Occurrence patterns of whistler mode (WM) echoes observed by RPI/IMAGE and their relation to geomagnetic activity

Abstract

This thesis presents an analysis of whistler mode (WM) echoes observed at altitudes less than 5,000 km by the Radio Plasma Imager (RPI) on the IMAGE satellite. WM echoes are generated either by specular reflection (SR) of RPI signals at the Earth-ionosphere boundary (~90 km) or by magnetospheric reflection of RPI signals [...] at altitudes greater than 1,000 km [Sonwalkar et al., 2004; Sonwalkar et al., 2006]. These echoes are further influenced by field aligned irregularities (FAI) and are categorized into discrete, multipath or diffuse SR- and MR- WM echoes, based on their characteristic spectral forms. A survey of WM echoes observed during January 2004- December 2005 showed that WM echoes occurred at all latitudes and under moderate geomagnetic conditions. Occurrence patterns of WM echoes observed in August-December 2005 during geomagnetically quiet and disturbed periods indicate that geomagnetic storms lead to significant changes in FAI that affect the propagation of WM echoes. Our results help (1) in better understanding propagation and generation mechanisms of naturally occurring WM waves, and (2) in planning future WM wave injection experiments in space.