Dear Alison,
1) The outcome of the ongoing discussion (Alison, Ian, Jonathan and us)
are 2 possibilities for the standard name:
surface_direct_normal_shortwave_flux_in_air
or
surface_direct_along_beam_shortwave_flux_in_air
We prefer surface_direct_along_beam_shortwave_flux_in_air with following
description:
'"surface" means the lower boundary of the atmosphere. "direct" radiation
is radiation that has followed a direct path from the sun. ?along_beam?
refers to direct radiation on a plane perpendicular to the direction of
the sun. This is in contrast to quantities like
direct_downwelling_shortwave_flux_in_air, where the radiation falls on a
horizontal plane at the earth surface. The term "shortwave" means
shortwave radiation. In accordance with common usage in geophysical
disciplines, "flux" implies per unit area, called "flux density" in
physics.' Regarding solar energy applications, the given quantity is often
called Direct Normal Irradiance (DNI).
Our general opinion about the solar-related quantities is that the
CF-conventions and the related standard names do not clearly separate
between the following two aspects: 1) What is the orientation/tilt of the
collector measuring the incoming beam and 2) from which direction in space
the incoming radiation is received? For instance, the quantity
surface_downwelling_shortwave_flux_in_air contains the word ?downwelling?,
which refers a) to a collector oriented horizontal to the Earth surface
and b) to the radiation received from the upper half space (all points in
the sky). B) is in contradiction the your definition of ?downwelling?
which you, Alison, argued to be a solely vertical oriented flux.
Sometimes ?downwelling? was abused e.g. for the quantity
integral_wrt_time_of_surface_downwelling_shortwave_flux_in_air with
?Downwelling radiation is radiation from above.?
2) atmosphere_mass_content_of_rain is fine with us.
We definitely agree that all precipitation related quantities should get
the prefix surface_ (e.g. rainfall_amount to surface_rainfall_amount and
snowfall_amount to surface_snowfall_amount)
Best regards,
Ronny and Beate
Von: "Alison Pamment - UKRI STFC" <alison.pamment at stfc.ac.uk>
An: "beate.geyer at hzg.de" <beate.geyer at hzg.de>, "CF-metadata
(cf-metadata at cgd.ucar.edu)" <cf-metadata at cgd.ucar.edu>
Datum: 01.10.2019 13:39
Betreff: RE: [CF-metadata] New standard names for norm. direct
radiation and atm. mass [SEC=UNCLASSIFIED]
Dear Beate and Ronny,
Thank you for your proposals and apologies for the delay in responding.
Thank you also to Jonathan and Ian for comments on these proposals. I have
a number of comments and questions of my own and would welcome discussion
of the issues raised.
1. surface_normalized_direct_downwelling_shortwave_flux_in_air (W m-2)
'The surface called "surface" means the lower boundary of the atmosphere.
"Normalized_direct" radiation is radiation that has followed a direct path
from the sun to a plane perpendicular to the direction of the sun (in
contrast to the "direct" radiation, which falls on a plane horizontal at
the earth surface). Downwelling radiation is radiation from above. It does
not mean "net downward". The sign convention is that "upwelling" is
positive upwards and "downwelling" is positive downwards. The term
"shortwave" means shortwave radiation. In accordance with common usage in
geophysical disciplines, "flux" implies per unit area, called "flux
density" in physics.'
I agree with Jonathan that it is better not to include "downwelling" in
the name because that suggests the flux is vertically downwards through
the atmosphere which does not appear to be the case here. I agree also
that "normalized" can have a number of meanings, although certainly we
refer to "normal" in the sense of "perpendicular to a surface" in existing
names and definitions.
Ian's suggestion of
surface_direct_normal_downwelling_shortwave_flux_in_air is close to the
original proposal and uses similar terminology to the three existing
direct radiation names (which all refer to 'shortwave' rather than
'solar'). If we take out the 'downwelling' that leaves us with
surface_direct_normal_shortwave_flux_in_air. Adding 'normal' to Jonathan's
suggestion would give us surface_direct_normal_solar_irradiance_in_air. So
I think it comes down to a choice between calling it a 'shortwave_flux' or
a 'solar_irradiance'. The former is closer to existing direct names, the
latter is apparently closer to WMO and energy industry terminology. I
could live with either and am happy to go with whatever is the majority
view on this point. I note that during a 2018 conversation about the
definition of existing solar_irradiance and shortwave names Stephane Tarot
(
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2018/019809.html
)pointed us to a WMO reference which states that 'solar' and 'shortwave'
mean the same thing in meteorological terminology.
2. atmosphere_mass_content_of_rainwater (kg m-2)
' "Content" indicates a quantity per unit area. The "atmosphere content"
of a quantity refers to the vertical integral from the surface to the top
of the atmosphere. For the content between specified levels in the
atmosphere, standard names including "content_of_atmosphere_layer" are
used. "Rainwater" refers to the precipitating part of liquid water in the
atmosphere - the cloud liquid water is excluded.'
Existing names for rain/rainfall quantities don't use 'rainwater' as a
term so I'd agree with Jonathan's suggestion of
atmosphere_mass_content_of_rain. However, I think this proposal and the
accompanying one for atmosphere_content_of_snow reveal a weakness in the
definitions of some of our existing names.
We have existing names such as rainfall_amount, convective_rainfall_amount
and stratiform_rainfall_amount which all have the same units (kg m-2) as
the proposed name. Are these intended to apply to rainfall that has
already reached the earth's surface (and should therefore be made into
aliases by prepending them all with 'surface_')? The existing definitions
just say ' "Amount" means mass per unit area.' It's important to be clear
about exactly _where_ the existing names apply, otherwise rainfall_amount
could be interpreted to mean the same as the proposed
atmosphere_mass_content_of_rain. I'd welcome comments about this.
Also proposed is :
atmosphere_mass_content_of_snow (kg m-2)
' "Content" indicates a quantity per unit area. The "atmosphere content"
of a quantity refers to the vertical integral from the surface to the top
of the atmosphere. "Snow" refers to the precipitating part of snow in the
atmosphere - the cloud snow content is excluded. For the content between
specified levels in the atmosphere, standard names including
content_of_atmosphere_layer are used.
This proposal again made me wonder about existing names. We have
surface_snow_amount, which clearly does refer to snow already lying on the
surface, but also snowfall_amount. The definition of snowfall_amount
simply says ' "Amount" means mass per unit area' which doesn't really
help, but the fact that it says 'snowfall' makes me think that it means
snow in the atmosphere, which would then be the same as the proposed new
name. We need to clarify the existing names, decide whether we need the
new names, and be as consistent as possible in our treatment of rain and
snow quantities. Again, comments are most welcome!
3. Beate and Ronny wrote:
> The description of atmosphere_mass_content_of_cloud_liquid_water is
> incomplete, as "cloud_liquid_water" is not mentioned.
> New Description: "Content" indicates a quantity per unit area. The
> "atmosphere content" of a quantity refers to the vertical integral from
> the surface to the top of the atmosphere. "Cloud liquid water" refers to
> the liquid phase of cloud water. For the content between specified
levels
> in the atmosphere, standard names including content_of_atmosphere_layer
> are used.
I agree that we should improve the definition. In fact there are 45
existing cloud_liquid_water names, only one of which has a definition that
actually explains what the term means!
The definition of mass_concentration_of_cloud_liquid_water_in_air says:
'Cloud droplets are spherical and typically a few micrometers to a few
tens of micrometers in diameter. An upper limit of 0.2 mm diameter is
sometimes used to distinguish between cloud droplets and drizzle drops,
but in active cumulus clouds strong updrafts can maintain much larger
cloud droplets.' I suggest that we should add Beate and Ronny's sentence
'"Cloud liquid water" refers to the liquid phase of cloud water' at the
beginning of this explanation and then add it to all the existing names.
For example, atmosphere_mass_content_of_cloud_liquid_water would then be
defined as:
' "Content" indicates a quantity per unit area. The "atmosphere content"
of a quantity refers to the vertical integral from the surface to the top
of the atmosphere. For the content between specified levels in the
atmosphere, standard names including content_of_atmosphere_layer are used.
"Cloud liquid water" refers to the liquid phase of cloud water. Cloud
droplets are spherical and typically a few micrometers to a few tens of
micrometers in diameter. An upper limit of 0.2 mm diameter is sometimes
used to distinguish between cloud droplets and drizzle drops, but in
active cumulus clouds strong updrafts can maintain much larger cloud
droplets.'
Do others agree?
4. Beate and Ronny wrote:
> The standard name air_potential_temperature is misleading because the
> description refers to air and sea water.
> We recommend replacing the standard name by potential_temperature.
I agree with Jonathan that it is usual CF practice to have separate names
when similar quantities are measured in different media. Thus we have both
air_potential_temperature and sea_water_potential_temperature as standard
n air_potential_temperature and ames. In both cases the definition of
potential_temperature is the same, but the quantities labelled by the
standard names are distinct.
Best wishes,
Alison
-----------------------------------------------------------------------------------------------------------
Alison Pamment Tel: +44 1235 778065
NCAS/Centre for Environmental Data Analysis Email:
alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
-----Original Message-----
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> On Behalf Of Ian
Grant
Sent: 17 September 2019 04:58
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] New standard names for norm. direct radiation
and atm. mass [SEC=UNCLASSIFIED]
This is a comment on proposal 1 by Beate Geyer and Ronny Petrik on 20
August for a new standard name
surface_normalized_direct_downwelling_shortwave_flux_in_air. My response
was delayed by trouble posting due to my changed email address.
In the solar energy community, this quantity, as described by Beate and
Ronny, is almost universally referred to as "direct normal irradiance".
Here "normal" means measured on a plane perpendicular (that is, normal) to
the incoming solar beam. I note that the World Meteorological Organisation
follows a different convention, naming the quantity measured on a normal
plane "direct irradiance" and that measured on a horizontal plane "direct
horizontal irradiance", but that convention is not followed in the
renewable energy sector. Thus I suggest that the proposed name should be
changed to surface_direct_normal_downwelling_shortwave_flux_in_air to
better align with solar energy practice. However, there might be CF
rules/conventions/precedents I am unaware of that make the
normalized_direct form preferable.
Regards,
Ian Grant
Ian Grant | Research Scientist
Science To Services Program | Satellite Applications Team Bureau of
Meteorology GPO Box 1289, Melbourne VIC 3001, AUSTRALIA Level 9, 700
Collins Street, Docklands VIC 3008, AUSTRALIA
Tel: +61 3 9669 4080 | ian.grant at bom.gov.au www.bom.gov.au
-----Original Message-----
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Sent: Saturday, 31 August 2019 3:10 AM
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Subject: CF-metadata Digest, Vol 196, Issue 2
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Today's Topics:
1. New standard names for norm. direct radiation and atm. mass
content of rain and snow + comments on existing descriptions
(beate.geyer at hzg.de)
2. Re: New standard_name of quality_flag for corresponding
quality control variables (Kehoe, Kenneth E.)
----------------------------------------------------------------------
Message: 1
Date: Tue, 20 Aug 2019 09:08:59 +0200
From: beate.geyer at hzg.de
To: cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] New standard names for norm. direct radiation
and atm. mass content of rain and snow + comments on
existing
descriptions
Message-ID:
<OF5D396235.9078C54C-ONC125845C.002501BE-C125845C.00274681 at LocalDomain>
Content-Type: text/plain; charset="utf-8"
Dear CF-metadata group,
we have several proposals, which we send as a numbered list. Thanks for
your help beforehands!!
1.
Basing on surface_direct_downwelling_shortwave_flux_in_air we want to
apply for the new standard name
surface_normalized_direct_downwelling_shortwave_flux_in_air for use in
renewable energy tasks.
It is the surface_direct_downwelling_shortwave_flux_in_air on a plane,
oriented perpendicular to the incoming beam.
New name: surface_normalized_direct_downwelling_shortwave_flux_in_air
Description: The surface called "surface" means the lower boundary of the
atmosphere. ?Normalized_direct" radiation is radiation that has followed a
direct path from the sun to a plane perpendicular to the direction of the
sun (in contrast to the ?direct? radiation, which falls on a plane
horizontal at the earth surface). Downwelling radiation is radiation from
above. It does not mean "net downward". The sign convention is that
"upwelling" is positive upwards and "downwelling" is positive downwards.
The term "shortwave" means shortwave radiation. In accordance with common
usage in geophysical disciplines, "flux" implies per unit area, called
"flux density" in physics.
Unit: W m-2
<snip>
Best regards,
Beate Geyer and Ronny Petrik
Helmholtz-Zentrum Geesthacht
Zentrum f?r Material- und K?stenforschung GmbH Max-Planck-Stra?e 1 I 21502
Geesthacht I Deutschland/Germany
Gesch?ftsf?hrung/Board of Management: Prof. Dr. Wolfgang Kaysser, Silke
Simon Vorsitzender des Aufsichtsrates/Chairman of the Supervisory Board:
Ministerialdirigent Dr. Herbert Zeisel Amtsgericht L?beck HRB 285 GE
(Register Court)
Internet:
http://www.hzg.de
<snip>
_______________________________________________
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Helmholtz-Zentrum Geesthacht
Zentrum f?r Material- und K?stenforschung GmbH
Max-Planck-Stra?e 1 I 21502 Geesthacht I Deutschland/Germany
Gesch?ftsf?hrung/Board of Management: Prof. Dr. Matthias Rehahn, Silke Simon
Vorsitzender des Aufsichtsrates/Chairman of the Supervisory Board: Ministerialdirigent Dr. Herbert Zeisel
Amtsgericht L?beck HRB 285 GE (Register Court)
Internet:
http://www.hzg.de
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