Extensive lower positive charge centers and their role in lightning in thunderstorms in tropical regions
In addition to the main positive dipole, large number of the past observations show the presence of positive charge pockets in the bases of thunderstorms. The measurements of atmospheric electric field, Maxwell current and thunder made at the Atmospheric Electricity Observatory, Pune, (18 o 32’N, 73 o 51’E, 559 above msl) below isolated, tall convective thunderstorms, are analyzed. From the data obtained over last several years, it is concluded that the lower positive charge pockets observed in the thunderstorms occurring in this region are quite extensive. Further, these pockets have been observed to persist for a long duration during the life-time of a storm. The positive charge accumulating in the bases of thunderclouds is found to be sufficiently wide -spread to reverse the anti-fair weather polarity of the electric field below thunderclouds for upto 75％ of the duration of the storm. Moreover, such electric fields of fair-weather polarity on earth’s surface are often large enough to initiate coronae at sharp points raised above the earth’s surface. The observations made during five such cases of reversed electric field below different thunderstorms occurring in this region are reported, analyzed and discussed. Similar conclusions have been drawn from the observations made below thunderstorms that occur over the Tibetian plateau. Validity and efficiency of different mechanisms proposed to operate for the generation of positive charge in the lower charge pockets is critically examined from the electrical and meteorological conditions that prevail in different cases and the most probable mechanism is identified. Observations also suggest lower rate of charge separation in the lower positive charge regions as compared to that in the main positive dipole of thunderstorms. Lower positive charge pockets have been observed to actively participate in initiating/triggering both intracloud and/or cloud-to-ground lightning discharges. Differentiation of intracloud from cloud-to-ground discharges has been made from the overshoot criteria of Maxwell current which has been found to hold good in this region as evident from some visual observations of cloud-to-ground lightning discharges.
A K Kamra S D Pawar
Indian Institute of Tropical Meteorology, Pune, India
国际会议
第13届国际大气电学会议(The 13th International Conference on Atmospheric Electricity)
北京
英文
2007-08-13（万方平台首次上网日期，不代表论文的发表时间）