Morphological and ionospheric aspects of quasiperiodic scintillations

Abstract

Mult́i-satellite scintillations, at a transmission frequency of 150 MHz, and associated vertical-incidence ionosonde data were recorded at Brisbane from November 1973–January 1976. A distinct type of regular amplitude fadings, so-called quasiperiodic (QP) scintillations, was most frequently recorded in a time interval: 2200 to 0200 LT in the southern summer, and to a lesser extent in autumn. The maximum in the occurrence number of QP scintillations coincided with the largest simultaneous increases in the intensities of nocturnal sporadic- E ( Es) and spread- F. QP scintillations were rarely recorded in winter at the time of pronounced Es activity. The majority of QP scintillations occurred at zenith angles in excess of 70°, and at north-west azimuth angles centered on 330°. The azimuth preference in the occurrence of QP scintillations is similar to the prevailing north-west direction of arrival of ionospheric reflections at Brisbane. It appears that the generation of these scintillations is associated with the frontal structure of irregularities responsible for spread- F and Es in southern midlatitudes.