Hi all,
The term "sea level anomaly" is indeed used in the context given by
St?phane; I know my colleagues are using it in exactly the same way. So,
I don't agree with Jonathan that the term "anomaly" wouldn't be correct,
however, he's probably equally right when indicating that it's in other
contexts used to refer to the difference from a multi-year climatology.
Since in climate research the sun is the most important celestial body
besides the earth, I can imagine that it's sufficient to compare a value
with the average value for the same date/time in multiple years.
However, in tidal analysis the sun is not the only gravitational force
with significant influence, the attraction of the moon is also very
important and the moon's orbit is not perfectly periodic over the period
of a year. In this context an sea level anomaly is the deviation of the
water level from the level that could have been foreseen by means of a
proper tidal analysis (either based on long-term local measurement
series or a good hydrodynamic model). Tidal analysis may show periodic
behavior with frequencies up to 18.6 years which in the absence of
storms enables you to predict rare but deterministic flooding events of
low cities like Jakarta many years ahead. Storms cause local and remote
"random" deviations from this tidal signal and that's what St?phane is
referring to.
The two variables suggested by Phil could indeed be used to store both
the reference tidal signal (water_surface_reference_datum_altitude) and
the deviation thereof (water_surface_height_above_reference_datum). However:
a) this will make the water_surface_reference_datum_altitude time
dependent which is unusual for reference levels, and
b) nobody will recognize the physical interpretation of the two
variables without further metadata, and
c) would one be allowed to store only the "sea level anomaly" variable
(water_surface_reference_datum_altitude) without the corresponding
water_surface_height_above_reference_datum variable?
Best regards,
Bert
----------------------
Bentley, Philip wrote:
> Hi Stephane,
>
> Would one or both of the following two standard names cover your
> use-case? The first is in effect your residual, I think.
>
> --------------
> standard name: water_surface_height_above_reference_datum
> canon units: m
> description: 'Water surface height above reference datum' means the
> height of the upper surface of a body of liquid water, such as sea,
> lake or river, above an arbitrary reference datum. The altitude of the
> datum should be provided in a variable with standard name
> water_surface_reference_datum_altitude. The surface called "surface"
> means the lower boundary of the atmosphere.
> --------------
> standard name: water_surface_reference_datum_altitude
> canon units: m
> description: Altitude is the (geometric) height above the geoid,
> which is the reference geopotential surface. The geoid is similar to
> mean sea level. 'Water surface reference datum altitude' means the
> altitude of the arbitrary datum referred to by a quantity with
> standard name 'water_surface_height_above_reference_datum'. The
> surface called "surface" means the lower boundary of the atmosphere.
> --------------
> Regards,
> Phil
>
> ------------------------------------------------------------------------
> *From:* cf-metadata-bounces at cgd.ucar.edu
> [mailto:cf-metadata-bounces at cgd.ucar.edu] *On Behalf Of *Stephane
> TAROT
> *Sent:* 26 January 2012 13:58
> *To:* cf-metadata at cgd.ucar.edu
> *Subject:* [CF-metadata] Sea surface height
>
> Hi,
>
> In the MyOcean european project, we are using
> sea_surface_height_above_sea_level for the insitu data mesured by
> tide gauges.
>
> By substracting these measures and the predicted tide sea level,
> we calculate the residual due to atmospheric (pressure and wind)
> conditions.
>
> Is there an existing standard name for the residual ?
> Should we consider that the predicted tide sea level is a sort of
> climatology and therefore use
> "sea_surface_height_above_sea_level__anomaly_" for the residual ?
>
>
> Thanks for your help
>
> St?phane Tarot (Ifremer)
>
>
> ------------------------------------------------------------------------
>
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