Abstract
Abstract. Voyager spacecraft measurements of Saturn kilometric radiation (SKR) identified two features of these radio emissions: that they pulse at a period close to the planetary rotation period, and that the emitted intensity is correlated with the solar wind dynamic pressure (Desch and Kaiser, 1981; Desch, 1982; Desch and Rucker, 1983). In this study the inter-relation between the intensity and the pulsing of the SKR is analysed using Cassini spacecraft measurements of the interplanetary medium and SKR over the interval encompassing Cassini's approach to Saturn, and the first extended orbit. Cassini Plasma Spectrometer ion data were only available for a subset of the dates of interest, so the interplanetary conditions were studied primarily using the near-continuously available magnetic field data, augmented by the ion moment data when available. Intense SKR bursts were identified when solar wind compressions arrived at Saturn. The intensity of subsequent emissions detected by Cassini during the compression intervals was variable, sometimes remaining intense for several planetary rotations, sometimes dimming and rarely disappearing. The timings of the initial intense SKR peaks were sometimes independent of the long-term pulsing behaviour identified in the SKR data. Overall, however, the pulsing of the SKR peaks during the disturbed intervals was not significantly altered relative to that during non-compression intervals.
Highlights
In 1980 the Voyager spacecraft made the first detections of kilometre wavelength radiation from Saturn (Kaiser et al, 1980)
Voyager spacecraft measurements of Saturn kilometric radiation (SKR) identified two features of these radio emissions: that they pulse at a period close to the planetary rotation period, and that the emitted intensity is correlated with the solar wind dynamic pressure (Desch and Kaiser, 1981; Desch, 1982; Desch and Rucker, 1983)
These Saturn kilometric radiation (SKR) emissions cover a broad frequency range from a few kHz to ∼1200 kHz, with a spectral peak at ∼100–400 kHz. They are believed to be generated by the cyclotron maser instability (CMI) mechanism, first proposed to explain terrestrial auroral radio emissions by Wu and Lee (1979), whereby the radio wave is excited by energy lost from electrons on auroral field lines
Summary
In 1980 the Voyager spacecraft made the first detections of kilometre wavelength radiation from Saturn (Kaiser et al, 1980). (The RTN coordinate system is a righthanded spherical polar system referenced to the Sun’s spin axis, with BR directed radially outward from the Sun, BT azimuthal in the direction of solar rotation, and BN normal to the other two components, that is, positive northwards from the equatorial plane.) When solar wind dynamic pressure data were available from CAPS they have been analysed and found to show an excellent correspondence with the signatures of compression regions identified in the IMF measurements One example demonstrating this correspondence during the post-SOI interval will be presented in Sect. A summary of the features of all thirteen events is discussed
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