<p>I am also getting negative relative humidity from the GFS (Global Forecast System): 36-hour predicted atmosphere dataset (Provider: NOAA/NCEP/EMC, their website: <a href="http://www.emc.ncep.noaa.gov/index.php?branch=GFS" rel="nofollow noreferrer">http://www.emc.ncep.noaa.gov/index.php?branch=GFS</a>)</p>

<p>I found this link that answers as to why relative humidity is possible in their dataset: </p>

<p><a href="http://ftp.cpc.ncep.noaa.gov/wd51we/reanal/random_notes/negative.h2o" rel="nofollow noreferrer">http://ftp.cpc.ncep.noaa.gov/wd51we/reanal/random_notes/negative.h2o</a></p>

<p>This might apply to the one you have access too. </p>

<p>Let me know if this helps.</p>

CC BY-SA 3.0
2017-02-25T11:51:26.060Z
2017-02-25T11:51:26.060Z
ziggy
<p>I recently started using the Climate Forecast System Reanalysis (CFSR) 6-hourly products (<a href="http://rda.ucar.edu/datasets/ds093.0/" rel="nofollow">http://rda.ucar.edu/datasets/ds093.0/</a>), and I noticed many values of relative humidity are negative. Is this an error in the dataset? If not, how should I interpret negative values?</p>

CC BY-SA 3.0
2015-01-24T02:27:30.400Z
Have you tried accessing the data through a THREDDS data server: http://nomads.ncdc.noaa.gov/thredds/dodsC/modeldata/cmd_pgbh/2011/201101/20110101/pgbh06.gdas.2011010100.grb2? That usually provides information about valid ranges
arkaia
CC BY-SA 3.0
2015-01-24T03:27:06.990Z
@aretxabaleta thanks for the comment - No I have not, is this can FTP server? I typed that address in my browser and it says "Unrecognized request". By "valid ranges", do you mean valid humidity ranges, date ranges or else? But I'll look it up and see what I can find.
user2490
CC BY-SA 3.0
2015-01-24T12:04:05.937Z
@aretxabaleta is it the link you wanted to give http://nomads.ncdc.noaa.gov/thredds/dodsC/modeldata/cmd_pgbh/2011/201101/20110101/catalog.html?dataset=modeldata/cmd_pgbh/2011/201101/20110101/pgbh06.gdas.2011010100.grb2 ? I got an "Unrecognized request" as well with yours.
plannapus
CC BY-SA 3.0
2015-01-24T15:11:09.727Z
Yes, that is it. Sorry. I just posted the one I use to get the data directly. I tend to use THREDDS and Matlab and the function ncgeodataset (https://code.google.com/p/nctoolbox/wiki/ncgeodataset) to subsample the netcdf without having to dowload large datasets
arkaia
CC BY-SA 3.0
2015-01-24T18:00:51.583Z
What negative values specifically? Seemingly randomly distributed numbers, or the sort of numbers used to denote missing data: -1, -99, -999. What does the metadata say?
410 gone
CC BY-SA 3.0
2015-01-25T01:34:20.087Z
Thanks - @aretxabaleta I use ncgeodataset with MATLAB too, but I always download the grib2 or netcdf files, then use it to read the file. Are you saying you can use ncgeodataset to download only part of a large grib2 file?
user2490
CC BY-SA 3.0
2015-01-25T01:35:40.490Z
@EnergyNumbers I could not find documentation on negative numbers. They are not a "missing value" indicator like -99 or -9999. For the file I was looking at they range from about -50 to -1e-3.
user2490
CC BY-SA 3.0
2015-01-25T03:16:41.657Z
And what's the largest value in that particular file where the negative value went down to -50? Was it above or below +50?
410 gone
CC BY-SA 3.0
2015-01-25T04:45:58.540Z
@user2490, definitely! For instance, nc = ncgeodataset('http://thredds.jpl.nasa.gov/thredds/dodsC/ncml_aggregation/OceanTemperature/ghrsst/aggregate__ghrsst_JPL_OUROCEAN-L4UHfnd-GLOB-G1SST_OI.ncml');
gvar = nc.geovariable('analysed_sst');
s.time={'20-May-2012', '24-May-2012'};
s.lat=[40 41.5];
s.lon=[0 2.0];
sub = gvar.geosubset(s); % Subset method
pcolor(sub.grid.lon,sub.grid.lat,double(squeeze(sub.data(1,:,:)))-273.15);
arkaia
CC BY-SA 3.0
2015-01-25T23:45:32.470Z
Can you please post a filled contour plot of global RH, with the range of 0 to 1 (or 0 to 100, if RH is a percentage), at the time when you find negative values? This should show where it is negative (out of range being white). Since RH is a positive definite quantity, I suspect this is an issue of either nonconservative advection scheme or nonconservative convection or microphysics parameterization schemes, although the latter typically employ hard limiters on positive definite quantities to make sure they stay in range.
milancurcic
CC BY-SA 3.0
2015-01-28T16:17:14.833Z
Small negative values are common in numerical models, but values down to -1e3 are too small for that.
gerrit
<meteorology><models><open-data>
Negative values of relative humidity in CFSR
user2490
# Negative values of relative humidity in CFSR

(Asked by: username_0 on 2015-01-24)

I recently started using the Climate Forecast System Reanalysis (CFSR) 6-hourly products (<http://rda.ucar.edu/datasets/ds093.0/>), and I noticed many values of relative humidity are negative. Is this an error in the dataset? If not, how should I interpret negative values?

**Tags:** meteorology, models, open-data

> **Comments:**
> **username_1**: Have you tried accessing the data through a THREDDS data server: http://nomads.ncdc.noaa.gov/thredds/dodsC/modeldata/cmd_pgbh/2011/201101/20110101/pgbh06.gdas.2011010100.grb2? That usually provides information about valid ranges  
> **username_0**: @aretxabaleta thanks for the comment - No I have not, is this can FTP server? I typed that address in my browser and it says "Unrecognized request". By "valid ranges", do you mean valid humidity ranges, date ranges or else? But I'll look it up and see what I can find.  
> **username_2**: @aretxabaleta is it the link you wanted to give http://nomads.ncdc.noaa.gov/thredds/dodsC/modeldata/cmd_pgbh/2011/201101/20110101/catalog.html?dataset=modeldata/cmd_pgbh/2011/201101/20110101/pgbh06.gdas.2011010100.grb2 ? I got an "Unrecognized request" as well with yours.  
> **username_1**: Yes, that is it. Sorry. I just posted the one I use to get the data directly. I tend to use THREDDS and Matlab and the function ncgeodataset (https://code.google.com/p/nctoolbox/wiki/ncgeodataset) to subsample the netcdf without having to dowload large datasets  
> **username_3**: What negative values specifically? Seemingly randomly distributed numbers, or the sort of numbers used to denote missing data: -1, -99, -999. What does the metadata say?  
> **username_0**: Thanks - @aretxabaleta I use ncgeodataset with MATLAB too, but I always download the grib2 or netcdf files, then use it to read the file. Are you saying you can use ncgeodataset to download only part of a large grib2 file?  
> **username_0**: @EnergyNumbers I could not find documentation on negative numbers. They are not a "missing value" indicator like -99 or -9999. For the file I was looking at they range from about -50 to -1e-3.  
> **username_3**: And what's the largest value in that particular file where the negative value went down to -50? Was it above or below +50?  
> **username_1**: @username_0, definitely! For instance, nc = ncgeodataset('http://thredds.jpl.nasa.gov/thredds/dodsC/ncml_aggregation/OceanTemperature/ghrsst/aggregate__ghrsst_JPL_OUROCEAN-L4UHfnd-GLOB-G1SST_OI.ncml'); gvar = nc.geovariable('analysed_sst'); s.time={'20-May-2012', '24-May-2012'}; s.lat=[40 41.5]; s.lon=[0 2.0]; sub = gvar.geosubset(s); % Subset method pcolor(sub.grid.lon,sub.grid.lat,double(squeeze(sub.data(1,:,:)))-273.15);  
> **username_4**: Can you please post a filled contour plot of global RH, with the range of 0 to 1 (or 0 to 100, if RH is a percentage), at the time when you find negative values? This should show where it is negative (out of range being white). Since RH is a positive definite quantity, I suspect this is an issue of either nonconservative advection scheme or nonconservative convection or microphysics parameterization schemes, although the latter typically employ hard limiters on positive definite quantities to make sure they stay in range.  
> **username_5**: Small negative values are common in numerical models, but values down to -1e3 are too small for that.  

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## 1 answers

### Answer by username_6 on 2017-02-25. Score: 1

I am also getting negative relative humidity from the GFS (Global Forecast System): 36-hour predicted atmosphere dataset (Provider: NOAA/NCEP/EMC, their website: <http://www.emc.ncep.noaa.gov/index.php?branch=GFS>)

I found this link that answers as to why relative humidity is possible in their dataset:

<http://ftp.cpc.ncep.noaa.gov/wd51we/reanal/random_notes/negative.h2o>

This might apply to the one you have access too.

Let me know if this helps.


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