So you want every arrow to originate at the z=0 plane, but the vector can point in any direction? If so, here is an example, adapted from "help quiver3":
[x,y] = meshgrid(0:.5:2,-1:.2:1);
z = x .* exp(-x.^2 - y.^2);
[u,v,w] = surfnorm(x,y,z);
z = zeros(size(x));
quiver3(x,y,z,u,v,w);
