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 4 August 2015
It has been an active week for tropical cyclones, with activity in Bay of Bengal, the Philippine Sea, and both sides of the equator in the central Pacific region. Cyclonic storm Komen formed over the Bay of Bengal last week, impacting Bangladesh and later India, with widespread heavy rainfall causing flooding, damage to property and loss of life. Tropical storm Guillermo developed in the central Pacific Ocean last week and has moved steadily west-northwest in recent days. Guillermo is forecast to weaken as it approaches Hawaii in the coming days and is not expected to make landfall. Typhoon Soudelor, which developed rapidly north of Guam on 2 August, is currently moving west-northwest over the Philippine Sea and is forecast to maintain its category five strength until later in the week. A southern hemisphere tropical depression, about 1000 km northwest of Fiji, weakened yesterday and has a low chance of further development.
El Niño well established
The 2015 El Niño event is well established. The latest weekly NINO3.4 sea surface temperature anomaly is +1.7 °C and the 30-day SOI value to 2 August is −14.4. The weakened trade winds remain and contribute to the continued warming of the tropical Pacific Ocean. Cloudiness near the date line in the tropical Pacific Ocean is also consistent with El Niño. International climate models surveyed by the Bureau of Meteorology all indicate the El Niño will likely strengthen further, and persist into early 2016.
See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.
Madden-Julian Oscillation weak
During the last week, the Madden-Julian Oscillation (MJO) weakened over Africa—hence is unlikely to have contributed significantly to tropical activity this past week. International climate models suggest a weak to moderate MJO signal will reappear over the western tropical Pacific Ocean this week. However, it is possible that climate models are detecting an El Niño signal, rather than the MJO. If the MJO does reappear over the western Pacific Ocean, typical impacts at this time of year would include suppressed convection over the Indian Ocean and an increased chance of tropical activity over the northwest Pacific Ocean.
See the Bureau's MJO Monitoring for current MJO information.
Next update expected by 11 August 2015 | Product Code IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Product Code: IDCKGEWWOO