  We study the solar energetic particle (SEP) event associated with the 2012
July 23 extreme solar storm, for which STEREO and the spacecraft at L1 provide
multi-point remote sensing and in situ observations. The extreme solar storm,
with a superfast shock and extremely enhanced ejecta magnetic fields observed
near 1 AU at STEREO A, was caused by the combination of successive coronal mass
ejections (CMEs). Meanwhile, energetic particles were observed by STEREO and
near-Earth spacecraft such as ACE and SOHO, suggestive of a wide longitudinal
spread of the particles at 1 AU. Combining the SEP observations with in situ
plasma and magnetic field measurements we investigate the longitudinal
distribution of the SEP event in connection with the associated shock and CMEs.
Our results underscore the complex magnetic configuration of the inner
heliosphere formed by solar eruptions. The examinations of particle
intensities, proton anisotropy distributions, element abundance ratios,
magnetic connectivity and spectra also give important clues for the particle
acceleration, transport and distribution.
