Long term variation of solar activity
Sami K. Solanki

Solar activity varies on nearly all observed timescales. The short-term variability is driven by processes acting in the solar chromosphere and corona, while the longer term changes are driven by events acting in the photosphere and beneath the solar surface at the location of the main dynamo. A particular challenge is following solar magnetic activity on timescales longer than a few years, in particular when the period of time becomes longer than the lifetime of space missions or even ground-based instruments or of individual observers. When going further back in time, the available proxies of solar activity become increasingly simple, with the longest directly measured dataset being the sunspot number, reaching back to 1610. Recently, there has been considerable controversy surrounding even this seemingly simple dataset. To determine solar activity at earlier times indirect proxies must be used. In this talk selected proxies of solar activity will be critically evaluated and some of the results obtained therewith will be discussed.


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