[Liwg-core] Relevant co-chairs notes

Miren Vizcaino M.Vizcaino at tudelft.nl
Wed Jan 11 04:13:21 MST 2017

Hi Jan, and All

sorry to be so persistent: I do not understand Julio, Jan and Marcus when they call “ad hoc change” or “tuning” or “non-defendable” to non-smoothing the mean topography and leave it as it was originally. I’d rather call “tuning” to erase the topographic forcing

with smoothing. My understanding is that it was done to increase winds by reducing friction - not because the topography field was unrealistic -, but please tell me if I am missing something else here.

Also, I disagree that there are detrimental effects. I’ll explain

From eye-balling the last Marcus’ plots, now GRNL03 underestimates precipitation - changes have been very effective, that’s great! - compared with RACMO along the SE margin, and overestimates in the southern interior.

GRL04 puts some of the precip in the margin instead of inland, so it should get us closer to reality?  The metrics to test this would be to calculate the spatial correlation between RACMO-GRNL03/04, and the precipitation gradient with elevation for the southern

dome transect. I think Marcus has the data ready for this - the same as for the aforementioned plots-

In any case GRNL03 is great improvement already, and I will go with the decision that you take today.

Thanks to everybody for your hard work to improve precipitation and your contributions to the discussion, we’ve done excellent progress, Miren

On Jan 10, 2017, at 7:13 PM, Lenaerts, J.T.M. (Jan) <j.lenaerts at uu.nl<mailto:j.lenaerts at uu.nl>> wrote:

Thanks Bill, I am going to try to make some plots tomorrow. I am also in favour of going with GRNL03 since the topography change is at least defendable.

We probably will have to change the repartitioning because it looks like 126 has become a lot colder as well.

All the best,


On 10 Jan 2017, at 19:05, Bill Sacks <sacks at ucar.edu<mailto:sacks at ucar.edu>> wrote:

Here are the relevant co-chairs notes from today's meeting. I think we'd need to make a strong and unified argument for GRNL04 at this point if we wanted that over GRNL03. I don't get the sense that there is that sort of unified feeling, so I think CAM will move ahead with GRNL03.

126 vs 125 (Rich & Julio)

126 looks similar to 125 in terms of global metrics (which is what we'd expect)

126 has a ring of high SGH around Greenland. There is cooling over Greenland, which may be responsible for the cooling in the North Atlantic. Feeling is that the Pacific changes are just internal variability.

Precip over Greenland has gone down significantly in 126 (about 100 Gt) relative to 125... and 125 was already drier than 119.

Gokhan: Decreased precip over Greenland could lead to even higher salinity in the nearby ocean. We'll need to keep an eye on this.

126 is the same as GRNL03.

There was also discussion about GRNL04, which goes back to old topography over Greenland. Miren from the land ice group likes GRNL04, but Julio feels it's not worth doing another ad hoc change to get this small improvement – especially given that there are detrimental effects elsewhere in Greenland.
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Jan Lenaerts
IMAU, Utrecht University
@lenaertsjan<https://twitter.com/lenaertsjan> || IMAU website<http://www.staff.science.uu.nl/~lenae101/> || CU<http://www.colorado.edu/lab/icesheetclimate/> website<http://www.colorado.edu/lab/icesheetclimate/>

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