We derive explicit formulas for the characteristic curves associated with the multipeakon solutions of the Camassa-Holm equation. Such a curve traces the path of a fluid particle whose instantaneous velocity equals the elevation of the wave at that point. The peakons themselves follow characteristic curves, and the remaining characteristic curves can be viewed as paths of "ghostpeakons" with zero amplitude; hence, they can be obtained as solutions of the ODEs governing the dynamics of multipeakon solutions. However, the previously known solution formulas for multipeakons only cover the case when all amplitudes are nonzero, since they are based upon inverse spectral methods unable to detect the ghostpeakons. We show how to overcome this problem by taking a suitable limit in terms of spectral data, in order to force a selected peakon amplitude to become zero.

This is part of a joint work with Hans Lundmark from Linköping University.