RCM simulation of a single bubble and twin bubbles: dependence on tail initiation location and effect on the inner magnetosphere

To understand how large-scale convection affects inward transport of plasma sheet bubbles (that is, low total entropy) coming from a pre-midnight or post-midnight tail location (X -20 R_E), we conduct simulations based on the Rice Convection Model with 3 scenarios of mesoscale bubbles (0.5 MLT wide and 10 min): (1) A single pre-midnight bubble initiated at 23 MLT. (2) A single post-midnight bubble initiated at 01 MLT. (3) Twin bubbles consisting of (1) and (2). The simulated large-scale convection, consistent with statistical observational results, has a substantial dawnward component that is stronger in the post-midnight than pre-midnight sector because of higher auroral conductance. In general, the bubble, as it is moving inward, expands azimuthally at smaller radial distances. The dawnward expansion is due to electric drift and is affected by the large-scale convection, while the duskward expansion is a result of proton's magnetic drift. Because of the dawn-dusk asymmetry of the large-scale convection, the pre-midnight bubble is able to extend substantially deeper into the inner magnetosphere (r < 10 R_E) and azimuthally wider than does the post-midnight bubble. The pre-midnight bubble intensifies the Sub-Auroral Polarization Stream (SAPS) and the Harang reversal, while the post-midnight bubble only enhances the Harang reversal. In the twin bubble scenario, both bubbles are weakened by their interaction. High-energy protons in the post-midnight sector are pushed inward by the post-midnight bubble, and their subsequent duskward drift to the pre-midnight bubble confines the dawnward expansion of the pre-midnight bubble and weakens its effect on SAPS. On the other hand, the stronger pre-midnight bubble pushes the weaker post-midnight bubble to move further toward dawn, thus reducing its inward motion and subsequent effects on the inner magnetosphere.