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negative SWDDIF

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I modified the WRF Registry to get SWDDIF in the wrfout files.
To my surprise I often find negative values within my grid for times near sunset.
The same is observed near sunrise, but less frequent.
I looked at the WRF code, but could not find safeguards agains negative values.
Could negative values be related to the choice of ra_sw_physics?
Please find attached 2 examples, regions with negative values are blue.
Regards, Gerard


  • Screenshot from 2019-02-27 15-27-37.png
    Screenshot from 2019-02-27 15-27-37.png
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  • Screenshot from 2019-02-27 15-10-13.png
    Screenshot from 2019-02-27 15-10-13.png
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Please send me your namelist.input to take a look.
By the way, which version of WRF are you running?
Dear Ming Chen
Please find attached the namelist.input file.
I am using version WRFV4.0.1.DM.
Kind regards, Gerard


  • namelist.input
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Your namelist.input looks fine except the option of radt=15, which might be better to set to radt=27 (same as the grid interval in km).
However, I don't think this is the reason for the problem of swddiff, which shouldn't be negative anyway.

Please try other options like RRTMG and avoid using Goddard scheme at present. The negative swddif indicates possible bugs in Goddard scheme,