The amplitudes of 11-year solar cycles vary in a wide range, sometimes displaying sudden marked changes from one cycle to the next. The decadal time scales involved are comparable to the life cycle of space missions -and of human beings. The impact of solar activity on space climate and terrestrial climate calls for a prediciton capability, a precondition for which is a good understanding of the mechanism driving intercycle variations in the solar dynamo.
The past decade has seen significant advance in this direction. A promising scenario has emerged in which intercycle variations are driven by the vagaries of magnetic flux emergence from the solar interior into the atmosphere in the form of active regions (ARs). A variety of nonaxisymmetric dynamo models incorporating individual Ars have been developed, along with surface flux transport models used for prediction relying on the polar magnetic field as a proxy for the next cycle amplitude. The results indicate that a combination of nonlinear feedback effects and stochastic noise may govern the run-of-the-mill intercycle variations, while a low number of large “rogue” ARs with unusual properties bear the brunt of the responsibility for large, unexpected intercycle changes.
The talk will review these developments, focusing on the issue of how the properties of individual ARs determine their “dynamo effectivity”, i.e. how they will impact on the polar magnetic field built up during a cycle that will serve as the seed for the next solar cycle. The importance of maintaining and, where possible, reconstructing long term data sets on solar activity will be stressed and some aspects of the Sun’s unexpected historical changes will be discussed.
The seminar will be recorded and published later on the SCOSTEP website.
Photo by Justin Dickey on Unsplash
