HR: 1340h
AN: SA53A-1150    [Abstracts]
TI: Spectral properites and scale dependent transport in simplified stratified systems subject to sporadic threshold adjustment
AU: * Liu, H
EM: liuh@ucar.edu
AF: National Center for Atmospheric Research, High Altitude Observatory, P.O.Box 3000, Boulder, CO 80307-3000 United States
AB: A stratified atmosphere can be essentially characterized by systems subject to stochastic forcing and threshold adjustment due to convective and shear instability, and the vertical transport can be approximated by eddy diffusion/viscosity. In the linear limit, the equations can be solved explicitly, and the spectra could be determined and are shown to follow power-law distributions, and the eddy transport coefficients are scale independent. The nonlinear equations are also shown to support scale invariance under rather general conditions, and the power-law indices of the spectra are derived from the analysis. These indices, as well as those in the linear limit, are confirmed by numerical simulations. The power-law indices of the ``universal'' spectra of temperature and horizontal wind versus vertical wavenumber and frequency from previous observations are shown to fall in the range determined by the linear and nonlinear limit. This theory, therefore, provides a possible explanation to the universal vertical wavenumber and frequency spectra and their variability. By relating the universal spectra with the sporadic threshold adjustment due to convective or shear instability, which is ubiquitous in stratified fluid systems, the difficulty of previous theories to associate the time and location independent spectral feature with the highly time and location dependent gravity waves is avoided. The analysis also suggests that the vertical eddy transport coefficients are scale dependent, and the implication of this scale dependence will be explored.
DE: 0341 Middle atmosphere: constituent transport and chemistry (3334)
DE: 3265 Stochastic processes (3235, 4468, 4475, 7857)
DE: 3379 Turbulence (4490)
DE: 3384 Acoustic-gravity waves
SC: SPA-Aeronomy [SA]
MN: Fall Meeting 2005