Onset of the event as observed in 1-min LET proton sectored rates, summed to correspond to LETB (blue, viewing particles traveling in the +T direction) and LETA (black, viewing particles traveling in the −T direction), for 2−4 MeV (upper panel). The ratio of these rates for the 2−4 MeV (black), 4−8 MeV (blue), and 8−16 MeV (cyan) protons indicates whether particles are predominantly flowing in the +T direction (values > 1) or the −T direction (values < 1). For comparison, the T component of the magnetic field is given in red symbols (right axis). The dashed vertical line indicates when the spacecraft rolled 180° resulting in LETA viewing the +T-flowing protons and LETB viewing −T-flowing protons.