NASA Spacecraft Tracks Raging Saturn Storm

NASA Spacecraft Tracks Raging Saturn Storm

ScienceDaily (Apr. 30, 2008) — As a powerful electrical storm rages on Saturn with lightning bolts 10,000 times more powerful than those found on Earth, the Cassini spacecraft continues its five-month watch over the dramatic events.

Scientists with NASA's Cassini-Huygens mission have been tracking the visibly bright, lightning-generating storm--the longest continually observed electrical storm ever monitored by Cassini.

Saturn's electrical storms resemble terrestrial thunderstorms, but on a much larger scale. Storms on Saturn have diameters of several thousand kilometers (thousands of miles), and radio signals produced by their lightning are thousands of times more powerful than those produced by terrestrial thunderstorms.

Lightning flashes within the persistent storm produce radio waves called Saturn electrostatic discharges, which the radio and plasma wave science instrument first detected on Nov. 27, 2007. Cassini's imaging cameras monitored the position and appearance of the storm, first spotting it about a week later, on Dec. 6.

"The electrostatic radio outbursts have waxed and waned in intensity for five months now," said Georg Fischer, an associate with the radio and plasma wave science team at the University of Iowa, Iowa City. "We saw similar storms in 2004 and 2006 that each lasted for nearly a month, but this storm is longer-lived by far. And it appeared after nearly two years during which we did not detect any electrical storm activity from Saturn."

The new storm is located in Saturn's southern hemisphere--in a region nicknamed "Storm Alley" by mission scientists--where the previous lightning storms were observed by Cassini. "In order to see the storm, the imaging cameras have to be looking at the right place at the right time, and whenever our cameras see the storm, the radio outbursts are there," said Ulyana Dyudina, an associate of the Cassini imaging team at the California Institute of Technology in Pasadena, Calif.

Cassini's radio plasma wave instrument detects the storm every time it rotates into view, which happens every 10 hours and 40 minutes, the approximate length of a Saturn day. Every few seconds the storm gives off a radio pulse lasting for about a tenth of a second, which is typical of lightning bolts and other electrical discharges. These radio waves are detected even when the storm is over the horizon as viewed from Cassini, a result of the bending of radio waves by the planet's atmosphere.

Amateur astronomers have kept track of the storm over its five-month lifetime. "Since Cassini's camera cannot track the storm every day, the amateur data are invaluable," said Fischer. "I am in continuous contact with astronomers from around the world."

The long-lived storm will likely provide information on the processes powering Saturn's intense lightning activity. Cassini scientists will continue to monitor Storm Alley as the seasons change, bringing the onset of autumn to the planet’s southern hemisphere.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of Caltech, manages the Cassini mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo. The radio and plasma wave science team is based at the University of Iowa, Iowa City.

WEATHER NOTE

I just can't let this date go without mentioning that on May 7, 2007 the United States Coast Guard rescued three sailors aboard the sailboat Sean Seamour II during Tropical Storm Andrea in the Hatteras Trench region. This was one dramatic and dangerous rescue. My thanks to USCG H-60 Aircraft Commander, Lt. Commander Nevada Smith, his crew and the Master of the Sean Seamour II, Jean Pierre de Lutz.

MARITIME NOTE

Passengers rescued from cruise ship

Latvia's coastguard evacuated a stranded cruise ship of more than 650 people after tug boats failed to pull the luxury liner off an underwater sand bank in the Baltic Sea.

In a five-hour operation, 651 passengers - mostly elderly Germans - and 11 crew members were transferred from the 660ft-long Mona Lisa on to two naval ships, coastguard officials said.

They were taken about 22 miles to Ventspils, a port city in north-western Latvia, for onward travel to the capital, Riga.

'Weigh every box', urges ship manager

Seven 30-foot boxes collapsed in to the Annabella's hold.

A SHIP manager caught up in an accident involving crushed containers is lobbying for every box to be weighed before loading.

That would prevent many of the incidents when either stacks have collapsed or containers have been washed overboard, Döhle (IOM) non-executive chairman Jörg Vanselow told an industry audience this week.

No single cause can be blamed for the sizeable number of container losses recorded in recent years, but Capt Vaneslow is pressing for more information about the cargo to be supplied to the ship’s master by the shipper or terminal operator.

That would enable senior officers to make a decision about the safest height of a container stack, said Capt Vaneslow, who was at sea for 16 years before joining the German shipping group Peter Döhle.

The company managed the 868 teu Annabella, which has become a cause celebre in shipping circles after seven 30 ft containers collapsed in to the hold early last year.

The UK’s Marine Accident Investigation Branch made a number of recommendations, including the need for a code of best practise that the industry is now working on.

Statistics on the number of container losses is hard to come by, but one industry estimate puts the figure at around 10,000 boxes a year. Of those, about 25% are lost over the side, according to Jos Koning, senior project manager at the Maritime Research Institute in the Netherlands, which is now working on a study of the dynamics and tolerances of a container stack on a super post-panamax ships which may be piled seven or eight boxes high.

The value of annual losses would probably be around $500m, an amount easily covered by insurance, but the real risk is the consequential damage such as schedule disruption, risk of a toxic leak, and a negative public image.

Addressing Containerisation International’s Global Liner Shipping Conference, Mr Koning said numerous contributory factors had been identified when investigating container loss accidents.

Some were caused by parametric rolling, others by bow slamming. Faulty twistlocks, ship size or design, poor stowage, lack of maintenance, or basic human error could all be blamed at various times.

“There is no one singe reason why cargo is being lost,” Mr Koning said.

Small ships may be more at risk than bigger vessels because of their lower freeboard and greater vulnerability to weather conditions or overweight containers.

But the Dutch institute has also embarked on its TallShip project to examine whether rules developed when containerships were very much smaller are still suitable for the latest generation of boxships with much higher stacks. The conclusions should be ready by June 2009 and may be submitted to the International Maritime Organization.

One concern is the relative inexperience of many ships’ crews and whether they have sufficient seafaring skills in the rare event of hitting exceptionally severe weather.

Pressure on the crew of small ships such as the Annabella is intense these days, with far more hectic sailing schedules then ever before, according to Capt Vanselow. In busy ports like Rotterdam, where feeders may have to call at several different berths, the crew is working virtually round-the-clock.

Furthermore, the captain may not receive details about the next port of call until he is alongside the quay.

But what a ship’s officers should be supplied with is information about the weight of containers being loaded, Capt Vanselow argues.

Procedures could easily be adapted so that each container is weighed as it is lifted onto the ship, and that information immediately conveyed to the captain.

Should an accident occur, a legal nightmare begins because of the highly complex contractual web covering a ship and its cargo.

There is no straightforward way of determining who is responsible, with each and every contract likely to be unique in some way, according to Holman Fenwick & Willan partner Craig Neame.

Contracts “are a complete and utter minefield”, with any parties involved in a loss advised to map out the relationships with each other that could involve the cargo owner, forwarder, shipowner, shipping line, terminal operator P&I club, hull underwriter, cargo insurer and more.

• A device designed by former insurance broker Toby Priestly could help solve the hazards posed by semi-submerged containers.

He has patented an automatic two-way valve that opens either on contact with water, or when under pressure, so that air can escape.

Four of these simple-to-manufacture valves fitted to each container would enable water to flood into a box lost overboard, ensuring it should sink quickly rather than floating just beneath the surface.

RS