Comparison of GOES HEP fluxes for two cases. (a) 2003 October 28 X17 flare occurrence that peaked at UT 11:10. HEP fluxes are strongly enhanced more than 40 hr prior to the flare. Protons with energy higher than 1, 5, and 10 MeV are close to the post-flare level and even protons with energy higher than 50–100 MeV are significantly enhanced. (b) Series of X-class and M-class flares during a limited time interval. The level of high energy particles remained normal throughout the interval.