4DIAU bug when iau_filter_increments=T

[jswhit]

Description

The 4DIAU produces incorrect results when when the parameter iau_filter_increments=T and more than one increment file is specified. The time bounds for the IAU interval are computed incorrectly, leading to incorrect filter weights that were applied outside the designated time range. The 4DIAU with constant weights, and 3DIAU (with a single increment file specified) were not affected by this bug.

To Reproduce:

set iau_filter_increments=T and specify more than one file in iau_inc_files. In the model stdout, look for 'filter wt' and you will see that the weights are incorrect and applied outside the time range specified in iaufhrs. If only a single file is specified in iau_inc_files, the results are correct, or if iau_filter_increments=F (the operational setting) the results are correct.

[jswhit]

FIx in NOAA-GFDL/GFDL_atmos_cubed_sphere#167

also see
#990
NOAA-EMC/fv3atm#458

[yangfanglin]

Jeff, does this bug exist in current operation ?

[jswhit]

@yangfanglin yes the bug exists, but it is not activated with the current operational settings (since iau_filter_increments=F in operations)

[junwang-noaa]

The code was committed. The issue will be closed.