| dc.description.abstract | Whistler mode waves are strong electromagnetic emissions naturally occurring in the Earth’s magnetosphere. It is well recognised that these waves play a pivotal role in controlling the particle dynamics in the Van Allen radiation belt. This thesis investigates the characteristics of whistler mode waves using spacecraft observations and plasma simulations. Initially, nonlinear isolated whistler structures are studied by considering plasma fluid simulations. The nonlinear effects on whistler oscilliton and periodic wave packets in a cold plasma are investigated using stationary whistler waves as initial conditions. The solutions of parallel and obliquely propagating whistler waves are found to be unstable, as observed in their long-term evolution. The behaviour of whistler mode waves is further studied by conducting a survey of Magnetospheric Multiscale (MMS) Mission observations when the spacecraft is located at the dayside outer magnetosphere. Wave polarization analysis is employed for several chosen periods of MMS burst mode data that contain narrow-band emissions. This analysis identifies several whistler mode wave events from which we present nine events. Three events exhibit discrete elements having rising tone frequencies showing a typical whistler mode lower band chorus. Another three events show the presence of unstructured broadband emissions with behaviour close to plasmaspheric hiss. A particular type called multiband whistler mode emissions is also observed from the survey of MMS data, consisting of a power gap between successive bands in the spectrograms. Bicoherence analysis and simulation studies are carried out to explore their generation mechanism. For one of the observed multiband events, these investigations suggest that a higher-frequency whistler band is possibly generated due to the coupling between two lower-frequency whistler bands. The existence of multiband whistler mode emissions reveals the diversity of the nonlinear evolution of whistler mode waves. The origin and different spectral forms of whistler mode waves, including their multiband type, need to be considered for modelling Earth’s magnetosphere. | en_US |
