Cloud variable modifications required to align with OSCAR requirements #265
Comments
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This issue is related to #190. Changes:
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If "cloud amount" is kept in the code list, it requires a definition. This should be unique, and not the same as "cloud cover" (which is cloud fraction from OSCAR requirements). If "cloud amount" meaning is not defined and unique, then users could select either variable which is opposite to standardization goals. |
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@fstuerzl Can you please verify if 'cloud amount' originates from the GOS Manual, also what other cloud variables are listed there? I don't know where the cloud variables in OSCAR/Requirements come from, but these terms need to be consolidated and properly defined. @RMaerz and @nuneslf might be able to provide more insight also. |
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I found the term "Cloud amount" listed in the Guide to the Global Observing System a cloud variable. The table below contains all GOS cloud variables: The document does not provide definitions of these terms, but refers to the Guide to Meteorological Instruments and Methods of Observation (WMO-No. 8), in which "cloud amount" is defined as follows:
Definitions in the International Cloud Atlas:
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@fstuerzl Please include these definitions in the branch. Please refer to the respective other variable explicitly, i.e.: "Also, see 'cloud amount'"; "Also, see 'cloud cover'" or something similar. |
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Since some variables are to be included that are not in the OSCAR requirements, I would also add to my original proposal to add "cloud phase" as a variable in the WMDR code registry for observedVariableAtmosphere. This is a useful indication of water, ice, or mixed phase of observed clouds. This variable is documented in BUFR: http://codes.wmo.int/bufr4/codeflag/0-20-056 |
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Updates:
View differences in branch: f5ddee9#diff-160fbee712206a9a655a755c35b0b78b48ab1514bf8937984c6069c5fdf6ba6d |
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Descriptions of 180, 181, 329 above include attributes '3D field of' and '2D field', which should be dropped, and the descriptions updated. The description for 'cloud phase' could be: Aggregate state of cloud particles, either liquid, ice, or mixed. |
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Updates:
View differences in branch: af8bcce#diff-160fbee712206a9a655a755c35b0b78b48ab1514bf8937984c6069c5fdf6ba6d |
chenxiaoxia2019
assigned chenxiaoxia2019 and IgorZahumensky and unassigned chenxiaoxia2019
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I concur with the definition for cloud phase. |
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Aggregate state of cloud particles, either liquid, solid (instead of ice), or mixed. |
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A minor suggestion: should we change effective radius to effective size as I have seen some in-situ measurement investigators reported radius while others reported diameter. Effective size will be more inclusive. |
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Or more accurate, according to: https://cloudatlas.wmo.int/en/height-and-altitude.html: |
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@IgorZahumensky Thanks for your comments that will be taken into account and are greatly appreciated. But you are not supposed to close the issue until the amendment is approved, so I have re-opened it. |
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sorry for closing; done incidentally clicking on the wrong button; I am aware of my task to be done here |
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I think there is a larger issue to consider here, based on Gao's suggestion above on effective radius. I was going to bring this up during the ACV group meeting yesterday but we never made it past agenda item 1 ... 8) Gao's suggestion to rename effective radius to effective size, and his justification, is at odds with the original approach: namely the variable name and its definition were very specific. I was attempting to follow the original approach where specific definitions were used for many atmospheric comp variables. Same for cloud base and top, whereby we provide a specific definition of height as above ground or altitude. Following Gao's approach, those other variables would just be cloud base and top, and defined as something like "height above ground OR altitude above mean sea level" because various projects report this parameter using both. The more I thought about it, there are many instances of variables in the code lists where some are very specific and others are more vague. The vague definitions capturing a true "concept" rather than an actual, specific variable definition. So I guess this is for @joergklausen, should we be defining these variables as "concepts" as the "type" column implies? or actual, specific variable definitions that might be different from project to project. If the former, then we don't want to be too specific about units and definitions in the code list. This may require a larger scrubbing of atmospheric composition variables than we've even touched on yet in the ACV group. |
Definition of the cloud amount: I believe that the definition from the "WMO-No. 8, Vol. I, 15.1.1 Definitions, p. 487) should be used: |
The "GOS Manual" (WMO-No. 544) was terminated in 2019; Cloud amount originates from The International Cloud Atlas: Manual on the Observation of Clouds and Other Meteors (WMO-No. 407), now an electronic version; the definition of the amount at: https://cloudatlas.wmo.int/en/total-cloud-cover-and-cloud-amount.html |
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Updates:
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Branch updated: https://github.com/wmo-im/wmds/blob/issue265/tables_en/1-01-01.csv |
Two definitions of optical depth/thickness within each cloud layer are offered here:
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Optical depth has a specific definition within remote sensing, the one used in the code list already for cloud optical depth is sufficient: Effective depth of a cloud from the viewpoint of radiation propagation. OD = exp(-K.Δz) where K is the extinction coefficient [km-1] and Δz the vertical path [km] between the base and the top of the cloud. This is also in agreement with optical depth definition for aerosol. The issue is that the existing definition for cloud optical depth specifies that it is for a cloud layer, not total column cloud optical depth. Thus the other existing variable called "optical depth of a layer" is redundant and should be retired. I would recommend adding a new variable called total cloud optical depth if this is needed to distinguish layer from total. |
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I have got a review from remote sensing expert (Steinar Eastwood) at METNO. For the optical depth/thickness we would support the first definition: The optical thickness of a cloud is the degree We would also be in favor of adding a total cloud optical depth entry to distinguish from cloud layer. |
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@IgorZahumensky @RMaerz Your input is required: 2 different variables for 'cloud optical depth' and 'cloud optical thickness'? If not, which term to use? Description? The WMO Cloud Atlas uses only optical thickness. What about @ferrighi's request to add 'total cloud optical depth'? |
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My proposal would be to follow the WMO Cloud Atlas, i.e. only optical thickness |
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I would agree that optical thickness is more likely to describe it. The other (depth) might confuse with another traditional used term of something like 'vertical visibility' for measurements i.e. in fog. To have a 'total cloud optical depth' (like @ferrighi requested) would avoid calculating a virtual value , for instance if it needs to be validated against radiation measurements on the surface. So it would be surely useful. |
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@ejwelton Could you weigh in again on depth vs thickness? |
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Optical depth and thickness are used interchangeably in remote sensing, at least for aerosol it is common. However, the exact definition of this term is the integrated extinction coefficient over a defined distance (ie, the definition I have provided above). Using a definition such as "the degree to which a cloud prevents light from passing through it" is something one would expect to see in an elementary school science book. I do not understand the argument here. If a data user is providing optical depth (or call it thickness), then they provide a value (ie number) that is in fact the integrated extinction coefficient over a distance thru the cloud or aerosol layer. Its the same as the more vague description being proposed, so why not use the more specific definition that is already in the WIGOS code list? If there is a desire to try to align with a cloud atlas, then perhaps just add the more vague description to the existing one (ie plain language). |
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I have decided to include both definitions for sake of mathematical rigor and to reflect the official WMO definition. |
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@fstuerzl Please update issue summary with final decision. The branch does not currently match the last table in the comments: #265 (comment) |
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@amilan17, I have included the final proposal in the first comment of this issue. |
Branch
https://github.com/wmo-im/wmds/blob/issue265/tables_en/1-01-01.csv
Summary and Purpose
Improvement of the vocabulary for clouds: Variables are missing definitions or the definitions are unclear and should be modified.
Stakeholder(s)
Proposal
Add the following variable:
Add descriptions:
Rename the following variables to align with OSCAR/Requirements and add a definitions
Rename the following variable to provide context
Reason
This proposal will better align these cloud variables with the OSCAR requirements.
Original comment:
Branch
https://github.com/wmo-im/wmds/blob/issue265/tables_en/1-01-01.csv (edited)
Summary and Purpose
Some cloud variables should be deprecated because they do not map to OSCAR requirements. Other variables are missing definitions or the definitions are unclear and should be modified.
Stakeholder(s)
Proposal
Reason
This proposal will better align these cloud variables with the OSCAR requirements.
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