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 Earth’s magnetic field causing them to precipitate into the ionosphere via resonant interaction. In order to incorporate EMIC-related loss processes into global magnetospheric models one needs to know solar wind and magnetospheric conditions favorable for EMIC wave excitation as well as the localization of the waves in the magnetosphere.
EMIC waves are generated by anisotropic (Tperp/Tpara> 1) proton distributions. Generally, any process that leads to the formation of such distributions may be responsible for EMIC wave initiation. I will discuss magnetospheric compression as a principal source of EMIC wave generation in the dayside magnetosphere, address possible physical mechanisms which can lead to the generation of anisotropic proton distributions, and present EMIC wave observations from multiple satellite missions including THEMIS, Cluster, and GOES.