  Radio emission in atmospheric showers is currently interpreted in terms of
radiation due to the deviation of the charged particles in the magnetic field
of the Earth and to the charge excess (Askaryan effect). Each of these
mechanisms has a distinctive polarization. The complex signal patterns can be
qualitatively explained as the interference (superposition) of the fields
induced by each mechanism. In this work we explicitly and quantitatively test a
simple phenomenological model based on this idea. The model is constructed by
isolating each of the two components at the simulation level and by making use
of approximate symmetries for each of the contributions separately. The results
of the model are then checked against full ZHAireS Monte Carlo simulations of
the electric field calculated from first principles. We show that the simple
model describes radio emission at a few percent level in a wide range of
shower-observer geometries and on a shower-by-shower basis. As a consequence,
this approach provides a simple method to reduce the computing time needed to
accurately predict the electric field of radio pulses emitted from air showers,
with many practical applications in experimental situations of interest.
