SGER: Understanding Tropical-Subtropical Forcing and Predictability of Long-Term North American Drought in Coupled Models

University Of Maryland, College Park, College Park MD

Investigators

Abstract

This is a grant under a Climate Variability and Predictability (CLIVAR) Program pilot project called DRICOMP, for the Drought in Coupled Models Project, which focuses on making initial explorations into the mechanisms of drought as they are represented in the output of global climate models and on attempting to assess the reliability of these models in simulating drought. A growing body of literature indicates that El Nino - Southern Oscillation (ENSO) is a fundamental driver of global drought variability and that La Nina-like conditions play a key role in the circulation anomalies leading to North American drought. An important yet poorly understood process with strong implications for understanding and predicting long-term North American drought is how the coupled ocean-atmosphere system maintains persistent cool conditions in the equatorial Pacific Ocean. This project will make an initial attempt to answer four questions: (1) how are persistent cool episodes in the equatorial Pacific Ocean represented in state-of-the-art coupled climate models, (2) through what physical mechanisms do such conditions lead to persistent North American drought, (3) how can an understanding of such questions serve to extend the predictive lead time for long-term North American drought, and (4) how do the mechanisms and prospects for predictability depend on the essence of a climate in transition? A two-pronged approach will be taken: first, a selection of coupled models as determined from the details of their ocean component will be used to characterize and explain the representation of persistent cool equatorial Pacific conditions; secondly, long-term North American drought variability (in terms of the Palmer drought severity index - PDSI) and its relationships with the equatorial Pacific, including how that appears to depend on anthropogenic forcing, will be analyzed in the full suite of Climate Model Intercomparison Project 3 (CMIP3) climate models. The problem of predictability at extended lead times will be explored by ascertaining how the remote forcing field itself (i.e., low-frequency evolution of equatorial Pacific SST) is modulated, and the coherence between that signal and the PDSI. Broader impacts of these are in its potential contribution to improved prediction of North American drought at extended leads and in supporting the principal investigator, who is a graduate student.