ON THE REALITY OF UPPER MESOSPHERIC LOWER THERMOSPHERIC TURBULENT EDDIES

The structure of atmospheric turbulence and its relationship to the re fractive index discontinuities responsible for the scattering of radio waves are discussed. Emphasis is placed more on the nature of the int ermittent scatterers observed at upper mesospheric/lower thermospheric altitudes than on volume scattering. The preferred model is of transi ent patches composed of vortex strings. An overview of the methods use d to estimate the rate of dissipation of turbulent energy using MF rad ar data which emphasizes the advantages of imaging Doppler interferome try is presented, together with a review of pertinent laboratory inves tigations of coherent structures. An attempt is made to remove the con tamination by gravity waves from imaging Doppler interferometry fluctu ating velocity data. Emphasis is given to the fact that all radar meas urements of turbulent intensity to date are upper estimates, not only because of the presence of gravity wave fluctuations contaminating the data, but also because the turbulence itself is not stationary and ho mogeneous but intermittent in both space and time. The intermittent na ture of the turbulence, in which the refractive index discontinuities responsible for the radar backscatter are associated with decaying, ho mogeneous turbulent coherent structures, is in contrast to the theory of volume scattering, which assumes the radar pulse volume to be parti ally filled with stationary, homogeneous turbulence.