Fig. 1

Geotail location in a X _GSM and b Z _GSM for October 1992 to October 2015. Integral fluxes of c H⁺, d He⁺, e O⁺, and f He²⁺ ions for October 1992 to October 2015. The integral fluxes are averaged over 27 days corresponding to the synodic rotation period of the Sun. Open and filled circles represent the integral fluxes measured in the mid-tail plasma sheet (X _GSM  = −32 to −100 R _E and Y _GSM  = −14 to 14 R _E ) and in the near-Earth plasma sheet (X _GSM  = −8 to −32 R _E and Y _GSM  = −8 to 8 R _E ), respectively. g Plasma ion mass in the plasma sheet calculated from data points in Fig. 1c–f