quantification of divergence in aladin
DESCRIPTION
QUANTIFICATION OF DIVERGENCE IN ALADIN. Vanja Blažica, Benedikt Strajnar, Nedjeljka Žagar. The a im of this study. T o quantify the divergent part of the kinetic energy in the mesoscale; To observe horizontal and vertical dependency of the divergent energy distribution. The methodology. - PowerPoint PPT PresentationTRANSCRIPT
QUANTIFICATION OF DIVERGENCE IN ALADINVanja Blažica, Benedikt Strajnar, Nedjeljka Žagar
THE AIM OF THIS STUDY To quantify the divergent part of the kinetic energy in
the mesoscale; To observe horizontal and vertical dependency of the
divergent energy distribution.
THE METHODOLOGY Quantification through the use of
model spectrum ALADIN/SI 4.4 km, 6-hour forecasts IC/BC by ECMWF 4D-Var
assimilation system Extension zone included in the
spectra One month average (July 2007),
with two runs per day2
BACKGROUND Vorticity and divergence Rossby and IG waves The KE spectrum can be split into divergent and
vortical part
Left: Average model spectrum over levels between 9 and 13 km. Right : The difference between KE from U+V and from VOR+DIV in percents.
3
RESULTS: AVERAGE ENERGY SPECTRA
4
PBL AND OROGRAPHY SPECTRUM
3/5k
101
102
103
10-4
10-3
10-2
10-1
100
101
(km)
E (
m2 /s
2 )
PBL
VOR
DIVVOR+DIV
3/5k
3k
5
RESULTS: THE DIVERGENT ENERGY CONTRIBUTION
The percentage of the divergent energy in the total kinetic energy in a selected layer.
)),(),((
),(
)(2
1
2
1
knEknE
knE
kr
VOR
n
nDIV
n
nDIV
6
RESULTS: THE DIVERGENT ENERGY
CONTRIBUTION
)),(),((
),(
)(
2
1
knEknE
knE
kr
VOR
n
nDIV
n
nDIV
bottom
top
The percentage of the divergent energy in a selected layer in the total kinetic energy over all layers.
7
RESULTS: THE DIVERGENT ENERGY
CONTRIBUTION
),(),(
),(),(
nkEnkE
nkEnkr
VORDIV
DIV
Distribution of percentage of divergent energy in the total energy with respect to height and wavenumber. Relative - for each level separately. Contour interval is 0.05.
8
RESULTS: THE DIVERGENT ENERGY
CONTRIBUTION
Vertical distribution of the average percentage of divergent energy in the total energy.
k DIVVOR
DIV
nkEnkE
nkEnr
),(),(
),()(
9
CONCLUSIONS
The role of the divergent energy increases in the mesoscale,
particularly at shortest scales and near the surface.
The vertical dependency is more complex.
The slope of both variables becomes shallower towards the surface.
At scales above/below 100 km most of the divergent energy comes
from the free troposphere/PBL.
Below 50 km, divergent energy presents more than 50 % of total
energy in all layers.
What is the reason for the bump at cca 50 km?
Is the similar slope of PBL energy spectrum and orography spectrum
a coincidence?
Why the maximum in the stratosphere?10
ADDITIONAL SLIDE: SENSITIVITY TO DIFFUSION SCHEME
From previous to current settings: the spectral diffusion was reduced (the order from 4 to 2 and the
enhancing coefficients by a factor of five) the SLHD enhancing coefficients were increased (vorticity by two
and divergence by ten).
Distribution of average percentage of divergence in the total energy with respect to height and wavenumber. Relative - for each level separately. Contour interval is 0.05.Left: previous diffusion scheme settings.Right: current diffusion scheme settings.
11
U AND V COMPONENTS OF THE WIND VECTOR AT 6TH MODEL LEVEL (~100
HPA)
12