The NOAA IR serves as an archival repository of NOAA-published products including scientific findings, journal articles, guidelines, recommendations, or other information authored or co-authored by NOAA or funded partners.
As a repository, the NOAA IR retains documents in their original published format to ensure public access to scientific information.
i
A model of gravity-wave-induced variability and turbulence in the stratified free atmosphere
-
1990
[PDF-60.02 MB]
Details:
-
Personal Author:
-
Corporate Authors:
-
NOAA Program & Office:
-
Description:The atmosphere exhibits variability on many spatial and temporal scales. Much of the variability of the free atmosphere can be characterized using an internal gravity wave spectral model such as the one originally developed by Garrett and Munk for the ocean. In this paper we examine the consequences of using a vertical wavenumber spectral model (Sidi et al., 1988) to describe variations of vertical profiles of atmospheric variables (horizontal and vertical wind, temperature, and other scalars) about a mean profile. At high wavenumbers the model exhibits a wavenumber to the -3 dependence, which is characteristic of a continuum of internal gravity waves whose amplitudes are controlled by a breaking process (sometimes referred to as a 'saturated'
gravity wave spectrum). By employing a random phase between wavenumber amplitude components, a reverse Fourier transform of the spectrum yields simulated profiles of velocity and thermal variability as well as shear and Brunt-Vaisala frequency
variability. The horizontal wind components of shear and the Brunt-Vaisala frequency exhibit Gaussian distributions; the square of the magnitude of the shear exhibits a Rice-Nakagami distribution. If regions with Richardson number less than a critical value of 0.25 are assumed to be turbulent, then we can examine a number of aspects of the occurrence of clear-air turbulent breakdown in the stratified free atmosphere including the probability distributions for Ri and the vertical extent of turbulent layers. For a typical tropospheric condition, the average turbulent layer thickness turns out to be about 35 m and about 20% of the troposphere appears to be actively turbulent. The majority of the turbulent layers appear to be due to autoconvective overturning instead of Kelvin-Helmholtz dynamic instability. In other words, mean shear appears to play a relatively minor role in producing the background of clear-air turbulence. Straightforward computations of profiles of refractive index structure function parameter C and the rate of dissipation of turbulent kinetic energy, e, are similar to observations in Colorado but nearly an order of magnitude greater than observations from flatter terrain (which are deemed more relevant to the model parameters). Agreement with the more representative flat terrain values can be obtained either by arbitrarily adjusting the ratio of the turbulence length scale to the layer thickness or by allowing the layers to expand vertically until their Richardson number exceeds the critical value of 0.25 and then by using layer average values for the shear and potential temperature gradient.
This model has application to optical propagation, thermal blooming, clear-air radar performance, extreme shear probability forecasts (e.g., for shuttle launches), the editing of atmospheric data (i.e., when is it likely that a 'bad' point is just natural variability?), and the general issue of sampling errors in atmospheric measurements.
-
Keywords:
-
Series:
-
Document Type:
-
License:
-
Rights Information:CC0 Public Domain
-
Compliance:Library
-
Main Document Checksum:
-
Download URL:
-
File Type:
