Our knowledge of the long-term evolution of solar activity and of its primary modulation, the
11-year cycle, largely depends on a single direct observational record: the visual sunspot …

Solar activity has a cyclic nature with the≈ 11-year Schwabe cycle dominating its variability
on the interannual timescale. However, solar cycles are significantly modulated in length …

Based on various diagnostics and corrections established in the framework of several
Sunspot Number Workshops and described by Clette et al.(Space Sci. Rev. 186, 35, 2014) …

We report progress on the ongoing recalibration of the Wolf sunspot number (SN) and group-
sunspot number (GN) following the release of version 2.0 of SN in 2015. This report …

Presented here is a review of present knowledge of the long-term behavior of solar activity
on a multi-millennial timescale, as reconstructed using the indirect proxy method. The …

The Sun is the main energy source to Earth, and understanding its variability is of direct
relevance to climate studies. Measurements of total solar irradiance (TSI) exist since 1978 …

We describe a revised collection of the number of sunspot groups from 1610 to the present.
This new collection is based on the work of Hoyt and Schatten (Solar Phys. 179, 189, 1998) …

The Sun is nowadays observed using di? erent techniques that provide an almost
instantaneous 3-D map of its structure. Of particular interest is the studyofthevariabilityinthesolaroutputproduc …

We describe the defining observations of the solar cycle that provide constraints for the
dynamo processes operating within the Sun. Specifically, we report on the following topics …

The primary task of the Debrecen Heliophysical Observatory (DHO) has been the most
detailed, reliable, and precise documentation of the solar photospheric activity since 1958 …