A theoretical model is proposed for the nonlinear saturation of high-m Alfv¿n-ballooning instabilities in magnetospheric plasmas. Here, m is the azimuthal wave number. In the present model, a broad spectrum of Alfv¿n waves nonlinearly generate ion-sound density perturbations; which, in turn, scatter the Alfv¿n turbulence toward lower frequencies. Balancing the linear instability growth rate with the nonlinear scattering (Landau damping) rate then yield the corresponding saturated spectrum, which tends to peak near the bottom of the eigenmode frequencies. The theory also gives estimates of wave amplitudes at saturation in reasonable agreement with satellite observations.