Radio emissions from Jupiter and the sun
thesisposted on 2023-05-26, 19:57 authored by Peter McCulloch
Section A. Radio Emissions From Jupiter. The thesis begins with a detailed review of the observed properties of Jupiter's decimetric and decametric radio emissions. It then describes observations of the mean power of Jupiter's emissions at six frequencies in the range 4.7 to 28.0 MHz which were used to prepare histograms of relative power and probability of occurrence at each frequency. The spectral variations of mean flux density and peak flux density were determined and the data at several frequencies examined for the influence of Jupiter's satellite Io. Observations of linear polarisation at 2500 MHz were made to determine the radio rotation period of Jupiter and the configuration of Jupiter's magnetic field. An explanation of the decametric emission was sought in terms of natural emission from energetic charged particles. All emission processes other than Cerenkov and cyclotron radiation were eliminated on general grounds and further close examination of the Cerenkov process showed that it was unable to account for the observed size of the emission region and intensity of the radiation. Analysis shoms that coherent cyclotron radiation can explain in detail the observed properties of the emission. This theory has been used to derive a model of Jupiter's magnetosphere which has a maximum electron density of about 10\\(^6\\)/cc near the surface of Jupiter decreasing to 1500/cc when extrapolated to the orbit of lo. The magnetic field is basically a dipole closely centered on the disc of Jupiter with a polar field strength of about 30 gauss. The dipole axis is tilted 10¬¨‚àû to the rotational axis with the longitude of the north magnetic pole near 200¬¨‚àû system III in February, 1967. Using this model magnetosphere and the cyclotron process a theory has been developed to explain the influence of lo on the radiation. This theory proposes that Io's motion relative to Jupiter's magnetosphere accelerates large numbers of electrons which in turn emit low frequency electromagnetic waves. These waves propagate in the whistler mode towards the lower regions of Jupiter's magnetosphere where they interact with the electron streams by means of the gyroresonant interaction causing them to emit the decametric radiation. Sufficient energy may be transferred from the incoming whistler waves to the electron streams to induce them to emit cyclotron radiation above the local gyrofrequency. When allowance is made for the ray paths and attenuation of these waves the strength of the interaction is sufficient to account for the observed properties of the lo modulation. In particular it accounts for the enhanced emission at the appropriate orientations and longitudes of lo and explains the change in character of individual dynamic spectra with Io's position. Section B. Fine Structure in Solar Radio Emissions. A new type of solar radio burst showing frequency splitting has been observed regularly below 60 MHz. The bursts have a duration of 1 - 2 sec and a frequency interval between their elements of 0.1 - 1.0 MHz. heir wave frequency generally decreases with time at about 0.1 MHz/sec. The bursts may occur either in isolation, in chains associated with type III bursts, or in large numbers during noise storms. Triple splitting is observed in about 10% of the bursts. The properties of the bursts are consistent with those expected from magnetic splitting of the radiation.
Rights statementCopyright 1968 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (PhD) - University of Tasmania, 1970. Includes bibliographies