[Liwg-core] relevant co-chairs notes
sacks at ucar.edu
Tue Jan 31 11:50:08 MST 2017
Jan gave a very nice presentation this morning on where things stand with Greenland SMB – thank you, Jan! A summary of that and some other relevant notes are below:
January 31, 2017
Should we broadcast run 125 & related simulations for analysis for the winter WG meetings?
JF didn't hear from many people about this, but he thinks it's a good idea.
Unless he hears otherwise, he'd like each WG to take control of what to show & not show – and start communicating about this to your WG.
Gokhan: has mixed feeling about this: by then, we'll have 131, and most of our attention will be focused on that.
JF: This is more to keep people updated and generate some interest.
Gokhan: We should just be careful not to give people the impression that 125 is the main run we're focused on. JF agrees.
Greenland (Jan Lenaerts)
Now that precip is much better, LIWG is trying to get the melt right, too – since surface mass balance depends on both.
Melt has been too low in recent runs – leading to too high surface mass balance
Changed some of the ice sheet-specific parameters in CLM
lower ice albedo
change rain-snow partitioning
fixed a bug in snow cover fraction
also played with lapse rate for longwave radiation downscaling
However, even with all of this, still significantly too low melt.
However, the general climate in Greenland looks good – except there are suggestions of too high sea ice in the summer to the east of Greenland.
JF: Do you expect differences due to the fact that our simulation is for 1850, rather than the 1960-1990 of RACMO? Jan: You do expect some difference, but not the magnitude that we see here.
Started exploring the parameterization of snow cover fraction vs. snow depth. The current parameter over ice sheets leads to snow fraction remaining high with thin snow cover. Changing this would only affect glaciers - not seasonal snow-covered regions. It turns out that changing this in a drastic way has big effects.
Their current test was just a sensitivity experiment where they made a big change, but this gives hope that changing this could help a lot.
Need to discuss this further with Dave Lawrence and Sean Swenson
Might explore making glaciers treated more like other landcover types in this respect?
Sea ice (Dave B)
Dave looked into sea ice because LIWG requested him to look at whether this could help explain what's happening over Greenland
Much less incoming LW in winter -> thicker sea ice in recent runs. But this is actually better than 119 in this respect (which was too thin)
But Dave feels: Let's see how 20th century run progresses, and see how things look at the end of the 20th cent - we can't tell right now how we're going to end up at the end of the 20th century.
Note that there's still sea ice tuning to be done – so we can do some tuning once we see how things end up in the 20th cent run.
Rule of thumb in Arctic: 1850 sea ice about 1m thicker than present-day
Connecting to LIWG question: We would expect warming around Greenland once there is less ice in present-day.
Some of the current biases are things we expect may remain at end of 20th cent - e.g., We've always had too much ice north of Iceland.
Joe: Now that we have a cooler and fresher region (fresher due to more melt coming off of Greenland), are we at risk of refreezing the Lab Sea? Dave & Marika: In current runs, no, though they haven't looked at Jan's runs.
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