Discovery of the near 158 day periodicity in group sunspot numbers during the eighteenth century

A new record of solar activity, made by compiling the daily number of sunsp ot groups visible on the Sun's surface between 1610 and 1995, has recently been made available by Hoyt & Schatten. Wavelet analysis of this record sho ws that an episode of the periodicity near 158 days occurred during the eig hteenth century, around the maximum of solar cycle 2, and that episodes of the periodicity, much weaker than that in solar cycle 2, have appeared arou nd the maxims of solar cycles 16-21 (covering the interval 1923-1986). The presence of the periodicity in the group sunspot number confirms that it is caused by a periodic emergence of magnetic flux. On the other hand, period ogram analysis allows one to compare the behavior of the periodicity in bot h sunspot groups and sunspot areas, and the results suggest that, at least during the twentieth century, the periodic emergence of magnetic flux has a dopted two different forms. In solar cycles 16 and 17, new sunspot groups w ere periodically formed, simultaneously increasing the number of sunspot gr oups and the total sunspot area on the Sun's surface, while during solar cy cles 18, 19, 20, and 21 the periodicity has occurred within already formed sunspot groups, increasing sunspot areas only. We point out that this secon d type of emergence, which enhances the magnetic complexity of sunspot grou ps, is responsible for the appearance of the periodicity in high-energy sol ar flares as detected by the Solar Maximum Mission during solar cycle 21.