  Cosmic ray air showers are known to emit pulsed radio emission which can be
understood as coherent geosynchrotron radiation arising from the deflection of
electron-positron pairs in the earth's magnetic field. Here, we present
simulations carried out with an improved version of our Monte Carlo code for
the calculation of geosynchrotron radiation. Replacing the formerly
analytically parametrised longitudinal air shower development with
CORSIKA-generated longitudinal profiles, we study the radio flux variations
arising from inherent fluctuations between individual air showers.
Additionally, we quantify the dependence of the radio emission on the nature of
the primary particle by comparing the emission generated by proton- and
iron-induced showers. This is only the first step in the incorporation of a
more realistic air shower model into our Monte Carlo code. The inclusion of
highly realistic CORSIKA-based particle energy, momentum and spatial
distributions together with an analytical treatment of ionisation losses will
soon allow simulations of the radio emission with unprecedented detail. This is
especially important to assess the emission strengths at large radial
distances, needed for event-to-event comparisons of the radio signals measured
by LOPES in conjunction with KASCADE-Grande and for considerations regarding
large arrays of radio antennas intended to measure the radio emission from
ultra-high energy cosmic rays, as with LOFAR or in the Pierre Auger
Observatory.
