Measurements of charged precipitation in a New Mexico thunderstorm: lower positive charge centers

Abstract

We designed an instrument to measure the charge and vertical velocity of individual precipitation particles inside thunderclouds. A balloon carried the particle charge instrument, an electric field meter, and a standard meteorological radiosonde upward into thunderclouds over Langmuir Laboratory in central New Mexico. During one balloon flight the instruments encountered two regions of positive charge below the main negative charge center. We identify these positive regions with the lower positive charge centers that have been described in the literature for many years. We find the following points: (1) One region had an estimated total charge of 0.4 C. The other had 2 C. (2) The charge resided on precipitation particles. The particles' charges typically ranged between 10 and 200 pC, but a few particles had charges up to 400 pC. Their diameters lay between an estimated 1–3 mm. The charges were too large to be explained by the polarization induction mechanism. We favor the hypothesis that lightning provided the positive charge in the lower positive charge centers. (3) The motion of the lower positive charge centers enhanced the electrical energy of the storm, but their contribution to the overall electrical budget was small. (4) The field excursions (at the ground) associated with precipitation (FEAWPs) described by C. B. Moore and B. Vonnegut are probably caused by lower positive charge centers descending on precipitation. The larger (2 C) lower positive charge center caused a FEAWP. Negatively charged precipitation particles passed through our instrument near the top of its trajectory just before the balloon was struck by lightning. The charge density on precipitation particles was substantial, but we do not have enough information to comment on the role the particles may have had in generating the main region of negative charge.