# 4km CMAQ run nested in 12km

**URL:** <https://forum.cmascenter.org/t/4km-cmaq-run-nested-in-12km/4854>\
**Category:** CMAQ\
**Tags:** cmaq\
**Created:** [April 10, 2024, 9:00pm UTC](https://forum.cmascenter.org/t/4km-cmaq-run-nested-in-12km/4854 "2024-04-10T21:00:54Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Hasibul](https://avatars.discourse-cdn.com/v4/letter/h/838e76/32.png) [@Hasibul](https://forum.cmascenter.org/u/Hasibul)\
**Post date:** [April 10, 2024, 9:00pm UTC](https://forum.cmascenter.org/t/4km-cmaq-run-nested-in-12km/4854/1 "2024-04-10T21:00:54Z")

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Hello all,

I want to run ICON and BCON for 4km grid to be run cctm for the timeframe of Feb 1,2023 through May 1,2023. I want to use 12km grid output that I will have for the regrid input. Do I need CONC or ACONC as input for ICON and BCON? For which timeframe I need to run 12Km domain for to be regridded in 4km domain? Thanks for your help.

Hasibul

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**Author:** ![Ryan](https://avatars.discourse-cdn.com/v4/letter/r/a8b319/32.png) [@Ryan](https://forum.cmascenter.org/u/Ryan)\
**Post date:** [April 11, 2024, 6:39pm UTC](https://forum.cmascenter.org/t/4km-cmaq-run-nested-in-12km/4854/2 "2024-04-11T18:39:34Z")

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> [@Hasibul](#):
>
> Do I need CONC or ACONC as input for ICON and BCON?

CONC files are needed because they contain 3-D data (especially vertical layers, make sure you include all vertical layer data in your 12km CMAQ runs).

> [@Hasibul](#):
>
> For which timeframe I need to run 12Km domain for to be regridded in 4km domain?

It depends on the temporal resolution of your 12km CMAQ CONC files. In general, hourly would be good.

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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:** [April 11, 2024, 6:49pm UTC](https://forum.cmascenter.org/t/4km-cmaq-run-nested-in-12km/4854/3 "2024-04-11T18:49:34Z")

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NO, not 3 or 4 hours: you need a time step that resolves the features of the 12KM concentration field both temporally and spatially.

As a rule of thumb, you can regard a 10 M/S top-of-the-PBL wind field as a conversion factor between temporal and spatial resolution.

The WRF model is known to resolve _3_DX\* features in its met-fields, so that corresponds to a temporal resolution of  
36,000 M / 10 M/S = 3600 S as the coarsest temporal resolution you should use (the Nyquist Theorem suggests you should use at most half of that; the direct translation of 12,000 M would be 1200 S = 20 minutes.

FWIW.