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Use the correct function to compute the rotation angle#5677

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simone-silvestri merged 3 commits into
mainfrom
ss/correct-rotation
Jun 11, 2026
Merged

Use the correct function to compute the rotation angle#5677
simone-silvestri merged 3 commits into
mainfrom
ss/correct-rotation

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@simone-silvestri

@simone-silvestri simone-silvestri commented Jun 11, 2026

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atan(sin / cos) might change the sign of the cosine function, atan(sin, cos) retains the sign, MWE:

function test_signs(θtrue)
    cosθ, sinθ = cos(θtrue), sin(θtrue)        
    θ1 = atan(sinθ / cosθ)                         
    θ2 = atan(sinθ, cosθ)                         
    @info θtrue, θ1, θ2
end

returns

julia> test_signs(deg2rad(30))
[ Info: (0.5235987755982988, 0.5235987755982987, 0.5235987755982987)

julia> test_signs(deg2rad(170))
[ Info: (2.9670597283903604, -0.17453292519943292, 2.9670597283903604)

julia> test_signs(deg2rad(-135))
[ Info: (-2.356194490192345, 0.7853981633974484, -2.356194490192345)

@simone-silvestri simone-silvestri merged commit 52369bf into main Jun 11, 2026
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@simone-silvestri simone-silvestri deleted the ss/correct-rotation branch June 11, 2026 09:40
@navidcy navidcy mentioned this pull request Jun 13, 2026
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@navidcy

navidcy commented Jun 13, 2026

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Did this had an effect on the tripolar seam issue?

@navidcy navidcy added the numerics 🧮 So things don't blow up and boil the lobsters alive label Jun 13, 2026
@simone-silvestri

simone-silvestri commented Jun 13, 2026

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I think it did, it changes the values of the rotated components inside the north halos (all interior values were correct). But we do use rotation inside the halos if we use a prescribed atmosphere (we interpolate inside the halos instead of filling the halos). I saw some differences in an arctic sea ice simulation forced by a prescribed atmosphere that had some artifacts at the north pole (on a rotated latitude longitude grid, so no tripolar involved!!) which now are absent

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