Deciphering the solar small-scale magnetic field

• Applicant: Dr. Catherine Fischer
• Subject Area: Astrophysics and Astronomy
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 273324322

The solar surface is completely covered by magnetic fields, which are known to have structures that are beyond the spatial resolution limit of current solar telescopes. Outside of active regions, in the quiet sun, these fields form dynamic short-lived features, the so-called small-scale magnetic fields, which are the drivers of phenomena such as supersonic jets and magneto-acoustic shocks.  These small-scale fields are responsible for the variability of the solar irradiance measured on Earth, the solar constant, and are the key to the holy grail of solar physics: the unexplained heating of the outer solar atmosphere.Whatever the true nature of these small-scale magnetic fields is, we presently cannot spatially resolve them, and the polarisation signals, with which they are identified, are at the noise limit. Nevertheless, different aspects of the small-scale magnetic field have been unraveled with novel tools and compared with sophisticated numerical simulations that reproduce high-resolution observations. This is where we believe our research will contribute.We will have full access to the new German GREGOR telescope, the biggest European solar telescope providing data with an unprecedented spatial resolution of around 70 km.We have identified 4 key science objectives which are at the front edge of current research of the solar small-scale magnetic field distribution, origin, evolution and destruction:(1) Simultaneous spectropolarimetric observations in the infrared and visible parts of the spectrum will be compared to reconcile their contradictory behaviour and to test the validity of numerical models. (2) By using complementary diagnostic methods, we will explore very different aspects of the magnetic field population to gain a complete picture of the magnetic field distribution at the scale of granulation, the smallest convective cells. (3) The intensification of the magnetic field and (4) the removal of magnetic flux will be investigated by observing the response of the chromosphere to these magnetic phenomena in the photosphere below.The interpretation of the observational data will be assisted by simulations which model the radiatively driven magneto-hydrodynamic processes in the solar atmosphere. We will use established codes such as CO5BOLD, a code capable of reproducing the solar atmosphere from the convection zone to the chromosphere, and MURaM, a code that has demonstrated the theoretical possibility of a local dynamo creating these small-scale, mixed polarity magnetic fields in the photosphere.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Nazaret Bello Gonzalez