  There have been numerous reports of quasiperiodicities in solar activity in
the intermediate period range. However, no accepted explanation for the
episodic occurrence of quasiperiodicities has emerged. This paper examines the
possibility that the periodicities are associated with a Mercury Sun
interaction of base period 88 days. To test this idea we band pass filter the
140 year long daily sunspot area data to obtain the 88 day period and 176 day
sub harmonic period components of the data and compare the time variation of
the components with the time variation of the orbital radius of Mercury, or
more specifically with the time variation of the tidal effect of Mercury. We
were able to show that, when successive episodes of the occurrence of the 88
day period component were discrete and not overlapping in time, the time
variation of this component of sunspot area was either exactly in-phase or
exactly in anti-phase with the time variation of tidal effect. A similar result
was obtained for the 176 day period component. When several discrete episodes
of the components occurred during a solar cycle the spectrum of the sunspot
area data exhibited strong sidebands with periods dependent on the duration of
the episodes. A simple model based on episode modulation and solar cycle
modulation of 88 day and sub harmonic period sinusoids reproduced most of the
spectral peaks observed in the intermediate range of sunspot area periodicity.
This is compelling evidence of a link between the motion of Mercury and the
periodic emergence of sunspots. It is proposed that the link involves magnetic
surface waves with mode periods close to the sub harmonic periods associated
with Mercury and the triggering of sunspot emergence by the waves.
