As the probability of an El Niño winter increases, Scripps Institution of Oceanography at UC San Diego researchers are following the climate phenomenon as it develops off Southern California and finding that local readings closely hew to El Niño monitoring taking place at the equator.
El Niño is a phenomenon characterized by warmer sea surface water in the equatorial Eastern Pacific Ocean. It is often associated with greater rainfall on much of the U.S. West Coast and frequently enhances the encroachment of storm surges by raising regional sea level for several months at a time. An El Niño is defined by a seasonal sea surface temperature anomaly in the eastern/central equatorial Pacific greater than 0.5 C° (0.9° F) warmer than historical average temperature. The opposite phenomenon known as La Niña is defined as a seasonal sea surface temperature anomaly 0.5° C (0.9° F) colder than the historical average.
An autonomous underwater glider known as Spray monitors water temperature and other parameters off Dana Point, Calif. Scripps physical oceanographer Dan Rudnick said the Southern California El Niño Index produced from Spray data so far strongly agrees with the El Niño/ Southern Oscillation Diagnostic Discussion, a measure of El Niño published by NOAA based on temperature data collected at the equator. Currently NOAA forecasts a probability of El Niño conditions 70 percent during the Northern Hemisphere summer and reaching 80 percent during the fall and winter.
The Spray data are distributed by the Southern California Coastal Ocean Observing System (SCCOOS), a region of the U.S. Integrated Ocean Observing System (IOOS®). SCCOOS is a multi-institutional network sponsored by NOAA and the California State Coastal Conservancy that makes ocean data available to the public and to entities such as the Naval Oceanographic Office, which uses the data to make model forecasts in support of U.S. national security.
“The long-term monitoring is critical for establishing the baseline for evaluating, tracking and predicting large storm events in the future,” said SCCOOS Executive Director Julie Thomas.
“The Southern California El Niño Index and the suite of data provided by SCCOOS are enabling decision-makers to prepare for this year's El Niño as well as for everyday variations that affect California commerce,” said Catherine Kuhlman, deputy secretary for ocean and coastal policy with the California Natural Resources Agency. “This measure of preparedness is evidence of the strong leadership of California in the use of science to guide state policy.”
The Spray data are one of several means by which scientists are following the developing El Niño. Deployment of Spray gliders off the Galapagos Islands began in October 2013 in a joint project with Woods Hole Oceanographic Institution and the Oceanographic Institution of the Ecuadorian Navy (INOCAR). The National Science Foundation (NSF) and NOAA fund this project, called Repeat Observations by Gliders in the Equatorial Region (ROGER). The next Spray deployment in the Galapagos is scheduled for July.
In coordination, Scripps oceanographers beefed up the coverage of the international Argo network in the equatorial Pacific Ocean as part of a larger endeavor to demonstrate how long-term observations in the tropical Pacific Ocean can be improved. Dean Roemmich, a Scripps oceanographer and Argo Steering Committee co-chair, said a commercially operated sailboat, SV Investigator, deployed 41 Argo floats along the equator in January - March. A global array of more than 3,500 Argo floats records ocean temperature, salinity and current data in the upper 2,000 meters (6,500 feet) of the ocean.
Roemmich said the new floats, in addition to the existing Argo array, have provided an unprecedented view of the Pacific-wide evolution of El Niño conditions. A burst of westerly wind in the western Pacific in January resulted in a strong subsurface pulse of energy that crossed the equatorial Pacific from February to April.
“This warm temperature anomaly became shallower in the eastern Pacific where it was felt as a warming of sea surface temperature,” said Roemmich. “The next few months will tell whether this warm pulse is followed by others and whether it will develop into an El Niño.”
“The Pacific Argo and glider observations from Scripps are especially critical for monitoring the development and enabling the prediction of El Niño and potential impacts on California,” said David Legler, director of NOAA’s Climate Observations program. “Scripps is an important partner with NOAA in observing the changing global ocean environment.”
Scripps oceanographers are also collaborating with the Naval Research Laboratory to improve a fine-resolution Navy model used to analyze El Niño among other phenomena. Oceanographer Julie McClean said the goal of the Navy's Hybrid Coordinate Ocean Model (HYCOM) development effort is to eventually use it in a fine-resolution fully-coupled forecast system to simulate coupled ocean and atmospheric phenomena leading to improved prediction of sea level rise and extreme weather events.
The term “El Niño” has existed since the 1890s, having been so nicknamed by South American fishermen, who acknowledged the birth of Christ by associating an onset of warming ocean water with its Christmastime appearance. Modern El Niño research, however, began mainly after a strong episode in 1982-83 that had gone largely undetected by scientists until it was well under way. That event caused more than $13 billion in economic loss worldwide and prompted more than a dozen countries to make large investments in El Niño research. Advances in data collection and computer modeling enabled researchers at Scripps and elsewhere to forecast a major El Niño in 1997-98 with success, though the models were relatively crude compared to current generations of models.
Scripps Oceanography Director Margaret Leinen noted that El Niño has the ability to exacerbate the effects of even moderate sea-level rise. As the phenomenon develops, she and NOAA officials are alerting federal funding agencies to the potential need for rapid-response measurements of ocean conditions that will enable improved risk assessments. Prior to the onset of El Niño conditions, Leinen said that researchers will be gathering baseline measurements of coastal features using light detection and ranging (LIDAR) and satellite data.
“Technology has advanced considerably since the last major El Niño struck the West Coast in 1998 and we can take advantage of our new capabilities,” said Leinen. “We have the tools we need to assess the accuracy of our understanding of El Niño-related risk.”
The Southern California El Niño Index uses data that have been continuously gathered since 2006. Its record shows that changes in temperature that take place at the equator are matched very quickly off California, Rudnick said.
“It suggests to me that if an El Niño is brewing at the equator, we’re going to feel the effects pretty much immediately here in Southern California,” he said.
In addition, the Scripps El Niño forecast model has been predicting since last December that an El Niño would occur in the winter of 2014.
“The forecast uses observations of ocean temperatures and surface winds in the equatorial Pacific Ocean to predict El Niño up to a year in advance,” said Scripps climate researcher David Pierce.
The forecast system has been operational since late 1996. As with the Southern California El Niño Index, its value increases as its dataset grows larger over time.
The NSF California Current Ecosystem Long-Term Ecological Research (CCE-LTER) program at Scripps also plans several studies of the effects of the 2014-15 El Niño on life in the California Current. CCE-LTER Lead Principal Investigator Mark Ohman said he is studying the effects of a 2009-10 El Niño that could suggest that the nature of the phenomenon in the 21st century could be different than most 20th century El Niños. CCE-LTER in conjunction with the long-running California Cooperative Oceanic Fisheries Investigations (CalCOFI) program will track El Niño using data from Spray and from moorings in the California Current. The continuity of measurements made by several programs at Scripps allows a significantly improved understanding of El Niño and La Niña.
“In the absence of a quantitative record of historical ocean conditions, it is impossible to attribute causality to El Niño,” said Ohman. “Because of our growing historical record, CCE-LTER, together with its partners, is ideally positioned to understand the effects of the forecast El Niño on living components of marine ecosystems.”