update snow overburden compaction parameter #250
Conversation
Snow viscosity for dry compaction was changed in 2016 and is described in more detail by (Van Kampenhout et al., 2017). Basically we adopted an expression from Crocus (Vionnet et al, 2012) and changed one parameter (c_eta) to better fit firn core observations. The original value of the c_eta parameter in Vionnet2012 is 250 kg/m3. In our study we tested different values (like 450) before arriving at the final value of 358 kg/m3. In this commit we change the value of c_eta from 450 to 358 kg/m3.
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FYI, this commit will be answer-changing but only to a very minor degree. Overburden compaction is a relatively weak force that only plays a dominant role in thick snow packs (> 1 m) |
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@lvankampenhout thanks for this. Have you run this by @dlawrenncar or others to determine the timing of bringing this to master? I'm particularly wondering if this is supposed to make it into CESM2, or if this is post-CESM2. If you haven't talked with @dlawrenncar about it yet, then I'm guessing this change will come in post-CESM2, since science is supposed to basically be frozen at this point. Also, assuming this is for post-CESM2: We'll also want to consider pulling this out to a namelist parameter, so that its value can remain as is for CLM5.0 physics, but change for future physics versions. |
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That's correct. This should be a post-CESM2 change. |
ekluzek
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priority: low
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OK, post-release is fine by me. In the Tech Note I wrote c_eta = 358 though (the new value) is that a problem? In that case we may want to change that to 450 to make it consistent to the code. |
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Yes, probably this should be changed in the tech note. I think it's not
too late; can you make that change?
Thanks,
Bill
…On 2/3/18, 2:08 AM, Leo van Kampenhout wrote:
OK, post-release is fine by me. In the Tech Note I wrote c_eta = 358
though (the new value) is that a problem? In that case we may want to
change that to 450 to make it consistent to the code.
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overburden compaction parameter c_eta = 450 kg/m3 in the code. This should have been 358 kg/m3 but it's too late to make that change now, this is post-CESM2. This commit updates the doc to make the doc consistent with the code. also see: ESCOMP/CTSM#250
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OK I just made the change in the Tech note: ESCOMP/ctsm-docs@073a899 |
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@lvankampenhout sorry for the silence here; we haven't forgotten about this. We just discussed it at our ctsm software meeting today, and felt that we'll want to
This might all take a while, so let us know if you need this sooner rather than later for any reason. |
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Hi Bill, Personally I feel that pulling this out to the namelist is somewhat overkill, but if you guys decided this is desirable, I won't object that. |
billsacks
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enhancement
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Leo, we are configuring the refined arctic simulations and am wondering if you still feel the c_eta value should be changed to 358 kg/m3. We are trying to improve the surface mass balance over greenland so if the 358 value is more realistic then I would favor this change. |
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Hi Adam, making this change is not going to do much, as it's only a slight deviation on a parameter of compaction. You can still try if it's not not a hassle. Much more important for melt are the parameters for snow initial grain size / refreezing grain size / grain growth rate / irreducible water content / bare ice albedo, all of which are only loosely constrained. |
overburden compaction parameter c_eta = 450 kg/m3 in the code. This should have been 358 kg/m3 but it's too late to make that change now, this is post-CESM2. This commit updates the doc to make the doc consistent with the code. also see: ESCOMP#250
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@Oleson, can you add this to the hard coded parameter bfb tag you're making. |
billsacks
added
PR status: ready
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This work is actually completed now with our updated paramsfile that sets ceta to 358 in ctsm5.1. This is the case in ctsm5.1.dev021. So the equivalent of this is done. So I'm closing this. |
overburden compaction parameter c_eta = 450 kg/m3 in the code. This should have been 358 kg/m3 but it's too late to make that change now, this is post-CESM2. This commit updates the doc to make the doc consistent with the code. also see: ESCOMP#250
Change ceta from 450 to 358 for CTSM5.1 See Leo VanKamenhout's work on this in ESCOMP#250. Note, this is used in the PPE work. See van Kampenhout et al. (2017). Turn Medlyn on for PHS off for clm51 and clm50. Make max CO2 partial pressure consistent in Photosynthesis. Change surface datasets to only use 78PFT versions Fix GSSUN and GSSHA history variables so now not just writing missing values. Changes FATES to run with use_nitrif_dentrif=T by default. Change dynlakes test to methane/use_nitrif_=T.
Change ceta from 450 to 358 for CTSM5.1 See Leo VanKamenhout's work on this in ESCOMP#250. Note, this is used in the PPE work. See van Kampenhout et al. (2017). Turn Medlyn on for PHS off for clm51 and clm50. Make max CO2 partial pressure consistent in Photosynthesis. Change surface datasets to only use 78PFT versions Fix GSSUN and GSSHA history variables so now not just writing missing values. Changes FATES to run with use_nitrif_dentrif=T by default. Change dynlakes test to methane/use_nitrif_=T.
Change ceta from 450 to 358 for CTSM5.1 See Leo VanKamenhout's work on this in ESCOMP#250. Note, this is used in the PPE work. See van Kampenhout et al. (2017). Turn Medlyn on for PHS off for clm51 and clm50. Make max CO2 partial pressure consistent in Photosynthesis. Change surface datasets to only use 78PFT versions Fix GSSUN and GSSHA history variables so now not just writing missing values. Changes FATES to run with use_nitrif_dentrif=T by default. Change dynlakes test to methane/use_nitrif_=T.
add namelist lookup to each namelist read call
Snow viscosity for dry compaction was changed around 2016 and is described in more detail by (Van Kampenhout et al., 2017). Basically we adopted the viscosity expression from Crocus (Vionnet et al, 2012) and changed one parameter (c_eta) to better fit firn core observations. The original value of the c_eta parameter in Vionnet2012 is 250 kg/m3. In our study we tested different values (like 450) before arriving at the final value of 358 kg/m3. In this commit we change the value of c_eta from 450 to 358 kg/m3.