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.

No signs of Australian Monsoon onset

There has been no sign of a significant southern hemisphere monsoon trough near the Australian region for the 2017-18 northern wet season to date. In the last week there has been limited monsoon trough development in the far western Indian Ocean near Madagascar, but none in the eastern Indian Ocean near Indonesia, which can be a pre-cursor to monsoon onset over northern Australia.

The broadscale climate pattern across the equatorial Indian and western Pacific oceans, where a double near-equatorial trough pattern is still apparent (see wind analysis chart), is still unfavourable for monsoon trough development in the Australian region. While a trough remains established in the northern hemisphere, cross-equatorial flow emanating from the South China Sea is unlikely to be of sufficient strength to activate a significant monsoon trough in the Australian region. It's unlikely the Madden–Julian Oscillation (MJO) will contribute to monsoon onset in the next fortnight.

Madden–Julian Oscillation over the Pacific Ocean

The Madden–Julian Oscillation (MJO) has maintained a steady eastwards progression during the last fortnight and currently lies over the central Pacific Ocean at moderate strength. Most climate models predict the MJO signal will slow down and weaken in the coming week. Some of these models suggest the signal will remain over the central or eastern Pacific Ocean, while others forecast it to weaken and become indiscernible. In either scenario, tropical rainfall patterns are not likely to be enhanced significantly across northern Australia and the Maritime Continent.

As the MJO moves over the central or eastern Pacific Ocean at this time of the year, the focus for enhanced convection and rainfall is most likely to be across the southwest Pacific region. Across the northern Australia and Maritime Continent region, weather is likely to be close to the climatological 'average' and influenced by regional weather patterns rather than broadscale climate drivers. However, predictions from several models indicate non-MJO tropical-wave activity may increase rainfall across parts of the Maritime Continent in the coming week.

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

La Niña in tropical Pacific Ocean

The Bureau's ENSO Outlook has been raised to LA NIÑA status, indicating that the tropical Pacific has reached La Niña levels. Climate models suggest this La Niña will be weak and short-lived, persisting until early southern autumn 2018. Most oceanic and atmospheric indicators show clear signs of La Niña. These include sea-surface temperature (SST) anomalies over the central tropical Pacific Ocean, the Southern Oscillation Index and cloudiness near the Date Line.

La Niña is typically associated with above-average rainfall during the northern wet season, average or above-average tropical cyclone numbers across the Australian region and an earlier onset of the Australian monsoon. The effects associated with the current late-developing and relatively weak La Niña are not expected to be typical. Near-average SSTs are expected to persist across waters to the north and west of northern Australia (atypical during La Niña), and current rainfall outlooks do not indicate above-average rainfall for December to February for northern Australia.

See the Bureau's current ENSO Wrap-Up for more information.

 

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

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