June 1, 2009 Understanding thundercloud electrification and lightning initiation is challenging because the ranges of electric potential and spatial extents of electric fields inside thunderclouds are not known. Directly measuring electric fields in thunderclouds is challenging—active regions of storms can cover many cubic kilometers with violent weather conditions, making it difficult to operate balloons and aircraft.
Florida Institute of Technology researchers J. R. Dwyer and H. K. Rassoul, along with the University of Florida's M. A. Uman, hypothesize that remote sensing of thundercloud electrostatic fields can be obtained through monitoring runaway electrons, which are produced when the rate of gain of energy by electrons moving through an electric field exceeds the rate of loss of energy from ionizing the air. Such runaway electrons trigger other runaway electrons, resulting in an exponentially growing avalanche of runaway electrons moving through the storm system.
The authors propose that radio frequency emissions produced by these avalanches can be monitored to map the magnitudes and directions of the electrostatic field within specific sections of a thundercloud. These radio frequencies are present only when the storm is bombarded by cosmic ray extensive air showers, allowing scientists quickly to identify particular storms that are favorable to the proposed remote sensing techniques.
Their research appears in a recent issue of the Journal of Geophysical Research-Atmospheres.
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- Dwyer, J. R., M. A. Uman, and H. K. Rassoul. Remote measurements of thundercloud electrostatic fields. Journal of Geophysical Research, 2009; 114 (d9): D09208 DOI: 10.1029/2008JD011386
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