compression levels for ncl_convert2nc

From: Jonathan Vigh <jvigh_at_nyahnyahspammersnyahnyah>
Date: Fri Jun 15 2012 - 16:05:09 MDT

Greetings NCL'ers,

     I'm contemplating the use of ncl_convert2nc to convert some large
model output files from grib format to netcdf. These netcdf files will
be used later to construct a climatology of the model data set over many
months, so I need to pay some attention to the precision in order to
compute accurate anomalies. I've done some tests -- if I use the default
settings on ncl_convert2nc (equivalent to a compression level of 0), the
resulting file is nearly three times the size of the original grib file.
I'd like to preserve as much practical numerical fidelity as possible
without adding in "wasteful" precision that doesn't add any information.
So my questions are:

  * Does anyone have any information about how the different compression
    levels affect precision?
  * Does it follow that the precision in a grib file or netcdf file will
    be similar if their file sizes are similar?

I have no idea if data stored in a netcdf vs. grib should be of similar
sizes. I thought they might be, since they are both a type of binary,
except I realize that the details of how the data are packed could lead
to significant differences.

Thanks,
    Jonathan

-- 
Jonathan Vigh						
Project Scientist I, Joint Numerical Testbed	
Research Applications Laboratory (RAL)
National Center for Atmospheric Research (NCAR)
P.O. Box 3000            tel: +1 303 497 8205
Boulder, CO 80307-3000   fax: +1 (303) 497-8171
http://www.ral.ucar.edu/staff/jvigh/
http://www.ral.ucar.edu/hurricanes/

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Received on Fri Jun 15 16:05:17 2012

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