  The radio approach for detecting the ultra-high energy cosmic neutrinos has
become a mature field. The Cherenkov pulse in radio detection originates from
the charge excess of particle showers due to Askaryan effect. The conventional
way of calculating the Cherenkov pulse by making far- field approximation fails
when the size of elongated showers become comparable with detection distance.
We investigate the Cherenkov pulse in near-field by a numerical code based on
the finite- difference time-domain (FDTD) method. Our study shows that the
near-field radiation exhibits very different behaviors from the far-field one
and therefore can be easily recognized. For ground array neutrino detectors,
the near-field radiation would provide a unique signature for ultra high energy
electromagnetic showers induced by the electron neutrino charge-current
interaction. This can be useful in neutrino flavor identification.
