Radar-Echo Structure of Middle-Level Precipitating Clouds and the Charge of Raindrops (I)

[摘要] Observations of middle-level precipitating clouds were made using a vertically pointing radar, a field mill and an optical spectrometer with a charge detector. It was studied how the electrical properties of raindrops varied with the fine structure of clouds and microphysical processes in clouds.Main results are as follows. In a part of the cloud system in which most of generating cells were in a vigorous stage and in which a large increase in echo intensity with decreasing height was found between the levels of -10°C and 0°C, positively charged raindrops were predominant on the ground and averaged charges were observed to be quite large. In the whole cloud system averaged values of positive charge per raindrop varied almost in phasewith those of negative charge and both absolute values were nearly equal each other. But the number flux of positively or negatively charged drops did not necessarily vary with time in phase with the averaged charge of each sign. There was a rather good correlation between the time variation of maximum diameter of raindrops and that of the value of raindrop charge.Main results can be accounted for reasonably if we suppose that positively charged particles falling from the generating cell of a vigorous stage were mixed with negatively charged ones falling from the cell of a decaying stage in the region above 0°C level and that precipitation particles grew by aggregational process and they were recharged through friction process.

[学科分类] 大气科学