Good morning Jonathon,
Was nice to have a weekend's reflection on this, not least because I also got a bit more feedback from some of my other waves colleagues (thanks Fabrice).
A quick fundamental, the reason we need to have some form of 'along' and 'across' follows the same argument as the 'spread' conversation. Basically, wave energy in a given sea-state is not uni-directional, so we have a dominant/mean direction that gets calculated, but there will be a component of wave energy (with associated height, period, slope characteristics etc.) that runs normal to this.
In terms of what the "direction" really is, the suggestion I've been given is "upwave", i.e. a wave equivalent of "upwind" and, therefore, same as "wave_from_direction" (correcting my initial suggestion of "to" in the previous post).
This gives us a few choices for names I think?
Least verbose:
Direction: sea_surface_upwave_mean_square_slope_direction / sea_surface_wave_mean_square_slope_from_direction*
Parallel component: sea_surface_upwave_mean_square_slope
Normal component: sea_surface_cross_wave_mean_square_slope
More verbose (but perhaps more clear?):
Direction: sea_surface_upwave_mean_square_slope_direction / sea_surface_wave_mean_square_slope_from_direction*
Parallel component: sea_surface_wave_mean_square_slope_along_upwave_direction
Normal component: sea_surface_wave_mean_square_slope_across_upwave_direction
More consistent with existing names (but possibly least clear?):
Direction: sea_surface_wave_mean_square_slope_from_direction
Parallel component: sea_surface_wave_mean_square_slope_along_from_direction
Normal component: sea_surface_wave_mean_square_slope_across_from_direction
* if we use _from_direction in conjunction with _upwave, then we need to add some text to link the two terms in the standard name definition.
Any of these make sense?
Cheers
Andy
PS. Devon is geographically 'up' from Cornwall - but definitely 'down' in terms of the quality of pasties, clotted cream and beer....
-----Original Message-----
From: Jonathan Gregory <j.m.gregory at reading.ac.uk>
Sent: 28 September 2018 13:46
To: Saulter, Andrew <andrew.saulter at metoffice.gov.uk>
Cc: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] standard names for sea surface roughness variables
Dear Andy
> Re the direction of the _mean_square_slope, the parameter and calculation method from the wave spectrum is sufficiently different from that for _wave_[to/from]_direction that it should stand alone. There has already been a precedent set for this with waves, where different forms of parameter calculation from the spectrum are given their own names because there is not only a calculation difference but a different physical interpretation of each parameter (e.g. the various type of wave period).
OK, fair enough. So you need sea_surface_wave_mean_square_slope_to_direction.
I'm still stuck with what this "direction" really is. Can we insert anything else for ? in
sea_surface_wave_mean_square_slope_along_?_direction
sea_surface_wave_mean_square_slope_across_?_direction
Apparently you want to quantify the mean square slope along and across the direction of the mean square slope. Is that right? I'm not sure what it means.
Without the "mean square", I'd think that the slope normal to the direction of the slope must be zero, but it must be more subtle than that in this case!
Is there really an ambiguity of to/from with a mean square slope? It seems to me that it must be the same (unsigned) number regardless of whether you go backwards or forwards on a particular direction.
Is Devon up or down from Cornwall?
Best wishes
Jonathan
Received on Mon Oct 01 2018 - 03:30:03 BST
