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Monsoon pulse

Updated: Oct 14, 2023

You will see me write a lot about the monsoon pulse during the wet season. What is it? Well, it is where the most cloud is over the equator at any particular time. The cloud is produced on what is called the monsoon trough, as a low-pressure trough, it sends warm humid air up into the sky and as it cools it forms cloud and then rain. The pulse is where the monsoon trough is at it's most active.


The equator is divided into phases, which are regions where we can plot the location of the monsoon pulse. This plot goes onto a chart called the Madden-Julian Oscillation or MJO. The phases are labelled 1 through 8 and shown in anti-clockwise order. The location is plotted around that circle, the distance from the circle is the distance of the monsoon trough relative to the equator. As the plot moves towards the outer regions of the phase, this means the monsoon trough is reaching further South.


Looking at the plot above it is a little complex but the pink part is the forecast for the MJO towards the end of October 2023. In this we can see it heading away from the inner circle meaning the trough will drop a little South, probably close to Thursday Island and then we should see a tropical low North of the Gulf of Carpentaria to Solomon Sea between PNG and the Solomon Islands.


The areas we are concerned with in Australia are 5,6 or 7. The approximate rainfall we see from these pulses is represented below, and will be weaker in an El Nino event and stronger in a La Nina event.



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