The ability of HiGEM to simulate known
drivers of Queensland rainfall variability
5.1 The El Nino–Southern Oscillation
Shaffrey et al. (2009) and Roberts et al. (2009) contain a detailed analysis of the spatial and temporal pattern of the
ENSO in HiGEM, which will not be repeated here. Instead, this report focuses on the fidelity of the teleconnection
in HiGEM between the ENSO and Queensland rainfall.
HiGEM successfully simulates a negative correlation of approximately the observed magnitude (from SILO and
HadISST; Fig. 5a) between May–April annual-mean Niño 4 SST anomalies and May–April annual-mean rainfall
across Queensland (Fig. 5b). Similar to observations (e.g., Murphy and Ribbe, 2004; Hendon et al., 2007), HiGEM
produces a stronger correlation between Queensland rainfall and the central Pacific Niño 4 index than the eastern
Pacific Niño 3 (not shown). The May–April annual mean is used to limit mixing phases of the ENSO in a single
annual period, as the ENSO often changes sign during austral autumn. The HiGEM correlation is weaker than
observed across northern Australia, which is likely due to low correlation magnitudes in HiGEM during MAM
(Fig. 5h) relative to SILO/HadISST (Fig. 5d). Klingaman (2012b) found that the third MAM EOT of SILO rainfall,
which described coherent rainfall variations in the Cape York Peninsula and across northern Australia, was
associated with the impact of the ENSO on the strength of the late-season monsoon. The weak correlations in
HiGEM in MAM may indicate that these ENSO–late-monsoon interactions are missing or suppressed in HiGEM;
section 5 explores this further. In DJF (Figs. 5c and 5g), JJA (Figs. 5e and 5i) and SON (Figs. 5f and 5j), the
strength and spatial pattern of the Niño 4–Queensland rainfall correlations in HiGEM closely resemble those in
observations, although the HiGEM correlation is occasionally too strong. With the exception of the Cape York
Peninsula, the ENSO in HiGEM explains a similar fraction of variance (approximately 30 per cent) in Queensland
rainfall as the observed ENSO.