The shape of midlatitude scintillation irregularities

Scintillation measurements of the 150 MHz NNSS beacon satellites at two midlatitude locations spaced approximately 400 km east-west revealed that as the east-west zenith angle increased the scintillation index decreased. The explanation of this observation is that the F region irregularities are in the form of (approximately) north-south magnetically field aligned sheets. The likely formation mechanism of the irregularities probably involves the Perkins instability.