual variations in the height of the ionospheric F2-layer. Annales Geophysicae, 18 (3), 285-299.

Record type: Article

Abstract

Ionosonde data from sixteen stations are used to study the semiannual and annual variations in the height of the ionospheric F2-peak, hmF2. The semiannual variation, which peaks shortly after equinox, has an amplitude of about 8 km at an average level of solar activity (10.7 cm flux = 140 units), both at noon and midnight. The annual variation has an amplitude of about 11 km at northern midlatitudes, peaking in early summer; and is larger at southern stations, where it peaks in late summer. Both annual and semiannual amplitudes increase with increasing solar activity by day, but not at night. The semiannual variation in hmF2 is unrelated to the semiannual variation of the peak electron density NmF2, and is not reproduced by the CTIP and TIME-GCM computational models of the quiet-day thermosphere and ionosphere. The semiannual variation in hmF2 is approximately "isobaric", in that its amplitude corresponds quite well to the semiannual variation in the height of fixed pressure-levels in the thermosphere, as represented by the MSIS empirical model. The annual variation is not "isobaric". The annual mean of hmF2 increases with solar 10.7 cm flux, both by night and by day, on average by about 0.45 km/flux unit, rather smaller than the corresponding increase of height of constant pressure-levels in the MSIS model. The discrepancy may be due to solar-cycle variations of thermospheric winds. Although geomagnetic activity, which affects thermospheric density and temperature and therefore hmF2 also, is greatest at the equinoxes, this seems to account for less than half the semiannual variation of hmF2. The rest may be due to a semiannual variation of tidal and wave energy transmitted to the thermosphere from lower levels in the atmosphere.

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Published date: 2000
Keywords: Atmospheric composition and structure (thermosphere - composition and chemistry) - Ionosphere (mid-latitude ionosphere)

Identifiers

Local EPrints ID: 9180
URI: http://eprints.soton.ac.uk/id/eprint/9180
ISSN: 0992-7689
PURE UUID: 15c957b2-32d4-4592-8bfb-d09f0aa00e9f

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Date deposited: 24 Sep 2004
Last modified: 08 Jan 2022 03:42

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Contributors

Author: H. Rishbeth
Author: K.J.F Sedgemore-Schulthess
Author: Th. Ulich

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