MetOffice / opsinputs

JEDI library generating VarObs and Cx files
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Unrotate winds #132

Closed ctgh closed 1 year ago

ctgh commented 2 years ago

If the UKV model is used then the wind components u and v are rotated to match the coordinates of the domain. Before writing out the CX columns, the wind components are unrotated back to their original values. In Jopa, the rotation is performed in the UM interface, but the unrotation is not currently performed. This leads to offsets between the CX values of u and v obtained in OPS and Jopa.

In OPS, the original wind components are stored in a dummy variable which is used to overwrite the rotated components before the CX columns are produced. However, this won't be possible in Jopa because of the fact that the GeoVaLs of u and v produced by the UM interface are already rotated and the original values are not stored. It seems likely that obtaining both rotated and unrotated GeoVaLs from the UM interface would be tricky. Instead, a new routine is added to the Cx Writer that reverses the rotation performed.

Two things to note: