A New Reconstruction of Solar Activity, 1610–1993

Abstract

In the one hundred years since Wolf died, little effort has gone into research to see if improved reconstructions of solar activity can be made. We have gathered more than 348,000 observations of daily sunspot group counts from more than 350 observers active from 1610 to 1993. Based upon group counts alone, it is possible to make an objective and homogeneous reconstruction of solar activity. From our study, it appears that the Sun has steadily increased in activity since 1700 with the exception of a brief decrease in the Dalton Minimum (1795–1823). The significant results here are the greater depth of the Dalton Minimum, the generally lower activity throughout the 1700’s, and the gradual rise in activity from the Maunder Minimum to the present day. This solar activity reconstruction is quite similar to those Wolf published before 1868 rather than the revised Wolf reconstructions after 1873 which used geomagnetic fluctuations.