Dual spacecraft observations of energetic particles in the vicinity of the magnetopause,bow shock,and the interplanetary medium

This article presents some of the new and important particle features that have been detected in the energy range 1 keV to 290 keV by the ISEE-1 and -2 spacecraft near the magnetopause, bow shock, and the interplanetary space. Only examples of data from the first few orbits, when the spacecraft were on the front side, are shown.Paper presented at 13th ESLAB Symposium, Innsbruck, Austria (June 5, 1978).     

A Rader Clutter Model: Average Scattering Coefficients of Land, Snow, and Ice

A model has been developed for average radar backscatter from terrain based on recent carefully controlled wide-bandwidth measurements of vegetation, snow-covered ground, and sea ice and on a comparison with measurements over North America by the Skylab S-193 scatterometer. The models for the thiree cases take the form ?° dB = A + B? + Cf+ Df?, 20° ? angle of incidence ? 70°, where the constants vary depending on polarization and terrain class. They also differ above and below a critical frequency (6 GHz for general terrain, 8 GHz for sea ice, and between 8 and 12 GHz for snow). For angles of incidence of 0° (vertical) and 10°, the model is of the form ?° dB = M(?) + N(?)f over the range 1 to 18 GHz. Hundreds of thousands of measurements contributed to the general (vegetated terrain) model, and smaller numbers contributed to the snow and sea ice models. Since 1974 all measurements have been made with University of Kansas microwave spectrometers. A brief discussion of fading shows that insufficient data are available to describe the ranges adequately.     

Oxygen Isotope Processes and Transfer Reactions

A unique kinetic isotope effect has been found in the formation process of ozone molecules. Isotope enrichments of about 10% above statistically expected values were first discovered in atmospheric isotopomers ⁴⁹O₃ and ⁵⁰O₃ and later in many other molecular combinations. Most recently the source of this effect was identified through measurement of isotope-specific ozone formation rate coefficients which show a large variability of over 50%. Ozone molecule formation is a complex process since different reaction channels contribute to a specific isotopomer. In addition, fast oxygen isotope exchange reactions determine the abundance of atomic oxygen participating in ozone formation. The isotope enrichments observed are both pressure and temperature-dependent and they decrease at pressures above 100 mbar and toward lower temperatures. Ozone possesses not only one of the most unusual isotope anomalies, it also serves as a mediator by transferring heavy oxygen from the O₂ reservoir to other species. Stratospheric isotope composition of CO₂ has been recently measured with high accuracy and a pronounced isotopic signature was found which shows that ¹⁷O is preferentially transferred from O₃ into CO₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

The elemental composition in energetic particle events at high heliospheric latitudes

The relative abundances of low energy ions (0.6–2.0 MeV/n) in solar energetic particle (SEP) and corotating interaction region (CIR) events have been measured by the EPAC experiment aboard Ulysses since launch in October 1990 until the present time. We give an overview of the abundances of heavy ions (He, C, Ne, Fe) relative to oxygen during energetic particle events lasting longer than 5 days during the in- and out-of-ecliptic phase of the mission. While the period Oct. 1990 to Aug. 1992 was dominated by high solar activity the Ulysses out of ecliptic passage at solar latitudes up to 45° went parallel to the declining phase of solar activity. Thus a very clear structure of corotating interaction regions was observed. While the in-ecliptic composition is in general agreement with measurements made near the Earth, the development of the CIR-composition shows two phases: From Aug. 1992 to May 1993 the C/O-ratio is 0.55–0.70, afterwards it increases to 0.8–0.9. This increase is correlated to the disappearance of the current sheet at 30° solar latitude reported by Smithet al. (1993).     

THE DIGITAL WAVE-PROCESSING EXPERIMENT ON CLUSTER

The wide variety of geophysical plasmas that will be investigated by the Cluster mission contain waves with a frequency range from DC to over 100 kHz with both magnetic and electric components. The characteristic duration of these waves extends from a few milliseconds to minutes and a dynamic range of over 90 dB is desired. All of these factors make it essential that the on-board control system for the Wave-Experiment Consortium (WEC) instruments be flexible so as to make effective use of the limited spacecraft resources of power and telemetry-information bandwidth. The Digital Wave Processing Experiment, (DWP), will be flown on Cluster satellites as a component of the WEC. DWP will coordinate WEC measurements as well as perform particle correlations in order to permit the direct study of wave/particle interactions. The DWP instrument employs a novel architecture based on the use of transputers with parallel processing and re-allocatable tasks to provide a high-reliability system. Members of the DWP team are also providing sophisticated electrical ground support equipment, for use during development and testing by the WEC. This is described further in Pedersen et al. (this issue).     

CIR Morphology, Turbulence, Discontinuities, and Energetic Particles

Corotating interaction regions (CIRs) in the middle heliosphere have distinct morphological features and associated patterns of turbulence and energetic particles. This report summarizes current understanding of those features and patterns, discusses how they can vary from case to case and with distance from the Sun and possible causes of those variations, presents an analytical model of the morphological features found in earlier qualitative models and numerical simulations, and identifies aspects of the features and patterns that have yet to be resolved. This revised version was published online in August 2006 with corrections to the Cover Date.     

Martian Seeps and their Relation to Youthful Geothermal Activity

Gullies found on Martian hillsides by Malin and Edgett (2000) appear in many cases to be formed by water seeps produced by underground aquifers. It is proposed that these aquifers result from geologically recent melting of permafrost ice by sporadic, localized geothermal activity. This is consistent with evidence from crater counts and Martian meteorites that much higher-temperature geothermal activity has produced volcanic activity and lava flows within the last 200 Myr, and perhaps within the last 10 Myr. This hypothesis explains an aspect initially described as surprising, namely concentration of the gullies at high latitudes and on shadowed slopes. Similar features are found on Icelandic basaltic hillsides, which may be ideal analogs for further studies that may clarify the Martian phenomena.     

First results from the six-axis electron spectrometer on ISEE-1

A survey, using results from the first 25 orbits of ISEE-1, has been made of some aspects of electrons in the dawn magnetosheath. There are indications that the flow of plasma is not uniformly turbulent over this region. The electron heat flux is observed to be directed away from the shock and to have an average value of about twice the interplanetary heat flux. Many magnetopause crossings were observed and usually resemble abrupt transitions from one well-defined plasma state to another. The ejection of plasma from flux tubes converted up against the magnetopause is observed for about half the time, and its thickness and dependence on the solar wind mach number agree with theoretical predictions. A full traversal of the whole forward hemisphere of the magnetosheath is required to fully confirm these deductions.     

The Lunar Radar Sounder (LRS) Onboard the KAGUYA (SELENE) Spacecraft

The Lunar Radar Sounder (LRS) onboard the KAGUYA (SELENE) spacecraft has successfully performed radar sounder observations of the lunar subsurface structures and passive observations of natural radio and plasma waves from the lunar orbit. After the transfer of the spacecraft into the final lunar orbit and antenna deployment, the operation of LRS started on October 29, 2007. Through the operation until June 10, 2009, 2363 hours worth of radar sounder data and 8961 hours worth of natural radio and plasma wave data have been obtained. It was revealed through radar sounder observations that there are distinct reflectors at a depth of several hundred meters in the nearside maria, which are inferred to be buried regolith layers covered by a basalt layer with a thickness of several hundred meters. Radar sounder data were obtained not only in the nearside maria but also in other regions such as the farside highland region and polar region. LRS also performed passive observations of natural plasma waves associated with interaction processes between the solar wind plasma and the moon, and the natural waves from the Earth, the sun, and Jupiter. Natural radio waves such as auroral kilometric radiation (AKR) with interference patterns caused by the lunar surface reflections, and Jovian hectometric (HOM) emissions were detected. Intense electrostatic plasma waves around 20 kHz were almost always observed at local electron plasma frequency in the solar wind, and the electron density profile, including the lunar wake boundary, was derived along the spacecraft trajectory. Broadband noises below several kHz were frequently observed in the dayside and wake boundary of the moon and it was found that a portion of them consist of bipolar pulses. The datasets obtained by LRS will make contributions for studies on the lunar geology and physical processes of natural radio and plasma wave generation and propagation.