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(Over-)Reaction of the Cometary Plasma to Extreme Solar Wind Conditions

Abstract : The magnetometer onboard ESA's Rosetta orbiter detected its highest magnetic field magnitude of 250nT in July 2015, close to perihelion. This magnitude was an enhancement of a factor of five compared to normal values, which makes this the highest interplanetary magnetic field ever measured. We have examined the solar wind conditions at the time and found that a corotating interaction region (CIR), accompanied by a fast flow is the trigger for this unusual event. Because Rosetta does not have solar wind observations during the comet's active phase, we use ENLIL simulations as well as observations at Earth and Mars to constrain the solar wind parameters at the comet. Using a simple model for the magnetic field pile-up we can trace back the field in the coma to corresponding structures in the CIR. The large field is accompanied by a dramatic increase in electron and ion fluxes and energies. However, the electrons and ions in the field of view are not, as expected, increasing at the same time, instead the electrons follow the magnetic field, while the ion density increase is delayed. This is seen as evidence of the kinetic behaviour of the ions as opposed to a magnetized electron fluid. Combining the information on the plasma, we are able to identify at least three different regions in the plasma that have fundamentally different parameters. This allows us to separate the solar wind influence from the comet's effects on the plasma, a problem that is usually not solvable without a spacecraft monitoring the solar wind at the comet.
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https://hal-insu.archives-ouvertes.fr/insu-03570125
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Submitted on : Sunday, February 13, 2022 - 10:14:30 AM
Last modification on : Tuesday, May 10, 2022 - 3:24:58 PM

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C. Goetz, B. Tsurutani, P. Henri, N. J. T. Edberg, M. Volwerk, et al.. (Over-)Reaction of the Cometary Plasma to Extreme Solar Wind Conditions. American Geophysical Union, 2017, San Francisco, United States. ⟨insu-03570125⟩

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