[MITgcm-support] Negative Specific Humidity

[Andrea Molod]

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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