Fig.3(a)and(b) show the surface E field for thunderstorm
and CG flash rate on April 8,2007. The positive E field
gradually increased when the storm moved to observatory and
passed it, E field at the ground always kept positive until
21:30,lightning discharges in the thunderstorm are all positive.
The average flash rate of thunderstorm is 1fl/5min. Fig.3(c)
and (d) show the surface E field for thunderstorm and CG flash
rate on July 15, 2006. The negative E field gradually increased
when the storm moved to observatory and passed it, E field at
the ground always kept negative until 17:00, lightning
discharges in the thunderstorm are almost negative. The
average flash rate of thunderstorm is 10 fl/5min.