Climate System Dynamics on Long Time Scales

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AbstractATM-0082131Ghil, MichaelUniversity of California, Los AngelesThe research bears on the problems of internal and external causes of climatic change. It emphasizes the role of the atmosphere in climate variability from months to years, of the oceans in variability from years to decades, and of the coupled ocean-atmosphere-ice-sheet system from decades to millennia. The methodology uses tools from fluid dynamics, dynamical systems theory, scientific computing and nonparametric statistics. The dynamical tools will be applied to a hierarchy of atmospheric, oceanic and coupled models. These models range from the simplest models with a small number of variables, such as box models of the ocean, to fully coupled general circulation models (GCMs).The PIs will study coupling of climate subsystems across timescales using various mathematical and statistical techniques. On the intraseasonal time scale of 10-100 days, the PIs will consider two complementary descriptions of low-frequency atmospheric variability, episodic and periodic, i.e. multiple weather regimes and intraseasonal oscillations. On the subannual-to-interannual time scale of 100 days to 10 or more years, the research emphasizes internal variability of the mid-latitude oceans' wind-driven circulation. This circulation is studied for prescribed time-constant and seasonally varying wind stress acting on ocean-only models, as well as for fully coupled ocean-atmosphere models. On time scales of decades-to-centuries and longer, the PIs will use comprehensive coupled models such as CSM and IPSL. The simulations will be analyzed and compared with instrumental and paleo-records to determine and describe the relative importance of natural variability and anthropogenic climate change on these time scales. The work is important because it will increase understanding of climate variability across various time scales.