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 19 May 2015
Northern hemisphere tropics become active
The northern hemisphere tropics have shown an increase in convective activity over the past week. In the northwest Pacific Ocean, typhoon Dolphin impacted on Guam on 16 May as it tracked between the islands of Guam and Rota, and is currently located south of Japan and weakening. Dolphin is the fourth storm to reach typhoon strength in the northwest Pacific region this year.
This past week also saw southwesterly surface winds cross the equator and surge into the Bay of Bengal. This reversal of the prevailing winds along with northeasterly return flow at the upper-levels of the atmosphere are indicators of developing monsoonal weather conditions over southwest Myanmar and the Andaman Islands. According to the Indian Meteorological Department, the development of the monsoon over the Bay of Bengal is a precursor to the onset of the monsoon over the Indian sub–continent at Kerala, which is expected during the last days of May or first days of June.
The Madden–Julian Oscillation (MJO) is usually the primary driver of variability in monsoon patterns. However, the MJO is weak or indiscernible and is unlikely to be influencing current tropical weather. Climate models indicate the MJO will remain weak for the coming fortnight and will be unlikely to influence tropical weather. The developing El Niño in the Pacific remains a stronger driver of tropical weather.
See the Bureau's MJO Monitoring for current MJO information.
El Niño likely to strengthen
The tropical Pacific Ocean is in the early stages of El Niño. Climate models monitored by the Bureau indicate the tropical Pacific Ocean will continue to warm over the coming months. The average value of the model forecasts of NINO3.4 for October is +2.4 °C. This value of NINO3.4 has only been observed on a few occasions since 1980: during the 1982–83 and 1997–98 El Niño events.
The most recent NINO3.4 value is +1.1 °C for the week ending 17 May 2015. The latest 30–day Southern Oscillation Index value is −16.5 to 17 May.
See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.
Next update expected by 26 May 2015 | Product Code IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
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