  We present a new mechanism for air shower radio emission due to the sudden
absorption of secondary particles when the shower front hits the ground. The
electrons present in excess during the air shower development imply a net
residual negative charge in the shower front. We show that for showers hitting
the ground before the complete extinction of their electromagnetic component,
the sudden vanishing of the net residual negative charge generates an electric
field contribution in the kHz---MHz range. We characterize this radio
contribution as a function of primary energy, arrival direction and antenna
position, using the simulation code SELFAS2. We discuss the interest of this
new predicted signal on detection and analysis of ultra-high energy cosmic-rays
and we argue that the region in the shower of maximum emission of the electric
field should not coincide with the region of maximum development.
