HF observations of the vertical structure of mid-latitude spread-Es

Abstract

The Bribie Island HF radar array (27°S, 153° E) can be set up to make angle of arrival and Doppler shift measurements throughout the range of spread-Es, layers. Results of this experiment show that the range spread seen on ionograms is not due to multiple reflection with varying obliquity, but rather a genuine height spread exists. Where velocity measurements can be reliably made, reflector velocity appears to be a slowly varying function of height. Spread-Es, can be blanketing or non-blanketing, sequential or non-sequential and at first impression it seems that the chief difference between spread-Es, and normal Es, is a small scale, partially transparent structure in lower regions that allows higher regions to be observed. It is suggested that on occasion spread-Es, irregularities are further modulated by the passage of gravity waves. © 1993.