Unearthing storm clues in West Africa
A US research effort targets the many storms that form off Africa's coast and cross the Atlantic.
KAWSARA, SENEGAL — Ed Zipser knew Ernesto as a baby. The meteorologist flew through the weather system a little over a week ago when it was just a patch of turbulence off the coast of West Africa. Ernesto then grew up to be the first hurricane of the 2006 season.
Scientists know that 4 out of 5 tropical storms hitting the United States – including the deadly and destructive hurricane Katrina a year ago – start out in the waters off Africa before bowling across the Atlantic.
What they don't really understand is why some systems fizzle and others whip up into monster hurricanes. So Professor Zipser and his colleagues are in West Africa, trying to unlock the secrets of the storm as part of the NASA-backed study known as NAMMA (Nasa African Monsoon Multidisciplinary Analyses).
Using a DC-8 jet, they fly through thunderstorms trying to map the precise contours with banks of sensors measuring wind speed and direction, cloud shapes and contents, rainfall rates, temperature, humidity, and atmospheric pressure.
"It's a bit like taking a bumpier-than-average commercial flight – you'd maybe spill a cup of coffee," says the storm expert from the University of Utah, describing his field research.
The scientists have also set up three state-of-the-art radars – one on the coast of Senegal, one on the Cape Verde Islands to the west, and another in landlocked Niger to the east.
Residents in the tiny Senegalese hamlet of Kawsara crane their necks to look at the radar that pokes its head up incongruously between the gingerbread-plum and cashew-nut trees that dot the scrubland.
The people of this area generally have a more traditional take on meteorology, banging drums or slaughtering a cow on the beach to summon the rains.
Now, 6 million pieces of electronic data are being collected on their doorstep every 15 minutes as scientists try to discover why 95 percent of West African storms collapse out at sea, and – more centrally – why the other 5 percent don't.
For about a month ending in mid-September, the NASA-backed researchers will collect information about the initial stages of a storm. Once the storm's life cycle is complete, and scientists know whether it ultimately intensified or weakened, they will look back over the early data and try to pick out the characteristics that gave birth to a big storm.
One theory the NAMMA scientists want to test is that dust from the Sahara desert can get inside a storm, dampening it down and inhibiting the formation of cyclones. Previously, they have had to rely on satellite images that only captured what was happening on top of the clouds, not inside them. Now they can pierce right to the heart of West Africa's storms.
"It's a dream come true for me. I've thought about what's going on inside these systems for years, but it's been a case of guessing," says Greg Jenkins, director of the program in atmospheric sciences at Howard University in Washington, who has studied West African weather for two decades.
He pulls up examples of radar images of the region and points out storm clouds. Swaths of red indicate high levels of the Saharan dust fading to sunflower yellow.
"Now, with aircraft and radars on the ground, we can see. We're filling in this void of knowledge about West African systems," Dr. Jenkins says.
The potential impact of NAMMA research on US residents living in hurricane hot spots takes on particular significance as the US commemorates the first anniversary of Hurricane Katrina that killed more than 1,000 people and devastated the Gulf Coast.
"We'll be able to feed our data into weather models and improve them so that forecasting is more accurate. It will be a huge leg up," Jenkins explains.
And with experiments like this happening only every few decades (the last one researching West African storms was in 1974), the data are likely to provide research fodder for generations of meteorologists to come.
For now, Americans living along the hurricane belt are closely following the development of Ernesto. Although it was downgraded to a tropical storm on Sunday night, forecasters expected it to strengthen into a hurricane again, prompting Florida to declare a state of emergency Sunday and order tourists out of the vulnerable Keys area.