A. D. Johnstone

The temporal evolution of electron distributions and associated wave activity following substorm injections in the inner magnetosphere

The temporal evolution of electron distributions and associated wave activity following substorm injections in the inner magnetosphere are investigated using data from the CRRES satellite. Equatorial electron distributions and concomitant wave spectra outside the plasmapause on the nightside of the Earth are studied as a function of time since injection determined from the auroral-electrojet index (AE). The electron cyclotron harmonic (ECH) wave amplitudes are shown to be very sensitive to small modeling errors in the location of the magnetic equator. They are best understood at the ECH equator, defined by the local, maximum in the ECH wave activity in the vicinity of the nominal magnetic equator, suggesting that the ECH equator is a better measure of the location of the true equator. Strong ECH and whistler mode wave amplitudes are associated with the injected distributions and at the ECH equator, in the region 6.0 less than or equal to L < 7.0, exponential fits reveal wave amplitude decay time constants of 6.3+/-1.2 and 4.6+/-0.7 hours, respectively. Pancake electron distributions are seen to develop from injected distributions that are nearly isotropic in velocity space and, in this region, are seen to form on a similar timescale of approximately 4 hours suggesting that both wave types are involved in their production. The timescale for pancake production and wave decay is comparable with the average time interval between substorm events so that the wave-particle interactions are almost continually present in this region leading to a continual supply of electrons to power the diffuse aurora. In the region 3.8 less than or equal to L < 6.0 the timescale for wave decay at the ECH equator is 2.3 +/- 0.6 and 1.1 +/- 0.2 hours for ECH waves and whistler mode waves respectively, although the pancakes in this region show no clear evolution as a function of time.

Low energy plasma analyzer

The low energy plasma analyzer (LEPA) that operates in a direct wave-particle mode in which waves (below 30 kHz), measured by separate onboard electric field and wave experiments, and LEPA signals that are directly cross-correlated, is described. LEPA was developed for the Combined Release and Radiation Effects Satellite (CRRES). LEPA is capable of determining the three-dimensional distribution function of electrons and positive ions in this energy range while simultaneously determining the location in the distribution function and the frequency at which coherent wave-particle interactions may be occurring. The LEPA measurement system uses tri-quadrispherical electrostatic analyzers with microchannel plate detectors. >

The AMPTE UKS Three-Dimensional Ion Experiment

This instrument measures the three-dimensional (3-D) distribution function of positive ions at the UKS. Novel electrostatic analyzers using 2600 turning angle cover all viewing angles as the spacecraft rotates. The instrument has sufficient resolution to measure the solar wind as well as giving full 3-D coverage within a spin period. The operation of the experiment and organization of the data are synchronized to the spacecraft spin. A sample of the real-time data showing magnetospheric boundary crossings is presented.

Waves in the magnetic field and solar wind flow outside the bow shock at comet P/Halley

The existence of hydromagnetic waves in the mass-loaded solar wind upstream from the bow shock of a comet is well-established both for comet Giacobini-Zinner and for comet Halley. Whereas previous reports have been concerned either with the magnetic field observations or with plasma observations, here we combine observations of the magnetic field with the solar wind proton and alpha particle distributions. This allows the three possible modes of propagation for these waves to be separated. The magnetic component is predominantly transverse to the magnetic field and linearly polarised. The flow vector also has a substantial amount of power parallel to the magnetic field. A examination of the pressure variations shows that slow magnetosonic waves are more common than the fast mode.

Ionospheric Photoelectrons Observed in the Magnetosphere at Distances up to 7 Earth Radii

Abstract Photoelectrons of ionospheric origin have been observed for the first time at high altitudes (up to 7RE geocentric distance) using the suprathermal plasma analysers (SPA) on the GEOS satellites. At such high altitudes the photoelectron flux is confined within a few degrees of the magnetic field direction. We show how this flux may be identified and extracted from the background which is a combination of locally produced photoelectrons and ambient plasma. GEOS-2 results are presented to illustrate the “turn-on” of the photoelectron flux at dawn in the ionosphere. Data from GEOS-1 are used to study the behaviour of the photoelectron flux with equatorial geocentric distance from 3 to 7RE. The results compare favourably with theoretical models and with ionospheric observations at mid latitudes.

Pickup water group ions at comet Grigg-Skjellerup

The density and velocity distribution of cometary water group ions was measured by the Giotto spacecraft in the regions upstream and downstream of the ‘bow shock’ at comet Grigg-Skjellerup. The results show that the distributions of ions are ring-like until quite close to the shock, the timescales for pitch angle and energy diffusion appear similar and the ion density follows a r−2 dependence.

Beagle 2: A proposed exobiology lander for ESA's 2003 Mars Express mission

Abstract The aim of the proposed Beagle 2 small lander for ESAs 2003 Mars Express mission is to search for organic material on and below the surface of Mars and to study the inorganic chemistry and mineralogy of the landing site. The lander will have a total mass of 60kg including entry, descent, and landing system. Experiments will be deployed on the surface using a robotic arm. It will use a mechanical mole and grinder to obtain samples from below the surface, under rocks, and inside rocks. Sample analysis by a mass spectrometer will include isotopic analysis. An optical microscope, an X- ray spectrometer and a Mossbauer spectrometer will conduct in-situ rock studies.

The outer radiation belt during the 10 january, 1997 CME event

On 10 January 1997 a magnetic cloud of a coronal mass ejection impinged upon the earth magnetosphere and caused considerable variations of the relativistic electron population in the earths outer radiation belt in the following days. Data obtained with radiation detectors on board a pair of satellites, STRV-1a and STRV-1b in a nearly equatorial geostationary transfer orbit show that the electron flux variations during the days following the arrival of the magnetic cloud can be characterized by four phases during which the fluxes alternatingly decreased and increased. The close relation between flux and Dst variations suggest the magnetic field variations in the inner magnetosphere to play an important role. However, the observed injection of electrons into the trapping region in the morning of 10 January seems to be crucial for the large electron flux enhancement during the afternoon of 10 January.

Bifurcated cusp ion signatures: Evidence for re‐reconnection?

Toroidal Imaging Mass-Angle Spectrograph (TIMAS) ion composition measurements during a pass of the POLAR spacecraft through the Earths magnetospheric cusp show a bifurcated ion signature. High energy (several keV/e) solar wind ions are observed simultaneously with a low energy (up to several hundred eV/e) component. The high energy component exhibits an energy-latitude dispersion consistent with magnetic reconnection at the dayside magnetopause and velocity filtering in the cusp. The low energy component exhibits no such dispersion. Simultaneous observations of the solar wind ion composition from the WIND spacecraft indicate that the high and low energy components in the cusp have a higher He2+/H+ density ratio than that in the solar wind. Additional solar wind data show that the IMF was southward and the solar wind plasma and magnetic field were relatively steady. These POLAR and WIND observations are interpreted as evidence for continuous re-reconnection of magnetospheric field lines that thread the high latitude cusp.

Cometary ion pickup processes: Halley and Grigg-Skjellerup compared

Abstract After Giottos encounters with two comets of quite different gas production rates we attempt to compare the results to see:- 1. a) to what extent theories which fitted the results at Halley could be applied to the much smaller Grigg-Skjellerup; 2. b) whether the different relationship between the various scale lengths involved created any observable effects.