Abstract
Abstract. In the solar wind at 1 AU, coherent electrostatic waveforms in the ion acoustic frequency range (~ 1 kHz) have been observed by the Time Domain Sampler (TDS) instrument on the Wind spacecraft. Small drops of electrostatic potential (Df > 10-3 V) have been found across some of these waveforms, which can thus be considered as weak double layers (Mangeney et al., 1999). The rate of occurrence of these potential drops, at 1 AU, is estimated by a comparison of the TDS data with simultaneous data of another Wind instrument, the Thermal Noise Receiver (TNR), which measures continuously the thermal and non-thermal electric spectra above 4 kHz. We assume that the potential drops have a constant amplitude and a constant rate of occurrence between the Sun and the Earth. The total potential drop between the Sun and the Earth, which results from a succession of small potential drops during the Sun-Earth travel time, is then found to be about 300 V to 1000 V, of the same order of magnitude as the interplanetary potential implied by a two-fluid or an exospheric model of the solar wind: the interplanetary potential may manifest itself as a succession of weak double layers. We also find that the hourly average of the energy of the non-thermal ion acoustic waves, observed on TNR between 4 and 6 kHz, is correlated to the interplanetary electrostatic field, parallel to the spiral magnetic field, calculated with a two-fluid model: this is another evidence of a relation between the interplanetary electrostatic field and the electrostatic fluctuations in the ion acoustic range. We have yet to discuss the role of the Doppler effect, which is strong for ion acoustic waves in the solar wind, and which can bias the measure of the ion acoustic wave energy in the narrow band 4–6 kHz.Key words. Interplanetary physics (plasma waves and turbulence; solar wind plasma) Space plasma physics (electro-static structures)
Highlights
The solar wind is a weakly collisional plasma so that the validity of the fluid equations that are generally used to describe its flow is questionable
The total potential drop between the Sun and the Earth, which results from a succession of small potential drops during the Sun-Earth travel time, is found to be about 300 V to 1000 V, of the same order of magnitude as the interplanetary potential implied by a two-fluid or an exospheric model of the solar wind: the interplanetary potential may manifest itself as a succession of weak double layers
We find that the hourly average of the energy of the non-thermal ion acoustic waves, observed on Thermal Noise Receiver (TNR) between 4 and 6 kHz, is correlated to the interplanetary electrostatic field, parallel to the spiral magnetic field, calculated with a two-fluid model: this is another evidence of a relation between the interplanetary electrostatic field and the electrostatic fluctuations in the ion acoustic range
Summary
The solar wind is a weakly collisional plasma so that the validity of the fluid equations that are generally used to describe its flow is questionable. A second result of the TDS observations is that a small jump of electrostatic potential ≥ 10−3 V is found across some of the coherent electrostatic waves (CEW) Such potential jumps imply that the corresponding CEW are weak double layers, with a charge separation on a scale comparable to the Debye length. It is tempting to speculate that SE is the result of a succession of small potential drops in weak double layers (hereafter WDL), due to small charge separations between the protons and the escaping electrons (Salem et al, 1999) To check this hypothesis, we have to estimate the rate of occurrence of the WDL in the solar wind. An increase in the Doppler shift on 1 kHz waves will give an apparent increase in E2, even if there is no increase in the wave intensity in the whole ion acoustic range
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
