Multi-satellite scintillations, spread- F and sporadic- E over Brisbane—1

Abstract

Associated amplitude scintillation and vertical-incidence ionosonde data were obtained during a two-year recording period at Brisbane. Scintillations were recorded using radio-satellite transmissions at a frequency of 150 MHz from six U.S. Navy Navigational Satellites (NNSS). It was found that a consistent decrease of scintillations in the morning from 0200 to 0600 LT coincided with an increase in the occurrence and intensity of the frequency spread of spread-F, especially in the southern Winter. A midnight (2200 to 0200 LT) maximum in scintillations coincided with increases of the range spread of spread-F and nocturnal sporadic E( E S), especially in the Summer. A second increase in scintillations was consistently recorded in the afternoon from 1400 to 1800 LT in the Winter, and was associated with a pronounced enhancement in the occurrence and range spread of daytime E S; the occurrence of spread- F was insignificant during this period. The Winter of 1974 was associated with an unusually high occurrence of E S in the afternoon period. Simultaneously, average scintillation index reached its highest level. The diurnal variation in the spatial occurrence pattern of scintillations indicates an equatorwards drift of scintillation patches as the night progresses. Scintillations tended to occur at relatively large zenith angles, especially during the post-midnight hours. The equatorwards drift direction of scintillations is in agreement with the reported movement of ionization patches responsible for spread- F and E S at Brisbane. It appears that the spatial difference in the reflection of ionosonde echoes, associated with the frequency and range spread, is responsible for the varying degree of correlation of scintillations with these two types of spread- F.