How Multiscale Interactions Affect Large Tropical Convection Systems
The Madden-Julian oscillation (MJO)—a continent-sized cyclic pattern of rainy and dry weather moving slowly eastward across the tropical Indian and Pacific Oceans—is strongly affected by seasonal and year-to-year sea-surface temperature (SST) variations, yet MJO drivers and variability remain a subject of uncertainty and ongoing research. A recent Department of Energy-supported study explored how MJO is impacted by atmospheric interactions across a wide range of space-time scales. The superparameterized Community Atmosphere Model (SPCAM), a modified climate model using a sophisticated approach to explicitly simulate tropical convective clouds fundamental to MJO, is used to explore MJO response to anomalies in seasonal SST distributions associated with the Indian Ocean dipole (IOD). The simulations demonstrate critical new findings: (1) SPCAM reproduces the observed disruption on the MJO signal as it crosses Indonesia, (2) MJO disruption is linked to circulation and moisture anomalies on seasonal time scales as well as variations driven by atmospheric eddies that are active on weekly time scales, and (3) SST perturbations in the equatorial Pacific Ocean, not the Indian Ocean, are the dominant contributor to MJO disruption over Indonesia. Interestingly, IOD-driven MJO weakening does not occur due to local dynamics over the Indian Ocean as might be expected. Rather, the MJO disruption dynamics are traced back to Central Pacific SST perturbations that coexist with the IOD event and seem to be indirectly associated with an El Niño-IOD relationship. This finding has profound implications for understanding MJO’s future based on the future pattern of SSTs.
Benedict, J. J., M. S. Pritchard, and W. D. Collins. 2015. “Sensitivity of MJO Propagation to a Robust Positive Indian Ocean Dipole Event in the Superparameterized CAM,” Journal of Advances in Modeling Earth Systems 7(4), 1901-17. DOI: 10.1002/2015MS000530.