ScienceDaily (Nov. 2, 2008) — In a paper published in the journal Science, scientists Gabriel A. Vecchi of NOAA's Geophysical Fluid Dynamics Laboratory, Kyle L. Swanson of the University of Wisconsin - Milwaukee Atmospheric Sciences Group and Brian J. Soden from the University of Miami's Rosenstiel School of Marine and Atmospheric Science teamed up to study hurricane data observed over more than 50 years.
The study explores the relationship between sea surface temperature (SST) and seasonal hurricane activity, and show how differing interpretations of the observational record can imply vastly different futures for Atlantic hurricane activity due to global warming. The two interpretations arise from assumptions of whether it is the local SST in the Atlantic in isolation, or whether it is the SST in the Atlantic 'relative' to the rest of the tropics, that drives variations in Atlantic hurricane activity.
If one assumes the former (the local SST hypothesis), then by 2100, the lower bound on Atlantic hurricane activity is comparable to that of 2005, when four major hurricanes struck the continental United States, causing more than $100 billion in damage. The upper bound exceeds 2005 levels by more than a factor of two. However, if one assumes the latter (the relative SST hypothesis), then the future is similar to the recent past, with periods of higher and lower hurricane activity relative to present-day conditions due to natural climate variability, but with little long-term trend.
The statistical relationship between either interpretation of the SST/hurricane activity link is ambiguous over the period 1946-2007 (they are statistically indistinguishable, though both are significant), but they imply fundamentally different projections for the future and interpretations of the past. The team further argues that the consistency between theory, numerical models, and historical observations offers compelling evidence that the 'relative' SST hypothesis is more accurate and provides a better framework for projections of future changes in hurricane activity.WEATHER NOTE
Massive waves a mystery at Maine harbor
Dockworker Marcy Ingall saw a giant wave in the distance last Tuesday afternoon and stopped in her tracks. It was an hour before low tide in Maine's Boothbay Harbor, yet without warning, the muddy harbor floor suddenly filled with rushing, swirling water.
In 15 minutes, the water rose 12 feet, then receded. And then it happened again. It occurred three times, she said, each time ripping apart docks and splitting wooden pilings.
"It was bizarre," said Ingall, a lifelong resident of the area. "Everybody was like, 'Oh my God, is this the end?' " It was not the apocalypse, but it was a rare phenomenon, one that has baffled researchers. The National Weather Service said ocean levels rapidly rose in Boothbay, Southport, and Bristol in a matter of minutes around 3 p.m. on Oct. 28 to the surprise of ocean watchers. Exactly what caused the rogue waves remains unknown.
"The cause of it is a mystery," said National Weather Service meteorologist John Jensenius, who first reported the waves from a field office in Gray, Maine. "But it's not mysterious that it happened."
Specialists have posed a variety of possible explanations, saying the waves could have been caused by a powerful storm squall or the slumping of mountains of sediment from a steep canyon in the ocean - a sort of mini tsunami. The last time such rogue waves appeared in Maine was at Bass Harbor in 1926.
Jensenius said the occurrence is so unusual, that specialists don't have a name for the phenomenon.
"That's part of our problem," he said.
A similar occurrence in Florida more than 15 years ago continues to baffle researchers. A series of 12- to 15-foot waves hit Daytona Beach on July 3, 1992, injuring more than 20 people and lifting and tossing dozens of cars.
Jeff List, an oceanographer at the US Geological Survey at Woods Hole said he and other researchers studied the occurrence, but no one has been able to pinpoint the cause. And he said similarly enormous waves appeared once on the Great Lakes.
Could such a wave or waves enter Boston Harbor, or even engulf the Massachusetts coast?
"It seems a little unlikely one could hit Boston," List said. "But then again, these things are always surprises when they occur."
A squall line surge, which occurs when fast-moving storm winds sweep over water that is traveling the same speed, can create such a wave. (The speed of waves is directly related to wind speed and the depth of the ocean at any given point.)
List and other specialists said such an occurrence is exceedingly rare, but when it occurs, "you get this interaction that causes a large bulge of water to rise up."
Jensenius said that might have been a factor last week, when a major storm front brought rain to most of the East Coast, particularly southern New England. But he said that does not solve the mystery, adding that he had not ruled out a massive "land slump" underwater. Such slumps can create waves that may be classified as tsunamis, although no where near the size and scale of the tsunami that occurred in the Indian Ocean in 2004. Those fast-moving and deadly waves were caused by a massive earthquake.
Tsunami-like waves may not be as rare on the East Coast as most people think. Jensenius referenced a 2002 article in the International Journal of the Tsunami Society that called the threat of tsunami and tsunami-like waves generated in the Atlantic Ocean "very real despite a general impression to the contrary."
The article said such waves appear "in most cases to be the result of slumping or landsliding associated with earthquakes or with wave action associated with strong storms."
Explosive decompression of underwater methane could also be a factor.
Jensenius said he is trying to gather information on the waves that hit Boothbay Harbor, adding that he has asked local businesses such as banks whether the event might have been recorded on security videos.
"It could be this or it could be that, but as a science, it is very difficult to tie it down," he said of the waves.
List also said the waves could have been triggered by the same conditions that cause a tsunami, including a breaking glacier. Rogue waves can result from a tsunami traveling through the ocean that breaks "down into numerous waves."
According to the National Weather Service, no earthquakes or seismic activity were reported in the area when the Boothbay waves appeared. List noted that there was no seismic reading when the Daytona waves struck.
Tom Lippmann, an oceanographer in the Marine Sciences Department at the University of New Hampshire, said he also suspected that the Maine wave was a squall line surge. The National Weather Service incorrectly called it a tide surge, he said.
"Tides in the Gulf of Maine are essentially driven by celestial bodies' pull on the earth's water," he said. "They're very well predicted and very well known."
Residents and business owners in Boothbay said they were glad the phenomenon didn't happen at high tide, when it might have caused massive flooding and more extensive damage. Janice Newell, who lives nearby in Head of the Harbor, told the local newspaper the rushing water "was of biblical proportion."
"There were three large whirlpools in the inner harbor, up to within a foot of my neighbor's wall," she told the Boothbay Register. "It was beautiful, but it was scary."
Elena Smith, a waitress and part-owner of McSeagull's restaurant overlooking the harbor, said the late-afternoon lunch crowd sat speechless as the waters rose and receded. She was stunned to see the normally safe and placid harbor suddenly run like rapids. Some residents reported seeing massive whirlpools of water that disappeared, leaving clam shells and seaweed in vortex patterns on the harbor floor.
"It felt like somebody took the plug out somewhere" in the ocean, Smith said. "It felt like there must have been water missing in the ocean someplace."MARINE NOTE
Cosco Busan incident spurs search for safety
It was the mariner's worst nightmare - from the bridge of the container ship Cosco Busan, Capt. John Cota, the man who was in charge of navigating the vessel, could see one of the towers of the San Francisco Oakland Bay Bridge looming out of the fog.
He was headed right for it. The Cosco Busan is 901 feet long - longer than the Transamerica Pyramid is tall - and the ship's diesel engine, which generated 77,600 horsepower, was set on full speed ahead. There was no way to stop. Cota took quick evasive action, but the Cosco Busan sideswiped the tower, ripping a hole on the left side of the ship, spilling 53,000 gallons of heavy fuel oil that fouled miles of shoreline and killed nearly 3,000 birds.
That was a year ago this Friday.
The question is: Could it happen again?
"Absolutely," said Kelly Sweeney, a ship captain who writes a column for Professional Mariner magazine.
The main question is not how to prevent accidents - there will always be plane crashes and train wrecks, for example - but how to minimize the risks.
Experts say there are three ways: restrict operations of large ships in poor visibility, provide better tools to pilots, and construct better protections for the footings of bridges and other structures.
The Cosco Busan accident cost more than $90 million so far and Cota faces criminal charges in federal court. The accident also damaged the careers of several Coast Guard officers, and is likely to cost Regal Stone Ltd., which owns the ship, and Fleet Management Ltd., which operated it, millions of dollars.
There have been congressional hearings, and several investigations. A report by the National Transportation Safety Board and the Coast Guard into the cause of the accident is due in January.
"This is the most investigated accident ever," said Capt. Peter McIsaac, president of the Bar Pilots Association. Only the Exxon Valdez spill in Alaska, which had a much larger environmental impact, was more closely investigated.
A report by the state Board of Pilot Commissioners found seven serious errors in Cota's piloting of the ship and concluded that "pilot misconduct was a factor" in the accident.
Cota, 60, is a veteran ship's officer who had been a pilot for more than 25 years. He had taken big ships under the Bay Bridge hundreds of times. "Oh yeah, it was so foggy," he said later, his voice picked up by the ship's recording system. "I shouldn't have gone."
The role of the pilot
The report and the subsequent investigations raise serious questions about the role of ship pilots and how to reduce the risk of another encounter between a big ship and a fixed object, an event that is technically called an allision.
Pilots are experienced mariners, required to have command experience at sea, or on tugboats, and qualified for both a federal ship master's license and a state piloting license.
It is a select community. There are only 60 members of the San Francisco Bar Pilots Benevolent and Protective Association, which dates from 1850. They handle about 9,000 ship movements a year, in and out of the Golden Gate, on San Francisco Bay and its tributaries and up the rivers as far as Sacramento and Stockton.
New pilots go through an extensive selection process and then a training period that lasts a minium of 18 months. Pilots are well paid: upwards of $400,000 a year in most cases.
They provide local knowledge and guidance to the masters of ships. Bar pilots are the area experts who know how to handle a ship past the big sandbar outside the Golden Gate, through the channels in the bay, and to the docks and piers around the harbors.
"They have the local expertise," said Sweeney. "A pilot should know the area like the back of his hand."
They need this kind of knowledge. "You might be out there in a storm, rain and wind blowing, and the engine conks out, and there you are," said Capt. James Nolan, a veteran pilot who now teaches at the Massachusetts Maritime Academy. "No other pilot around. It's just you."
A pilot does not command the ship. That is the responsibility of the ship's master. Nor do they touch the helm. That is the responsibility of one of the ship's able seamen. But they give advice, usually in the form of orders. A pilot will tell the helmsman what course he wants steered; he will tell the mate on duty what speed to run the engine.
It is only advice, but it must be taken seriously. "You can overrule the pilot," said one ship's captain, "but you better be right."
In practice, few masters overrule pilots. In the Cosco Busan case, the master, Capt. M.C. Sun, was new to the ship, had never taken the Cosco Busan into San Francisco Bay, and apparently had limited English skills. It was highly unlikely he would challenge the pilot.
Nor did he. Sometimes, many pilots say, there is pressure to sail on time, even in bad weather. "They want to make a schedule," one pilot said. "Time is money." However, the pilot commission report concluded there was no pressure to depart at its scheduled time.
There was heavy fog, and, according to recordings, some members of the Chinese crew had doubts about the wisdom of proceeding in such low visibility.
Chain of errors
Cota made the first in a series of mistakes - mariners call this a chain of errors - when he decided to sail in the fog.
McIsaac, the president of the Pilots Association, and Capt. Paul Gugg, the Coast Guard officer commanding the San Francisco sector, say pilots will no longer take ships to sea in such limited visibility. Under new guidelines, a ship over 1,600 gross tons may not leave the dock or sail in certain restricted areas if the visibility is less than half a mile. When the Cosco Busan sailed a year ago, the visibility was less than a quarter mile.
Cota also had trouble with the ship's radar, which he considered unreliable. He depended instead on an electronic chart, which was part of the ship's equipment.
Cota was not familiar with the ship's electronic chart, and asked the Cosco Busan's captain to point out the channel between two of the bridge towers. Perhaps because he misunderstood Cota, Capt. Sun pointed to a bridge tower instead.
Now pilots are considering using their own laptop equipment, instead of having to depend on someone else's. Pilots in other areas carry laptops, but it's not required here.
There is a problem with pilots carrying laptops - for one thing, they have to board and disembark from ships by climbing up and down a rope device called a Jacob's ladder. Transferring pilots from small boats to big ships is very hazardous. Some pilots have been killed doing it.
"I have a handheld radio, that's 6 pounds. I have 15 pounds worth of flotation devices I wear, and now I'd have to have a 16-pound laptop?" said one pilot. "If I fell in, I'd be sunk for good."
Next, when Cota found himself on a collision course with the bridge tower, he took evasive action, first ordering the helm hard right to point the bow away from the tower, then hard left to keep the stern of the ship from hitting the tower.
Disastrous glancing blow
The result was a glancing hit; still, it did $2 million in damage to the wooden fenders around the tower. Had the ship hit the bridge head-on, the damage to the Bay Bridge might have been substantial.
However, Isaac says, there should be consideration of a better fendering system on the bridge - perhaps one that acts as a shock absorber or prevents a head-on crash.
"There was an error chain," said Sweeney. "If any link in the chain is broken, it doesn't happen. But all the ducks were lined up. There's plenty of blame to go around. You can't blame it all on the pilot. There were other people on the (ship's) bridge and they were not saying anything.
"If all those things happen again, it can certainly happen again."