Lunar Tide in Sporadic E at Brisbane

Abstract

Accurate measurements have b een made at Brisbane of the virtual height of reflection of radio echoes from the E region of the ionosphere, 'using a pulse transmitter operating at 2·28 Mc/s . The recordings were made by using a cathode-ray tube displaying echoes received from virtual heights between 80 and 150 km; black-out modulation of the cathode-ray tube trace was employed so that echoes appeared as gaps in the trace. To avoid the broadening of the gap with increase of echo signal strength, an automatic gain control was used, which kept the peak output within the time interval corresponding to 80-150 km at a fixed level. The gap width then remained fairly constant (about 16 km), and the recorded h eight showed no dependence on (input) signal strength. A stable triggered oscillator was used to produce height marks at 10 km intervals every 6 min on the cathode-ray display. The oscillator was started at full amplitude by a triggering wave synchronized with the transmitter modulation pulse; there was a constant delay of 0·1 km. A typical record is shown in Plate 1.With these precautions it has been possible to take measurements of the virtual h eight of E reflections with an accuracy of ±O· 2 km. It has been found, however, that the levels of both the normal E and sporadic E reflections vary in a random manner with a quasi-period of about 15 min and a most probable amplitude of about i km. This result is to be expected for sporadic E reflections and is now well established for the normal E region. For this reason there is generally little point in making height measurements to any accuracy greater than ±0·5 km. These accurate height measurements lend themselves to lunar tidal analysis. However, at Brisbane the day-timeE region echo at 2·28 Mc/s may (and generally does) consist of a mixture of normal E and sporadic E reflections. Sometimes * Manuscript

Motion in the Night-time Es Region at Brisbane

“…It has been shown in previous papers (Thomas and Svenson 1955;Thomas 1956a) that the two types of Es at Brisbane (" sequential" type (Ess), and " constant-height" type (Esc)) ' show considerable vertical motion of a tidal nature. It is logical to expect large horizontal motions to accompany the vertical movements in the ionosphere.…”

Sporadic E at Brisbane

“…The confinement to a single frequency makes possible a number of subsidiary experiments such as the measurement of the direction of arrival of the downcoming waves (Thomas and McNicol 1955), phase-path measurements, and the measurement of the relative intensity of echoes by the swept-gain technique* (McNicol, Webster, and Bowman 1956).…”