Calculating Amplitude of Elliptically Polarized EM Wave

[TriTertButoxy]

Suppose I have an eliptically polarizied EM wave, whose electric field can be written as

\vec{E}=A\cos(kz-\omega t)\vec{e}_x+B\sin(kz-\omega t)\vec{e}_y,

where the constants A and B are amplitudes of the x and y components of the beam, respectively.
How would I report the amplitude of the whole beam?

(Please note that I am not looking for intensity of the beam -- I know how to report that).

 

[mezarashi]

This question is similar to asking, what is the magnitude of a voltage source with time function:

V = A\cos (\omega t) + B\sin(\omega t)

There are two out of phase components superimposed on each other. In my opinion, it would only make sense to have some RMS value if you are doing power calculations.