Conrad Schwanitz


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Schwanitz

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Conrad

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0000-0002-7669-5078

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Publications 1 - 3 of 3
  • Small-scale coronal upflows in the quiet Sun and coronal holes
    Item type: Doctoral Thesis
    Schwanitz, Conrad (2023)
    The Sun is the star at the centre of our Solar System. It has been studied by humans for many generations but it still holds many secrets and is far from being fully understood. Solar research is an extensive field of astrophysics and is now more important than ever before. In the highly technological society that we live in it is crucial to understand solar activity and its impact on Earth; in particular with respect to the Earth’s atmosphere, technology and life. A key driver of solar activity is the solar corona (the outermost layer of the Sun’s atmosphere) and the solar wind (plasma that is continuously emitted by the Sun which frequently reaches Earth). Both the corona and the solar wind are not fully understood to date. The heating mechanism(s) of the corona and the source of the slow solar wind are especially intersting open questions. In this thesis, I present my work on small-scale, coronal plasma upflows. While previous studies have mostly focused on large and prominent upflows, smaller upflow regions have usually been overlooked. However, recent observations of the solar wind have shown a very detailed structure which can not be explained by large and stable sources. This raises the need to better understand all kinds of small coronal transients and upflows. I use data from four different satellites and one ground-based telescope to study various regions of coronal upflows. I analyse their photospheric, chromospheric, transition region and coronal properties by using magnetic, spectroscopic and imaging data. In total 17 regions of coronal upflows in the quiet Sun and in coronal holes are found from spectroscopic data. The upflow regions typically have Doppler velocities between -6 km s−1 and -25 km s−1. To better understand the observed upflows I combine spectroscopic data with imaging data fromvarious instruments covering photospheric to coronal temperatures. I find new features that cause small-scale coronal upflows, especially small-scale brightenings and small-scale eruptions. They only partly resemble known jets or other transients and are usually smaller and fainter. Furthermore, I find new evidence for the importance of smallscale activity as drivers of coronal upflows in loop footpoints and in coronal bright points. Several small coronal upflows do not only show activity in the corona but can be traced back to photospheric magnetic and chromospheric activity. A few selected upflows are explained in more detail. In addition, models of the local situation are presented. Many of the observed features are located in regions with open magnetic fields which allow the ejected plasma to escape. This thesis provides a new perspective on small-scale upflows in the solar corona. It presents previously unknown coronal transients which are capable of producing upflows and provides a better understanding of known sources of upflow. Furthermore, it shows that small-scale transients and upflows are an important component in the total picture of the solar corona as they might be relevant for the slow solar wind. Whether they have a significant impact on the global conditions of the solar corona and potentially feed into the solar wind can not be answered yet and this question is left to future generations of solar physicists.
  • Coronal voids and their magnetic nature
    Item type: Journal Article
    Nölke, Jonathan D.; Solanki, Sami K.; Hirzberger, J.; et al. (2023)
    Astronomy & Astrophysics
    Context. Extreme ultraviolet (EUV) observations of the quiet solar atmosphere reveal extended regions of weak emission compared to the ambient quiescent corona. The magnetic nature of these coronal features is not well understood. Aims. We study the magnetic properties of the weakly emitting extended regions, which we name coronal voids. In particular, we aim to understand whether these voids result from a reduced heat input into the corona or if they are associated with mainly unipolar and possibly open magnetic fields, similar to coronal holes. Methods. We defined the coronal voids via an intensity threshold of 75% of the mean quiet-Sun (QS) EUV intensity observed by the high-resolution EUV channel (HRIₑᵤᵥ) of the Extreme Ultraviolet Imager on Solar Orbiter. The line-of-sight magnetograms of the same solar region recorded by the High Resolution Telescope of the Polarimetric and Helioseismic Imager allowed us to compare the photospheric magnetic field beneath the coronal voids with that in other parts of the QS. Results. The coronal voids studied here range in size from a few granules to a few supergranules and on average exhibit a reduced intensity of 67% of the mean value of the entire field of view. The magnetic flux density in the photosphere below the voids is 76% (or more) lower than in the surrounding QS. Specifically, the coronal voids show much weaker or no network structures. The detected flux imbalances fall in the range of imbalances found in QS areas of the same size. Conclusions. We conclude that coronal voids form because of locally reduced heating of the corona due to reduced magnetic flux density in the photosphere. This makes them a distinct class of (dark) structure, different from coronal holes.
  • Small-Scale Upflows in a Coronal Hole – Tracked from the Photosphere to the Corona
    Item type: Journal Article
    Schwanitz, Conrad; Harra, Louise; Barczynski, Krzysztof; et al. (2023)
    Solar Physics
    Coronal transients are known as sources of coronal upflows. With the commissioning of Solar Orbiter, it became apparent that coronal small-scale features are even more frequent than previously estimated. It was found that even small coronal features seen by Solar Orbiter can produce visible upflows. Therefore, it is important to study the plasma flows on small scales better and understand their atmospheric driving mechanisms. In this article, we present the results from a two-week coordinated multi-spacecraft observation campaign with Hinode, IRIS, and the GREGOR telescope. We identify a small region of coronal upflows with Doppler velocities of up to 16.5 km s⁻¹. The upflows are located north of a coronal bright point in a coronal hole. We study the corona, the transition region, the chromosphere and the photospheric magnetic field to find evidence of underlying mechanisms for the coronal upflow. We find a complex photospheric magnetic field with several small mixed polarities that are the footpoints of different loops. Flux emergence and cancellation are observed at the constantly changing footpoints of the coronal loops. Reconnection of loops can be identified as the driver of the coronal upflow. Furthermore, the impact of the coronal activity triggers plasma flows in the underlying layers. This work highlights that frequent small coronal features can cause considerable atmospheric response and ubiquitously produce plasma upflows that potentially feed into the solar wind.
Publications 1 - 3 of 3