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.
2015-16 Australian northern wet season review
Many parts of northern Australia (i.e. areas north of latitude 26° South) experienced drier-than-average conditions during the northern wet season which concluded 30 April. The northern tropics, including the Northern Territory’s Top End, far northern Western Australia, Cape York Peninsula and the Torres Strait Islands in Queensland had significantly below-average rainfall during the October to April period. Apart from one substantial active monsoon period in the second half of December, the season was characterised by infrequent and weak monsoonal activity. Rainfall totals across northern regions were generally 20 to 40 per cent below average.
Northern Australia also experienced record heat during the wet season. Averaged over northern Australia, mean and overnight temperatures were warmest on record, while daytime temperatures were second warmest. The heat was particularly pronounced north of 20° South during the January to April period, with daytime and overnight temperatures all highest on record.
Tropical cyclone activity was significantly below average, with only three tropical cyclones – Stan, Uriah and Tatiana – observed in the Australian region. Of the three cyclones, only Stan made a coastal crossing: east of Port Hedland as a category 2 system late in January. Tropical cyclone Winston, which affected the Queensland coast during February, had weakened to below tropical cyclone intensity prior to entering the Australian region. The average number of tropical cyclones observed during a season is eleven, and the previous all-time low was five.
Madden–Julian Oscillation strengthens in western hemisphere
The Madden–Julian Oscillation (MJO) has been weak since the beginning of April. It has recently strengthened and moved into the western hemisphere. Some models forecast a moderate MJO over the Indian Ocean in the coming week. When the MJO moves over the Indian Ocean at this time of the year, rainfall is typically near-average over northern Australia, while daytime temperatures are typically higher than normal.
See the Bureau's MJO Monitoring for current MJO information.
El Niño a major factor in the 2015-16 northern wet season
El Niño typically brings warmer and drier conditions to much of northern Australia, particularly during the January to April period - as was experienced across northern Australia during the most recent wet season. El Niño also typically reduces tropical cyclone activity in the Australian region. The previous record low seasons when only 5 tropical cyclones were observed - 1987-88 and 2006-07 - were both El Niño years.
The current El Niño is now in its last stages, with 50% likelihood of La Niña forming later in 2016 – about double the normal chance. La Niña is often, but not always, associated with above-average winter-spring rainfall over northern, central and eastern Australia.
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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