When Hurricane Karl slammed into Veracruz, Mexico, earlier this month, dozens of scientists had a ringside seat. They were aboard a NASA DC-8 that serves as a flying laboratory for studying hurricanes.
The purpose of the flight was to get a better understanding of why some hurricanes weaken unexpectedly while others suddenly become monster storms. That's important because even though forecasters have become good at predicting where hurricanes will go, they aren't so good at predicting how strong a hurricane will be when it arrives, says Ed Zipser, a professor of atmospheric sciences at the University of Utah.
"We don't do as good a job because we don't completely understand the process," Zipser says.
So Zipser and other scientists have been taking part in a NASA experiment called Genesis and Rapid Intensification Processes (GRIP). For more than a month, they have been gathering data on storms in the Atlantic, hoping they will eventually find clues to explain why some weather disturbances become hurricanes and why some hurricanes suddenly grow stronger.
An Ideal Storm To Study
The GRIP scientists had been studying Karl since it appeared as a weather disturbance in the Caribbean. On the day the storm was expected to hit Mexico, Zipser and many of his colleagues boarded the DC-8 in Fort Lauderdale, Fla., to gather one last day's worth of data.
For the first couple of hours after takeoff, the scientists onboard studied weather maps and checked their instruments, which are bolted to the cabin floor in spaces usually occupied by rows of seats. The equipment includes devices that sample the outside air for particles and laser beams to measure the height of cloud tops.
Robert Pasken, a meteorologist from St. Louis University, checks the dropsondes he will launch through a hole in the belly of the plane. The dropsondes will transmit information about winds, temperature, humidity and pressure as they parachute toward the ocean.
Karl is an ideal storm to study because it has consistently defied predictions, Pasken says.
"It looked like it was beginning to spin up -- nothing happened," he says. "Next day, it looked like it was going to spin up -- nothing happened. And then all of a sudden it did spin up."
Karl was getting stronger fast when it ran into the Yucatan Peninsula. Usually, crossing such a big piece of land would severely weaken a tropical storm. But that didn't happen with Karl, says Michael Black from the Hurricane Research Division of the National Oceanic and Atmospheric Administration. So when it emerged in the Gulf of Mexico, Mexican officials were suddenly facing a much bigger hurricane than they'd expected, he says.
"You've got a storm that a day ago was barely a hurricane and turned into a Category 3 in a matter of about 18 hours," Black says. "That's a huge difference in preparation and plans when you've got a hurricane bearing down on you."
By the time the plane reached Karl, part of the eyewall was already over land. So the scientists worked quickly. They start launching dropsondes and begin pulling data from onboard radars, which will reveal things that aren't visible from a satellite, Black says.
"You could view those as sort of a CAT scan of the storm," he says. "We'll be able to peer in and look at the structures of rainfall and winds within the storm."
Factors In Storm Strength
Researchers have known for years that factors such as water temperature and prevailing winds affect a storm's strength. But they've also learned that these factors alone don't explain why storms like Karl sometimes intensify so rapidly.
One missing element may be clouds known as hot towers that can carry hot moist air through the high layer of cirrus clouds that form above a hurricane. For decades, scientists have been trying to figure out how they are involved in rapid intensification.
Hot towers are usually hard to study because they go so high. But Black says that hasn't been a problem during this experiment, thanks to a new unmanned plane known as the Global Hawk.
"That aircraft is flying about 60,000 feet," he says. "They get a very clear view plus very detailed measurements with their radars onboard of these hot towers that will pop up."
Four other aircraft have also been involved in studying Karl.
As the DC-8 follows Karl inland, the scientists try to figure out how bad things are on the ground. Ed Zipser hunches over his laptop, which is showing an area about 100 miles from the coast where the storm is colliding with 10,000-foot mountains.
"As the winds blow this moist air up the mountain, we don't have any idea if it's going to be a beneficial rain or a disastrous rain," he says.
The plane's radar expert, Simone Tanelli from the Jet Propulsion Laboratory at Caltech, says he's worried by the intensity of rain he's seen in one small area near the foot of the mountains.
"It was coming down more rain than what you can imagine," he says. "And the nasty thing, the thing that scares me a little bit, is that we have two shots one hour apart, and in both shots I see the same thing. If for one hour it kept raining like that, those people must be under a meter of water."
Ground measurements would show that some places were getting as much as an inch of rain every 10 minutes.
In the end, Karl killed at least 16 people and caused billions of dollars of damage.
But scientists say they are pretty sure they will learn something from this storm -- and the other ones they've studied in the past few weeks. And that could mean they'll be able to warn people earlier about the next Karl.
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