JREyre
commented
1 year ago @fstuerzl @gaochen-larc @joergklausen @amilan17
For the record, I am copying here the comments from Sebastian Schmidt on my comments (above), together with my replies. I reviewed all the comments again, and so some of my replies are modified from previous emails:
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John: Diffuse short-wave irradiance: Is a definition of the net flux direction needed? The direction would normally be downward, but it is theoretically possible that it could be upward. Sebastian: Upward flux is always diffuse. When talking about diffuse irradiance, I can confirm that we typically mean downward, but I also agree that we could be more specific if that's preferable. John: I don’t think I agree that the upward flux is always diffuse. Over cloud it will often be close to diffuse. But, for example, over a calm (mirror-like) ocean with a cloud-free sky, it is close to specular. (I am taking “diffuse” to mean no variation with nadir angle but, from a measurement perspective, it will usually mean that the measurement integrates over all nadir angles, over the whole hemisphere. However, these are definitions of geophysical variables, not measurements.) However, Sebastian’s comment does not affect the definition. Sebastian: I think there's a confusion here between net irradiance (difference between downwelling and upwelling), and diffuse irradiance (component of the downwelling shortwave irradiance). Am I mis-reading something there? John: Net flux v upward and downward fluxes. The “requirement” is (usually) to observe the net, but measurements are usually of upward or downward. So, I think there is good reason to have both on the list, but we need to check that this is done consistently. I think they currently are consistent (if, perhaps, not complete). Does everyone agree?
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John: Background luminance: Is the note included in the definition needed? (Note: "Luminous flux is a quantity derived from radiant flux by evaluating the radiation according to its action upon the International Commission on Illumination standard photometric observer.") Sebastian: I would say an explanation would be helpful because it's not a typical quantity that we come across very often. That said, I am not sure I understand the note 🙂 What is meant by "background" in this context? Sorry to not have a straight answer for you here..... John: I agree with Sebastian - I too do not understand the comment. Can we identify an expert who is more familiar with this area? Alternatively, we could drop "Background luminance" from the list for the time being, in order to move this Issue along.
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Long-wave irradiance (direction unspecified). Sebastian: I think that's fine, but irradiance is often just specified w.r.t. a horizontal reference. (There are exceptions to this, for example, when quantifying horizontal photon flux density, but that is only rarely measured – almost never in the longwave). John: I agree with the comment, but I don't this affects the definition. noting that this is a geophysical variable, not a measurement.
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Earth surface short-wave bidirectional reflectance. Sebastian: This is of course correct, but the specification of the wavelength band seems somewhat arbitrary. In practice, most BRDF measurements are done spectrally and not averaged over the visible band. John: Spectrally integrated v spectrally resolved. It is true that most new missions measure spectrally resolved quantities, but some old missions measured spectrally integrated, and so there is good reason to include both.
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Albedo Sebastian: While we are on the topic: If BRDF is included, it might be useful to include albedo also since it is one of the primary modulators of Earth's radiation budget. It can be derived from upwelling and downwelling shortwave spectral or broadband irradiance, and therefore is not a primary parameter – maybe have a discussion amongst your team whether it's appropriate to include? John: We have an observed variable called "surface albedo" under "atmosphere". It currently lacks a definition. Franziska: why have we not addressed this before?
To summarise, Sebastian has given us some good comments, but I don't think they affect our proposed variables or their definitions, with the following exceptions:
- Background luminance. What to do about this? I suggest 2 options above.
- Albedo. What to do about the lack of definition?
gaochen-larc
amilan17
AnnWebb
joergklausen
Proposal Summary
Summary and Purpose
Provide consistent names and descriptions/definitions for radiation terminology; align terminology in use in OSCAR/Surface (based on the WMO codes registry) and OSCAR/Requirements.
Proposal
Add definitions and include the term "radiation" in the UV variables:
Include the following new variables in table 1-01-01 (Atmosphere):
Reason
Some radiation variables in OSCAR/Requirements currently have no corresponding WMDR variable:
Stakeholder(s)
@JohnEyre
Consultations
@laurentvuilleumier, @PeterBlattner, @AnnWebb
Context
[include references to manuals or guides that are reviewed to ensure alignment, if proposal differs then document how and why]
Expected Impact of Change
LOW for new codes and changes of names and descriptions