function [ga] = sw_gpan(S,T,P) % SW_GPAN Geopotential anomaly %========================================================================= % SW_GPAN $Id: sw_gpan.m,v 1.1 2003/12/12 04:23:22 pen078 Exp $ % Copyright (C) CSIRO, Phil Morgan 1992. % % USAGE: [gpan]= sw_gpan(S,T,P) % % DESCRIPTION: % Geopotential Anomaly calculated as the integral of svan from the % the sea surface to the bottom. Thus RELATIVE TO SEA SURFACE. % % INPUT: (all must have same dimensions) % S = salinity [psu (PSS-78)] % T = temperature [degree C (ITS-90)] % P = Pressure [db] % (P may have dims 1x1, mx1, 1xn or mxn for S(mxn) ) % % OUTPUT: % gpan = Geopotential Anomaly [m^3 kg^-1 Pa == m^2 s^-2 == J kg^-1] % % AUTHOR: Phil Morgan 92-11-05, Lindsay Pender (Lindsay.Pender@csiro.au) % % DISCLAIMER: % This software is provided "as is" without warranty of any kind. % See the file sw_copy.m for conditions of use and licence. % % REFERENCE: S. Pond & G.Pickard 2nd Edition 1986 % Introductory Dynamical Oceanogrpahy % Pergamon Press Sydney. ISBN 0-08-028728-X % % Note that older literature may use units of "dynamic decimeter' for above. % % Adapted method from Pond and Pickard (p76) to calc gpan rel to sea % surface whereas P&P calculated relative to the deepest common depth. %========================================================================= % Modifications % 03-12-12. Lindsay Pender, Converted to ITS-90. % % CALLER: general purpose % CALLEE: sw_svan.m %---------------------- % CHECK INPUT ARGUMENTS %---------------------- if nargin ~=3 error('Must pass 3 parameters') end %if % CHECK S,T,P dimensions and verify consistent [ms,ns] = size(S); [mt,nt] = size(T); [mp,np] = size(P); % CHECK THAT S & T HAVE SAME SHAPE if (ms~=mt) | (ns~=nt) error('S & T must have same dimensions') end %if % CHECK OPTIONAL SHAPES FOR P if mp==1 & np==1 % P is a scalar. Fill to size of S P = P(1)*ones(ms,ns); elseif np==ns & mp==1 % P is row vector with same cols as S P = P( ones(1,ms), : ); % Copy down each column. elseif mp==ms & np==1 % P is column vector P = P( :, ones(1,ns) ); % Copy across each row elseif mp==ms & np==ns % PR is a matrix size(S) % shape ok else error('P has wrong dimensions') end %if [mp,np] = size(P); % IF ALL ROW VECTORS ARE PASSED THEN LET US PRESERVE SHAPE ON RETURN. Transpose = 0; if mp == 1 % row vector P = P(:); T = T(:); S = S(:); Transpose = 1; end %if %***check_stp %------ % BEGIN %------ db2Pascal = 1e4; [m,n] = size(P); svan = sw_svan(S,T,P); mean_svan = 0.5*(svan(2:m,:) + svan(1:m-1,:) ); if n==1 top = svan(1,1).*P(1,1)*db2Pascal; else top = svan(1,:).*P(1,:)*db2Pascal; end %if %press_diff = diff(P); delta_ga = (mean_svan.*diff(P))*db2Pascal; ga = cumsum([ top; delta_ga]); if Transpose ga = ga'; end %if