Reflection and refraction by tilted layers: An explanation for VHF auroral backscatter at large aspect angles



Auroral structures are often accompanied by tilts to the electron density contours on the underside of the E-region. By including the effects of these tilts on radio wave refraction and reflection it is possible to understand many of the previously puzzling observations of VHF auroral backscatter at large angles away from perpendicularity to the earth's magnetic field. It is shown that many of the characteristics of echoes from the VHF Canadian Bistatic Auroral Radar System (BARS) are consistent with this process. For BARS observations for which the tilt hypothesis is correct, the resulting Doppler velocities can be interpreted in the same way as those from STARE, and used to give electric fields and convection patterns over the BARS field of view.