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| INSTITUTET FÖR RYMDFYSIK | UPPSALA |
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| Swedish Institute of Space Physics | (59°50.272′N, 17°38.786′E) |
Master Project (45 c)/Masterprojekt (45 hp)
Determination of the Plasma Density in the Solar Wind from MMS Electric Field and Spacecraft Potential Measurements
Student: Atlas Silverhult, Uppsala UniversitySupervisors: Yuri Khotyaintsev, Daniel Graham
Period: 2024-2025
Abstract
We present a method for deriving the electron number density in the solar wind using electric field wave data and spacecraft potential measurements from the Magnetospheric Multiscale (MMS) mission. The electron density is inferred from the local electron plasma frequency, identified as spectral peaks corresponding to Langmuir waves in electric field power spectra. When such wave activity is present, this provides a measurement of the electron density. To refine the method, we calibrate the inferred electron density against the spacecraft potential, establishing an empirical relationship that allows for a robust, high-resolution estimate of the electron density. The method is applied on time intervals where MMS was located in the solar wind ranging from 2017 to 2025, and the calibration is performed separately for each MMS spacecraft. We validate our results by comparing the derived electron densities to those obtained from the Fast Plasma Investigation (FPI) instrument on MMS. In particular, we study the impact of the modified energy table used during the solar wind mode of operation. We find that in its default mode, FPI systematically underestimates the electron density in the solar wind by approximately 40%, while the solar wind mode reduces this discrepancy to about 20%. Finally, we compare our electron density estimates to the proton density provided by the OMNI solar wind data set. We similarly find that the OMNI proton density is systematically lower than our derived electron density by roughly 20%. Our method is independent of particle measurements from FPI, and demonstrates a reliable approach to estimating solar wind electron densities with improved temporal resolution, which is valuable for studies of solar wind structure, plasma processes, and space weather monitoring.Results
Final report
Example plot from the report:
![[MMS]](plot.png)