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.
Read more: About the MJO
MJO phase diagram
*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.
Download data: RMM Data Postscript: RMM 40 days | RMM 90 days
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).
Print (PDF): JFM | FMA | MAM | AMJ | MJJ | JJA | JAS | ASO | SON | OND | NDJ | DJF
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).
Print (PDF): JFM | FMA | MAM | AMJ | MJJ | JJA | JAS | ASO | SON | OND | NDJ | DJF
Global maps of outgoing longwave radiation (OLR)
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.
Postscript: 1 day | 3 days | 7 days | 3 months | 6 months | 1 year
Regional maps of outgoing longwave radiation (OLR)
Below: 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.
Postscript: Coral Sea Dateline Fiji Guam & Marianas Indochina Malyasia & Indonesia Micronesia Nauru & Tuvalu New Guinea Northern Australia Philippines Solomon Island Southern India & Sri Lanka Vanuatu
Daily averaged OLR anomalies
Westerly wind anomalies
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.
Widespread rainfall for northern Australia this week
Weather models indicate much of northern Australia could see rainfall of between 25 and 100 mm, with some parts of the far northwest of the country likely to see rainfall totals in excess of 150 mm. The predicted rainfall is associated with humid, deep-layer westerly winds over the north of the continent. This wind flow and humidity is likely to combine with surface troughs over the continent to generate significant rainfall, extending from the Kimberley region of Western Australia, across nearly all of the Northern Territory and throughout Queensland.
The current conditions across northern Australia are monsoon-like, based on the humidity and westerly wind flow. However, some characteristics of this environment differ from a typical monsoon, in particular the lack of a well-defined monsoon trough. In addition to widespread rainfall across northern Australia in the coming week, some models predict a low pressure system may develop over the inland Northern Territory or eastern Kimberely region; this could potentially generate locally heavy falls well in excess of 100 mm.
If the technical definition of a monsoon is not met during the current weather situation over northern Australia, it is likely that 2019–20 will observe the latest on record monsoon onset at Darwin—the latest since records commenced in 1957–58 was 25 January, 1972.
Strong Madden–Julian Oscillation over Pacific Ocean
A factor that might reduce the chance of a 'true monsoon' developing over northern Australia is the location of a strong pulse of the Madden–Julian Oscillation (MJO), which has moved well east of Australian longitudes and is approaching the tropical central Pacific Ocean. While the presence of an active MJO is not a necessary component of monsoon development, as the MJO pulse moves further away the environment across the Australian region becomes less favourable for widespread cloudiness and rainfall.
At this time of the year, an MJO pulse over the central Pacific typically enhances rainfall to a moderate degree over northern Queensland, but has an insignificant influence on rainfall patterns across the remainder of northern Australia. If the MJO pulse tracks further east over the tropical eastern Pacific Ocean, northern Australia and the Maritime Continent would typically enter a period of suppressed cloudiness and rainfall. However, the MJO pulse is forecast to weaken steadily before this happens and become indiscernible in about a week.
Read more about the Madden–Julian Oscillation
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ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
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