# Differences between CH4 and CH4\_C

**URL:** <https://forum.ecmwf.int/t/differences-between-ch4-and-ch4-c/1036>\
**Category:** CAMS - Datasets and Usage\
**Tags:** ghg, cams\
**Created:** [8 October 2019 14:28 UTC](https://forum.ecmwf.int/t/differences-between-ch4-and-ch4-c/1036 "2019-10-08T14:28:47Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Michela](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/m/898d66/32.png) [@Michela](https://forum.ecmwf.int/u/Michela)\
**Post date:** [8 October 2019 14:28 UTC](https://forum.ecmwf.int/t/differences-between-ch4-and-ch4-c/1036/1 "2019-10-08T14:28:47Z")

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What's the difference between CH4 data accessible on request only (or through MARS) and the CH4\_C forecast data (latest three days) available on the [ECMWF FTP server](https://confluence.ecmwf.int/display/CKB/FTP+access+to+CAMS+global+data)?

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**Author:** ![Michela](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/m/898d66/32.png) [@Michela](https://forum.ecmwf.int/u/Michela)\
**Post date:** [8 October 2019 14:30 UTC](https://forum.ecmwf.int/t/differences-between-ch4-and-ch4-c/1036/2 "2019-10-08T14:30:35Z")

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The methane data differ as follows:

- CH4 comes from the CAMS Greenhouse Gases (GHG) analysis and forecasts and has a simplified chemistry but it is based on the assimilation of IASI and GOSAT methane observations.
- CH4\_C is a model-only product with full chemistry but no assimilation of CH4 observations . It's available from the [ECMWF FTP server](https://confluence.ecmwf.int/display/CKB/FTP+access+to+CAMS+global+data).

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**Author:** ![UnknownUser](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/u/35a633/32.png) [@UnknownUser](https://forum.ecmwf.int/u/UnknownUser)\
**Post date:** [11 January 2021 10:34 UTC](https://forum.ecmwf.int/t/differences-between-ch4-and-ch4-c/1036/3 "2021-01-11T10:34:24Z")

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- CH4 is the official value from CAMS and it is produced by from the Greenhouse Gases (GHG) analysis and forecasts suite: it is based on the near-real-time assimilation&nbsp;of IASI, GOSAT and TROPOMI satellite observations and uses a simplified chemistry with climatological OH fields.