New results on energetic particles at the Earth\'s bow shock

D. Burgess

Key problems in particle acceleration, such as injection from the thermal populations, depend on understanding the multiscale properties of collisionless shocks. The Cluster mission is collecting data which can, in principle, answer questions about the multiscale nature and time variability. The data has not led to easy answers, but highlighted the difficulty of extracting quantitative results. This talk will summarize recent advances, including results on the determination of the smallest scales at quasiperpendicular shocks. The results obtained have implications for the thermalization of electrons, and hence any injection process to other acceleration mechanisms. Work on transitory events such as Hot Flow Anomalies will be discussed, since they represent a new process for particle injection and acceleration which is not included in steady state models. Since they are caused by the interaction between magnetic discontinuities and the shock, any injection mechanism might be applicable to structured coronal plasmas. Finally, new results on computer modelling of particle acceleration at the Earth\'s bow shock will be presented, in particular the role of sub-structure and time variability will be presented. These results indicate that explaining electron acceleration simply by adiabatic conserving reflection is probably simplistic for conditions at the Earth\'s bow shock.