Viscosity waves and thermal-conduction waves as a cause of “specular” reflectors in radar studies of the atmosphere

We present a new theory to explain the cause of the atmospheric structures which are responsible for specular reflection of radar signals from the atmosphere. Evidence recorded with the middle and upper atmosphere (MU) VHF radar at Shigaraki in Japan, as well as previous reports of specular reflections from other radars and at other frequencies, is used to support our assertions. The theory postulates that the reflectors are produced by a form of highly damped wave which arises in a fluid as a result of the effects of viscosity and thermal conduction. They occur at altitudes where gravity waves are partially reflected and in the vicinity of gravity wave critical levels but are particularly prevalent when such reflections and critical level interactions occurs in a laminar region of the atmosphere. The typical scales of the waves, their reflection efficiency, and their likely location are all considered and found to be consistent with what is currently known about specular reflectors in the atmosphere. Some predictions which will allow further tests of the model are also presented.