Fig. 1

Fitting to the altitude profile of Mg (a), Ca (b), and Na (c). For Mg and Ca, fitting was performed while ignoring the observations with a tangential altitude lower than 500 km (the gray region). The Na profile was fitted assuming two components: a lower-energy component and a higher-energy component following Cassidy et al. (2015), and only the production rate of the lower-energy component derived from PSD was used. The Levenberg–Marquardt method was used for fitting