Present State of Studying and Forecasting the Aviation Turbulence in the Free Atmosphere

Three main physical processes are responsible for generation of turbulence affecting the aircraft: (1) hydrodynamic instability of the airflow stratified in wind and temperature (Kelvin–Helmholtz instability), which manifests itself in origination of turbulent patches called clear-air turbulence (CAT) in the free atmosphere; (2) breaking of large-amplitude mountain waves over the obstacles and at their leeward slopes, which causes so called orographic turbulence or mountain wave turbulence (MWT); (3) outflow of highly turbulent air from convective storms, which leads to the formation in their vicinity of turbulent zones of deep convection, that is, convectively induced turbulence (CIT). In the paper, the state of the art in studying and forecasting the turbulence generated by the mentioned physical processes is considered. The present short-range forecasting and nowcasting techniques are characterized by transition to the universal standard for intensity of aviation turbulence, that is, to the energy dissipation rate (EDR) defined in terms of the theory of homogeneous and isotropic turbulence, and by taking into account the informativity of empirical turbulence diagnostics. For the CIT nowcasting, special techniques for convection diagnosis are developed based on the satellites, radars, and lightning registers data.