E9.6 Predicting the Rainfall over the Indonesian-Australian Continent

Abstract

Barrier layers in the tropics trap heat in a shallow and stable near-surface layer limiting entrainment of cooler water from below and increasing sea surface temperature (SST); warmer SSTs enhance convection and possibly rainfall. In this study, we test the hypothesis that the thickness of salt-stratified barrier layers in the southeastern Indian Ocean is significantly related to rainfall over the Indonesian-Australian Continent (IAC). Our study area focuses on two regions: 1) west of Sumatra where observations show a local maximum of barrier layer thickness (BLT) in December-January-February; and 2) south-west of Java where we investigate the effect of the barrier layer on the upwelling processes typifying this region. Using the high resolution (0.25° atmosphere/land and 0.1° ocean/sea ice) fully coupled pre-industrial Energy Exascale Earth System Model version 0.1 (E3SMv0.1) simulation, we first assess regional model fidelity and then analyze relationships between BLT and SST, and BLT with outgoing long-wave radiation at the top of the atmosphere (OLR). Mixed layer depth (MLD) is also correlated with SST and OLR. BLT-SST and MLD-SST relationships are mostly semi-annual whereas BLT-OLR correlations are consistently negative through the entire year (thicker BLT results in stronger OLR negative anomalies and stronger convection). Using partial correlations, we assess the skill of BLT, mixed layer depth (MLD), isothermal layer depth (ILD), SST, sea surface salinity (SSS) in these two regions, as well as El Niño 3.4 and Indian Ocean dipole (IOD) indices as predictors of the IAC rainfall. Key results indicate that austral summer BLT in the west Sumatra region is the best predictor of IAC rainfall particularly over northeastern Australia and New Guinea, while austral fall MLD is the best predictor of rainfall over most of Australia in austral winter.