Evolution of Field Aligned Electron and Ion (H+, He+, O+) Densities as a Function of Geomagnetic Storm Activity

Abstract:

Field aligned electron and ion densities and their variations as a function of geomagnetic storm activity are important parameters in the physics of the thermosphere, ionosphere, and magnetosphere. Whistler mode radio sounding [Sonwalkar et al., JGR, 2011] from the IMAGE satellite during 16 Aug – 06 Oct 2005, covering 3 major, 3 moderate, and one minor storm, has permitted first measurements of field aligned electron and ion densities inside the plasmasphere (L = 1.7-2.4, Alt = 90-4000 km, MLT~13-15) as a function of geomagnetic storm activity. The whistler mode sounding results are augmented by observations from CHAMP, DMSP satellites, and ground ionosonde stations during the same period.

We found the following as a function of geomagnetic activity: (1) Plasmapause moved from Lpp~4.5 during the quiet time to Lpp~2.4 during the disturbed time. (2) Variations in the plasma parameters below the O+/H+ transition height were different than those above. (3) Below O+/H+ transition height, variations in plasma parameters measured by CHAMP (350 km) and DMSP (850 km) were in agreement with those obtained from whistler mode sounding. (4) The electron density, relative ion concentrations, and O+/H+ transition height undergo temporal changes as a function of geomagnetic storm activity, and each species has different temporal behavior that appears to be indicative of different recovery times.

The results presented here on temporal variations in the field aligned plasma parameters provide novel methods to: (1) test current theories and physics based models (e.g. SAMI2) of thermosphere-ionosphere-magnetosphere coupling, (2) build empirical models of field aligned electron and ion densities, and (3) relate variations in plasma density and composition to those in thermospheric neutral wind and dynamo electric fields during geomagnetically active periods.

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