Question about RTTOV-SCATT input profiles

[Tianheng Wang]

Hello,
I am using RTTOV v12.1 and I want to calculate the inputs for RTTOV-SCATT Forward from WRF model. But since I’m currently unsure how to compute ‘cld_profiles % sp’ from the variables in WRF, I haven’t included ‘sp’ in the input profiles for RTTOV-SCATT Forward, yet it can still run. May I ask if ‘cc’, ‘rain’, and ‘sp’ are optional variables? Can I perform MW forward simulations when one or more of the cld_profiles profile variables are missing? I haven’t found more explanations about these input profiles in the user guide.

[James Hocking]

Hi,

The cc(:) member is the cloud fraction (0-1) so is mandatory: you must always provide this. All hydrometeors (clw, ciw, rain, sp) are optional inputs. If you do not have data for them then do not specify them: they are simply not included in the simulation. However in general you should specify the profiles for all hydrometeors for which you have information.

Best wishes,
James

[Tianheng Wang]

Thank you for your reply but I still have a quenstion. In UserGuide v12.1, cc(:) seems like cloud cover instead of cloud fraction,and the cloud fraction can be optional if opts_scatt%lusercfrac=false. so should I consider the cloud cover is necessary?

Here is origin paragraph of UserGuide v12.1:
cfrac Optional: if opts_scatt%lusercfrac=true., supply the effective cloud fraction, C, here.
This is normally calculated internally in RTTOV-SCATT
ph(:) nlevels + 1 of half-level pressures (hPa)
cc(:) nlevels of cloud cover (0-1)

[James Hocking]

Hi,

Yes, that is true: if you set the lusercfrac option to true and specify the effective cloud fraction yourself, then the input per-layer cloud fractions (cc) are not used.

If you have better information regarding the effective cloud fraction then it might be interesting to compare the simulated outputs to those obtained by using the effective cloud fraction computed by RTTOV-SCATT based on the input per-layer cloud fractions (in the cc(:) member). Per-layer cloud fractions should usually be available from the NWP model.

Best wishes,
James

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