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Cloudbase
Posted: Wed 10 Jan 2024 3:09 pm
by Stigian
Hi,
What am I doing wrong here when calculating cloud base. It gives me a different result than CMX. This is the formula I am using
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Cloudbase EVAL [ ((Temperature - Dewpoint ) / 4.5 ) * 1000 + 15
[EDIT]
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2024-01-10 16:12:11.321 Information CeckAllVariablesInThisSetOfCharts (found: False): Keyword: Dewpoint; Plotvar: dew; Datafile: tempdata.json
2024-01-10 16:12:11.321 Information CeckAllVariablesInThisSetOfCharts (found: False): Keyword: Temperature; Plotvar: temp; Datafile: tempdata.json
Re: Cloudbase
Posted: Wed 10 Jan 2024 4:58 pm
by HansR
Hi,
I am not sure what you are showing me here I am anyway missing the closing square bracket at the end of the EVAL.
Could you post the CutilsCharts.def please (change the extension to .txt to be able to attach it).
Could you also post the full logfile for this run (CompileOnly would be enough I guess)
Re: Cloudbase
Posted: Wed 10 Jan 2024 5:37 pm
by Stigian
Hi,
Sorry for not being clearer
CutilsCharts.txt
2401101833cumulusutils.log
Re: Cloudbase
Posted: Wed 10 Jan 2024 6:29 pm
by HansR
I use:
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CloudBase EVAL [ (Temperature - DewPoint) / 10*1247 ]
but I can't find the reference anymore
You use:
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Cloudbase EVAL [ ((Temperature - Dewpoint ) / 4.5 ) * 1000 + 15
which comes from
the wiki (I presume).
The point is that your temperatures are in Celsius but the formula expects Fahrenheit (and I think that is where my equation differs) so you have to convert the temperature and dewpoint to fahrenheit or (as the wiki says):
For metric divide the spread in °C by 8 and multiply by 1000 and get the cloud base in meters.
Hope this helps.
Re: Cloudbase
Posted: Wed 10 Jan 2024 6:40 pm
by Stigian
I've changed the formula into;
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Cloudbase EVAL [ ((Temperature - DewPoint ) / 8 ) * 1000 + 15 ]
The result is now correct. Thanks again for your help.