About ISR
Evans, J. V. (1969), Theory and practice of ionosphere study by Thompson scatter radar, Proc. IEEE, 57, 496-530. PDF file
Science Pages about Annual Ionospheric Variations
Balan, N., Y. Otsuka, S. Fukao, and G. J. Bailey (1998), Equinoctial asymmetries in the ionosphere and thermosphere observed by the MU radar, J. Geophys. Res., 9481-9486. http://www.agu.org/pubs/crossref/1998/97JA03137.shtml
Kawamura, S., N. Balan, Y. Otsuka, and S. Fukao (2002), Annual and semiannual variations of the midlatitude ionosphere under low solar activity, J. Geophys. Res., 107, 10.1029/2001JA000267. http://www.agu.org/pubs/crossref/2002/2001JA000267.shtml
Millward, G. H., H. Rishbeth, T. J. Fuller-Rowell, A. D. Aylward, S. Quegan, and R. J. Moffett (1996), Ionospheric F2 layer seasonal and semiannual variations, J. Geophys. Res., 101, 5149-5156. http://www.agu.org/pubs/crossref/1996/95JA03343.shtml
Rishbeth, H. (1998), How the thermospheric circulation affects the ionospheric F2-layer, J. Atmos. Sol. Terr. Phys., 60, 1385-1402. (Most important paper!!!) Link to the Paper
Zhang, S.-R. and J. M. Holt (2007), Ionospheric Climatology and Variability from Long-term and Multiple Incoherent Scatter Radar Observations: Climatology in Eastern American Sector, J. Geophys. Res., 12, A06328, doi:10.1029/2006JA012206. http://www.agu.org/pubs/crossref/2007/2006JA012206.shtml
Zhang, S.-R., J. M. Holt, A. P. van Eyken, M. McCready, C. Amory-Mazaudier, S. Fukao, and M. Sulzer, Ionospheric local model and climatology from long-term databases of multiple incoherent scatter radars, Geophys. Res. Lett., 32, L20102, doi:10.1029/2005GL023603. http://www.agu.org/pubs/crossref/2005/2005GL023603.shtml
Other Relevant Papers
Holt, J. M., S.-R. Zhang, and M. J. Buonsanto (2002), Regional and local ionospheric models based on Millstone Hill incoherent scatter radar data, Geophys. Res. Lett., 29, 1207, doi:10.1029/2002GL014678. http://www.agu.org/pubs/crossref/2002/2002GL014678.shtml
Zhang, S.-R., J. M. Holt, A. M. Zalucha, and C. Amory-Mazaudier, Mid-latitude ionospheric plasma temperature climatology and empirical model based on Saint Santin incoherent scatter radar data from 1966-1987, J. Geophys. Res., 109, A11311, doi:10.1029/2004JA010709, 2004. http://www.agu.org/pubs/crossref/2004/2004JA010709.shtml