[MITgcm-support] Negative Specific Humidity

[Yuan Lian]

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
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