Older stars often show cyclic behavior with their activity, as the sun does with its 10-11 year cycle. Younger stars usually show more chaotic behavior. A few per cent of cool dwarfs show little or no magnetic activity. The several of the following papers investigate the variations of physical parameters of individual stars over a number of years. Depending on the star, these can include temperature, granulation, yellow and blue magnitude, color index, and HK emission.
Stellar variations are often much larger than solar variations.
Some of the measured parameters lag in time behind others. This is remarkable. The size of the lag appears to depend on the effective temperature of the star. Through a Magnetic Minimum . David F. Gray 1994 Astrophys.