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 28 July 2015
Madden-Julian Oscillation weakens over the Indian Ocean
Over the past week, an active Madden-Julian Oscillation (MJO) has moved eastwards into the western tropical Indian Ocean, enhancing the Indian monsoon and likely contributing to the recent suppressed convection over much of South-East Asia and the northwest Pacific Ocean. The MJO has weakened in recent days. Forecasts for the MJO this week are mixed, however, there is an indication that a weak signal may reappear somewhere over the western hemisphere. When models forecast a retrogression of the MJO signal (westward rather than eastward movement), this is often an indicator of interaction with other large scale drivers or tropical waves, as this is counter to the current understanding of MJO behavior. Current forecasts indicate the MJO signal will be weak and therefore not likely to have a strong influence on tropical activity over the coming fortnight.
See the Bureau's MJO Monitoring for current MJO information.
Widespread heat across northern Australia
Much of northern tropical Australia has experienced widespread unseasonably warm daytime maximum temperatures in recent days, with several locations recording record high temperatures for this time of the year. This warming was associated a slow moving high pressure system centred over central Australia. The high pressures system directed light and humid winds over the tropics. This weak and humid flow allowed daytime temperatures to reach as high as 36.8 degrees Celsius in various locations across northern Australia. The heat is expected to ease in Northern Australia but likely to traverse south to the Pilbara and Gascoyne regions of Western Australia in the next few days.
El Niño continues to strengthen
El Niño continues to develop in the tropical Pacific Ocean. Weakened (or reversed) trade winds continue to cause the tropical Pacific Ocean to warm. All international climate models surveyed by the Bureau of Meteorology indicate El Niño is likely to strengthen and persist into early 2016. The latest weekly NINO3.4 sea surface temperature anomaly is +1.5 °C and the 30-day SOI value to 26 July is −14.7.
Cloudiness near the Date Line in the tropical central Pacific was enhanced this last week; a typical pattern during El Niño. Meanwhile, to the west of the Date Line and across the Maritime Continent suppressed convection was observed, a feature of El Niño compounded recently by the Madden-Julian Oscillation (MJO).
See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.
Next update expected by 4 August 2015 | Product Code IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
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