The Cross-field Current Instability for Substorm Expansion Onset

A challenging problem in the topic of the nonlinear dynamics of the magnetosphere is the physical process responsible for the onset of magnetospheric substorms. The early collaboration with Dr. K. Papadopoulos has led to the proposal of a kinetic plasma instability, called the cross-field current instability, as the onset process. This has developed into a full-blown research effort, supplementing the initial theoretical analysis with in-depth data analysis and particle simulations. Several theoretical predictions based on this instability are successfully verified in observations. Data from the present NASA THEMIS mission provide some evidence for its validity. Further investigations for this substorm onset process are also discussed.