Dear Andy Yes, I agree, that is a sufficiently different quantity that it can't clearly be seen as a statistic describable by cell_methods and so needs its own name. Maybe you could add something more to the definition.
Best wishes and thanks Jonathan ----- Forwarded message from "Saulter, Andrew" <[email protected]> ----- > Date: Thu, 3 May 2018 10:34:03 +0000 > From: "Saulter, Andrew" <[email protected]> > To: "[email protected]" <[email protected]> > 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:[email protected]] On Behalf Of > Jonathan Gregory > Sent: 02 May 2018 13:32 > To: [email protected] > 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" > <[email protected]> ----- > > > Date: Wed, 2 May 2018 07:28:05 +0000 > > From: "Saulter, Andrew" <[email protected]> > > To: "[email protected]" <[email protected]> > > 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:[email protected]] On Behalf > > Of Saulter, Andrew > > Sent: 01 May 2018 09:27 > > To: [email protected] > > 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 > > [email protected]<mailto:[email protected] > > > http://www.metoffice.gov.uk > > > > > _______________________________________________ > > CF-metadata mailing list > > [email protected] > > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > > ----- End forwarded message ----- > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
