C. Perche

WAVES: The radio and plasma wave investigation on the wind spacecraft

The WAVES investigation on the WIND spacecraft will provide comprehensive measurements of the radio and plasma wave phenomena which occur in Geospace. Analyses of these measurements, in coordination with the other onboard plasma, energetic particles, and field measurements will help us understand the kinetic processes that are important in the solar wind and in key boundary regions of the Geospace. These processes are then to be interpreted in conjunction with results from the other ISTP spacecraft in order to discern the measurements and parameters for mass, momentum, and energy flow throughout geospace. This investigation will also contribute to observations of radio waves emitted in regions where the solar wind is accelerated. The WAVES investigation comprises several innovations in this kind of instrumentation: among which the first use, to our knowledge, of neural networks in real-time on board a scientific spacecraft to analyze data and command observation modes, and the first use of a wavelet transform-like analysis in real time to perform a spectral analysis of a broad band signal.

Plasma diagnosis from thermal noise and limits on dust flux or mass in comet Giacobini-Zinner

Thermal noise spectroscopy was used to measure the density and temperature of the main (cold) electron plasma population during 2 hours (1.5x105 kilometers perpendicular to the tail axis) around the point of closest approach of the International Cometary Explorer (ICE) to Comet Giacobini-Zinner. The time resolution was 18 seconds (370 kilometers) in the plasma tail and 54 seconds (1100 kilometers) elsewhere. Near the tail axis, the maximum plasma density was 670 per cubic centimeter and the temperature slightly above 1 electron volt. Away from the axis, the plasma density dropped to 100 per cubic centimeter (temperature, 2x 104 K) over 2000 kilometers, then decreased to 10 (1.5x 105K) over 15,000 kilometers; outside that region (plasma tail), the density fluctuated between 10 and 30 per cubic centimeter and the temperature between 1x 105 and 4 x105 K. The relative density of the hot population rarely exceeded a few percent. The tail was highly asymmetrical and showed much structure. On the other antenna, shot noise was recorded from the plasma particle impacts on the spacecraft body. No evidence was found of grain impacts on the antennas or spacecraft in the plasma tail. This yields an upper limit for the dust flux or particle mass, indicating either fluxes or masses in the tail smaller than implied by the models or an anomalous grain structure. This seems to support earlier suggestions that these grains are featherlike. Outside the tail, and particularly near 105 kilometers from its axis, impulsive noises indicating plasma turbulence were observed.

Determination of accurate solar wind electron parameters using particle detectors and radio wave receivers

We present a new, simple, and semiempirical method for determining accurate solar wind electron macroscopic parameters from the raw electron moments obtained from measured electron distribution functions. In the solar wind these measurements are affected by (1) photoelectrons produced by the spacecraft illumination, (2) spacecraft charging, and (3) the incomplete sampling of the electron distribution due to a nonzero low-energy threshold of the energy sweeping in the electron spectrometer. Correcting fully for these effects is difficult, especially without the help of data from other experiments that can be taken as a reference. We take here advantage of the fact that high-resolution solar wind electron parameters are obtained on board Wind using two different instruments: the electron electrostatic analyzer of the three-dimensional Plasma experiment (3DP), which provides 3-D electron velocity distribution functions every 99 s as well as 3-s resolution computed onboard moments, and the thermal noise receiver (TNR), which yields unbiased electron density and temperature every 4.5 s from the spectroscopy of the quasi-thermal noise around the electron plasma frequency. The present correction method is based on a simplified model evaluating the electron density and temperature as measured by the electron spectrometer, by taking into account both the spacecraft charging and the low-energy cutoff effects: approximating the solar wind electron distributions by an isotropic Maxwellian, we derive simple analytical relations for the measured electron moments as functions of the real ones. These relations reproduce the qualitative behavior of the variation of the raw 3DP electron density and temperature as a function of the TNR ones. In order to set up a precise “scalar correction” of the raw 3DP electron moments, we use the TNR densities and temperatures as good estimates of the real ones; the coefficients appearing in the analytical relations are obtained by a best fit to the data from both instruments during a limited period of time, chosen as a reference. This set of coefficients is then used as long as the mode of operation of the electron spectrometer is unchanged. We show that this simple scalar correction of the electron density and temperature is reliable and can be applied routinely to the high-resolution 3DP low-order moments. As a by-product, an estimate of the spacecraft potential is obtained. The odd-order moments of the distribution function (electron bulk speed and heat flux) cannot be corrected by the model since the distribution is assumed to be an isotropic Maxwellian. We show, however, that a better estimate of the electron heat flux can be obtained by replacing the electron velocity by the proton velocity.

A shock associated (SA) radio event and related phenomena observed from the base of the solar corona to 1 AU

We present for the rst time an almost com- plete frequency coverage of a Shock Associated (SA) radio event and related phenomena observed on May 6, 1996 at 9:27 UT. It is observed from the base of the solar corona up to almost 1 Astronomical Unit (AU) from the Sun by the following radio astronomical instruments: the Ond rejov spectrometer operating between 4.5 GHz and 1 GHz (radi- ation produced near the chromosphere); the Thermopyles Artemis-IV spectrograph operating between 600 MHz and 110 MHz (distance range about 1.1-1.4R from sun center); the Nan cay Decameter Array operating between 75 and 25 MHz (distance range about 1.4-2 R); and the RAD2 and RAD1 radio receivers on the WIND spacecraft covering the range from 14 MHz to about 20 kHz (distance range be- tween 3 R and about 1 AU). Observations at the Nan cay Decameter Array clearly show that the SA event starts from a coronal type II radio burst which traces the progression of a shock wave through the corona above 1.8 R-2 R from the sun center. This SA event has no associated radio emis- sion in the decimetric-metric range, thus there is no evidence for electron injection in the low/middle corona. The SA event enigma: What does SA stand for? Type II and type III solar radio bursts result from the interaction of a disturbing agent {a beam of energetic elec- trons or a shock wave{ with the ambient plasma (Wild and Smerd, 1972). Radiation is produced near the fundamen- tal of the local plasma frequency f p (kHz) =9 n 1 = 2 e (cm 3 ) and/or its second harmonic through various plasma mech- anisms (see e.g. Robinson, 1997). The observed frequency can be converted into an altitude in the corona, assuming a density model and the radiated mode. Dierent frequency drifts reflect dierent velocities along the density gradient in the corona and interplanetary medium, helping us to charac- terize the nature of the exciter: 0.05-0.3c electron beam for

Solar wind thermal electrons in the ecliptic plane between 1 and 4 AU - Preliminary results from the Ulysses radio receiver

The radio receiver of the Unified Radio and Plasma (URAP) experiment aboard the Ulysses spacecraft records spectra of the quasi-thermal plasma noise. The interpretation of these spectra allows the determination of the total electron density Ne and of the cold (core) electron temperature Tc in the solar wind. A single power law does not fit the variations of Ne which result from the contribution from different solar wind structures. The distribution of the values of Tc suggests that, on the average, the solar wind is nearly isothermal.

Solar type II and type IV radio bursts observed during 1998–2000 with the ARTEMIS-IV radiospectrograph

A catalogue of the type II and type IV solar radio bursts in the 110-687 MHz range, observed with the radio spectrograph ARTEMIS-IV operated by the University of Athens at Thermopylae, Greece from 1998-2000 is presented. These observations are compared with the LASCO archives of Coronal Mass Ejections and the Solar Geophysical Reports of solar flares (Ha & SXR) and examined for possible associations. The main results are: - 68% of the catalogue events were associated with CMEs. - 67% of the type II events were associated with CMEs, in accordance with previous results. This percentage rises to 79% in the case of composite type II/IV events. - 77% of the type IV continua were associated with CMEs, which is higher that the CME-type II association probability. - The type II associated CMEs had an average velocity of (835 ± 380) km s -1 , while the CMEs not associated with type IIs had an average velocity of (500 ± 150) km s -1 . - All events, but one, were well associated with Ha and/or SXR flares. - Most of the CME launch times precede by 5-60 min (30 min on average) the associated SXR flare peak; an important fraction (72%) precede the flare onset as well.

Wind-Ulysses in-situ thermal noise measurements of solar wind electron density and core temperature at solar maximum and minimum

The radio receivers on the Wind and Ulysses spacecraft in the solar wind continuously record spectra of the quasi-thermal plasma noise near the electron plasma frequency, from which the electron density and core temperature can be determined using the method of quasi-thermal noise spectroscopy. Such in-situ thermal noise measurements were obtained by Wind in the in-ecliptic solar wind upstream of the Earth, and by Ulysses during its two pole-to-pole fast latitude scans, in 2000–2001 at solar maximum and in 1994–1995 at solar minimum. We present histograms of these measurements performed over common time spans of several months by the two spacecraft. We compare and discuss these histograms, together with those provided by Ulysses in 1990–1991 at solar maximum, thus extending our study to over a full solar activity cycle. From the resulting distributions, we classify the solar wind flow into distinct populations both in density and temperature. Their variations in number and importance with the solar activity and heliolatitude are also investigated.

Interplanetary fast shock diagnosis with the radio receiver on Ulysses

ABSTRACT The Radio receiver on Ulysses records the quasi-thermal noise which allows a determination of the density and temperature of the cold (core) electrons of the solar wind. Seven interplanetary fast forward or reverse shocks are identified from the density and temperature profiles, together with the magnetic field profile from the Magnetometer experiment. Upstream of the three strongest shocks, bursts of non-thermal waves are observed at the electron plasma frequency f peu. The more perpendicular the shock, the longer is the time interval during which these upstream bursts are observed. For one of the strongest shocks we also observe two kinds of upstream electromagnetic radiation: radiation at 2 f peu , and radiation at the downstream electron plasma frequency, which propagates into the less dense upstream regions.

Correction [to “A shock associated (SA) radio event and related phenomena observed from the base of the solar corona to 1 AU”]

In the paper “A shock-associated (SA) radio event and related phenomena observed from the base of the solar corona to 1 AU” by J.-L. Bougeret, P. Zarka, C. Caroubalos, M. Karlický, Y. Leblanc, D. Maroulis, A. Hillaris, X. Moussas, C. E. Alissandrakis, G. Dumas, and C. Perche, Geophysical Research Letters, 25 [14], 2513-2516, Figure 3 was not printed in its entirety. It is printed correctly below with its caption: