Turbulence and the associated turbulent transport of scalar and vector fields is a classical
physics problem that has dazzled scientists for over a century, yet many fundamental …

We present a contemporary view of how solar active region magnetic fields are understood
to be generated, transported and dispersed. Empirical trends of active region properties that …

In the presence of strong density stratification, hydromagnetic turbulence attains qualitatively
new properties: the formation of magnetic flux concentrations. We review here the theoretical …

Context. Solar spots appear to decay linearly proportional to their size. The decay rate of
solar spots is directly related to magnetic diffusivity, which itself is a key quantity for the …

We investigate the dynamics of solar activity using a nonlinear one-dimensional dynamo
model and a phenomenological equation for the evolution of Wolf numbers. This system of …

Context. The formation of magnetic flux concentrations within the solar convection zone
leading to sunspot formation is unexplained. Aims. We study the self-organization of initially …

Aims. This work presents an extensive study of the previously discovered formation of
bipolar flux concentrations in a two-layer model. We interpret the formation process in terms …

We consider strongly stratified forced turbulence in a plane–parallel layer with helicity and
corresponding large-scale dynamo action in the lower part and non-helical turbulence in the …

In this chapter, we discuss a mean field solar dynamo model with algebraic and dynamic
nonlinearities, various mechanisms of sunspot formation, and prediction of solar activity. The …

Context. The formation of sunspots requires the concentration of magnetic flux near the
surface. The negative effective magnetic pressure instability (NEMPI) might be a possible …