A simulation reveals possible end of El Nino/ La Nina
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| Surface ocean temperature (Institute of Basic Science) |
The cycling between warm El Nino and cold La Nina conditions in the eastern Pacific (commonly referred to as the El Nino- Southern Oscillation, ENSO) has persisted without major interruptions for at least the last 11,000 years. This may change in the future according to a new study published in the journal Nature Climate Change by a team of scientists from the IBS Center for Climate Physics (ICCP) at Pusan Natinoal University in South Korea, the Max Planck Institute of Meteorology, Hamburg, Germany, and the University of Hawai'i at Manoa, USA.
As the ENSO collects irregular periodic variation in winds and sea surface temperatures, high air surface in the tropical western of Pacific is accompanied by the El Nino, while low air surface pressure is in La Nina. Hence, the team conducted a series of global climate model simulations with an unprecedented spatial resolution of 10 km in the ocean and 25 km in the atmosphere. Boosted by the power of one of South Korea's fastest supercomputer (Aleph), the new ultra-high-resolution climate model simulations can now realistically simulate tropical cyclones in the atmosphere and tropical instability waves in the equatorial Pacific Ocean, which both play fundamental roles in the generation and termination of El Nino and La Nina events. This supercomputer employs two different global warming levels covering present-day climate as well as century-long data, subsequently; two quadrillion bytes of data are generated, which implies enormous dataset.
To analyse this huge data, the team focused on a long-standing problem, which is how will ENSO change in response to increasing greenhouse gas concentrations. Instead of using the temperatures in the equatorial Pacific, west of Galapagos, which are always too cold to the observations, the ICCP team selected small-scale climatic processes at the highest computationally possible resolution. Then, they were able to alleviate the ocean temperature biases, leading to substantial improvements in the representations of ENSO and its response to Global Warming. The results obviously is an increase of CO2 concentrations will weaken the intensity of the ENSO temperature cycle. By also tracing the movement of heat in the coupled atmosphere/ ocean system, the scientists identified the main culprit of the collapse of the ENSO system: Future El Nino events will lose heat to the atmosphere more quickly due to the evaporation of water vapor, which has the tendency to cool the ocean. In addition, the reduced future temperature difference between the eastern and western tropical Pacific will also inhibit the development of temperature extremes during the ENSO cycle.
Even though the year-to-year fluctuations in eastern equatorial Pacific temperatures are likely to weaken with human-induced warming according to this new study, the corresponding changes in El Nino and La Nina-related rainfall extremes will continue to increase due to an intensified hydrological cycle in a warmer climate, as shown in recent studies by scientists from the ICCP and their international collaborators.
Source: Eurekalert