RAPID: Predictability of Atmospheric Teleconnections in Initialized Decadal Forecasts

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

This is one of 16 Rapid Response (RAPID) projects funded as the result of a Dear Colleague Letter (NSF 11-006) encouraging diagnostic analyses of climate model simulations prepared for the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5). Research conducted in these projects is expected to lead to more detailed model intercomparisons, better understanding of robust model behaviors, and better understanding and quantification of uncertainty in future climate simulations. This project considers the potential predictability of decadal climate variabiality in hindcast simulations prepared for the AR5. These 10-year hindcast experiments are performed with models in which ocean properties, principally sea surface temperature (SST), are initialized using observations every five years starting in 1960, with additional 30-year hindcasts starting in 1960, 1980, and 2005 (actually a forecast in the later years). The hindcast experiments are a novel feature in AR5 with no counterpart in the Fourth Assessment Report, and they are designed to determine the extent to which decadal-scale climate changes of relevance to policy makers are predictable given the state of the ocean and the beginning of the forecast period. Research conducted in this project assess the skill of atmospheric teleconnections forced by SST anomalies in the Pacific and Indian Oceans that are predictable on decadal timescales in the hindcast ensemble. Skill is assessed by comparisons between observed and hindcasted patterns of rainfall, air temperature, and circulation anomalies. Additional comparisons are performed with uninitialized simulations of the 20th century forced by greenhouse gas increases and other external forcings (e.g. volcanos, aerosols, and solar variability), so that the extent to which predictability depends on external forcing rather than initialized internal variability can be assessed. The broader impact of the project lies in its support of the IPCC AR5, which is intended to provide information on climate change and its consequences to decision makers worldwide. Successful decadal climate forecasts could be of value to to resource managers developing informed adaptation strategies, but first the degree to which such forecasts are achievable must be determined.