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.
Australian monsoon takes a break
The monsoonal flow which affected Australia, and contributed to the formation of tropical cyclone Stan during the past fortnight, retreated in recent days, but is expected to redevelop over the Coral Sea this week. Widespread heavy rainfall which had affected parts of northern Australia last week has since become isolated, apart from parts of Queensland which have received some significant falls in recent days. Weather models suggest that the monsoon trough will not reform over continental Australia in the coming week, with below average rainfall expected.
Madden–Julian Oscillation present over the Maritime Continent
This past week, a weak to moderate strength Madden–Julian Oscillation (MJO) moved slowly eastwards into the Maritime Continent region. Climate models indicate the MJO will continue its eastward progression over the Maritime Continent in the coming days, entering the western Tropical Pacific over the weekend at similar strength.
Usually, when a MJO crosses the Maritime Continent at this time of year, tropical activity over northern Australia increases. However, the strong El Niño currently in the Pacific Ocean may be counteracting the influence of the MJO on this occasion. Local-scale factors are also expected to contribute to reduced tropical activity over northern Australia, by focussing convective activity over waters to the east and west of the Australian mainland. El Niño typically reduces tropical activity over Australia and weather models indicate below average rainfall is most likely over northern Australia in the coming weeks.
See the Bureau's MJO Monitoring for current MJO information.
El Niño gradually declining
El Niño remains strong, but continues its gradual decline. Climate models suggest a return to neutral levels in the second quarter of 2016.
Close to the equator, the surface of the Pacific Ocean has cooled by 0.5 °C since the El Niño peaked in late 2015. Below the ocean surface, cooler than average waters now extend into the central tropical Pacific Ocean. The Southern Oscillation Index (SOI) has eased in magnitude in the last week, after dipping to strongly negative values in recent weeks. During Australia's northern wet season, it is not unusual to see big fluctuations in the SOI, due to the passage of tropical systems, and hence its value is not always representative of the overall El Niño-Southern Oscillation state.
Based on the 26 El Niño events since 1900, around 50% have been followed by a neutral year, and 40% have been followed by La Niña. Models suggest the neutral state is the most likely for the second half of 2016, followed by La Niña, with a repeat El Niño assessed as very unlikely.
See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.
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ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
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