\vsssub
\subsubsection{Gridded output NetCDF post-processor} \label{sec:ww3ounf}
\vsssub

\proddefH{ww3\_ounf}{w3ounf}{ww3\_ounf.ftn}
\proddeff{Input}{ww3\_ounf.nml}{Namelist configuration file.}{10} (App.~\ref{sec:config132})
\proddefa{ww3\_ounf.inp}{Tradition configuration file.}{10} (App.~\ref{sec:config131})
\proddefa{mod\_def.ww3}{Model definition file.}{20}
\proddefa{out\_grd.ww3}{Raw gridded output data.}{20}
\proddefa{NC\_globatt.inp}{Additional global attributes (deprecated)}{994}
\proddefa{ounfmeta.inp}{User defined meta data attributes}{60}
\proddeff{Output}{standard out}{Formatted output of program.}{6}
\proddefa{\opt  .nc}{NetCDF file}{}


\vspace{\baselineskip}

\noindent
When a single field is put in the file, the abbreviated field name (file
extensions from ww3\_outf) for each data type is given in
Table~\ref{tab:fields} on page~\pageref{tab:fields}.

\noindent
\paragraph{User configuration of meta-data:}

\noindent
Default meta data (attributes) are generated in the output netCDF file
for each WW3 output variable. If desired, the user can override existing or
configure extra metadata via an input text file with the filename `ounfmeta.inp'.


\noindent
The `ounfmeta.inp' file can be used to override/configure the following:
\begin{itemize}
  \item Modify/extend netCDF attributes for gridded output variables
  \item Modify/extend "global" netCDF attributes
  \item Define/redefine a coordinate reference system
  \item Define template strings for generating attributes for
        partitioned parameter output variables.
\end{itemize}

\noindent
Entries are made in the ounfmeta.inp file via \emph{sections} marked with a keyword.
Blank lines and comments lines (starting with \texttt{\$}) are ignored.
Note: All keywords and `Field Name ID' strings (e.g. \texttt{HS}) are
case insensitive. All netCDF attribute names are case sensitive.

\noindent
\paragraph{Modify/add attributes for a WW3 gridded output field:}

\noindent
An output field is selected using the META keyword followed by
either an integer pair \texttt{GroupNum} and \texttt{ParamNum}
or via a \texttt{FldTag} string; these values which relate to the
`Output field parameter definitions table' in ww3\_shel.nml
or ww3\_shel.inp.
Either form may be followed by an optional integer value \texttt{IFC}
to select the component in multi-component fields (such as the U and
V components in the WND and CUR output fields).

\begin{verbatim}
  META  <GroupNum ParamNum>  |  <FldTag>  [IFC]
    attr_name  = attr_value
    attr_name  = attr_value
    extra_attr = extra_value [type]
    extra_attr = extra_value [type]
  ... repeated as many times as required.
\end{verbatim}


\noindent
Each \texttt{attr\_name} relates to an existing variable attribute and
can be one of the following (alternative internal name shown in parenthesis):
\begin{itemize}
 \item  \texttt{standard\_name (varns)} [string] : CF Standard name
 \item  \texttt{long\_name (varnl)} [string] : Descriptive long name
 \item  \texttt{globwave\_name (varng)} [string] : Optional GlobWAVE name
 \item  \texttt{direction\_reference} or \texttt{dir\_ref (varnd)} [string] : Optional reference
 frame for directional fields.
 \item  \texttt{comment (varnc)} [string] : Optional comment.
 \item  \texttt{units} [string] : Units of field
 \item  \texttt{valid\_min (vmin)} [float] : Minimum valid value of data
 \item  \texttt{valid\_max (vmax)} [float] : Maximum valid value of data
 \item  \texttt{scale\_factor (fsc)} [float] : Scaling factor for data - used only when
 variable type is SHORT.
\end{itemize}

\noindent
Any other attribute name is assumed to be an optional `extra'
attribute. This extra attribute can take an optional `type'
keyword to specify the variable type of the metadata. If
no type is supplied, it defaults to a character type. Valid
types are one of \texttt{[c, r, i]} for character/string,
real/float or integer values respectively. Note: space
separated string an extra field should be quoted.

\noindent
\paragraph{Modifying `global' meta data:}

\noindent
Global metadata (i.e. associated with the file, not any particular variable)
can be specified with a special \texttt{META global} keyword combination:

\begin{verbatim}
  META global [nodefault]
    extra_attr = extra_value [type]
    extra_attr = extra_value [type]
\end{verbatim}

\noindent
The optional \texttt{nodefault} keyword will surpress the output of the
default WW3 global metadata.

\noindent
\paragraph{Modifying/defining a coordinate reference system:}


\noindent
A `coordinate reference system' (CRS) can be specified for all gridded
output fields using the \texttt{CRS} keyword. As a minimum, the
\texttt{grid\_mapping\_name} attribute must be specified. If the CRS
section is defined, all output fields will have a \texttt{grid\_mapping}
attribute added referencing the CRS variable. \texttt{crs\_vaname} will
be created as a scalar NF90\_CHAR variable in the output file.

\begin{verbatim}
  CRS <crs_varname>
    grid_mapping_name = <mapping name>
    attr = value
    attr = value
\end{verbatim}

\noindent
For normal latitude/longitude grids and rotated pole grids, ww3\_ounf will
generate an appropriate coordinate reference system, but this may be
overridden using the CRS keyword.


\noindent
\paragraph{Partitioned parameter template strings}

\noindent
Specifying metadata for partitioned outputs is handled slightly differently;
one meta data entry is used for all partitions of a field. The metadata
is made specific to a particular partition number via \emph{template strings}.
There are two built-in template strings: \texttt{SPART} and \texttt{IPART}.
These provide a `string' description (e.g. `wind sea', `primary swell', etc) or
an integer partition number (1, 2, 3, etc.) These can be referenced in the meta data
attribute values using the template name surrounded by \texttt{< ... >},
e.g. \texttt{<SPART>}.

\noindent
It is also possible to supply user defined partitioned parameter
template strings in the ounfmeta.inp file using the \texttt{TEMPLATE}
keyword, as below:

\begin{verbatim}
  TEMPLATE <template-name>
    String for partition 0
    String for partition 1
    String for partition 2
    String for partition 3
    ... etc
\end{verbatim}

\noindent
Specifying the \texttt{<template-name>} with a trailing underscore will
provide an underscore separated (\texttt{\_}) string, rather than space
separated (this is useful for netCDF `standard name' values).


\noindent
\paragraph{Example ounfmeta.inp file:}
\begin{verbatim}
   $ Lines starting with dollars are comments.
   $ The line starts a meta-data section for the depth field
   META DPT
     standard_name = depth
     long_name = "can be quoted string"
     comment = or an unquoted string
     vmax = 999.9

   $ Next one is HSig (group 2, field 1)
   META 2 1
     varns = "sig. wave height"
     varnl = "this is long name"

   $ Next one is second component of wind. It also sets an
   $ "extra" meta data value (height - a float)
   META WND 2
     standard_name = "v-wind"
     height = 10.0 "r"

   $ User defined partitioned parameters template strings:
   TEMPLATE PARTSTR
     wind wave
     primary swell
     secondary swell

   $ Use partition templates in partitioned Hs field:
   $ (SPART and IPART are built-in)
   META PHS
     standard_name = "<SPART_>_sigificant_wave_height"
     long_name = "<PARTSTR>"
     partition_number = "<IPART>"

   $ Coordinate reference system:
   CRS crs
     grid_mapping_name = "latitude_longitude"
     semi_major_axis = 6371000.0 f
     inverse_flattening = 0 f

   $ Global metadata:
   META global
     institution = UKMO
     comment "space seperated strings should be quoted" c
     version = 1.0 r

\end{verbatim}


\noindent
\paragraph{Addition of `forecast variables':}
When using the ww3\_ounf.nml input file, it is possible to add optional
auxiliary `forecast variables' to the output netCDF file (see ww3\_ounf.nml).
When \texttt{FCVARS = T}, the following variables will be generated:
\begin{itemize}
 \item \texttt{forecast\_reference\_time}: The time associated with the
 "analysis" of the current forecast. Useful for files that are split over
 several days as it allows the forecast at a particular time to be referenced
 back to it's analysis or start time.
 
 \item \texttt{forecast\_period}: the time period elapsed (in seconds)
 since the associated "forecast\_reference\_time".
\end{itemize}

\noindent
The \texttt{forecast\_reference\_time} defaults to \texttt{TIMESTART} specified in
ww3\_ounf.nml. However, it might be the case that the model run includes some
sort of hindcast period in which case the \texttt{forecast\_reference\_time}
should be set to the appropriate analysis time. Also, if ww3\_ounf is invoked
with a \texttt{TIMESTART} that is not the same as the model start time, it will
be required in this case to explicitly specify the correct
\texttt{forecast\_reference\_time} to ensure the \texttt{forecast\_period} is
correctly calculated.

\pb