# CERRA hybrid sigma levels

**URL:** <https://forum.ecmwf.int/t/cerra-hybrid-sigma-levels/1370>\
**Category:** C3S - Datasets and Usage\
**Tags:** c3s, cerra, regional\_reanalysis\
**Created:** [15 November 2023 18:54 UTC](https://forum.ecmwf.int/t/cerra-hybrid-sigma-levels/1370 "2023-11-15T18:54:24Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Edward\_Carroll](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/e/f4b2a3/32.png) [@Edward\_Carroll](https://forum.ecmwf.int/u/Edward_Carroll)\
**Post date:** [15 November 2023 18:54 UTC](https://forum.ecmwf.int/t/cerra-hybrid-sigma-levels/1370/1 "2023-11-15T18:54:24Z")

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I'm accessing model level data and have found the list of A and B values along with level and half-level pressures in a standard atmosphere for each level number - using this information I can construct a converter to get the pressure of the level given the level number and pressure at the surface. My question is, how do I know which of the parameters (specific humidity, temperature u and v winds) are held on full levels and which on half-levels? As far as I remember, for Met Office Unified Model data the winds are held on levels intermediate to those on which temperature is held. I can see no information on this in the CERRA documentation. Have I missed something?

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**Author:** ![Semjon\_Schimanke](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/s/cc9497/32.png) [@Semjon\_Schimanke](https://forum.ecmwf.int/u/Semjon_Schimanke)\
**Post date:** [16 November 2023 22:44 UTC](https://forum.ecmwf.int/t/cerra-hybrid-sigma-levels/1370/2 "2023-11-16T22:44:41Z")

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Hi Edward,

all parameters are on full-levels in CERRA.&nbsp;  
 The reason to provide even information for half levels is that the lowest level is at the ground and sometimes you need to compute gradients, e.g. T\*dp.

Best regards, Semjon

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**Author:** ![Edward\_Carroll](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/e/f4b2a3/32.png) [@Edward\_Carroll](https://forum.ecmwf.int/u/Edward_Carroll)\
**Post date:** [17 November 2023 20:58 UTC](https://forum.ecmwf.int/t/cerra-hybrid-sigma-levels/1370/3 "2023-11-17T20:58:33Z")

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Thanks very much Semjon!

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**Author:** ![Xavier\_Bonnemaizon](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/x/db5fbb/32.png) [@Xavier\_Bonnemaizon](https://forum.ecmwf.int/u/Xavier_Bonnemaizon)\
**Post date:** [26 January 2026 14:26 UTC](https://forum.ecmwf.int/t/cerra-hybrid-sigma-levels/1370/4 "2026-01-26T14:26:50Z")

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Hello Edward,

Where did you find these A and B coefficients for the 106 model levels of CERRA ? I couldn’t find it in order to compute the vertical pressure.

Thank you for your help,

Regards

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**Author:** ![Sinan\_Sahinoglu](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/s/2acd7d/32.png) [@Sinan\_Sahinoglu](https://forum.ecmwf.int/u/Sinan_Sahinoglu)\
**Post date:** [10 March 2026 13:55 UTC](https://forum.ecmwf.int/t/cerra-hybrid-sigma-levels/1370/5 "2026-03-10T13:55:35Z")

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Any update about the A and B coefficients of CERRA model levels?

Thanks