E.C Butcher

Wavelike variations in the F-region in the path of totality of the eclipseb of 23 October 1976

Abstract In this paper we present the results of accurate group height measurements of the ionosphere which were taken in the path of totality of a solar eclipse. A strong oscillation of period near 30–35 min was observed in the F -region about 17 min after totality occurred at the 45 km level and a smaller amplitude wave of period near 15 min appeared after the longer period wave had died away. These waves appear to be associated with the eclipse and a tentative model is proposed that explains these periods and the periods reported for the 1973 West African eclipse.

A simple sounder to measure the properties of ionospherically reflected radio waves

Abstract A system which measures the direction of arrival, amplitude, group path and phase path of high frequency radio waves reflected from the ionosphere is described. A CW double sideband modulated signal was used and the measurements were made over a slightly oblique path. Comparisons between the group height determined using this ionospheric sounder and an ionosonde located near the midpoint of the transmission are given and results of fast fluctuations in the measurements are presented.

The effect of travelling ionospheric disturbances on the group path, phase path, amplitude and direction of arrival of radio waves reflected from the ionosphere

Abstract A fixed frequency amplitude modulated transmission was reflected from the ionosphere and changes in the group path, phase path, signal amplitude and directions of arrival of this transmission caused by travelling ionospheric disturbances were measured. These measurements enabled approximate determinations of the horizontal wavelength, period and horizontal phase velocity of the disturbances, which were compared with the theory of disturbances for atmospheric waves. A simple model is proposed to explain the phase relationships between the TIDs observed in the group and phase paths, and the faster decrease in power of the phase path than the other measured parameters indicated by spectral analysis.

The measurement of the lunar tide in the group height of the E-region on several frequencies

Abstract Digital measurements of the group delay mode on six frequencies reflected from the E-region have been analyzed to render a lunar semi-diurnal tidal variation for several months in the Summer of 1971. All the tides determined have a similar phase, the maximum occurring around 0400–0500 lunar hours, but their amplitudes vary between 0.2 and 0.9 km. It is shown that these results are consistent with the original redistribution theory proposed by Martyn (1947).

Scattering from F.region irregularities at 4.5 and 7.5 MHz

Abstract This paper reports observations which clearly show that at mid-latitudes scattering byF-region irregularities can be an important propagation mode at HF. Rate of change of phase path (Doppler Shift) measurements of CW signals on 4.5 and 7.5 MHz were recorded over a nearly vertical incidence path (transmitter and receiver separated by 40 km) and an ionosonde was operated nearby. Signals from the CW transmitters were received via the ionosphere even when the F-region critical frequency was less than 4.5 MHz so that the ionosphere could not reflect either 4.5 or 7.5 MHz signals in the normal way. The Doppler records showed that at these times an unusually large number of signals with a wide range of Doppler shifts was being received. The characteristics of the signals indicates that they are due to scattering by F-region irregularities nearly overhead rather than large off-angle F-region reflections or reflections from sporadic-E. This scattering phenomena has been observed on frequencies above the critical frequency when there was no spread-F on the ionograms but it is also observed on frequencies less than the critical frequency when spread-F is present. References

Direction of arrival of radio waves reflected from the E-region

Abstract A simple system for measuring the direction of arrival of continuous high frequency radio waves reflected obliquely from the ionosphere is described. Results obtained over a near vertical path are used to evaluate changes in the electron density gradients (tilts) in the E-region. Wave interference on the transmission due to multiple hop or ground wave propagation is discussed.

DISTORTION OF THE E-REGION BY THE Sq CURRENT SYSTEM.

The amount of distortion of the E-region electron density at the magnetic equator caused by the Sq current system has been computed using measured electron density and current density profiles. It is found that the distortion is quite significant and is dependent on the α(z) profile taken. The results obtained are used to explain other measurements on the E-region affected by Sq.

Distortion measurements on the E-region using group and phase height measurements

Abstract In this paper we consider the effect of distortions in the electron density profile of the E -region caused by the lunar and regular solar (S R ) ionospheric currents, on the group and phase heights of radio waves reflected in the E -region. A simple model is proposed to predict the amplitude variation and phase of the variations in group and phase height. Phase height results obtained at equivalent vertical frequencies of 1.8 and 2.4 MHz are presented and with previously obtained group height results are shown to be in agreement with the model.

Measurements of the distortion effect of the Sq current on the E-region

Abstract Digital measurements of group height have been made on several frequencies to investigate the distortion of the E -region by the Sq current system. The sign of the distortion in the group height was found to change with frequency although no change of sign occurred when the data was reduced to true height data. It is shown that the results are consistent with those predicted by the redistribution theory for an east-west current. It is noted that although over Melbourne the Sq current is east-west, the current associated with the lunar semi-diurnal tide is west-east ( Rodgers and Butcher , 1976), a fact that may explain the difference in the group height distortion with frequency caused by the two currents.

Effective electron collision frequency measurements in the E- and F-regions

Abstract The collision frequency v in the ionosphere has often been determined by measuring differences in the amplitude and group path of two closely spaced signals reflected in the region of high group retardation. In this paper we describe a method of measuring v using a CW double-side-band modulated signal reflected obliquely in the ionosphere. This allows v to be determined on a continuous basis and it is found that the value of v obtained is 1–5 × 10 4 s −1 for the E -region and ~ 10 3 s −1 for the F -region. It is shown that measurements made just after sunset, when the E -region is still present, are more representative of E -region values than F -region.