MJO Sensitivity to the Indian Ocean Dipole in the Superparameterized CAM

Friday, 19 December 2014: 8:45 AM
James J Benedict, Lawrence Berkeley National Lab, Davis, CA, United States, Michael S Pritchard, University California Irvine, Carlsbad, CA, United States and William Collins, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
Several key features of the Madden-Julian Oscillation, the dominant mode of intraseasonal (20-100-day) variability in the Tropics, remain poorly understood and inadequately depicted in global climate models. Two primary challenges that impede progress toward more accurate MJO simulation include the representation of multiscale cloud processes and air-sea coupling over a range of space-time scales. To address these challenges, we examine composite MJO behavior in Superparameterized CAM (SP-CAM) simulations using prescribed SST distributions corresponding to neutral and positive Indian Ocean Dipole (IOD) phases. The SP-CAM, which explicitly simulates multiscale cloud interactions by using cloud-resolving models to replace CAM's conventional convective parameterizations, produces realistic intraseasonal variability and is an optimal testbed to investigate the impact of different air-sea background states on the MJO. Previous observational studies demonstrate that the IOD, a zonal shift of SST anomalies in the equatorial Indian Ocean, strongly modulates the MJO and the background atmosphere-ocean state in which it operates. Our SP-CAM results provide new insights into the impact of IOD-modified SST distribution (applied both locally in the Indian Ocean and globally) on the propagation and intensity of the MJO.