For those unfamiliar with the Madden-Julian Oscillation (MJO) or how to interpret it, I’ve previously detailed this in my blogs, including the Monthly, Long Range, and Pulse blogs.
Here's a brief explanation:
The MJO is often visualised on a circular plot, with movement shown in an anti-clockwise direction. Each point on the plot corresponds to a specific day and represents the most active area of the monsoon. This activity is determined by the amount of cloud generated by the monsoon trough. The monsoon trough is a little e of low pressure where air is sucked in, and pushed up. As it rises, it condenses and creates cloud. It is shown on a synoptic chart as a special trough showing dot dash dot rather than just dashes. It is super heated and can generate tropical cyclones. You do not need the monsoon trough for a Cyclone, but they have a high chance of forming on the monsoon trough.
From a satellite the monsoon trough looks like a long line of cloud with a gap between the cloud.
The motion of the MJO resembles a pulse that travels from east to west along the equator. Hence, the anti-clockwise movement on the plot reflects this east-to-west propagation.
This pulse indicates regions where cyclones are most likely to form. Although not all cyclones occur within this pulse, most tend to do so on a given day.
The plot is divided into eight segments or phases, with each phase corresponding to a specific region. Queensland (QLD) falls under phase 6 but can also be affected when the pulse is in phases 5 or 7. Generally, phase 6 signifies the Gulf of Carpentaria to the Coral Sea region.
The position of the plot relative to the circle’s centre provides information about the clarity and intensity of the pulse. When the plot is closer to the centre, the pulse is less defined, whereas the farther it is, the stronger and more pronounced the pulse becomes.
It generally takes a week per phase, so you can pretty much forecast each pulse a long way ahead, and we did this to the day this year. We use the SOI and a few other clues to fine tune the actual day, but it's not rocket science.
For example, the SOI measures when low pressure is lower near Darwin or near Tahiti, this links in with the MJO. When the line moves up into the positives, the pressure near Darwin is less than Tahiti and visa versa. That means when it is really up in the positives, during the wet season, the monsoon trough is likely to be there. It's like a second plot point for the monsoon.
Then you can look at the satellite and see what systems are common, and tell what you are likely to see and where when the pulse comes around. Currently the air is flowing in a curve NW of WA, and to a lesser extent the Gulf. So two possible lows, one more likely to be a cyclone. The other is a convergence of air on a trough, that is likely to turn into a monsoon trough, heavy rain.
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