[en] A new magnetic spectrometer is described it is used as part of the experimental equipment of the european satellite GEOS. The spectrometer was developed to measure distribution functions f(E, α, t) for electrons in the energy range 18 KeV < E < 250 KeV and for protons in the energy range 30 KeV < E < 3.3 MeV. Several methods are discussed to measure pitch-angular distributions. The image characteristics of the spectrometer are analysed. Further, the scattering of electrons inside the instrument, the backscattering of electrons from detectors and all relevant background problems are considered. The detectors and the electronic components of the equipment are described in detail. (KBE)

[en] Interaction of energetic electrons (16 - 300 keV) and ELF waves (100 Hz - 3 kHz) has been studied by using data of the GEOS-1 and -2 satellites. In steady-state, it is demonstrated that this interaction enters quite well into the framework of the quasi-linear theory of pitch-angle diffusion. By calculating the wave growth rate at different magnetic latitudes, it is shown that inside the plasmasphere the path integrated gain is large enough for explaining generation of hiss, in agreement with theoretical and experimental results on wave propagation. Outside the plasmasphere hiss generation deserves further study. At the time of storm sudden commencements, non-steady state behavior is observed that results in antiphase oscillations of the maximum of the wave spectrum and of the corresponding growth rate and anisotropy. 53 refs

[en] The detection of polymeric organic compounds in the mass spectrum of Comet Halley obtained with the Positive Ion Cluster Composition analyzer on Giotto are examined. It is found that, in addition to polyoxymethylene, other polymers and complex molecules may exist in the comet. It is suggested that polymerized hydrogen cyanide may be a source for the observed CN and NH2 jets. 31 refs

[en] The distribution of energetic electrons and ions with L-value (L<8) as measured by the Electron-Proton Angle Spectrometer onboard CRRES over the whole mission lifetime is presented. The outer radiation belt is shown to be highly dynamic, both in position and in strength. Substantial enhancements of electron and ion flux on short timescales are seen throughout most of the magnetosphere sampled by CRRES, and are strongly related to the Kp index and the ring current as measured by D_ST. These enhancements decay over less than 30 days. There is evidence of a magnetospheric electron and ion acceleration mechanism of considerable strength and efficiency. Very intense periods of activity can lead to the creation of an additional, high-energy belt in the slot region, which persists over a a period of many months. 11 refs., 1 fig

[en] The distribution of energetic electrons and protons with L-value over the whole CRRES lifetime from July 1990 until October 1991 is presented. Since this distribution shows little variability with MLT it is ideally suited for examining the energetic particle budget over long periods. It shows the region occupied by the outer radiation belt to be very dynamic, both in position and in strength of the inner and outer boundary of the belt, and strongly related to the K_p index, D_ST, SSC close-quote s and the 27 day rotation period of the sun. The position of the inner boundary of the outer radiation belt is variable but fixed for a given period, particle energy and level of activity, while the strength of this belt always decays over a period of ∼30 days after initiation. Overlapping storm-related injections with different inner boundary levels can give rise to a short-lived double-belt appearing. The inner radiation belt is very stable and virtually unaffected by outside disturbances. Very intense periods of activity (such as the March 1991 storm) can lead to the creation of an additional, high energy belt in the slot region, which persists over a period of many months. We examine also the dependance of the behavior on particle energy and pitch angle as measured by the EPAS instrument on CRRES in the outer radiation belt. copyright 1996 American Institute of Physics

[en] Eighteen months of data provided by the magnetometer and energetic particle spectrometer on board the geosynchronous satellite GEOS 2 were used to investigate compressional ULF waves with frequencies of a few megahertz associated with large anticorrelated modulations of the ion pressure. The events are classified into two groups according to the behavior of the background magnetic field/plasma configuration at the onset of the oscillations. For one group the oscillation onset is preceded by a sharp increase of the plasma energy density due to the arrival of drifting ion bunches at the satellite and a corresponding diamagnetic decrease of the magnetic field strength. The other group is observed in a steady configuration in the presence of an enhanced ring current. Besides striking differences between the two groups as regards the average event duration and wave frequency, as well as the phase relation between electron and ion flux modulations, the authors present evidence that both groups of events are of antisymmetric structure with respect to the geomagnetic equator and have a small field-aligned wavelength. Furthermore, for both groups the frequency variation with local time and the azimuthal propagation are closely connected with the ion magnetic gradient curvature drifts, and the waves are associated with a plasma distributed anisotropically in velocity space. Therefore the waves most likely represent the excitation of a single wave mode generated via wave-particle interactions. Using plasma parameters measured in situ the authors calculated the growth rate of different hydromagnetic wave modes. It was found that the plasma is able to support a wave mode similar to the drift mirror mode wtih a large parallel wave number, if the effects of a strongly curved magnetic field are taken into account

[en] Observations by GEOS 1, supported by data collected by IMP 7, IMP 8, and ATS 6 during the July 29, 1977, sudden storm commencement (SSC) have been used to derive the magnetopause's position (7.8R_E before and 6.1 R_E after the SSC), velocity (inward speed of about 95 km/s by two independent methods) and thickness (approx.500 km measured by the change in drift pattern). Particle, field and wave data from GEOS 1 have been used to establish the satellite's position with respect to the magnetopause. After the initial crossing of the magnetopause, the satellite remained in the magnetosheath for most of the interval considered, occasionally encountering what are interpreted as 'open magnetic field lines.' When the spacecraft was in the magnetosheath, duskward plasma flows tangential to the magnetopause are derived from our electric field measurements. The flow velocity was higher during periods when the interplanetary magnetic field assumed a southward component as compared to periods when a northward component was present. On three occasions, an environment was encountered which was neither typical magnetospheric or magnetosheath-like. It is argued that in the instances GEOS 1 either reentered the magnetosphere or encountered a 'magnetic island,' caused by a tearing mode instability at the magnetopause. The electric field dropped to zero or very small values in these instances

[en] Measurements made with the charged particle spectrometer of the Max-Planck-Institut fuer Aeronomie onboard GEOS-1 were used to investigate the behaviour of energetic electrons and ions in the dusk sector of the magnetosphere. During substorms the integral ion flux (> approximately 24 keV) increased whereas the integral electron flux (> approximately 20 keV) first decreased and later on also increased. The dependences of these flux variations on pitch-angle and particle energy are described and discussed in terms of particle drift in the geomagnetic and geoelectric fields and adiabatic energy variations. The results also provide some information on the source region of the drifting particles. (Auth.)

[en] Observations on the satellite GEOS 1 have shown the presence of banded emissions whose frequency spacing is of the order of the local He(+) cyclotron frequency. Above the proton cyclotron frequency, the emissions are electrostatic in character whereas below they are electromagnetic. It is believed that these form the first observations of electrostatic ion cyclotron harmonic waves detected in the earth's magnetosphere beyond approximately 1 earth radius. An investigation of the cold ion population at the times of the observed events indicates that helium ions form a large percentage of the total concentration, and occasionally may entirely dominate the population. Energetic ion distribution functions appear to peak in the energy range less than or equal to 30 keV, and show anisotropic pitch-angle distributions. Preliminary instability calculations using these observations are beginning to yield an insight into a mechanism whereby the waves can be produced

[en] Coordinated observations on board GEOS 2 of energetic particles (20 to 400 keV), plasma particles (300 eV to 20 keV), dc electric fields, and ULF waves (0.2 to 10 Hz) at the geostationary orbit reveal several occasions on which sharp increases in particle flux occurred near 1400 LT without any appreciable energy dispersion for ions at 90 ⁰Z pitch angle. The intensity increases of ions with pitch angles away from 90⁰ preceded those at 90⁰ and showed clear energy dispersion that is consistent with the idea that these particles are injected in the midnight sector and drift toward noon. The global electric field establishes boundaries that particles of given adiabatic invariants cannot penetrate. A change or reversal of the electric field moves these boundaries so as to permit their observation at GEOS 2. Such boundaries seem to be associated with intense ULF waves observed close to the proton gyrofrequency and its harmonics. The waves may be compressional drift waves destabilized by plasma pressure gradients