[MITgcm-support] KPP diffusivities
mlosch at awi-bremerhaven.de
mlosch at awi-bremerhaven.de
Mon Oct 31 16:37:33 EST 2005
Stefano,
KPP was designed for (global) open ocean applications at a time
when no-one could afford 50cm layers in a global ocean model. I
wonder if the scheme can handle such a resolution. I haven't
seen it in applications with a vertical resolution of less than 5m, so
far, but that may be my lack of education.
Just a thought: at high horizontal resolution with a hydrostatic
model, the model may actually develop something that is called
"grid-cell storms" in meteorology. These are cells of 2dx width
with vigorous vertical upward/downward motion, basically
hydrostatic convection, that eventually will lead to the model's
explosion. With 250m you are not yet at very critical scales, but
close (with 50m horizontal resolution I did get these grid cell
storms); maybe you should turn on the nonhydrostatic part of the
code (compile with #define ALLOW_NONHYDROSTATIC in
CPP_OPTIONS.h and run with nonHydrostatic = .true. in
PARMS01 in data). However, with dz=50cm you'll have a severe
limit on your time step.
M.
Martin Losch
Alfred Wegener Institute
Postfach 120161, 27515 Bremerhaven, Germany;
Tel./Fax: ++49(0471)4831-1872/1797
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Hi,
I'm having some problems with the KPP eddy viscosity/diffusivity =
profiles.
I'm running the MITgcm model with kpp, obcs, exf and cal packages to =
study a very shallow gulf (max depth 25 m). The model domain is 88 x 128 =
x 28 points, with resolution of 250 x 250 x (0.5 for the 6 upper layers, =
1.0 for the remaining 22) m.
I attach a time-depth plot of temperature (filled color) and KPP =
temperature eddy diffusuvity (contours). The simulated event is a strong =
wind episode after some days of hot summer weather (strongly stratified =
water column): the wind breaks the initial stable thermohaline =
stratification. During all the simulation, it seems that the increase in =
turbulent motions due to night surface cooling is shifted to noon and =
(even stranger...) to the bottom of the water column!!!
Regarding the exf pkg, I'm using the configuration specified below:
c WIND |TEMP |DOWN |BULK |EVAP | actions
c -----|-----|-----|-----|-----|-------------------------------------
...
c def | def | - | def | - | Read-in uwind, vwind, atemp, aqh,
c | | | | | swflux, lwflux, precip, and runoff.
c | | | | | Compute ustress, vstress, hflux,
c | | | | | and sflux.
c | | | | |
The sign and magnitude of surface fluxes is right (I checked it twice =
against the exf_fields.h values), also because the temperature plot =
seems reasonable (surface warming during the day). I'm rather sure that =
the diffusivity plot is not flipped: the increase of turbulent motions =
caused by the wind is near the surface, as it should...
It seems that the turbulent activity due to wind is computed correctly, =
while the one caused by convection is somehow inverted (in time and =
depth).
I'm also rather sure that I made some mistakes somewhere but I really =
don't know where! Probably it's something trivial (shame on me...)!
Any guess? In the meantime, I will contine to look into the KPP related =
routines...
Thanks!
Stefano
P.S.: have a nice and frightening Halloween!
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<DIV><FONT face=3DArial size=3D2>Hi,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>I'm having some problems with the KPP =
eddy=20
viscosity/diffusivity profiles.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>I'm running the MITgcm model with kpp, =
obcs, exf=20
and cal packages to study a very shallow gulf (max depth 25 m). The =
model domain=20
is 88 x 128 x 28 points, with resolution of 250 x 250 x (0.5 for the 6 =
upper=20
layers, 1.0 for the remaining 22) m.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>I attach a time-depth plot of =
temperature (filled=20
color) and KPP temperature eddy diffusuvity (contours). The =
simulated event=20
is a strong wind episode after some days of hot summer weather (strongly =
stratified water column): the wind breaks the initial stable =
thermohaline=20
stratification. During all the simulation, it seems that the =
increase in=20
turbulent motions due to night surface cooling is shifted to noon and =
(even=20
stranger...) to the bottom of the water column!!!</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Regarding the exf pkg, I'm using the =
configuration=20
specified below:</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT face=3DCourier>c WIND |TEMP |DOWN |BULK =
|EVAP=20
| =20
actions<BR>c =20
-----|-----|-----|-----|-----|-------------------------------------<BR></=
FONT></DIV>
<DIV><FONT face=3DCourier>...</DIV></FONT>
<DIV><FONT face=3DCourier></FONT> </DIV>
<DIV><FONT face=3DCourier>c def | def | =
- |=20
def | - | Read-in uwind, vwind, atemp,=20
aqh,<BR>c =20
| | =
| =20
| | swflux, lwflux, precip, and=20
runoff.<BR>c =20
| | =
| =20
| | Compute ustress, vstress,=20
hflux,<BR>c =20
| | =
| =20
| | and=20
sflux.<BR>c =20
| | =
| =20
| |<BR></FONT></DIV>
<DIV><FONT face=3DCourier><FONT face=3DArial size=3D2>The sign and =
magnitude of=20
surface fluxes is right (I checked it twice against the<FONT =
size=3D3> =20
exf_fields.h</FONT><FONT size=3D2> values), also because the =
temperature=20
plot seems reasonable (surface warming during the day). I'm rather sure =
that the=20
diffusivity plot is not flipped: the increase of turbulent motions =
caused by the=20
wind is near the surface, as it should...</FONT></FONT></FONT></DIV>
<DIV><FONT face=3DCourier><FONT face=3DArial size=3D2>
<DIV><FONT face=3DCourier><FONT face=3DArial size=3D2>It seems that the =
turbulent=20
activity due to wind is computed correctly, while the one caused by =
convection=20
is somehow inverted (in time and depth).</FONT></FONT></DIV>I'm also =
rather sure=20
that I made some mistakes somewhere but I really don't know where! =
Probably it's=20
something trivial (shame on me...)!</FONT></FONT></DIV>
<DIV><FONT face=3DCourier><FONT face=3DArial size=3D2>Any guess? In the =
meantime, I=20
will contine to look into the KPP related =
routines...</FONT></FONT></DIV>
<DIV><FONT face=3DCourier><FONT face=3DArial =
size=3D2></FONT></FONT> </DIV>
<DIV><FONT face=3DCourier><FONT face=3DArial =
size=3D2>Thanks!</FONT></FONT></DIV>
<DIV><FONT face=3DCourier><FONT face=3DArial =
size=3D2></FONT></FONT> </DIV>
<DIV><FONT face=3DCourier><FONT face=3DArial =
size=3D2>Stefano</FONT></FONT></DIV>
<DIV><FONT face=3DCourier><FONT face=3DArial =
size=3D2></FONT></FONT> </DIV>
<DIV><FONT face=3DCourier><FONT face=3DArial size=3D2>P.S.: have a nice=20
and <U>frightening</U> Halloween!</FONT></DIV></FONT></BODY></HTML>
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