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Williams, M. A.

Publications and source records attributed to Williams, M. A..

3 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Lightning in the Jovian water cloud

The vertical location of the lightning superbolts seen on the Voyager images of Jupiter has been determined using a comparison between the measured spot sizes for single flashes with the intensity distributions calculated from various assumptions about the altitude of the flash. A Monte Carlo model was used to describe the light scattering in the clouds, aerosols, and gases of the Jupiter atmosphere. Best agreement between the measurements and the model predictions was obtained when the lightning activity was assumed to occur in a lower cloud centered at the 5-bar pressure level, whereas the width predicted for lightning in the ammonia cloud was much smaller than the measured widths. The results imply that the lightning observed by the Voyager must be in a cloud much deeper than the ammonia cloud. The lower cloud is expected to be composed of water or a mixture of water and ammonium hydrosulfide.

Borucki, W. J.↗
NASA NTRS1983

Planetary lightning - Earth, Jupiter, and Venus

The principal characteristics of lightning on earth are reviewed, and the evidence for lightning on Venus and Jupiter is examined. The mechanisms believed to be important to the electrification of terrestrial clouds are reviewed, with attention given to the applicability of some of these mechanisms to the atmospheres of Venus and Jupiter. The consequences of the existence of lightning on Venus and Jupiter for their atmospheres and for theories of cloud electrification on earth are also considered. Since spacecraft observations do not conclusively show that lightning does occur on Venus, it is suggested that alternative explanations for the experimental results be explored. Since Jupiter has no true surface, the Jovian lightning flashes are cloud dischargaes. Observations suggest that Jovian lightning emits, on average, 10 to the 10 J of optical energy per flash, whereas on earth lightning radiates only about 10 to the 6th J per flash. Estimates of the average planetary lightning rate on Jupiter range from 0.003 per sq km per yr to 40 per sq km per yr.

Williams, M. A.↗