Hi CMS, I’ve been trying to get a simulation going over the Arctic. I’ve tried three or four different domains and every time I get the dreaded “NaNs in error term in BiCGstab after 1 iterations” error in the first timestep of the first forecast. A few things I’ve tried: I’ve had a look at…

Hi Simon, I still can’t get the UM to produce a global EC domain, but I have tried using the global model, but forcing it with ERA5 data, as per: [image] It’s a method I’ve used previously with ERA-Interim + vn 11.1 and it worked okay. However, I’m getting “NaNs in error term in BiCGstab after …

Hi Ella, Bad ancils could well be the issue. I’ve re-run your old config with the regional intermediate file for the ERA data on a slightly bigger domain using the data with extra levels which you obtained. I also added a branch /home/simon/branches/vn12.0_gribfix which hacks the polar values to b…

Hi Simon, Thanks so much. I’ll check again with the soil moisture ancils to see if I can see anything that might be causing it to fall over. The fact that it happens in the global forecast too is quite strange though, and suggests that there might be something awry in the config. I’m away until t…

Hi Ella I’ve been trying to fix this problem myself for 200m resolution nest (ERA5 RA3 nest) so was having a nosey at this thread. Just thought I’d share the fix that worked for me in case it works for your too. I couldn’t get my ancils to generate for my 200m domain using the nesting suite ancill…

Thanks Helen, I’ve been looking into this. Have managed to make some ancils with the RAS but now struggling to get past the glm as it keeps complaining about the topographic index ancils - have you seen that? No worries if not, I’ll keep ploughing through with this method. Thanks again for the sugge…

[image] Porting RAS to ARCHER2 Unified Model Doug Copied topographic_index.nc to /work/y07/shared/umshared/ancil/atmos/master/soil_data/hwsd/v4 Grenville Any help?

Thanks Grenville it could be, but I’m getting an HDF error when I try to read the file with either xancil or xconv. I also would’ve thought there’s a topographic index ancil for the glm somewhere, but I can’t find one in the umshared/ancil directories - do you know if one exists? Cheers Ella

ah, that must have been corrupted during transfer Doug Lowe has put a working one in /work/n02/n02/shared/RAS_Archer2/input_data

Thanks, that one works! I’ve tried selecting ‘initialise from external file’ but I imagine it might not work as it’s not on the n512 grid. I’m actually still getting ‘required field is not in input dump’, seemingly regardless of which option I select to reconfigure topographic index, which is stran…

I’m not familiar with how to use this file – as a work around until we understand how to use it, could you try changing i_rad_topography to 0 or 1

Suggestions for debugging BICGstab "NaNs in error term"

Unified Model

grenville 21 November 2022 10:47 37

Any help?

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Error in glm_um_fcst Unified Model	3	200	13 December 2023
NaNs in error term in BiCGstab for high res domain Unified Model ARCHER2 , Nesting-Suite	0	467	7 April 2022
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Sudden "NaNs in error term in BiCGstab" after model running smoothly Unified Model ARCHER2	2	192	29 February 2024
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Suggestions for debugging BICGstab "NaNs in error term"

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