clarify 4.2 Direction of Combined Wind Waves and Swell

[tomkralidis]

Branch

https://github.com/wmo-im/GRIB2/tree/issue-22

Summary and purpose

We are looking for clarification on https://github.com/wmo-im/GRIB2/blob/master/GRIB2_CodeFlag_4_2_CodeTable_en.csv#L896.

Action proposed

1. update the parameter description to "Mean Direction of Combined Wind Waves and Swell"
2. if 1 is not possible add a note to explain that the parameter implies a mean direction?

Discussions

Requirements and purposes of the proposal along with other background information, which could be included in the SUMMARY OF MEETING REPORT.

Detailed proposal

Does 'Direction of Combined Wind Waves and Swell' intend to communicate a mean direction?

[sebvi]

@tomkralidis : It is indeed a mean direction so I support the idea to rename the parameter "Mean Direction of Combined Wind Waves and Swell"

[efucile]

Do we want to say that the word "combined" refers to a mean? Is it to specify better what we mean for combined. I agree that "combined" doesn't explain how, but I am not sure that Mean clarifies combined in the proposed name. Can we find a better solution and possibly delete combined? However, I think that we need to involve someone from the ocean community before changing this.

[edouardsandrine]

Thanks a lot for your comment. In fact we would like to know if this parameter represents a mean direction , if it is the case, then we suggest to update the definition from "Direction of combined wind waves and swell" to "Mean direction of combined wind waves and swell". Hope it helps....

[sebvi]

I have discussed this with our wave expert at ECMWF (Jean) before answering last week. He confirmed to me that the name should indeed be "Mean direction of combined wind waves and swell"

[benoitp-cmc]

Thanks @sebvi (and Jean), this answers the question. Updating the name to clarify would be desirable and I agree with "Mean direction of combined wind waves and swell".

@efucile "combined" indicates we are looking at the total sea which includes wind waves and all the swells. It is also used for "Significant height of combined wind wave and swell" and "Mean period of combined wind waves and swell".

[chenxiaoxia2019]

@tomkralidis Hi, Tom. A new branch for this issue has been created. The parameter description has been updated to "Mean Direction of Combined Wind Waves and Swell". Could you please check the branch? Thanks.

[tomkralidis]

@chenxiaoxia2019 +1 thanks.

[amilan17]

SUMMARY: Modify entry 14 in Code Table 4.2, discipline 10, category 0.

[amilan17]

Approved by FT-2020-2.