Question about HYCOM of water level

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Chu-En Hsu

Jul 8, 2019, 4:56:56 PM7/8/19

Hello, everyone,

My name is Chu-En. I am pretty new to HYCOM but will keep working on HYCOM in the near future. Recently, I encountered a problem about the vertical datum of water level. That is, I found that there exist different values of shifts in water levels between the observation and simulation using boundary conditions from HYCOM. Thus, I think there might be problems with my simulation datum. I would like to ask, what is datum/ vertical coordinate reference of water level of HYCOM in North Atlantic Ocean and Gulf of Mexico (e.g. NAVD88, MSL, MHHW)?

Thanks so much!
Best regards!


Alan Wallcraft

Jul 9, 2019, 3:30:25 PM7/9/19
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HYCOM runs on a earth sized sphere, and 0m is the surface of that sphere.

By water level you may mean sea surface height, which is positive upward and again w.r.t. the sphere surface at 0 m SSH.

GOFS global mean SSH is constrained by climatological T&S, and this means that its long term global average is very close to 0.0.  The observed SSH has a sea level rise of about 3 mm per year, and this is *not* in the GOFS SSH.

The attached plots are from the GOFS 3.1 reanalysis averaged over 1994 to 2015.  I used the native grid, but this is available on the GLBv0.08 grid at

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