In September 2006, NASA satellite data indicated that El Niño had returned
to the tropical Pacific Ocean, although it was relatively weak. As of
early October, scientists were not sure if the event would persist, and it
was much less intense than the last major El Niño episode, which happened
in 1997-1998. That event brought devastating floods to California that
cost millions of dollars in damage while severe drought struck Indonesia,
Australia, and the Philippines.
Among the ocean characteristics that signal developing El Niño events is a
change in average sea surface height compared to normal sea level. When
water warms, it expands a little, which changes its volume slightly. When
heat begins to build up in the Pacific during an El Niño event, the sea
surface height begins to creep up. NASA observes changes in average sea
surface height using its Jason satellite. The image is based on the
average of 10 days of data centered on September 15, 2006, compared to the
long-term average of observations from 1993-2005. In this image, places
where the Pacific sea surface height is higher (warmer) than normal are
yellow, orange, and red, and places where the sea surface is lower
(cooler) than normal are blue and purple. Green shows where conditions are
near normal. The swath of red in the center of the scene reveals that an
El Niño was in progress when Jason observed the Pacific.
El Niño is a cyclical warming of the ocean waters in the central and
eastern tropical Pacific that generally occurs every 3 to 7 years. It is
linked with changes in air pressure and high-level winds that can affect
weather worldwide. Typically peaking during the Northern Hemisphere winter
months, El Niño is the warm phase of the El Niño/Southern Oscillation. It
alternates with La Niña, the cooling of ocean waters in the same region of
the Pacific.
According to Bill Patzert, oceanographer and climatologist at NASA's Jet
Propulsion Laboratory, "The present conditions indicate that the intensity
of this El Niño is too weak to have a major influence on current weather
patterns. But, if the ocean waters continue to warm and spread eastward,
this event would likely strengthen, perhaps bringing much-needed rainfall
to the southwestern and southeastern United States this winter."
The Jason satellite carries a dual-frequency radar altimeter. This
instrument beams microwave pulses-at 13.6 and 5.3 Gigahertz,
respectively-downward toward the Earth. To determine the ocean's height,
the instrument precisely measures the time it takes for the microwave
pulses to bounce off the surface and return to the spacecraft. This
measure, multiplied by the speed of light, gives the range from the
satellite to the ocean surface.
The joint U.S.-French Topex/Poseidon mission is managed by the JPL for
NASA's Science Mission Directorate, NASA Headquarters, Washington, D.C. JPL
is a division of the California Institute of Technology in Pasadena.
Research on Earth's oceans using Jason and other space-based capabilities
is conducted by NASA's Science Mission Directorate to better understand and
protect our home planet.
For more information on NASA's ocean surface topography missions, see http://sealevel.jpl.nasa.gov/ or to view the latest Jason data see http://sealevel.jpl.nasa.gov/science/jason1-quick-look/.
