ALBERT

Description: The time domain sampler (TDS) experiment on WIND measures electric and magnetic wave forms with a sampling rate which reaches 120 000 points per second. We analyse here observations made in the solar wind near the Lagrange point L1. In the range of frequencies above the proton plasma frequency fpi and smaller than or of the order of the electron plasma frequency fpe, TDS observed three kinds of electrostatic (e.s.) waves: coherent wave packets of Langmuir waves with frequencies f ~ fpe, coherent wave packets with frequencies in the ion acoustic range fpi 〈 f 〈 fpe, and more or less isolated non-sinusoidal spikes lasting less than 1 ms. We confirm that the observed frequency of the low frequency (LF) ion acoustic wave packets is dominated by the Doppler effect: the wavelengths are short, 10 to 50 electron Debye lengths λD. The electric field in the isolated electrostatic structures (IES) and in the LF wave packets is more or less aligned with the solar wind magnetic field. Across the IES, which have a spatial width of the order of ~ 25λD, there is a small but finite electric potential drop, implying an average electric field generally directed away from the Sun. The IES wave forms, which have not been previously reported in the solar wind, are similar, although with a smaller amplitude, to the weak double layers observed in the auroral regions, and to the electrostatic solitary waves observed in other regions in the magnetosphere. We have also studied the solar wind conditions which favour the occurrence of the three kinds of waves: all these e.s. waves are observed more or less continuously in the whole solar wind (except in the densest regions where a parasite prevents the TDS observations). The type (wave packet or IES) of the observed LF waves is mainly determined by the proton temperature and by the direction of the magnetic field, which themselves depend on the latitude of WIND with respect to the heliospheric current sheet.Key words. Interplanetary physics (plasma waves and turbulence; solar wind plasma). Space plasma physics (electrostatic structures).

Description: In this report we present the first results from the Cluster wideband plasma wave investigation. The four Cluster spacecraft were successfully placed in closely spaced, high-inclination eccentric orbits around the Earth during two separate launches in July – August 2000. Each spacecraft includes a wideband plasma wave instrument designed to provide high-resolution electric and magnetic field wave-forms via both stored data and direct downlinks to the NASA Deep Space Network. Results are presented for three commonly occurring magnetospheric plasma wave phenomena: (1) whistlers, (2) chorus, and (3) auroral kilometric radiation. Lightning-generated whistlers are frequently observed when the spacecraft is inside the plasmasphere. Usually the same whistler can be detected by all spacecraft, indicating that the whistler wave packet extends over a spatial dimension at least as large as the separation distances transverse to the magnetic field, which during these observations were a few hundred km. This is what would be expected for nonducted whistler propagation. No case has been found in which a strong whistler was detected at one spacecraft, with no signal at the other spacecraft, which would indicate ducted propagation. Whistler-mode chorus emissions are also observed in the inner region of the magnetosphere. In contrast to lightning-generated whistlers, the individual chorus elements seldom show a one-to-one correspondence between the spacecraft, indicating that a typical chorus wave packet has dimensions transverse to the magnetic field of only a few hundred km or less. In one case where a good one-to-one correspondence existed, significant frequency variations were observed between the spacecraft, indicating that the frequency of the wave packet may be evolving as the wave propagates. Auroral kilometric radiation, which is an intense radio emission generated along the auroral field lines, is frequently observed over the polar regions. The frequency-time structure of this radiation usually shows a very good one-to-one correspondence between the various spacecraft. By using the microsecond timing available at the NASA Deep Space Net-work, very-long-baseline radio astronomy techniques have been used to determine the source of the auroral kilometric radiation. One event analyzed using this technique shows a very good correspondence between the inferred source location, which is assumed to be at the electron cyclotron frequency, and a bright spot in the aurora along the magnetic field line through the source.Key words. Ionosphere (wave-particle interactions; wave propagation) – Magnetospheric physics (plasma waves and instabilities; instruments and techniques)

Description: 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)

Description: Using the extensive and uniform data on coronal mass ejections (CMEs), solar energetic particle (SEP) events, and type II radio bursts during the SOHO era, we discuss how the CME properties such as speed, width and solar-source longitude decide whether CMEs are associated with type II radio bursts and SEP events. We discuss why some radio-quiet CMEs are associated with small SEP events while some radio-loud CMEs are not associated with SEP events. We conclude that either some fast and wide CMEs do not drive shocks or they drive weak shocks that do not produce significant levels of particle acceleration. We also infer that the Alfvén speed in the corona and near-Sun interplanetary medium ranges from