# \[v4.2.x\] Computation errors for Lupkes parameterization in \*sbcblk\_algo\_ice\_cdn.F90\*

**URL:** <https://nemo-ocean.discourse.group/t/v4-2-x-computation-errors-for-lupkes-parameterization-in-sbcblk-algo-ice-cdn-f90/298>\
**Category:** v4.2.x\
**Tags:** SBC, ICE\
**Created:** [13 May 2022 09:07 UTC](https://nemo-ocean.discourse.group/t/v4-2-x-computation-errors-for-lupkes-parameterization-in-sbcblk-algo-ice-cdn-f90/298 "2022-05-13T09:07:20Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![vguemas](https://avatars.discourse-cdn.com/v4/letter/v/7ab992/32.png) [@vguemas](https://nemo-ocean.discourse.group/u/vguemas)\
**Post date:** [13 May 2022 09:07 UTC](https://nemo-ocean.discourse.group/t/v4-2-x-computation-errors-for-lupkes-parameterization-in-sbcblk-algo-ice-cdn-f90/298/1 "2022-05-13T09:07:20Z")

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Hi,

In routine _sbcblk\_algo\_ice\_cdn.F90_, l. 86 computes equation (31) of Lupkes et al (2012) which gives `Sc*Sc` rather than not `Sc`. Hence, when the result is used in l.106, `zSc` should be used instead of `zSc*zSc`. The same mistake appears l.252.

Best regards  
Virginie

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**Author:** ![Guillaume\_Mercator](https://yyz2.discourse-cdn.com/free1/user_avatar/nemo-ocean.discourse.group/guillaume_mercator/32/252_2.png) [@Guillaume\_Mercator](https://nemo-ocean.discourse.group/u/Guillaume_Mercator)\
**Post date:** [13 May 2022 14:34 UTC](https://nemo-ocean.discourse.group/t/v4-2-x-computation-errors-for-lupkes-parameterization-in-sbcblk-algo-ice-cdn-f90/298/2 "2022-05-13T14:34:18Z")

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Hello Virginie,

Thank you for pointing out this bug ! I have corrected it in the last revision of the main & 4.2 branches (see [bug in Lupkes sea-ice transfert coefficients formula (#48) · Issues · NEMO Sources / Nemo · GitLab](https://forge.nemo-ocean.eu/nemo/nemo/-/issues/48) for details).

Here is an illustration of the differences induced by this bug in terms of sea-ice fraction averaged over one month of ORCA025 + Lupkes 2012 simulation:

 ![diff_LU12BF-LU12](https://global.discourse-cdn.com/free1/uploads/nemo_ocean/original/1X/91a1fd49a6e8d946d26f363353ce0eea6c27da0a.png)

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**Author:** ![vguemas](https://avatars.discourse-cdn.com/v4/letter/v/7ab992/32.png) [@vguemas](https://nemo-ocean.discourse.group/u/vguemas)\
**Post date:** [13 May 2022 14:38 UTC](https://nemo-ocean.discourse.group/t/v4-2-x-computation-errors-for-lupkes-parameterization-in-sbcblk-algo-ice-cdn-f90/298/3 "2022-05-13T14:38:27Z")

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Thanks a lot  
Virginie

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**Author:** ![ntmlod](https://yyz2.discourse-cdn.com/free1/user_avatar/nemo-ocean.discourse.group/ntmlod/32/6_2.png) [@ntmlod](https://nemo-ocean.discourse.group/u/ntmlod)\
**Post date:** [13 May 2022 14:41 UTC](https://nemo-ocean.discourse.group/t/v4-2-x-computation-errors-for-lupkes-parameterization-in-sbcblk-algo-ice-cdn-f90/298/4 "2022-05-13T14:41:34Z")

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