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Twin Convergence Zones
This page contains archived content and is no longer being updated. At the time of publication, it represented the best available science. However, more recent observations and studies may have rendered some content obsolete.
NASA’s QuikSCAT satellite has confirmed a 30-year old largely unproven theory
that there are two areas near the equator where the winds converge year after
year and drive ocean circulation south of the equator. By analyzing winds,
QuikSCAT has found a year-round southern and northern Intertropical Convergence
Zone. This find is important to climate modelers and weather forecasters because
it provides more detail on how the oceans and atmosphere interact near the
The Intertropical Convergence Zone (ITCZ) is the region that circles the
Earth near the equator, where the trade winds of both the Northern and Southern
Hemispheres come together. North of the equator, strong sun and warm water of
the equator heats the air in the ITCZ, drawing air in from north and south and
causing the air to rise. As the air rises it cools, releasing the accumulated
moisture in an almost perpetual series of thunderstorms. Satellite data,
however, has confirmed that there is an ITCZ north of the equator and a parallel
ITCZ south of the equator.
Variation in the location of the ITCZ is important to people around the world
because it affects the north-south atmospheric circulation, which redistributes
energy. It drastically affects rainfall in many equatorial nations, resulting in
the wet and dry seasons of the tropics rather than the cold and warm seasons of
higher latitudes. Longer term changes in the ITCZ can result in severe droughts
or flooding in nearby areas.
“The double ITCZ is usually only identified in the Pacific and Atlantic
Oceans on a limited and seasonal basis,” said Timothy Liu, of NASA’s Jet
Propulsion Laboratory and California Institute of Technology, Pasadena, Calif.,
and lead researcher on the project. In the eastern Pacific Ocean, the southern
ITCZ is usually seen springtime. In the western Atlantic Ocean, the southern
ITCZ was recently clearly identified only in the summertime.
However, QuikSCAT’s wind data has seen the southern ITCZ in all seasons
across the entire Atlantic Ocean and the eastern Pacific. “QuikSCAT’s wind data
confirms there is a double ITCZ, and that they exist all year long,” Liu
This is a major find for the science community, as the existence, location,
and seasonality of the double ITCZ had remained controversial since 1969.