Re: calculating pCFC ages

[Niki Gruber <gruber@xxxxxxxxxxxxxxxxxxxx>]

Hi all,

I had the following problem:

> I am trying to compute pCFC ages from a 3-D field of partial pressures
> of CFC (pCFC[x,y,z]) and a one dimensional field of atm. CFC history
> (CFC_a[t]). The pCFC age is determined by matching the oceanic pCFC
> with the atmospheric history, i.e. in the single point case by
> applying
> the @loc command to an embedded expression:
>
> pCFC_age[x=1,y=1,z=1] = 1990 - CFC_a[t=@loc:`pCFC[x=1,y=1,z=1]`]
>
> I now would like to compute this for all grid cells of my original
> pCFC[x,y,z] field and obtain a fully 3-D pCFC_age field
> (pCFC_age[x,y,z]).
> I tried several things (following the examples given in Ch3 Sec2.4.26. 
> of the documentation) but didn't find a solution yet.

Steve Hankin was of invaluable help in solving this problem. Thousand
thanks!! Here is the solution:

!
!------------------------------------------------------------------
! define a variable that is zero wherever the pCFC matches the age
!   record
!------------------------------------------------------------------
!
LET pCFC11_0 = pCFC11 - cfc11_a   ! a fcn of (x,y,z,t)
!
!------------------------------------------------------------------
! scaling factor sec_to_yr
!------------------------------------------------------------------
!
let sec_to_year = 24*365*3600
!
!------------------------------------------------------------------
! locate the time at which it was zero (years B.C.)
!------------------------------------------------------------------
!
LET pCFC11_age_tmp = pCFC11_0[T=@loc:0]/sec_to_year + 1887   ! a fcn of
(x,y,z)
!
!------------------------------------------------------------------
! limit maximum age to years after 1950
!------------------------------------------------------------------
!

define variable/title="CFC11-age of water mass"/units="years" 
pcfc11_age  IF pcfc11_age_tmp gt 1950. THEN this_year - pcfc11_age_tmp


Anybody interested in the complete routines for computing CFC-ages from
CFC data can contact me directly: gruber@splash.princeton.edu

-- happy ferreting!