Controls on South Pacific Convergence Zone Precipitation and Its Variability

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This project studies the South Pacific Convergence Zone (SPCZ), a large region of cloudiness and rainfall south of the equator extending southeastward from the Western Pacific (the warm pool region) past Fiji and American Samoa to about 30S, 140W. The basic dynamics that produce the SPCZ are still poorly understood, and climate models have difficulty in simulating it correctly (the simulated SPCZ is often too zonally oriented and too close to the equator). This project has two objectives: first, to diagnose multiscale SPCZ circulation-moisture-precipitation relationships evident in observations, reanalysis datasets, and simulations of current generation coupled climate models (from the Coupled Model Intercomparison Project version 5). Second, to develop an SPCZ region air mass trajectory climatology using a parcel dispersion model. A fully 3-dimensional, Lagrangian perspective of the pathways of air masses interacting with the SPCZ will be produced and analyzed, motivated by the idea that variations in the flow of dry air into the SPCZ drives precipitation variability in the region.Aside from its scientific merit, the work is expected to produce results of interest to decision makers and stakeholders in the South Pacific, who would benefit from better understanding of rainfall variability given vulnerability to floods and droughts in the region. The Pacific Centre for Environmental and Sustainable Development (PACE-SD) will serve as a venue for interactions between the PI of this project and South Pacific researchers, forecasters, and decision makers. The project also fosters international collaborations, including collaborations with the Australian Bureau of Meteorology and the participation of a Costa Rican scientist with expertise on Lagrangean trajectory analysis. In addition, the project supports and trains a graduate student, thereby providing for the future work force in this research area.