ASPECT ANGLE DEPENDENCE OF THE RADAR AURORA DOPPLER VELOCITY

The aspect angle dependence of the Doppler velocity of radar auroral e choes was studied by means of a comparison between the signals receive d simultaneously on four 50-MHz CW links. In most of the events, the o bserved Doppler velocity decreased with increasing aspect angle but th e rate of decrease was lower than that predicted by linear theory. The velocity decrease was about a factor of 0.4 between geometrical aspec t angles of 1.5 degrees and 4.0 degrees and 0.6 to 0.7 between 3.2 deg rees and 5 degrees. A model for the Doppler velocity behavior of the r adar auroral signals is proposed, combining both propagation and scatt ering effects. Allowance is made for ''ray spreading'' arising from pr ocesses like refraction and diffraction during propagation. In additio n, height integration over the scattering volume is taken into account .