# What does 'Spin-up', 'Ramp-up' and 'Pre-run' mean?

**URL:** https://forum.cmascenter.org/t/what-does-spin-up-ramp-up-and-pre-run-mean/2474
**Category:** CMAQ
**Created:** [July 7, 2021, 7:27am UTC](https://forum.cmascenter.org/t/what-does-spin-up-ramp-up-and-pre-run-mean/2474 "2021-07-07T07:27:27Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![CCBB](https://avatars.discourse-cdn.com/v4/letter/c/77aa72/32.png) [@CCBB](https://forum.cmascenter.org/u/CCBB)
#### Post date: [July 7, 2021, 7:27am UTC](https://forum.cmascenter.org/t/what-does-spin-up-ramp-up-and-pre-run-mean/2474/1 "2021-07-07T07:27:27Z")

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Hi,  
I’m beginner of wrf-smoke-cmaq model.  
I wonder what the difference is because the concepts of ‘Spin-up’, ‘Ramp-up’ and ‘Pre-run’ look similar, but they will be marked differently.

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### Author: ![lizadams](https://avatars.discourse-cdn.com/v4/letter/l/49beb7/32.png) [@lizadams](https://forum.cmascenter.org/u/lizadams)
#### Post date: [July 7, 2021, 9:06pm UTC](https://forum.cmascenter.org/t/what-does-spin-up-ramp-up-and-pre-run-mean/2474/2 "2021-07-07T21:06:07Z")

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Spin-up refers to how CMAQ starts with a “clean” initial conditions concentration and runs for approximately 2 weeks, after that point, the effect of the “clean” initial conditions is reduced. The Start Date of the modeling can proceed using well-mixed atmospheric conditions that take into consideration meteorology, chemical reactions, and emissions.

I am not familiar with the terms “ramp-up” or “pre-run”.