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
- See also: Links open in new window
- About Australian climate influences
- Climate model summary
- Long-range outlook
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 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.
International climate model outlooks
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 outlook
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
- Table of monthly SOI values
- 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
The following links provide further information regarding the El Niño Southern Oscillation and its impact on the Australian Climate.
El Niño, La Niña and Australia's Climate (pdf) provides further detail on ENSO and its impact on Australia.
The Latest Climate Driver Update provides the latest information on the state of ENSO and the likely effect this will have on Australia.
Australian Rainfall Patterns during El Niño and La Niña Events gives further case studies for the Australian region.
- Past La Niña events
- Past El Niño events
- Rainfall during El Niño
- Rainfall during La Niña
- 2010–11 and 2011–12 La Niña events
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 outlooks
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 outlook
- 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) outlook
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
- Have a look at the latest atmospheric circulation patterns.
- Current values of the Antarctic Oscillation Index (an index related to the strength and phase of the SAM) are available from the US National Weather Service (NOAA)
- The relationship between the SAM and Australian rainfall is discussed in detail in this research paper.
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.
Weekly tropical climate note
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 note
- Tropical monitoring (MJO)
About the Madden–Julian Oscillian (MJO) outlook
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 Weekly Tropical Climate Note 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
The July monthly SST map shows a decrease in extent and intensity of cooler than average SSTs in the eastern tropical Pacific Ocean, compared to June, in some of the equatorial Pacific, while anomalies have strengthened closer to the South American coast. Cool anomalies persist along the equator extending from the South American coast to 150°W. Warmer than average SSTs in the western equatorial Pacific and in the Tasman Sea generally weakened compared to June.
The July values of the three key NINO indices were: NINO3 −0.3 °C, NINO3.4 0.0 °C, and NINO4 +0.2 °C.
The sea surface temperature (SST) map for the tropical Pacific Ocean for the week ending 2 August show cool SST anomalies in the eastern equatorial Pacific, extending along the coastline of South America in the tropics, and along the equator well into the central Pacific. Compared to two weeks ago cool anomalies have strengthened and now extend further into the central Pacific.
Warm SST anomalies are still present in the far west of the equatorial Pacific, and in waters close to the continent around much of Australia.
The latest values of the three NINO indices in the tropical Pacific for the week ending 2 August were: NINO3 −0.4 °C, NINO3.4 −0.3 °C, NINO4 0.0 °C. All three indices have cooled over the past fortnight.
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 2 August was +3.2. The 90-day value was −0.4. Both are within the ENSO-neutral range.
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 2 August were close to average across the tropical Pacific, which is consistent with neutral ENSO conditions.
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.
MJO currently weak
The Madden-Julian Oscillation (MJO) is currently weak but continues to track eastward and is now located to Australia's north, in the western Maritime Continent. Most climate models indicate the pulse will slow down in the coming days before weakening and likely becoming indiscernible.
At this time of the year, an MJO pulse over the Maritime Continent has only a small influence on rainfall patterns across northern Australia.
Much of the eastern Indian Ocean remains warmer than average, although the Indian Ocean Dipole (IOD) is currently neutral. The latest weekly value to 2 August was +0.28 °C.
One of the six international climate models surveyed by the Bureau exceeds the negative IOD threshold during August, a second joins in September, and a third reaches the threshold in October. The other three models maintain neutral values throughout the outlook period.
A negative IOD typically brings above average winter–spring rainfall to much of southern Australia.
Cloudiness near the Date Line was below average over the past fortnight and has generally been below average since early to mid-March. Overall, cloud patterns are consistent with neutral ENSO conditions.
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 July) shows areas of cooler than average water in both the central and eastern equatorial Pacific, between about 100 and 200 m in the central equatorial Pacific and the top 100 m depth in the east. Compared to June, the strength and extent of cooler than average water has decreased.
Weak warm anomalies persist across much of the column depth west of the Date Line.
Since January, the pattern of cooler anomalies at depth has persisted, providing conditions favourable for potential La Niña development, although July has seen some weakening of these patterns.
For the five days ending 2 August, sub-surface temperatures were slightly cooler than average in the central equatorial Pacific between 100 and 200 m, while water was very slightly warmer than average in the top 100 m of the far eastern equatorial Pacific. Cool anomalies reached just over 2 degrees cooler than average around 150°W. Elsewhere in the sub-surface of the equatorial Pacific Ocean temperatures were close to average. The volume and intensity of cooler than average water is generally similar to two weeks ago, but anomalies are located further east.
The El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are neutral. The Bureau's ENSO Outlook remains at La Niña WATCH, indicating the chance of La Niña forming in 2020 is around 50%— roughly twice the average likelihood.
In the tropical Pacific Ocean, surface and sub-surface waters have cooled since April 2020. The latest weekly values have continued this trend. All surveyed international climate models anticipate further cooling is likely in the coming months with most models exceeding the La Niña threshold during spring.
Other ENSO indicators, such as the Southern Oscillation Index (SOI), trade winds, and cloudiness near the Date Line are ENSO neutral but show signs consistent with a developing La Niña. The latest trade winds have been stronger than average while the SOI has increased since the beginning of July. Equatorial cloudiness near the Date Line is below average.
Large parts of the eastern Indian Ocean are warmer than average. The Indian Ocean Dipole (IOD) is currently neutral. Half of the six surveyed models indicate negative IOD thresholds could be met or exceeded during spring.
Both La Niña and negative IOD typically increase the chance of above average rainfall across much of Australia during spring.
The Southern Annular Mode (SAM) is positive and is expected to increase to strongly positive values over the coming week before decreasing over August. In winter, a positive SAM typically reduces rainfall in southern parts of the country, but can enhance rainfall in New South Wales and southern Queensland.
The Madden–Julian Oscillation (MJO) is over the Maritime Continent but is forecast to weaken over the coming week. Its influence on rainfall patterns across northern Australia is likely to be weak.
SAM currently positive, likely to strengthen
The Southern Annual Mode (SAM) is currently positive, and is expected to further increase to strongly positive values over the coming week before declining but remaining positive for the remainder of August.
A positive SAM at this time of year would typically see below average rainfall across far southern parts of the country, but can increase rainfall in northern New South Wales and southern Queensland.
All of the international climate models surveyed by the Bureau indicate central tropical Pacific sea surface temperatures in the NINO3.4 region will cool further in the coming months. One of the eight surveyed models reaches the La Niña threshold during August, with four more models approaching the threshold by October. The remaining three models maintain neutral levels through the outlook period.
ENSO events—El Niño or La Niña—typically begin to develop during the southern hemisphere autumn to winter, before strengthening in winter to spring.
Product code: IDCKGEWW00
