Environmental Steering Layer (mean vector) for TCs...any ideas?

[Jason E Patla]

Hi GRADS Users,
I'm trying to come up with a simple way to create an environmental steering layer mean vector for TCs (versus their actual movement vector) in ERA-40 reanalysis data.  Using previous studies (Chan and Gray 1982), I would like to basically take the mean wind vector value (u,v components) for 7 degrees around some point (the TC at a specific lat lon) through a number of levels (say 200 mb to 850 mb) for each time step.  I would then subtract off the inner 5 degrees (set to zero) to create a mean vector for the 5-7 degree annulus around a TC at a given time.  Sounds pretty simple.

However, I can only get GRADS to give 2D fields of output instead of a single vector/value representing the average over the area and depth.  Any ideas?   How can you combine horizontal and vertical values to give one mean of it all (hopefully in vector form)?

I'm sure this has been done before and is pretty straight forward for some of you.  Thanks for any help you can provide.
Jason

PS: I searched the archives extensively but with no luck.   :(