Moist convection as an energy source for the large-scale motions in Jupiter's atmosphere. Galileo Imaging Team

Jupiter's dominant large-scale weather patterns (dimensions approximately 10,000 km) are zonal jets and long-lived ovals. The jets have been flowing east and west at constant speeds of up to 180 m s(-1) for over 100 years. These jets receive energy from small-scale eddies, which pump eastward momentum into the eastward jets and westward momentum into the westward jets. This momentum transfer was predicted by numerical models before it was observed on Jupiter. The large ovals roll between the jets in an anticyclonic direction-clockwise in the northern hemisphere and counterclockwise in the southern hemisphere--where they regularly assimilate small anticyclonic eddies. But from where the eddies receive their energy has been an open question. Here we argue that the eddies, which ultimately drive both the jets and the ovals, receive their energy from moist convection. This hypothesis is consistent with observations of jovian lightning, which is an indicator of moist convection. It also explains the anticyclonic rotation and poleward drift of the eddies, and suggests patterns of upwelling and downwelling that resemble the patterns of large-scale axisymmetric overturning in the Earth's atmosphere.

Observation of moist convection in Jupiter's atmosphere. Galileo Imaging Team

The energy source driving Jupiter's active meteorology is not understood. There are two main candidates: a poorly understood internal heat source and sunlight. Here we report observations of an active storm system possessing both lightning and condensation of water. The storm has a vertical extent of at least 50 km and a length of about 4,000 km. Previous observations of lightning on Jupiter have revealed both its frequency of occurrence and its spatial distribution, but they did not permit analysis of the detailed cloud structure and its dynamics. The present observations reveal the storm (on the day side of the planet) at the same location and within just a few hours of a lightning detection (on the night side). We estimate that the total vertical transport of heat by storms like the one observed here is of the same order as the planet's internal heat source. We therefore conclude that moist convection-similar to large clusters of thunderstorm cells on the Earth-is a dominant factor in converting heat flow into kinetic energy in the jovian atmosphere.