Clarification of Precipitation Outputs

[Tom Hultquist]

I may be misinterpreting precip output variables, so wanted to quickly make sure I understand what the variables are.

rainc is obvious, and is indicated to be the convective precipitation.

rainnc indicates "accumulated total grid-scale precipitation". At first I'd thought this was the total accumulated precipitation, but now I'm thinking it is what is says it is, just the grid scale precipitation. So, would one need to combine rainc and rainnc to get the complete total precipitation? 

In addition, there does not appear to be an output for convective precipitation of snow (snownc is there for grid-scale, but snowc indicates it's a flag for snow on the ground, not convective precipitation as snow). Although this likely wouldn't happen often, I was just curious if precipitation as snow may result from the CP scheme.

Thanks for any info you might have.

tom

[Laura Fowler]

Hi Tom:

You are correct: rainc and rainnc are the accumulated convective and
grid-scale precipitation, respectively (see their description in
./src/core_atmosphere/Registry.xml). Therefore, the accumulated total
precipitation is rainc + rainnc, assuming that you keep the variable
config_bucket_update set to none in namelist.atmosphere (default).

Unlike cloud microphysics schemes, convective schemes do not keep
track of precipitation of snow and rain separately, because you would
not expect convection to occur at high latitudes anyway.

Microphysics processes in convective cloud models are also a lot
simpler than in cloud microphysics parameterizations and convective
rain falls instantaneously to the ground in one time-step. With
additional assumptions like the surface temperature, or making sure
that the entire column is below freezing and only detrains cloud ice,
you could figure out if the convective rain is rain or snow, for
instance. But this is a different process than tracking the falling of
snow and ensure that it remains "snow" as in cloud microphysics
parameterizations. Hope this helps.

Regards,
Laura

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!-------------------------------------------------------------------------------------------------------------
Laura D. Fowler
Mesoscale and Microscale Meteorology Division (MMM)
National Center for Atmospheric Research
P.O. Box 3000, Boulder CO 80307-3000

e-mail: la...@ucar.edu
phone: 303-497-1628

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[Tom Hultquist]

Thank you for the clarification. I figured out my first question pretty quickly once I looked at some plots along the ITCZ.. And, I assumed that would be the issue with snow, but wasn't sure (since there are some cases with convective snow, although it would be elevated (and potentially slantwise) convection, so I didn't know if the CP scheme attempted to do anything like that). Do you know if there are any plans to output a precipitation-type from the simulations, such as what the WRF ARW does (categorical precip-type from the microphysics parameterization, rain vs snow vs sleet vs freezing rain? Thanks again.

tom

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