Is NEMO considering any specific GEOID?

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Hello everyone,

I am trying to figure out if NEMO uses any specific geoid. I read in the manual that both the sea surface height and the depth of the ocean bottom are referenced to a surface of constant geopotential (i.e. a mean sea surface height) on which z = 0. So this level of reference does not consider any geoid…it seems a bit arbitrary?

Also, when constructing NEMO bathymetry, again no geoid is used? I saw in the manual that one option for the calculation of the bathymetry, is using ETOPO datasets. And these datasets as far as I saw, consider the EGM2008 geoid surface and they then convert it in WGS84 ellipsoid elevation heights. Can someone confirm that indeed this option is used for calculating NEMO bathymetry?

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In NEMO, the earth is defined as a perfect sphere with a radius defined in src/OCE/DOM/phycst.F90:

   REAL(wp), PUBLIC ::   ra       = 6371229._wp       !: earth radius                       [m]

Earth gravity is constant and also defined in src/OCE/DOM/phycst.F90:

   REAL(wp), PUBLIC ::   grav     = 9.80665_wp        !: gravity                            [m/s2]
1 Like
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Thank you for your reply. So, this surface of constant geopotential where z = 0 and is the level of reference for NEMO is the perfect sphere?