
TY  - JOUR
A1  - Singleton, DG 
T1  - A Study of "Spread?F" Ionospheric Echoes at Night at Brisbane. III. Frequency Spreading
JF  - Australian Journal of Physics
JO  - Aust. J.  Phys.
Y1  - 1957
VL  - 10
IS  - 1
SP  - 60
EP  - 76
KW  - 
UR  - https://doi.org/10.1071/PH570060 
N2  - Virtual range versus frequency (P'f) records of the ionosphere made at Brisbane (lat. 27·5 °S., long. 152·9 °E.) during 1952 and 1953 have been examined. It is found that occasionally neither the o nor the x mode of propagation penetrates the F2 layer at a unique frequency, the upward sweeping traces either being blurred out over a range of penetration frequencies (diffuseness) or possessing a fine structure (penetration-frequency multiplicity). Temporal analysis of the occurrence of these. effects reveals that they occur only at night; penetration-frequency multiplicity appearing more frequently in the hours before dawn, while the diurnal distribution of diffuseness has a maximum between 0100 and 0500 hr in summer and represents a more even distribution between 2100 and 0500 hr in winter. The seasonal distribution has a pronounced peak in the winter months and minima in the equinoctial months. These data are compared with the world-wide picture of these variations as it has emerged from the recent literature. 
ER  -

