# How do I start a new perturbation experiment?

**URL:** <https://forum.access-hive.org.au/t/how-do-i-start-a-new-perturbation-experiment/262>\
**Category:** COSIMA\
**Tags:** access-om2, perturbation, experiment, user-story\
**Created:** [9 December 2022 06:08 UTC](https://forum.access-hive.org.au/t/how-do-i-start-a-new-perturbation-experiment/262 "2022-12-09T06:08:26Z")\
**Posts on this page:** 1\
**Showing post:** 12

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**Author:** ![aekiss](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.access-hive.org.au/aekiss/32/46_2.png) [@aekiss](https://forum.access-hive.org.au/u/aekiss)\
**Post date:** [11 October 2023 01:49 UTC](https://forum.access-hive.org.au/t/how-do-i-start-a-new-perturbation-experiment/262/12 "2023-10-11T01:49:05Z")

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Disconcertingly, we now have a [2nd example of a non-reproducible run](https://forum.access-hive.org.au/t/inconsistent-ocean-and-sea-ice-in-final-7-5yr-of-0-1-iaf-cycle-4/1492). It’s unclear how often this occurs, as we don’t discover it unless we re-run and check the restarts.

The lesson is: **always check the md5 hashes in the manifests** in a re-run - they should match those from the original run (the only exception being `ocean_barotropic.res.nc.*` which always differ - but this doesn’t affect any other restarts so is presumably benign, maybe a datestamp in the file or something).

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