  Both the Cosmic Ray Flux (CRF) and Solar Energetic Particles (SEPs) have left
an imprint on SOHO technical systems. While the solar array efficiency degraded
irreversibly down to ~77% of its original level over roughly 1 1/2 solar
cycles, Single Event Upsets (SEUs) in the solid state recorder (SSR) have been
reversed by the memory protection mechanism. We compare the daily CRF observed
by the Oulu station with the daily SOHO SEU rate and with the Degradation curve
of the solar arrays. The Oulu CRF and the SOHO SSR SEU rate are both modulated
by the solar cycle and are highly correlated, except for sharp spikes in the
SEU rate, caused by isolated SEP events, which also show up as discontinuities
in the otherwise slowly decreasing solar ray efficiency. This allows to
discriminate between effects with solar and non-solar origin and to compare the
relative strength of both. We find that during solar cycle 23 (1996 Apr 1 --
2008 Aug 31) only 6% of the total number of SSR SEUs were caused by SEPs; the
remaining 94% were due to galactic cosmic rays. During the maximum period of
cycle 23 (2000 Jan 1 -- 2003 Dec 31), the SEP contribution increased to 22%,
and during 2001, the year with the highest SEP rate, to 30%. About 40% of the
total solar array degradation during the 17 years from Jan 1996 through Feb
2013 can be attributed to proton events, i.e. the effect of a series of
short-lived, violent SEP events is comparable to the cycle-integrated damage by
cosmic rays.
