'Coupled' task fails on second model cycle

Hi CMS, I am trying to run the UKESM1 historical suite (u-bc613/archer2) which has been ported to Archer2 and updated since the Archer2 o/s upgrade. My copy is u-cy797.

It runs fine for the first cycle, but fails on the second, with an error in the ‘coupled’ task:
UnboundLocalError: local variable ‘checkpoint_date’ referenced before assignment.

I noticed that Ros suggested in reference to a different suite that having a cycling frequency of at least 1 month might get around this error, but I tried a 2 month run with 1 month cycling and this didn’t solve it.

The only significant change i’ve made to u-bc613 in my version is to add the following line to /site/archer2.rc (as suggested in this thread):


This addition fixed an error i had previously, where the postproc_nemo task failed with insufficient memory.

Do you have any advice on solving this issue with cycling?



Hi Alistair,

You have the suite set to 1 month cycling but the UM is set to write the restart dumps every 90 days. So when it comes to the second month there is no dump available.

In UM → namelist → Model Input & Output → Dumping and Meaning set dumpfreqim to 30 days.


Ah, ok. I’ll make that change and try re-running. Thanks very much!