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Fundamental issue with etkf: or just a simple not understanding the logic

satjemkes

New member
Hi,
I am trying to run the etkf function of wrfda and encounter something which i do not understand.

I am running the system on an observational dataset which consists of surface observations, and new dataset (Aeolus HLOS and Transformed Retrievals) which need to add to the drivers.

There are several steps involved an one is to filter the observations, and then generate an ob.etkf.ensemble_number file by running wrfvar using 'Verify' option. (e.g. ob.etkf.0001)

The interesting part is that 5th and 6th column of this file ALWAYS reads -889. in my case

It is interesting as the last step of the mult-step approach check if((apm_type(o,1).ne.220.) .and. (apm_type(o,1).ne.120.)) THEN REJECT.

In the end ALL filtered observations are rejected and consequently the output for the various ensemble members does not make sense (all zoro)

The code which generates the ob.etkf.ensemble_number has a statements like
apm_plc = -888.88
if ( iv%synop(n)%u%qc >= 0 .and. ob%synop(n)%u /= missing_r ) then
apm_index = apm_index + 1
write(ounit,1000) ob%synop(n)%u, iv%synop(n)%u%inv, iv%synop(n)%u%error, &
'WNU', apm_plc, -888.88, iv%info(synop)%lat(1,n), iv%info(synop)%lon(1,n), &
.
.
.
endif


If i read the code it means that under no situation we can have in column 5 and 6 of the ob.etkf.0001 file a number different than -889 and -889 and these will be rejected.

In summary: the second step of the etkf-generation process generates a file which has -888.88 in column 5 and 6, and the third step rejects all observations which not have 220. and 120 in these columns.

Thus there are no valid surface observations: and thus the etkf process fails.

Going over the writing code it appears that the ETKF system is only applicable to Radiosonde observations. Can anybody confirm this?
Has it been applied to Surface observations? I am running wrf 4.3.3.

The suggestion is now to switch to the DTC version of etkf.

If this is confirmed i urge the WRF support team to add some statements in the README files and the user guide regarding the limited applicability of the ETKF functionality of WRF. It would save a lot of time of the naive users.
 
Hi satjemkes, I encounted the issue in WRFDA v4.2 as same as yours.
I found that only observation types of:
1) "sound, sonde_sfc", with apm_plc = 120.
2) "tamdar, tamdar_sfc", with apm_plc = 220.
can be filtered.
I am curious about your resolution or any understanding of the setting. Could you please give me a clue? Thank you so much in advance!
 
Dear Catrainy
So far i was busy with the hybrid 4dEnVar module and had no time to go into the EnKF method in more detail. This might change in the the next months as i want to run some dual resolution experiments, for which i might want to explore the EnKF method as well.
For this i need to modify the EnKF method to add more observations than the currently listed ones. if you were able to get the enkf method going with additional observational type it would be appreciated to exchange experience
best
stephen
 
Dear Catrainy
So far i was busy with the hybrid 4dEnVar module and had no time to go into the EnKF method in more detail. This might change in the the next months as i want to run some dual resolution experiments, for which i might want to explore the EnKF method as well.
For this i need to modify the EnKF method to add more observations than the currently listed ones. if you were able to get the enkf method going with additional observational type it would be appreciated to exchange experience
best
stephen
Dear Stephen
Thank you for your message. I appreciate your efforts about the issue. It sounds like you have a lot on your plate with 4dEnVar.

Recently, I have been working on modifying the ETKF method to include additional observation types. So far, I have managed to filter a small subset of the observation files. However, I am currently encountering an issue with the following error: "[6] Output ETKF analysis ensemble: NCVPT: : NetCDF: Start+count exceeds dimension bound." Meanwhile, the output files are as same as the input files. I am actively searching for a solution to this problem.

If I make any further progress, I will be sure to leave a message here to keep you updated. Thank you again for your message, and I look forward to make further communication.

Best regards
 
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