# Nan Error When Prescribing Land Use **URL:** \ **Category:** Uncategorized\ **Tags:** Monsoon2, ARCHER2\ **Created:** [25 July 2022 21:01 UTC](https://cms-helpdesk.ncas.ac.uk/t/nan-error-when-prescribing-land-use/667 "2022-07-25T21:01:08Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![James\_Weber](https://avatars.discourse-cdn.com/v4/letter/j/e495f1/32.png) [@James\_Weber](https://cms-helpdesk.ncas.ac.uk/u/James_Weber)\ **Post date:** [25 July 2022 21:01 UTC](https://cms-helpdesk.ncas.ac.uk/t/nan-error-when-prescribing-land-use/667/1 "2022-07-25T21:01:08Z")
Hi, I keep getting the EG\_BICGSTAB (NaNs in error term in BiCGstab after 1 iterations) or the North/South halos too small for advection error when attempting to prescribe PFT fraction (stash 216) in a Archer2 run (u-cp508). I have run with Diagnostic Print Status but can’t see any obvious solution. The suite runs for ~10 mins before crashing. u-cp508 is coupled and I am overwriting the land use generated by Triffid to investigate a particular LU scenario. I know this general approach works as I have had coupled Archer2 suites (with Triffid on) (e.g. u-cp448) succeed when prescribing LULC derived from UKESM CMIP6 model output (e.g. u-be690\_m01s00i216\_2015-2100\_monthly\_timeseries\_land\_cover\_frac.anc.nc). However, in this case I am trying to prescribe LULC from a scenario I have developed from an external source (CESM). I did the necessary PFT conversions, created a netCDF file and used xancil to make the ancil file (/work/n02/n02/jweber/Ancils\_CESM\_Land/Timeseries/maxforest\_216\_timeseries\_OUT.anc). I followed Jeff’s advice in [Using xancil and xconv to create timeslice ancillary files](https://cms-helpdesk.ncas.ac.uk/t/using-xancil-and-xconv-to-create-timeslice-ancillary-files/311) for this. The maxforest\_216\_timeseries\_OUT.anc fails on Archer2 but succeeds when run in coupled suites on Monsoon (e.g. u-cn793). I have looked at the ancil in xconv and it looks reasonable. To test my processing code, I extracted the raw data from the UKESM model derived stash (u-be690\_m01s00i216\_2015-2100\_monthly\_timeseries\_land\_cover\_frac.anc.nc) and ran this through my processing script - u-cp508 ran fine with the resulting ancil. I’ve also done further tests where I duplicated the UKESM data and replaced one PFT field with the field corresponding field from my new data - this also caused the model to crash. This is quite confusing as the new ancil file runs on Monsoon and makes me think I may need to adjust my Archer2 suite. Would you have any suggestions? Many thanks for your help, James ---
**Author:** ![James\_Weber](https://avatars.discourse-cdn.com/v4/letter/j/e495f1/32.png) [@James\_Weber](https://cms-helpdesk.ncas.ac.uk/u/James_Weber)\ **Post date:** [7 August 2022 16:42 UTC](https://cms-helpdesk.ncas.ac.uk/t/nan-error-when-prescribing-land-use/667/2 "2022-08-07T16:42:04Z")
Just an update on this, it is only a problem when i\_co2\_opt = 3 / l\_co2\_interactive = True and I think it is being caused by a sudden large change in the PFT land cover (stash 216). From adding various print statements to my branch (dev/jamesweber/vn12.1\_base) I think the error is occurring in the UM code somewhere after atmosphere/convection/tracer\_total\_var.F90 and before atmosphere/dynamics\_diagnostics/sl\_tracer\_norm.F90. Is there any documentation about the order in which modules are called in the UM? On a separate issue, I’ve trying to setup pptransfer to Jasmin but one links on the CMS webpage discussing this doesn’t seem to be working. The main page is [UKESM1.1-coupled Release Notes](https://cms.ncas.ac.uk/unified-model/configurations/ukesm/relnotes-1.1/coupled/#archer2) and the link is [https://cms.ncas.ac.uk/\_archer2/pptransfer](https://cms.ncas.ac.uk/_archer2/pptransfer). Could you point me to the update version of this page? Many thanks, James ---
**Author:** ![RosalynHatcher](https://dub1.discourse-cdn.com/flex013/user_avatar/cms-helpdesk.ncas.ac.uk/rosalynhatcher/32/11_2.png) [@RosalynHatcher](https://cms-helpdesk.ncas.ac.uk/u/RosalynHatcher)\ **Post date:** [9 August 2022 14:19 UTC](https://cms-helpdesk.ncas.ac.uk/t/nan-error-when-prescribing-land-use/667/3 "2022-08-09T14:19:45Z")
Hi James, In answer to your pptransfer question there’s an extraneous `_` in the link: [https://cms.ncas.ac.uk/archer2/pptransfer](https://cms.ncas.ac.uk/archer2/pptransfer). I’ll fix the UKESM page shortly. Cheers, Ros. ---
**Author:** ![James\_Weber](https://avatars.discourse-cdn.com/v4/letter/j/e495f1/32.png) [@James\_Weber](https://cms-helpdesk.ncas.ac.uk/u/James_Weber)\ **Post date:** [16 August 2022 20:54 UTC](https://cms-helpdesk.ncas.ac.uk/t/nan-error-when-prescribing-land-use/667/4 "2022-08-16T20:54:45Z")
Great, thanks Ros, I’ll give that a go. James