, cloud radius W and the distance of the surface observation point D. The charge within the charging zone of the thundercloud is computed by the combination of both precipitative and convective charging mechanisms. We have obtained: (Eout)max≈-9×103 Vm-1 within 1200s at the ground surface (D=2km) due to a thundercloud (W=1.0km), if p0=10mmh-1 and U=3 ms-1 (taking H=0.5km, L=1.5km, h=5.0km, f1=f2=0.25, τ=100s,
=1), where H is the vertical length of both lower main negative and upper main positive charge regions; L is the length of charging zone on each side from the center of the cloud; h is the vertical height of the cloud base from the ground; f1, f2 are the fractional constants for screening charge density and electric field, respectively; and τ is the relaxation time. The obtained results are consistent with the observations of electric field due to a thundercloud at the ground surface.
