"The Sun has an 11-year cycle that involves, among other things, the occurrence and disappearance of sunspots. The phenomena that occur in the Sun - including the cycle - change with time, so the solutions need to be integrated over time. Short-term variation is not interesting for the purposes of studying the space climate, for example", stated Maarit Käpylä, head of the DYNAMO team, who conducts astroinformatics or computational astrophysics and data-analysis at the Department of Computer Science.
As a result of the computation carried out, currently the world's longest numerical simulation was created that produces a solar-like dynamo solution complete with its long-term variation.
"The Sun as such is impossible to replicate on present-day computers - or those of the near future - due to its strong turbulence. And indeed we are not claiming that this modelling would really be the Sun. Instead, it is a 3D construction of various solar phenomena by means of which the star that runs our space climate can be better understood", Maarit Käpylä explained.
What exactly is a grand minimum?
The largest surprise of the study relates to the Sun's silent periods known as grand minima, of which the Maunder Minimum is perhaps the best known. The solar magnetic field is thought to wither during it and be so weak as not being capable of generating sunspots or other activity.
"In fact, the magnetic field is at its maximum during the Maunder Minimum. Thus far, we have only been able to examine what is visible on the solar surface, but simulations enable us to see below the surface. During the Maunder Minimum, the magnetic field sinks to the bottom of the convection zone and is very strong there", stated Maarit Käpylä
The outer layer of the Sun, the convection zone, is like a boiling kettle with its moving and heat-transferring bubbles, and this not only generates a magnetic field, but also makes the entire area turbulent.
Maarit Käpylä will start as an independent group leader at one of Europe's leading solar research units, Max Planck Institute for Solar System Research, in the summer of 2016. The operations of the Aalto DYNAMO team at the ReSoLVE Centre of Excellence will continue under Maarit Käpylä's direction, focusing on even larger simulations using graphical processing units.
The article titled " Multiple dynamo modes as a mechanism for long-term solar activity variations " is authored by M.J. Käpylä, P.J. Käpylä, N. Olspert, A. Brandenburg, J. Warnecke, B.B. Karak and J. Pelt. The paper was published online on 13 April 2016 inAstronomy & Astrophysics, 589 (2016) A56 - DOI: http://dx.doi.org/10.1051/0004-6361/201527002 .