Vhf Imaging Radar Observations And Theory Of Banded Midlatitude Sporadic E Ionization Layers

Observations of backscatter from field-aligned plasma density irregularities in sporadic E (E-s) layers made with a 30-MHz coherent scatter radar imager in Ithaca, New York are presented and analyzed. The volume probed by the radar lies at approximately 54 degrees geomagnetic latitude, under the midlatitude trough and at the extreme northern edge of the zone where E-s layers are prevalent. Nonetheless, the irregularities exhibit many of the characteristics of quasiperiodic echoes observed commonly at lower middle latitudes. These include a tendency to occur in elongated bands stretching from the northwest to southeast in the Northern hemisphere separated by tens of kilometers and propagating to the southwest. In addition, the irregularities were found to exhibit finer-scale structures with secondary bands oriented nearly normally to the primary bands. We investigate the proposition that the primary bands are telltale of E-s-layer structuring caused by neutral Kelvin Helmholtz (KH) instability in the lower thermosphere and that the secondary bands signify secondary KH instability. Results from a 3D numerical simulation of KH support this proposition.