I have been looking into this, and believe it is from the equation, I = (1/2) p w^2 A^2 v In that case intensity is proportional to angular frequency squared, and of course, energy and intensity are directly proportional from other equations.
So, how does this square with the notion that E=hf? How can energy be proportional to frequency in that case, and in the prior paragraph, energy is proportional to angular frequency squared?