K. Rinnert

The ROSE project. Scientific objectives and discussion of first results

Abstract The scientific objective of the ROSE (Rocket and Scatter Experiments) project is outlined together with a description of the rocket payload. The launch conditions are explained. Highlights of the results from the in situ as well as from the ground-based experiments are discussed with respect to the E -region plasma instabilities which are investigated.

Plasma waves observed in the auroral E-region—ROSE campaign

Abstract The ROSE campaign 1988/1989 was a combined effort of RO cket and Scatter Experiments to further investigate the dynamics and the structure of the auroral E -region. This paper presents rocket-borne d.c. and a.c. electric field measurements. It concentrates on the evaluation of low frequency fluctuations around 25 Hz which dominated the wave activity at about 100km altitude. A statistical analysis of the observed field structure led to a simplified model wave field. Destabilized plasma waves are assumed to propagate in a cone perpendicular to the Earths magnetic field, according to theory, and grow to a maximum amplitude. Many of such ‘fundamental waves’ randomly distributed in space and time interfere and may create localized ‘wave packets’. The resulting field structure exhibits the observed individual field variations as well as their statistics.

Measurements of radio frequency signals from lightning in Jupiter's atmosphere

During the descent of the Galileo probe through Jupiters atmosphere, the lightning and radio emissions detector (LRD) instrument measured radio frequency signals presumably from electrical discharges in the planets atmosphere. The LRD was the only instrument that provided remote sensing, as well as in situ, measurements of atmospheric characteristics. The LRD measurements are presented here and some estimates are given on the energetics and frequency of occurrence of lightning in Jovian clouds. Propagation calculations of RF discharges in the Jovian atmosphere system and the statistics data obtained by the LRD, together with one very distinct lightning waveform, permit a unified and consistent interpretation of the data. We conclude that at the time of probe entry, Jovian discharges occur with a rate about one hundredth that of the global yearly average on Earth (Earth value is about 6 flashes km−2 yr−1) within about 15,000 km radius of the probe and that the average radiated power is of the order of 5 × 1011 W. The change in the electric dipole moment in Jovian lightning is about 107 coulomb in, roughly 100 times that of a typical terrestrial discharge.

EISCAT results during the ROSE campaign and comparison with STARE measurements

Abstract EISCAT measurements were performed during the four ROSE rocket launches. The results are presented. It is shown that the upper altitude limit of instabilities observed by in-situ measurements agrees with calculations using EISCAT results of drift and ion sound speed and assuming the two-stream-instability mechanism. The EISCAT results together with the STARE observations were used to calculate the ion velocity and the ψ-values from the dispersion relation of two-stream-instabilities. A comparison of EISCAT, STARE and in-situ measurements is discussed.

Radio wave propagation below the Jovian ionosphere

The lightning and radio emission detector (LRD) instrument on board the Galileo probe measured the spectral intensity and other characteristics of radio frequency (RF) signals during descent. The measured spectra show a frequency dependent height profile with a maximum at the beginning of descent around the 1 bar level and a minimum around the 3–6 bar level [Rinnert et al., 1998]. The RF propagation is modeled assuming a source region in the water cloud level between 0 and −25 km altitude, an ionospheric reflector above 300 km, and a primarily absorbing interior below about −2000 km altitude (zero altitude is at 1 bar). This paper shows that the LRD observations can be described by an electrical discharge source at a distance of about 15,000 km; we conclude that no sources existed within the equatorial clouds inside this approximate radius around the probe. We also conclude from the propagation modeling that the measured spectral frequency dependence can be interpreted in terms of a source spectrum that is dominated by low frequencies.

Electric field configuration and plasma parameters in the vicinity of a faint auroral arc

Abstract To study auroral arc physics, coordinated rocket and EISCAT measurements were made across a faint arc. Observed plasma parameters and d.c. electric fields from both methods are discussed. The precipitation event was a moderate one and obviously a localized and temporary disturbance. The electric field configuration in the vicinity of the associated arc measured on board the rocket payload (apogee at 703 km) and deduced from EISCAT measurements of the plasma drift are discussed. The main features of the electric field in the arc region can be explained by polarization fields, but there is also some evidence of field-aligned electric fields.