The IOD and ENSO asymmetric teleconnection pathway to Australian rainfall
Abstract
El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are known to influence Australian climate, but the manner in which this influence is exerted has not been fully understood. This is particularly so in austral spring, when a strong relationship exists between the IOD and ENSO. ENSO is known to influence global climate via tropical and extratropical responses to sea surface temperature (SST) anomalies. These anomalies induce an equatorially trapped baroclinic response in the atmosphere, generating anomalous vertical motions in the tropical Pacific. These vertical motions cause convection and pressure responses, manifested as the Southern Oscillation. The convection leads to anomalous divergence in the upper troposphere, which acts as a source of Rossby waves. These waves are equivalent-barotropic and propagate into the higher latitudes over the Pacific Ocean and South America, carrying the ENSO signal to remote regions downstream. Southern Australia is situated in the upstream, so how does ENSO exert an influence? We show that the IOD also induces Rossby waves that propagate into higher latitudes with an anomaly centre affecting southern Australia, and that the impact of ENSO on southern Australia is conducted through its coherence with the IOD. We further show that a strong asymmetry exists within this teleconnection, with a stronger impact during the positive phase of the IOD and ENSO. The asymmetry is mainly driven through the IOD, with a greater convection anomaly and wave train response occurring during positive IOD (pIOD) events than during negative IOD (nIOD) events. This is linked with an asymmetry in the ENSO-IOD relationship, with El Niño-pIOD events being far more coherent than La Niña-nIOD events, and the positive IOD skewness. The inherent positive skewness of the IOD occurs despite a greater damping on the IODE negative SST anomalies. Our result suggests that the severity of the recent drought over southern Australia is at least in part attributable to the high frequency of pIOD events.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMOS43G..02V
- Keywords:
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- 3305 ATMOSPHERIC PROCESSES / Climate change and variability;
- 3339 ATMOSPHERIC PROCESSES / Ocean/atmosphere interactions;
- 4522 OCEANOGRAPHY: PHYSICAL / ENSO