The temperature of the ionosphere in the auroral zone

In the absence of man-made interference and atmospherics, it has been found possible to measure radio frequency thermal radiation from the ionosphere at medium frequencies. The temperature of the ionospheric D-region has been previously measured by this method at 2 Mc/s in temperate latitudes (Pawsey, McCreddy and Gardner, 1951, and Gardner, 1954). In a companion paper (Gardner and Pawsey, 1953), the absorbing structure of the lower ionosphere was determined from D-region echoes to find the heights to which the temperatures applied. However, it was felt that conditions might be very different in an auroral zone. Echoes from the D6-region (apparently) of much greater intensity and at only half the height of those observed by the above authors, were reported at Macquarie Island which is close to the centre of the auroral zone. Experiments were carried out by the author at the Australian National Antarctic Research Station at Macquarie Island as a member of the 1956 party. The apparent D-region echoes mentioned above were found to be not from the ionosphere, however, but from sea waves (Dowden, 1957). This thesis describes radio noise experiments at a number of medium frequencies carried out at a site twenty miles from the Main Station where interference was negligible. This thesis is divided into two parts. The first part describes observations of high accuracy at 2 Mc/s using a half wave dipole aerial to provide a direct comparison with Gardner's (1954) observations in a temperate latitude (300 0. The second part describes observations of lower accuracy at a number of frequencies (7 Mc/s., 5.6 Mc/s., 2.0 Mc/s. and 450 Kc/s.), using a terminated \long wire\" aerial."