Causes and Predictability of Multi-year Variability of Northern Australia Wet-season Rainfall   — Australian Meteorological and Oceanographic Society

Causes and Predictability of Multi-year Variability of Northern Australia Wet-season Rainfall   (#202)

Sur Sharmila 1 2 , Harry H Hendon 2 , Yu Kosaka 3
  1. Centre for Applied Climate Sciences, University of Southern Queensland, Toowoomba, QLD, Australia
  2. Bureau of Meteorology, Melbourne, VIC, Australia
  3. The University of Tokyo, Tokyo, Japan

The rainfall over Northern Australia (NA, north of 26°S) during the northern wet season (October to April) shows a large variation on seasonal-to-multiyear timescales, which has profound impacts on many agricultural sectors. Beyond seasonal timescales, however, the underlying source of multi-year wet/dry conditions over the NA is still unclear. Here, we investigate the nature of multi-year rainfall variability and its potential predictability during 1900-present. The multi-year rainfall variations are found to exhibit coherence across the western and eastern halves of the NA. Across the east, wet conditions are associated with a La Niña-like sea-surface temperature (SST) pattern in the Pacific, while dry conditions are associated with an El Niño Modoki-like SST pattern. These SST patterns are meridionally broader than those typically associated with a La Niña or El Niño event and bear a strong resemblance to Inter-decadal Pacific Oscillations (IPO). Across the west, wet conditions show similar association with a La Niña-like SST pattern, while dry conditions show a very weak association with tropical SST. This implies limited predictability of multi-year episodes of dry conditions in the west, whereas wet conditions are predictable to the degree that the cold phase of the IPO is predictable.

The role of tropical-Pacific SST variability in driving multi-year NA rainfall variation is further explored with the Pacific Ocean-Global Atmosphere (POGA) pacemaker experiments from the GFDL-CM2.1 coupled model. The fully-coupled model is run globally but the SST anomalies in the equatorial eastern Pacific are restored to follow observed SST for the period 1900-2014. The ongoing work is untangling the potential contributions of tropical-Pacific SST for generating multi-year variations of NA rainfall, along with analysis of the pre-industrial control and the historical runs to provide more insight into the role of external forcing and internal noise for generating such multi-year rainfall variability.

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