Articles | Volume 18, issue 8
Ann. Geophys., 18, 927–944, 2000
Ann. Geophys., 18, 927–944, 2000

  31 Aug 2000

31 Aug 2000

Annual and semiannual variations in the ionospheric F2-layer. I. Modelling

L. Zou1, H. Rishbeth1, I. C. F. Müller-Wodarg2,1, A. D. Aylward2, G. H. Millward4,3,2, T. J. Fuller-Rowell3, D. W. Idenden4, and R. J. Moffett4 L. Zou et al.
  • 1Department of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
  • 2Atmospheric Physics Laboratory, University College London, 67-73 Riding House Street, London WIP 7PP, UK
  • 3CIRES, University of Colorado and NOAA Space Environment Center, 325 Broadway, Boulder, CO 80303, USA
  • 4School of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH, UK
  • Correspondence to: H. Risbeth
  • e-mail:

Abstract. Annual, seasonal and semiannual variations of F2-layer electron density (NmF2) and height (hmF2) have been compared with the coupled thermosphere-ionosphere-plasmasphere computational model (CTIP), for geomagnetically quiet conditions. Compared with results from ionosonde data from midlatitudes, CTIP reproduces quite well many observed features of NmF2, such as the dominant winter maxima at high midlatitudes in longitude sectors near the magnetic poles, the equinox maxima in sectors remote from the magnetic poles and at lower latitudes generally, and the form of the month-to-month variations at latitudes between about 60°N and 50°S. CTIP also reproduces the seasonal behaviour of NmF2 at midnight and the summer-winter changes of hmF2. Some features of the F2-layer, not reproduced by the present version of CTIP, are attributed to processes not included in the modelling. Examples are the increased prevalence of the winter maxima of noon NmF2 at higher solar activity, which may be a consequence of the increase of F2-layer loss rate in summer by vibrationally excited molecular nitrogen, and the semiannual variation in hmF2, which may be due to tidal effects. An unexpected feature of the computed distributions of NmF2 is an east-west hemisphere difference, which seems to be linked to the geomagnetic field configuration. Physical discussion is reserved to the companion paper by Rishbeth et al.

Key words: Atmospheric composition and structure (thermosphere-composition and chemistry) - Ionosphere (mid-latitude ionosphere; modelling and forecasting)