Madden-Julian Oscillation (MJO)

The Madden-Julian Oscillation (MJO) is the major fluctuation in tropical weather on weekly to monthly timescales. The MJO can be characterised as an eastward moving 'pulse' of cloud and rainfall near the equator that typically recurs every 30 to 60 days.


MJO phase diagram

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*Note: There are missing satellite observations from 16/3/1978 to 31/12/1978.

The MJO phase diagram illustrates the progression of the MJO through different phases, which generally coincide with locations along the equator around the globe. RMM1 and RMM2 are mathematical methods that combine cloud amount and winds at upper and lower levels of the atmosphere to provide a measure of the strength and location of the MJO. When the index is within the centre circle the MJO is considered weak, meaning it is difficult to discern using the RMM methods. Outside of this circle the index is stronger and will usually move in an anti-clockwise direction as the MJO moves from west to east. For convenience, we define 8 different MJO phases in this diagram.

Average weekly rainfall probabilities

These maps show average weekly rainfall probabilities and expected 850 hPa (approximately 1.5 km above sea level) wind anomalies for each of the 8 MJO phases. Green and blue shading indicates higher than normal rainfall would be expected, while red and orange shading indicates lower than normal rainfall would be expected. The direction and length of the arrows indicate the direction and strength of the wind anomaly. The darker the arrow, the more reliable the information is. The relationship of the MJO with Australian rainfall and winds changes with the season (which can be selected at the top).

Average outgoing longwave radiation (OLR)

Outgoing longwave radiation (OLR) is often used as a way to identify tall, thick, convective rain clouds. These maps show the difference from expected cloudiness based on the position of the MJO. The violet and blue shading indicates higher than normal, active or enhanced tropical weather, while orange shading indicates lower than normal cloud or suppressed conditions. The direction and length of the arrows indicate the direction and strength of the wind anomaly. The darker the arrow, the more reliable the information is. The relationship of the MJO with tropical weather patterns changes with the season (which can be selected above the maps).

Global maps of outgoing longwave radiation (OLR)

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Global maps of outgoing longwave radiation (OLR) highlight regions experiencing more or less cloudiness. The top panel is the total OLR in Watts per square metre (W/m²) and the bottom panel is the anomaly (current minus the 1979-1998 climate average), in W/m². In the bottom panel, negative values (blue shading) represent above normal cloudiness while positive values (brown shading) represent below normal cloudiness.

Regional maps of outgoing longwave radiation (OLR)

Click on the boxes to view a timeseries of cloudiness for that region.
Map of regional cloudiness Dateline Vanuatu Coral Sea Fiji Nauru & Tuvalu Solomon Islands New Guinea Northern Australia Micronesia Malaysia & Indonesia Guam & Marianas Philippines Indochina Southern India & Sri Lanka

Below: OLR totals over the dateline

Click to see full-size graph of OLR totals over the dateline.

The graphs linked to this map show the OLRs for the different regions within the Darwin RSMC area. The horizontal dashed line represents what is normal for that time of year (based on the 1979 to 1998 period). The coloured curve is the 3-day moving average OLR in W/m². Below normal OLR indicates cloudier than normal conditions in this particular area, and is shown in blue shading. Above normal OLR indicates less cloudy conditions and is shown in yellow shading.

Daily averaged OLR anomalies

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Westerly wind anomalies

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Time-longitude plots of daily averaged OLR anomalies (left) and 850 hPa (approximately 1.5 km above sea level) westerly wind anomalies (right) are useful for indicating the movement of the MJO.

How to read the Time-Longitude plots

The vertical axis represents time with the most distant past on the top and becoming more recent as you move down the chart. The Horizontal axis represents longitude.

Eastward movement of a strong MJO event would be seen as a diagonal line of violet (downward from left to right) in the OLR diagram, and a corresponding diagonal line of purple in the wind diagram. These diagonal lines would most likely fall between 60°E and 150°E and they would be repeated nearly every 1 to 2 months.

Northern Australia still waiting for monsoon onset

The Australian monsoon has not yet arrived for the 2018-19 season. A weak trough north of Australia is likely to persist through the coming week. If the trough moves south over northern Australia in the coming days, it will likely bring showers and possibly storms. The trough is not expected to deepen significantly and Australian Monsoon onset is unlikely in the coming days. Monsoon onset normally occurs in late December around Darwin. Later than normal onsets are often associated with El Niño in the Pacific Ocean. Tropical Pacific Ocean sea surface temperatures exceeded El Niño levels at the end of 2018, but have since receded.

Madden-Julian Oscillation to redevelop over Maritime Continent later this week

The past week saw the Madden-Julian Oscillation (MJO) weaken over the eastern Pacific Ocean. The MJO is currently indiscernible. This means it is unlikely the MJO will influence tropical rainfall at the beginning of this week. However, climate models indicate the MJO is likely to redevelop over the Maritime Continent later this week. Under these conditions, at this time of year, parts of Australia's tropical north tend to observe above average rainfall, and typically convection is enhanced over South East Asia. It may also provide a favourable environment for monsoon development.

See the Bureau's current MJO monitoring for more information on the MJO.

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ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.

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