Variation of plasmaspheric field-aligned electron and ion densities as a function of geomagnetic storm activity

摘要

This paper presents whistler mode (WM) radio sounding measurements of field-aligned electron and ion density in the 90-4000 km altitude as a function of 30 August major storm activity. Electron and ion density measurements were obtained at altitudes below 4000 km including F2 peak, L~2 and MLT~15. The plasmapause was located at L>2.5. WM sounding measurements were augmented by in situ measurements from the CHAMP (350 km) and DMSP (850 km) satellites. Even at such low L-shells significant variations in electron and ion densities in both the ionosphere (<; O⁺/H⁺ transition height) and plasmasphere (> O⁺/H⁺ transition height) were observed as a function of storm activity. The variation of electron density below and above O⁺/H⁺ transition height (~1000 km) is different. Our results show that: (1) O⁺/H⁺ transition height increased during the main phase and it remained high during the recovery phase; (2) below transition height, Ne and O⁺ significantly increased during storm's main phase and decreased close to their average quiet time values during the recovery phase; (3) Above transition height, Ne oscillated about their quiet time values as a function of storm activity. it decreased during the onset, increased during the main phase and progressively decreased during first two days of recovery phase; The same is true for H⁺ at all altitudes (4) He⁺ (at all altitudes) increased during storm onset, decreased during main phase and increased during the recovery phase. Our results on the variations of electron density below 1000 km, O⁺ and He⁺ densities are consistent with the past results. Our results also showed significant variations in Ne above 1000 km and H⁺ density at low L-shells which were not observed in the past. Our results obtained here combined with physics based model simulations such as SAMI3 provides a unique method to study the relative importance of neutral winds and dynamo and prompt penetrations electric fields in determining the storm time variations in electron and ion densities.