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).     

Signatures of Coronal Hole Spectra Between 660 Å and 1460 Å Measured with Sumer on Soho

Spectra of the northern polar coronal hole measured with the SUMER spectrometer on SOHO on 25 October 1996 are analyzed. We present spectra taken at locations on the solar disk where part of the spectrometer slit intersects a polar coronal hole region and an area of brighter emission from outside of the coronal hole area. By comparing the line intensities between the parts of the spectrum taken inside the "dark" area of the coronal holes and the brighter regions, we work out the signatures of the specific coronal hole in the chromosphere, transition region and lower corona. We find that emissions of neutral atom lines, of which there are many in the spectrum of SUMER, show no difference between the coronal hole and the bright boundary areas, whereas all ionized species show strong intensity enhancements, including the continuum emissions of carbon and hydrogen. These enhancements are larger than in normal quiet Sun areas. This revised version was published online in June 2006 with corrections to the Cover Date.     

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.     

Joint Ulysses and ACE observations of a magnetic cloud and the associated solar energetic particle event

On day 49 of 1999 a strong interplanetary shock was observed by the ACE spacecraft located at 1 AU from the Sun. This shock was followed 10 hours later by a magnetic cloud (MC). A large solar energetic particle (SEP) event was observed in association with the arrival of the shock and the MC at ACE. The Ulysses spacecraft, located at 22° S heliolatitude and nearly the same ecliptic longitude as ACE, observed a large SEP event beginning on day 54 that peaked with the arrival of a solar wind and magnetic field disturbance on day 61. A magnetic cloud was observed by Ulysses on days 63–64. We suggest a scenario in which both spacecraft intercepted the same MC, although sampling different regions of it. We describe the effects that the MC produced on the streaming of energetic particles at both spacecraft. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Combustion modeling in a model combustor

The flow-field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was numerically studied.Results obtained from four combustion models,combined with the re-normalization group(RNG) k-ε turbulence model,discrete ordinates radiation model and enhanced wall treatment are presented and discussed.The results are compared with a comprehensive database obtained from a series of experimental measurements.The flow patterns and the recirculation zone length in the combustion chamber are accurately predicted,and the mean axial velocities are in fairly good agreement with the experimental data,particularly at downstream sections for all four combustion models.The mean temperature profiles are captured fairly well by the eddy dissipation(EDS),probability density function(PDF),and laminar flamelet combustion models.However,the EDS-finite-rate combustion model fails to provide an acceptable temperature field.In general,the flamelet model illustrates little superiority over the PDF model,and to some extent the PDF model shows better performance than the EDS model.      

The THEMIS Digital Fields Board

The Digital Fields Board (DFB) performs the data acquisition and signal processing for the Electric Fields Instrument and Search Coil Magnetometer on each of the THEMIS (Time History of Events and Macroscale Interactions during Substorms) satellites. The processing is highly flexible and low-power (～1.1 watt orbit-averaged). The primary data products are time series waveforms and wave power spectra of the electric and magnetic fields. The power spectra can be computed either on the raw signals (i.e. in a system co-rotating with the spacecraft) or in a coordinate system aligned with the local DC magnetic field. Other data products include spectral power from multiple passbands (filter banks) and electric power in the 30–500 kHz band. The DFBs on all five spacecraft have been turned on and checked out in-flight, and are functioning as designed.     

Composition and Measurement of Charged Atmospheric Clusters

Atmospheric charged clusters are formed in a series of rapid chemical reactions after ionisation, leaving a central ion X⁺ or X^? clustered with n ligands (Y) _n . In solar system tropospheres and stratospheres there are two distinct cluster regimes: the terrestrial planets contain largely hydrated clusters (i.e. Y=H₂O), whereas the gas planets and their moons have organic or nitrogenated cluster species. These classifications are largely based on model predictions, since hardly any measurements are available. The few existing composition measurements are reviewed, including the recent detection of massive charged particles in Titan’s upper atmosphere. Technologies for both remote sensing and in situ measurements of atmospheric charged clusters are discussed. Preliminary measurements in the terrestrial atmosphere are presented indicating that ambient charged cluster species interact with downwelling infra-red radiation at 9.15 μm, even in the presence of cloud. This supports the possibility of future infrared detection of charged clusters.