[CF-metadata] Waves

From: Jonathan Gregory <j.m.gregory>
Date: Tue, 3 May 2016 15:49:22 +0100

Dear Elodie

Thanks for your postings. I hope you don't mind my making some more comments.

> - *sea_surface_wave_significant_height*
> The already existing definition is "Height is the vertical distance
> above the surface." We believe that this definition defines the
> "sea_surface_wave_height" part, but not the "significant" part. Could it
> be possible to revise it to make it more precise? We think that a more
> precise definition could be :"Height is the vertical distance above the
> surface. The significant height is defined as the average height of the
> highest third of observed sea surface waves over a 30 minutes period."

"height" by itself in CF names means above the land surface or the sea
surface. I don't think that's what you mean in "wave height", really. What
is the level with respect to which the wave height is measured?

I agree that "significant wave height" can't be described by existing
cell_methods. We could introduce a new cell_method for this purpose i.e. the
mean of the largest third. This would be an alternative to naming it
as a different quantity from "wave height". However, mean wave height and
maximum wave height could be described by existing cell_methods.

I wonder why the definitions all refer to a 30-minute period. If the data
variable has a time dimension, it could indicate any time interval to which
the statistical operations apply.

> - *sea_surface_wave_height_of_highest_tenth*
> Height is the vertical distance above the surface. The height of the
> highest tenth is defined as the average height of the highest tenth of
> observed sea surface waves over a 30 minutes period.

This is a similar sort of definition to "significant height", but with a
different percentile (1/10 instead of 1/3). Again, we could define a
cell_method for this. If it's named specifically, why is it not
mean_wave_height_of_highest_tenth?

> - *sea_surface_wave_height_of_the_highest_crest*
> The crest is the vertical distance above the mean sea surface to the
> maximum in a wave. Height of the highest crest is the maximum value of
> wave crests observed over a 30 minutes period.
>
> - *sea_surface_wave_deepest_trough*
> Trough is the vertical distance below the mean sea surface to the
> minimum in a wave. The deepest trough is the maximum value of wave
> troughs observed over a 30 minutes period.

These two names look like they should be opposites, but they are not named
in a corresponding way.

What's the difference between maximum wave height and height of the highest
crest?

Best wishes

Jonathan
Received on Tue May 03 2016 - 08:49:22 BST