Can multiple shocks trigger ground level events?

A total of 16 Ground Level Events (GLE) occurred in solar cycle 23. These events, in which particle energies reach above 1 GeV/nuc, are the most energetic examples of Gradual Solar Energetic Particle (SEP) events. Over the past solar cycle, a great deal has been learned about these events observationally. However, the process by which particles are accelerated to these high energies is still presently unknown. We know the fact that they are often associated with both flares and Coronal Mass Ejection (CME) driven shocks, yet in many other SEP events where both strong flares and fast CMEs are found, the intensities and the maximum energies of energetic particles are often more than 10 to 100 times smaller. So questions such as what triggers a GLE and what differentiates a GLE from other gradual SEP events remain open. We discuss here a scenario in which two CMEs occur closely in time but offset in propagation direction. We show that the resulting magnetic field configuration can lead to magnetic reconnection. This reconnection process will provide both an excess of seed population and enhanced turbulence level at the shock front of the second CME-driven shock. Enhanced particle acceleration can therefore be achieved. The implications of our proposed scenario will be discussed.