C. C. Harvey

Observation of similar radio signatures at Saturn and Jupiter: Implications for the magnetospheric dynamics

We report on radio signatures observed at Saturn by the Cassini RPWS experiment which are strikingly similar to the Jovian “energetic events” observed by Galileo. They consist of sudden intensifications of the auroral radio emission (SKR) followed by the detection of a periodic narrowband radiation which most likely originates from Saturns plasma disk. About ten “events” have been observed in 2006, showing on average temporal scales ∼3 times longer than their Jovian counterparts. We analyze the conditions of generation and the visibility of the narrowband radiation and conclude that the Kronian “events” are most likely associated with plasma evacuation from the disk. These observations provide new insights on the role of internal energy releases in Saturns magnetosphere, known from other observations to be mainly driven by the solar wind.

Early results from the ISEE electron density experiment

The ISEE-1 and 2 spacecraft contain two complementary experiments to measure the ambient electron density by radio techniques: a propagation experiment which measures the integrated electron density between ISEE-1 and 2, and a resonance sounder which measures the electron density in the vicinity of ISEE-1, and also provides AC electric field data. These experiments have been described elsewhere (Harvey et al., 1978). Results from these two experiments are presented here for the first time. The propagation experiment permits high time resolution studies of density fluctuations in the solar wind and magnetospheric frontier regions. The sounder experiment has detected for the first time plasma resonances in the solar wind and in the Earths magnetosheath, as well as in the regions of the magnetosphere where resonances have already been observed by the spacecraft GEOS-1. We present here a preliminary review of the different types of electric field noise observed in the solar wind and magnetosheath, and discuss their relationship to the measured plasma density.

Solar wind thermal electrons in the ecliptic plane between 1 and 4 AU - Preliminary results from the Ulysses radio receiver

The radio receiver of the Unified Radio and Plasma (URAP) experiment aboard the Ulysses spacecraft records spectra of the quasi-thermal plasma noise. The interpretation of these spectra allows the determination of the total electron density Ne and of the cold (core) electron temperature Tc in the solar wind. A single power law does not fit the variations of Ne which result from the contribution from different solar wind structures. The distribution of the values of Tc suggests that, on the average, the solar wind is nearly isothermal.

Interplanetary fast shock diagnosis with the radio receiver on Ulysses

ABSTRACT The Radio receiver on Ulysses records the quasi-thermal noise which allows a determination of the density and temperature of the cold (core) electrons of the solar wind. Seven interplanetary fast forward or reverse shocks are identified from the density and temperature profiles, together with the magnetic field profile from the Magnetometer experiment. Upstream of the three strongest shocks, bursts of non-thermal waves are observed at the electron plasma frequency f peu. The more perpendicular the shock, the longer is the time interval during which these upstream bursts are observed. For one of the strongest shocks we also observe two kinds of upstream electromagnetic radiation: radiation at 2 f peu , and radiation at the downstream electron plasma frequency, which propagates into the less dense upstream regions.

Density fluctuations measured by ISEE 1-2 in the Earth's magnetosheath and the resultant scattering of radio waves

Radio waves undergo angular scattering when they propagate through a plasma with fluctuating density. We show how the angular scattering coefficient can be calculated as a function of the frequency spectrum of the local density fluctuations. In the Earth’s magnetosheath, the ISEE 1–2 propagation experiment measured the spectral power of the density fluctuations for periods in the range 300 to 1 s, which produce most of the scattering. The resultant local angular scattering coefficient can then be calculated for the first time with realistic density fluctuation spectra, which are neither Gaussian nor power laws. We present results on the variation of the local angular scattering coefficient during two crossings of the dayside magnetosheath, from the quasi-perpendicular bow shock to the magnetopause. For a radio wave at twice the local electron plasma frequency, the scattering coefficient in the major part of the magnetosheath is b(2fp) ≃ 0.5–4 × 10−9 rad2/m. The scattering coefficient is about ten times stronger in a thin sheet (0.1 to IRE) just downstream of the shock ramp, and close to the magnetopause.

Observations of nonlinear turbulence in the upstream solar wind

SummaryPlasma, electric-field and magnetic-field data from several experiments on board the spacecraft ISEE 1 and 2 have been analysed in the interaction region upstream of the Earths bow shock. Upstream waves which are known to be associated with diffuse distributions of backstreaming protons are shown to correlate also with variability in the distribution of the incoming solar-wind protons. Both phenomena are also clearly connected with the presence of enhanced electric-field turbulence. On the basis of these relations, a preliminary discussion can be given of the complex nonlinear plasma processes occurring in the foreshock region.

Virtual observatories for space and solar physics research

As soon as the first data became available online over the Internet, it was obvious that different sites holding related datasets should appear to the end user as a single data system, even if the data itself is stored at multiple locations. To achieve this objective in the context of continuing parallel development of multiple data centres, in 2003 several actors in the realm of space plasmas created the international consortium Space Physics Archive Search and Extract (SPASE). Since 2005 US participation in SPASE has been supported by NASA, and early in 2006 NASA funded five new Virtual Observatories to cater for different aspects of solar system plasma science. This paper outlines the current status of the SPASE effort, the opportunities it offers, its specificities with respect to other parts of the astronomical virtual observatory, and the possibilities it offers for space weather.

Density and field structure of a FTE observed in the magnetosphere

ISEE1 and 2 high resolution electron density and magnetic field measurements have been used to study characteristic structures, identified as FTEs, observed inside the magnetosphere close to the magnetopause. We investigate new properties: a volcano-like signature in the magnetic field strength, a thin sheet structure at the leading edge, and a wake. The plasma compressibility is analysed through the structure. Auto and cross spectral analysis of the data reveal the signature of compressive modes in the wake of the FTE.

SPASE and the Heliophysics Virtual Observatories

The Space Physics Archive Search and Extract (SPASE) project has developed an information model for interoperable access and retrieval of data within the Heliophysics (also known as space and solar physics) science community. The diversity of science data archives within this community has led to the establishment of many virtual observatories to coordinate the data pathways within Heliophysics subdisciplines, such as magnetospheres, waves, radiation belts, etc. The SPASE information model provides a semantic layer and common language for data descriptions so that searches might be made across the whole of the heliophysics data environment, especially through the virtual observatories.