Climate Driver Update
Climate drivers in the Pacific, Indian and Southern oceans and the Tropics


Average of international model outlooks for NINO3.4

Average of international model outlooks for IOD


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.

Sea surface temperature maps (select map for larger view)

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 Niños typically produce drier seasons, and La Niñas drive wetter years, but the influence of each event varies, particularly in conjunction with other climate influences.

NINO3.4 SST plumes from Bureau model forecasts, updated daily
Select to see full-size map of NINIO3.4 SST plumes from Bureau model forecasts, updated daily.

International climate model outlooks

Nino 3.4 2 month outlook
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.

Weekly sea surface temperatures

Graphs of the table values

Monthly sea surface temperatures

Graphs of the table values

5-day sub-surface temperatures

Monthly temperatures

Southern Oscillation Index

30-day SOI values for the past two years
Select to see full-size map of 30-day Southern Oscillation Index values for the past two years, updated daily.

Trade winds

5-day SST and wind anomaly from TAO/TRITON
Select to see full-size map of 5-day SST and wind anomaly from TAO/TRITON.

Cloudiness near the Date Line

About El Niño and La Niña (ENSO)

El Niño Southern Oscillation

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.

Map diagram of Neutral ENSO

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.

Map diagram of Negative ENSO

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.

Map diagram of Positive ENSO

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.

 

graph of SOI

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

Timeline graph of ENSO and SOI index

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.

IOD SST plumes from Bureau model forecasts, updated daily
Select to see full-size map of IOD SST plumes from Bureau model forecasts, updated daily.

International climate model outlooks

Latest IOD outlook
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.

  1. 1960
  2. 1961
  3. 1963
  4. 1964
  5. 1972
  6. 1974
  7. 1981
  8. 1982
  9. 1983
  10. 1989
  11. 1992
  12. 1994
  13. 1996
  14. 1997
  15. 1998
  16. 2006
  17. 2010
  18. 2012
  19. 2014
  20. 2015
  21. 2016
Since 1960, when reliable records of the IOD began, to 2016 there have been 11 negative IOD and 10 positive IOD events.

About the Indian Ocean Dipole (IOD)

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.

Map diagram of Neutral IOD

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.

Map diagram of Positive IOD

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.

Map diagram of Negative IOD


Indian Ocean Dipole years

  1. 1960
  2. 1961
  3. 1963
  4. 1964
  5. 1972
  6. 1974
  7. 1981
  8. 1982
  9. 1983
  10. 1989
  11. 1992
  12. 1994
  13. 1996
  14. 1997
  15. 1998
  16. 2006
  17. 2010
  18. 2012
  19. 2014
  20. 2015
  21. 2016
Since 1960, when reliable records of the IOD began, to 2016 there have been 11 negative IOD and 10 positive IOD events.

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) outlook

Southern Annular Mode

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

Map diagram of Neutral sam

SAM summer positive phase

Map diagram SAM summer positive phase

SAM winter negative phase

Map diagram of SAM winter negative phase

SAM winter positive phase

Map diagram of SAM winter positive phase

Where, when and for how long does it occur?

 

Where, when and for how long does the Southern Annular Mode 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.

 

diagram showing the impact of the SAM

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

rainfall deciles thumbnail image

During July 2007, the SAM was in a strong negative phase. This was reflected in rainfall patterns across southern Australia.

Read more.

Further information and latest updates

 

Page updated: 12 June 2019

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

Archive:     

*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.

Daily averaged OLR anomalies

OLR Archive:   

Westerly wind anomalies

Winds Archive:

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.

About the Madden–Julian Oscillation (MJO) outlook

Madden-Julian Oscillation

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?

 

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

monthly rainfall deciles thumbnail image

During late January 2006, an active phase of the MJO coincided with an active monsoon period, resulting in enhanced rainfall over northern Australia.

Read more.

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.

 

SSTs for August 2021 were close to average across most of the equatorial Pacific Ocean, although warmer than average SSTs continued in the eastern equatorial Pacific Ocean and in waters around the north and east to south-east of Australia.

Values of the three key NINO indices for August 2021 were: NINO3 0.0 °C, NINO3.4 −0.1 °C, and NINO4 +0.2 °C.

Sea surface temperatures (SST) for the tropical Pacific Ocean for the week ending 12 September 2021 were close to average across much of the equatorial Pacific Ocean, with small areas of slightly cooler than average SSTs in the central to eastern equatorial Pacific.

These cool SST anomalies are generally located just to the south of the equator, rather than directly along the equator, which is reflected in sub-surface anomaly patterns.

Warmer than average SSTs continue over the far western Pacific Ocean, including parts of the Maritime Continent. Warm anomalies close to the Australian continent have decreased compared to two weeks ago.

All three NINO indices are within the ENSO-neutral range. The latest values of the three NINO indices in the tropical Pacific for the week ending 12 September 2021 were: NINO3 −0.2 °C, NINO3.4 −0.2 °C, and NINO4 −0.1 °C.

Persistent NINO3 or NINO3.4 values warmer than +0.8 °C are typical of El Niño, while persistent values cooler than −0.8 °C typically indicate La Niña.

The 30-day Southern Oscillation Index (SOI) for the 30 days ending 12 September 2021 was +9.1. The 90-day SOI value was +9.1.

The 30-day value has increased over the past week, mostly reflecting a decrease in pressure over Darwin.

Sustained negative values of the SOI below −7 typically indicate El Niño while sustained positive values above +7 typically indicate La Niña. Values between +7 and −7 generally indicate neutral conditions.

Trade winds for the 5 days ending 12 September 2021 were close to average across most of the tropical Pacific, and stronger than average around and west of the Date Line.

During El Niño there is a sustained weakening, or even reversal, of the trade winds across much of the tropical Pacific. Conversely, during La Niña, there is a sustained strengthening of the trade winds.

The Madden–Julian Oscillation (MJO) has stalled over the Indian Ocean. Most models indicate the MJO is likely to move across Australian longitudes in the coming fortnight, but there is divergence in the forecast strength of the MJO.

If the MJO remains moderately strong over Australia longitudes, it would likely lead to increased rainfall over the tropics to Australia's north, and strengthen the trade flow across the central Pacific region. If on the other hand it remains weak or indiscernable, it is unlikley to have a significant influence on Australian rainfall patterns.

The negative Indian Ocean Dipole (IOD) event has weakened, with index values falling just shy of the negative IOD threshold (i.e. −0.4 °C) in recent weeks. The latest weekly value of the Indian Ocean Dipole (IOD) index to 12 September 2021 was −0.34 °C.

Three of the five international climate models surveyed by the Bureau anticipate the IOD index will return to negative IOD levels during October. All models indicate a return to a neutral IOD pattern by December. This is consistent with the typical life cycle of an IOD event, which sees events dissipating in early summer with the arrival of the Australian monsoon.

Weekly sea surface temperatures (SSTs) in the Indian Ocean were warmer than average across much of the eastern half of the basin. Compared to two weeks ago, SSTs in the Arabian Sea and around the Horn of Africa have cooled and are generally close to average.

A negative IOD, and a warmer eastern Indian Ocean generally, increase the chances of above average winter–spring rainfall for parts of southern and eastern Australia. Negative IOD events also makes below average maximum temperatures more likely across southern Australia, while maximum and minimum temperatures are more likely to be above average for the northern tropics of Australia.

Cloudiness near the Date Line has generally been close to or slightly below average (positive OLR anomalies) since April, and tended to be a little more consistently below average since June.

Equatorial cloudiness near the Date Line typically increases during El Niño (negative OLR anomalies) and decreases during La Niña (positive OLR anomalies).

The four-month sequence of equatorial Pacific sub-surface temperature anomalies (to August) shows a pattern consistent with a neutral ENSO state, despite the emergence of cool anomalies in the sub-surface of the central to eastern equatorial Pacific during August. Waters were up to two and a half degrees cooler than average across a region of the eastern equatorial Pacific between about 75 m and 125 m depth during August.

The stronger sub-surface anomalies seen in this plot compared to the weekly plot aligns with the slightly off-equatorial position of cool surface anomalies—the month sub-surface plot spans 5° north and south of the equator, while the weekly plot spans a slightly narrower band 2° north and south of the equator.

Weak warm anomalies continue across parts of the column depth west of the Date Line, but were weaker during August than they were in July.

For the five days ending 13 September 2021, sub-surface temperatures were close to average across the equatorial Pacific.

Sub-surface temperatures remain consistent with an ENSO-neutral state.

The El Niño–Southern Oscillation (ENSO) is currently neutral. However, strengthening model outlooks and recent cooling in the tropical Pacific Ocean has raised the chance of La Niña forming in 2021. Consequently, the Bureau has lifted its ENSO Outlook status to La Niña WATCH, meaning around a 50% chance of La Niña forming. This is approximately double the normal likelihood.

Most oceanic and atmospheric indicators of ENSO remain within the ENSO-neutral range. However, sea surface temperatures in the central tropical Pacific Ocean have cooled over the past two months, supported by cooler than average waters beneath the surface. Climate models continue this cooling trend over the coming months, with three of the seven models surveyed by the Bureau meeting La Niña criteria, while two additional models briefly touch La Niña thresholds.

La Niña events increase the chances of above-average rainfall for northern and eastern Australia during spring and summer.

The negative Indian Ocean Dipole (IOD) has weakened, with IOD values at marginal negative IOD levels. However, the pattern of sea surface temperatures in the Indian Ocean remains likely to influence Australian rainfall over the coming months. Models suggest this weak negative IOD pattern could persist at borderline levels through October before easing further. A negative IOD increases the chances of above-average spring rainfall for much of southern and eastern Australia.

The Madden–Julian Oscillation (MJO) has recently stalled over the eastern Indian Ocean. The MJO's influence on the wind patterns across the Maritime Continent region, north of Australia, may have contributed to weakening of the IOD. Most models indicate the MJO is likely to move across Australian longitudes in the coming fortnight, but there is divergence in the forecast strength of the MJO. If the MJO remains moderately strong over Australia longitudes, it would likely lead to increased rainfall over the tropics to Australia's north, and strengthen the trade flow across the central Pacific region.

The Southern Annular Mode (SAM) index has been positive over the past three weeks, and is forecast to remain positive for several weeks to come. This is supported by a strengthened polar vortex over Antarctica. A positive SAM during spring typically brings wetter weather to eastern parts of Australia, but may be drier for western Tasmania.

Climate change continues to influence Australian and global climate. Australia's climate has warmed by 1.44 ± 0.24 °C over 1910–2019, while southern Australia has seen a reduction of 10–20% in cool season (April–October) rainfall in recent decades. Rainfall across northern Australia during its wet season (October–April) has increased since the late 1990s with a greater proportion of high intensity short duration rainfall events.

The Southern Annular Mode (SAM) index is positive, and has been so for the past three weeks. SAM is forecast to remain positive for the next three weeks, and also more generally for October to December.

A strengthened polar vortex over Antarctica is currently assisting this positive phase of SAM.

A positive SAM during spring typically brings wetter weather to eastern parts of Australia, but typically has a drying influence on south-westerly exposed coasts such as western Tasmania.

The El Niño–Southern Oscillation (ENSO) is currently neutral. Most of the international climate models surveyed by the Bureau anticipate tropical Pacific sea surface temperatures will cool during the coming months.

Model outlooks have increased their forecast liklihood of La Niña forming in 2021. Along with cooling in the Pacific, this has led the Bureau to raise its ENSO Outlook status to La Niña WATCH. This means that while ENSO currently remains neutral, the chance of La Niña forming during the southern hemisphere spring has increased to around 50%—twice the normal likelihood.

Five of the seven surveyed models anticipate La Niña thresholds will be met or surpassed for some or all of the months from October to January. Three of the seven surveyed models clearly sustain NINO3.4 above La Niña thresholds for long enough to indicate a full-fledged event (i.e. at least three months). However, only one model currently forecasts La Niña will continue into February, with all other models returning to neutral values by then.

La Niña typically enhances spring rainfall in northern and eastern Australia, and the shift towards cooler forecast values of NINO3.4 may already be contributing to the wetter than average rainfall outlooks for parts of the country.

Product code: IDCKGEWW00