Climate Driver Update
Climate drivers in the Pacific, Indian and Southern oceans and the Tropics
Average of international model forecasts for NINO3.4
Average of international model forecasts for IOD
- See also: Links open in new window
- About Australian climate influences
- Climate model summary
- Long-range forecast
Sea surface temperature maps
Sea surface temperature maps are not available for forecasts before Spring 2018
Global sea surface temperature outlooks for the months and season ahead. Anomalies indicate the difference from normal.
SST outlooks for the next 3 months
Pacific Ocean
ENSO is the oscillation between El Niño and La Niña states in the Pacific region. El Niño typically produces drier seasons, and La Niña drives wetter years, but the influence of each event varies, particularly in conjunction with other climate influences.
International climate model forecasts
Graph details
The graphs are based on the ensemble mean for the most recent model run.
These graphs show the average forecast value of NINO3.4 for each international model surveyed for the selected calendar month. If the bars on the graph are approaching or exceeding the blue dashed line, there is an increased risk of La Niña. Similarly, if the bars on the graph are approaching or exceeding the red dashed line, there is an increased chance of El Niño.
- See also: Links open in new window
- Climate model summary
- Long-range forecast
Weekly sea surface temperatures
Graphs of the table values
Monthly sea surface temperatures
Graphs of the table values
- See also: Links open in new window
- Animation of recent SST changes
- Weekly index graphs
- Sea temperature analyses
- Map of NINO and IOD regions
5-day sub-surface temperatures
Monthly temperatures
- See also: Links open in new window
- Animation of recent sub-surface temperature changes
- Archive of sub-surface temperature charts
Southern Oscillation Index
- See also: Links open in new window
- Monthly SOI graph
- 30-day SOI values
Trade winds
- Data Source: Links open in new window
- TAO/TRITON data
Cloudiness near the Date Line
About El Niño and La Niña (ENSO)
Video: Understanding ENSO. Described transcript available below
summary
summary
At a glance
ENSO is the oscillation between El Niño and La Niña conditions.
This climate influence is related to: El Niño La Niña The Australian Monsoon
What is it?
The term El Niño refers to the extensive warming of the central and eastern tropical Pacific Ocean which leads to a major shift in weather patterns across the Pacific. This occurs every three to eight years and is associated with a weaker Walker Circulation (see diagram below) and drier conditions in eastern Australia. El Niño Southern Oscillation(ENSO) is the term used to describe the oscillation between the El Niño phase and the La Niña, or opposite, phase.
In the eastern Pacific, the northward flowing Humbolt current brings cooler water from the Southern Ocean to the tropics. Furthermore, along the equator, strong east to southeasterly Trade winds cause the ocean currents in the eastern Pacific to draw water from the deeper ocean towards the surface, helping to keep the surface cool. However in the far western Pacific there is no cool current, and weaker Trades mean that this "upwelling" effect is reduced. Hence waters in the western equatorial Pacific are able to warm more effectively under the influence of the tropical sun. This means that under "normal" conditions the western tropical Pacific is 8 to 10°C warmer than the eastern tropical Pacific. While the ocean surface north and northeast of Australia is typically 28 to 30°C or warmer, near South America the Pacific Ocean is close to 20°C. This warmer area of ocean is a source for convection and is associated with cloudiness and rainfall.
However, during El Niño years, the trade winds weaken and the central and eastern tropical Pacific warms up. This change in ocean temperature sees a shift in cloudiness and rainfall from the western to the central tropical Pacific Ocean.
Neutral ENSO phase
Trade winds push warm surface water to the west and help draw up deeper, cooler water in the east. The warmest waters in the equatorial Pacific build up to the north of Australia and that area become the focus for cloudiness and rainfall.
La Niña
Trade winds strengthen, increasing the temperature of the warm water north of Australia. Cloudiness and rainfall north of Australia are enhanced, typically leading to above average winter–spring rainfall for eastern and central parts of the country, and a wetter start to the northern wet season.
El Niño
Trade winds weaken (or reverse) and warmer surface water builds up in the central Pacific. Cloudiness and rainfall north of Australia are supressed, typically leading to below average winter–spring rainfall for eastern parts of the country, and a drier start to the northern wet season.
The Southern Oscillation Index, or SOI, gives an indication of the development and intensity of El Niño or La Niña events in the Pacific Ocean. The SOI is calculated using the pressure differences between Tahiti and Darwin. The following figure demonstrates the typical fluctuations in SOI over a period of 11 years. Positive SOI values are shown in blue, with negative in orange. Sustained positive values are indicative of La Niña conditions, and sustained negative values indicative of El Niño conditions.
This graph shows the values of the SOI between 1991 and mid-2015. Monthly SOI data.
How does it affect Australia?
Each phase of the ENSO has a very different effect on the Australian climate. Events generally have an autumn to autumn pattern of evolution and decay. That is, they typically begin to develop during autumn, strengthen in winter/spring, then decay during summer and autumn of the following year. These effects are described in further detail on the following pages: El Niño and La Niña.
Further information and latest updates
Further information about the El Niño Southern Oscillation and its impact on the Australian Climate.
The Climate Driver Update provides the latest information on the state of ENSO and the likely effect this will have on Australia.
Timeline of monthly Southern Oscillation Index (SOI) values since 1876
Sustained negative values (bottom/yellow) of the SOI below −7 may indicate El Niño, while sustained positive values above +7 may indicate La Niña. La Niña and El Niño events since 1900 are indicated on the graph.
Drag graph slider to see full history and y-axis scale.
The Indian Ocean Dipole (IOD) is defined by the difference in sea surface temperatures between the eastern and western tropical Indian Ocean. A negative phase typically sees above average winter-spring rainfall in Australia, while a positive phase brings drier than average seasons.
International climate model forecasts
Graph details
The graphs are based on the ensemble mean for the most recent model run.
Thse graphs show the average forecast value of the IOD index for each international model surveyed for the selected calendar month. If the majority of models are approaching or exceeding the blue dashed line, then there is an increased risk of a negative IOD event. If the majority of models are approaching or exceeding the red dashed line, then there is an increased risk of a positive IOD event.
- See also: Links open in new window
- Climate model summary
- Long-range forecast
- See also: Links open in new window
- SST timeseries graphs
- Sea temperature analyses
- Map of NINO and IOD regions
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About the Indian Ocean Dipole (IOD)
Video: Understanding IOD. Described transcript available below
Indian Ocean sea surface temperatures impact rainfall and temperature patterns over Australia. Warmer than average sea surface temperatures can provide more moisture for frontal systems and lows crossing Australia.
Indian Ocean Dipole
Sustained changes in the difference between sea surface temperatures of the tropical western and eastern Indian Ocean are known as the Indian Ocean Dipole or IOD. The IOD is one of the key drivers of Australia's climate and can have a significant impact on agriculture. This is because events generally coincide with the winter crop growing season. The IOD has three phases: neutral, positive and negative. Events usually start around May or June, peak between August and October and then rapidly decay when the monsoon arrives in the southern hemisphere around the end of spring.
Neutral IOD phase
Water from the Pacific flows between the islands of Indonesia, keeping seas to Australia's northwest warm. Air rises above this area and falls over the western half of the Indian Ocean basin, blowing westerly winds along the equator.
Temperatures are close to normal across the tropical Indian Ocean, and hence the neutral IOD results in little change to Australia's climate.
Positive IOD phase
Westerly winds weaken along the equator allowing warm water to shift towards Africa. Changes in the winds also allow cool water to rise up from the deep ocean in the east. This sets up a temperature difference across the tropical Indian Ocean with cooler than normal water in the east and warmer than normal water in the west.
Generally this means there is less moisture than normal in the atmosphere to the northwest of Australia. This changes the path of weather systems coming from Australia's west, often resulting in less rainfall and higher than normal temperatures over parts of Australia during winter and spring.
Negative IOD phase
Westerly winds intensify along the equator, allowing warmer waters to concentrate near Australia. This sets up a temperature difference across the tropical Indian Ocean, with warmer than normal water in the east and cooler than normal water in the west.
A negative IOD typically results in above-average winter–spring rainfall over parts of southern Australia as the warmer waters off northwest Australia provide more available moisture to weather systems crossing the country.
Indian Ocean Dipole years
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- See also: Links open in new window
- Indian Ocean Dipole outlook
- Indian Ocean outlook model summary
- Graph of latest IOD Index
The Southern Annular Mode, or SAM, refers to the north-south shift of rain-bearing westerly winds and weather systems in the Southern Ocean compared to the usual position.
Southern Annular Mode (SAM) history
About the Southern Annular Mode (SAM) forecast
At a glance
The Southern Annular Mode can result in enhanced rainfall in regions of southern Australia.
This climate influence is related to: ENSO Frontal Systems
What is it?
The Southern Annular Mode, or SAM, also known as the Antarctic Oscillation (AAO), is a mode of variability which can affect rainfall in southern Australia. The SAM refers to the north/south movement of the strong westerly winds that dominate the middle to higher latitudes of the Southern Hemisphere. The belt of strong westerly winds in the Southern Hemisphere is also associated with the storm systems and cold fronts that move from west to east.
During the summer and autumn months (December through to May) the SAM is showing an increasing tendency to remain in a positive phase, with westerly winds contracted towards the south pole.
The contribution that the SAM makes to the climate variability in Australia and the apparent positive trend in the SAM are relatively recent discoveries and as such are still active areas of research.
SAM summer negative phase
SAM summer positive phase
SAM winter negative phase
SAM winter positive phase
Where, when and for how long does it occur?
The diagram above shows the area affected by the Southern Annular Mode, when it occurs and how long it may last.
In terms of mean sea level pressure, the SAM affects the coastal regions of southern Australia throughout the year. Extreme negative phases of the SAM can cause increased rainfall and cold air outbreaks in southern Australia.
Each SAM event, both positive and negative, tends to last for around ten days to two weeks. The time frame between positive and negative events however is quite random, but is typically in the range of a week to a few months.
How does it affect Australia?
The impact that the SAM has on rainfall varies greatly depending on season and region. If Australia were a few degrees further south, then the impact of changes in SAM would be much more pronounced. The diagram below describes the average impact on rainfall during a "positive" (westerly winds further south) SAM event.
The SAM also has an impact on temperatures. In general, in areas where rainfall is increased, temperature is decreased whilst where rainfall is decreased, temperature is increased.
The diagram above shows the impact that a "positive" SAM event (decreased westerly winds) has on Australian rainfall. Shading indicates daily rainfall anomaly in mm/day for each of the seasons. (Source: Hendon et al. 2007)
An example
During July 2007, the SAM was in a strong negative phase. This was reflected in rainfall patterns across southern Australia.
Further information and latest updates
- Find the latest SAM information in the Climate Driver Update Southern Ocean section
- Have a look at the latest atmospheric circulation patterns.
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' of cloud and rainfall near the equator that typically recurs every 30 to 60 days.
Tropical Climate Update
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.
Download data: RMM Data Postscript: RMM 40 days | RMM 90 days
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.
- See also: Links open in new window
- Tropical update
- Tropical monitoring (MJO)
About the Madden–Julian Oscillation (MJO) forecast
At a glance
The Madden-Julian Oscillation is associated with weekly to monthly periods of enhanced and suppressed rainfall over parts of Australia.
This climate influence is related to: The Australian Monsoon Tropical Cyclones Tropical Depressions
What is it?
The Madden-Julian Oscillation (MJO) is a global-scale feature of the tropical atmosphere.
The MJO is the major fluctuation in tropical weather on weekly to monthly timescales. The MJO can be characterized as an eastward moving "pulse" of cloud and rainfall near the equator that typically recurs every 30 to 60 days. However, the signal of the MJO in the tropical atmosphere is not always present.
MJO effects are most evident over the Indian Ocean and western equatorial Pacific. It influences the timing, development and strength of the major global monsoon patterns, including the Indian and Australian monsoons.
Tropical cyclones are also more likely to develop in association with certain phases of a strong MJO event.
The MJO is associated with variations in wind, cloudiness, and rainfall. Most tropical rainfall comes from tall thunderstorms which have very cold tops. Thunderstorms that have cold tops emit only low levels of longwave radiation. Therefore, the MJO can be monitored by using satellite measurements of outgoing longwave radiation (OLR) to identify areas of cloudiness (low OLR) within the tropics.
Where, when and for how long does it occur?
The diagram above shows the area most affected by the Madden-Julian Oscillation (MJO), the seasons during which the MJO's influence on Australia is greatest, and for how long each active phase of the MJO typically lasts.
How does it affect Australia?
The MJO has its greatest effect on the tropical areas of Australia during summer. It may have some effect on parts of southern Australia, however this impact appears small when compared to the effect on northern regions, and remains the subject of research.
The MJO can have an effect on the timing and intensity of "active" monsoon periods in northern Australia. This can lead to enhanced rainfall - in both the intensity of the rainfall and the duration of the rainfall.
An example
During late January 2006, an active phase of the MJO coincided with an active monsoon period, resulting in enhanced rainfall over northern Australia.
Further information and latest updates
The following links provide further information on the MJO.
- The Tropical Climate Update provides information on the current phase of the MJO.
- Technical information and maps relating to the Real-time Multivariate MJO Index, which is a way of monitoring the climate and weather variations caused by the MJO. Please note that this product is a research product, and as such is not always updated and may be under-going continual changes as it is developed.
Archive
SSTs for February 2023 were close to average across much of the tropical Pacific Ocean. Weak cool anomalies existed from around 165°E to around 120°W, being less than 1 °C cooler than average. Warm anomalies up to 2 °C warmer than average were present east of 110°W, increasing to up to 3 °C warmer than average close to the Peruvian coast.
Compared to January, cool SST anomalies in the tropical Pacific have weakened while warm SST anomalies have strengthened in the far east of the basin.
Warm anomalies up to 2 degrees above average were observed in a band across the South Pacific stretching from the South American coast around 40°S towards the Coral Sea, while weaker warm anomalies were present over northern areas of the Maritime Continent. Warm SST anomalies also continued to the west and south-east of Australia, especially around Tasmania and in waters close to New Zealand.
For the week ending 12 March 2023, sea surface temperatures (SST) were close to average across much of the equatorial Pacific Ocean. Compared to two weeks ago, warm anomalies east of 130°W have increased in strength and spatial extent, reaching more than 1 °C warmer than average in some areas. The small area of weak cool anomalies which was present in the central equatorial Pacific two weeks ago has dissipated.
Weak warm SST anomalies continue across parts of the north of Maritime Continent and in areas to the north-east of Australia. Warm SST anomalies continue to the south-west and south-east of Australia, especially around Tasmania and in waters close to New Zealand.
The latest values of the three NINO indices for the week ending 12 March 2023 were: NINO3 +0.4 °C, NINO3.4 0.0 °C, and NINO4 −0.1 °C.
Persistent NINO3 or NINO3.4 values cooler than −0.8 °C are typical of La Niña, while persistent values warmer than +0.8 °C typically indicate El Niño.
The 30-day Southern Oscillation Index (SOI) for the 30 days ending 12 March 2023 was +5.4, while the 90-day SOI value was +13.2. The 30-day SOI has decreased over the past fortnight, and is now within neutral values for the first time since November 2022.
Sustained positive values of the SOI above +7 typically indicate La Niña, while sustained negative values below −7 typically indicate El Niño. Values between +7 and −7 generally indicate neutral conditions.
Trade winds for the 5 days ending 12 March 2023 were close to average across the tropical Pacific Ocean.
During La Niña there is a sustained strengthening of trade winds across much of the tropical Pacific, while during El Niño there is a sustained weakening, or even reversal, of trade winds.
The Madden–Julian Oscillation (MJO) is currently very strong over the eastern Pacific Ocean but is forecast to move into the Atlantic Ocean in the coming fortnight. This may bring drier conditions to Australia for the latter half of March.
The Indian Ocean Dipole (IOD) is currently neutral. The IOD typically has little influence on Australian climate while the monsoon trough is in the southern hemisphere (December to April). The IOD index value for the week ending 12 March 2023 was +0.19 °C; within neutral bounds (between −0.40 °C and +0.40 °C).
Sea surface temperatures (SSTs) are generally close to average along the equator of the Indian Ocean. A small area of cool SST anomalies exists off the African coastline while warm SST anomalies are present off the west coast of Australia and over much of the south of the basin.
Most international climate models surveyed by the Bureau anticipate neutral values of the IOD index will continue through the southern hemisphere autumn, though one model forecasts the positive IOD threshold will be exceeded in April. While models suggest positive IOD values may emerge during winter, IOD forecasts made at this time of the year have very low accuracy when forecasting through the autumn.
Cloudiness near the Date Line has been mostly below average (i.e. positive outgoing longwave radiation (OLR) anomalies) since June 2021. Despite OLR values returning to near average late in February, OLR anomalies have been positive for the past fortnight after dipping below zero in late February.
Equatorial cloudiness near the Date Line typically decreases during La Niña (positive OLR anomalies) and increases during El Niño (negative OLR anomalies).
The four-month sequence of equatorial Pacific sub-surface temperature anomalies (to 28 February 2023) shows weak cool anomalies across the top 150 m of the central to eastern equatorial Pacific. Warm anomalies are in place between around 50 and 300 m depth in the western to central equatorial Pacific (west of 160°W). Anomalies reached more than 3 °C warmer than average across much of this region.
Compared to previous months, cool anomalies have decreased in strength steadily over the summer, while warm anomalies have remained consistent during February when compared to those for January.
For the five days ending 12 March 2023, sub-surface temperatures were significantly warmer than average across the western to central equatorial Pacific between about 100 m depth and 250 m depth, reaching more than 4 °C warmer than average west of the Date Line. Weak cool anomalies were present between 140°W and 120°W at depths between 100 m and 150m depth.
Compared to two weeks ago, warm anomalies in the western Pacific sub-surface have increased in strength and extent.
La Niña has ended in the tropical Pacific Ocean. The El Niño–Southern Oscillation (ENSO) is now neutral (neither La Niña nor El Niño) with oceanic and atmospheric indicators having returned to neutral ENSO levels.
International climate models suggest neutral ENSO conditions are likely to persist through the southern autumn. However, there are some signs that El Niño could form later in the year. Hence the Bureau has issued an El Niño WATCH. This means there is around a 50% chance of an El Niño in 2023.
The Madden–Julian Oscillation (MJO) is currently very strong over the Pacific Ocean but is forecast to move into the Atlantic Ocean in the coming fortnight. This may bring drier conditions to Australia for the latter half of March.
The Southern Annular Mode (SAM) index is currently strongly negative but is expected to return to neutral values over the coming week.
Warmer than average sea surface temperatures persist around south-east Australia, New Zealand and the west coast of Australia, but close to average temperatures prevail around northern Australia.
The Indian Ocean Dipole (IOD) is neutral – the IOD typically has little influence on Australian climate while the monsoon trough is in the southern hemisphere (typically December to April). Forecasts for the IOD made at this time of the year have low accuracy beyond April.
Climate change continues to influence Australian and global climates. Australia's climate has warmed by around 1.47 °C over the period 1910–2021. There has also been a trend towards a greater proportion of rainfall from high intensity short duration rainfall events, especially across northern Australia. Southern Australia has seen a reduction of 10 to 20% in cool season (April–October) rainfall in recent decades.
The Southern Annular Mode (SAM) index is currently the strongest negative value since June 2022, but is expected to return to neutral values over the coming week.
Neutral SAM has little influence on the rainfall and temperature outlook for Australia.
The 2022–23 La Niña has ended, having been declared in September 2022. Oceanic and atmospheric indicators have returned to ENSO-neutral (neither El Niño nor La Niña) values.
All but one of the seven international climate models surveyed by the Bureau anticipate central Pacific sea-surface temperatures will remain ENSO-neutral through the southern hemisphere autumn; one model exceeds El Niño thresholds in May. While several models suggest El Niño may develop later in 2023, model accuracy when forecasting through autumn is lower than at other times of the year, and ENSO outlooks that extend past autumn should be viewed with some caution.
The Bureau's ENSO Outlook has been moved to El Niño WATCH. An El Niño WATCH means that there is around a 50% chance that an El Niño will develop. This is about twice the normal likelihood of an El Niño forming in any year. An El Niño WATCH is not a guarantee that El Niño will occur, rather it is an indication that some of the typical precursors of an event are currently observed.
Product code: IDCKGEWW00
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