Relation between daytime and nighttime values of the critical frequency foF2

Time and spatial variations in the ratio of nighttime and daytime critical frequencies of the F2 layer

“…The following regularities in the R(foF2) behavior were revealed by Danilov (2006b) and Vanina-Dart and Danilov (2006). The value of R(foF2) was found to depend on geomagnetic activity determined by the Ap index.…”

“…However, in some years an increase in the absolute value of R(foF2) is observed also in the fall period (September-November). So, to characterize each year for the particular station and limitation in magnetic activity, Danilov (2006b) and Vanina-Dart and Danilov (2006) took the maximum negative value of R(foF2) regardless of the season it was obtained.…”

Critical frequency foF2 as an indicator of trends in thermospheric dynamics

“…Vanina-Dart and Danilov (2006a) were the first to draw attention to the fact that there is a significant negative correlation between the nighttime and daytime values of foF2 for the same day. Danilov (2006) described the phenomenon in detail.…”

“…In order to study the behavior of R(foF2) during the year, Vanina-Dart and Danilov (2006a) performed the following procedure. For a given year they took a running 3-month window (January-March, February-April, and so on).…”

“…Vanina-Dart and Danilov (2006a) considered the correlation coefficient R(foF2) between nighttime and daytime values of foF2. Later, Danilov (2008a) derived long-term trends in the minimal values of R(foF2) on the basis of the data of a few ionospheric stations.…”