[GTP] James Riley--Seminar at NCAR

[Silvia Gentile]

Joint GTP MMM Seminar

On Pathways to Turbulence in Strongly-Stratified Flows
James J. Riley
University of Washington
Seattle, Washington




Important issues in stable, strongly-stratified flows, often occurring 
in the atmosphere and oceans, are when and how “classical” 3D turbulence 
appears, and the properties of the resulting turbulence. In the oceans, 
at horizontal scales above a few meters, for example, buoyancy often 
exerts a dominant influence on the flows, and hence how turbulence is 
generated.  One pathway to classical 3D turbulence in a strongly 
stratified flow is through the generation and breakdown of propagating 
internal waves.  In this seminar another, possibly more general, pathway 
is proposed, that of “stratified turbulence”; these are motions at 
horizontal scales large enough to be dominated by buoyancy.

To address these flows very high resolution direct numerical simulations 
are utilized.  The flows are initiated at low Froude number (buoyancy 
dominated) but with the Reynolds number as large as possible in order 
that smaller-scale, 3D turbulence can occur.  It is found that strong, 
vertical shearing of the horizontal motions develops, resulting in 
intermittent, smaller-scale turbulence, and in a strong cascade of 
kinetic and potential energy to small scales.  At length scales larger 
than the overturning scales, this appears to result in an inertial 
subrange in the horizontal, but not in the vertical, energy spectra. 
The subrange, distinct from the classical inertial subranges of 
Kolmogorov, Oboukov, and Corrsin, and strongly affected by the stable 
density stratification, is characterized by the dissipation rates of 
kinetic and potential energy.  The results are shown to be consistent 
with some previously unexplained oceanographic and atmospheric field data.


June 10, 2010
Foothills Laboratory 2
Room 1022
Lecture 10:30am
Refreshments served at 10:15am
-- 
Silvia Gentile
NCAR IMAGe
1850 Table Mesa Drive
Boulder, CO 80305
www.image.ucar.edu