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 15 April 2014
Madden-Julian Oscillation forecast to weaken
This past week saw active tropical convection near the equator from Indonesia through to the central Pacific, including northern Queensland. In the northern hemisphere, tropical storm Peipah brought heavy rainfall to the Philippines, while in the southern hemisphere tropical cyclone Ita impacted on northern Queensland. Tropical moisture from the Indian Ocean was drawn inland over Australia's central deserts, during the week, bringing heavy rainfall to northwest, central and southern Australia.
The Madden-Julian Oscillation (MJO) has been an active contributor to enhanced tropical convection across the Asia-Pacific region this week. However, most climate models predict the MJO will weaken later this week as it enters the western Pacific region, thus lessening its impact on tropical weather. As the MJO moves away from Australia and weakens, northern Australia is likely to transition into a more dry season-like weather pattern.
See the Bureau's MJO Monitoring for more information on location and tracking of the MJO.
El Niño likely to develop
While the Pacific is currently in a neutral state, recent changes across the Pacific and climate model forecasts indicate an El Niño is likely to develop in the coming months. El Niño is often, but not always, associated with below normal rainfall across large parts of southern, eastern and northern Australia during the second half of the year.
El Niño is a natural part of the global climate system. It occurs when the ocean surface temperatures in the central and eastern tropical Pacific Ocean change from a neutral ('normal' or 'average') state to a warmer than normal state for several seasons. Changes in sea surface temperature in the Pacific Ocean are commonly measured across several regions. The latest sea surface temperature anomaly across the NINO3.4 region, in the central Pacific, is +0.3 °C and has shown steady warming since February.
The Southern Oscillation is the atmospheric response to the changing ocean. During El Niño, it is common for areas of active tropical weather to shift east toward Tahiti and coincide with the region of warmer sea surface temperatures while northern Australia sees less tropical activity. Hence, the Southern Oscillation Index (SOI) is measured as the difference in mean sea level pressure between Tahiti and Darwin, Australia. The latest 30–day average SOI value to 13 April is −4.3; a sustained value of less than −8 usually indicates an El Niño.
Climate scientists often describe the oceanic and atmospheric components of this phenomenon together as the El Niño—Southern Oscillation, or ENSO. Learn more about ENSO or read the Bureau's ENSO Wrap-Up for official information about the current ENSO state and to learn more about how ENSO can affect Australia.
Next update expected by 22 April 2014| Product Code IDCKGEWOOO
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
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