Seminarium: Electrostatic Plasma Waves Associated with Magnetic Reconnection: Properties, causes, and effects
- Datum: –15.00
- Plats: Zoom: https://uu-se.zoom.us/j/62091586806
- Föreläsare: Konrad Steinvall, IRF Uppsala
- Kontaktperson: Anish Amarsi
In this 6-month seminar I will give an introduction to, and summarize, the projects I’ve been working on over the last couple of years, regarding electrostatic plasma waves in the context of collisionless magnetic reconnection.
Magnetic reconnection is an important plasma process responsible for explosive phenomena such as coronal mass ejections, the aurora, and disruptions of fusion reactors. In addition, magnetic reconnection is believed to be a large contributor to the heating of the chromosphere, corona, and the solar wind. While reconnection is well studied and a hot topic in modern space plasma physics, there are still fundamental aspects of the process which are poorly understood. In particular, the impact plasma waves have on the process has not yet been fully established. My work has been focused on using spacecraft data to analyze electrostatic waves found during magnetic reconnection events.
The first two papers deal with an important type of non-linear, electrostatic, plasma structure, Electron Holes (EHs), which are frequently observed during magnetic reconnection. Using NASA’s four spacecraft mission, magnetospheric multiscale (MMS), we use multi-spacecraft analysis to investigate EH properties with high accuracy. In paper 1, we found that the EH properties were in good agreement with both theoretical predictions and previous results based on single-spacecraft methods, thereby validating those methods. In paper 2 we investigated the magnetic structure of EHs and found observational evidence of whistler waves being Cherenkov-radiated from EHs.
In the third paper we investigated strong electrostatic waves near the ion plasma frequency often observed at the magnetopause. We found a strong correlation between the waves and the presence of cold ions of ionospheric/plasmaspheric origin and ongoing reconnection. We concluded that the waves were driven by an interaction between strong parallel currents in the separatrix region of magnetic reconnection and the cold ion population. Moreover, we argued that this instability will dissipate the parallel currents and that the waves might heat the cold ion population.
Inspired by discussions with colleagues, we investigated the accuracy of three different single-spacecraft interferometry methods in the fourth paper. Such methods are necessary when analyzing electrostatic waves observed only by a single spacecraft, as they provide a means for the wave’s phase velocity to be estimated, making it possible to determine both the wave potential and wavelength. We use synthetic data from an analytical model to understand which method is preferable under different circumstances and why. Our results are important for future studies of waves where single-spacecraft analysis might be necessary.
Finally in the fifth and final(?) paper, we move from the small scale analysis of magnetic reconnection in the Earth’s magnetosphere to the much larger scales of the solar wind, using ESA’s recently launched Solar Orbiter spacecraft. Here, we use solar wind current sheets (reconnecting and non-reconnecting) to assess the accuracy of the low-frequency electric field measurements made by the instrument. We develop a method to use our E-field data to deduce the solar wind speed. Our velocity estimates have been used to provide plasma context to many other studies when data from particle instruments have been unavailable.
I will also briefly mention the current science project which, if time permits, will be ready as a draft by the end of my studies.