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extreme value of precipitation over tropic

Added by Bo Huang about 8 years ago

Dear all,

I am working on CCLM dynamic downscaling in CORDEX-EA. The driving data is ERA-Interim, and simulating period from 1979 to 2010. I found some grids have extreme precipitation (like 400 mm/3hr), especially in tropics. Is there anyone can help me?


Replies (18)

RE: extreme value of precipitation over tropic - Added by Burkhardt Rockel about 8 years ago

Which CCLM version do you use? Also, please upload your YUSPECIF file. Other members running simulations in the tropics may want to compare their YUSPECIF with yours to find differences.
I have also found such overshootings in single grid points when I used the default Tiedtke convection itype_conv=0, but have no explanation. With the IFS convection itype_conv=4 it seems to be smoother.

RE: extreme value of precipitation over tropic - Added by Bo Huang about 8 years ago

the CCLM version is cosmo_090213_4.8_clm19. So, I will make a sensitivity experiment for choosing IFS convection itype_conv=4. Let’s see how it will come.

thank you very much.

YUSPECIF YUSPECIF 43.8 KB

RE: extreme value of precipitation over tropic - Added by Bo Huang about 8 years ago

Hallo Burkhardt,

I found that there is no option of itype_conv=4. So, what should I do?

RE: extreme value of precipitation over tropic - Added by Burkhardt Rockel about 8 years ago

itype_conv is in the name list block &PHYCTL

RE: extreme value of precipitation over tropic - Added by Bo Huang about 8 years ago

yes, I know. There are only four options: 0,1,2,3. But no itype_conv=4.

To specify the type of convection parameterization
0: Tiedtke scheme
1: redThis option has been eliminated
2: redThis option has been eliminated
3: Shallow convection based on Tiedtke scheme

RE: extreme value of precipitation over tropic - Added by Burkhardt Rockel about 8 years ago

The namelist tool is probably not up-to-date. There should be a line
4: IFS convection scheme

RE: extreme value of precipitation over tropic - Added by Andreas Will about 8 years ago

Hello Bo,
most probably the high values of precipitation at individual grid points originate in the numerics of advection which cannot deal with convection at individual grid points.
Instead of cooling feedback at the surface it is enhancing the convection.

In cosmo_4.8_clm19 there is still this problem.
This has been fixed in a more recent version by Uli Blahak and will be available with 5.0.
I would appreciate if you could implement this modification of advection in 4.8_clm19 and test it.
Please contact me in the case, you would like to do that.

Greetings, Andreas

RE: extreme value of precipitation over tropic - Added by Bo Huang about 8 years ago

Hi Andreas,

thank you for your information. I would like to do some effort for clm-community. However, I do not have any experience of work like that. Please tell me how to implement that modification of advection in 4.8_clm19, then I can do some tests.

Regards,
Bo

RE: extreme value of precipitation over tropic - Added by Hans-Juergen Panitz about 8 years ago

Hi Bo,

Hi Bo,

I saw in your YUSPECIF file that you use a value of 11000m for the parameter rdheight, which defines
the lower boundary the Rayleigh damping layer in y=

In the tropics I strongly recommend a value of about 18000 m. The CCLM default
value is 11000 m, which is too low.

But: when increasing rdheight you also have to increase the height of the model domain to
about 30000m, which requires re-running of INT2LM.

However, I recommend to do this and to see what happens to your precipitation.

A possbible model setup that has been used for the CORDEX Africa simulations is available from the
CLM Communities homepage
http://www.clm-community.eu/namelist-tool/namelist-tool_portal/texts/cosmo_clm_4/CCLM-AFR440_4.8_clm17.txt

Since I assume that you do not use the MODIS derived albedo, please change the parameter itype_albedo from 2 to 1.

Best

Hans-Juergen

RE: extreme value of precipitation over tropic - Added by Bo Huang about 8 years ago

Hi Hans-Juergen,

thank you very much. I want to do some test as your suggestion. But how to change the height of the model domain? I didn’t find a parameter to control that.

Best regards,

Bo

RE: extreme value of precipitation over tropic - Added by Hans-Juergen Panitz about 8 years ago

Hi Bo,
please read my recent comment properly.

In order to modify the height of the model domain, you have to re-run INT2LM.
The vertical structure of your model domain is defined there and transferred via the laf/lbfd files to CCLM.

Hans-Juergen

RE: extreme value of precipitation over tropic - Added by Bo Huang about 8 years ago

Hi Hans-Juergen,

but if I don’t change any parameter in run_int2lm, the output of int2lm should be the same. I found only kelm_tot to control the output of int2lm on vertical height. Now, the kelm_tot=40, and the height_toa=22700m. Shall I increase the kelm_tot?

Best,

Bo

RE: extreme value of precipitation over tropic - Added by Burkhardt Rockel about 8 years ago

Unfortunately, the corresponding INT2LM namelist to the link Hans-Jürgen provided above is not given in the namelist tool (at least I cannot find it). In the following is the list of the namelist block you need to adapt in the INT2LM. Replace the @{xxxx} by the values you use. ke_tot=35

&LMGRID
  ivctype = 2,
  irefatm = 2,
ielm_tot=@{IE_TOT}, jelm_tot=@{JE_TOT}, kelm_tot=@{KE_TOT},
  pollat =  @{POLLAT}, pollon = @{POLLON}, polgam = @{POLGAM}, 
  dlon=@{DLON}, dlat=@{DLAT}, 
startlat_tot  = @{STARTLAT_TOT}, startlon_tot  = @{STARTLON_TOT},
ke_soil_lm=@{KE_SOIL},   
czml_soil_lm = @{CZML_SOIL},
vcflat=11000.0,
vcoord_d=30000., 27800., 25710., 23730., 21860., 20090., 18420., 16840., 15360., 13970., 
12670., 11450., 10320.,  9260.,  8280.,  7370.,  6540.,  5770.,  5060.,  4420., 
 3830.,  3300.,  2820.,  2390.,  2010.,  1670.,  1370.,  1110.,   880.,   690., 
  520.,   370.,   250.,   150.,    70.,     0., 
 /END

RE: extreme value of precipitation over tropic - Added by Hans-Juergen Panitz about 8 years ago

Hi Burkhardt,

it wasn’t a link to INT2LM Namelist but to CCLM Namelist, which exists.
Of course, one has to be logged into the CLM Homepage as a member.

@Bo:
You have to change the model levels in the way Burkhardt indicates in his comment.
Using the Namelist parameter vcoord_d (I am talking about INT2LM namelist) you can define your own levels.
They must be provided in descending order.

The example Burkhardt gave is again from the CORDEX Africa simulations with kelm_tot=35 (ke_tot=35 in CCLM Namelist).

In vcoord_d you have to define kelm_tot+1 values!!!!!!!!!!!!!!!!!!!

By the way, Bo.
The whole system INT2LM/COSMO-CLM is not self-explaining.
What users has really to do is to read the model documentations, at least the User’s Guide of CCLM which is Part VII of the general
documentation, and the documentation of INT2LM which is Part V.
All the questions you pose are answered in these documentations.
And these documentions are available from the COSOM web-page
www.cosmo-model.org
Links to this page exist also on the CLM-Homepage.

Sorry for being a little bit harsh.
But this is also some kind of user training.

Best

Hans-Juergen

RE: extreme value of precipitation over tropic - Added by Andreas Will about 8 years ago

Dear Colleagues,

I agree with the suggestion of Hans-Juergen.

Please replace the link to the old namelist-tool whereever it still exists by the following link to the
updated namelist-tool:
http://www.clm-community.eu/namelist-tool/namelist-tool_portal/index.htm
Here you find int2lm as well.

Greetings, Andreas

RE: extreme value of precipitation over tropic - Added by Kristina Trusilova about 8 years ago

Dear Colleagues,

what happens if the atmophere in CCLM is “lifted” up to 30000 km (as Burkhardt suggested) but the Rayleigh damping height remains low (11000 m)?
I assume the damping layer is thicker than with rdheight=18000 and, therefore, the damping is smoother. Has anybody tested such setup for the tropics? Did it work well or not?

Kristina

RE: extreme value of precipitation over tropic - Added by Hans-Juergen Panitz about 8 years ago

Hi Kristina,

relative easy answer:
I did such excercise when “searching” an appropriate setup for the CORDEX Africa simulation.

“Did it work well?”
Clear answer, NO!

The important and physically reasonable change is the increase of rdheight, which then implies the
increase of the height of the model domain.
Rule of thumb: the thickness of the damping layer should be approx. 1/3 of the whole vertical extent of the model domain.

Hans-Jürgen

RE: extreme value of precipitation over tropic - Added by Andreas Will about 8 years ago

Important is to damp the gravity waves sufficiently.
Hereto a test series should be considered with the alternative wave damping where w is damped only.

Using the standard approach the coefficient nrdtau can be chosen smaller to make the damping stronger.
In this case the damping zone can be made thinner. However, too strong damping reflects the waves within the damping layer.
A typical optimisation problem.
In any case, the damping should be rather too strong than too weak.
Higher mountains need stronger damping because the vertical propagation speed is increasing with the slope of the mountains.

I plan an article for the COSMO newsletter on this topic and a revision of the namelist parameter description.

Greetings, Andreas

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