output at flexible time levels

[guoqing-noaa]

Currently, we can configure output_interval in a stream to be a specific interval, none, or initial_only to output MPAS forecasts.

In operational workflows, we would like the output_interval to be more flexible.

For example, for 10 day global forecasts, we may want to output every 15 minutes in the first 3 hours, every 1 hour up to 3 days, every 3 hours to 7 days, and every 6 hours to 10 days.

Another example is that we make 84 hours regional forecasts. We output history.nc files every 1 hour. We would like to be able to only output mpasout.nc files at forecast hours f001, f002 and f003 to enable hourly cycling data assimilation (with a possible fallback).

It will be great if we can have another stream attribute, such as output_timelevels, and then we can enumerate the time levels to write forecast outputs based on that stream.

It may be something like:

<stream name="output"
        type="output"
        filename_template="history.$Y-$M-$D_$h.$m.$s.nc"
        io_type="pnetcdf,cdf5"
        clobber_mode="replace_files"
        output_timelevels="0-3-15m  4-72  75-168-3  174-240-6">
        <file name="stream_list/stream_list.atmosphere.output"/>
</stream>