Dear Jonathan,
I totally agree with Andy on this point.
Cheers, Roy.
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From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Saulter, Andrew <andrew.saulter at metoffice.gov.uk>
Sent: 03 May 2018 11:34
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] proposed additional names for sea_surface_wave parameters
Thanks Jonathon,
Re the directional_spread parameters in section 4, the "one-sided directional width" as its described in Holthuijsen's book (Waves in Oceanic and Coastal Waters) is perhaps more precisely defined by Tucker and Pitt (Waves in Ocean Engineering) as "half the beam-width as usually described: that is, it is from the beam axis to the root mean square width".
So in principle there is a statistical relationship between this value and a mean_wave_direction that is also computed from moments of the directional wave spectrum. However, there is a lot of detail here; first Tucker and Pitt note that this is an approximation. Rather more detail is given by Kuik et al. (1988,
https://doi.org/10.1175/1520-0485(1988)018%3C1020:AMFTRA%3E2.0.CO;2 ) who explain potential differences in calculation of directional characteristics using linear or circular moments - the latter being necessary for wave measurements, where spreading is then estimated based on the Fourier components of the directional wave spectrum rather than a direct calculation of directional spectrum statistics.
So the parameter feels a bit more complex and nuanced than a cell_methods application to wave_direction would allow. I think giving it its own name is more appropriate in this case?
Cheers
Andy
-----Original Message-----
From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Jonathan Gregory
Sent: 02 May 2018 13:32
To: cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] proposed additional names for sea_surface_wave parameters
Dear Andy
Your new proposals of sections 1-3 following existing patterns, as you say, and look fine to me.
For those of section 4, can you say precisely what "one-sided directional width" means? The way you describe it, I wonder whether it could be described as a processed version of the wave_direction theta. For example, if it was the standard deviation of theta, cell_methods could describe it.
Best wishes
Jonathan
----- Forwarded message from "Saulter, Andrew" <andrew.saulter at metoffice.gov.uk> -----
> Date: Wed, 2 May 2018 07:28:05 +0000
> From: "Saulter, Andrew" <andrew.saulter at metoffice.gov.uk>
> To: "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
> Subject: Re: [CF-metadata] proposed additional names for sea_surface_wave
> parameters
>
> Adding a minor amendment to the units for the 'wave_energy_at_variance_spectral_density_maximum' parameters. These should be 'm2 s' rather than 'm2s' in order to be parsed by UDUNITS.
>
> Andy
>
> From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf
> Of Saulter, Andrew
> Sent: 01 May 2018 09:27
> To: cf-metadata at cgd.ucar.edu
> Subject: [CF-metadata] proposed additional names for sea_surface_wave
> parameters
>
> Hi all,
>
> Please find proposals for some additional sea_surface_wave parameters, which will be provided as part of Met Office operational forecast products in the near future. Hopefully nothing too contentious as mostly an extension of some existing CF names.
>
>
> 1. Addition of 'tertiary_swell' names for existing wave parameters defined under 'wind_wave', 'primary_swell' and 'secondary_swell' categories. So would add:
>
> sea_surface_tertiary_swell_wave_from_direction
> units: degree
> The quantity with standard name sea_surface_tertiary_swell_wave_from_direction is the direction from which the third 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 tertiary swell wave is the third 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.
>
> sea_surface_tertiary_swell_wave_mean_period
> units: s
> The quantity with standard name sea_surface_tertiary_swell_wave_mean_period is the mean period of the third most energetic swell waves. Swell waves are waves on the ocean surface and are the low frequency portion of a bimodal wave frequency spectrum. The tertiary swell wave is the third most energetic wave in the low frequency portion of a bimodal wave frequency spectrum. A period is an interval of time, or the time-period of an oscillation. Wave period is the interval of time between repeated features on the waveform such as crests, troughs or upward passes through the mean level. Wave mean period is the mean period measured over the observation duration.
>
> sea_surface_tertiary_swell_wave_significant_height
> Swell waves are waves on the ocean surface and are the low frequency portion of a bimodal wave frequency spectrum. The tertiary swell wave is the third most energetic wave in the low frequency portion of a bimodal wave frequency spectrum. Significant wave height is a statistic computed from wave measurements and corresponds to the average height of the highest one third of the waves, where the height is defined as the vertical distance from a wave trough to the following wave crest.
>
>
>
> 2. Addition of peak wave period parameter to 'wind_wave', 'primary_swell', 'secondary_swell' and 'tertiary_swell' categories. This follows the existing standard for 'sea_surface_wave_period_at_variance_spectral_density_maximum' and adds:
>
> sea_surface_wind_wave_period_at_variance_spectral_density_maximum
> units: s
> The quantity with standard name sea_surface_wind_wave_period_at_variance_spectral_density_maximum is the period of the most energetic waves within the wind wave component of a sea. Wind waves are waves on the ocean surface and are the high frequency portion of a bimodal wave frequency spectrum. A period is an interval of time, or the time-period of an oscillation. The phrase "wave_period_at_variance_spectral_density_maximum", sometimes called peak wave period, describes the period of the most energetic waves within a given sub-domain of the wave spectrum.
>
> sea_surface_primary_swell_wave_period_at_variance_spectral_density_max
> imum
> units: s
> The quantity with standard name sea_surface_primary_swell_wave_period_at_variance_spectral_density_maximum is the period of the most energetic waves within the primary swell wave component of a sea. 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 wave component in the low frequency portion of a bimodal wave frequency spectrum. A period is an interval of time, or the time-period of an oscillation. The phrase "wave_period_at_variance_spectral_density_maximum", sometimes called peak wave period, describes the period of the most energetic waves within a given sub-domain of the wave spectrum.
>
> sea_surface_secondary_swell_wave_period_at_variance_spectral_density_m
> aximum
> units: s
> The quantity with standard name sea_surface_secondary_swell_wave_period_at_variance_spectral_density_maximum is the period of the most energetic waves within the secondary swell wave component of a sea. 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 most energetic wave component in the low frequency portion of a bimodal wave frequency spectrum. A period is an interval of time, or the time-period of an oscillation. The phrase "wave_period_at_variance_spectral_density_maximum", sometimes called peak wave period, describes the period of the most energetic waves within a given sub-domain of the wave spectrum.
>
> sea_surface_tertiary_swell_wave_period_at_variance_spectral_density_ma
> ximum
> units: s
> The quantity with standard name sea_surface_tertiary_swell_wave_period_at_variance_spectral_density_maximum is the period of the most energetic waves within the tertiary swell wave component of a sea. Swell waves are waves on the ocean surface and are the low frequency portion of a bimodal wave frequency spectrum. The tertiary swell wave is the third most energetic wave component in the low frequency portion of a bimodal wave frequency spectrum. A period is an interval of time, or the time-period of an oscillation. The phrase "wave_period_at_variance_spectral_density_maximum", sometimes called peak wave period, describes the period of the most energetic waves within a given sub-domain of the wave spectrum.
>
>
>
> 3. Addition of energy_at_variance_spectral_density_maximum parameter to existing 'wind_wave', 'primary_swell', 'secondary_swell' and 'tertiary_swell' categories. This follows the existing standard for 'sea_surface_wave_energy_at_variance_spectral_density_maximum' and adds:
>
> sea_surface_wind_wave_energy_at_variance_spectral_density_maximum
> units: m2s
> The quantity with standard name sea_surface_wind_wave_energy_at_variance_spectral_density_maximum is the energy of the most energetic waves within the wind wave component of a sea. Wind waves are waves on the ocean surface and are the high frequency portion of a bimodal wave frequency spectrum. The phrase "wave_energy_at_variance_spectral_density_maximum", sometimes called peak wave energy, describes the maximum value of the wave_variance_spectral_density within a given sub-domain of the wave spectrum.
>
> sea_surface_primary_swell_wave_energy_at_variance_spectral_density_max
> imum
> units: m2s
> The quantity with standard name sea_surface_primary_swell_wave_energy_at_variance_spectral_density_maximum is the energy of the most energetic waves within the primary swell wave component of a sea. 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 wave component in the low frequency portion of a bimodal wave frequency spectrum. The phrase "wave_energy_at_variance_spectral_density_maximum", sometimes called peak wave energy, describes the maximum value of the wave_variance_spectral_density within a given sub-domain of the wave spectrum.
>
> sea_surface_secondary_swell_wave_energy_at_variance_spectral_density_m
> aximum
> units: m2s
> The quantity with standard name sea_surface_primary_swell_wave_energy_at_variance_spectral_density_maximum is the energy of the most energetic waves within the secondary swell wave component of a sea. 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 component in the low frequency portion of a bimodal wave frequency spectrum. The phrase "wave_energy_at_variance_spectral_density_maximum", sometimes called peak wave energy, describes the maximum value of the wave_variance_spectral_density within a given sub-domain of the wave spectrum.
>
> sea_surface_tertiary_swell_wave_energy_at_variance_spectral_density_ma
> ximum
> units: m2s
> The quantity with standard name sea_surface_tertiary_swell_wave_energy_at_variance_spectral_density_maximum is the energy of the most energetic waves within the tertiary swell wave component of a sea. Swell waves are waves on the ocean surface and are the low frequency portion of a bimodal wave frequency spectrum. The tertiary swell wave is the third most energetic wave component in the low frequency portion of a bimodal wave frequency spectrum. The phrase "wave_energy_at_variance_spectral_density_maximum", sometimes called peak wave energy, describes the maximum value of the wave_variance_spectral_density within a given sub-domain of the wave spectrum.
>
>
>
> 4. And finally... Addition of 'directional_spreading' parameter to 'sea_surface_wave', 'wind_wave', 'primary_swell', 'secondary_swell' and 'tertiary_swell' categories. Giving the additional parameters:
>
> sea_surface_wave_directional_spread
> units: degree
> Directional spread is the (one-sided) directional width of the wave directional spectrum, 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.
>
> sea_surface_wind_wave_directional_spread
> units: degree
> The quantity with standard name sea_surface_wind_wave_directional_spread is the directional width of the wind wave component of a sea. Wind waves are waves on the ocean surface and are the high frequency portion of a bimodal wave frequency spectrum. The phrase "wave_directional_spread" describes is the (one-sided) directional width within a given sub-domain of the wave directional spectrum, 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 .
>
> sea_surface_primary_swell_wave_directional_spread
> units: degree
> The quantity with standard name sea_surface_primary_swell_wave_directional_spread is the directional width of the primary swell wave component of a sea. 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 wave component in the low frequency portion of a bimodal wave frequency spectrum. The phrase "wave_directional_spread" describes is the (one-sided) directional width within a given sub-domain of the wave directional spectrum, 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 .
>
> sea_surface_secondary_swell_wave_directional_spread
> units: degree
> The quantity with standard name sea_surface_secondary_swell_wave_directional_spread is the directional width of the secondary swell wave component of a sea. 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 component in the low frequency portion of a bimodal wave frequency spectrum. The phrase "wave_directional_spread" describes is the (one-sided) directional width within a given sub-domain of the wave directional spectrum, 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 .
>
> sea_surface_tertiary_swell_wave_directional_spread
> units: degree
> The quantity with standard name sea_surface_secondary_swell_wave_directional_spread is the directional width of the tertiary swell wave component of a sea. Swell waves are waves on the ocean surface and are the low frequency portion of a bimodal wave frequency spectrum. The tertiary swell wave is the third most energetic wave component in the low frequency portion of a bimodal wave frequency spectrum. The phrase "wave_directional_spread" describes is the (one-sided) directional width within a given sub-domain of the wave directional spectrum, 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 .
>
>
> Phew!
> Many thanks
> Andy
>
> Andy Saulter
> Surge, Waves and Metocean Projects Manager Met Office FitzRoy Road
> Exeter Devon EX1 3PB
> Tel: +44 (0)1392 884703 Fax: +44 (0)1392 885681
> andrew.saulter at metoffice.gov.uk<mailto:andrew.saulter at metoffice.gov.uk
> > http://www.metoffice.gov.uk
>
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