FORTE satellite observations of very narrow radiofrequency pulses associated with the initiation of negative cloud-to-ground lightning strokes

[1] The FORTE satellite's radiofreqency receiver/recorder system has been used to study extremely narrow (similar to100 ns width) radiofrequency pulses accompanying the initiation of negative cloud-to-ground strokes. These pulses have been observed from the ground for over two decades. The FORTE space-based observations are substantially consistent with the prior ground-based results, at least in regard to pulsewidth, distance-scaled pulse amplitude, and the pulses' basic association with negative cloud-to-ground strokes, relative to either positive cloud-to-ground or intracloud strokes. New results from the FORTE observations include (1) information on the radiation pattern (versus elevation angle), (2) the tendency of the underlying fast-pulse radiation process to occur preferentially in marine, rather than dry-land, locations, and (3) the high degree of linear polarization of the radiated signal. These three new results were not accessible to ground-based measurements, which do not sample elevation angles other than zero, whose signal distortion with overland propagation paths (at zero elevation angle) tends to confuse the issue of the (land versus sea) location affinity of the pulse source itself, and whose received signal is a fortiori linearly polarized because of the adjacent ground plane. The narrow radiofrequency pulse that accompanies negative cloud-to-ground strokes provides a useful identifier, in the satellite's radiofrequency datastream, of the occurrence of this particular kind of stroke. Additionally, the observations reported here indicate that the radiating element is a single, vertical current stalk, rather than a collection of randomly oriented, mutually incoherent dipoles, such as are believed to be responsible for most very high frequency signals from lightning.