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.
Weekly Tropical Climate Note
Issued 21 April 2015
Northern Australia transitions into dry season
While the official end of the northern wet season is 30 April, recent weather patterns across tropical Australia are more reminiscent of the dry season. A strong high pressure system currently located over the Great Australian Bight has pushed a surge of dry southerly air northwards, reducing humidty across much of Australia's tropical north.
Recent rainfall over the Kimberley region and central Australia resulted from the development of a cloudband which transported moist, tropical air from the warm Indian Ocean over central parts of the continent over the weekend. Northwest cloudbands are usually a weather feature of late autumn and early winter.
The near-equatorial trough has now begun its steady annual northward migration and is not expected to impact on the Australian continent again this wet season. The onset of the South East Asian and Indian monsoons will be monitored over the coming months. India has already seen above average rainfall this year even before the onset of the Indian Monsoon.
A weak Madden-Julian Oscillation (MJO), currently located over the central Indian Ocean, is forecast to weaken further and remain weak for the coming fortnight. Hence, the MJO is unlikely to influence tropical convection in the coming weeks. See the Bureau's MJO Monitoring for more information.
At least 70% chance of El Niño in 2015
Recent warming of the tropical Pacific Ocean has primed the Pacific for El Niño. All international climate models monitored by the Bureau indicate the tropical Pacific will exceed El Niño thresholds by mid-year. However, the accuracy of model outlooks at this time of year is lower than outlooks made at other times of the year. The Bureau's ENSO Tracker indicates that the likelihood of El Niño developing in the coming months is at least 70%.
El Niño is often, but not always, associated with below average rainfall across eastern Australian during the second half of the year. Daytime temperatures tend to be above average over the southern half of Australia.
See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.
Next update expected by 28 April 2015 | Product Code IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Product Code: IDCKGEWWOO