SSC 9 Process Study Review of Pacific Implementation Panel's proposed process studies.

Team reviewers: Dr. Isaac Held and Dr. Detlef Stammer

Comments of the SSC on the report of the U. S. Pacific Basin Panel
presented by William Kessler 

The report was consistent with the existing Pacific Basin Implementation Plan and, in particular, the planning for PBECS. Existing activity is focused on the EPIC process study that is underway. The SSC remains very supportive of this program. It addresses basic problems with regard to the climate of the Eastern Tropical Pacific, an area that has proven very difficult for existing climate models, with errors in this region often radiating out to contaminate the entire Pacific ocean and Pan American simulation. The committee is also very supportive of the planning for future phases of the EPIC program, including coordination with VAMOS and planned studies in the Pan-American region. 

Other process studies under consideration include several that track the subtropical/tropical information pathways in the Pacific that may exert a strong control on the modulation of ENSO and interdecadal variability in the Pacific. These include process studies focusing on the subduction, boundary currents, and equatorial upwelling branches of this circulation. In light of the fact that the panel did not present any prioritization of these studies, the SSC suggests that the panel consider using the relevance of a process study for improving interannual prediction models, as well as models of interdecadal variability, to help in developing priorities in the Pacific. From this perspective, for example, studies of mixing processes that effect equatorial upwelling might take precedence over subduction studies in the subtropics.  

More generally, the problems that current models have in simulating the mean climate and the seasonal and ENSO cycles, must also help set priorities for process studies, rather than having the interdecadal variability problem being the sole determining factor. We suggest that the Pacific panel consider priorities and time lines from this more general perspective at its next meeting. 

Also, in setting timetables and priorities, studies primarily focused on technology development need to be distinguished from process studies to be conducted with proven technologies. This is of particular relevance to the proposed western boundary current activities in PBECS, and the panel may wish to highlight the importance of such technology development so as to avoid serious holes in the program in the coming decade. 

The presentation focused on studies motivated by hypotheses in which the dynamics of low frequency climatic variability is controlled from the tropics, with little discussion of extratropical sources of variability. With the KESS program having received some funding, there is evidently less need for CLIVAR to confront the issue of the relative importance of midlatitude and tropical/subtropical dynamics in its attempts at prioritization. On the other hand, the recent 1000 year coupled integration of the CCSM with a 1 degree oceanic component exhibits very interesting Pacific extratropical variability, with a 17 year time scale, with a clear extratropical source. The panel may wish to evaluate whether there is new information about possible sources of interdecadal variability from this important integration, despite the serious model deficiencies in the tropical Pacific. 

There was also some concern expressed that the panel does not appear to have a focus on anthropogenic climate change issues. For example, there has been some discussion recently of the possibility that changing aerosol loading over the Indian and Western Pacific oceans could influence the statistics of ENSO. The panel may wish to consider if any hypotheses of this type are sufficiently interesting and important to alter priorities in the Pacific basin. As another example, cloud feedbacks over the extratropical oceans, especially the Pacific, are very important in determining the total cloud feedback and climate sensitivity in climate models, yet this important issue does not seem to be a concern of the panel. 

Other topics discussed at the meeting that impact planning in the Pacific include the ARGO float program and data assimilation for CLIVAR. Alongside an ENSO observing system, these efforts provide the central core of any PBECS-like effort and the panel and the SSC must work to assure that they are adequately supported.