# North/South halos too small for advection

**URL:** <https://cms-helpdesk.ncas.ac.uk/t/north-south-halos-too-small-for-advection/1529>\
**Category:** Unified Model\
**Tags:** Monsoon2\
**Created:** [23 September 2024 09:10 UTC](https://cms-helpdesk.ncas.ac.uk/t/north-south-halos-too-small-for-advection/1529 "2024-09-23T09:10:12Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![mdalvi](https://avatars.discourse-cdn.com/v4/letter/m/ad7895/32.png) [@mdalvi](https://cms-helpdesk.ncas.ac.uk/u/mdalvi)\
**Post date:** [23 September 2024 09:57 UTC](https://cms-helpdesk.ncas.ac.uk/t/north-south-halos-too-small-for-advection/1529/2 "2024-09-23T09:57:48Z")

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Hi Masaru,

This process needs to be done manually -(edit settings → run → wait for month to complete-\> stop run → revert settings → resubmit for next segment).  
The preferred method nowadays is to perturb the theta field as a way to change the model evolution, see [tips\_CRgeneral – MOCI (metoffice.gov.uk)](https://code.metoffice.gov.uk/trac/moci/wiki/tips_CRgeneral#Restartingifthemodelblowsup) for explanation, and [this comment](https://cms-helpdesk.ncas.ac.uk/t/bicgstab-error-20-years-into-nudged-run/1519/4) for using the method on Monsoon :

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