Incoherent scattering of radar waves in the auroral ionosphere

Abstract

We have systematically studied the effects that non‐Maxwellian ion velocity distributions produce on the ionic part of the spectrum of radar waves incoherently scattered from the disturbed high‐latitude ionosphere in the upper E and lower F regions. For ion to electron temperature ratios smaller than or equal to unity and electric field strengths greater than about 70 mV/m the spectrum is seriously distorted from the shape that it would normally have if the ion velocity distribution were Maxwellian. In events where the magnetospheric convection electric field exceeds 70 mV/m the interpretation of the data is affected if the erroneous assumption of a Maxwellian distribution is used to analyze the data. The electron temperature is the property most seriously affected by the erroneous interpretation, as it can be underestimated by as much as a factor of 2. Finally, the spectra obtained under disturbed conditions are anisotropic, the least distortions from a Maxwellian‐type spectrum being found along the magnetic field direction. The apparent ion temperature seen along the line of sight of the radar as it scans from parallel to the magnetic field to nearly perpendicular to the magnetic field also increases as the angle with the magnetic field increases, even for dc electric field strengths as small as 20 mV/m.