Seasonal and solar cycle variations of the ionospheric peak electron density: Comparison of measurement and models

Abstract

Abstract. This paper examines the ability of empirical and physical models to reproduce the peak electron density of the midlatitude ionospheric F2 region (NrnF2) from 1976 to 1980. The data from all midlatitude stations show a tendency toward a semiannual variation in noon NrnF2 with peaks at the equinoxes for all levels of solar activity. The Southern Hemisphere semiannual variation is more pronounced than in the Northern Hemisphere primarily because the winter density is relatively low in the Southern Hemisphere. At most locations the equinox density peaks are approximately equal. However, the September peak is much weaker than the March peak at most

On the mechanism of seasonal and solar cycleNmF2variations: A quantitative estimate of the main parameters contribution using incoherent scatter radar observations

“…This basically agrees with Richards [2001], who found that the increase in N m F 2 was due to approximately equal contributions of neutral composition (O/N 2 ratio) near the F 2 layer peak and the EUV ionization frequency. That is, the contribution of neutral composition and reaction rate coefficients is large in winter.…”

“…[24] Our analysis has shown that seasonal differences in daytime N m F 2 solar activity variations are due to the different roles which neutral composition (O, O 2 , N 2 ) and temperature play in summer and in winter, and the observed seasonal difference in N m F 2 is not simply reduced to seasonal O/N 2 variations [e.g., Millward et al, 1996;Rishbeth et al, 2000;Richards, 2001;Yu et al, 2004].…”

“…However, these models are widely used to find out physical mechanisms of F 2 layer parameters variation. For instance, Richards [2001] analyzed seasonal and solar cycle F 2 region parameter variations using daily calculations with the MSIS-86 thermospheric model.…”

“…[2] Seasonal and December anomalies in N m F 2 variations have been studied since the beginning of ionospheric observations [Appleton and Naismith, 1935;Seaton and Berkner, 1939;Yonezawa and Arima, 1959]; however, the mechanisms of their formation are still discussed in publications [Richards et al, 1994c;Rishbeth et al, 2000;Richards, 2001;Kawamura et al, 2002;Yu et al, 2004;Pavlov and Pavlova, 2005;Rishbeth and Müller-Wodarg, 2006;Zhao et al, 2007]. Among different explanations proposed during the decades of the problem analysis [see Rishbeth, 1998], the suggestion by Rishbeth and Setty [1961] that F 2 layer seasonal anomaly is due to neutral composition variation may be considered as generally accepted [Rishbeth et al, 2000].…”

“…[6] A thorough and comprehensive consideration of the problem was undertaken by Richards [2001]. The analysis was performed using calculations with the FLIP (field line interhemispheric plasma) model in comparison with daily observations at six midlatitude ionosonde stations in the Northern and Southern hemispheres.…”