High-m Alfv¿n waves can be driven by drift-bounce resonance with energetic protons in the magnetosphere. We calculate the trajectories of protons in a dipole magnetosphere, including the effects of corotation and convection electric fields. We propose that the boundary between open and closed orbits, following a particle injection, can represent a region where unstable particle distributions with df/dW>0 can develop. Hence we can model the energetically favorable locations in particle energy, W, and L shell space for high-m wave growth by finding the positions where the open-closed orbit boundary intersects a drift-bounce resonance curve. Our model can provide a physical explanation for the observed asymmetry between the properties of high-m Alfv¿n waves in the morning and afternoon sectors, and it predicts wave properties which are in excellent agreement with observations. In particular, the observed properties of storm-time Pc5 waves in the afternoon sector and giant pulsations (Pgs) in the morning sector are in excellent agreement with our model, these waves predicted to be fundamental (N=0) and second harmonic (N=1) resonances, respectively. Moreover, our model can explain why Pgs are so monochromatic, so highly localized in latitude, and only produced in the auroral zone. ¿ 2001 American Geophysical Union