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 31 March 2015
Monsoon break continues for Northern Australia
The Australian wet season formally ends on the last day of April. While in the wet season, there is always a chance of wet weather, including impacts from tropical cyclones. However April is a transitional month where periods of either wet or dry season type weather patterns can occur. The Madden-Julian Oscillation (MJO) has been contributing to the current dry conditions observed across northern Australia. The MJO often determines if Australia sees a final burst of wet weather conditions in the month of April.
Currently an active MJO is located over the far western equatorial Indian Ocean, enhancing tropical activity in this region. The MJO is also likely to be contributing to the lull in tropical activity currently observed across South-East Asia, northern Australia and parts of the southwest Pacific Ocean. Forecast models indicate that active convection over the western tropical Indian Ocean is likely to move slowly eastwards. However, most models suggest the MJO will weaken as it moves towards the Maritime Continent region in the week ahead. If the MJO weakens it will have little influence on northern Australia; neither suppressing nor enhancing tropical rainfall. Occasional storms may return to the tropical north, especially in coastal regions where humidity remains high. While another burst of the monsoon is unlikely, wet conditions can develop without the influence of the MJO.
See the Bureau's MJO Monitoring for more information.
Typhoon Maysak in northwest Pacific region
An early season tropical cyclone has formed over the northwest Pacific Ocean. Typhoon Maysak has already made a direct hit on the Micronesian state of Chuuk and is tracking westward. It is expected to impact the Philippines later this week.
El Niño may develop in 2015
There is about a 50% chance of El Niño developing in 2015. Sea surface temperatures (SSTs) in the far eastern Pacific Ocean have warmed for the second consecutive week. The SST anomalies in the NINO1 and NINO2 regions in the far eastern Pacific are now above +1 °C for the first time since August last year. The latest weekly NINO3.4 sea surface temperature anomaly in the central Pacific is +0.7 °C. All regions show a warming trend pointing toward a potential El Niño later this year. The latest 30-day value of the Southern Oscillation Index (SOI) is −10.7. An SOI value of less than −8 that is sustained for several weeks can be an indication of El Niño.
All international climate models monitored by the Bureau predict the tropical Pacific Ocean will reach or exceed El Niño thresholds by mid-year. However, predictions from climate models at this time of the year have less accuracy than predictions made at other times of the year. Hence caution should be used when using model guidance alone to predict the likelihood of El Niño.
See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.
Next update expected by 7 April 2015 | Product Code IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
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