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 26 May 2015
Unseasonal rainfall for Australia's north coast
A short burst of wet weather is expected over the north coast of Australia's Top End this coming weekend, even though northern Australia is well into the dry season. A weak trough which extends over the Arafura Sea is forecast to deepen and shift toward the southwest over the coming days. While there is still some uncertainty as to the strength and location of the trough, it is possible that it will dip far enough south to create showers and storms along the north and northwest coasts of the Top End.
Rain in May over northern Australia is not unprecedented, and the current synoptic set-up is a common cause of May rainfall. Darwin Airport, for example, records two rain days on average in May and sees a rainfall event of more than 10 mm about once every other May.
Southwest Indian Monsoon
Temperatures over the Indian subcontinent have increased recently ahead of the southwest Indian monsoon, with severe heatwave conditions reported to be impacting in large parts of the country. A southwesterly surge of wind has pushed into the Bay of Bengal and is advancing toward the northwest. According to the Indian Meteorological Department the onset of the annual monsoon at Kerala is expected within the coming week. This signals the arrival of the monsoon over the Indian subcontinent and represents the beginning of the rainy season over the region.
The Madden-Julian Oscillation (MJO) is often a major driver of monsoonal variability. However, for the past five weeks it has been weak or indiscernible and is unlikely to have contributed to the current monsoonal flow over the Bay of Bengal. A strong shift in the cloud and wind patterns due to El Niño can make an MJO signal difficult to detect. Forecasts for the MJO show a great deal of uncertainty in the strength, position, and progression of the MJO in the coming weeks. Most indicating the MJO will remain weak, although some models indicate a strengthening over the western hemisphere over the coming week, which could act to enhance tropical activity over the western tropical Pacific.
See the Bureau's MJO Monitoring for current MJO information.
El Niño strengthens
Large scale rainfall patterns across the tropics are consistent with the developing El Niño in the Pacific Ocean. Cloudiness and rainfall near the dateline and across the central Pacific has been enhanced for several weeks, while tropical activity over the Maritime Continent region for the same period has been suppressed. The latest 30–day Southern Oscillation Index value is −17.4 to 24 May. Climate models monitored by the Bureau indicate the tropical Pacific Ocean will continue to warm over the coming months.
See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.
Next update expected by 2 June 2015 | Product Code IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
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