Radar studies of small-scale e-region plasma irregularities.
thesisposted on 19.11.2015, 09:18 by Paul. Eglitis
Coherent scatter radars are extensively employed in the study of important geophysical processes in the Earth's upper atmosphere and magnetosphere. The science relies on the ability of coherent scatter radars to detect plasma irregularities in the Earth's ionosphere and relate their properties to the geophysical process under consideration. This thesis is concerned with the physical characteristics of the plasma irregularities deduced from coherent scatter radar observations. Data from three coherent scatter radar systems, PACE, SABRE and COSCAT, each sensitive to a different irregularity wavelength, are analysed. Statistics for the backscatter power, phase speed and spectral width at each wavelength are calculated and compared. Furthermore, the functional dependence of the irregularity parameters on each other has been investigated. Strong relationships between the spectral width and irregularity phase speed and the spectral width and backscatter power are identified. The spectral widths tend to exhibit a minimum at phase speeds close to the ion-acoustic speed. There is a decrease in the average backscatter power as the spectral width increases. A new measurement of the dependence of the spectral width on the irregularity wave number is deduced. These results have important significance for the general interpretation of coherent scatter radar measurements. Special experimental campaigns with SABRE and COSCAT in conjunction with EISCAT have been undertaken to enable the irregularity phase speed and the plasma drift speed to be compared. This is a very important relationship since the plasma drift speed is routinely estimated from the irregularity phase speed. The analysis confirms the non-linear behaviour of the relationship between these two parameters. Similar results are obtained for COSCAT and SABRE. Differences can be attributed to the expected variations with wave number and to variations in the height of the observed irregularities, consistent with the kinetic theory of Robinson and Honary (1990).