Using Simulations to Quantify High-Latitude Type-I Radar Backscatter Spectra as a Function of Flow Angle
Abstract:Observations of high-latitude ionospheric E-region turbulence with meter-scale irregularities are caused by the Farley-Buneman instability, also called the modified two-stream instability. In general, turbulence produces a complex spectrum of waves, and radars with wavelengths in the few-meter range can detect such irregularities when there is a component of the spectrum that is aligned with the radar line-of-sight (LoS) and has wavelength equal to half the radar wavelength. The angle between the radar LoS and the direction of electron ExB drift is called the flow angle. Previous studies have attempted to quantify the spectral width of backscattered power as a function of flow angle, but those studies required many simplifications and assumptions, including significant spatial and temporal averaging, to arrive at their results.
We have performed fully kinetic particle-in-cell plasma simulations with parameters typical of the E-region auroral ionosphere at multiple altitudes and with a range of driving electric fields, in order to quantify the expected relationship between backscattered power and flow angle. These simulations also show the relationship between spectral width and flow angle, a frequently measured relationship. We compare spectral widths from 2-D simulations to 3-D ones in order to assess the usefulness of 2-D results. Our results can be compared to existing measurements and used to design future radar experiments at auroral latitudes.