  In this paper we examine the possibility that intermediate range
periodicities in sunspot area can be linked to Mercury or to Mercury-planet
conjunction periods. We show that peaks at the 45 day Mercury-Jupiter
conjunction period, the 116 day first harmonic period of the Mercury-Earth
conjunction and the 289 day period of the sub harmonic
Mercury-Venus/Mercury-Earth conjunctions are prominent in spectra of sunspot
area. We observe two prominent peaks close to the 88 day Mercury periodicity
and two prominent peaks close to the 176 day first sub harmonic of Mercury
periodicity. To confirm that the peaks arise as sidebands we band pass filter
the sunspot area record to isolate the 88 and 176 day components of sunspot
area. The components occur in episodes of duration from 1.5 to 4 years, with
successive episodes usually overlapping in time but, for significant intervals
in the record, the episodes were discrete, i.e. not overlapping. The time
variation of the components was compared with the time variation of the tidal
effect of Mercury. We were able to show that whenever episodes were discrete
the component of sunspot area during the episode was either in-phase or in
anti-phase with the Mercury tidal effect. We interpret this as indicating a
connection between planetary motion and sunspot emergence. When several
discrete episodes of the components occurred during a solar cycle the spectrum
of sunspot area during that solar cycle exhibited periodicities at sidebands to
the 88 day or 176 day periods, the periodicity of the sidebands depending on
the duration of the episodes. A simple model based on amplitude modulation of
88 day and 176 day period sinusoids was able to consistently reproduce the
spectral peaks, or Rieger quasi-periodicities, observed in the spectra of
sunspot area.
