I am wondering how to derive the incident longwave radiation from MERRA-2, such as the one commonly used to drive land surface models offline as one of the main near-surface meteorological forcing variables.
I find several relevant variables in radiation diagnostics of MERRA-2 (M2T1NXRAD), such as
surface net downward longwave flux (LWGNT)
surface absorbed longwave radiation (LWGAB)
Longwave flux emitted from surface (LWGEM)
I am wondering if the incident longwave radiation is simply equal to "LWGAB + LWGNT"
This short FAQ may assist with your question:
https://disc.gsfc.nasa.gov/information/ ... diation%3F
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