Discrete phase changes within nonlinear steepened magnetosonic waves: Comet Giacobini‐Zinner

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Abstract
In this letter, we will illustrate the intricate complexities of nonlinear wave evolution and briefly discuss their consequences. We will show examples of nonlinear steepened magnetosonic waves that have subintervals without phase rotation (linearly polarized) and other subintervals with discrete, rapid phase rotation. Some specific features are: 1) the trailing (∼half) portion of the wave sometimes has no phase rotation and is simply compressive; 2) just behind the leading adge of the wave front where there is a sharp rotation (called a partial rotation), there is often a second region with no phase change; 3) between these two regions is an interval with a distinct phase change; 4) in the examples shown in this paper, the distinct phase changes have right‐hand polarizations in the spacecraft frame; 5) the magnetosonic wave appears to split into two parts with time; the right‐hand rotation is located where the splitting occurs.Possible explanations for the right‐hand rotation will be explored. One plausible explanation is that a right‐hand wave is generated through the decay instability of a magnetosonic wave, i.e., a magnetosonic wave propagating towards the sun decays into a sound wave and a magnetosonic wave propagating away from the sun. If right‐hand daughter waves are actually present, this will have important consequences. Even though these waves are present only ∼ 10% (or less) of the time, this may allow significant wave‐particle interactions to make the self‐consistent second‐order Fermi acceleration mechanism of energetic cometary ions feasible.