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Re: [netcdfgroup] Negative dust values

Hi Richard,F
If you find strange/unexpected values in your data you should contact the data creator. Possibly a contact person is noted in the global attributes of your netCDF file. I am not sure whether ECMWF provides only their own data or also data of third parties.
What might be the reason for the negative values: If you look into the original netCDF file (e.g. with "ncdump -h FILENAME") you will possibly find an attribute "_fillvalue". Depending on the software you used to process the netCDF file, all values equal to "_fillvalue" are ignored or not (they should be ignored and kept untouched). Because _fillvalue is often negative, it came to my mind that your software possibly treats the _fillvalues like normal values. Because the atmospheric pressure is not constant, you will get slightly different negative values in space and time (where the _fillvalues have been before). At least this might be a reason for getting the negative values. 

Cheers,
Daniel


On 04.11.2017 15:07, Richard Cloete wrote:


Hi all,

Pretty new to NetCDF and ECMWF data.
Just a quick (probably with an obvious answer) question: What do I do with negative values? For example, I am using aermr04, aermr05 and aermr06 (dust) data from ECMWF. I have noticed many negative values.
What do I do with these data? Shall I just treat them as zeros? I ask because I am calculating the concentrations using the following formula: https://software.ecmwf.int/wiki/display/CKB/How+to+compute+concentration+from+a+mixing+ratio+field 

Many thanks,

Richard
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