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 cyclone activity persists across the western Pacific
Tropical cyclone activity has continued to affect parts of the northwest Pacific Ocean and eastern Asia. Following the three tropical cyclones of last week (Conson, Chanthu and Dianmu), two recently formed systems are impacting Japan. Typhoon Mindulle made landfall near Tokyo on Monday 22 August, then tracked to the north and weakened, bringing heavy rainfall to Japan’s east coast. Tropical storm Lionrock, near the southern tip of Japan, is forecast to move slowly toward the southwest, away from the main islands of Japan, and reach typhoon intensity in the next day or two. Warnings and information for these systems are available from the Japanese Meteorological Agency.
The tropical activity in this region has coincided with a moderate strength Madden–Julian Oscillation (MJO) which has been prevalent in the western Pacific Ocean region for the last fortnight. Nearly all models surveyed by the Bureau of Meteorology forecast the MJO to remain in the western Pacific region for the coming week, however most models also indicate the MJO is likely to weaken during the period. With an active MJO in the region, the risk of tropical cyclone development is expected to remain higher than normal in the northwest Pacific.
To date, there have been eight named tropical systems in the western Pacific during August, well above the long-term average of between five and six. In addition to the eight named systems, four tropical depressions which did not develop to tropical cyclone intensity formed during the month as an active monsoon trough persisted in the region. Significant tropical activity is also apparent in the Atlantic Ocean, with two tropical cyclones and several weaker tropical lows currently affecting the area.
See the Bureau's MJO Monitoring for current MJO information.
Negative Indian Ocean Dipole continues
The Indian Ocean Dipole (IOD) peaked in July as the strongest negative IOD event recorded in at least 50 years of records. In recent weeks, the negative IOD has weakened slightly. The most recent weekly IOD value is -0.6 °C for the week ending 21 August.
Climate models suggest the negative IOD will remain at a similar strength before weakening during the second half of the southern hemisphere spring. Typically, the IOD returns to neutral prior to the austral summer as a monsoon flow develops in the southern hemisphere. Rainfall across northern Australia is typically greater than normal in September to November during a negative IOD. A negative IOD typically also brings warmer daytime and night-time temperatures to northern Australia. Find out more about the Indian Ocean Dipole.
El Niño–Southern Oscillation indicators remain neutral, but the possibility of La Niña remains. Recently, some international climate models monitored by the Bureau suggest La Niña may develop late in the austral spring or early summer, and persist into early 2017. The remaining models suggest neutral or near-La Niña conditions. A La Niña WATCH remains in place, but if La Niña does develop it is likely to be weak.
Some La Niña-like effects can still occur even if thresholds are not met. During La Niña, rainfall over northern Australia in the build-up months and during the northern wet season is typically above average.
See the Bureau’s ENSO Wrap-Up for official El Niño and La Niña information.
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ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
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