[aspect-devel] Dynamic Topography vs Topography

Rene Gassmoeller rene.gassmoeller at mailbox.org
Mon Nov 7 11:58:03 PST 2016

Hi Payman,

I guess the short answer is: They do different things. The topography
postprocessor measures the actual deformation of the mesh (i.e. you will
only see significant values, if you use a deforming mesh / free
surface). The dynamic topography however is calculated as: How much
topography would be here, if the pressure were to be balanced by
overlying topography (for a longer explanation including formulas take a
look at the postprocessor description in the manual or the source code).

So as long as you do not use a free surface, the values of the
'topography' postprocessor will be close to zero (there might be a tiny
value). And if you use a free surface the 'dynamic topography'
postprocessor will likely no longer calculate anything useful (because
the pressure is already compensated by building a topography).

Hope that helps,



On 11/06/2016 01:58 PM, Payman Janbakhsh wrote:
> Hi
> When running a model, postprocessor outputs min and max topography at
> the end of each time step. In my case shows  values around + - 1.5m
>  (early steps).
> Then when using dynamic topography postprocessor to plot dynamic
> topography vs X, with or without the option of Subtract mean of
> topography, my plot  shows values between -150m to 200m in some areas
> and zero(in the case of subtracted mean)  for the rest of the x
> dimension.
> Why is there a discrepancy between Topography min/max  and dynamic
> topography at the same time step? Shouldn’t the topography min/max
> reflect the min /max on my dynamic topography plot?
> Thank you
> Payman
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> Aspect-devel at geodynamics.org
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