Spatial Distribution of Plasma Sheet Entropy Reduction Caused by a Plasma Bubble: Rice Convection Model Simulations

We conduct simulations based on the Rice Convection Model to evaluate the spatial distributions of total flux tube entropy (S) in the near‐Earth plasma sheet resulting from an earthward moving plasma bubble, and their dependences on two parameters: (1) the bubble's initial magnetic local time location and (2) strength of large‐scale convection. The plasma and magnetic field changes caused by the simulated bubble as it moves earthward qualitatively agree with an observed event. The simulated large‐scale convection is weaker in the premidnight than postmidnight sector because auroral conductance becomes lower toward dusk. The S reduction region resulting from the bubble expands azimuthally at smaller radial distances. The dawnward expansion is due to electric drift, while the duskward expansion is a result of proton's magnetic drift. The S within the bubble is not conserved as the bubble moves because particles of different energies within the bubble drift apart. The radial and azimuthal extents of the S reduction vary with the bubble's initial magnetic local time location. The S reduction region caused by a premidnight bubble extends substantially closer to the Earth and azimuthally wider than does a postmidnight bubble. This difference is mainly due to the weaker convection in the premidnight sector. Comparing with those under strong convection, the bubble plasma is colder under weak convection so that the bubble transport is affected more by electric drift. The S reductions under weak convection are much more confined in their azimuthal width and do not extend as far inward. Key Points RCM simulation of earthward transport of a plasma bubble qualitatively explains the two‐point THEMIS observation of a BBF event Simulated entropy reduction caused by a plasma bubble varies significantly with bubble's initial MLT and background convection M‐I coupling plays a key role in the motion of the plasma bubble and the entropy reduction