Electric Field at the Ground Due to a Thundercloud of Finite Dimensions

Abstract

A time dependent model for the rate of growth of electric field at various points at the ground surface due to a thundercloud of finite dimensions has been presented. Calculations have been made for various sets of paramters viz., precipitation intensity *0, vertical cloud motion U, rebound mean angle probability <*>, 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*103Vm-1 within 1200s at the ground surface (D=2km) due to a thundercloud (W=1.0km), if *0=10mm h-1 and U=3 ms-1 (taking H=0.5km, L=1.5km, h=5.0km, *1= *2=0.25, *=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; *1, *2 are the fractional constants for screening charge density and electric field, respectively; and * is the relaxation time. The obtained results are consistent with the observations of electric field due to a thundercloud at the ground surface.

The Effect of Screening Charge Transport on Electrification and Precipitation Processes in Thunderclouds

“…P. Singh, T. S. Verma, K. C. Mathpal and N. C. Varshneya 679 electric field, *1*2, assuming N=5, *=45*, C1=. 75*, tc/*=*, C3=.5, *p=.6*103gm m-3, E0=500Vm-1, *1*2=.1, R4=200*m, R1=rc= 10*m Levin et al 1977;Mathpal et al 1982;Singh et al 1984). The coalescence efficiencies, C2, are determined from Whelpdale and List )1971).…”

“…Here, it should be pointed out than cloud particles carrying screening charge reach into lower region of thundercloud through its outer boundary. Therefore, their fall velocities, V E, should be influenced by the electric field present on the outer periphery of thundercloud, not by the field present in-side the thundercloud as considered by Mathpal et al (1982). Now, substituting eqs.…”

“…From the convective charge transport point of view, similar to Kamra (1979) and Mathpal et al (1982), we assume that space charge density Qc, on the cloud particles is a frac tion, *1, of the saturation space charge, Qs, in the screening layer i. e. Qc=*1Qs.…”

“…Various investigators (Chiu and Klett,1976 ;Moore and Vonnegut, 1977;Adler and Fenn, 1979;Mathpal et al, 1982Mathpal et al, , 1983Singh et al, 1984) have represented downdraft from cloud top to lower region in thunderclouds.…”

“…Considering convective charge transport and inductive charging mechanism supplement to each other, Mathpal et al (1982) have reported that combined mechanism produces high electric fields even in thunderclouds having low precipitation intensities. But, Mathpal et al have considered only the growth of electric field without allowing growth of precipitation particles and ignoring interactions among all categories of particles at all.…”