Abstract
Context. Recent studies of the solar wind sunward of 0.25 AU reveal that it contains quiescent regions, with low-amplitude plasma and magnetic field fluctuations, and a magnetic field direction similar to the Parker spiral. The quiescent regions are thought to have a more direct magnetic connection to the solar corona than other types of solar wind, suggesting that waves or instabilities in the quiescent regions are indicative of the early evolution of the solar wind as it escapes the corona. The quiescent solar wind regions are highly unstable to the formation of plasma waves near the electron cyclotron frequency (fce). Aims. We examine high time resolution observations of these waves in an effort to understand their impact on electron distribution functions of the quiescent near-Sun solar wind. Methods. High time resolution waveform captures of near-fce waves were examined to determine variations of their amplitude and frequency in time as well as their polarization properties. Results. We demonstrate that the near-fce wave intervals contain several distinct wave types, including electron Bernstein waves and extremely narrowband waves that are highly sensitive to the ambient magnetic field orientation. Using the properties of these waves, we suggest possible plasma wave mode classifications and possible instabilities that generate these waves. The results of this analysis indicate that these waves may modify the cold core of the electron distribution functions in the quiescent near-Sun solar wind.
Highlights
Recent studies have demonstrated that solar wind particle distributions are highly unstable to the growth of plasma waves at distances from the Sun smaller than ∼55 solar radii (∼0.25 astronomical units)
This study focuses on plasma waves near the electron cyclotron frequency in the near-Sun solar wind
This study found that the converse can occur, that is, an electrostatic electron Bernstein wave in the presence of low-frequency, low-wavelength ion acoustic wave can generate electromagnetic electron cyclotron harmonics
Summary
Recent studies have demonstrated that solar wind particle distributions are highly unstable to the growth of plasma waves at distances from the Sun smaller than ∼55 solar radii (∼0.25 astronomical units). Fluctuations, Parker-spiral B vector, higher 1/ f spectral break frequency, and strong sunward electron core drift, are consistent with the interpretation that these regions of high wave growth represent portions of the solar wind that are most directly magnetically connected to the solar corona. These near- fce waves may play an important role in the evolution of solar wind electrons early in their escape from the solar corona. The waves under study are frequently observed in the continuously recorded survey data (Malaspina et al 2020)
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