High Flying Balloons Track Atlantic Hurricanes in Formation

BOULDER, Colorado, September 1, 2006 (ENS) - In a unique collaboration, U.S. and French researchers are launching large, specialized balloons into the stratosphere to drop nearly 300 instrument packages over wide swaths of Africa and the Atlantic Ocean. Over the next month, the packages will gather detailed data from critical regions of the atmosphere where some of the most dangerous U.S. hurricanes develop.

The first launch of a balloon with its instruments, called a driftsonde, took place at Zinder, Niger, on August 28.

Up to seven more driftsondes will be released from Zinder through late September, coinciding with the peak period of hurricane formation over the tropical Atlantic.

"Data from the driftsondes should help characterize the conditions that either foster or suppress hurricane formation," said the National Science Foundation's Cliff Jacobs, who oversees support for the National Center for Atmospheric Research, NCAR, in Boulder, Colorado.

Scientists and engineers at NCAR and the French space agency, CNES, developed the driftsondes. The research was funded by the National Science Foundation, NCAR's primary sponsor, and the National Oceanic and Atmospheric Administration, NOAA.


This sunrise launch in Wyoming was part of driftsonde testing during the summer of 2006. The driftsonde package, designed by NCAR, includes a gondola and weather instruments that descend by parachute carried aloft by a ballooning system designed by the French space agency, CNES. (Photo by Joe VanAndel courtesy UCAR)
Each balloon will drift from Africa toward the Caribbean at heights of around 65,000 to 70,000 feet, where light easterly winds prevail.

Twice a day, each balloon will release an instrument known as a dropsonde that falls by parachute, sensing the weather conditions during its 20-minute descent and sending data back to the balloon and then to the researchers by satellite.

Scientists will control the process from an operations center in Paris. If a weather system develops, they can signal the balloon to release additional dropsondes as often as once per hour.

The Niger site was selected to study weak weather systems, called easterly waves, that serve as seedlings of hurricanes. Dozens of these waves move across Africa into the Atlantic between about 10 and 20 degrees North. A small number develop into tropical storms and hurricanes, some of which reach the U.S. Atlantic and Gulf coasts.

"The driftsondes will provide unique data on the conditions that lead to Atlantic hurricanes," said NCAR scientist David Parsons, U.S. coordinator for the project. "They float at a speed close to the movement of the easterly waves, so we can stay above those waves and monitor them from their earliest stages."

In order to make the driftsonde concept practical, NCAR developed a compact instrument package, roughly the size of a small bottle of water but weighing only about five ounces, less than half as much as older dropsondes designed at NCAR in the 1990s. Hundreds of dropsondes based on the original design are deposited by NOAA and the U.S. Air Force aircraft into hurricanes each year.

"We needed a lightweight instrument package, because more weight means larger and more expensive balloons," says Parsons.


At the airport in Zinder, Niger, technicians from the French space agency CNES prepare for the historic launch on August 28 of the first driftsonde used for weather research. (Photo bu Terry Hock courtesy NCAR)
To build the driftsonde system, scientists, engineers, and machinists had to overcome many hurdles. Each driftsonde had to be robust enough to endure days of extreme stratospheric cold - averaging minus 80 degrees Fahrenheit - as well as the intense sunlight of the high, thin atmosphere.

For the balloon deployment to be affordable and practical, the system also required low cost, lightweight, off the shelf instruments capable of operating reliably in low pressure and in temperature extremes with very low power.

Because of their flexible and relatively inexpensive nature, scientists believe, driftsondes may soon become a popular way to monitor and study many types of weather across the world's oceans and other remote regions.

"Future projects are being discussed for Antarctica and the western Pacific," says Philippe Cocquerez, the CNES project leader.

"It would take a fleet of research aircraft to gather the same data that we hope to obtain with these driftsondes," says Philippe Drobinski, the project's scientific co-lead from the French National Center for Scientific Research.

In addition to tracking potential hurricanes, the driftsondes will gather data on surges of hot, dry air that cascade into the Atlantic from the Sahel region of Africa. These surges carry huge amounts of dust as far west as Florida, influencing air chemistry, upper ocean biology, and Atlantic weather systems.