  We use multiwavelength data from space and ground based instruments to study
the solar flares and coronal mass ejections (CMEs) on January 23, 2012 that
were responsible for one of the largest solar energetic particle (SEP) events
of solar cycle 24. The eruptions consisting of two fast CMEs (1400 km/s and
2000 km/s) and M-class flares that occurred in active region 11402 located at
N28 W36. The two CMEs occurred in quick successions, so they interacted very
close to the Sun. The second CME caught up with the first one at a distance of
11-12 Rsun. The CME interaction may be responsible for the elevated SEP flux
and significant changes in the intensity profile of the SEP event. The compound
CME resulted in a double-dip moderate geomagnetic storm (Dst = -73 nT). The two
dips are due to the southward component of the interplanetary magnetic field in
the shock sheath and the ICME intervals. One possible reason for the lack of a
stronger geomagnetic storm may be that the ICME delivered a glancing blow to
Earth.
