Change order of operations for ensemble mean of derived parameters - #257
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sqrt(mean(U)^2 + mean(V)^2) <= mean(sqrt(U^2 + V^2)) the speed of the mean wind vector is not equal to the mean wind speed. Derive DERIVED_PARAMS (e.g. SP_10M) per member before accumulating into the ensemble-mean accumulator so the final division gives the correct mean wind speed. _disaggregated_and_derived_params already guards with `if p in DERIVED_PARAMS and p not in ds.data_vars` so it skips recomputing SP_10M from the now-averaged components.
cosunae
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Sep 11, 2026
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good catch.
I checked that the derived params wont be computed later on, if variables are already in ds.data_vars so this looks good to me
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For all derived quantities, the order of operation to compute the ensemble mean needs fixing. First we need to compute the derived parameter per ensemble member, then average (now we're doing it in reverse).
For aggregated parameters, this is a non-issue as long as we only compute the ensemble mean (not median or other ensemble statistics).
Summary of changes