La Niña's Exit Leaves Climate Forecasts in Limbo

It's what Bill Patzert, a climatologist and oceanographer at NASA's Jet Propulsion Laboratory in Pasadena, Calif., likes to call a "La Nada" – that puzzling period between cycles of the El Niño-Southern Oscillation climate pattern in the Pacific Ocean when sea surface heights in the equatorial Pacific are near average.

The comings and goings of El Niño and La Niña are part of a long-term, evolving state of global climate, for which measurements of sea surface height are a key indicator. For the past three months, since last year's strong La Niña event dissipated, data collected by the U.S.-French Ocean Surface Topography Mission (OSTM)/Jason-2 oceanography satellite have shown that the equatorial Pacific sea surface heights have been stable and near average. Elsewhere, however, the northeastern Pacific Ocean remains quite cool, with sea levels much lower than normal. The presence of cool ocean waters off the U.S. West Coast has also been a factor in this year's cool and foggy spring there.

The current state of the Pacific is shown in this OSTM/Jason-2 image, based on the average of 10 days of data centered on June 18, 2011. The image depicts places where Pacific sea surface height is higher (warmer) than normal as yellow and red, while places where the sea surface is lower (cooler) than normal are shown in blue and purple. Green indicates near-normal conditions. Sea surface height is an indicator of how much of the sun's heat is stored in the upper ocean.

For oceanographers and climate scientists like Patzert, "La Nada" conditions can bring with them a high degree of uncertainty. While some forecasters (targeting the next couple of seasons) have suggested La Nada will bring about "normal" weather conditions, Patzert cautions previous protracted La Nadas have often delivered unruly jet stream patterns and wild weather swings.

In addition, some climatologists are pondering whether a warm El Niño pattern (which often follows La Niña) may be lurking over the horizon. Patzert says that would be perfectly fine for the United States.

"For the United States, there would be some positives to the appearance of El Niño this summer," Patzert said. "The parched and fire-ravaged southern tier of the country would certainly benefit from a good El Niño soaking. Looking ahead to late August and September, El Niño would also tend to dampen the 2011 hurricane season in the United States. We've had enough wild and punishing weather this year. Relief from the drought across the southern United States and a mild hurricane season would be very welcome."

Jason-2 scientists will continue to monitor Pacific Ocean sea surface heights for signs of El Niño, La Niña or prolonged neutral conditions.

For more information visit http://www.nasa.gov/topics/earth/features/lanada20110629.html