Actually, it's all electromagnetic-related...

Solar minimum is the period of least solar activity in the 11-year solar cycle of the Sun. During this time, sunspot and solar flare activity diminishes, and often does not occur for days at a time. The date of the minimum is described by a smoothed average over 12 months of sunspot activity, so identifying the date of the solar minimum usually can only happen 6 months after the minimum takes place. Solar minimum is contrasted with the solar maximum, when hundreds of sunspots may occur.

~ https://en.wikipedia.org/wiki/Solar_minimum

Sunspots are temporary phenomena on the Sun's photosphere that appear as spots darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic field flux that inhibit convection. Sunspots usually appear in pairs of opposite magnetic polarity. Their number varies according to the approximately 11-year solar cycle.

~ https://en.wikipedia.org/wiki/Sunspot

A solar flare is a sudden flash of increased brightness on the Sun, usually observed near its surface and in close proximity to a sunspot group. [...]

[...] Although originally observed in the visible electromagnetic spectrum, especially in the Hα emission line of hydrogen, they can now be detected from radio waves to gamma-rays.

Flares are closely associated with the ejection of plasmas and particles through the Sun's corona into outer space; flares also copiously emit radio waves. [...] High-energy particles, which may be relativistic, can arrive almost simultaneously with the electromagnetic radiations.

~ https://en.wikipedia.org/wiki/Solar_flare