# Subsetting existing inputs for CCTM

**URL:** <https://forum.cmascenter.org/t/subsetting-existing-inputs-for-cctm/340>\
**Category:** CMAQ\
**Created:** [October 5, 2018, 9:25pm UTC](https://forum.cmascenter.org/t/subsetting-existing-inputs-for-cctm/340 "2018-10-05T21:25:44Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![LGS](https://avatars.discourse-cdn.com/v4/letter/l/839c29/32.png) [@LGS](https://forum.cmascenter.org/u/LGS)\
**Post date:** [October 5, 2018, 9:25pm UTC](https://forum.cmascenter.org/t/subsetting-existing-inputs-for-cctm/340/1 "2018-10-05T21:25:44Z")

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Hello!

Is it possible to create subsets from existing CCTM inputs and run CCTM simulation with them? For example, all my inputs are for a coarse domain (US1) but I would like to simulate a smaller domain which is centered on the SE US. Unfortunately, I do not have WRF outputs to use the nested simulation.

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**Author:** ![cgnolte](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.cmascenter.org/cgnolte/32/53_2.png) [@cgnolte](https://forum.cmascenter.org/u/cgnolte)\
**Post date:** [October 9, 2018, 4:39pm UTC](https://forum.cmascenter.org/t/subsetting-existing-inputs-for-cctm/340/2 "2018-10-09T16:39:32Z")

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No, this is not possible.  
The CCTM is the CMAQ Chemical Transport Model. Meteorological data is essential for the “transport” aspect of CMAQ.

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**Author:** ![LGS](https://avatars.discourse-cdn.com/v4/letter/l/839c29/32.png) [@LGS](https://forum.cmascenter.org/u/LGS)\
**Post date:** [October 9, 2018, 7:50pm UTC](https://forum.cmascenter.org/t/subsetting-existing-inputs-for-cctm/340/3 "2018-10-09T19:50:59Z")

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Just to clarify. So, there is no way to run a CCTM simulation for a smaller domain with the MCIP and emissions inputs for a coarse domain by bypassing the nested simulation? Thanks!

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**Author:** ![cjcoats](https://avatars.discourse-cdn.com/v4/letter/c/ac8455/32.png) [@cjcoats](https://forum.cmascenter.org/u/cjcoats)\
**Post date:** [October 22, 2018, 12:04am UTC](https://forum.cmascenter.org/t/subsetting-existing-inputs-for-cctm/340/4 "2018-10-22T00:04:40Z")

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Now, what is it you mean by “smaller domain”? Do you mean a domain with the same resolution  
and grid-alignment, but smaller dimensions (a “proper window” domain)? (For example, if the existing domain is 300x400, a smaller domain consisting of rows 50:150 and columns 75:200 from the original domain?)

If so, this is exactly the task for which M3TOOLS programs “bcwindow” and “m3window” were designed…

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**Author:** ![LGS](https://avatars.discourse-cdn.com/v4/letter/l/839c29/32.png) [@LGS](https://forum.cmascenter.org/u/LGS)\
**Post date:** [October 24, 2018, 7:51pm UTC](https://forum.cmascenter.org/t/subsetting-existing-inputs-for-cctm/340/5 "2018-10-24T19:51:47Z")

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That’s exactly what I meant by a smaller domain. Thank you for the details how to define the window from a larger domain and for pointing out the existing m3tools for this task. I will give it a try!