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We review the modulation stability of parallel propagating/field alignedWhistler Mode Chorus waves propagating in a warm plasma from a formalperspective with a focus on wave-particle interactions. The modulationinstability criteria is characterised by a curvature of the dispersion relationfor Whistler mode waves and a condition on the ratio between the group velocity$c_g$ and the electron sound speed $c_{s,e}$. We also demonstrate the in orderto investigate the spatiotemporal evolution of the envelope and the formationof packets, one necessarily needs to account for the motion of ions within thesystem, leading to an ionic influence on the modulation instability thresholddetermined by the ion fraction of the plasma. Finally, we demonstrate thatchirping may be captured when higher order effects are included within thespatiotemporal evolution of the amplitude. This yields not only an explicitexpression for the sweep rate but identifies a possible origin for the powerband gap that occurs at half the electron gyrofrequency. Numerical validationdemonstrates that the interaction between wave packets is a source for theemergence of tones observed within mission data, and such interactions may be amajor source of the electron energisation which Whistler-Mode chorus areresponsible for.

The Nonlinear Evolution of Whistler-Mode Chorus Revisited: Modulation Instability as the Source of Tones