Two dimensional hybrid simulations of small scale obstacles in the solar wind
Hopcroft, Matthew William
arxiv: Astrophysics::Earth and Planetary Astrophysics | Physics::Space Physics
The structure and dynamics of the solar wind interaction with two small\ud scale obstacles (of the order of a pickup ion gyroradius) is examined. These are a\ud comet, comparable to Grigg-Skjellerup, and a weakly ionospheric planet. We also\ud perform a pilot study of an intrinsically magnetized planet in such flow, in preparation\ud for a future three-dimensional simulation. Here, we use two-dimensional hybrid\ud simulations (particle ions, fluid electrons) and consider different solar wind Alfven\ud Mach number flow (MA) and interplanetary magnetic field orientation relative to\ud this plane. This allows control of the available wave types.\ud The cometary simulations display magnetosonic "turbulence" as MA is increased,\ud when the field is perpendicular to the simulation plane. If we allow parallel\ud propagating modes by setting the field parallel to the plane, we find the "turbulence"\ud significantly changes in scale and extent, suggesting resonant growth of Alfven ion\ud cyclotron waves in the presence of magnetosonic "turbulence" occurs. Free energy\ud is available from picked up cometary ions. The process depends on the cometary ion\ud density, which strongly varies, and we conclude this explains the broadband nature\ud of the disturbances.\ud In the perpendicular field orientation, the planetary source produces a novel\ud two tail structure which continuously strips the planetary ionosphere. We find these\ud tails have very distinct characteristics, resulting in the wake being filled relatively\ud quickly downstream, by complex structure. At higher MAl magnetosonic "turbulence"\ud again appears. Switching the field parallel to the plane causes massive field\ud line draping and pile-up, and causes instability. A long lasting wake appears, and\ud we conclude that a three-dimensional simulation is required.\ud The magnetized ionospheric planet pilot study proved difficult to scale accurately\ud in two dimensions. The planetary field failed to penetrate the solar wind,\ud however it appears the simulation would be stable and achieve equilibrium in three\ud dimensions.