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The point of highest sunspot activity during a cycle is known as solar maximum, and the point of lowest activity as solar minimum. This period is also observed in most other solar activity and is linked to a variation in the solar magnetic field that changes polarity with this period.
Reconstruction of solar activity over 11,400 years. Sunspot numbers over the past 11,400 years have been reconstructed using carbon-14 and beryllium-10 isotope ratios. [10] The level of solar activity beginning in the 1940s is exceptional – the last period of similar magnitude occurred around 9,000 years ago (during the warm Boreal period).
Solar cycles are nearly periodic 11-year changes in the Sun's activity that are based on the number of sunspots present on the Sun's surface. The first solar cycle conventionally is said to have started in 1755. The source data are the revised International Sunspot Numbers (ISN v2.0), as available at SILSO. [1]
A prediction for Sunspot Cycle 24 (2008-2020) gives a smoothed sunspot number maximum of about 66 in the Summer of 2013. Current observations make this the smallest sunspot cycle since records began in the 1750s. [1] Solar maximum is the regular period of greatest solar activity during the Sun's 11-year solar cycle.
Sunspot and infrared spectral line measurements made in the latter part of the first decade of the 2000s suggested that sunspot activity may again be disappearing, possibly leading to a new minimum. [48] From 2007 to 2009, sunspot levels were far below average. In 2008, the Sun was spot-free 73 percent of the time, extreme even for a solar minimum.
Both this year’s storms are part of the same broad pattern of increasing sunspot activity. CMEs often form around sunspots, although scientists aren’t entirely sure why.
One historical long-term correlation between solar activity and climate change is the 1645–1715 Maunder minimum, a period of little or no sunspot activity which partially overlapped the "Little Ice Age" during which cold weather prevailed in Europe. The Little Ice Age encompassed roughly the 16th to the 19th centuries.
Solar cycle 21 was the 21st solar cycle since 1755, when extensive recording of solar sunspot activity began. [1] [2] The solar cycle lasted 10.5 years, beginning in March 1976 and ending in September 1986. The maximum smoothed sunspot number observed during the solar cycle was 232.9, in December 1979, and the starting minimum was 17.8. [3]