>> clear
>> load NWtopex
>> whos
  Name      Size         Bytes  Class

  SSH      31x66         16368  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 2943 elements using 23544 bytes

>> pcolor(lon,lat,SSH);shading('interp');
>> colormap(rkb);caxis([-1 1]*45);colorbar;hold on
>> I=1:30;J=1:65;
>> I2=1:2:30;J2=1:2:65;
>> dZdx=diff(SSH,1,2).*((1./dx)*ones(1,65));
>> dZdy=diff(SSH,1,1)./dy;dZdy=diff(SSH,1,1)./dy;
>> h=quiver(lon(J2)+0.5,lat(I2)+0.5,dZdx(I2,J2),dZdy(I2,J2),2,'g');
>> delete(h)
>> 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);
>> h=quiver(lon(J2)+0.5,lat(I2)+0.5,U(I2,J2),V(I2,J2),2,'g');
>>