Characteristics of theE_sregion at Brisbane

Abstract

The Es region as recorded on routine h'f records taken at Brisbane (latitude 27°.5 south, longitude 153°.0 east) between June 1943 and December 1949 has been studied. At all seasons the critical frequency is lowest at dawn. In summer months, the critical frequency reaches a maximum at about 10h and then declines gradually, remaining high until after midnight. In winter, the rise is slower and the maximum critical frequency occurs around 14h, dropping markedly by sunset. In general, a high Es critical frequency is accompanied by blanketing of F echoes up to a comparatively high frequency; but, whereas the occurrence of high critical frequencies shows a summer maximum and a winter sub‐maximum, the occurrence of high blanketing frequencies is least frequent in winter. The observations suggest that there are two distinct types of Es common at Brisbane—one formed at greater heights and descending to its final position, the other formed in situ. The first, the predominant type in summer, blankets strongly and has probably a uniform ionization density; but the second, the winter type, blankets little and probably has pronounced lateral irregularities. No evidence of correlation could be found with sunspot numbers, ionospheric storms, or meteor occurrence frequency, and the conclusion is reached that the Brisbane Es is not predominantly of meteor origin. There is some slight evidence of correlation between the constant‐height type of Es and F region diffuseness.

Galactic Radiation at Radio Frequencies. VI. Low Altitude Scintillations of the Discrete Sources

“…It will be seen that, although the form of the three curves is similar, the critical frequency of the echoes is lower in midwinter than midsummer, and the two maxima of the scintillation index curve are about equal. The reason for the difference in the relative heights of the maxima is probably to be found in the seasonal characteristics of the sporadic E. Sporadic E a.t Brisbane has been studied extensively by McNicol and Gipps (1951). They…”

“…(d) Correlation with Sporadic EThe seasonal and diurnal components in the scintillation index suggest an association with sporadic E (seeMcNicol and Gipps 1951). A day-to-day correlation of the two phenomena was examined on the following basis.…”

Metallic ion transport associated with midlatitude intermediate layer development

“…For over 50 years, midlatitude intermediate or descending layers have been observed in the E region by ionosondes [ McNicol and Gipps , 1951; Wakai , 1967]. These layers of plasma form on the bottom side of the F peak and descend over several hours to altitudes near 120 km.…”

The Mean Thickness of Night-time Es Clouds at Brisbane

“…HOSKINGt It has been stated that the sporadic E region of the ionosphere at Brisbane is very thin, with a maximum thickness of the order of a few hundred metres (McNicol and Gipps 1951). The mea~urements reported below indicate that at Brisbane Esc clouds (patches of enhanced ionization in the sporadic E region which maintain an almost constant height) at night are, on the average, almost certainly less than ~ km thick.…”