Accession Number:

ADA413349

Title:

Fundamental Theoretical and Numerical Issues of Turbulence in the Middle Atmosphere

Descriptive Note:

Final rept. 1 Oct 1998-31 Dec 2001

Corporate Author:

ARIZONA STATE UNIV TEMPE

Personal Author(s):

Report Date:

2002-01-21

Pagination or Media Count:

49.0

Abstract:

This project falls within the realm of the USAF Airborne Laser ABL Program. One of the challenges of the ABL program is the development of laser-beam propagation codes. Such codes must account for beam propagation through an extended turbulent medium of the bulk of the troposphere and stratosphere. From the operational perspective, accurate modeling of the refractive index structure function for long nearly horizontal path under high scintillation conditions characteristic of the atmosphere is important. Direct numerical simulations have been performed to study the dynamics of an inhomogeneous stratified shear flow modeling an atmospheric jet in the tropopause in the ABL context. The basic state is characterized by a jet at the tropopause in which the density stratification is vertically non-uniform. Small to moderate background stratifications are selected, and simulations are conducted for a range of Reynolds numbers. Quasi-equilibrium turbulent flow-fields are obtained by long-time integration of governing equations. The structure of the mean flow and turbulence fields are calculated and interpreted using relevant length scales. The jet core is found to support sustained mechanical active turbulence, outside of which lay a region of patchy turbulence and non-linear gravity wave activity characterized by spatially decaying velocity fluctuations and strong temperature fluctuations.

Subject Categories:

  • Atmospheric Physics
  • Theoretical Mathematics
  • Fluid Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE