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We present a study of 7 large solar proton events (SPEs) of current solarcycle 24 (from 2009 January up to date). They were recorded by GOES spacecraftwith highest proton fluxes over 200 pfu for energies $>$10 MeV. In situparticle measurements show that: (1) The profiles of the proton fluxes arehighly dependent of the locations of their solar sources, namely flares orcoronal mass ejections (CMEs); (2) The solar particle release (SPR) times fallin the decay phase of the flare emission, and are in accordance with the timeswhen the CMEs travel to an average height of 7.9 solar radii; (3) The timedifferences between the SPR and the flare peak are also dependent of thelocations of the solar active regions (ARs). The results tend to support theconcept of proton acceleration by the CME-driven shock, even though thereexists a possibility of particle acceleration at flare site with subsequentperpendicular diffusion of accelerated particles in the interplanetary magneticfield (IMF). We derive the integral time-of-maximum (TOM) spectra of solarprotons in two forms: a single power-law distribution and a power law brokenwith an exponential tail. It is found that the unique Ground Level Enhancement(GLE) event on 2012 May 17 displays a hardest spectrum and a largest brokenenergy that may explain why the this event could extend to relativistic energy.

Proton activity of the Sun in current solar cycle 24