Volume 656, December 2021
Solar Orbiter First Results (Cruise Phase)
|Number of page(s)||7|
|Section||The Sun and the Heliosphere|
|Published online||14 December 2021|
Solar wind current sheets and deHoffmann-Teller analysis
First results from Solar Orbiter’s DC electric field measurements
Swedish Institute of Space Physics (IRF), Uppsala 75121, Sweden
2 Space and Plasma Physics, Department of Physics and Astronomy, Uppsala University, Uppsala 75120, Sweden
3 Division of Space and Plasma Physics, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm 11428, Sweden
4 LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
5 Space Sciences Laboratory, University of California, Berkeley, CA, USA
6 Physics Department, University of California, Berkeley, CA, USA
7 LPP, CNRS, Ecole Polytechnique, Sorbonne Université, Observatoire de Paris, Université Paris-Saclay, Palaiseau, Paris, France
8 LPC2E, CNRS, 3A avenue de la Recherche Scientifique, Orléans, France
9 Université d’Orléans, Orléans, France
10 CNES, 18 avenue Edouard Belin, 31400 Toulouse, France
11 Technische Universität Dresden, Helmholtz Str. 10, 01187 Dresden, Germany
12 Institute of Atmospheric Physics of the Czech Academy of Sciences, Prague, Czech Republic
13 Space Research Institute, Austrian Academy of Sciences, Graz, Austria
14 Astronomical Institute of the Czech Academy of Sciences, Prague, Czech Republic
15 Radboud Radio Lab, Department of Astrophysics, Radboud University, Nijmegen, The Netherlands
16 Imperial College London, South Kensington Campus, London SW7 2AZ, UK
17 Institut de Recherche en Astrophysique et Planétologie, 9 avenue du Colonel Roche, BP 4346, 31028 Toulouse Cedex 4, France
18 Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, Pessac, France
19 Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
Accepted: 26 April 2021
Context. Solar Orbiter was launched on 10 February 2020 with the purpose of investigating solar and heliospheric physics using a payload of instruments designed for both remote and in situ studies. Similar to the recently launched Parker Solar Probe, and unlike earlier missions, Solar Orbiter carries instruments designed to measure low-frequency DC electric fields.
Aims. In this paper, we assess the quality of the low-frequency DC electric field measured by the Radio and Plasma Waves instrument (RPW) on Solar Orbiter. In particular, we investigate the possibility of using Solar Orbiter’s DC electric and magnetic field data to estimate the solar wind speed.
Methods. We used a deHoffmann-Teller (HT) analysis, based on measurements of the electric and magnetic fields, to find the velocity of solar wind current sheets, which minimises a single component of the electric field. By comparing the HT velocity to the proton velocity measured by the Proton and Alpha particle Sensor (PAS), we have developed a simple model for the effective antenna length, Leff of the E-field probes. We then used the HT method to estimate the speed of the solar wind.
Results. Using the HT method, we find that the observed variations in Ey are often in excellent agreement with the variations in the magnetic field. The magnitude of Ey, however, is uncertain due to the fact that the Leff depends on the plasma environment. Here, we derive an empirical model relating Leff to the Debye length, which we can use to improve the estimate of Ey and, consequently, the estimated solar wind speed.
Conclusions. The low-frequency electric field provided by RPW is of high quality. Using the deHoffmann-Teller analysis, Solar Orbiter’s magnetic and electric field measurements can be used to estimate the solar wind speed when plasma data are unavailable.
Key words: solar wind / plasmas / magnetic reconnection / methods: data analysis
© ESO 2021
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