Cometosheath structures and tail rays: Outcome of bi-ion fluid simulations

Momentum coupling between the solar wind (SW) and the cometary plasma is a crucial element in the plasma dynamics around comets. A bi-ion fluid model is applied instead of one-fluid MHD normally used in 3D global simulations. This new approach accounts for the observational fact of spacecraft measurements at comets that in a region inside the bow shock beginning from about cometary distances, where the mass density of cometary ions and protons becomes comparable, complex interaction processes take place. They are manifested in pronounced plasma structures and additional plasma boundaries. An essential signature of the bi-ion fluid description consists in the occurrence of new (bi-ion) wave modes which may grow to large amplitudes due to a drift of protons relative to the heavies. In this way, a structuring of all plasma parameters results. Additionally, steepening of the underlying bi-ion waves and their phase bunching in multiple "Mach cones'' are suggested to be responsible for cometary tail ray formation. Corresponding results of 2D bi-ion fluid simulations are presented.