Fig. 4

a–d MLT variations in the Na densities at 97–103-km heights during the quiet days (the daily averaged ap \(< 10\)). e MLT variation in the CNA during the quiet days. f–i Same as a–d, but for the active days (the daily averaged ap \(\ge 10\)). j Same as e, but for the active days. Light gray lines show variations on each day. Black lines show median values, and lower and upper quantile values of each dataset. Red points indicate data which have significant differences (\(>98\%\) probability) in the median values between the quiet and active days