  Air showers from cosmic rays emit short, intense radio pulses. LOFAR is a new
radio telescope, that is being built in the Netherlands and Europe. Designed
primarily as a radio interferometer, the core of LOFAR will have a high density
of radio antennas, which will be extremely well calibrated. This makes LOFAR a
unique tool for the study of the radio properties of single air showers.
  Triggering on the radio emission from air showers means detecting a short
radio pulse and discriminating real events from radio interference. At LOFAR we
plan to search for pulses in the digital data stream - either from single
antennas or from already beam-formed data - and calculate several parameters
characterizing the pulse shape to pick out real events in a second stage. In
addition, we will have a small scintillator array to test and confirm the
performance of the radio only trigger.
