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 16 December 2014
Madden—Julian Oscillation to strengthen over Indian Ocean
The moderate to strong Madden—Julian Oscillation (MJO) that recently moved eastwards along the equator at Australian longitudes has weakened over the western Pacific this past week. It is now so weak that it is unlikely to still be influencing tropical weather.
Model forecasts indicate a slow moving MJO will strengthen in the tropical central or eastern Indian Ocean this week. While there is some uncertainty concerning its strength and speed, some models indicate a weak MJO will be over Australian longitudes during the last week of December moving eastwards into the west Pacific Ocean in early January.
When the MJO is located over the Indian Ocean at this time of year, as some models are indicating will be the case for the next fortnight, it increases the risk of tropical cyclone development in the region. Likewise, as the active MJO moves over Australian longitudes, it increases the chance of monsoonal rainfall over northern Australia as well as tropical cyclone development across the Australian region.
See the Bureau's MJO Monitoring for more information.
Northern Australia heats up
This past week has seen a rise in temperatures across northern Australia. A heat-low, an area of low pressure that forms over very warm land surfaces, has formed over central Australia. This weather pattern has increased westerly wind flow and temperatures across northern Australia and caused some rainfall over the Kimberley region. High temperatures are expected to continue for most of this week.
El Niño—Southern Oscillation nears El Niño thresholds
Oceanic indicators of El Niño—Southern Oscillation (ENSO) are hovering near El Niño thresholds; however, atmospheric indicators such as trade winds, cloudiness and rainfall have either remained near average or only temporarily approached thresholds. The latest NINO3.4 sea surface temperature anomaly is +0.9 °C. The latest Southern Oscillation Index value up to 14 December is −5.1.
Regardless of whether El Niño is declared, El Niño-like impacts are likely to continue. For Australia, this means a drier and warmer summer than normal is likely for many.
See the Bureau's ENSO Wrap up for official El Niño information.
Next update expected by 23 December 2014 | Product Code IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Product Code: IDCKGEWWOO