The Structure of Coronal Holes, and Properties of the Young Solar Wind

• Applicant: Dr. Stefan Hofmeister
• Subject Area: Astrophysics and Astronomy
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448336908

Wider research contextCoronal holes are the solar source regions of high-speed solar wind streams (HSS), which transcend the interplanetary space. Whenever these hit the Earth, they can cause geomagnetic storms, which lead to polar lights, but also pose a threat to satellites. Therefore, their forecast is of high interest. At the moment, several issues prevent us to reliable identify the boundaries of coronal holes on the Sun from extreme-ultraviolet images, respectively, from magnetic field extrapolations. Therefore, we have to look for new, more sophisticated methods, and consequently, we have to deepen our understanding in the physics of coronal holes and its fine-structure. For modeling the main acceleration phase of HSSs, detailed in-situ measurements at the end of the acceleration phase have been missing, but become available by the unprecedented Parker Solar Probe.Research questions/ObjectivesThis leads us to the following research questions:1. How are coronal holes different from the quiet Sun in various atmospheric layers from the photosphere to the corona, and how can this information be used to provide a more stringent and physics-based definition of coronal hole boundaries?2. How can the terminal properties of the solar plasma leaving the Sun in the individual magnetic funnels, which are the small-scale source regions of the solar wind within coronal holes, be estimated by knowing the magnetic properties and fine-structure of their foot-points?3. How are the mean plasma properties of HSS at the end of the acceleration region related to the average coronal hole parameters?MethodsWe will reconstruct a full coronal hole including its fine-structure from the photosphere to the low corona, using unique ground-based infrared spectropolarimetric measurements from the photosphere to the upper chromosphere, and space-born spectroscopic measurements for the transition region and lower corona. These measurements are complemented by the unprecedented in-situ measurements taken by Parker Solar Probe at the end of the main acceleration region of HSSs at 10-20 solar radii. InnovationWe will relate for the very first time spectroscopic observations of a coronal hole to the properties of a high-speed stream at the end of the main acceleration phase as measured by the unprecedented Parker Solar Probe.

• DFG Programme: Research Grants