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Tommy R. Shepherd, W. David Rust, and Thomas C. Marshall


Earlier studies of mesoscale convective system stratiform regions have shown that large electric fields and charge densities are found near the 0°C level. Here 12 soundings of the electric field were analyzed through the 0°C level in various types of electrified stratiform clouds. For each electric field sounding, the thermodynamic sounding and supporting radar data were also studied. For comparison, five soundings not from stratiform clouds were included. Charge densities were found at or near 0°C in the stratiform clouds of at least 1 nC m−3 in eight of the soundings, and four of those had charge densities of at least 2 nC m−3. Of the stratiform soundings, 11 had an electric field magnitude of greater than 50 kV m−1 near 0°C, and 7 of those had an electric field magnitude of at least 75 kV m−1. The evidence suggests that melting may be the primary cause of the charge density found at and below 0°C in electrified stratiform clouds. In all 12 of the stratiform soundings, positive charge density was found at or near 0°C, and 11 of those had weaker negative charge density below. The evidence further suggests these two features do not exist in the absence of a bright band and (usually) an associated quasi-isothermal layer.

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