Solar wind current sheets and deHoffmann-Teller analysis

First results from Solar Orbiter’s DC electric field measurements

¹ Swedish Institute of Space Physics (IRF), Uppsala 75121, Sweden
e-mail: konrad.steinvall@irfu.se
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

Received: 22 March 2021
Accepted: 26 April 2021

Abstract

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, L_eff 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 E_y are often in excellent agreement with the variations in the magnetic field. The magnitude of E_y, however, is uncertain due to the fact that the L_eff depends on the plasma environment. Here, we derive an empirical model relating L_eff to the Debye length, which we can use to improve the estimate of E_y 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.