Imaging coherent backscatter radar studies of equatorial spread F

A new interferometric imaging technique has been used at Jicamarca to study the morphology and dynamics of plasma irregularities occurring during spread F conditions. The technique produces two-dimensional, in-beam images of the coherent scatter from these irregularities, instantaneously mapping the structure of the underlying plasma instabilities in the equatorial plane. We present sequences of images depicting backscatter from bottom-type layers, bottomside layers, and topside plumes drifting and rising through the ionospheric regions illuminated by the Jicamarca radar. The high spatial and temporal resolution of the images permits us to observe dynamical phenomena missed by conventional fixed- and steered-beam techniques. The new images show evidence of intermediate- and large-scale plasma depletions bifurcating and pinching off from the bottomside as they ascend. Analytic models are presented to describe these dynamical effects. The images also differentiate between bottom-type and bottomside spread F layers, the former being shown to have much smaller scale primary waves than the latter. Ample evidence of secondary plasma instabilities appear throughout the images. The consequences of these secondary instabilities and of shear flow are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.