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 30 June 2015
Madden–Julian Oscillation strengthens over western Pacific region
During the last week, the Madden–Julian Oscillation (MJO) strengthened as it moved over the eastern Maritime Continent, where it enhanced convection and increased local rainfall. The MJO has now moved into the western Pacific region where all international models expect it to strengthen over the next week. In the wake of the MJO, the southwest Indian monsoon has eased in the last few days, apart from the east and northeast where it remains active.
In combination with other tropical waves, the MJO has generated areas of significant weather over the western Pacific region—both north and south of the equator—which have the potential to develop into a tropical cyclone in the coming days. Tropical cyclone formation in the southern hemisphere in this region is rare in June and unprecedented in July (since reliable satellite records became available).
Historically, when the MJO moves over western Pacific longitudes at this time of the year, the southeast trade winds become weaker than normal over northern Australia. This can increase the likelihood of above-average rainfall over the centralwest of Western Australia and western New South Wales, but reduce the likelihood of above-average rainfall for coastal Queensland. There is no significant rainfall trend for far-northern parts of the continent in this climatic scenario.
See the Bureau's MJO Monitoring for current MJO information.
El Niño persists in tropical Pacific
After a series of recent short-term fluctuations in the Southern Oscillation Index (SOI), the index has shown a return to negative values. The 30-day SOI value to 28 June is −9.0, while the 90-day SOI is −9.3.
Oceanic and cloud indices are consistent with El Niño, with sea surface temperatures (SST) well above El Niño levels across the equatorial eastern and central Pacific Ocean, and enhanced convection apparent near the International Date Line.
International climate models surveyed by the Bureau indicate sea surface temperatures will remain well above El Niño thresholds at least til the end of the year. The latest weekly NINO3.4 sea surface temperature anomaly is +1.3 °C.
See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.
Next update expected by 7 July 2015 | Product Code IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Product Code: IDCKGEWWOO