MOIST CONVECTIVE STORMS IN THE ATMOSPHERES OF JUPITER AND SATURN Atmospheric storms in Jupiter and Saturn

Abstract

Moist convective storms might be a key constituent of the global energy budget in the atmospheres of the Giant Planets. The storms extract their energy from the release of latent heat produced in the condensation of water which is only abundant hundreds of kilometers below the observable cloud deck. Because these atmospheres are made of hydrogen and helium, dry air is lighter than moist parcels, providing a strong stabilization against vertical motions in the atmosphere. However, very large-scale convective storms have been observed in the atmospheres of the giant planets. Among them, Jupiter is the most convectively active, showing frequent storms with sizes on the order of 3000 km that occasionally trigger planetary scale disturbances. Observations from Voyager, Galileo and Cassini spacecrafts confirm the overall convective activity of Jupiter through observations of lightning flashes below the upper ammonia cloud deck. The energy associated to these storms is large enough to constitute a relevant fraction of the total internal heat source of the planet. Although Saturn presents a more quiescent atmosphere where storms are rarely observed, about once every 30 years, a giant storm has been observed to develop with sizes of 20000 km also triggering a planetary scale disturbance. We will review the current observational background of these giant storms in both Jupiter and Saturn presenting also numerical results obtained by different teams in simulating this vigorous meteorology. In both planets water storms may develop upward velocities of 50-150 m/s. The interaction of the storms with the powerful winds are not clear. In Saturn the giant storm of 1990 could have played a key role in originating the recently discovered change of 200 m/s in the broad and intense equatorial jet.

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