Eddy diffusion coefficient and atmospheric models

Since the importance of the coupling mechanisms between the mesosphere and the thermosphere has increasingly been recognized, the structure and variation of turbulence has become one of the subjects of extended investigations and discussions. In spite of the fundamental role of turbulence, theoretical difficulties and lack of observational information restrict its applicability to atmospheric modeling. In the following paper the basic ideas of the parameterization of turbulence and the most important observational techniques and results are reviewed. The comparison of observations with theoretical model calculations shows the difficulties which underly current investigations and indicates the trends of future research.