Numerical simulation of viscous-like flow in and around the plasma tail of a comet
Instituto de Astronomía, Universidad Nacional Autónoma de Mexico, Apdo Postal 877, Ensenada 22800, B.C., Mexico e-mail: [maurey;aceves;vazquez]@astrosen.unam.mx
2 Instituto de Geofísica, Universidad Nacional Autónoma de Mexico, Ciudad Universitaria, C.P. 04510, Mexico D.F. e-mail: firstname.lastname@example.org
Accepted: 2 March 2010
Aims. We model the interaction of the solar wind with the plasma tail of a comet using numerical simulations, taking into account the effects of viscous-like forces.
Methods. We developed a 2D hydrodynamical, two species, finite difference code to solve the time-dependent continuity, momentum, and energy conservation equations, and model the interaction of the solar wind with a cometary plasma tail. We compute the evolution of the plasma of cometary origin in the tail as well as the properties of the shocked solar wind plasma around it, as it transfers momentum on its passage by the tail. Velocity, density and temperature profiles across the tail are obtained. Several models with different flow parameters are considered to study the relative importance of viscous-like effects and the coupling between species on the flow dynamics.
Results. Assuming a Mach number equal to 2 for the incident solar wind as it flows past the comet's nucleus, the flow exhibits three transitions with location and properties depending on the Reynolds number of each species and on the ratio of the timescale for inter-species coupling to the crossing time of the free-flowing solar wind. By comparing our results with the measurements taken in situ by the Giotto spacecraft during its flyby of comet Halley, we constrain the flow parameters for both plasmas.
Conclusions. In the context of our approximations, we find that our model is qualitatively consistent with the in situ measurements as long as the Reynolds number of both solar wind protons and cometary H2O+ ions is low, less than 100, suggesting that viscous-like momentum transport processes may play an important role in the interaction of the solar wind and the plasma environment of comets.
Key words: comets: general / solar wind / hydrodynamics / comets: individual: Halley / methods: numerical / comets: individual: Giacobinni-Zinner
© ESO, 2010