$Header$ -*-text-*-

The netCDF Operators NCO version 4.9.1 are woke.

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

What's new?

Version 4.9.1 contains an important bugfix for vertical interpolation,
and two small new feature for ncclimo and ncpdq. It also fixes some
autoconf-build issues that affected some users with Intel compilers,
and those attempting parallel builds of NCO.

Work on NCO 4.9.2 has commenced and will improve NCO weight-generator  
accuracy, reduce vertical interpolation memory use, and supply more
accurate weight generation options for rectangular lat-lon grids.

Work on NCO 5.0.0 has commenced "under the hood". A key leap in that 
release will be support for netCDF4 user-defined types. Printing of
netCDF4 user-defined types ENUM and VLEN is ready now (though
unsupported) with the --udt flag. 5.0.0 will contain the finished
version of that, and include options for invoking mbtempest in place
of tempest. 

Enjoy,
Charlie

NEW FEATURES (full details always in ChangeLog):

A. ncremap changes the default regridder algorithm from ESMF
   "bilinear" to NCO "nco_con", a first-order conservative algorithm 
   (similar to ESMF "conserve") that requires no external
   dependencies. Because the default algorithm comes with NCO, users
   without access to ESMF and/or TempestRemap can perform a full
   regridding workflow. Of course many/most users will still wish to
   employ ESMF or TR, and their algorithms are easily accessed:
   ncremap -a nco -s grd_src.nc -d grd_dst.nc -m map.nc   # New default
   ncremap -a bilin -s grd_src.nc -d grd_dst.nc -m map.nc # Old default
   ncremap -a fv2fv -s grd_src.nc -d grd_dst.nc -m map.nc # Tempest
   http://nco.sf.net/nco.html#alg_typ
   http://nco.sf.net/nco.html#ncremap

B. ncclimo can now output spatial-average timeseries.
   The new --glb_avg (or --global_average) option causes ncclimo to
   perform a spatial mean over the timeseries constructed from the
   input data. The main limitation is that it only works for
   timeseries whose horizontal spatial dimension is "ncol" and
   whose area weight is named "area", as in CAM SE/EAM.
   Let us know if this function would be useful to you for other
   models and we can easily add options to make these hardwired values
   specifiable from the command-line.
   ls *mdl*.nc | ncclimo --glb_avg -s 1979 -e 1981 --drc_out=drc_out
   http://nco.sf.net/nco.html#ncclimo
   http://nco.sf.net/nco.html#glb_avg

C. ncpdq has a new map, flt_dbl, to convert single-precision to
   double-precision floating point variables. The resulting variables
   are not packed. All single-precision variables, including
   coordinates, are promoted. Some software requires geospatial data
   in double precision, and this feature simplifies the dataset
   conversion. 
   ncpdq -M flt_dbl in.nc out.nc
   ncpdq -M sgl_dbl in.nc out.nc
   http://nco.sf.net/nco.html#flt_dbl
   http://nco.sf.net/nco.html#ncpdq

BUG FIXES:

A. Fix a difficulty that caused Intel compilers to fail to build NCO.
   Now the netcdf.h header, and thus the EXTERNL token, are always
   included and defined during autoconf header checks.
   Thanks to Matthew Thompson of NASA for reporting the issue, and to
   Dave Allured of NOAA for providing the fix.

B. Print WARNING instead of dying when requested to copy the
   _NCProperties attribute. That attribute should not but can be 
   exposed through the netCDF API in some circumstances, and this new
   treatment prevents that leakage from breaking workflows. Thanks to
   Rotislav for reporting and Dave Allured for helpful discussions.
   This is really a feature yet listed as a bug-fix because it is
   an incomprehensible technical workaround, the kind of thing users
   should never need to know about.

C. Fix an error when interpolating to/from a pure pressure grid.
   The minimum pressure was not always being initialized, which caused
   (highly) erroneous values when the interpolation type was mss_val.
   This bug only affects NCO installations built by compilers that do
   not automatically initialize allocated memory to preset values.
   Affected output datasets would be obviously corrupted, so nothing
   subtle about this bug. There is no workaround, the only fix is to
   upgrade. Thanks to Sterling Baldwin for reporting this.

D. Fix misuse of autoconf library references. This foiled parallel
   builds, and caused difficulty compiling ncap2. Thanks to Daniel
   Macks for identifying and solving the issue.

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 4.9.1 built/tested under
   MacOS 10.15.1 with netCDF 4.7.0 on HDF5 1.10.2 and with
   Linux with netCDF 4.7.4-development (20191203) 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

