Deriving the bulk properties of solar wind electrons observed by Solar Orbiter: A preliminary study of electron plasma thermodynamics

TL;DR

This study develops methods to derive solar wind electron bulk parameters from Solar Orbiter data, examines their thermodynamic behavior, and validates the techniques with artificial data, despite challenges like spacecraft charging.

Contribution

The paper introduces a novel analysis approach for deriving electron bulk parameters from Solar Orbiter observations and assesses their thermodynamic properties using a preliminary dataset.

Findings

Validation with artificial data confirms method accuracy.

Revealed nearly isothermal electron core in observations.

Identified challenges from spacecraft charging and photo-electrons.

Abstract

We demonstrate the calculation of solar wind electron bulk parameters from recent observations by Solar Wind Analyser Electron Analyser System on board Solar Orbiter. We use our methods to derive the electron bulk parameters in a time interval of a few hours. We attempt a preliminary examination of the polytropic behavior of the electrons by analyzing the derived electron density and temperature. Moreover, we discuss the challenges in analyzing the observations due to the spacecraft charging and photo-electron contamination in the energy range < 10 eV. Aims: We derive bulk parameters of thermal solar wind electrons by analyzing Solar Orbiter observations and we investigate if there is any typical polytropic model that applies to the electron density and temperature fluctuations. Methods: We use the appropriate transformations to convert the observations to velocity distribution functions in the instrument frame. We then derive the electron bulk parameters by a) calculating the statistical moments of the constructed velocity distribution functions and b) by fitting the constructed distributions with analytical expressions. We firstly test our methods by applying them to an artificial data-set, which we produce by using the forward modeling technique. Results: The forward model validates the analysis techniques which we use to derive the electron bulk parameters. The calculation of the statistical moments and the fitting method determines bulk parameters that are identical within uncertainty to the input parameters we use to simulate the plasma electrons in the first place. An application of our analysis technique to the data reveals a nearly isothermal electron "core". The results are affected by the spacecraft potential and the photo-electron contamination, which we need to characterize in detail in future analyses.