NCAR / NCAR/wrf-python

UVMET does not correctly rotate winds to Earth coordinates for the rotated pole projection

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Dominant language
Python
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Description

For the rotated pole, the uvmet product does not perform any wind rotation. This behavior is correct for the standard lat/lon projection, but not when the pole is rotated. This is also broken in NCL and has been for years.

As a workaround, users should use the COSALPHA and SINALPHA variables and perform the rotation manually using:

u_earth = u * COSALPHA - v * SINALPHA
v_earth = v * COSALPHA + u * SINALPHA

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Locate the uvmet product implementation and inspect how wind components are handled for standard and rotated-pole projections. Verify the rotated-pole case against the stated Earth-coordinate behavior, while preserving the existing standard latitude/longitude behavior; done means the product no longer requires manual COSALPHA and SINALPHA rotation.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
data
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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