Magnetic activity and variations in solar luminosity

Abstract

Attempts to detect changes in the solar luminosity suggest that the solar constant has been misnamed1–4. Although the Nimbus satellite data4 show no significant fractional variations above 5 × 10−3 during the period 1975–78, results from recent balloon5 and rocket6 flights show changes of 4 × 10−3. Intense magnetic fields in sunspots hamper convection locally7 but active regions are believed not to be directly responsible for long term variations in luminosity of the Sun8 or of RS CVn and BY Dra stars9. The cause of luminosity variations over spot cycles should be sought in more deep-seated global features. Here we indicate how strong magnetic fields at the base of the convective zone can alter the local convection. The resulting changes in thermal energy are large enough to produce variations of order 0.1% in the solar luminosity over the 11-yr sunspot cycle.