[Liwg-core] Rain-snow repartitioning

Bill Sacks sacks at ucar.edu
Wed Jan 11 15:31:27 MST 2017


Thanks for your thoughts Bill and Jan.

I did a quick literature search, which turned up the attached papers. I have given these only the briefest of skims, mostly looking at the figures, but they suggest to me that – for the land surface as a whole – the current ramp from 0 - 2 C is more physically justifiable than a -2 to 2 C ramp. In fact, if anything, the ramp should be shifted more in the positive direction – say from 0 - 3 C. Someone else should look at these more closely to make sure I'm interpreting them correctly. There's still the possibility that the relationship could be different over the ice sheet, I suppose, as well as the possibility that we can acknowledge that we're making this change in order to get good answers despite lack of physical justification....

Bill S




> On Jan 11, 2017, at 3:09 PM, Lipscomb, William Henry <lipscomb at lanl.gov <mailto:lipscomb at lanl.gov>> wrote:
> 
> Hi Bill S.,
> 
> You raise some good questions.  I think the answer to (1) is yes.  We would be exchanging an excess of snow for an excess of rain.  My reasoning would be that it may be better to get the right answer (good SMB) for the wrong reason (excessive rain) than the wrong answer (poor SMB) for a different wrong reason (excessive snow).  Either way, we have too much precip, and we’re tuning to limit the damage.
> 
> A subtlety, though, is whether the recently improved precip is causally related to colder temperatures.  If so, then the knobs we’re using to reduce precip are not very effective knobs for reducing SMB.  Do others have thoughts on this?
> 
> As for (2), I’d expect that in warmer climates we’ll see more rain.  With modified repartitioning, we'd be starting from a different preindustrial baseline, with the usual caveats about possible differences in climate sensitivity when you have a different baseline.
> 
> I haven’t looked at Antarctica.  Maybe Jan and Leo have?
> 
> Thanks,
> 
> Bill L.
> 
> 
> 
> 
> 
>> On Jan 11, 2017, at 2:39 PM, Bill Sacks <sacks at ucar.edu <mailto:sacks at ucar.edu>> wrote:
>> 
>> Hi all (just including LIWG folks here),
>> 
>> I was just giving Bette a recap of our discussion on rain-snow repartitioning, and this raised a couple of questions for us:
>> 
>> (1) For Greenland, is it correct that a change to the rain-snow partitioning would lead to more rain, which is a degradation relative to observations – but that Jan and Bill L feel we can (and should) live with this degradation in order to boost the melt?
>> 
>> (2) Particularly if (1) is true: Since it feels like this achieves the right answer (net SMB) for the wrong reasons (too much rain): Has any thought been given to whether this makes sense in a climate change (future or paleo) world?
>> 
>> (3) Has anyone looked at what this change to rain-snow partitioning does over Antarctica? We want to be sure that we're not substantially degrading the Antarctica SMB from this change....
>> 
>> Thanks,
>> Bill S
>> _______________________________________________
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> 
> ---
> William Lipscomb
> Los Alamos National Laboratory
> Group T-3, MS B216
> Los Alamos, NM 87545
> 505-667-0395
> 
> 
> 
> 

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