[CF-metadata] Wave Direction, Energy and Steepness Sub-Proposal

Lowry, Roy K. rkl at bodc.ac.uk
Sun Mar 12 08:38:26 MDT 2017


Hi Alison,


Thanks for this. I am totally comfortable with your cosmetic changes to the definitions and now you've incorporated them I now understand Nan's comments.


I can also understand the logic of your changes to sea_surface_wave_from_direction_at_spectral_peak and sea_wave_spectrum_peak_energy based on the precedent in existing Standard Names that refer to 'spectral_peak' as 'variance_spectral_density_maximum'. To my understanding of spectral wave data these are synonyms and so I'm happy with your changes providing Elodie and her colleagues can see no problem.


Cheers, Roy.


Please note that I partially retired on 01/11/2015. I am now only working 7.5 hours a week and can only guarantee e-mail response on Wednesdays, my day in the office. All vocabulary queries should be sent to enquiries at bodc.ac.uk. Please also use this e-mail if your requirement is urgent.


________________________________
From: alison.pamment at stfc.ac.uk <alison.pamment at stfc.ac.uk>
Sent: 11 March 2017 12:48
To: Lowry, Roy K.; elodie.fernandez at mercator-ocean.fr; Stephane.Tarot at ifremer.fr; cf-metadata at cgd.ucar.edu
Cc: mar at puertos.es
Subject: RE: Wave Direction, Energy and Steepness Sub-Proposal

Dear Roy, Elodie, Stephane, et al,

I promised to look again at the outstanding standard name proposals needed for the Copernicus Marine Service to try and finalise them. Apologies for the time it has taken for these names to come back to the top of my 'To Do' list. My detailed comments on the wave direction, energy and steepness sub-proposal names are given below. With some cosmetic tweaks I have accepted all the proposed modifications to the definitions of existing names. Several of the new names are also close to agreement and I'd just like to check that you are happy with the wording of the definitions which I've modified for consistency with existing names. I've also taken into account a suggestion from Nan Galbraith regarding the ordering of the sentences in the definitions. There are a couple of the new names regarding spectral peak energy and direction that may need a bit more discussion.

I will be preparing the next standard name table update on 20th March and any names accepted by that date will be included in the next version of the table. My comments on the wave periods sub-proposal will follow in a separate message.

---

Changes to Existing Standard Name Definitions

>
> 1. sea_surface_swell_wave_from_direction
>
> Current Definition
> Swell waves are waves on the ocean surface. "from_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X > is coming.
>
> New Definition
> "From_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming. The direction is a bearing in the
> usual geographical sense, measured positive clockwise from due north. Swell waves are the low frequency portion of a bimodal wave frequency distribution.

I agree with modifying the definition to be consistent with the improved description of swell waves that arose from the discussion of the (now published) wave height names. I note that for those names we used the sentence "Swell waves are waves on the ocean surface and are the low frequency portion of a bimodal wave frequency spectrum." Adding the description of how the angle is measured is a good idea. A minor niggle is that I'd prefer not to capitalise "From_direction" in the definition as it refers to a part of the standard name and we don't use upper case in standard names. I've changed the order of the sentences to define swell waves first, followed by the explanation of direction, as suggested by Nan Galbraith in the discussion of these names. Thus, the definition now reads:

'Swell waves are waves on the ocean surface and are the low frequency portion of a bimodal wave frequency spectrum. The phrase "from_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north.'

With these cosmetic adjustments, this change of definition is accepted for publication in the standard name table.

> 2. sea_surface_swell_wave_to_direction
>
> Current Definition
> Swell waves are waves on the ocean surface. "to_direction" is used in the construction X_to_direction and indicates the direction towards which the velocity vector of X is
> headed. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north.
>
> New Definition
> "To_direction" is used in the construction X_to_direction and indicates the direction towards which the velocity vector of X is headed. The direction is a bearing in the
> usual geographical sense, measured positive clockwise from due north. Swell waves are the low frequency portion of a bimodal wave frequency distribution.

As in proposal 1, I've changed the order of the sentences and I'd like to avoid capitalising "To_direction". The wording should be completely consistent with the wave height names, so I think the definition should read:
'Swell waves are waves on the ocean surface and are the low frequency portion of a bimodal wave frequency spectrum. The phrase "to_direction" is used in the construction X_to_direction and indicates the direction towards which the velocity vector of X is headed. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north.'

With these cosmetic adjustments, this change of definition is accepted for publication in the standard name table.

> 3. sea_surface_wave_from_direction
>
> Current Definition
> 'from_direction' is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming.
>
> New Definition
> "From_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming. The direction is a bearing in the
> usual geographical sense, measured positive clockwise from due north.

As before I'd write this as:
'The phrase "from_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north.'

With this minor adjustment, this change of definition is accepted for publication in the standard name table.

> 4. sea_surface_wave_to_direction
>
> Current Definition - No Change Proposed
> "to_direction" is used in the construction X_to_direction and indicates the direction towards which the velocity vector of X is headed. The direction is a bearing in the
> usual geographical sense, measured positive clockwise from due north.

For consistency with proposals 1 - 3 I'd like to add the words "The phrase" at the start of the definition:
'The phrase "to_direction" is used in the construction X_to_direction and indicates the direction towards which the velocity vector of X is headed. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north.'

This change is accepted for publication in the standard name table.

> 5. sea_surface_wind_wave_from_direction
>
> Current Definition
> Wind waves are waves on the ocean surface. Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the
> atmosphere has the standard name "upward_air_velocity".) "from_direction" is used in the construction X_from_direction and indicates the direction from which the
> velocity vector of X is coming.
>
> New Definition
> "From_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming. The direction is a bearing in the
> usual geographical sense, measured positive clockwise from due north. Wind waves are the high frequency portion of a bimodal wave frequency distribution.

I agree with modifying the definition to be consistent with the improved description of wind waves that arose from the discussion of the (now published) wave height names. I note that for those names we used the sentence "Wind waves are waves on the ocean surface and are the high frequency portion of a bimodal wave frequency spectrum." I agree that we don't need the definition text for "wind" itself in these wave names. As with the other proposals I'd like to remove the capitalisation of "From_direction" and I've changed the ordering of the sentences. Thus I think the definition should read:

'Wind waves are waves on the ocean surface and are the high frequency portion of a bimodal wave frequency spectrum. The phrase "from_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north.'

With these cosmetic adjustments, this change of definition is accepted for publication in the standard name table.

> 6. sea_surface_wind_wave_to_direction
>
> Current Definition
> Wind waves are waves on the ocean surface.  Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the
> atmosphere has the standard name "upward_air_velocity".) "to_direction" is used in the construction X_to_direction and indicates the direction towards which the velocity
> vector of X is headed. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north.
>
> New Definition
> "To_direction" is used in the construction X_to_direction and indicates the direction towards which the velocity vector of X is headed. The direction is a bearing in the
> usual geographical sense, measured positive clockwise from due north. Wind waves are the high frequency portion of a bimodal wave frequency distribution.

As in proposal 5, I'd like to avoid capitalising "To_direction" and the wording should be completely consistent with the wave height names. Again I've reordered the sentences, so the definition reads:
'Wind waves are waves on the ocean surface and are the high frequency portion of a bimodal wave frequency spectrum. The phrase "to_direction" is used in the construction X_to_direction and indicates the direction towards which the velocity vector of X is headed. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north.'

With these cosmetic adjustments, this change of definition is accepted for publication in the standard name table.

---

New Standard Names

> 1. sea_surface_wave_from_direction_at_spectral_peak
>
> The direction from which the waves at the spectral peak are coming. The spectral peak comprises the most energetic waves encountered during the measurement period.
> The direction is a bearing in the usual geographical sense, measured positive clockwise from due north.
>
> Canonical units = degrees.

I've compared this proposal and its definition to existing wave spectral names, in particular, the name sea_surface_wave_period_at_variance_spectral_density_maximum defined as 'The sea_surface_wave_period_at_variance_spectral_density_maximum, sometimes called peak wave period, is the period of the most energetic waves in the total wave spectrum at a specific location.' Based on this, I think the correct name for this new quantity should be
sea_surface_wave_from_direction_at_variance_spectral_density_maximum.

Again, based on existing names, I suggest the definition should then be as follows:
'The quantity with standard name sea_surface_wave_from_direction_at_variance_spectral_density_maximum is the direction from which the most energetic waves are coming. The spectral peak is the most energetic wave in the total wave spectrum. The phrase "from_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north. The wave directional spectrum can be written as a five dimensional function S(t,x,y,f,theta) where t is time, x and y are horizontal coordinates (such as longitude and latitude), f is frequency and theta is direction. S has the standard name sea_surface_wave_directional_variance_spectral_density.  S can be integrated over direction to give S1= integral(S dtheta) and this quantity has the standard name sea_surface_wave_variance_spectral_density.'

What do you think? (N.B. I have similar comments regarding proposal 5).

> 2. sea_surface_primary_swell_wave_from_direction
> "From_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming. The direction is a bearing in the
> usual geographical sense, measured positive clockwise from due north.  The primary swell wave is the most energetic wave in the low frequency portion of a bimodal
> wave frequency distribution.
>
> Canonical units = degrees.

The name and units look fine.

For consistency with the wording of the accepted definition changes, the definitions of the existing wave height names, and for readability, I suggest the definition should be as follows:
'The quantity with standard name "sea_surface_primary_swell_wave_from_direction" is the direction from which the most energetic swell waves are coming. Swell waves are waves on the ocean surface and are the low frequency portion of a bimodal wave frequency spectrum. The primary swell wave is the most energetic swell wave. The phrase "from_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north.'

OK?

> 3. sea_surface_secondary_swell_wave_from_direction
> "From_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming. The direction is a bearing in the
> usual geographical sense, measured positive clockwise from due north.  The secondary swell wave is the second most energetic wave in the low frequency portion of a
> bimodal wave frequency distribution.
>
> Canonical units = degrees.

The name and units look fine.

Again for consistency and readability, I suggest the definition should read as follows:
'The quantity with standard name "sea_surface_secondary_swell_wave_from_direction" is the direction from which the second most energetic swell waves are coming. Swell waves are waves on the ocean surface and are the low frequency portion of a bimodal wave frequency spectrum. The secondary swell wave is the second most energetic wave in the low frequency portion of a bimodal wave frequency spectrum. The phrase "from_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north.'

OK?

> 4. sea_surface_wave_maximum_steepness
> Wave steepness is defined as the ratio of the wave height divided by the wavelength. The maximum wave steepness is the greatest value observed during the
> observation period. Wave height is defined as the vertical distance from a wave trough to the following wave crest. The wavelength is the horizontal distance from this
> trough to the next trough.
>
> Canonical units = dimensionless.

The name and units look fine.

Again for consistency of wording with existing names I suggest some minor changes to the definition. I've also borrowed some words from your wave period name proposals to give a more general definition for wavelength:
'Wave steepness is defined as the ratio of the wave height divided by the wavelength. Maximum wave steepness is the maximum value measured during the observation period. Wave height is defined as the vertical distance from a wave trough to the following wave crest. The wavelength is the horizontal distance between repeated features on the waveform such as crests, troughs or upward passes through the mean level.'

OK?

> 5. sea_wave_spectrum_peak_energy
> The wave directional spectrum can be written as a five dimensional function S(t,x,y,f,theta) where t is time, x and y are horizontal coordinates (such as longitude and
> latitude), f is frequency and theta is direction. S has the standard name sea_surface_wave_directional_variance_spectral_density.  S can be integrated over direction to
> give S1= integral(S dtheta) and this quantity has the standard name sea_surface_wave_variance_spectral_density. Wave spectrum peak energy is the maximum value of
> the variance spectral density (max(S1)).
> Canonical units = Square metre seconds (m^2.s)

The units look fine.

I've compared this proposal and its definition to existing wave spectral names, in particular, the name sea_surface_wave_period_at_variance_spectral_density_maximum defined as 'The sea_surface_wave_period_at_variance_spectral_density_maximum, sometimes called peak wave period, is the period of the most energetic waves in the total wave spectrum at a specific location.' Based on this, I think the correct name for this new quantity should be sea_surface_wave_energy_at_variance_spectral_density_maximum.

I think the definition should then read as follows:
'The wave directional spectrum can be written as a five dimensional function S(t,x,y,f,theta) where t is time, x and y are horizontal coordinates (such as longitude and latitude), f is frequency and theta is direction. S has the standard name sea_surface_wave_directional_variance_spectral_density.  S can be integrated over direction to give S1= integral(S dtheta) and this quantity has the standard name sea_surface_wave_variance_spectral_density. The quantity with standard name sea_surface_wave_energy_at_variance_spectral_density_maximum, sometimes called peak wave energy, is the maximum value of the variance spectral density (max(S1)).'

Do you agree?

---

Best wishes,
Alison

 ------
Alison Pamment                                                       Tel: +44 1235 778065
Centre for Environmental Data Analysis         Email: alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Campus, Didcot, OX11 0QX, U.K.

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