Observations and Simulations of the Interaction of Magnetic Clouds with the Bow Shock and Implications for their Couplings to the Magnetosphere

Abstract:

Magnetic clouds are among the most geoeffective solar events capable to trigger strong magnetic storms in the terrestrial magnetosphere. However, the storm occurrence and strength are not yet fully explained. The magnetic clouds’ orientation, the presence of events/structures on their leading or trailing edges are presently discussed in the literature. In complement to these effects, we investigate here the interaction of magnetic clouds with the bow shock, the structure and propagation of the modified clouds downstream of it in the magnetosheath and the consequences for their interaction with the magnetosphere. This question is first tackled from observations. Correlated observations upstream (ACE) and downstream (CLUSTER) of the bow shock show that the interaction of magnetic clouds with the bow shock can strongly modify their downstream structure and lead to inexpected interactions with the magnetosphere. We also discuss this question from hybrid simulations of the interaction of magnetic clouds with the bow shock. We show that this interaction may produce in the magnetosheath very asymmetric distributions of magnetic field, density, temperature, velocity and that they depend on the shock configuration (quasi-perpendicular, quasi-parallel). We investigate the effects this asymmetric magnetosheath on key parameters for the interaction with the magnetopause, responsible for the development of geomagnetic activity in the magnetosphere.