[Liwg-core] target: ablation areas

Miren Vizcaino M.Vizcaino at tudelft.nl
Thu Jan 26 07:05:26 MST 2017


Dear All,

I apologize of the lack of context on the previous email. It was originally aimed to Leo, Jan, Bill L and Raymond, and I did not adjusted it sufficiently for the whole group.

The quoted text is from Leo. Leo and Raymond have identified a cold bias in N Greenland that makes seasonal snow over tundra to grow and become permanent.

Bill L suggested to contact the sea-ice group on this regard.

We’ve discussing also how the snow physics improvements by Leo/Jan reduce snow melt. Leo and Bill L. suggested to revise them to see if there is possibility to enhance current low melt rates.

Thanks, Miren



On Jan 26, 2017, at 10:52 AM, Miren Vizcaino Trueba <M.Vizcaino at tudelft.nl<mailto:M.Vizcaino at tudelft.nl>> wrote:

Morning, -

Let’s plan on immediate steps for the LIWG towards CESM2.0

Target: having sufficient snow melt in (all) the observed ablation areas as to expose bare ice.

Motivation: ablation areas expose bare ice at some point during the melt season (this is confirmed by remote sensing - I checked with Stef - and regional modeling - this is how RACMO operates. He told me there is no super-imposed ice in the model, so ice albedo comes from getting rid of the snow. There is some weighting in RACMO between bare ice albedos - around 0.4, that come from MODIS- and snow albedos, when the snow thickness is low)

Where we are now: difficulties to get the ablation areas in the north and northwest, and too narrow SW ablation area

Please let me know asap if you disagree with target.

There are three ingredients here:

1- snow physics
2- climate forcing
3- sub-grid simulation

1-

It could be worthwhile to revisit some of the changes that I made to fresh snow density as perhaps this prevents early melt and associated albedo changes.  But I doubt whether this solves the bias completely.

Leo, would you like to discuss how to do some testing here?

2-

I'd like to think that CESM suffers from a cold bias in the North and East of about 2 degrees:
https://www.dropbox.com/s/wqu2n4f6ad5lemb/maps_JJA_b.e20.B1850.f09_g16.pi_control.all.129_liwg_Hmax1m_0019-0021.pdf?dl=0


Raymond is going to look to the sensitivity of snow melt to the forcing in N Greenland with the column model

I’ll contact Dave Bailey

I vaguely remember from CESM1.0 that there was N cold bias and permanent snow pack over the tundra, - same problem?-, but ablation areas where ok. Perhaps the bias in snow melt from wrong densities explains this.

3-  Hinit, Hmax : here we have a bunch of runs, none very conclusive, because of bugs, multiple things changed, too short runs (e.g., B5 is only 3-years-long).

Hinit seems to matter, and should be 0.1-0.5 m w.e. both for ice-sheet and tundra - For Hmax, let’s address it at a later stage

Thanks, Miren



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