amilan17
commented
2 months ago 2024-05-02 notes:
- Bruce described the request for amendments to B/C and GBON regulations.
- Jeff approved of the suggestion but expressed concern that this team is not the experts
- It was noted that provisional text in WMO-No. 8 was probably approved and this proposal has been discussed in ET-UAM.
- Does the team need to test an example? (Bruce) Vaisalla has had not problems with this (Jeff) don't see a need to test from a BUFR creation perspective.
Initial request
2024-04-19 The intention is to replace the concept of a ‘special coordinate system’ near the poles with a requirement that wind direction should be reported relative to the current reported longitude. It is argued that this is more consistent with the move to reporting the position at each level in BUFR. The proposal was discussed within ET-UAM (including a representative from Vaisala) and it was supported by TT-TDCF in July 2022 (email from Pekka Rossi). A minor change appeared in the provisional 2023 edition of the B/C manual, but unfortunately the change has not been made cleanly, hence the need for this amendment.
Amendment details
2024-04-19 Delete Note: Wind direction measured at a station within 1° of the North Pole or within 1° of the South Pole shall be reported in such a way that the azimuth ring shall be aligned with its zero coinciding with the Greenwich 0° meridian.
Replace with: Note. The wind direction at each level should be consistent with the reported longitude (launch longitude plus longitude displacement) at that level. This is particularly important near the Poles.
B/C26.5.2.8
Delete Note: Wind direction measured in sounding originated from a launch site within 1° of the North Pole or within 1° of the South Pole shall be reported in such a way that the azimuth ring shall be aligned with its zero coinciding with the Greenwich 0° meridian.
Replace with: Note. The wind direction at each level should be consistent with the reported longitude (launch longitude plus longitude displacement) at that level. This is particularly important near the Poles.
GBON 2.2.6.2.8. Wind direction and speed
Delete Wind direction measured at a station within 1° of the North Pole or within 1° of the South Pole shall be reported in such a way that the azimuth ring shall be aligned with its zero coinciding with the Greenwich 0° meridian. The wind direction at each level should be consistent with the reported longitude at that level..
Replace with: The wind direction at each level should be consistent with the reported longitude (launch longitude plus longitude displacement) at that level. This is particularly important near the Poles.
Comments
One arbitrary aspect of the old 1° rule is that it is quite possible for a radiosonde launched at say 88.8°N to pass over, or very close to, the North Pole. We have received ‘BUFR SHIP TEMP’ reports that passed very close to the North Pole. They reported wind directions consistent with the longitude at each level and were processed/assimilated correctly in the ECMWF. (Talking to Vaisala, the manufacturer, there was confusion at the time as to whether the 1° rule applied to both Poles or just the South Pole.)
So far, the South Pole station has only provided TAC reports (with longitude = 1°, some have been converted to BUFR but without displacement positions) and so can be said to be consistent with both the old and the new rule.
Requestor(s)
Bruce Ingleby (ECMWF and ET-UAM).
Stakeholder(s)
High-latitude radiosonde stations (mainly South Pole and occasional research ships near the North Pole), NWP centres and other radiosonde users.
Publication(s)
Manual on Codes (WMO-No. 306), Volume I.2 Part B/C
Expected impact of change
None
Collaborators
No response
References
A change was made to WMO-No. 8, Vol III, in Section 13.1.2 consistent with the proposal here.
The text in the Provisional 2023 version of WMO-No.8 13.1.2 is: "Particular care is needed in reporting wind direction near to the North or South Pole especially with the reporting of position at each level. A radiosonde crossing the North Pole must be in a southerly airflow just before crossing the Pole and in a northerly airflow just afterwards. BUFR reports should give wind direction relative to the longitude at each level. (The older alphanumeric codes used a special coordinate system for stations within 1° latitude of the pole.)"
Validation
No response