# [CIG-MC] Setting surface T doesn't work?

Dan Bower danb at gps.caltech.edu
Thu Apr 19 10:18:51 PDT 2012

```Hi Matt,

Surface T is a parameter used in the compressible /
extended-Boussinesq formulation of the code.  It is equal to the
absolute temperature of the surface, and is needed to correctly
compute the adiabatic cooling/heating term in the energy equation.  It
is not required if you are only using the Boussinesq formulation (i.e.
Di=0).  Remember that in simple Boussinesq convection it is only the
temperature difference that is relevant.

toptbcval is the non-dimensional value of the surface temperature -
usually zero (which could correspond to approx 300 K).  In
compressible / Ex-B modeling, with dT=3000 K, you might set the
following:

Tsurf=0.1
toptbcval=0

Note that Citcoms may assume that the temperature always lies between
0 and 1 - I believe there is truncation in the viscosity formulation.
So I wouldn't advise setting any temperature boundary conditions > 1
(or < 0 !).

Hope this helps,

Dan

On Thu, Apr 19, 2012 at 10:00 AM, Matt Weller <Matt.B.Weller at rice.edu> wrote:
>
> Hi All,
>
> I noticed that when I set surface T to any value, there was no change in the
> surface temperature. However, if I set toptbc=1 and toptbcval=X, where X is
> any value, then the surface T is the value X. Is there any particular reason
> why the surfaceT switch wouldn't work?
>
> While on this subject, if surfaceT is not utilized, and toptbcval is set to
> the default of 0, is it a safe assumption that the body would be in direct
> contact, and in thermal equilibrium, with space (surface value of 0)? i.e.
> No thermal contributions from exterior (e.g. stellar), or interior (e.g.
> trapped heat from atmosphere/ conductive lid ) sources.
>
> Thanks,
>
> ~Matt
> --
> --
> ________________________________
> ________________________________
> ________________________________
>
> Matt B. Weller
> Keith-Weiss Geological Lab 232-B
> Department of Earth Sciences
> Rice University
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> Houston, TX 77005-1892
>
> Matt.B.Weller at rice.edu
> weller at lpi.usra.edu
>
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```