load NWtopex
whos
  Name      Size                   Bytes  Class

  SSH      31x66                   16368  double array
  ans       1x162                    324  char array
  dx       31x1                      248  double array
  dy        1x1                        8  double array
  lat       1x31                     248  double array
  lon       1x66                     528  double array
  rkb     256x3                     6144  double array

Grand total is 3105 elements using 23868 bytes

pcolor(lon,lat,SSH);shading interp
colormap(rkb)
caxis([-1 1]*55)
I=1:30;J=1:65;
I2=1:2:30;J2=1:2:65;
dZdy=diff(SSH,1,1)./dy;dZdy=diff(SSH,1,1)./dy;
dZdx=diff(SSH,1,2).*((1./dx)*ones(1,65));
whos
  Name       Size                   Bytes  Class

  I          1x30                     240  double array
  I2         1x15                     120  double array
  J          1x65                     520  double array
  J2         1x33                     264  double array
  SSH       31x66                   16368  double array
  ans        1x162                    324  char array
  dZdx      31x65                   16120  double array
  dZdy      30x66                   15840  double array
  dx        31x1                      248  double array
  dy         1x1                        8  double array
  lat        1x31                     248  double array
  lon        1x66                     528  double array
  rkb      256x3                     6144  double array

Grand total is 7243 elements using 56972 bytes

f=2*7.29e-5*sin(pi/180*lat(:));
g=9.8;
U=(-g./f(I)*ones(1,length(J))).*dZdy(I,J);
V=(g./f(I)*ones(1,length(J))).*dZdx(I,J);
hold
Current plot held
h=quiver(lon(J2)+0.5,lat(I2)+0.5,U(I2,J2),V(I2,J2),2,'g');
diary off