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 characterized 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 is 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 on Tuesday 29 July 2014
Tropical activity picks up over the Pacific Ocean
The Madden-Julian Oscillation (MJO) has gained some strength over the Pacific Ocean during the past week. Active tropical weather has increased along South East Asian monsoon and extends across the western and central Pacific Ocean just north of the equator. It is likely that the MJO has contributed to this increase in activity. In contrast, the tropical Indian Ocean has continued to experience a lull in tropical activity, as is often observed when a MJO is active in the Pacific Ocean. While the MJO remains active over the Pacific Ocean, the risk of tropical cyclone formation across the tropical Pacific Ocean remains elevated.
The outlook for the MJO for the coming two weeks indicates it is likely to continue to move east across the western hemisphere, reappearing in the Indian Ocean region by late next week. However, the models do not completely agree on the strength of the MJO signal over the coming weeks. Some models maintain a weak wave as it moves east while others predict it will weaken, having little influence on tropical weather for the next two weeks.
See the Bureau's MJO Monitoring for more information on location and tracking of the MJO.
ENSO state: neutral
Early this year a warming trend across the tropical Pacific Ocean primed the climate system for El Niño in 2014. However a general lack of atmospheric response to the warm ocean has caused El Niño development to stall. The El Niño-Southern Oscillation (ENSO) is a coupled ocean and atmosphere system with feedback required from both the atmosphere and ocean for an El Niño to develop fully. This lack of atmospheric response over the last two months has resulted in some cooling of the central tropical Pacific Ocean, with the latest NINO3.4 sea surface temperature (SST) anomaly now near the long-term average. The latest 30-day Southern Oscillation Index value to 27 July is −5.2—weakly negative, but not low enough to indicate an El Niño pattern is present.
When the MJO is in the Pacific Ocean, it often weakens trade wind flow over the western Pacific Ocean. This change in trade wind strength could act to re–invigorate and reinforce the El Niño pattern of ocean warming currently observed in the tropical Pacific Ocean.
See the Bureau's ENSO Wrap-Up for official information about the current state of the El Niño-Southern Oscillation.
Indian Ocean Dipole update
The Indian Ocean is currently showing a negative Indian Ocean Dipole (IOD) pattern, with warmer than normal SSTs in the east near the equator and cooler than normal SSTs in the tropical west. This pattern has been in place since mid-June. The Bureau's IOD index reflects this observed SST pattern and is currently below −0.6 °C. Most climate models indicate the IOD index will return to neutral levels by October.
Next update expected by 5 August 2014| Product Code IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Product Code: IDCKGEWWOO