Possible Detection of Large Solar Particle Event at Balloon Altitudes during the 2001-2002 TIGER Flight

The Trans-Iron Galactic Element Recorder (TIGER) was launched on December 21, 2001 and flew for about 32 days on a long-duration balloon mission from McMurdo Base in Antarctica. On December 26, 2001 at about 5:30 UT, a ground-level solar particle event (M7.6 flare) was observed by a number of neutron monitors. The SIS instrument aboard the ACE spacecraft measured the elemental composition and particle energy spectra up to ∼150MeV/nuc. While not designed to operate under such conditions, TIGER data for the same period show interesting variations in the count rate and composition of the measured particles that may be related to the detection of heavy Solar particles (Si to Fe) in the ∼GeV/nuc range. We discuss the TIGER observations in relation to other available data from this event.