What data type is the “solar activity” data shown in the figure? Possibilities are sunspot number, solar cycle length, estimated solar irradiance, or something else.
Arctic surface air temperature compared with total solar irradiance as measured by sun spot cycle amplitude, sunspot cycle length, solar equatorial rotation rate, fraction of penumbral spots, and decay rate of the 11-year sunspot cycle. Solar irradiance correlates well with Arctic temperature, while hydrocarbon use does not correlate.
Solar Activity generally refers to all three. Increased sunspot activity defines active cycles which tend to have shorter lengths and tend to emit more solar radiance. Solar Activity in laymen terms is Solar Weather. Once that weather escapes the sun, NASA refers to it as Space Weather and surprisingly they watch it like a hawk. After gravitational field strength, it is probably the most important metric in our solar system.