Magnetic Helicity: diagnostic signatures and effects

Abstract:

In situ measurements of the solar wind provide us with a unique opportunity to determine the magnetic helicity and to look for a systematic hemispheric dependence. Although this has been done, the results still remain puzzling and point to a reversal of magnetic helicity some distance above the solar surface. No observational evidence for an actual reversal exists as yet. This leads us to the exploration of proxies of helicity, which could be used to verify the reality of a reversal and to determine its location. Of particular interest is the technique of decomposing images of linear polarization into its parity-even and parity-odd constituents, and to associate the latter with a helicity proxy. In my talk, I will illuminate the dynamo-theoretical background of helicity, such as what is known as catastrophic quenching, and will then discuss the status of magnetic helicity proxies using both observational and numerical results. Many of these techniques are rather general and can also be applied to intensity maps, including terrestrial cloud patterns of hurricanes, for example.