There's a lot of ugly all through this. Is there a geodesist
(geodesyst?) in the house?
On 3/17/17 3:17 PM, Karl Taylor wrote:
> Hi all,
>
> I've been looking at the standard names used to describe the vertical
> location of the sea surface and have some questions.
>
> sea_surface_height_above_geoid
>
> The geoid is a surface of constant geopotential with which mean sea
> level would coincide if the ocean were at rest. (The volume enclosed
> between the geoid and the sea floor equals the mean volume of water in
> the ocean.) In an ocean GCM the geoid is the surface of zero depth, or
> the rigid lid if the model uses that approximation. "Sea surface
> height" is a time-varying quantity. By definition of the geoid, the
> global average of the time-mean sea surface height (i.e. mean sea
> level) above the geoid must be zero.
>
> I'm not sure it's true that "In an ocean GCM the geoid is the surface
> of zero depth". Many ocean models have an ocean surface that rises
> above the geoid in some areas and falls below in other areas.
> Moreover, under conditions of sea level change, the global mean model
> surface of zero depth will vary and not necessarily coincide to some
> fixed geoid. Would it be better to omit the sentence about ocean models?
>
> depth_below_geoid
>
> As above, we should consider omitting the sentence about ocean
> models.
>
> sea_surface_height_above_sea_level
>
> sea_level means mean sea level, which is close to the geoid in sea
> areas. "Sea surface height" is a time-varying quantity. The standard
> name for the height of the sea surface above the geoid is
> sea_surface_height_above_geoid.
>
> Is there a convention for what interval of time applies to the
> "mean"? I presume the interval is longer than the tidal period and
> seasonal changes (due to seasonal circulation changes and temperature
> changes), but shorter than climate change time-scales.
>
> Finally, what would be the appropriate standard name for a variable
> measuring global mean sea level (say relative to ca. 1850) or global
> mean sea level change? I don't think any of the above would do.
>
> Also, I noticed that in the standard names table,
>
> 1. geopotential_height includes an explanatory note: " Geopotential
> is the sum of the specific gravitational potential energy relative to
> the geoid and the specific centripetal potential energy. Geopotential
> height is the geopotential divided by the standard acceleration due to
> gravity. It is numerically similar to the altitude (or geometric
> height) and not to the quantity with standard name height, which is
> relative to the surface."
>
> 2. altitude includes an explanatory note: " Altitude is the
> (geometric) height above the geoid, which is the reference
> geopotential surface. The geoid is similar to mean sea level.
>
> For geopotential_height, "numerically similar to" could be better
> stated, I think, as "approximately the same as".
>
> best regards,
> Karl
>
>
>
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Received on Fri Mar 17 2017 - 14:17:45 GMT
