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 lows to bring rain to northern Australia
A monsoon trough currently extends across far northern Australia, between a tropical low over the Timor Sea and a second tropical low over the northern Coral Sea (see chart here). Widespread rainfall totals of more than 50 mm were observed in the northern Kimberley region of Western Australia, the Top End of the Northern Territory and far northern Queensland in the past week.
The monsoon trough is expected to remain in a similar location but weaken later in the week, reducing widespread rainfall over much of northern Australia. The focus of rainfall is expected to move to the vicinity of the tropical lows on either side of the continent. Rainfall impacts for the Australian mainland will heavily depend on the movement and degree of development of the lows. The tropical low over the Timor Sea is currently rated by the Bureau to have a high (>50%) chance to attain tropical cyclone intensity from Thursday this week, and may cross the Pilbara coast of Western Australia on Friday. The Coral Sea low is not expected to develop significantly in the next few days, but may strengthen towards the end of the week. Weather models also indicate that another tropical low, near the Cocos Islands in the Indian Ocean, may strengthen and develop into a tropical cyclone towards the end of this week.
For the latest update on tropical cyclones in the Australian region, go to the Bureau’s current tropical cyclones information.
Madden-Julian Oscillation remains weak
The Madden-Julian Oscillation (MJO) has been weak or indiscernible for most of the last week. Nearly all climate models surveyed by the Bureau predict the MJO signal will remain weak or indiscernible for the coming seven days. Tropical influences other than the MJO are also predicted to be weak during this time and have little effect on rainfall and cloud patterns over northern Australia and the Maritime Continent. In the coming week, the monsoon trough and associated tropical lows will be the primary influence on local wind and rainfall over tropical Australia.
For more information on the MJO, see the Bureau's current MJO monitoring information.
El Niño WATCH in place
Most atmospheric and oceanic indicators of the El Niño-Southern Oscillation (ENSO) are currently neutral. However, sea surface temperatures (SSTs) in the eastern tropical Pacific Ocean have warmed since the start of the year, and climate model outlooks suggest further warming of the tropical Pacific Ocean will occur in the coming months. These changes mean the likelihood of El Niño forming in 2017 has risen. As a result, the Bureau's ENSO Outlook status is now at El Niño WATCH.
If El Niño forms in the tropical Pacific Ocean, it is not likely to become established until the second half of 2017. However, waters more than 2°C above normal have been observed in the far eastern Pacific, along the South American coast. This ‘coastal El Niño’ effect contributed to heavy rainfall and widespread flooding in Peru, causing multiple fatalities in recent days.
For northern Australia, overnight temperatures are typically cooler than usual during the dry season months of May to September in El Niño years.
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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