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 th
e 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 names. 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
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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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Received on Tue Oct 01 2019 - 05:39:34 BST
