Aspect angle dependence of backscatter intensity of 1‐m auroral plasma waves

Abstract

The backscatter intensities of primary and secondary 1‐m unstable plasma waves in the auroral E region have been measured as a function of magnetic aspect angle (α) for electric field values between 25 and 30 mV/m. The variation of the absorption A, measured in decibels, is of the form A = −IaCo cos² α/(1 + Co cos² α). The best fits to the observed attenuation yield parameter values of (Ia, Co) = (49.6, 530) and (48.8, 900) for primary and secondary waves, respectively. The backscatter intensity from primary waves has the same aspect angle dependence as the mean Doppler velocity aspect angle dependence observed in previous auroral radar data sets (Nielsen, 1986). The observations suggest that the radar backscatter cross section of the primary waves maximizes a few kilometers higher in altitude than that of the secondary waves.