Observations every 10 minutes

Problems with data in 3DVAR.

Observations every 10 minutes

Postby dmoreno1 » Fri Feb 27, 2015 12:38 pm

Hello,

I'm trying to run OBSGRID to make observational nudging, and my observation files have data every 10 minutes.

However, it seems like OBSGRID cannot process obs with a temporal sampling higher than one hour (the field intf4d in the namelist.oa cannot be lower than 3600 seconds). Moreover, according to WRF Uers Guide, the little_r obs files need to have the format "obs_filename:<YYYY-MM-DD_HH>". So, if I have 10 min obs, I cannot name the files with this format (I would have 6 data records per obs_filename:<YYYY-MM-DD_HH> file).

Is there any way for me to use the 10-mins measurements to make observational nudging?

Thank you
dmoreno1
 
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Re: Observations every 10 minutes

Postby allenea » Fri Aug 03, 2018 6:22 pm

Hi,

This is several years old, but I am replying for others who have the same question.

As of V3.8, OBSGRID is not set up for handling observations below 1 hour (as you have found out). But that is not to say that you cannot make it handle 10 minute nudging. As you have found out, the intf4d field has a restriction where if it is set below 3600 it throws an error and tells you it can't do that. You can remove that restriction without OBSGRID giving you much of a fit. You can also change it to make it expect files including minute values to handle observations in the sub-hour format. But when it parses the input file it's going to cut off the minute values, but it should still read the files at this point. It might have trouble sequencing, but I am not sure. That's the easy part.

The hard part is going to be changing the entire date/time structure which is built to only have a date/char string of 13 (which gets parsed down to YYYY-MM-DD-HH). I would start with the datepack module and anything that uses date_pack. I would also look at the namelist module (what the namelist expects) and driver module (for the input file naming structure). Once you change the date/time structure you are going to have to be careful with all the different pieces relying on that information because those will need to be changed too. It is definitely doable, but there are a lot of places that you could break it. Finding the error might be very difficult to impossible. I would regularly test whatever changes you make to make sure it is still working. Also be careful that it's not changing the data either.

Currently, the only thing that gets read out to the full date string is the variable that holds the date string from the OBS: file.

You will have to compile and configure after you make any changes for them to take affect.

Good luck to anybody attempting this in the future. Putting your code on github (with version control of the original to find the changes) would surely be beneficial. If you do that reply to this with the URL.

It might make your life easier if you print everything out ahead of time so you can map out what needs to be changed on paper before trying to change the code. This might eliminate/minimize the risk for potential issues or errors.


- Eric
allenea
 
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