Tropical monitoring and outlooks
Madden-Julian Oscillation (MJO)
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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.
Forecast MJO location and strength
The chart shows the strength and progression of the MJO through 8 different areas along the equator around the globe.
Area 3 is north west of Australia, 4 and 5 are to the north (the Maritime Continent), and 6 is to the north east.
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 this index is within the centre circle the MJO is considered weak. 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.
Tropical atmospheric waves
About tropical atmospheric waves
MJO
The Madden–Julian Oscillation (MJO) is the major fluctuation in tropical weather on weekly to monthly timescales. It can be characterised as an eastward moving pulse or wave of cloud and rainfall near the equator that typically recurs every 30 to 60 days.
Other tropical waves in the atmosphere
In addition to the MJO, other large-scale atmospheric waves also occur in the tropics. The main ones are the convectively-coupled Kelvin wave (KW), equatorial Rossby wave (ER), and mixed Rossby-Gravity wave (MRG). They can provide further insight into the current tropical weather, such as the location and development of tropical cyclones, and what may occur over the coming days to weeks. These waves occur year-round, but typically have a greater influence on tropical weather in the Australian region during the wet-season months of October to April.
Kelvin wave (KW)
Equatorial Kelvin waves are alternating low and high pressure centres along the equator that move from west to east. For consistency with the theoretical structure of Kelvin waves, convection (leading to cloudiness and rainfall) near the equator should be on the western side of the low pressure regions. In contrast, clear conditions should be found on the eastern side of the low pressure. Like other atmospheric tropical waves, alternating zones of cloudiness and clear weather can be seen on satellite imagery in association with an active Kelvin wave. The waves move in the same direction as the Madden–Julian Oscillation, from west to east, but typically 2 to 3 times faster.
Equatorial Rossby (ER) wave
In theory there are several different equatorial Rossby waves. The most commonly seen atmospheric ER wave, and the one we discuss here, has high and low pressure regions centred at latitudes about 10 degrees north and south of the equator. To be consistent with theory, the lows and highs should form a symmetric pattern about the equator. Due to the wind flow around these high and low pressure regions, some regions along the equatorial zone favour cloud and rain formation, while other regions favour stable, clear conditions. On satellite imagery equatorial Rossby waves can often be identified due to the presence of cloud systems at similar longitudes on both sides of the equator. These cloud systems, in conjunction with the off-equatorial low pressure, can be the precursors to tropical cyclones on either side of the equator. While equatorial Rossby waves move at a speed close to that of a typical Madden–Julian Oscillation pulse, they move in the opposite direction—from east to west.
Mixed Rossby-Gravity (MRG) wave
Like equatorial Rossby waves, mixed Rossby-Gravity waves also move towards the west, but MRG waves have their pressure centres arranged anti-symmetrically on either side of the equator. This means a low pressure centre on one side of the equator will be opposite a high pressure centre in the other hemisphere. Satellite analysis of mixed Rossby-Gravity waves shows favoured zones for deep convection, often with thunderstorm clusters, in an antisymmetric arrangement about the equator. Their speed of movement to the west is faster than that of an ER wave.
Images are from The COMET® Program, from Introduction to Tropical Meteorology.
The COMET® Website is at http://meted.ucar.edu/ of the University Corporation for Atmospheric Research (UCAR), sponsored in part through cooperative agreement(s) with the National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce (DOC). © 1997–2021 University Corporation for Atmospheric Research. All Rights Reserved.
MJO location and strength
These graphs show the strength and progression of the MJO through 8 different areas along the equator around the globe.
Area 3 is north west of Australia, 4 and 5 are to the north (the Maritime Continent), and 6 is to the north east.
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 this index is within the centre circle the MJO is considered weak. 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.
Download data: RMM Data
*Note: There are missing satellite observations from 16/3/1978 to 31/12/1978.
Methodology: Until the end of 2013 we use the exact method of Wheeler and Hendon (2004, https://doi.org/10.1175/1520-0493(2004)132%3C1917:AARMMI%3E2.0.CO;2) and from 2014 we use the modified method of Gottschalck et al. (2010, https://doi.org/10.1175/2010BAMS2816.1).
Average weekly rainfall probabilities
These maps show average weekly rainfall probabilities for each of the 8 MJO phases. Green shades indicate higher than normal expected rainfall, while brown shades indicates lower than normal expected rainfall.
Select the 'Wind' checkbox to also show the expected 850 hPa (approximately 1.5 km above sea level) wind anomalies. 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 global weather patterns changes with the season.
Read more: The Combined Influence of the Madden–Julian Oscillation and El Niño–Southern Oscillation on Australian Rainfall.
These maps show average minimum or maximum temperature anomalies for each of the 8 MJO phases. Red-yellow colours indicate higher than normal temperature, while blue colours indicate lower than normal temperature.
Select the 'Wind' checkbox to also show the expected 850 hPa (approximately 1.5 km above sea level) wind anomalies. 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 global weather patterns changes with the season.
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.
Select the 'Wind' checkbox to also show the expected 850 hPa (approximately 1.5 km above sea level) wind anomalies. 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 global weather patterns changes with the season
These maps show the atmospheric troughs and ridges (in blue and red, respectively) associated with the different phases of the MJO at the 500hPa level. The 500 hPa level is approximately 5500 m above sea level and is about the middle of the troposphere. Colour shading is only used where the geopotential height anomalies are determined to be statistically-significant at the 5% level.
Select the 'Wind' checkbox to also show the expected 850 hPa (approximately 1.5 km above sea level) wind anomalies. 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 global weather patterns changes with the season
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.
OLR totals over the dateline
Regional maps of outgoing longwave radiation (OLR)
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.
Time longitude plots
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.
Daily averaged OLR anomalies
Westerly wind anomalies
Australian region
Recent conditions
For the week ending 12 January, a monsoon trough and low pressure areas generated showers, thunderstorms and rain with locally heavy falls in parts of the tropical north, while Tropical Cyclone Koji brought widespread rainfall and thunderstorms to much of eastern Queensland (see section below for details on Tropical Cyclone Koji). Weekly rainfall totals of 50 to 300 mm, locally higher, were recorded across parts of eastern and tropical Queensland, the Top End of the Northern Territory and areas in the north of Western Australia. The highest weekly total (at a Bureau gauge) was 395.0 mm at Mt Jukes in Queensland, which included the highest daily total of 251.0 mm in the 24 hours to 9 am on 12 January.
During the week, low-intensity to severe heatwave conditions developed across southern parts of the Northern Territory extending into Western Australia, which were part of the broader severe to extreme heatwaves further south.
Maximum temperatures were below average in parts of northern Australia on most days during the week. Daily maximum temperature anomalies were up to 4 °C below average in parts of the tropics, with areas in Queensland more than 8 °C below average on some days.
Fortnightly forecast
The forecast for the fortnight of 17 to 30 January, issued on 12 January, shows rainfall is likely to be below average for tropical Western Australia, the Northern Territory and parts of western Queensland. For northern and eastern Queensland, the forecast signal is weak meaning roughly equal chances of a wetter or drier fortnight.
Maximum temperatures are likely to be below average for parts of eastern Queensland and above average across Western Australia and the Northern Territory extending into western Queensland. Minimum temperatures are likely to be below average for central and western Queensland extending into eastern parts of the Northern Territory and above average for much of remaining tropical north.
Madden–Julian Oscillation
As of 10 January, the Madden–Julian Oscillation (MJO) has strengthened in the Western Pacific, though it remains relatively weak. Most forecast from surveyed models suggest that over the coming week the MJO is likely to strengthen further in the Western Pacific region and progress eastwards across the Western Pacific. At this time of year, the MJO in the Western Pacific is typically associated with enhanced rainfall and westerly wind anomalies in parts of Australia's tropical north.
Severe Tropical Cyclone Jenna
Tropical low 11U developed on 4 January in the Indian Ocean, north-west of the Cocos (Keeling) Islands. It initially moved to the south-east before reaching tropical cyclone intensity on 5 January and was named Jenna. Tropical Cyclone (TC) Jenna passed close to the Cocos (Keeling) Islands as a Category 1 system as it tracked southwards, before turning to the south-west and intensifying. It briefly reached its peak intensity as Category 3 system (Severe TC) on 7 January, with sustained winds of 150 km/h and central pressure of 967 hPa. On 8 December, it weakened below tropical cyclone strength just prior to exiting the Australian area of responsibility (AOR). Jenna was the sixth TC in the Australian AOR this season,
Cocos (Keeling)Islands experienced a period of strong winds and heavy rainfall on 5 January as Tropical Ciclone Jenna passed close by. It is the first time since reliable observations began in 1970 that the Cocos (Keeling) Islands were impacted by two tropical cyclones in one season (Tropical Cyclones Grant and Jenna).
Tropical Cyclone Koji
Tropical low 12U developed in the Coral Sea north of Willis Island on 8 January. Moving south-westwards towards Queensland's north-east coast it rapidly intensified, reached tropical cyclone strength on 10 January and was named Koji. It was the seventh tropical cyclone in the Australian AOR this season. Tropical Cyclone (TC) Koji reached its peak intensity early on 11 January as Category 2 system with sustained winds of 95 km/h and central pressure of 989 hPa. It quickly weakened before making landfall on the morning of 11 January as a Category 1 system. TC Koji made landfall between Ayr and Bowen, bringing heavy rainfall and strong winds with gusts exceeding 80 km/h to the area between Bowen and Mackay. After crossing the coast, it weakened below tropical cyclone intensity while moving to the south-west continuing to bring heavy rainfall to areas along its track, including daily totals of over 200 mm in some areas. Further rainfall over mostly saturated soils contributed to flooding in some river catchments. Ex-TC Koji is forecast to track westwards through the Gulf Country in the following days.
See the tropical cyclone 7-day forecast for the latest advice on systems in the Australian region.
Product code: IDCKGEW000
ACKNOWLEDGEMENT: Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Product Code: IDCKGEM000
