Recent Results From the Whistler- and Z-mode Radio Sounding From the IMAGE Satellite
Wednesday, 17 December 2014
Whistler mode radio sounding method [Sonwalkar et al., JGR, 2011] was applied to two case studies: (1) daytime and nighttime cases of whistler mode echoes observed on IMAGE inside the plasmasphere (L<4, altitude <5000 km), and (2) cases of whistler mode echoes observed during geomagnetic storm activity. Preliminary results indicate: (i) O+/H+ and O+/ (H+ + He+) transition heights at nighttime are a few hundred kilometers lower than that at daytime. (ii) Electron and ion densities found from whistler mode sounding are consistent with those from the past in situ and radio sounding measurements, but differ from those predicted by IRI-2012 and GCPM. (iii) Electron and ion densities undergo temporal changes as a function of geomagnetic storm activity, and each species has different recovery period. (iv) Major, moderate, and minor storms affect Ne, H+, and O+ densities in a similar manner, but affect He+ density differently-the minor storm did not affect it. By comparing the electron and ion densities measured by whistler mode radio sounding with those predicted by physics based ionospheric models (e.g. SAMI 2) it may be possible to understand how thermospheric winds influence the evolution of the ionospheric electron and ion densities during geomagnetic storms. The application of Sonwalkar et al.  method to nonducted and ducted fast Z mode echoes observed on IMAGE has led to the measurement of field aligned electron density and duct width and enhancement factor from ~1000 km up to the equator. In two cases, ducts with widths of ~0.05-0.1 L and density depletions of ~5-10 % accounted for the observed properties of ducted Z mode echoes. The measurements of both electron density and ducts are consistent with past measurements. The results from the whistler and Z mode sounding will lead to new empirical models of field aligned electron and ion densities and a statistical characterization of ducts in the magnetosphere.