Imaging coherent scatter radar studies of midlatitude E-region ionospheric irregularities

*D. L. Hysell[1] ,M. Yamamoto [1],S. Fukao [1]
Radio Science Center for Space and Atmosphere, Kyoto University[1]

Coherent backscatter from midlatitude E-region plasma irregularities in the form of quasiperiodic (QP) echoes was observed by the middle and upper (MU) atmosphere radar and by the Clemson 30 MHz radar. Interferometry with multiple spatial baselines was performed, permitting the computation of images of the scatterers in the illuminated scattering volume. The images reveal the morphology and dynamics of the scatterers. A computational model shows how large polarization electric fields arise in irregular sporadic E layers. These fields can drive the gradient drift and Farley-Buneman instabilities which generate the small-scale irregularities responsible for coherent scatter.

Coherent backscatter from midlatitude E region plasma rregularities in the form of quasiperiodic (QP) echoes were observed by the middle and upper (MU) atmosphere radar located at Shigaraki, Japan, and by the Clemson 30 MHz radar in South Carolina, USA. A new imaging mode which utilizes interferometry with multiple antenna baselines was employed for the observations. Data were recorded from 11 and 9 independent baselines at the MU and Clemson radars, respectively, and images were constructed using statistical inverse theory and regularization techniques. The mode reveals the morphology of the scatterers within the radar beam as a function of range, azimuth, elevation, and Doppler frequency. Animated sequences of images illustrate how the scatterers underlying the QP echo phenomenon evolve and traverse the radar beam over time. The behavior and morphology of the scatterers, which are spatially localized rather than beam filling and which evidently exist in regions of strong, localized polarization electric fields, are analyzed and interpreted in terms of gradient drift and Farley-Buneman instability theory. A static model of the midlatitude ionosphere which includes E/F region coupling predicts the polarization of large polarization electric fields in irregular sporadic E ionization layers and may explain some characteristics of the radar images.