Triggered Ion-acoustic Waves in the Solar Wind

F S Mozer,J L Verniero,I Y Vasko

doi:10.3847/2041-8213/ac2259

F S Mozer, J L Verniero + Show 1 more

Open Access

https://doi.org/10.3847/2041-8213/ac2259

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Abstract

Abstract For more than 12 hr beginning on 2021 January 18, continuous narrowband electrostatic emissions were observed on the Parker Solar Probe near 20 solar radii. The observed <1000 Hz frequencies were well below the local ion-plasma frequency. Surprisingly, the emissions consisted of electrostatic wave packets with shock-like envelopes, appearing repetitively at a ∼1.5 Hz rate. This repetitiveness correlated and was in phase with low-frequency electromagnetic fluctuations. The emissions were associated with simultaneously observed ion beams and conditions favorable for ion-acoustic wave excitation, i.e., Te/Ti ∼ 5. Based on this information and on their velocity estimates of about 100 km s−1, these electrostatic emissions are interpreted as ion-acoustic waves. Their observation demonstrates a new regime of instability and evolution of oblique ion-acoustic waves that have not been reported previously in theory or experiment.

Highlights

II INTRODUCTION Ion acoustic waves have been observed via spectral measurements on early satellites in the solar wind [Gurnett and Anderson, 1977; Gurnett and Frank, 1978; Kurth et al, 1979]
The instabilities that produce these broadband electrostatic fluctuations might include the ion beam instability [Lemons et al, 1979; Gary and Omidi, 1987], and electrostatic electron heat flux instability [Forslund, 1970], but no consensus had been reached on the origin of these waves in the solar wind [Gurnett, 1991]
Previous time-domain burst electric field measurements allowed analysis of electric field waveforms that showed the ion-acoustic fluctuations consisted of ion-acoustic wave packets [Mozer et al, 2020a] and nonlinear electrostatic structures interpreted as ion and electron phase space holes [Mozer et al, 2020b]

Summary

Introduction

Ion acoustic waves have been observed via spectral measurements on early satellites in the solar wind [Gurnett and Anderson, 1977; Gurnett and Frank, 1978; Kurth et al, 1979]. These waves and structures are observed as broadband wave activity above the local ion plasma frequency.

Results

Conclusion