Characterization of High Altitude Turbulence for Air Force Platforms

Abstract

The Air Force has a pressing and unique need to characterize and predict high-altitude (z > 10 km MSL) turbulence (HAT). Mechanical turbulence at these altitudes will impact surveillance and reconnaissance aircraft, both manned and unmanned. To address this problem the Air Force Research Laboratory, including the Air Force Office of Scientific Research, is conducting a research program with the ultimate goal of developing viable methods of predicting both mechanical and optical turbulence at these altitudes. A key factor in developing real-time forecasting ability for HAT is that the techniques must rely on input from the output of mesoscale numerical weather prediction (NWP) models. This is a challenge since HAT typically occurs within small vertical extents that are currently beyond the ability of the mesoscale NWP models to resolve. Challenge proj ect C1W was established in 2005 to support this program. Last year important simulations of Kelvin-Helmholtz shear instabilities (leveraged with CAP project time; see Werne 2005 for details) and inertial-gravity waves emitted and propagating from a jet stream were carried out. For a review of the 2005 effort see Ruggiero et al. (2005). Simulations of the above phenomena continued this year, along with more detailed analysis of the results including matching the simulations to observations. In this paper, the simulations of the atmospheric microscale code for jet stream induced gravity waves and turbulence will be presented. A case study over Greenland including a comparison of observations and direct numerical simulations (DNS) for Kelvin-Helmholtz instabilities and its implication for existing Kelvin-Helmholtz turbulence evolution theory and parameterizations are discussed