NBIA Colloquium – Niels Bohr Institute - University of Copenhagen

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NBIA Colloquium

Speaker: Axel Brandenburg (Nordita)

Title:  Sunspot Activity at a Record Low

Abstract:  It is now exactly 400 years ago, in 1609, when Galileo started systematic telescopic observations of sunspots. At the time it was not proper to even think that the Sun could have impurities such as spots, and Galileo thought they were clouds orbiting the Sun. Although sunspot observations were recorded at many observatories since then, there was no coherent record of their number, and only in 1864 did Heinrich Schwabe propose, based on 15 years of own observations, that the sunspot number varies in an approximately 10 years cycle. By now it is well established that the Sun undergoes an 11 year cycle. In addition, however, deep and extended outages of solar activity have occurred repeatedly throughout history. The most famous one is the Maunder Minimum.

During usual sunspot minima, the number of spotless days is around 485, but now, after the last maximum of 2001, the number of spotless days is already 754, and is still growing with every new spotless day. Is there a chance that we are running into a new grand minimum? In my talk I will put this question into context and discuss additional features including measures of the poloidal field, variability of the differential rotation, as well as the variation of the Sun's irradiance and the solar wind pressure. I will comment on various approaches to understanding this intermittent variability and how the extraordinary behavior in recent years can help us in pinning down questions regarding the location of the solar dynamo.