Dear Martin > 15,WINDSPEED,m/sec,"Vector wind speed; m/sec.",NUMBER,"16,4", > and > 23,WINDSPEED_SCALAR,m/sec,"Scalar wind speed; m/sec.",NUMBER,"16,4", > > The first appears to be a vector average = sqrt( mean(u)**2 + mean(v)**2 ) > the second is = mean( sqrt(u**2 + v**2) ) > > Are both tied to "wind_speed" as standard_name and should they differ in > the cell_method attribute?
Yes, I think these are both wind_speed. The difference between them is some- thing like cell_methods, but it doesn't entirely fit into cell_methods, which is a way to record how the value given relates to subgrid variation. The second of these is really a time-mean in the sense that cell_methods implies, I would say; wind_speed is defined at higher temporal resolution and your values are means over time-intervals. The first isn't really a time-mean. It's as if the data from which wind_speed had been calculated had a low temporal resolution in the first place, since the higher temporal resolution has already been lost by calculating the time-mean of u and v. Since this is an intensive quantity, if it's not a time-mean, it really has to be a "point" as if it were instantaneous in cell_methods. That doesn't sound quite right, does it? It makes sense in the respect that, for model output, you would probably record the u and v, and hence the wind_speed, as instantaneous (point) values in time, even if the model timestep was very long, because for a model there is truly no information at higher temporal resolution than the timestep. Best wishes Jonathan _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
