Cause of Odd Arctic Ozone 'Hole' Found
Maps of ozone concentrations over the Arctic on March 19, 2010 (left) and the same day in 2011 (right), measured by the Ozone Monitoring Instrument on NASA's Aura satellite.
Oct. 28, 2012 --
The Earth has the most complicated atmosphere in the solar system, so complicated that meteorologists look to other planets to understand how our weather works. Combined with its constantly active plate tectonics, our planet is truly an adventurous place to live. As the East Coast of the United States braces for a storm of historic proportions in Hurricane Sandy, we take a look back at awesome Earth events past, from earthquakes, to blizzards, to floods.
1. 1900 Galveston Hurricane This was the deadliest natural disaster ever to strike the United States. Approximately 8,000 people lost their lives on Sept. 8, 1900 in what was the biggest city in Texas at that time. Ship reports were the prevalent tool for observing hurricanes at sea, and because the wireless telegraph was in its infancy, there was precious little warning. Plus, Galveston residents had seen such storms before. Or so they thought. Many believed that they had already weathered the worst that Mother Nature could throw at them, but this hurricane brought winds above 100 mph. The storm surge knocked buildings off their foundations, leveling virtually every one in town. When it was over, 3,600 homes had been destroyed. The few buildings that withstood the enormous storm (mostly the more solidly built mansions of the wealthier residents) are maintained as tourist attractions today.
2. 2005 Hurricane Katrina Katrina was the sixth-most powerful Atlantic hurricane ever recorded, and the costliest in terms of damage. Peaking on Aug. 28, 2005, with winds hitting 175 mph, it originated in the Bahamas and was christened "Katrina" on Aug. 24. The early warnings quickly declared the potential devastation, as Katrina would weaken for short periods and then come back stronger than before. When the hurricane's sheer size became apparent, mandatory and voluntary evacuation orders were put into place and state and federal resources were targeted to minimize the impact of the coming storm. However, even today the government's response in preparation and recovery is a controversial issue. In the end, Katrina caused 53 different levee breaches in greater New Orleans, devastated the coasts of Mississippi and Alabama and did more than $80 billion in damages. Nearly 2,000 people were killed.
3. Blizzard of 1888 In the northeastern United States, March is supposed to be well past the peak time for dramatic snowfall. However, in March 1888, one of the most severe blizzards in U.S. history hit the New Jersey, New York, Connecticut and Massachusetts. Sustained 45-mph winds drove the 40 to 50 inches of snow, which fell into snowdrifts 50 feet high. Railroads were shut down, fire stations were immobilized and people were confined to their homes for up to a week. The transportation freeze from this event was partially responsible for the creation of the first underground subway system in the United States, which opened nine years later in Boston. About 400 people died from the blizzard and the cold of the week that followed -- 200 of them in New York City alone.
4. 2004 Indian Ocean Tsunami On the day after Christmas in 2004, the Sumatra-Andaman earthquake struck beneath the Indian Ocean. It was the second-strongest earthquake ever recorded on a seismograph, at a magnitude of 9.1 to 9.3, and it unleashed a killing wall of water that would claim more than 230,000 lives in 11 countries. In deep water, tsunamis travel at great speeds (300 to 600 mph) while creating small, barely noticeable waves. However, as they reach land, they slow down dramatically and those waves become enormous. On this day the waves reached as high as 100 feet, about the height of a 10-story building. Among the dead were about 9,000 tourists (mostly European) enjoying the peak holiday travel season. An estimated one-third of the dead were children.
5. 1906 San Francisco Earthquake The earthquake that hit San Francisco and parts of Northern California at just after 5 a.m. on April 18, 1906, is estimated to have been a magnitude 7.7 to 8.2. It ruptured along the San Andreas Fault, booth north and south, for about 300 miles, with the quake center located two miles offshore from the city. As a result of the quake itself, and the ensuing fires that blazed for days, the city of San Francisco was virtually leveled. At first, city and state officials announced the death toll at 376. This would have been a miraculous total had it been true. Fearing that the true figures would adversely affect real estate prices and investment in rebuilding the city, the officials had simply made up that figure. Also, hundreds of casualties in Chinatown had been ignored and unrecorded. Today the number of dead is estimated at 3,000, with 300,000 (about 70 percent of San Francisco's population) left homeless.
6. 1887 Yellow River Flood (Hwang Ho River Flood), China Flood For centuries, farmers along the Yellow River have built dikes to contain the flooding caused by silt accumulation along the riverbed. And for centuries those dikes have eventually given way to the mighty power of the rising river. In 1887, after days and days of heavy rain, the river burst through the man-made restraints and covered the low-lying surrounding areas with such speed and at such volume that most people were trapped without warning. Eventually 50,000 square miles of what had been homes, farms and villages were covered in water from the river. After the flood, millions were left homeless. The resulting pandemic and lack of basic essentials claimed as many lives as the flood itself. Total deaths are estimated to be an almost unthinkable number: between 900,000 and 2 million.
7. 1925 Great Tri-State Tornado This tornado has the dubious distinction of being the longest sustained tornado ever recorded (traveling 219 miles), as well as the deadliest (approximately 700 dead). It moved across Missouri, Illinois and Indiana and was on the ground for three and a half hours. On March 18, it touched down at around 1 p.m. just outside Ellington, Mo., and didn't dissipate until 4:30 p.m., near Petersburg, Ind. Along the way, the tornado destroyed 15,000 homes. The U.S. Weather Bureau's forecast for that day called for "rains and strong shifting winds," which one witness to the tornado later described as "a huge understatement."
Courtesy Mt. Washington State Park
8. 1934 Mount Washington Hurricane On April 12, 1934, the highest surface wind measured anywhere on Earth was clocked by the staff of the Mount Washington Observatory located in New Hampshire. The figure recorded -- 231 mph -- has become the stuff of legend. The day before seemed to indicate a typical spring storm to the three meteorologists on duty, but early the next morning that was obviously not going to be the case. By 5 a.m., winds had reached 150 mph. The readings slowly climbed until 1:21 p.m., when the 231 number was recorded. Meteorologist Sal Pagliuca wrote in the official log, "Our first thought was, will anyone believe it?" The beauty of this incredible show of nature's force? No reported injuries, no recorded property damage.
9. 1991 Halloween Storm (aka The Perfect Storm) The locals call it "the Halloween Nor'easter of 1991." In his book describing the almost unbelievable confluence of circumstances, Sebastian Junger called it "The Perfect Storm." Three separate weather events built slowly over the course of five days. First, a seemingly harmless low-pressure system formed over the Great Lakes. On its way east, it met up with an icy-cold high-pressure system from Canada. This combination formed a storm in the North Atlantic just off the coast of Nova Scotia. But it was the third, most unexpected event that made this real-life Halloween horror so historically devastating. Late-season Hurricane Grace blew up from the south to collide with the ongoing storm, and it was as if the forces of heat and cold, summer and winter, were at war. Waves 30 to 40 feet high hit the New England coast Halloween afternoon, and when it was over damages had amounted to an estimated $208 million. Twelve people were dead, six of them from the crew of the Andrea Gail, the fishing boat documented in Junger's book.
10. The Johnstown Flood On May 31, 1889, Johnstown, Penn., was a town of about 30,000 people and growing, known for the high quality of its steel production. After that day it would become synonymous with disaster. The area was (and is) prone to flooding due to its position at the confluence of the Stony Creek and Little Conemaugh River, and there is speculation that modifications made to a nearby reservoir to convert it to a luxury hunting and fishing club increased the vulnerability of the dam. The rain came to Johnstown from the west and would total as much as 10 inches in 24 hours. Creeks became rampaging rivers. By daybreak, railroad tracks and telegraph lines had been washed away. At mid-morning, the water was 10 feet high on the streets. Just after 3 p.m. the South Fork Dam burst, and for the next 40 minutes, 20 million tons of water had its way with Johnstown and the surrounding towns and villages.
Cold temperatures, chlorine and a stagnant atmosphere caused a thinning in the ozone layer over the Arctic in 2011, a new NASA study finds.
This ozone loss is not the more famous ozone hole, found seasonally over Antarctica, which has been shrinking since the phase-out of chlorofluorocarbons, or CFCs, that interact with ozone molecules in the atmosphere. These ozone molecules are made of three oxygen atoms bound together. Their high concentration in the stratosphere about 12 miles to 19 miles (20 to 30 kilometers) above the Earth's surface blocks harmful ultraviolet light from the sun.
Arctic ozone depletion is typically not as severe as that in the Antarctic. Over the South Pole, the sun barely or never sets around Christmas, creating a confluence of sunlight and cold in the atmosphere. Under these conditions, chlorine from CFCs eats away at ozone molecules. (See Ozone Animation)
Up north, however, the sun reappears in the sky in the spring as temperatures start to warm, so the conditions aren't as favorable for ozone depletion. But in 2011, the ozone concentration in the late winter Arctic was about 20 percent lower than average. [North vs. South Pole: 10 Wild Differences]
"You can safely say that 2011 was very atypical: In over 30 years of satellite records, we hadn't seen any time where it was this cold for this long," study researcher Susan Strahan, an atmospheric scientist at NASA Goddard Space Flight Center, said in a statement.
Using atmospheric simulations, Strahan and her colleagues found that a mix of cold temperatures, chlorine and an unusually strong Arctic vortex caused the odd thinning. The Arctic vortex is a region of fast-blowing circular winds that get stronger each fall, creating an eddy of chilled air around the pole.
In 2011, the atmosphere was unusually quiet, allowing the Arctic vortex to remain strong well into the spring, after it usually breaks up. The reappearance of the sun in March while it was still especially cold created the conditions that led to the ozone thinning, the researchers report in the Journal of Geophysical Research - Atmospheres.
"Arctic ozone levels were possibly the lowest ever recorded, but they were still significantly higher than the Antarctic's," Strahan said. "There was about half as much ozone loss as in the Antarctic," and the levels remained above the threshold for calling the ozone loss an actual "hole," Strahan added.
Strahan and her team calculate that two-thirds of the thinning was caused by a combination of chlorine pollution and extreme cold. The remaining third was caused by the oddly quiet atmosphere, which prevented ozone molecules from elsewhere from moving in to fill the gap.
The ozone layer over the Arctic returned to normal in April 2011. It's unlikely that such thinning will become a reoccurring problem, because the meteorological conditions were so odd, Strahan said. Not only that, but CFC levels in the atmosphere are still declining.
"If 30 years from now we had the same meteorological conditions again, there would actually be less chlorine in the atmosphere, so the ozone depletion probably wouldn't be as severe," she said.
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