Magnetic dynamos and Solar cycle

It is now well recognised that the magnetic fields on the Sun are the basic cause of this variability. Solar dynamo models that can predict the solar cycle are now possible (Choudhuri et al. 2007). Understanding how the magnetic fields are generated and maintained on the Sun, i.e. understanding the solar dynamo, hence, is basic to understanding the origin and nature of solar cycle and variability, and to predict in advance its behaviour both on short and long time scales.

Micro- and macro physics of magnetic dynamos

Ever since Parker (1955) formulated the turbulent dynamo theory, varieties of very different dynamo models for the Sun have appeared in the literature. Global dynamo models, based on Parker's original ideas on the contributions of cyclonic convection and differential rotation, depend a lot also on the micro-physics associated with turbulent interaction and diffusion of magnetic fields throughout the solar convection zone. These processes are the most vigorous in the observable photospheric layers. Studying energy and momentum coupling between radiation, convection and magnetic fields in these layers is crucial to understand near-surface contribution to the overall working and sustenance of the solar dynamo.

Figure 1 Solar cycle and latitudinal distribution of sunspots known as "butterfly diagram". Observations on the left and a dynamo model based simulation from Chatterjee et al. 2004 on the right.

A high spatial, spectral and temporal resolution observation over a sustained period of time is a key requirement for such studies. NLST will fulfill such requirements to facilitate answering the following questions pertaining to the above aspects of solar dynamo: (1) how do the convective flows and associated turbulence stretch, twist and fold the local small-scale magnetic fields, and, how do such processes change the magnetic flux budget, locally and globally?; (2) how do strong fields in the large scale, e.g. sunspots, filaments, etc., interact with the small-scale fields?; and (3) how do large scale convective (super-granular and other possible larger scale) and meridional flows advect and diffuse the magnetic field?; and how do they change with time?.

Answers to these questions will provide key observational inputs to constrain the global interior dynamo models and thus in improving the predictive capabilities of such models