DIURNAL_SRFLUX and cloud fraction

[adnelson]

Greetings,

I'm developing a ROMS setup for an estuarine region that will eventually be coupled with the bio model CoSiNE, so it's important to have the diurnal cycle of net shortwave radiation properly resolved. I'd like to use DIURNAL_SRFLUX using daily-averaged values of net swrad from NAM (as done in DOPPIO) along with time-variable cloud fraction, rain, and other meteorological variables. What I'm curious about is, does DIURNAL_SRFLUX only use the average swrad value to estimate the daily cycle? Or can it use cloud fraction to modulate the daily cycle? Is this modulation in swrad due to cloud cover even important enough to implement for physical and/or biological purposes?

I've done a bit of searching on this forum and Google but haven't found any answers, so thanks for your input!

[kate]

The best place to search is the code itself. The file to look at is ROMS/Functionals/ana_srflux.h, which has options both including ALBEDO_CLOUD and not including it.

[wilkin]

Kate's advice is right on. Look at the code.

A quick search of where the option is active is accomplished with ...

Code: Select all

grep -r DIURNAL_SRFLUX .

The only relevant entry is ...

Code: Select all

./Functionals/ana_srflux.h

My reading of the code in there is that daily average SWRAD is converted to a diurnal cycle of swrad, OR, cloudiness information is converted to swrad. So, if your CLOUD data resolves the diurnal cycle you might be OK, but daily average cloud data is not "extrapolated" into a diurnal cycle.

This said, NAM output is now available at 1-hourly interval which reasonably resolves the diurnal cycle, so you might consider building your workflow so as to download those data for SWRAD and skip the whole DIURNAL_SRFLUX option altogether.

[adnelson]

Great advice, thank you both! Eventually we'd like to do hindcasts, but hourly NAM will suffice for now.