Cooperative Institute for Research in Environmental Sciences

Special Seminar: Understanding the Tropical Pacific Response to Climate Change: Roadblocks, Progress, and Future Challenges

Special Seminar: Understanding the Tropical Pacific Response to Climate Change: Roadblocks, Progress, and Future Challenges

sam.jpgSam Stevenson is a National Science Foundation Ocean Sciences Postdoctoral Fellow in the Oceanography Department at the University of Hawaii at Manoa (UH). Her primary research interests are tropical Pacific Ocean dynamics, atmosphere/ocean interaction, paleoclimate reconstruction, and impacts of climate variability on natural resources. She was a postdoctoral fellow in the International Pacific Research Center at UH from January 2012 to July 2013, working on the effects of tropical ocean variability on decadal 'megadroughts' in North America. Prior to joining the University of Hawaii, she received her PhD from the University of Colorado at Boulder in atmospheric and oceanic sciences, where she was funded by a NASA Earth and Space Sciences Fellowship to study the response of the El Nino/Southern Oscillation (ENSO) to climate change as simulated by coupled climate models. Sam is currently developing an isotope-enabled version of the Regional Ocean Modeling System (ROMS), to allow direct estimation of the effects of ENSO on the isotopic composition of tropical Pacific corals and aid in validating ENSO physics in coupled models. She is always excited to meet new potential collaborators and would welcome discussions with any interested scientists.

Abstract: Interannual variability in the tropical Pacific strongly influences both ocean ecosystems and worldwide weather patterns: this takes place mainly through the El Nino/Southern Oscillation (ENSO), an irregular coupled atmosphere/ocean phenomenon which is expected to be extremely sensitive to anthropogenic climate change. Model projections of 21st century ENSO strength vary dramatically, but naturally occurring modulations in ENSO strength make it difficult to completely explain the physical causes of inter-model differences. In this seminar, I will address two methods for gaining better insight into the ENSO dynamical response to climate change: idealized model experiments and comparison with paleoclimate proxy data. Using 1000-year 'control' experiments with the NCAR Community Climate System Model at a variety of fixed atmospheric CO2 concentrations, it can be seen that the interaction between ENSO and the annual cycle takes place primarily via climatological changes in the trade winds, rather than wave reflection off the western boundary of the Pacific Basin. This suggests that improvements to model representation of seasonal winds are an important target for correctly capturing El Nino evolution. Proxy records of ENSO during past epochs can potentially provide a valuable check on model results like these, and the oxygen isotopic composition of tropical coral skeletons are an ideal recorder of past ENSO variability. However, an error analysis shows that in the absence of better conversions between climate variables (temperature/salinity/currents) and seawater oxygen isotopic composition, obtaining sufficiently accurate variance estimates is not possible. Corals are able to capture the observed late-20th century weakening of the Walker circulation with reasonable accuracy, and provide high fidelity longer-term Walker reconstructions as well. More quantitative ENSO studies will require a fully isotope-enabled ocean simulation at multiple spatial scales, which is currently being developed for use during future research.


CIRES Auditorium - CIRES - University of Colorado