[GTP] GTP Seminar at NCAR-August 6

[Silvia Gentile]

GTP Seminar

The Effect of Asymmetric Ekman Damping on Energy and Enstrophy Injection 
in Two-layer Quasi-geostrophic Turbulence
Eleftherios Gkioulekas
University of Texas-Pan American

An analysis of wind and temperature measurements taken during the Global 
Atmospheric Sampling Program by Nastrom and Gage showed that there is a 
robust $k^{-3}$ energy spectrum extending from approximately 3,000 km to 
1,000 km in wavelength and a robust $k^{-5/3}$ energy spectrum extending 
from 600 km down to a few kilometers. Tung and Orlando have demonstrated 
numerically that the two-layer quasi-geostrophic model, forced at large 
scales by baroclinic instability, can reproduce this energy spectrum as 
a combined downscale enstrophy and energy cascade. However, their result 
is considered, by some, to be controversial. More detailed models have 
been shown to reproduce the Nastrom-Gage energy spectrum as well. 
However, the question remains: what is the simplest model that can 
account for the Nastrom-Gage spectrum?
In this talk I will present the recent progress that has been made 
towards addressing this question. First, we will argue that, contrary to 
the case of two-dimensional turbulence where the downscale energy flux 
is constrained to vanish rapidly with increasing scale separation, in 
the two-layer QG model, asymmetric dissipation loosens this constraint 
thereby allowing an inertial range  transition from $k^{-3}$ scaling to 
$k^{-5/3}$ scaling. Furthermore, we have shown that in the two-layer QG 
model energy and enstrophy are injected at a proportion that places the 
transition wavenumber near the Rossby wavenumber in agreement with 
observation. Finally, we show that the effect of asymmetric Ekman 
damping at the forcing range is to decrease the rate of enstrophy 
injection as well as the ratio of enstrophy to energy injection, thus 
tending to decrease the transition wavenumber further.

August 6, 2010
Fleischmann Building (1850 Table Mesa Drive), Board Room
Lecture 11:00am

-- 
Silvia Gentile
NCAR IMAGe
1850 Table Mesa Drive
Boulder, CO 80305
www.image.ucar.edu