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RE: Enquiry about SST Update in WRF

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K

kunaldayal

Member
Hi,

I am running long-term wind simulations using the WRF model and I am using the following settings for SST update:

&time_control:
- auxinput4_inname = 'wrflowinp_d<domain>',
- auxinput4_interval = 360, 360, 360,

&physics:
- sst_update = 1

And I have "avhrr-only-v2.20171231.nc" files for each of the days for the SST data from Optimum Interpolation Sea Surface Temperature (OISST) at 0.25º × 0.25º resolution (https://www.ncei.noaa.gov/data/sea-surface-temperature-optimum-interpolation/access/avhrr-only/) in the wrf/run folder where the real.exe and wrf.exe are located.

Is this sufficient setting for sst_update or do I have to specify the filename and locations in the namelist.input file?

Appreciate your assistance and advice.

Regards
Kunal
 
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Hi,
You will need to input your SST data during the WPS process. Take a look at the SST Example from our WRF Online Tutorial for information on how to do this. Because your SST data are in netcdf format, however, you will need to write them to intermediate format in order for metgrid to incorporate the data. To do so, you can follow the instructions in Chapter 3 of the WRF Users' Guide. You can also find an example script for writing a netcdf file to intermediate format here. Just note that this script was provided to us from a user who wrote it specifically for their application, so you will need to make modifications for your own use.
 
Hi,

I was able to convert the SST data from NetCDF to grib2 format using CDO.

I was also able to perform ungrib on the converted SST data using ungrib.exe.

But, ungrib created input SST files which have zero (0) size whereas the converted SST in grib2 format had approximately 4.8 MB size per day.

I am sure something is wrong that's why the SST files have zero size?

Appreciate your assistance and advice.

Regards
Kunal
 
Kunal,
It is recommended to convert the files from NetCDF format, to intermediate format, instead of trying to convert them to grib2 format. Can you give this a try and see if you have better luck that way? I provided some linkable resources in the previous message I sent. Thanks.
 
Hi,

I take note and I will try your recommendation.

I have a few other questions as well:

If my input atmospheric data, for instance, NCEP-FNL or others already have SST temperature for each time record do I still have to use SST data from another source?

Or just the following settings should suffice?
"
&time_control:
- auxinput4_inname = 'wrflowinp_d<domain>',
- auxinput4_interval = 360, 360, 360,
&physics:
- sst_update = 1
"
Appreciate your advice.

Regards
Kunal
 
Hi,
If you are planning to run simulations that go out for more than about a week, it's advised to use an outside source for SST data. Most datasets (for e.g., GFS) typically come with an SST field, but they are usually coarse and not reliable for an extended time. If you are not doing long simulations, then it's okay to skip the outside SST source. In that case, you don't even need to specify anything extra in the namelist.input file - so you don't need to add sst_update, and it's corresponding settings.
 
Hi,

I take note and thank you for the information.

I will get back to you after trying the mentioned recommendations for the long simulations using SST.

Regards
Kunal
 
Hi,

I managed to locate high-resolution SST data from RTG-SST_HR at 0.083 deg x 0.083 deg resolution in Grib format for my simulations.

Thank you.

Regards
Kunal
 
Hi,

This is already helping me a lot. But I have 2 follow-up questions on SST in WRF:

1.) What is the best practise, if no external SST is available for 3 month simulations? Better use the GFS-FNL or is it no good at all?

2.) According to my default Vtable.GFS, the SST field of my GFS-FNL data is not used. Even for short term simulations, where the SST field does not have to be updated, how is the skin temperature of water bodies initialized? Do I have to add the SST entry in the Vtable.GFS? Or is it determined another way?

I appreciate any help.

Best regards,
Julian
 
Julian,

1) Have you checked the sources mentioned on slide #6 in this presentation for SST data?

2) You do not need to add SST into the Vtable. The model will use SKINTEMP for the values of SST.
 
Hi kwerner,

thanks a lot for your quick and helpful reply.

In your presentation slides, the first two links under SST do not work for me, as the servers are unavailable for a while already. I didn't know the last link which works well. I will give it a try.

Best regards,
Julian
 
Julian,
Great! And thanks for letting me know about the other 2 links. I'll check into that.
 
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