Atmospheric Waves and Turbulent Intermittency in Stable Boundary Layers During CASES99

We investigated turbulence intermittency and its relationship to atmospheric waves using the nighttime data collected during the Cooperative Atmosphere-Surface Exchange Study in 1999 (CASES-99). We found that cold air movement associated with local topography leads to sudden changes of the horizontal pressure gradient as well as horizontal convergence, air mass lifting, and generation of wave-like motions. As a result of the wave-like motions, the wind speed oscillates and spreads vertically. The wind oscillation adjacent to the ground periodically enhances bulk shear between the observational level and the ground, leading to periodic turbulence generation. In addition, the vertical variation of the wind oscillation leads to local shear enhancement and intermittent turbulence. Turbulent mixing can enhance the amplitude of wind speed oscillation through downward transport of high momentum air. Also this mixing can shorten the oscillation period through reduction of the vertical lifting, which forces the quick release of the gravity potential energy to the kinetic energy.