[cam-users] Hemispheric asymmetries

[David Noone]

Hi again,

Just having a quick look at the code, there IS a hard coded magic
number! Specifically a limiter on the value of QO under ice.  The
routine ./src/som/somqad.F is called as the first thing the SOM does
each time step. If the ocean is covered by sea ice, the heat flux is
modified to be greater than some minimum value. This minimum is hard
coded as:

    data qnhmin / -5.0   /
    data qshmin /  30.0  /

Have you set these to be the same? You might need to run some tests to
get reasonable ice distributions. This parameter controls how much heat
is lost by the ice, and translates in to amount of melt: more heat loss,
less ice. In a another GCM, ice formation was very sensitive to this
type of tuning. There is some discussion of this on page 129 of the
tech. report that described the CCM.

Cheers,

Dave





On Wed, 24 Jul 2002, Camille Li wrote:

>
> Hi David,
>
> Thanks for your response.  In answer to your questions, my MLD is 50 m
> everywhere all year round, and I have a seasonal cycle, but the
> eccentricity is set to zero.  I actually tried starting up in Septebmer
> and in March with the same symmetric ICs - the ice disappears in the SH in
> both cases, although as expected, it takes a few extra years for the March
> launch case.  It's puzzling as I was hoping that by making everything as
> symmetric as possible, I wouldn't see these types of asymmetries.
>
> Cheers,
> Camille
>
> > Hi Camille,
> >
> > As well as the ocean heat flux (Q0), do you set the mixed layer depth to
> > be the same in both hemispheres (i.e., MLD, the other boundary field for
> > the SOM)? When you say you have the orbital parameters set to be
> > symmetric, is this the same as saying that you have it running for a
> > perpetual equinox? My first thought is that if this is not the case, and
> > you start up in September, the Antarctic will be seeing a summer while
> > the Arctic a winter over, for instance, the subsequent DJF. As such, the
> > ice might melt in the SH, while grow in the NH (or something like that)
> > which would be consistent with your results.
> >
> > I can't imagine the diffusion is a problem, as it is set to be the same
> > globally.
> >
> >
> > Hope this helps,
> >
> > Dave
>
>

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