[ncl-talk] Strange behavior when reading data from OpenDAP server

[Tyle, Kevin R]

Hi,



We run a THREDDS server,http://thredds.atmos.albany.edu:8080/thredds/catalog.html (running TDS version 4.6.10) that serves out a variety of datasets.  One of the datasets consists of 4x/day yearly gridded data in NetCDF format.



NCL 6.5.0 (and earlier versions), when reading in data via OpenDAP, while not throwing an error, will typically produce output where a requested variable has values of 0 for all points.  This looks to be related to the size of the dataset.  The attached script attempts to read from files containing SLP data from Jan. 1 2018 to either present, 125 days in, or 25 days in.  Only the shortest time window produces expected output.



If I use the direct filepath (i.e. no OpenDAP) to where the data file actually sits on our filesystem, the expected values appear for all three time-extents.



This behavior occurs both on my THREDDS instance and another OpenDAP service (both point to the same physical files) when using NCL.  However, reading the data using Python’s opendap-capable libraries (e.g. xarray) works fine.



The attached script should work from any NCL client with OpenDAP built in.  I’ve also attached the output from running the script locally; one sees correct values of SLP min/max on the first URL, but zeroes for the next two.



Thanks for any insight!



Cheers,



Kevin





_____________________________________________
Kevin Tyle, M.S.; Manager of Departmental Computing
Dept. of Atmospheric & Environmental Sciences
University at Albany
Earth Science 235, 1400 Washington Avenue
Albany, NY 12222
Email: ktyle at albany.edu
Phone: 518-442-4578
_____________________________________________
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