[CF-metadata] standard names for sea surface roughness variables

Saulter, Andrew andrew.saulter at metoffice.gov.uk
Wed Sep 26 05:50:13 MDT 2018


Dear Jonathon

Thanks a lot for the response.

Glad you are happy with the Charnock

Re the _mean_square_slope, I was probably over-thinking it. I'd also be happy to lose the magnitude part; i.e. sea_surface_wave_[xy]_mean_square_slope

One further query, before I over-think something else! I've been speaking to my colleague Fabrice Ardhuin, who is significantly more expert in these parameters than I am. Fabrice highlighted that in addition to the grid x-y reference frame, it a number of users would wish to consider mean_square_slope in an along-across axis reference frame, where the axis used is a variable in its own right (e.g. a dominant slope direction derived from the wave spectrum, or estimated from wind direction). My suspicion is that x-y really implies 'grid' and not 'along-across', so that we would then need to additionally specify something like:

Along: sea_surface_wave_mean_square_slope_parallel_to_dominant_direction
Across: sea_surface_wave_mean_square_slope_normal_to_dominant_direction
Directional variable: sea_surface_wave_mean_square_slope_dominant_to_direction

But perhaps not, and a broader interpretation of x-y can be made that allows and interpretation of parallel-normal?? 

What do you reckon?

Cheers
Andy



-----Original Message-----
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> On Behalf Of Jonathan Gregory
Sent: 19 September 2018 15:50
To: cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] standard names for sea surface roughness variables

Dear Andy

Thanks for these proposals.

> charnock_coefficient_for_surface_roughness_length_for_momentum_in_air
> sea_surface_wave_mean_square_slope

are consistent with existing names and look fine to me.

I don't quite understand these ones.
> magnitude_of_sea_surface_wave_[xy]_mean_square_slope
You are considering the slopes in the x- and y-directions separately i.e.
deta/dx and deta/y, where eta is sea surface height. Maybe _[xy]_slope would be clearer, if that's right. If it's a mean square, it surely must be positive, mustn't it? If so, I don't see why it needs magnitude_of.

Best wishes

Jonathan

----- Forwarded message from "Saulter, Andrew" <andrew.saulter at metoffice.gov.uk> -----

> Date: Fri, 14 Sep 2018 12:20:57 +0000
> From: "Saulter, Andrew" <andrew.saulter at metoffice.gov.uk>
> To: "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
> Subject: [CF-metadata] standard names for sea surface roughness 
> variables
> 
> Hello everyone, hope you are all well.
> 
> I'd like to propose some new standard names for variables relating to sea surface roughness please. The v0 suggestions are:
> 
> charnock_coefficient_for_surface_roughness_length_for_momentum_in_air
> Units: 1
> Coefficient value, based on the Charnock (1955) empirical expression for deriving surface_roughness_length_for_momentum_in_air  over the ocean. The surface called "surface" means the lower boundary of the atmosphere.
> 
> [Not for description text, but see also 
> http://glossary.ametsoc.org/wiki/Charnock%27s_relation]
> 
> 
> sea_surface_wave_mean_square_slope
> Units: 1
> Wave slope describes an aspect of sea surface wave geometry related to sea surface roughness. Mean square slope describes a derivation over multiple waves within a sea-state, for example calculated from moments of the wave directional spectrum.
> 
> magnitude_of_sea_surface_wave_x_mean_square_slope
> Units: 1
> Wave slope describes an aspect of sea surface wave geometry related to sea surface roughness. Mean square slope describes a derivation over multiple waves within a sea-state, for example calculated from moments of the wave directional spectrum. Magnitude of "x" indicates that slope values are derived from vector components along the grid x-axis, with slope always taking a positive value.
> 
> magnitude_of_sea_surface_wave_y_mean_square_slope
> Units: 1
> Wave slope describes an aspect of sea surface wave geometry related to sea surface roughness. Mean square slope describes a derivation over multiple waves within a sea-state, for example calculated from moments of the wave directional spectrum. Magnitude of "y" indicates that slope values are derived from vector components along the grid y-axis, with slope always taking a positive value.
> 
> [My main concern with these latter variables, is the use of magnitude 
> and vector x/y descriptors. Hopefully the descriptive text explains 
> this OK; basically a negative slope makes no sense in the context in 
> which the data are derived and used, i.e. for surface roughness 
> estimation]
> 
> Will look forward to the comments :)
> Cheers
> 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 http://www.metoffice.gov.uk
> 
> 

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