Saturn’s Northern Storms Cause Disturbances in Its ‘Heartbeat’

Giant storms in Saturn’s northern hemisphere can disturb atmospheric patterns at the ringed giant’s equator, according to new research published in the journal Nature Astronomy.

Saturn’s Great Northern Storm churning through the atmosphere in the planet’s northern hemisphere overtakes itself as it encircles the planet in this true-color view from NASA’s Cassini spacecraft. This picture, captured on February 25, 2011, was taken about 12 weeks after the storm began, and the clouds by this time had formed a tail that wrapped around the gas giant. Image credit: NASA / JPL-Caltech / Space Science Institute.

Saturn’s Great Northern Storm churning through the atmosphere in the planet’s northern hemisphere overtakes itself as it encircles the planet in this true-color view from NASA’s Cassini spacecraft. This picture, captured on February 25, 2011, was taken about 12 weeks after the storm began, and the clouds by this time had formed a tail that wrapped around the gas giant. Image credit: NASA / JPL-Caltech / Space Science Institute.

Despite their considerable differences, the equatorial middle atmospheres of Earth, Jupiter, and Saturn all exhibit a similar phenomenon: vertical, cyclic patterns of alternating temperatures and wind systems that repeat over a period of multiple years.

These patterns — known as the Quasi-Periodic Oscillation (QPO) on Saturn and the Quasi-Quadrennial Oscillation (QQO) on Jupiter, due to their similarities to Earth’s Quasi-Biennial Oscillation (QBO) — appear to be a defining characteristic of the middle layers of a planetary atmosphere.

Earth’s QBO is regular and predictable, repeating every 28 months on average. However, it can be disrupted by events occurring at great distances from the equator of our planet — and a new study reveals that the same is true of Saturn’s QPO.

“These oscillations can be thought of as a planet’s heartbeat,” said lead author Dr. Leigh Fletcher, a researcher at the University of Leicester, UK, and co-investigator of Cassini’s Composite Infrared Spectrometer (CIRS).

“Cassini spotted them on Saturn about a decade ago, and Earth-based observations have seen them on Jupiter, too. Although the atmospheres of the distant gas giants may appear startlingly different to our own, when we look closely we start to discover these familiar natural patterns.”

To better understand Saturn’s QPO, Dr. Fletcher and co-authors studied data from the CIRS instrument covering this entire time period.

“We looked at data of Saturn’s ‘heartbeat,’ which repeats roughly every 15 Earth years, and found a huge disturbance — a palpitation, to continue the metaphor — spanning 2011 to 2013, where the whole equatorial region cooled dramatically,” said co-author Dr. Sandrine Guerlet, from the Laboratoire de Météorologie Dynamique, France.

“When we checked the timing, we realized this happened directly after the eruption of a giant storm that wrapped around Saturn’s entire northern hemisphere. This suggests a link between the two events: we think that the wave activity associated with this huge storm headed towards the equator and disrupted the QPO, despite the storm raging tens of thousands of miles away!”

This series of images from NASA’s Cassini spacecraft tracks the development of a giant storm whirling over Saturn’s mid-northern latitudes in December 2010, as seen at visible wavelengths during much of 2011. The earliest image of the storm, taken December 5, 2010, is in the top left of the panel. The storm appears only as a small, white cloud on the terminator between the day side and night side of the planet. The next view, in the top middle of the panel and taken January 2, 2011, shows that the head quickly grew much larger and a tail began to trail a great distance eastward. Some of the clouds moved south and got caught up in a current that flows to the east (to the right) relative to the storm head. In the top right of the panel, this tail, which appears as slightly blue clouds south and now west (left) of the storm head, can be seen encountering the storm in the February 25 image. The April 22 image, in the bottom left of the panel, is one of Cassini’s last views of the storm when it still had a recognizable head. In this view, the tail is south of the head and is well established by this time. The May 18 view, in the bottom middle, shows only the storm’s tail. The head still existed at this time, but it is beyond the horizon and out of the field of view here. Between the time of the May 18 image and the next image shown here (from August 12), the head of the storm was engulfed by the part of the storm’s tail that spread eastward at the same latitude as the head. The August 12 image, in the bottom right, shows that the head has lost its distinct identity and is now just part of the jumble of the storm. Also visible in these images are several of Saturn’s moons and the shadows cast onto the planet by moons. For example, the planet’s second largest moon, Rhea, can be seen in the February 25 view. The February 25 and August 12 views are true color. Images taken using red, green and blue spectral filters were combined to create these natural-color views. The December 5, January 2, April 22 and May 18 views are nearly true color. Because a visible red light image was not available, an image taken using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nm was used in place of red. So the color is close to natural color, but it is not exact. These views were acquired at distances ranges from approximately 1.4 million miles (2.2 million km) to 1.9 million miles (3.0 million km) from Saturn and at Sun-Saturn-spacecraft, or phase, angles of 41 degrees to 99 degrees. All the views are set to a scale of 101 miles (162 km) per pixel. Image credit: NASA / JPL-Caltech / Space Science Institute.

This series of images from NASA’s Cassini spacecraft tracks the development of a giant storm whirling over Saturn’s mid-northern latitudes in December 2010, as seen at visible wavelengths during much of 2011. The earliest image of the storm, taken December 5, 2010, is in the top left of the panel. The storm appears only as a small, white cloud on the terminator between the day side and night side of the planet. The next view, in the top middle of the panel and taken January 2, 2011, shows that the head quickly grew much larger and a tail began to trail a great distance eastward. Some of the clouds moved south and got caught up in a current that flows to the east (to the right) relative to the storm head. In the top right of the panel, this tail, which appears as slightly blue clouds south and now west (left) of the storm head, can be seen encountering the storm in the February 25 image. The April 22 image, in the bottom left of the panel, is one of Cassini’s last views of the storm when it still had a recognizable head. In this view, the tail is south of the head and is well established by this time. The May 18 view, in the bottom middle, shows only the storm’s tail. The head still existed at this time, but it is beyond the horizon and out of the field of view here. Between the time of the May 18 image and the next image shown here (from August 12), the head of the storm was engulfed by the part of the storm’s tail that spread eastward at the same latitude as the head. The August 12 image, in the bottom right, shows that the head has lost its distinct identity and is now just part of the jumble of the storm. Also visible in these images are several of Saturn’s moons and the shadows cast onto the planet by moons. For example, the planet’s second largest moon, Rhea, can be seen in the February 25 view. The February 25 and August 12 views are true color. Images taken using red, green and blue spectral filters were combined to create these natural-color views. The December 5, January 2, April 22 and May 18 views are nearly true color. Because a visible red light image was not available, an image taken using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nm was used in place of red. So the color is close to natural color, but it is not exact. These views were acquired at distances ranges from approximately 1.4 million miles (2.2 million km) to 1.9 million miles (3.0 million km) from Saturn and at Sun-Saturn-spacecraft, or phase, angles of 41 degrees to 99 degrees. All the views are set to a scale of 101 miles (162 km) per pixel. Image credit: NASA / JPL-Caltech / Space Science Institute.

This storm was known as the Great Northern Storm. Such storms occur roughly once every Saturnian year, which is equivalent to 30 Earth years.

The timing of the storm was thus serendipitous, allowing Cassini to observe it in detail from orbit around the ringed planet.

Although the influence of Saturnian storms was known to be substantial, this study suggests an even wider influence than expected, and confirms a connection between Saturn’s QPO and remote, distinct events occurring elsewhere in the planet’s atmosphere.

“We became especially excited when we compared this palpitation on Saturn to one observed in Earth’s QBO in 2016,” Dr. Fletcher said.

“It was disturbed in a similar way by waves carrying momentum from Earth’s northern hemisphere to the equator.”

“That disruption was unprecedented in over 60 years of monitoring the QBO — and yet we were lucky enough to capture a similar behavior at work on Saturn with Cassini.”

On Earth, this relationship between distant events in a planet’s climate system is known as teleconnection. Meteorological patterns across the globe are known to be delicately linked together, and can affect one another quite significantly. A key example of this is the El Niño Southern Oscillation, which can influence temperatures and climate patterns across the Earth.

“It’s remarkable to see this process occurring on another planet within our Solar System — especially one that’s so vastly different to our own,” said Dr. Nicolas Altobelli, ESA project scientist for the Cassini-Huygens mission.

_____

Leigh N. Fletcher et al. 2017. Disruption of Saturn’s quasi-periodic equatorial oscillation by the great northern storm. Nature Astronomy 1: 765-770; doi: 10.1038/s41550-017-0271-5

This article is based on text provided by the European Space Agency.

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