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July 26, 2006: "Winds will grow soon to
storms in Africa," laments Irish singer Enya in her song,
Storms in Africa. She might have added "And hurricanes
in the Americas."  Scientists
have long known that hurricanes that lash the Atlantic coasts
of North and Central America are born in storm systems off
the west coast of northern Africa. In an ironic twist, these
wettest of storms are driven by weather over one of Earth's
driest of places, the Sahara (the name means desert in Arabic).
Right:
Thunderclouds over western Africa. [More]
To
learn the details of what happens, NASA and university researchers
are flying to the west coast of Africa for an international
campaign called the African Monsoon Multidisciplinary Analysis,
or AMMA. The NASA portion of the campaign is called NAMMA.
"We
are going to observe the transition of thunderstorms off the
coast of Africa into hurricanes that we get in the U.S.,"
explains Robbie Hood of the Marshall Space Flight Center,
a member of the NAMMA science team. "This is an active
hurricane genesis region."
The
scientists will operate during the month of Aug. 15 to Sept.
15 from the Cape Verde Islands, a cluster of 18 volcanic islands
in the Atlantic about 300 miles off the west coast of Africa.
Dr. Ramesh Kakar of the Earth Science Division, Science Mission
Directorate, at NASA headquarters is the program manager.
Hurricanes
are massive, rotating heat engines powered by the warmth of
tropical waters. Category 5 hurricanes can pack winds of 150
mph or more. Hood explained that many of these powerhouses
originate with combinations of thunderstorms off Africa. But
not all thunderstorms lead to hurricanes.
Why
not? There's more to the story than warm water:
Another
ingredient is Sahara dust storms. Dry desert air blowing westward
can overrun and weaken Atlantic storm systems. Dust, on the
other hand, can serve as nucleation points for water vapor,
causing rain. This interplay between ocean and desert is not
fully understood.
 To
probe deeper, NAMMA will use NASA's DC-8 Airborne Laboratory.
This modified jetliner has been used in NASA's two Convection
and Moisture Experiments (CAMEX-3 and -4) conducted in 1998
and 2001. It is equipped with weather instruments to measure
winds, water vapor, moisture, atmospheric pressure, temperatures,
and the detailed physics of cloud formation and development.
Right:
NASA's DC-8 aircraft is no stranger to bad weather. [More]
NASA
will also use weather radar located at both Dakar, Senegal
and Praia, Cape Verde, and instruments on NASA satellites
such as the Tropical Rainfall Monitoring Mission (TRMM), CloudSat
and CALIPSO. The United Kingdom, France and other European
nations will operate aircraft and surface instruments out
of Dakar, Senegal, on the west coast of Africa. The National
Oceanic and Atmospheric Administration's Hurricane Research
Division will fly aircraft out of Barbados to measure hurricanes
as they approach Caribbean nations, the United States, Mexico,
and Central America. During the mission, a Web-based real
time mission monitor, developed by Marshall Space Flight Center,
will permit scientists to track the progress of the experiment
from anywhere on the globe using a standard internet connection.
Hood
anticipates collecting lots of data. "Our goal is to
use the results of this experiment to improve precipitation
and hurricane forecasting technology for the future."
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Author: Dave Dooling
| Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
|
