Magnetic Configuration of Coronal Holes

Coronal holes are large-scale structures in the Suns atmosphere and are believed to be the source regions of fast flowing solar wind streams. Due to their lower density and temperature in contrast to the surrounding quiet sun, coronal holes can be observed as dark regions in extreme UV and X-ray emission. In addition, coronal holes feature an open magnetic field topology. These are magnetic field lines that do not close in the vicinity of the Sun, but far out in interplanetary space. Along those fieldlines, solar plasma is accelerated and ejected as solar wind. The resulting fast flowing solar winds are the major cause of minor to moderate geomagnetic disturbances near Earth. At the Sun, these open magnetic fields are rooted in so-called magnetic elements. These are small unipolar structures with the same polarity of the containing coronal hole. From these footpoints, the magnetic field can expand upwards to eventually fill most of the space in the higher layers of the solar atmosphere. In the lower atmosphere, near the solar photosphere, closed fields (loops) are present in addition to the open fields. The interplay and abundance of closed and open fields defines the vertical magnetic structure of coronal holes near the Sun. The true vertical magnetic structure in coronal hole is not yet fully understood. By using modern potential field modeling techniques, we model the 3D atmospheric magnetic structure of coronal holes from 2D magnetic field observations. For this we, use current magnetic field observations taken by the Solar Dynamics Observatory and synthetically generated magnetic field maps. This enables us to analyze the vertical magnetic field structure of solar coronal holes. The goal is to understand the defining properties and parameters, derive underlying physical principles and gain insights on the solar wind outflow. The model results will be compared with observations from higher layers of the atmosphere. This will be done to validate the model and to explain the observed structures in terms of magnetic field. In addition, we will use observations taken by the new Solar Orbiter spacecraft, that will provide groundbreaking observations at high latitudes. These observations will be used to analyze the magnetic structure of polar coronal holes and compare them to equatorial coronal holes.