THEMIS will determine which competing model is correct
THEMIS will elucidate which magnetotail process is responsible for substorm onset:
At 60,000 km, a sudden disruption of electrical current can occur, known as "Current Disruption."
YOUR MAGNETOMETER MAY BE ABLE TO PICK UP THE CURRENT DISRUPTION SIGNATURE – Next Year’s science
At 120,000 km, a sudden merging of oppositely pointed magnetic fields can occur, known as "Magnetic Reconnection."