[aspect-devel] Earth radius in spherical shell models
Wolfgang Bangerth
bangerth at colostate.edu
Mon Jan 15 16:41:05 PST 2018
On 01/14/2018 04:22 PM, Max Rudolph wrote:
> I am wondering why the default outer radius of the Earth in ASPECT is set to
> 6336 km (based on the default value in Geometry model/Spherical shell)?
>
> 6,336 km is the equatorial radius of curvature
> 6,378 km is the equatorial radius
> 6,371 km is the radius of a sphere with equal volume
>
> I know that these differ only at the 0.5% level and for most practical
> purposes may not make any difference, but was wondering if there is a
> justification for defaulting to one over the other?
That number dates back to the very early days of ASPECT, and indeed step-32
has this line:
const double R0 = 6371000.-2890000.; /* m */
const double R1 = 6371000.- 35000.; /* m */
That would suggest that I used the radius of the sphere with equal volume
minus the average depth of the crust. It seems like a coincidence that it's
also the radius of curvature at the equator.
I'll document this in the parameter description in a minute.
Best
Wolfgang
--
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Wolfgang Bangerth email: bangerth at colostate.edu
www: http://www.math.colostate.edu/~bangerth/
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