[aspect-devel] Dynamic Topography vs Topography

Payman Janbakhsh payman.janbakhsh at mail.utoronto.ca
Wed Nov 9 05:40:05 PST 2016

Thanks Rene, sorry for late reply
It was my misunderstanding that for a free surface I can use the generated dynamic topography text files and see the surface evolution across my model domain at any given time step.
Is there an implemented option for it currently ?  (for a free surface).
Not the Topography postprocessor since it gives the max(min)  vs time(run time) ,
   Looking for a measure of surface mesh elevation(from its initial datum or a mean) vs X lateral dimension, at any given time step.

From: Aspect-devel [mailto:aspect-devel-bounces at geodynamics.org] On Behalf Of Rene Gassmoeller
Sent: November 7, 2016 2:58 PM
To: aspect-devel at geodynamics.org
Subject: Re: [aspect-devel] Dynamic Topography vs Topography

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:
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



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