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.
Early wet season rains in tropical Australia continue
The early start to the northern wet season rains has continued over the Northern Territory and central Queensland. Rainfall in the last week continued the pattern seen during much of September (officially the last month of the dry season), when nearly all of northern Australia, apart from some areas in Western Australia, saw significantly above-average rainfall.
A strong and persistent negative Indian Ocean Dipole (IOD), combined with a La Niña–like pattern in ocean temperatures in the western tropical Pacific Ocean, and areas around Australia’s northern coastline, is strongly influencing Australia’s climate. See the Climate Outlook for more information on what to expect in the coming months.
Climate models suggest the negative IOD is likely to return to neutral by the end of spring. In the tropical Pacific Ocean, the El Niño–Southern Oscillation (ENSO) remains neutral, though the Southern Oscillation Index (one ENSO indicator) has exceeded La Niña thresholds. Most climate models surveyed by the Bureau indicate a neutral ENSO will persist for the remainder of 2016; however, La Niña-like impacts can still occur. During La Niña, northern Australia typically experiences above-average wet season rainfall, with the first rains of the season typically arriving earlier than normal.
See the Bureau’s ENSO Wrap-Up for official El Niño, La Niña and IOD information.
Indian monsoon withdraws
The southwest monsoon began to withdraw on 15 September from parts of Rajasthan, in India, and continued to move south. This is a slightly later-than-average withdrawal—typically the southwest monsoon will have withdrawn to be near Madhya Pradesh by this time of year. The monsoon is forecast to continue its slow southward migration over the coming week. The Indian monsoon has so far yielded close-to-average rainfall across the sub-continent.
In the last week, the Madden–Julian Oscillation (MJO) weakened as it exited the Indian Ocean and crossed the Maritime Continent. Typically, when the MJO is over the Maritime Continent at this time of the year, there is an increase in cloudiness and rainfall over South-East Asia. Some international climate models predict that the MJO may strengthen slightly over the Maritime Continent before moving into the western Pacific. If this occurs then it may aid in the withdrawal of the southwest monsoon, as there is typically a reduction in cloudiness over India as the MJO moves in to the western Pacific.
See the Bureau's MJO Monitoring for current MJO information.
Typhoon activity in northwest Pacific
Typhoon Malakas made landfall over the southern Japanese island of Kyushu last week, generating significant flooding in mainland Japan, and causing widespread disruption across Taiwan.
More recently, Megi has reached typhoon strength and is predicted to make landfall today over Taiwan as a very strong typhoon, with maximum sustained winds of 90 knots, before tracking west towards southeast China. Warnings and information on Megi are available from the Japanese Meteorological Agency.
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ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
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