Wave-Turbulence Dynamics in the Stably Stratified Boundary Layer

Abstract

New data obtained at the Boulder Atmospheric Observatory (BAO) has been compared with a linear stability analysis of the background atmospheric state as measured by rawinsonde ascents. Good agreement was obtained between measured wave parameters such as wavelength, period, and vector phase velocity, and the eigenvalues of the linear solution, but linear eigenvectors scaled by measured pressure at the base of the BAO tower agreed less well with measurement. An investigation of the wave kinetic energy budget revealed that buoyant production of wave energy was a significant gain despite the strong stability (Ri ? 5). Further analysis of the budgets of wave heat flux and temperature variance revealed the essential role of wave-turbulence interaction in maintaining a large amplitude temperature wave and countergradient wave heat flux. A consideration of the turbulent kinetic energy budget showed many of the same features as the wave budget. A comparison with earlier near-neutral and stable cases analyzed in comparable detail suggests that countergradient wave heat fluxes maintained by nonlinear wave-turbulence interaction and an essential transfer of kinetic energy from wave to turbulence may be generic features of such situations. A mechanism for maintenance of turbulence by waves in strongly stratified boundary layers is described, which emphasizes that the time-mean Richardson number is an irrelevant parameter at such times. In the analysis of the data, general methods are described for extracting wave signals from nonstationary turbulence records and for assessing the statistical significance of the waveform so derived.