Macroscopic Model of Geomagnetic-Radiation from Air Showers
  We have developed a macroscopic description of coherent electro-magnetic radiation from air showers initiated by ultra-high energy cosmic rays in the presence of the geo-magnetic field. This description offers a simple and direct insight in the relation between the properties of the air shower and the time-structure of the radio pulse. As we show the structure of the pulse is a direct reflection of the important length scales in the shower. 
Olaf Scholten and Klaus Werner