[Met_help] MET questions

[John Halley Gotway]

Cory,

I figured out the issue in the computation of the Spearman's Correlation Coefficient.  While your netCDF observation file (nz_metar_08012118_TTTTT.nc) contains 130 observations, only 84 of them 
contain valid data.  And to put it concisely, in computing Spearman's, Point-Stat was using the wrong count value (84 instead of 130).  The fix is just to skip past any observations which contain bad 
data values.  So the matched pairs used in computing stats should now always consist of a "valid" forecast value and a "valid" observation value.

I had not anticipated that someone might submit a bad data value for the observation.

I posted a short explanation and fix on the known issues page of the MET website.  Please access it there:
http://www.dtcenter.org/met/users/support/known_issues/METv1.0/METv1.0_known_issues.php

Thanks for pointing out the problem.  It really helps us a lot.

And please let us know if any more questions come up.

John

Cory Davis wrote:
> Hi there,
> I have a few questions and concerns about MET and in particular the
> point_stat tool.  These issues are related to whether I am using 2D
> model output fields correctly, negative returned values for the Spearman
> rank correlation coefficient, and trouble verifying mean sea level
> pressure.
> 
> I have managed to write python code which converts our METAR
> observations (already in netcdf) into MET compatible netcdf files.
> Also, our operational system already produces grib output via RIP for
> several variables, for instance 2m temperature, 10m windspeed, and mean
> sea level pressure, and these should correspond directly to the METAR
> observations.  I got the impression from the MET documentation that it
> is really expecting 3D model fields. However point_stat does run with
> these 2D model files, and also produces sensible output, at least for 2m
> temperature and 10m wind speed.  However, there does seem to be a
> problem with the Spearman rank correlation coefficient.  It is negative.
> Given that all the other returned values seem reasonable - the first
> impression is that this is a bug or another architecture dependent
> problem.  I have attached, obs., model, config, and output that should
> reproduce this.
> 
> For the mean sea level pressure I have a different problem: point_stat
> detects no pairs and hence no statistics.  I don't know why this should
> be the case given that the obs. and model files were produced by the
> same process as the T2 and windspeed files.  It is possibly an issue
> about how one specifies the level in the PointStatConfig_PPmsl file.
> Also, I will have a closer look at the grib file to see if this is
> somehow different to the T2 and ws10 grib files.
> 
> Any help with this would be hugely appreciated.
> 
> Cheers,
> Cory.
> 
> 
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