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Climate Change in the Tropical Pacific: Mean Climate and ENSO Variability

PI: Mat Collins
Institution: Met Office Hadley Centre
Additional Investigators: Thomas Toniazzo
Model-predicted changes in the mean climate and variability of the tropical Pacific are highly uncertain. The strong coupling of the atmosphere and the ocean, in concert with the interplay of a large number of physical processes associated with clouds, radiation and the hydrological cycle suggests that the region is tough test for models. The database of new and improved IPCC models presents and opportunity to progress in our understanding and prediction of tropical Pacific climate change.

We propose the steps below in analysing changes in mean climate and variability. Noting the severe limitations on time, we are intentionally modest in our aspirations and plans. We have assembled a focused group of researchers who are both experienced in their examination of the output of climate models and who are enthusiastic and are likely to be able to devote considerable effort to the analysis.

* Analysis of changes in mean climate in the tropical Pacific: A simple examination of seasonal changes in SST, sub-surface ocean temperature change, SAT, precipitation, MSLP and surface winds will be performed. The study will use 20-30 year averages taken from the 1% and scenario experiments differenced with the control. Care will be taken to assess statistical significance based on inter-decadal variability estimated from the control runs. Should time allow, mechanisms for changes will be examined. [Jo]

* Analysis of changes in the amplitude and frequency of ENSO variability: Simple indices of ENSO variability will be extracted (NINO3, NINO3.4, NINO4, SOI etc.). Changes will be assessed by examining time series and using simple measures such as standard deviations, standard deviations partitioned by season to look a phase locking to the annual cycle and power spectra. Extended stabilisation scenarios and long control experiments will be used to assess statistical significance. Composite analysis of individual events will be performed if time allows. [Mat]

* Analysis of changes in the spatial structure of the seasonal cycle and ENSO variability: Changes in the spatial structure of the seasonal cycle of ENSO events will be examined using a combination of EOF and composite analysis. In the first instance, those variables examined in item 1 will be used but further variables will be examined if time allows. A particular focus will be on changes in ENSO teleconnections which are related to impacts. [Thomas]

* Synthesis: Results from the three work items above will be critically examined to highlight commonalities and differences between models and their responses. [All]

Data are required from control, 1%, scenario and stabilisation experiments.

Critical: Monthly mean SST, SAT, MSLP, precipitation, surface winds. Time-averaged sub-surface ocean temperatures.
Useful: Monthly mean sub-surface ocean temperatures and currents, 200hPa geopotential height
Non-critical: Decadal average column moisture, clouds, SW and LW could forcing, boundary-layer moisture flux, mid-level velocity, ocean mixed-layer depth.

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