Self-consistent solar wind model and the emergence of the FIP effect from Alfvén waves
Final Report Abstract
This project investigated the elemental composition of the solar wind. It is well-known that the elemental composition of the solar wind differs from the observed solar abundance at the photospheric level. The abundance of some elements appear to be enhanced in the solar wind compared to the photosphere, while others appear unchanged or even depleted. The strength of this apparent enhancement/depletion is ordered by the first ionization potential (FIP). Therefore, this is also called the FIP effect. Models of the FIP effect assume a mechanism that acts preferentially on ions (and not neutral particles). This requires comparatively low temperatures in the region where the FIP effect arises, which is therefore assumed to be located in the chromosphere or lower corona. The most promising model traces the origin of the FIP effect to the ponderomotive force which is exerted on ions in the solar wind plasma by resonant and non-resonant Alfv´en waves. This project focused on the observational side of the FIP effect and investigated the behavior of several low FIP elements. The FIP effect is observed to be more pronounced in slow solar wind than in coronal hole wind. Therefore, FIP models rely on two distinct coronal configurations to predict the strength of the FIP effect in both types of solar wind. This makes the implicit assumption that average properties of "typical coronal hole wind" and a "typical slow solar wind" are representative for the solar wind. The slow solar wind is known to be highly variable in all its properties. Thus, average properties are not necessarily ideally suited to represent any individual solar wind stream. Therefore, in this project, we investigated the variability of coronal hole wind as a first step. Surprisingly, we found that the Fe charge state is more variable in individual coronal wind streams than previously expected. In particular, we observed that coronal hole wind can have either high or low Fe charge states that are stable for at least several hours. The charge states of the solar wind are also determined in the solar atmosphere but in higher regions than the FIP effect. The high charge states observed in the solar wind can only be achieved in the hot corona, but for different elements and charge states this occurs at different heights in the solarcorona. This motivated us to extend this analysis to other Elements. In a separate publication to derive constraints for the temperature profile in the solar atmosphere. For this, coronal hole wind from a small equatorial coronal hole, which was observable over several solar rotations, was used as a test case and we developed tools to constrain the coronal temperature profile directly from observations without an additional model. From this, we learned that the temperature profile is more variable in the higher corona but comparatively stable in the lower corona. For the FIP effect which is determined in the lowest levels of the solar atmosphere, this validates the assumption that long term averages can be representative for the FIP effect in coronal hole wind. Further, we compared the long-term FIP effect measured by two spacecraft situated at the first Lagrange point, the Advanced Composition Explorer (ACE) and the Solar and Heliospheric Observatory (SOHO). Both measurements lead to comparable results. Since the Solar Orbiter mission (launched 10.2.2020) plans to exploit the FIP effect measured by two different instruments (a remote sensing instrument and an in situ instrument) to identify the source regions of slow solar wind, we investigated the capabilities of the underlying back-mapping procedure. The results stress the importance of the magnetic connection within the solar corona. The resulting publication recommended an observation strategy for Solar Orbiter that maximizes the probability to observe the same solar source region with remote-sensing and in situ instruments.
Publications
- FIP effect for minor heavy solar wind ions as seen with SOHO/CELIAS/MTOF, AIP Conference Proceedings, 1720.1, 040004„ (2016)
V. Heidrich-Meisner, L. Berger, R. F. Wimmer-Schweingruber, P. Wurz, P. Bochsler, F. M. Ipavich, J. A. Paquette, B. Klecker
(See online at https://doi.org/10.1063/1.4943815) - Investigation of solar wind source regions using Ulysses composition data and a PFSS model, AIP Conference Proceedings, 1720.1, 020003, (2016)
T. Peleikis, M. Kruse, L. Berger, C. Drews, R. F. Wimmer-Schweingruber
(See online at https://doi.org/10.1063/1.4943804) - Observations of high and low Fe charge states in individual solar wind streams with coronal-hole origin, Astron. & Astrophys., 593, A70, (2016)
V. Heidrich-Meisner, T. Peleikis, M. Kruse, L. Berger, R. Wimmer-Schweingruber
(See online at https://doi.org/10.1051/0004-6361/201527998) - Tracing heliospheric structures to their solar origin, AIP Conference Proceedings 1720.1, 100002, (2016)
R. F. Wimmer-Schweingruber and D. M. Hassler
(See online at https://doi.org/10.1063/1.4943857) - Evolution of an equatorial coronal hole structure and the released coronal hole wind stream: Carrington rotations 2039 to 2050, Astron. & Astrophys., 603, A84, (2017)
V. Heidrich-Meisner, T. Peleikis, M. Kruse, L. Berger, R. F. Wimmer-Schweingruber
(See online at https://doi.org/10.1051/0004-6361/201730574) - Origin of the solar wind: A novel approach to link in situ and remote observations. A study for SPICE and SWA on the upcoming Solar Orbiter mission, Astron. & Astrophys., 602, A24, (2017)
T. Peleikis, M. Kruse, L. Berger, R. Wimmer-Schweingruber
(See online at https://doi.org/10.1051/0004-6361/201629727) - Challenges in the determination of the interstellar flow longitude from the pickup ion cutoff, Astron. & Astrophys., 611, A61, (2018)
A. Taut, L. Berger, E. Möbius, C. Drews, V. Heidrich-Meisner, D. Keilbach, M. A. Lee, R. F. Wimmer- Schweingruber
(See online at https://doi.org/10.1051/0004-6361/201731796)
