CDO

Hello everyone

This is my first post in here so I will try my best to give a clear description of my problem... I am calculating the PDO index in a GCM. I extracted the SST and detrended the 19th century and cut out the global ocean SST anomalies and the North Pacific SST anomalies. Now I need to calculate a monthly mean SST anomaly from the global ocean and subtract that time series from the North Pacific Area I have extracted.(further details in: GCM projections for the Pacific Decadal Oscillation under greenhouse forcing for the early 21st century (Lapp et al. 2012)). As far as I understood it i should take the fealdmean from the global ocean grid for the 19th century and then subtract that time series from the north pacific grid. However it is not possible to subtract a fldmean TS from a Grid. What can I due here? I was thinking about making a new nc file from the North Pacific with the fldmean Timeseries and then subtract that new created nc file from the North Pacific SST anomaliy file. So for those of you who got confused by the PDO describtion --> a general view to my problem: How can I subtract a fldmean Time series from a Grid/Raster file? Thank you for the help

Best Matthias