Using the theoretical results of Mann et al. [1999>, we show how the characteristics of multiple field line resonances (FLRs), driven by waveguide mode harmonics, can be strongly local time dependent and how these characteristics can be used to differentiate between waves driven by solar wind stimuli or by the development of magnetopause shear flow instabilities. Using observations previously reported in the literature, we show examples of this diagnostic analysis and conclude that the dawn/dusk asymmetry in Pc5 FLR characteristics may be linked to different dominant excitation mechanisms operating either side of noon. In particular, we suggest there is a preference for dawn-side FLRs to be excited by waveguide modes which are amplified through the action of over-reflection at the magnetopause. ¿ 1999 American Geophysical Union