# Negative mass in set\_thermodynamic Error

**URL:** <https://cms-helpdesk.ncas.ac.uk/t/negative-mass-in-set-thermodynamic-error/2141>\
**Category:** Unified Model\
**Tags:** Nesting-Suite, Monsoon3\
**Created:** [5 August 2026 16:19 UTC](https://cms-helpdesk.ncas.ac.uk/t/negative-mass-in-set-thermodynamic-error/2141 "2026-08-05T16:19:12Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![kqiu](https://avatars.discourse-cdn.com/v4/letter/k/6a8cbe/32.png) [@kqiu](https://cms-helpdesk.ncas.ac.uk/u/kqiu)\
**Post date:** [5 August 2026 16:19 UTC](https://cms-helpdesk.ncas.ac.uk/t/negative-mass-in-set-thermodynamic-error/2141/1 "2026-08-05T16:19:12Z")

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Hi,

I am running the nesting suite u-eb261 on Monsoon3, and the following task has failed:

20190103T0000Z/Europe\_km11\_RAL3P3\_um\_fcst\_000

The error message says:

> Error code: 100
> 
> Error from routine: set\_thermodynamic
> 
> Error message: A total of 2 points had negative mass in set\_thermodynamic. This indicates the pressure fields are inconsistent between different levels and the model is about to fail.
> 
> Error from processor: 122
> 
> Error number: 55

I have another run using the same nesting-suite setup which did not encounter this error and completed successfully. The only difference between the two runs is the aerosol loading.

I’m not sure what has caused this error. Could you advise what might have caused this or any diagnostics I should run?

Many thanks for your help.

Best,

Kexin

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**Author:** ![jonnyhtw](https://dub1.discourse-cdn.com/flex013/user_avatar/cms-helpdesk.ncas.ac.uk/jonnyhtw/32/548_2.png) [@jonnyhtw](https://cms-helpdesk.ncas.ac.uk/u/jonnyhtw)\
**Post date:** [6 August 2026 11:18 UTC](https://cms-helpdesk.ncas.ac.uk/t/negative-mass-in-set-thermodynamic-error/2141/2 "2026-08-06T11:18:45Z")

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Hi Kexin.

Is this error reproducible? I.e. do you get exactly the same error at the same place if you run it again?

Cheers

Jonny

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<div class="post-metadata">

**Author:** ![kqiu](https://avatars.discourse-cdn.com/v4/letter/k/6a8cbe/32.png) [@kqiu](https://cms-helpdesk.ncas.ac.uk/u/kqiu)\
**Post date:** [7 August 2026 09:57 UTC](https://cms-helpdesk.ncas.ac.uk/t/negative-mass-in-set-thermodynamic-error/2141/3 "2026-08-07T09:57:55Z")

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Hi Jonny,

Yes, it is reproducible. I get it every time when the task is re-tried.

Thanks,

Kexin

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<div class="post-metadata">

**Author:** ![jonnyhtw](https://dub1.discourse-cdn.com/flex013/user_avatar/cms-helpdesk.ncas.ac.uk/jonnyhtw/32/548_2.png) [@jonnyhtw](https://cms-helpdesk.ncas.ac.uk/u/jonnyhtw)\
**Post date:** [7 August 2026 11:24 UTC](https://cms-helpdesk.ncas.ac.uk/t/negative-mass-in-set-thermodynamic-error/2141/4 "2026-08-07T11:24:15Z")

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Thanks Kexin

I’ve started a test run from the head of the trunk of `u-eb261` (see screenshot), I’ll see if I get any errors.

Couple of questions:

1. Is it the expected behaviour to lauch all the active cycle points simultaneously? As you can see from the screenshot, the cycle points for January 1, 2 and 3 are launched when the workflow starts.
2. If you have any local commits to `u-eb261` please commit them using `fcm commit` since I can’t see your `$HOME` directory.
3. Is there a particular reason why you are using a Cylc 7 setup (i.e. with a `suite.rc` file)? Currently Cylc 7 workflows can be run using Cylc 8 but not for long…

```auto
$ cylc val .
WARNING - Backward compatibility mode ON - support for suite.rc files will be removed at 8.7.0
Valid for cylc-8.6.5

```

Cheers

Jonny

 ![image](https://europe1.discourse-cdn.com/flex013/uploads/cms_support/original/1X/5db957d367efa4e705295ef59735169bf5b64a7d.png)

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**Author:** ![system](https://europe1.discourse-cdn.com/flex013/uploads/cms_support/original/1X/1fd2411499ffcbc299fe756cd5cdf26e44956558.png) [@system](https://cms-helpdesk.ncas.ac.uk/u/system)\
**Post date:** [6 September 2026 11:25 UTC](https://cms-helpdesk.ncas.ac.uk/t/negative-mass-in-set-thermodynamic-error/2141/5 "2026-09-06T11:25:11Z")

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