Runoff
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The runoff (RUNOF) has units of kg/m^2 (per 6 hours).  The model estimates 
the runoff for a 6 hour interval starting from the analysis.  However, in 
writing the GRIB file, the runoff was incorrectly described as a 6 hour 
forecast and not as the 0 to 6 hour accumulation.  In the monthly means, 
the runoff should be considered the average runoff per 6 hour period.  
In the 4 times daily data (full archive), the runoff should be considered 
the net for the 6 hours.

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The equations for the soil moisture include a gentle relaxation (60-day time 
scale) towards an arbitrary climatology.  This term should have been included
in the runoff term unless one wants to call this nudging term a vertical 
ground water flux into an unresolved aquifer (which was not archived).