Thank you, Roy, for heading up this effort.
I still have a problem with including the word mean in the standard
name for sea_surface_wave_period, and would like to suggest that
we add another standard name without that word. If this is model
data, or a high frequency record, it may not in fact be a mean. If
we need 2 terms for surface wave periods in order to make all the
wave standard names consistent, so be it.
Also, I think the word 'significant' is a modifier of the word wave,
and therefore sea_surface_wave_significant_period could be
sea_surface_significant_wave_period. The definition uses the phrase
'significant wave period', not wave significant period, as well.
I'm sorry I didn't work harder to resolve these issues in the off-list
discussion, it's been a busy time here.
Cheers - Nan
Quoting "Lowry, Roy K." <[email protected]>:
Hello Jonathan,
Whilst the cell-method approach might look feasible for the wave
period sub-proposal taken in isolation (remember I have split the
original proposal into three parts: wave heights, wave periods and
wave directions), it doesn't work well for the wave heights and for
other more complex wave statistics that could be encountered in the
future. Remember also the precedent of the existing wave Standard
Names that incude 'mean'.
Having one 'rule' for all wave Standard Names seems a much more
manageable approach than having some wave statistics with 'mean' and
'maximum' in the Standard Name, whilst using the cell method
approach for others.
Cheers, Roy.
-----Original Message-----
From: CF-metadata [mailto:[email protected]] On
Behalf Of Jonathan Gregory
Sent: 25 May 2016 15:34
To: [email protected]
Subject: [CF-metadata] Wave periods sub-proposal
Dear Roy
Thanks for these updated proposals. With the rephrasing, it now
seems to me there is a less strong argument for including "mean" and
"maximum" in the standard names. Why not have
sea_surface_wave_period and use cell_methods with time-bounds to
describe the period of observation over which the mean etc.
is calculated?
Best wishes
Jonathan
----- Forwarded message from "Lowry, Roy K." <[email protected]> -----
Date: Wed, 25 May 2016 10:09:21 +0000
From: "Lowry, Roy K." <[email protected]>
To: "[email protected]" <[email protected]>
CC: "[email protected]" <[email protected]>
Subject: [CF-metadata] Wave periods sub-proposal
Dear All,
What follows is a modification of part of the proposal initially
submitted by Elodie Fernandez following off-list work between
Elodie, Marta, Chris Barker, Nan Galbraith and myself. It includes
a change (deprecation plus creation of an alias) to three existing
Standard Names, plus the creation of six new wave period Standard
Names. Every effort has been made to maintain compatibility
between this and the separate wave height sub-proposal submitted a
couple of weeks ago.
Each proposed Standard Name is followed by its definition. All wave
periods have Canonical Units of seconds.
Cheers, Roy.
PS I have formatted this message in Rich Text to make it easier to
follow. It is also attached as a Word Document for those who prefer.
Wave Period Proposal
Existing Standard Name Changes
1) sea_surface_wave_zero_upcrossing_period
A period is an interval of time, or the time-period of an
oscillation. The zero upcrossing period is defined as the time
interval between consecutive occasions on which the surface height
passes upward above the mean level.
Replace this by:
sea_surface_wave_mean_period
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 average period
measured over the observation duration.
2) sea_surface_wind_wave_zero_upcrossing_period
A period is an interval of time, or the time-period of an oscillation.
The zero upcrossing period is defined as the time interval between
consecutive occasions on which the surface height passes upward above
the mean level. 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.)
Replace this by:
sea_surface_wind_wave_mean_period
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 average period
measured over the observation duration. Wind waves are the high
frequency portion of a bimodal wave frequency distribution.
3) sea_surface_swell_wave_zero_upcrossing_period
A period is an interval of time, or the time-period of an
oscillation. The zero upcrossing period is defined as the time
interval between consecutive occasions on which the surface height
passes upward above the mean level. Swell waves are waves on the
ocean surface.
Replace this by:
sea_surface_swell_wave_mean_period
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 average period
measured over the observation duration. Swell waves are the low
frequency portion of a bimodal wave frequency distribution.
Justification for change:
The classical Tucker-Draper analysis specifies multiple wave period
statistics such as zero-upcrossing period (Tz) and crest period
(Tc) and the protocols used could cause these to differ. However,
wave theory states that period of a waveform should be uniform for
all reference points on the waveform and so the possibility of
variation should be considered an artefact and the geophysical
variable should simply be wave period. The long name can be used if
required to specify the waveform reference and measurement protocol
used, as proposed for wave height Standard Names.
Additional Standard Names for Copernicus Proposal
1) sea_surface_wave_significant_period
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. Significant wave period is a statistic
computed from wave measurements and corresponds to the average wave
period of the highest one third of the waves.
2) sea_surface_wave_mean_period_of_highest_tenth
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 average period
measured over the observation duration. Mean period of the highest
tenth is the average period of the highest one-tenth of the waves
during the observation duration.
3) sea_surface_wave_maximum_period
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. The maximum period is the longest wave
period measured during the observation period.
4) sea_surface_wave_period_of_highest_wave
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 period of the highest wave is the
period determined from wave crests corresponding to the greatest
vertical distance above mean level during the observation period.
5) sea_surface_primary_swell_wave_mean_period
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 average period
measured over the observation duration. The primary swell wave is
the most energetic wave in the low frequency portion of a bimodal
wave frequency distribution.
6) sea_surface_secondary_swell_wave_mean_period
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 average period
measured over the observation duration. The secondary swell wave
is the second most energetic wave in the low frequency portion of a
bimodal wave frequency distribution.
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 [email protected]<mailto:[email protected]>. Please
also use this e-mail if your requirement is urgent.
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