The aim of this work is to collect and examine information on mid- latitude sporadic-E structure and study its effects on radio echoes from the F-region ionosphere. In general, horizontal structure in ES will affect the phase path of a traversing radio wave causing the F-region echo to appear refracted and diffracted. Data on this effect is collected with a highly directional HF radar, capable of precise angle of arrival and Doppler shift measurements in both the E and F-regions simultaneously. These measurements have been able to provide a quantitative experimental description of the effect.
Theoretical modelling of these experimental results has allowed an evaluation of the mechanisms that can produce horizontal structure in ES. Results show that non-blanketing- ES structure is best modelled by a horizontal variation in wind shear. The variation cannot be caused by a simple linear superposition of gravity waves because the measured variation in shear occurs over a scale which is more than an order of magnitude too small.
Blanketing- ES has little horizontal structure and therefore causes little refraction. The model ling shows that movements of fbES for blanketing- ES are caused by uniform changes in the metallic-ion concentration over a very large area ≥ 104 km2.
The F-region appears very disturbed at times when spread- ES is also present. The echo fades deeply and rapidly and it appears there is structure in the F-region with a scale smaller than a Fresnel zone. It is found that the structure does not actually exist in the F-region but is a refraction effect produced by a small-scale structure found in underlying spread- ES.
The vertical and horizontal structure of spread- ES is further investigated. Spread- ES is shown to have many properties similar to normal ES except that it contains a cluster of small, partially transparent irregularities with a scale size of the order of 1 km or smaller. This structure allows higher, co-existing ES -layers to be s observed thereby producing the range spread seen on ionograms . Measurements of the horizontal structure have shown its properties are consistent with being produced by the gradient instability.
In two examples of non-blanketing spread- ES, the effects of travelling disturbances, possibly gravity waves, are seen to modulate the intensity of spread- ES clusters. Velocity measurements of the clusters show that they are often moving with different and sometimes opposite velocities at adjacent heights.
Several other experiments were designed and run with the radar. These include an attempt to measure ocean backscatter and an attempt to detect partial reflections from ES layers.