[Liwg-core] relevant co-chairs notes 6-6-17

Lenaerts, J.T.M. (Jan) j.lenaerts at uu.nl
Tue Jun 6 11:39:09 MDT 2017

Hi Bill and others,

I already looked at #173 (yr 2-21).

Greenland SMB is ~500 Gt/yr, which is consistent with previous (good) simulations. I would argue that Greenland melt is a bit too low (but hard to say as this is 1850). Also consistent is the lack of N-Greenland runoff.

Antarctic melt looks great, which is also in line with previous simulations. Overall, no big red flags or alarm bells based on this preliminary analysis.

Please note that the land diagnostic set already includes the ice sheets, so everyone can take a look: http://webext.cgd.ucar.edu/B1850/b.e20.B1850.f09_g17.pi_control.all.173/lnd/b.e20.B1850.f09_g17.pi_control.all.173-obs.11_30/setsIndex.html



On 6 Jun 2017, at 19:09, Bill Sacks <sacks at ucar.edu<mailto:sacks at ucar.edu>> wrote:

Here are the most relevant notes from today's co-chairs meeting.

My executive summary:

(1) Based on Jan's analysis of the snow albedo changes, we won't go with that change – instead, the land group will try to get lower albedos by changing the snow cover fraction parameterization, which shouldn't impact the ice sheets much

(2) Run #173 (currently 30 years in) is a possible candidate for a "final, good" configuration. Once that gets a little further along (maybe in the next day or two?) it would be good for someone from the LIWG to look at some diagnostics for Greenland in that run.

Bill S


Snow albedos

Peter Lawrence: before tweaking land albedos, albedos were significantly higher than MODIS both in high latitudes and desert regions

Dave L: However, lowering albedos degrades simulation of ice sheet melt over Antarctica (and maybe Greenland?). So we don't want to do an extreme change to the albedos

Dave L: Expects we can get a similar response by changing snow cover fraction – and that probably wouldn't have negative impacts on the ice sheets.

Dave L: Also note that land albedos are actually a bit lower than CCSM4. It may still be that CLM's albedos are too high, but he doesn't have a lot of faith in the MODIS albedos.


Plan for runs

• Keep #173 going – this includes atmosphere changes without land snow changes

  *   Look at this – particularly over Greenland and throughout the Arctic, because that's where a lot of the changes are.
  *   If this looks good, then do a 20th century with this

• Start another run with land snow changes – probably get decreased albedos by changing snow cover fraction parameterization, rather than changing snow albedos more directly, because this will be better for the ice sheets. (#174)

• Start another run with new land snow changes plus the atmosphere changes (#174 changes on top of #173)


Tentative meeting Friday at 10 am
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Liwg-core at cgd.ucar.edu<mailto:Liwg-core at cgd.ucar.edu>

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Jan Lenaerts
IMAU, Utrecht University || University of Colorado
@lenaertsjan<https://twitter.com/lenaertsjan> || website<http://www.colorado.edu/lab/icesheetclimate/>

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