$Header$ -*-text-*-

The netCDF Operators NCO version 4.9.5 have arrived.

http://nco.sf.net (Homepage, Mailing lists, Help)
http://github.com/nco (Source Code, Issues, Releases, Developers)

What's new?
Version 4.9.5 is a minor NCO release that contains a few new features
and fixes to more smoothly work with current and future releases of
the E3SM climate model and with the next netCDF release. Unless the
features/fixes listed below affect you, chillax and upgrade next
time. 

Work on NCO 4.9.6 has commenced and will improve high-freqency
splitting and climo capabilities, more SIMD acceleration, and
more GPU offloading support.

Enjoy,
Charlie

NEW FEATURES (full details always in ChangeLog):

A. ncclimo supports alternates to "area" and "ncol" as names
for the area field and the horizontal dimension that it assumes
for computing global average means from splitter output with
the --glb_avg option, and for creating CMIP6-like timeseries that
automatically include the area variable.  
Two new options, --area_nm and --hrz_dmn, control the name
of the area variable (default is "area") and of the horizontal
dimension(s) (default="ncol") over which to average the
splitter output when invoked with --glb_avg.
For alternate names invoke with, e.g.,

ncclimo --glb_avg --area=area_p ...
ncclimo --glb_avg --area=area_d --hrz_dmn=ncol_d ...
ncclimo --glb_avg --hrz_dmn=lat,lon ...

In all cases the splitter will output the correct area variable. 
http://nco.sf.net/nco.html#glb_avg
http://nco.sf.net/nco.html#hrz_dmn

BUG FIXES:

A. The prototype for the nco_def_var_filterx() function
has been changed to agree with the next netCDF release.

B. An OpenMP incompatibility with the Intel Compiler Suite
has been fixed. NCO once again builds fine with Intel.

C. ncatted will now print the full list of parameters recorded
in a (netCDF4) variable's _Filter attribute.

D. Fix a bug in the computation of the intersection mesh
between two RLL grids that crept into the 4.9.4 release.

Full release statement at http://nco.sf.net/ANNOUNCE

KNOWN PROBLEMS DUE TO NCO:

   This section of ANNOUNCE reports and reminds users of the
   existence and severity of known, not yet fixed, problems. 
   These problems occur with NCO 4.9.5 built/tested under
   MacOS 10.15.6 with netCDF 4.7.4 on HDF5 1.10.2 and with
   Linux with netCDF 4.8.0-development (2020715) on HDF5 1.8.19.

A. NOT YET FIXED (NCO problem)
   Correctly read arrays of NC_STRING with embedded delimiters in ncatted arguments

   Demonstration:
   ncatted -D 5 -O -a new_string_att,att_var,c,sng,"list","of","str,ings" ~/nco/data/in_4.nc ~/foo.nc
   ncks -m -C -v att_var ~/foo.nc

   20130724: Verified problem still exists
   TODO nco1102
   Cause: NCO parsing of ncatted arguments is not sophisticated
   enough to handle arrays of NC_STRINGS with embedded delimiters.

B. NOT YET FIXED (NCO problem?)
   ncra/ncrcat (not ncks) hyperslabbing can fail on variables with multiple record dimensions

   Demonstration:
   ncrcat -O -d time,0 ~/nco/data/mrd.nc ~/foo.nc

   20140826: Verified problem still exists
   20140619: Problem reported by rmla
   Cause: Unsure. Maybe ncra.c loop structure not amenable to MRD?
   Workaround: Convert to fixed dimensions then hyperslab

KNOWN PROBLEMS DUE TO BASE LIBRARIES/PROTOCOLS:

A. NOT YET FIXED (netCDF4 or HDF5 problem?)
   Specifying strided hyperslab on large netCDF4 datasets leads
   to slowdown or failure with recent netCDF versions.

   Demonstration with NCO <= 4.4.5:
   time ncks -O -d time,0,,12 ~/ET_2000-01_2001-12.nc ~/foo.nc
   Demonstration with NCL:
   time ncl < ~/nco/data/ncl.ncl   
   20140718: Problem reported by Parker Norton
   20140826: Verified problem still exists
   20140930: Finish NCO workaround for problem
   20190201: Possibly this problem was fixed in netCDF 4.6.2 by https://github.com/Unidata/netcdf-c/pull/1001
   Cause: Slow algorithm in nc_var_gets()?
   Workaround #1: Use NCO 4.4.6 or later (avoids nc_var_gets())
   Workaround #2: Convert file to netCDF3 first, then use stride
   Workaround #3: Compile NCO with netCDF >= 4.6.2

B. NOT YET FIXED (netCDF4 library bug)
   Simultaneously renaming multiple dimensions in netCDF4 file can corrupt output

   Demonstration:
   ncrename -O -d lev,z -d lat,y -d lon,x ~/nco/data/in_grp.nc ~/foo.nc # Completes but produces unreadable file foo.nc
   ncks -v one ~/foo.nc

   20150922: Confirmed problem reported by Isabelle Dast, reported to Unidata
   20150924: Unidata confirmed problem
   20160212: Verified problem still exists in netCDF library
   20160512: Ditto
   20161028: Verified problem still exists with netCDF 4.4.1
   20170323: Verified problem still exists with netCDF 4.4.2-development
   20170323: https://github.com/Unidata/netcdf-c/issues/381
   20171102: Verified problem still exists with netCDF 4.5.1-development
   20171107: https://github.com/Unidata/netcdf-c/issues/597
   20190202: Progress has recently been made in netCDF 4.6.3-development
   More details: http://nco.sf.net/nco.html#ncrename_crd

C. NOT YET FIXED (would require DAP protocol change?)
   Unable to retrieve contents of variables including period '.' in name
   Periods are legal characters in netCDF variable names.
   Metadata are returned successfully, data are not.
   DAP non-transparency: Works locally, fails through DAP server.

   Demonstration:
   ncks -O -C -D 3 -v var_nm.dot -p http://thredds-test.ucar.edu/thredds/dodsC/testdods in.nc # Fails to find variable

   20130724: Verified problem still exists. 
   Stopped testing because inclusion of var_nm.dot broke all test scripts.
   NB: Hard to fix since DAP interprets '.' as structure delimiter in HTTP query string.

   Bug tracking: https://www.unidata.ucar.edu/jira/browse/NCF-47

D. NOT YET FIXED (would require DAP protocol change)
   Correctly read scalar characters over DAP.
   DAP non-transparency: Works locally, fails through DAP server.
   Problem, IMHO, is with DAP definition/protocol

   Demonstration:
   ncks -O -D 1 -H -C -m --md5_dgs -v md5_a -p http://thredds-test.ucar.edu/thredds/dodsC/testdods in.nc

   20120801: Verified problem still exists
   Bug report not filed
   Cause: DAP translates scalar characters into 64-element (this
   dimension is user-configurable, but still...), NUL-terminated
   strings so MD5 agreement fails 

"Sticky" reminders:

A. Reminder that NCO works on most HDF4 and HDF5 datasets, e.g., 
   HDF4: AMSR MERRA MODIS ...
   HDF5: GLAS ICESat Mabel SBUV ...
   HDF-EOS5: AURA HIRDLS OMI ...

B. Pre-built executables for many OS's at:
   http://nco.sf.net#bnr

