Madden-Julian Oscillation (MJO)


MJO phase diagram

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*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)

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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.

Regional maps of outgoing longwave radiation (OLR)

Click on the boxes to view a timeseries of cloudiness for that region.
Map of regional cloudiness Dateline Vanuatu Coral Sea Fiji Nauru & Tuvalu Solomon Islands New Guinea Northern Australia Micronesia Malaysia & Indonesia Guam & Marianas Philippines Indochina Southern India & Sri Lanka

Below: OLR totals over the dateline

Click to see full-size graph of OLR totals over the dateline.

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.

Daily averaged OLR anomalies

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Westerly wind anomalies

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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.

Late-season tropical cyclone in Australian Region

Ex-tropical cyclone Mangga interacted with a cold front to bring severe weather to much of Western Australia's south west coast from 24-26 May. A wind gust of 131 km/h was recorded at Cape Leeuwin on the southwest coast on the morning of 25 May, while many other southern locations experienced wind gusts in excess of 90 km/h. Sea level was also well in excess of normal along the coastline, with some areas of the southwest having sea levels around a metre higher than normal. Mangga formed over the southern Indian Ocean on 21 May, near Sumatra, and was briefly a category 1 tropical cyclone in the far west of Australia's tropical cyclone area of responsibility. Soon after entering the Australian region, Mangga lost its tropical characteristics, and was designated as an ex-tropical cyclone. However, the system maintained a low central pressure region which, combined with the cold front, generated severe winds.

While Australian tropical cyclones are uncommon in May, they are not unprecedented. Tropical cyclones have formed in the Australian Region as late as July. Early May tropical cyclones are relatively common, with three such storms in the last five years. The most recent tropical cyclone occurring in the second half of May was the category 1 storm, Pierre, in 2007.

With Mangga included, the total number of tropical cyclones during the 2019-20 Australian tropical cyclone season stands at eight.

Rare category 5 tropical cyclone in the Bay of Bengal

The broadscale climate drivers which aided the development of Mangga, also contributed to the development of tropical cyclone Amphan in the northern Indian Ocean. Both storms were associated with a strong burst of westerly winds over the equatorial Indian Ocean, related to Madden–Julian Oscillation and Kelvin wave activity. Amphan was designated a Super Cyclonic Storm on 19 May by the India Meteorological Department, equivalent to an Australian category 5 tropical cyclone. Storms of this intensity are relatively rare in the Bay of Bengal, with roughly one per decade observed.

Amphan weakened somewhat before reaching land and made landfall on 21 May, just west of the India/Bangladesh border at the head of the Bay of Bengal, with sustained winds to around 150 km/h (comparable to an Australian category 3 tropical cylcone). A storm surge, heavy rainfall and localised flooding was also reported with Kolkata, on India's east coast, seeing close to 200 mm of rain.

Madden–Julian Oscillation rapidly moved through Australian region

Recent analysis indicates a pulse of the Madden–Julian Oscillation (MJO) which assisted the formation of Amphan and Mangga, rapidly tracked eastwards through the Maritime Continent, to Australia's north, in recent days, and is now in the western Pacific region. However, the area of enhanced convection associated with the MJO remains over the eastern Indian Ocean, suggesting the rapid movement of the MJO is mixed up with a Kelvin wave, a faster-moving tropical atmospheric wave.

Most climate models indicate the MJO will slow down in the coming days while continuing to track eastwards across the Pacific Ocean. The combination of fast eastward propagation and a forecast location to the east of the Australian region, means that any significant influence on rainfall in the Australian region is unlikely in the next fortnight.

Read more about the Madden–Julian Oscillation

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ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.

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