Tuning autoconversion, entrainment, non-oro drag

AIFS, IFS and OpenIFS OpenIFS
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1

Good morning all

I've got some pesky model biases in both OpenIFS cy40 standalone (AMIP-type runs) and OpenIFS coupled to NEMO (piControl). Too much precipitation over the western tropical Pacific, warm SST bias over the Southern Ocean (in coupled runs) and weak atmosphere response to ENSO seem to be the biggest problems. 
I'd like to experiment with some model tuning to see if I can reduce the problem. 

I've found the NAMCUMF namelist, which sets some entrainment and autoconversion parameters, but doubling or halving these does not seem to have any effect at all. I end up with runs that are exactly identical to my control run. 
All runs are without SPPT or SKEB.  

My question is: How can I tweak the rain/snow autoconversion rates (is it different for shallow and deep convection?), entrainment for shallow and deep convection, and also the non-orographic drag? 

It would be great to find some tunable cloud parameters equivalent to ECHAM6 (cf. Mauritsen et al., https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2012MS000154), i.e.

1) autoconversion for convective clouds, 2) lateral entrainment for shallow convection, 3) lateral entrainment for deep conversion, 4) cloud inhomogeneity, and 5) convective mass flux above level of non-buoyancy. 

Any help is much appreciated! 

Best regards
Joakim 

2

Hi Joakim,

I think I can provide some answers to your questions.

Take a look at : Convection case studies and scroll down to the part about 'Sensitivity studies'. There you will find some changes you can make to the model code and namelists along the lines you are asking about.

I've also got some code changes somewhere for altering the autoconversion parameters for the different types. I'll dig it out and post it.

Cheers,  Glenn


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Hi Joakim,

I attach some changes that were made to openifs 38r1 (only) where the rain & snow autoconversion rates were altered by adding new namelist variables. This was done for an MSc student (search for variables beginning alice_*).  I have not checked to see how different the 40r1 code is but perhaps this helps.

If you need any more info, reply here and we'll go talk to the appropriate scientist at ECMWF, though as the school holidays have started people are away.

autoconversion_code.tgz (39.4 KB)

Cheers,   Glenn