The major goals of the project are to study and understand the storms in the atmospheres of Jupiter and Saturn. By terrestrial standards, these storms are extreme examples of weather phenomena. At Jupiter the winds are 3 times stronger than the jet streams of Earth, even though sunlight is 27 times weaker. At Saturn the winds are 8-10 times stronger and the sunlight is 90 times weaker than that of Earth. On Jupiter, storms last for decades, and one storm, the Great Red Spot, has lasted for centuries. By studying the extreme examples, we learn about weather in general. The giant planets are a stress test for computer simulations of weather. Even more extreme are the planets around other stars—exoplanets. Because they are close, Jupiter and Saturn provide “ground truth” for understanding these exotic worlds.

Storms are driven by convection – the rising of warm, low density air and the sinking of cold, high density air. A complication is when the warm air is weighed down by a chemical constituent that is heavier than the average constituents. The effect is known as mass loading. An example is water is a giant planet atmosphere, which is mostly made of lighter gases hydrogen and helium. The presence of water vapor makes the air more dense, but when water condenses the heat released makes the air less dense. Convection under the influence of competing forces—temperature and composition—leads to some interesting unexplored physics.

The giant planets are the most extreme example of this competition. We showed that the 30-year interval between giant storms on Saturn is due to mass loading. Another example is salt in the ocean. We showed that the 1000-2000-year interval between sudden warming events in the North Atlantic is also due to mass loading, i.e., the competing effects of heat and salt on the density of seawater.

Moist convection occurs when rising air becomes saturated and one of the constituents  condenses to form cloud. The heat that is released causes the air to rise further, sometimes with violent effects as in a tornado or a hurricane. Moist convection is a fundamental process on Earth and the giant planets, yet it is one of the most difficult processes to model and one of the least well understood. Moist convection defines the wet tropical zone and the dry subtropical zones that altogether cover half the Earth’s surface. The giant planets also have wet and dry latitudes, which are bounded by jet streams, but there are many climate zones and many jet streams in each hemisphere. The spacing of the jets is a fundamental question that bears on the width of climate zones on Earth. Our work helps scientists understand moist convection in a larger context. One cannot change the parameters of Earth’s atmosphere to see how it will respond, but one can study planets with different parameters to see how their weather differs. Our work will lead to state-of-the-art software for modeling giant planets in our solar system and beyond. The opportunities are expanding rapidly along with the number and diversity of extrasolar giant planets.

Specific outcomes: (1) We have discovered that mass loading coupled with moist convection causes the 30-year interval between Saturn's giant storms. (2) We have shown that the interplay between heat and salt plays a major part in the sudden warming events in the North Atlantic Ocean on 1000-2000 year time scales. (3) We have interpreted the Juno and Cassini data to imply that the giant planets have circulations similar to Earth's, with moist upwelling at the equator and dry downwelling to the north and south. (4) We have shown that mass loaded downdrafts substitute for rain in balancing the water and ammonia budgets, in which the amount going up must equal the amount going down.

Last Modified: 12/22/2017
Modified by: Andrew P Ingersoll