Characteristics Of Large Aspect Angle Vhf Radar Echoes In The Presence And Absence Of Optical Aurora
Date of Award
1990
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
For many years, researchers have been puzzled by the occurrence of strong, large aspect angle radar auroral echoes. Strong aspect sensitivities of up to 10 dB per degree have been observed at small aspect angles while large aspect angle measurements show much weaker and highly variable aspect sensitivities. It is the purpose of this thesis to attempt to understand the different results at the large aspect angles.;For this study, data from the radars and optical instruments of the CANOPUS ground based system in central Canada have been examined. The two radars (the BARS radars) operate at VHF (48.5 MHz) and have large aspect angles. A statistical study of the spatial relationship between the radar echoes and the optical aurora during 13 hours was performed. Also, data from the radar during daylight periods were examined for evidence of aspect sensitivity.;The most noticeable observation of the statistical study was that there was a strong tendency for the radar echoes to occur on the side of the optical aurora remote from the radar. This results is shown to be consistent with refraction reducing the apparently large aspect angles.;For the daylight periods, a self-consistent study found an aspect sensitivity which varied from 8 dB per degree at an aspect angle of 4.5{dollar}\sp\circ{dollar} down to about 4 dB per degree at an aspect angle of 6{dollar}\sp\circ{dollar}. These aspect sensitivities are in agreement with experiments at small aspect angles and higher frequencies.;This study has found two strikingly different kinds of large aspect angle echoes. The strongest echoes occurred on the remote side of optical features and generally had strong echo powers and strong echo power dependence on flow angle. The other type of echoes were the actual large aspect angle echoes which had moderate to weak powers and weak or non-existent flow angle dependence.
Recommended Citation
Hall, Gregory E., "Characteristics Of Large Aspect Angle Vhf Radar Echoes In The Presence And Absence Of Optical Aurora" (1990). Digitized Theses. 1989.
https://ir.lib.uwo.ca/digitizedtheses/1989