Difference in DSWRF (surface) and only DSWRF. And is there any way to find direct and diffuse component from NLDAS

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rabbanifm9
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Difference in DSWRF (surface) and only DSWRF. And is there any way to find direct and diffuse component from NLDAS

by rabbanifm9 » Wed Jul 01, 2020 4:42 pm America/New_York

Dear User Forum,
This might sound a rudimentary query for you all. But here is the problem I am facing. For some urban heat island study, it is important to get the direct and diffuse component from the Downward Shortwave Radiation. Here are the three model I have found in NLDAS that provides the related data.

1. NLDAS Noah Land Surface Model L4 Hourly 0.125 x 0.125 degree V002
This data provides DSWRF. Although for this (i.e. DSWRF = Downward shortwave radiation flux (W/m^2)) it does not mentioned if its on the surface or at TOA
It also has the NSWRS which clearly mentioned that it is on surface (i.e. NSWRS = Net shortwave radiation flux (surface) (W/m^2))

2. NLDAS VIC Land Surface Model L4 Hourly 0.125 x 0.125 degree V002
DSWRF = Shortwave radiation flux downwards (surface) (W/m^2)
NSWRS = Shortwave radiation flux net (surface) (W/m^2)

Please notice that for this model it clearly mentioned that DSWRF is on the surface

3. NLDAS Mosaic Land Surface Model L4 Hourly 0.125 x 0.125 degree V002
DSWRF = Downward shortwave radiation flux (W/m^2)
NSWRS = Net shortwave radiation flux (surface) (W/m^2)

Please notice that in this model it mentioned NSWRS as on the surface but not for the DSWRF.

So my question would be is it something with the naming convention?? Even though 'surface' is not mentioned for some of the products, does that mean we would assume they all at surface measurements?

Finally any way to know the direct and diffuse component of downward shortwave radiation?

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GES DISC - mgreene
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Re: Difference in DSWRF (surface) and only DSWRF. And is there any way to find direct and diffuse component from NLDAS

by GES DISC - mgreene » Mon Jul 06, 2020 9:22 am America/New_York

Thank you for your question. A Subject Matter Expert has been notified and will answer your question shortly.
Best regards,

njdvlsrule
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Re: Difference in DSWRF (surface) and only DSWRF. And is there any way to find direct and diffuse component from NLDAS

by njdvlsrule » Mon Jul 06, 2020 1:40 pm America/New_York

Thank you for your interest in the NLDAS datasets.

First, the variable DSWRF refers to downward shortwave radiation at the surface.

Our apologies for the incomplete documentation of this variable. From my investigation, it appears that the online Subsetter does not indicate that this variable is at the surface for the Mosaic and the Noah collections. The subsetter does indicate "(surface)" for the VIC and for the forcing collections. Also, the NLDAS-2 README file does not indicate "(surface)" in Table 5a, although it is indicated in the GRIB tables in Appendix B:
https://hydro1.gesdisc.eosdis.nasa.gov/ ... NLDAS2.pdf

Furthermore, running "wgrib" on the GRIB files indicates that the level of DSWRF is at the surface.

As mentioned above, the NLDAS-2 FORA and FORB forcing collections also contain the DSWRF variable. I would recommend that you use the DSWRF from the NLDAS-2 FORA primary forcing collection, which has a monthly bias-correction and was/is actually used to drive the NLDAS land-surface models (such as Mosaic, Noah, and VIC). You will see that the DSWRF from the FORA and from the LSMs are generally similar.

Unfortunately, we don't have the direct and diffuse components of the downward shortwave radiation available or saved - only the total.

David Mocko

rabbanifm9
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Re: Difference in DSWRF (surface) and only DSWRF. And is there any way to find direct and diffuse component from NLDAS

by rabbanifm9 » Mon Jul 06, 2020 9:33 pm America/New_York

Dear David, Thank you for your reply. This is really helpful. For the Direct and Diffuse component, I guess I have to find a new direction for my research. I was actually comparing the ERA5 from ECMWF with NLDAS products. Everything is quite similar with ERA5 and NLDAS (FORA) except this Direct and Diffuse component of SW at surface.

Thanks,
Fahad

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