[MITgcm-devel] depressed Eta and sIceLoad

Thu Oct 26 13:13:06 EDT 2006

Martin Losch wrote:

> Dear all,
>
> What should we/I do about pkg/seaice/growth.F
> The current status does not seem acceptable to me. I could check in  
> my version of growth.F which contains
> 1. masking evap with (1-area(:,:,2)); I consider that a bug fix and  
> that should definitely be included. It will get rid of many problems  
> with too much convection under ice.

Dear Martin et al., I don't think this was a bug since evap occurs in 
ice covered area too. However, if evap forcing in ice covered areas is 
causing problems, then you might want to blame the forcing (-; and at 
the same time  shut it down. So I would suggest this fix as an option, 
simply for avoiding forcing problem in ice areas if one prefers.

> 2. Jinlun's fix for snow, I guess that should be hard coded and not  
> put within #ifdef's. This fix gets rid of these enormous snow  
> accumulations without upsetting the fresh water flux, but it does not  
> get rid of all the snow over water (1e-3m seem to remain a little of  
> the ice edge).

This fix of mine has been included in all my newer models, but somehow I 
forgot to put it into mitgcm. So I agree with Martin that it should not 
be an option.

> 3. the little flooding algorithm (also in thsice), within #ifdef's  
> and a run time flag, off by default. This  fix does not get rid off  
> all the snow either, but it is appealing to convert snow into ice,  
> once it is below the water line.
>
> Further I have implemented advection of snow in pkg/seaice/ 
> seaice_advdiff.F. I feel that this should also be part of the code,  
> but it's probably not required for solving the problems that started  
> this discussion thread. Still I would include it hard wired.

It is nice to advect snow, particularly for the Antarctic. Martin, could 
you use the original (2nd order accuracy) advection scheme for all ice 
thickness, compactness, and snow?

Cheers, Jinlun

>
>
> All of this will change the lab_sea experiment and all other seaice  
> experiments. Since part of the changes (but the part with the most  
> impact) are due to the bug-fix with evap, none of the previous  
> results can be reproduced anyway, so maybe it's okay to just go ahead  
> and add all (or some) of the above things without caring too much  
> about backward-compatibility/reproducibility?
> Please let me know what you think and I'll go ahead and do it.
>
> Martin
>
> On 25 Oct 2006, at 10:25, Martin Losch wrote:
>
>> Hi Jinlun et al.,
>>
>> please have a quick look at 10day averages of HEFF and HSNOW in  July 
>> and January (after 100 years) in
>> http://mitgcm.org/~mlosch/ice_iter72360.png (Jul)
>> http://mitgcm.org/~mlosch/ice_iter72020.png (Jan)
>> run22 is without advection of snow (both runs are with evap*(1- 
>> area)), run26 is with advection of snow. Unfortunately, the runs  are 
>> not exactly comparable because I had to use a 1-order upwind  scheme 
>> for advection the snow, so that run26 uses the 1-order  upwind scheme 
>> (for HSNOW, HEFF and AREA) and run22 the traditional  2nd order 
>> central differences scheme (but only for HEFF and AREA),  no 
>> "flooding" in either case. What you see is that the advection  
>> reduces the amplitudes of the snow be a factor of 100, but maybe  
>> that's just the 1-order upwind scheme? Also the snow is in areas  
>> where it shouldn't be.
>> Not shown: My (it's not mine, but as opposed to Jinlun's  suggestion) 
>> simple flooding scheme removes this snow at the  "expense" of much 
>> increased ice thicknesses, Jinlun's scheme  reduces the snow heights 
>> even further (I only have 10year yet, but  it's already <20cm as 
>> opposed to <50cm in "my" runs), and the ice  thickness is not 
>> increased as much. Also the freshwater flux into  the ocean appears 
>> to be reduced (higher surface salinities) so that  as a first 
>> conclusion I would say that Jinlun's fix appears to be  quite 
>> appropriate (as opposed to mine). More analyses to follow.
>>
>> Martin
>>
>>
>> On 24 Oct 2006, at 23:19, Jinlun Zhang wrote:
>>
>>> Hi Martin,
>>> Advecting snow is certainly better than not, but I am not sure if  
>>> it would solve the problem of getting big numbers for snow.
>>> Jinlun
>>>
>>> mlosch at awi-bremerhaven.de wrote:
>>>
>>>> Hi Jinlun,
>>>> thanks, I'll try this out tomorrow. What about advecting HSNOW?  
>>>> Why can that be neglected?
>>>>
>>>> Martin
>>>>
>>>> Martin Losch
>>>> Alfred Wegener Institute Postfach 120161, 27515 Bremerhaven,  
>>>> Germany; Tel./Fax: ++49(0471)4831-1872/1797
>>>>
>>>>
>>>>
>>>> ----- Original Message -----
>>>> From: Jinlun Zhang <zhang at apl.washington.edu>
>>>> Date: Tuesday, October 24, 2006 7:56 pm
>>>> Subject: Re: [MITgcm-devel] depressed Eta and sIceLoad
>>>>
>>>>
>>>>> Dimitris and all,
>>>>> The ncep precip in Antarctic is way too much, but I have  moidfied 
>>>>> growth.F  to, hopefully, improve things a little bit.  The 
>>>>> modification would allow the ocean to melt  the left-over  snow 
>>>>> when ice is gone (seach jz for the modi's in the code) .  See if 
>>>>> there is any improvement ot of it.
>>>>> Jinlun
>>>>>
>>>>> Dimitris Menemenlis wrote:
>>>>>
>>>>>
>>>>>> It looks bad:
>>>>>> http://ecco2.jpl.nasa.gov/data2/cube/cube38/pickup/HSNOW.jpg
>>>>>> 20 to 60 m of snow over open water.  This is after a 12-year
>>>>>> integration on the cubed sphere.
>>>>>>
>>>>>> Dimitris
>>>>>
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-- 

Jinlun Zhang
Polar Science Center, Applied Physics Laboratory
University of Washington, 1013 NE 40th St, Seattle, WA 98105-6698

Phone: (206)-543-5569;  Fax: (206)-616-3142
zhang at apl.washington.edu
http://psc.apl.washington.edu/pscweb2002/Staff/zhang/zhang.html