The Length of the Sunspot Cycle
Determined by Different Methods
Thomas Ulich(1) and Kalevi Mursula(2)
(1) Geophysical Observatory, FIN-99600 Sodankylä, Finland
(2) Dept. of Physical Sciences, University of Oulu, FIN-90570 Oulu,
The sunspot numbers have traditionally been used as a measure for the
solar activity. The sunspot number is, e.g., well correlated to the
10.7cm radio flux emission rate.
Recently, solar activity has been related to the long-term evolution of
global temperature (Friis-Christensen and Lassen, 1991). The key
question is whether this connection dominates over the anthropogenic
effects on climate.
In this work we re-analyse the solar cycle lengths using traditional
methods and a novel technique based on determining the time (``median
time'') of half of the integrated sunspot number per cycle. While
traditional methods are sensitive to the different estimations of
sunspot minima or maxima, the median method is very stable to these
Finally we correlate the revised solar cycle data with the Oulu
temperature record, which is one of the longest available in Finland.
- Friis-Christensen, E., and K. Lassen, Science 254, 698-700, 1991.