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.

High temperatures likely as Madden–Julian Oscillation strengthens

Over the past week the Madden–Julian Oscillation (MJO) has strengthened over the Australian longitudes. At this time of year, this means the MJO is likely to increase temperatures across the Top End, and generally, tropical northwest Australia. The MJO is one possible factor contributing to severe heatwave conditions that are likely to affect the Top End region and the Kimberley District in Western Australia this week; see the Bureau's heatwave service for more information http://www.bom.gov.au/australia/heatwave/.

At this time of year, a strong MJO in Australian longitudes can increase the chance of above normal rainfall over southern Queensland and New South Wales. For tropical northern Australia, the MJO influence on rainfall is still about a week away. As the MJO moves east into the western Pacific—as it is forecast to do next week—the chance of rainfall will increase over the Top End and Cape York. The increased chance of rainfall will likely be welcomed by those in the Gulf of Carpentaria regions of the Northern Territory and Queensland that have not yet had any substantial rainfall following the end of the dry-season.

The MJO is usually associated with an increase in tropical convection. This is the case now, but at this time of year the increased activity is still sitting north of the equator and, this week, includes an active monsoon, typhoon Khanun (Odette) and tropical storm Lan. Active monsoon conditions stretch from the Bay of Bengal to the Philippine Sea. Typhoon Khanun (Odette) made landfall over southern China on Monday (16 October) and is expected to move over already-flood-battered northern Vietnam in the coming days. Tropical storm Lan has formed east of the Philippines and is forecast to track north toward southern Japan although it is unclear now if Lan will impact any landmass. This enhanced convection is expected to wane late next week as the MJO moves eastward over the Pacific Ocean.

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

Central Pacific Ocean cools

Sea surface temperatures (SSTs) in the eastern and central equatorial Pacific Ocean have resumed their cooling trend, which had stalled over the past few weeks. Overall, the SST pattern across the equatorial Pacific Ocean is indicative of an ENSO-neutral state, although the climate system is inching closer to a La Niña-like state. In addition to the SST trend, the Southern Oscillation Index (SOI) has bumped up a little over the last few days. The 30-day SOI value to 15 October was +9.5; sustained values greater than +8 are usually indicative of a La Niña state.

All international climate models surveyed by the Bureau suggest further cooling of the tropical Pacific Ocean is likely. Seven of the eight models suggest SSTs will cool to typical La Niña values during late 2017, and six maintain these values for long enough to be classified as a La Niña event. While it is not unprecedented, it is unusual for La Niña to form this late in the year. Historically, La Niña conditions in December have contributed to an early onset of the North Australian monsoon.

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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