An upper limit of sunspot activity during the Maunder minimum

Details An upper limit of sunspot activity during the Maunder minimum An upper limit of sunspot activity during the Maunder minimum

Aug 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd...8e..15u&link_type=abstract

Solar and Stellar Activity Cycles, 26th meeting of the IAU, Joint Discussion 8, 17-18 August 2006, Prague, Czech Republic, JD08,

Astronomy and Astrophysics

Astronomy

Scientific paper

The Maunder minimum (1645-1715) is of great interest for solar activity studies. During that period, sunspot activity was at the very low level, indicating a specific state of the solar dynamo corresponding to a grand minimum. However, the exact level of sunspot activity during the Maunder minimum is still debated. The Maunder minimum period was amazingly well covered by sunspot data, but some of these data are based not on direct daily drawings/ counts of sunspots but on general statements on the absence of spots during long periods. Although such statements were done by highly qualified astronomers, this fact has led to speculations that the actual sunspot activity level in the earlier part of the Maunder minimum could have been higher than suggested in the group sunspot number series. Here we have estimated conservative upper and lower limits of sunspot activity as obtained from direct sunspot observation records. We use the concept of active day fraction during the Maunder minimum, applied to the raw information on individual daily observations. Establishing the relation between the sunspot activity and active day fraction after 1850, we have evaluated the upper limit of annual group sunspot number during the deep Maunder minimum (1645-1700) which does not exceed 4. The solar cycle in 1700-1710 has been shown to be tiny, below 8 in sunspot numbers. The earlier finding of a dominant 22-year periodicity during the Maunder minimum is confirmed as well as the abrupt start of the minimum.

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