Why that Choice of Earth Radius

[nusculus]

Question:

It seems like an odd choice to use 6371229.0 m as the radius of the earth in MPAS. That number seems to be based on Hayford's 1910 estimate of the Earth. It's average radius is 6371229.31 m, by my calculation.

Here's a few sphere alternatives, all based on the more recent WGS84 ellipsoid:

average of the 3 radii: 6371008.7714 m
radius of sphere of equal area: 6371007.1809 m
radius of sphere of equal volume: 6371000.7900 m

These were taken from page 3-7 of the WGS84 definition at:
http://earth-info.nga.mil/GandG/publications/tr8350.2/wgs84fin.pdf

I might be missing something, of course, but thought I would speak up sooner rather than later.Either way, I am curious about the choice.

[mgduda]

Almost certainly, the radius 6371229 m was taken from the Jablonowski and Williamson test case (QJRMS, 2006), which was used in early testing of the original MPAS hydrostatic atmosphere core.
How this radius came to be used in that test case, though, I have no idea.

In future, scientific questions about any of the MPAS models are probably best directed to the Google groups forums for MPAS, while code and other technical issues can be posted there or to this github issue tracker.