Satellites Detect Signs Of El Nino
Satellites that measure winds and waves tracked a warm water mass the size of the United States as it moved across the Pacific Ocean, a sign that a weather-disrupting El Nino may be brewing, NASA scientists announced Thursday.
If so, California could have a much wetter-than-normal winter as in several recent El Nino years, although the condition can also cause drought in some areas of the West Coast.
An El Nino occurs when westward-blowing trade winds weaken, allowing a mass of warm water normally located off Australia to drive eastward to western South America. The phenomenon got its name from the Spanish words for baby Jesus because the huge, warm pool usually arrives around Christmas.
Simultaneous readings from two instruments are giving scientists strong suggestions about ocean and wind conditions that could foreshadow an El Nino.
Because water expands as it heats up, warmer seas are higher seas. A radar instrument aboard the U.S.-French TOPEX-Poseidon satellite detected a 6-inch to 8-inch rise in sea height in the equatorial Pacific, said Lee-Lueng Fu, TOPEX project scientist at NASA’s Jet Propulsion Laboratory in Pasadena.
Radar images from March and April, released Thursday, showed the sea-level hump moving east along the equator from Australia, through the tropical Pacific. It arrived at the west coast of South America in early May, Fu said.
The NASA Scatterometer aboard Japan’s Advanced Earth Observing Satellite showed that trade winds in the western Pacific reversed their westward movement at the end of December and at the end of February. Such shifts also signal an El Nino might be in the works.
With the shift, the hump of warm water that usually piles up at the western end of the Pacific “sloshes back eastward in the form of a Kelvin wave,” Fu said.
The first wave began in January and arrived at the South American coast in February. The second began in mid-March and arrived in early May, Fu said Wednesday in a telephone interview from the American Geophysical Union spring meeting in Baltimore.
On May 15, NOAA researchers said they detected early indications of an El Nino coming in late 1997. Their prediction was based in part on the satellite observations, Fu said.
There have been local signs of El Nino, too. Fishermen in Newport Beach this week reported their biggest haul of jumbo squid since 1990, when a warm Pacific current brought them north from Mexican waters. Klaus Weickmann, a meteorologist with the National Oceanographic and Atmospheric Administration in Boulder, Colo., said the squid swarm could be indicative of an El Nino.
El Ninos occurred in 1976-1977, 1982-1983, 1986-1987, 1991-1993 and 1994-1995. Although they typically take place every two to seven years, four of the first five years of the 1990s were marked by the warming. The effects of a cold episode in 1995-96 lingered until late 1996.
Although their cause remains unclear, scientists know El Ninos alter the strength and direction of jet stream winds and disturb weather.