stituent you desire, like this: 

% Load the M2 global tidal height amplitude: 
[M2,x,y] = tmd_data('Gr1kmTM_v1.nc','hAm','constituents','m2'); 

% Load the global ocean mask: 
ocean = tmd_data('Gr1kmTM_v1.nc','mask'); 

figure
h=imagesc(x,y,M2);
h.AlphaData = ocean; % makes land transparent
axis xy image % sets axes equal and normal cartesian coordinates 
cb = colorbar; 
ylabel(cb,'M2 height amplitude (m)') 
xlabel('x coordinate (km)')
ylabel('y coordinate (km)') 
cmocean amp % optional colormap from Clima