Store unspecified accumulation interval as 0 rather than bad data

[JohnHalleyGotway]

Describe the Problem

This issue arose via a Slack discussion with @mpm-meto. Investigation revealed a slight discrepancy in MET's handling of the accumulation interval value when it is not specified or does not apply. See below for detail.

Expected Behavior

When the accumulation interval does not apply to a given dataset, its value should be stored/reported consistently by MET, regardless of the input file type.

Environment

Describe your runtime environment:
*1. MacOS

To Reproduce

Describe the steps to reproduce the behavior:
1. Run pcp_combine on a GRIB input file:

bin/pcp_combine -add data/sample_fcst/2005080700/wrfprs_ruc13_12.tm00_G212 'name="RH"; level="Z2";' rh.nc

2. Run plot_data_plane with -v 4 on the GRIB input:

bin/plot_data_plane data/sample_fcst/2005080700/wrfprs_ruc13_12.tm00_G212 rh_grib.ps 'name="RH"; level="Z2";' -v 4

3. Run plot_data_plane with -v 4 on the NetCDF output:

bin/plot_data_plane rh.nc rh_nc.ps 'name="RH_Z2"; level="Z2";' -v 4

4: Observe the difference in accumulation interval reported:

DEBUG 4:    accum time: 000000

vs

DEBUG 4:    accum time: NA

These should be consistent.

Only need to fix this in the develop branch, not main_v10.1.

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Define Related Issue(s)

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• METplus, MET, METdataio, METviewer, METexpress, METcalcpy, METplotpy
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