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
*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)
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.
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.
Tropical activity increases to the north of Australia
A tropical low formed to north of the Solomon Islands on 13 April. Since then, it has slowly moved west over Papua New Guinea and into the Arafura Sea. The tropical low brought an increase in rainfall to southern parts of Papua New Guinea over recent days.
The Australian monsoon trough broke down on 11 April and is not expected to reform until next wet season. Instead of the tropical low being embedded within a monsoon trough, it is part of a weak equatorial Rossby wave that nearly mirrors a "twin" low in the tropical northern hemisphere east of the Philippines.
The tropical low over the Arafura Sea is forecast to continue west while slowly strengthening, and may cause heavy rainfall over Timor Leste in the coming days. Strong winds on the windward side of the ranges and rain bands associated with the tropical low increase the risk of flooding and landslides. A slight increase in rainfall over the northern part of the Northern Territory is also possible.
While the developing tropical low is unlikely to develop into a tropical cyclone, there is still a slight risk. For more information on any tropical cyclones affecting the Australian region, see the Bureau's current tropical cyclones warnings.
Madden-Julian Oscillation signal becomes weak again
After very briefly appearing over the western hemisphere, the Madden-Julian Oscillation (MJO) has become weak or indiscernible during the last week, and did not contribute significantly to tropical weather over the past week.
Most international climate models forecast an MJO signal to emerge over the western Pacific during the week, before moving east into the western hemisphere. However models show a large range of possible strengths from weak or indiscernible to moderately strong. An MJO signal over the western Pacific or western hemisphere at this time of year typically leads to a reduction in convective activity over the Maritime Continent and the tropical eastern Indian Ocean.
For more information on the MJO, see the Bureau's current MJO monitoring information.
El Niño WATCH remains as tropical Pacific sea surface temperatures warm
The El Niño-Southern Oscillation (ENSO) is currently neutral. Tropical Pacific sea surface temperatures (SSTs) have continued to warm since the start of the year. The Southern Oscillation Index (SOI) has been somewhat variable recently. Since the beginning of April, the SOI has returned to negative values, however it is still within neutral levels. Persistent values lower than -7 typically indicate El Niño conditions.
Climate model outlooks suggest the tropical Pacific Ocean will continue to warm over coming months, with most climate models predicting that SSTs in the NINO3.4 region will exceed El Niño thresholds during the second half of 2017. Over the past month, some climate models have reduced the likelihood of El Niño occurring. The Bureau's ENSO Outlook status remains at El Niño WATCH.
See the Bureau’s ENSO Wrap-Up for official El Niño, La Niña and Indian Ocean Dipole information.
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ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
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