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.
Heavy rainfall across Maritime Continent and northern Australia
Monsoonal conditions continued over the Maritime Continent and northern Australia last week. Many locations in the Kimberley region of Western Australia and the western part of the Northern Territory’s Top End observed weekly rainfall totals in excess of 200 mm. Heavy rainfall generated landslides and led to multiple fatalities in Bali, Indonesia. Further east, widespread rains generated floods in the South Pacific affecting an area which extended from the Papua New Guinea to Samoa, including the Solomon Islands, Fiji and Tonga.
Climate influences which contributed to the rainfall included an unusually strong westerly wind-flow across the Maritime Continent and a moderate to strong Madden–Julian Oscillation (MJO) which moved over the Western and central Pacific regions during the period. Cloudiness and rainfall over the western South Pacific Ocean was significantly more active than normal.
Madden–Julian Oscillation to maintain strength
International climate models indicate the Madden–Julian Oscillation (MJO) will maintain its strength as it continues east over the central Pacific Ocean and towards the Americas this coming week. Typically, rainfall over most of the Australian tropics is not enhanced significantly when the MJO signal is over the central Pacific Ocean; however, far eastern parts of the Maritime Continent and Cape York Peninsula can observe above-average rainfall. Suppressed rainfall and cloudiness is typically experienced over Australian longitudes when the MJO signal reaches the eastern Pacific region; however, smaller-scale weather systems can dominate the influence of the MJO and produce significant, localised rainfall. While no tropical cyclones have yet formed in the south Pacific region during the 2016-17 season, there is currently an enhanced risk with the MJO in the region.
For more information on the MJO, see the Bureau's current MJO monitoring information.
El Niño–Southern Oscillation remains neutral
The El Niño–Southern Oscillation (ENSO) remains neutral, with virtually all indicators close to their average values. In recent weeks, the central and eastern tropical Pacific Ocean has shown surface warming, and most climate models suggest this warming is likely to continue during the southern autumn.
However, as this is the time of year when both ENSO and climate models have greatest variability, some caution must be taken when extrapolating the recent Pacific warming to later in 2017. Hence, either neutral or El Niño is considered the most likely ENSO state for the southern winter/spring.
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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