I suspect that the 20CR.v2 ensemble mean wind speeds provided publicly were calculated incorrectly, and I will briefly explain.
As confirmed in the attached plots, the ensemble mean speeds provided for 20CR were computed as:
wspd = [<u>^2 +<v>^2]0.5
where <> indicates the ensemble mean. The correct calculation would be
wspd = < [u2 + v2]0.5 >
As you can see in the attached, the provided ensemble mean speeds look nothing like the speeds in the individual ensemble members, and appear wrong.
After downloading all the individual ensemble members and recalculating the speeds using the correct formula above, I get an ensemble mean which is perfectly
consistent with the individual members (i.e. falls in the middle of them), as would be expected.
The ensemble mean wind speeds provided also look physically unrealistic (e.g. too low at extratropical latitudes prior to the 1990's), and exhibit unrealistically
large trends. When using the individual ensemble members, or the correctly re-calculated ensemble mean speed, these issues are corrected.
I suspect many users could be affected by this, and I hope that this info might be useful.
Note in the time-series plot attached the data are all smoothed with a 5-year wide boxcar.