Dear authors,

Although the manuscript has undergone extensive revision and is improved, I would suggest considering two additional comments/suggestions:

 There is mentioned in the manuscript that you have used Canadian Advanced Digital Ionosonde (CADI) data for calibration purposes. Are the ionosonde data manually checked or you have used automatically scaled data? The data quality should be mentioned in the manuscript. Sometimes there could appear significant differences between manually checked and automatically scaled data sets. In the case, there is possible to check the ionosonde data manually, please, do it and introduce appropriate corrections in the Table 2 and in the text ;

 Please, replace the website address http://isgi.latmos.ipsl.fr (page 21, line 3) with the http://isgi.unistra.fr/, as the previous address is not recently accessible.

Kindest regards
Yours cordially
Dalia Buresova