Ocean Impacts on Australian Interannual to Decadal Precipitation Variability

Zachary Johnson,Jing-Jia Luo,Takashi Mochizuki,Yoshimitsu Chikamoto

doi:10.3390/cli6030061

Abstract

In Australia, successful seasonal predictions of wet and dry conditions are achieved by utilizing the remote impact of sea surface temperature (SST) variability in tropical oceans, particularly the Pacific Ocean, on the seasonal timescale. Beyond seasonal timescales, however, it is still unclear which processes and oceans contribute to interannual-to-decadal wet/dry conditions in Australia. This research examines the interannual-to-decadal relationship between global SST anomalies (SSTAs) and Australian wet/dry variability by analyzing observational data and global climate model experiments conducted with the NCAR Community Earth System Model (CESM) and the Model for Interdisciplinary Research on Climate (MIROC). A 10-member ensemble simulation suite for 1960–2015 (CESM) and 1950–2010 (MIROC) is conducted by assimilating the observed three-dimensional ocean temperature and salinity anomalies into fully coupled global climate models. In both observational analyses and ocean assimilation experiments, the most dominant annual mean precipitation variability shows a clear relationship with SSTAs in the tropical Pacific and the Atlantic. Our partial ocean assimilation experiment, in which the ocean component of the CESM and MIROC are assimilated by the observed ocean temperature and salinity anomalies in the equatorial Pacific only, shows that the tropical Pacific SST variability is the main driver of Australian precipitation variability on the interannual-to-decadal timescales. However, our additional partial ocean assimilation experiment, in which the climate models incorporate the observed anomalies solely in the Atlantic ocean, demonstrates that the Atlantic Ocean can also affect Australian precipitation variability on the interannual-to-decadal timescale through changes in tropical Pacific SSTAs and the modulation of the global Walker circulation. Our results suggest that about a half of Australian interannual-to-decadal precipitation variability originates from the Atlantic Ocean.

Highlights

Australia experiences prolonged or intermittent severe droughts that devastate local economies, put significant strain on the agriculture industry and contribute to wildfires [1,2]
We examine Australian the interannual-to-decadal precipitation variability originating from the ocean using two global climate models: the Community Earth System Model (CESM) and the Model for Interdisciplinary Research on Climate (MIROC)
The first singular value decomposition (SVD) mode in both the CESM and MIROC versus the observations explained most of the variance of the Australian precipitation variability through the square covariance fraction (SCF), the percentage of square covariance between the two fields explained in the leading SVD

Summary

Introduction

Australia experiences prolonged or intermittent severe droughts that devastate local economies, put significant strain on the agriculture industry and contribute to wildfires [1,2]. The Millennium Drought (1997–2010) impacted the populated areas of Australia, including cities like Melbourne, Brisbane, and Sydney causing severe water restrictions and a ban on outdoor water use [3]. Climate 2018, 6, 61 being surrounded by oceans on all sides, many studies have looked into the ocean’s impact on climate extremes in Australia, as introduced below. The El Niño Southern Oscillation (ENSO) interactions between large-scale sea surface temperature (SST) anomalies (SSTAs) and atmospheric circulation have a significant impact on drought conditions around the world, including Australia [7]. Previous studies have shown the linkage of El Niño to some of the major droughts in Australia [2,8,9,10,11]. Many studies have shown ENSO to affect a significant portion of Australian precipitation variability

Results

Discussion

Conclusion