Electromagnetic Ion Cyclotron (EMIC) waves are believed to play an important role in the dynamics of energetic particles (both electrons and ions) trapped by the Earths magnetic field causing them to precipitate into the ionosphere via resonant interaction. In order to incorporate the EMIC-related loss processes into global magnetospheric models one needs to know solar wind and magnetospheric conditions favourable for EMIC wave excitation as well as the localization of the waves in the magnetosphere. EMIC waves are generated by anisotropic (Tperp/Tpara > 1) ion distributions. Generally, any process that leads to the formation of such distributions may be responsible for EMIC wave initiation. This thesis discusses magnetospheric compression as a new principal source of EMIC wave generation in the inner dayside magnetosphere. First, using ground-based and satellite instrumentation, it is shown that EMIC waves are often generated in the inner dayside magnetosphere during periods of enhanced solar wind dynamic pressure and associated dayside magnetospheric compression. The compression-related EMIC wave activity usually lasts for several hours while the magnetosphere remains compressed. Also, it is demonstrated that EMIC waves are generated in radially narrow (1 Re wide) region of high plasma density, just inside the plasmapause. Test particle simulations of energetic ion dynamics performed for this study confirmed that anisotropic ion distributions are generated in the compressed dayside magnetosphere, the temperature anisotropy being dependant on the strength of magnetospheric compression. It is found that in the inner magnetosphere these anisotropic particle distributions are formed due to particle drift shell-splitting in an asymmetric magnetic field. Finally, the generation of EMIC waves was studied self-consistently using a hybrid particle-in-cell code in order to determine whether the degree of anisotropy estimated from the test particle simulations is sufficient to produce EMIC waves like those detected and to explain some of the observed wave properties.

No description available.