New Study Analyses El Nino Taimasa
20.02.2014 17:55 Age: 10 days
A new study will help predict sea level changes related to El Nino.
Click to enlarge. This shows flat-top Porites coral on a shallow reef near American Samoa. Coral heads are fully submerged under normal conditions. During El Niño Taimasa, tops of large flat coral on the reef are exposed to air at low tide. Courtesy: National Park of American Samoa.
During very strong El Niño events, sea level drops abruptly in the tropical western Pacific and tides remain below normal for up to a year in the South Pacific, especially around Samoa. The Samoans call the wet stench of coral die-offs arising from the low sea levels “taimasa” (pronounced [kai’ ma’sa]). Studying the climate effects of this particular variation of El Niño and how it may change in the future is a team of scientists at the International Pacific Research Center, University of Hawai’i at Mānoa and at the University of New South Wales, Australia.
Two El Niño Taimasa events have occurred in recent history: 1982/83 and 1997/98. El Niño Taimasa differs from other strong El Niño events, such as those in 1986/87 and 2009/10, according to Matthew Widlansky, postdoctoral fellow at the International Pacific Research Center, who spearheaded the study.
“We noticed from tide gauge measurements that toward the end of these very strong El Niño events, when sea levels around Guam quickly returned to normal, that tide gauges near Samoa actually continued to drop,” recalls Widlansky.
During such strong El Niño, moreover, the summer rain band over Samoa, called the South Pacific Convergence Zone, collapses toward the equator. These shifts in rainfall cause droughts south of Samoa and sometimes trigger more tropical cyclones to the east near Tahiti.
Using statistical procedures to tease apart the causes of the sea-level seesaw between the North and South Pacific, the scientists found that it is associated with the well-known southward shift of weak trade winds during the termination of El Niño, which in turn is associated with the development of the summer rain band.
Looking into the future with the help of computer climate models, the scientists are now studying how El Niño Taimasa will change with further warming of the planet. Their analyses show, moreover, that sea-level drops could be predictable seasons ahead, which may help island communities prepare for the next El Niño Taimasa.
During strong El Niño events, sea level drops around some tropical western Pacific islands by up to 20–30 cm. Such events (referred to as taimasa in Samoa) expose shallow reefs, thereby causing severe damage to associated coral ecosystems and contributing to the formation of microatolls. During the termination of strong El Niño events, a southward movement of weak trade winds and the development of an anomalous anticyclone in the Philippine Sea are shown to force an interhemispheric sea level seesaw in the tropical Pacific that enhances and prolongs extreme low sea levels in the southwestern Pacific. Spectral features, in addition to wind-forced linear shallow water ocean model experiments, identify a nonlinear interaction between El Niño and the annual cycle as the main cause of these sea level anomalies.
Widlansky, M.J., A. Timmermann, S. McGregor, M.F. Stuecker, and W. Cai, 2014: An interhemispheric tropical sea level seesaw due to El Niño Taimasa. J. Climate, 27 (3), 1070-1081, doi:10.1175/JCLI-D-13-00276.1.
Read abstract and get the paper here.
This story based on a news release from the University of Hawaii publicised via the EurekAlert! Service of the AAAS here.
At Ocean Sciences 2014: PROJECTIONS OF EXTREME SEA LEVEL VARIABILITY DUE TO EL NIÑO TAIMASA, Oral presentation Session #:079 Rising Sea Level: Contributions and Future Projections; Date: 2/26/2014; Time: 12:00; Location: 313 B; here.