The northern Australian summer monsoon is also modulated on 30-50 day timescales by the Madden Julian Oscillation (MJO) and as it passes through a given region, it can enhance or suppress convective activity and thus can lead to bursts and breaks in the northern Australian summer monsoon.
The MJO interacts with ENSO. In northern Australia, MJO-forced dry spells are drier in El-Niño years than in La Niña years. During winter, the rainfall response along the Queensland coast co-varies with the MJO phase due to modulation of the SE trade winds. While the spatial domain influenced by the MJO is not as great as for ENSO or the Inter-decadal Pacific Oscillation (IPO), the time domain is much shorter with variation in wind and rainfall expressed at scales of days to weeks rather than seasons and years
Differences in the strength of the summer monsoon circulation over northern Australia associated with ENSO events also result in marked differences in the occurrence of tropical cyclones along the GBR, with reduced activity during El Niño years when the tropical warm pool has receded into the east and enhanced activity during La Niña years.
Although there are several environmental conditions required for tropical cyclone formation, these highly energetic atmospheric disturbances require SST above 26°C. Even though the long-term trend in cyclone activity is unclear, the GBR has been impacted substantially by severe (Category 4,5) tropical cyclones since 2005. The cumulative exposure to cyclones since 1985 has been responsible for approximately half of an observed decline in coral cover across the whole GBR but the impacts have been much more severe in the southern GBR.
The following high-level science questions will guide the Queensland IMOS observing strategy in this area:
- Can we improve understanding and prediction of ENSO dynamics in the Coral Sea?
- Is there a predictable pattern of cyclone clustering, spatially or temporally?
- What is the spatial cyclone risk distribution now and in the future?
- How is the genesis of cyclones and east Coast Lows related to variability in the Coral Sea?
- Do we need to incorporate MJO intra-seasonal variability into predictive models?
- What are the dynamics of riverine flood plumes in the marine receiving waters?
- What are the physical stresses from the passage of cyclones across the continental shelf?
- What is the influence of extreme weather events upon sediment transport?