Vertical Structures of the Atmospheric Electrical Potential Gradient and the Behavior of the Precipitation Charges during Snowfalls near the Ground Surface

[摘要] In order to examine the vertical structures of the atmospheric electrical potential gradient and the behavior of charges on precipitation particles during snowfalls in the lower atmospheric layer, tethered balloon observations were carried out with several observation stages secured to its tether. Simultaneously, data observed on the ground and on the roof of the nearby building were analyzed. The main results obtained are as follows: i) The mirror image relation between the polarities of the electric potential gradient and precipitation charges was always observed near the ground, however, this relation was not always observed aloft. ii) Charges on snow particles were weaker aloft and stronger near the ground surface. Thus it is suggested that snow particles were electrified rapidly near the ground surface. iii) When the height of the cloud base was low and the highest observation stage of the tethered balloon was in the cloud or near the cloud base, snow particles were electrified weakly but positively at the highest stage. They were not directly correlated to the polarity of the local electric potential gradient. On the other hand, snow particles were electrified negatively near the ground and the electric potential gradient was positive on the ground. Therefore it is surmised that the snow particles acquired negative charges during their fall and the mirror image relation was present near the ground. iv) The atmospheric electrical potential gradient on the ground was modified by the ions which were emitted by the corona discharge. v) The most suitable electrification mechanism seems to be the Wilson's selective ion capture process below the cloud base. The behavior of atmospheric electrical elements was in good agreement with those of simple numerical experiments reported by Asuma and Kikuchi (1987).

[学科分类] 大气科学