PROPAGATION CHARACTERISTICS OF PC-3 COMPRESSIONAL WAVES GENERATED AT THE DAYSIDE MAGNETOPAUSE

New, three-dimensional ray tracing of Pc 3 compressional waves from th e magnetosheath reveals that the magnetosphere can present a major pro pagation barrier to the penetration of these waves to the plasmasphere . This barrier is the ion-ion cutoff between the He+ and O+ gyroresona nces. As a result of the frequency-dependent location of this cutoff, the magnetosphere behaves like a filter for Pc 3 compressional waves, and only low-frequency components of Pc 3 compressional waves can pene trate to inner magnetosphere. Results are in agreement with previous s atellite observations. This ''filter action'' strongly depends on the relative concentration of He+ and O+ and is therefore sensitive to sol ar and magnetic activity. Ray-tracing results are based on a cold plas ma dispersion relation, a semi-empirical model of plasma density, and the Mead-Fairfield magnetic field model.