Steepening of Magnetosonic Waves in the Inner Coma of 67P/Churyumov-Gerasimenko
Abstract
We present a statistical survey of steepened magnetosonic waves at comet 67P/Churyumov-Gerasimenko over a two year escort phase. First observations of steepened waves in a cometary environment were previously obtained at comet 21P/Giacobini-Zinner. However, all observations were made during fast flybys and therefore provided only a limited amount of data. As the first mission of its kind the ESA Rosetta spacecraft was able to study the plasma of the inner coma for a prolonged time and different stages of activity. This enables us to study the temporal evolution of steepened waves and their characteristics.
In total we identified 64447 waves in the magnetic field data by means of machine learning. We observe that the occurrence of steepened waves is linked to the activity of the comet. For several months around perihelion the steepened waves dominate the cometary interaction region in the inner coma, whereas they vanish at a weakly active comet. Characteristics like amplitude, skewness and width of the waves were extracted by fitting a skew normal distribution to the magnetic field magnitude. With decreasing distance to the electron exobase the average amplitude, skewness and width of the steepened waves increase. Using a 1D MHD model it was possible to show that such solitary structures can be described by the combination of nonlinear, dispersive and dissipative effects. By combining the model with observations of amplitude, width and skewness we obtain an estimate of the local plasma resistivity at the comet. Steepened waves, in particular, are an important building block in the understanding of the inner coma, since they dominate the interaction region for intermediate to high activity. Hence, the presented study expands our understanding of the physical processes governing the inner cometary interaction region.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P42B..02O
- Keywords:
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- 6005 Atmospheres;
- PLANETARY SCIENCES: COMETS AND SMALL BODIES;
- 6025 Interactions with solar wind plasma and fields;
- PLANETARY SCIENCES: COMETS AND SMALL BODIES;
- 6026 Ionospheres;
- PLANETARY SCIENCES: COMETS AND SMALL BODIES;
- 5435 Ionospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS