Observations of whistler mode waves by Solar Orbiter’s RPW Low Frequency Receiver (LFR): In-flight performance and first results

¹ LPP, CNRS, Ecole Polytechnique, Sorbonne Université, Observatoire de Paris, Université Paris-Saclay, Palaiseau, Paris, France
e-mail: thomas.chust@lpp.polytechnique.fr
² LPC2E, CNRS, University of Orléans, 3A avenue de la recherche scientifique, Orléans, France
³ Swedish Institute of Space Physics (IRF), Uppsala, Sweden
⁴ Department of Space and Plasma Physics, School of Electrical Engineering and Computer Science, Royal Institute of Technology, Stockholm, Sweden
⁵ Department of Space Physics, Institute of Atmospheric Physics of the Czech Academy of Sciences, Prague, Czech Republic
⁶ Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
⁷ CNES, 18 avenue Edouard Belin, 31400 Toulouse, France
⁸ Technische Universität Dresden, Würzburger Str. 35, 01187 Dresden, Germany
⁹ Space Research Institute, Austrian Academy of Sciences, Graz, Austria
¹⁰ Astronomical Institute of the Czech Academy of Sciences, Prague, Czech Republic
¹¹ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, Meudon, France
¹² Radboud Radio Lab, Department of Astrophysics, Radboud University, Nijmegen, The Netherlands
¹³ Space Sciences Laboratory, University of California, Berkeley, CA, USA
¹⁴ Physics Department, University of California, Berkeley, CA, USA
¹⁵ Stellar Scientific, Berkeley, CA, USA
¹⁶ Department of Physics, Imperial College, SW7 2AZ London, UK

Received: 30 March 2021
Accepted: 20 June 2021

Abstract

Context. The Radio and Plasma Waves (RPW) instrument is one of the four in situ instruments of the ESA/NASA Solar Orbiter mission, which was successfully launched on February 10, 2020. The Low Frequency Receiver (LFR) is one of its subsystems, designed to characterize the low frequency electric (quasi-DC – 10 kHz) and magnetic (∼1 Hz–10 kHz) fields that develop, propagate, interact, and dissipate in the solar wind plasma. Combined with observations of the particles and the DC magnetic field, LFR measurements will help to improve the understanding of the heating and acceleration processes at work during solar wind expansion.

Aims. The capability of LFR to observe and analyze a variety of low frequency plasma waves can be demontrated by taking advantage of whistler mode wave observations made just after the near-Earth commissioning phase of Solar Orbiter. In particular, this is related to its capability of measuring the wave normal vector, the phase velocity, and the Poynting vector for determining the propagation characteristics of the waves.

Methods. Several case studies of whistler mode waves are presented, using all possible LFR onboard digital processing products, waveforms, spectral matrices, and basic wave parameters.

Results. Here, we show that whistler mode waves can be very properly identified and characterized, along with their Doppler-shifted frequency, based on the waveform capture as well as on the LFR onboard spectral analysis.

Conclusions. Despite the fact that calibrations of the electric and magnetic data still require some improvement, these first whistler observations show a good overall consistency between the RPW LFR data, indicating that many science results on these waves, as well as on other plasma waves, can be obtained by Solar Orbiter in the solar wind.