Space Climate 7 Meeting Abstract
Challenges and Limitations of the Long-term Sunspot Number Record
Andrés Muñoz-Jaramillo (Southwest Research Institute, USA.)
Jose M. Vaquero (1), Victor Sanchez-Carrasco (1), Ilya Usoskin (2), Laure Lefevre (3) (1) Universidad de Extremadura, Spain. (2) University of Oulu, Finland. (3) Royal Observatory of Belgium, Belgium.
The solar cycle periodically reshapes the magnetic structure and radiative output of the Sun and determines its impact on the heliosphere roughly every 11 years. Besides this main periodicity, it shows century-long variations (including periods of abnormally low solar activity called grand minima). Recent reanalyses of sunspot observations have yielded a conflicted view on the evolution of solar activity during the past 400 years (a steady increase versus a constant level). This has ignited a concerted community wide effort to understand the depth of the Maunder Minimum and the subsequent secular evolution of solar activity. The principal challenge faced by such an endeavor is the sparsity (or non-existence) of concurrent observations during parts of the 18th and 19th centuries. This makes it impossible to make straight-forward calibration between observers, forcing the community to identify alternative methods of bridging this gaps.In this presentation we will overview our data coverage during the last 400 years, the location of the most important gaps, and the challenges and uncertainties that they bring. We will then follow with a discussion of one of the proposed methods for bridging this gap: the use of "Active day fractions", the challenges faced when using this technique, and the proposed solutions to ameliorate these challenges. We will finalize with an assessment of the applicability of this technique to historical periods, and a path forward towards integrating this technique with other direct calibration approaches to make better assessment of the long-term evolution of solar activity.
Mode of presentation: poster