[MITgcm-support] Negative Specific Humidity

[Yuan Lian]

Hi, Andrea,

I have some more questions about applying "fizhi_fillnegs.F" to my 
model. I am wondering if there is any way I can do the filling step 
without touching the main source codes under "MITgcm/model/src"? If I 
have to, in which code I should call "QCHECK" routine (as defined in 
"fizhi_fillnegs.F")? I have looked up the codes 
"tracers_correction_step.F", should I call "QCHECK" right before or 
after the shapiro filter and zonal filter applied?

Many thanks!

Yuan


Yuan Lian wrote:

> Hi, Andrea,
>
> Thanks for the tips. Currently I am using second order advection 
> scheme for water vapor, the negative specific humidity has order 10^-2 
> which is 1000 times smaller than averaged specific humidity. I will 
> use subroutine "fizhi_fillnegs.F" and see if I can remove all the 
> negative values (I do have a reservoir of water vapor in lower domain).
>
> cheers,
> Yuan
>
> Andrea Molod wrote:
>
>> hi yuan,
>>
>> i can tell you about the filling algorithm for specific humidity,
>> its pretty straightforward, but you may be able to get rid of the
>> 'negative' problem (or at least make it MUCH less) by going to a
>> second order advection scheme for water vapor. you specify this
>> in the 'data' namelist file that the model reads.
>>
>> as for the filling - it just 'takes' water from below when it
>> goes negative at any level. if it needs to it 'invents' water
>> at the bottom (can think of it as taking it from the ocean?).
>> the routine itself is argument list driven, and should be pretty
>> easy to use if you want to. there are certainly better ways to
>> do the filling (try to 'get it back' from where it went to drive
>> it negative).
>>
>> hope this helps,
>>
>> andrea
>>
>> On Tue, 19 Sep 2006, Yuan Lian wrote:
>>
>>> Hi,
>>>
>>> I am running atmospheric model with water vapor (as tracer). 
>>> Variable "salt" will be specific humidity in this case (accroding to 
>>> MITgcm manual). When I ran the model, there were negative values of 
>>> specific humidity. I found there is a solution for this in "fizhi" 
>>> package, where a filling algorithm is applied. Could anyone explain 
>>> how it works?
>>>
>>> I am not going to use fizhi package at current stage, so the best 
>>> solution is to understand how this filling algorithm works, then I 
>>> can add it to my atmospheric model.
>>>
>>> Thanks!
>>>
>>> Yuan
>>> _______________________________________________
>>> MITgcm-support mailing list
>>> MITgcm-support at mitgcm.org
>>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>>>
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