Bureau of Meteorology – What is El Nino?


What is El Niño and what might it mean for Australia?


Australia’s weather is influenced by many climate drivers. El Nino and La Nina have perhaps the strongest influence on year-to-year climate variability in Australia. They are a part of a natural cycle known as the El Nino Southern Oscillation (ENSO) and are associated with a sustained period (many months) of warming (El Nino) or cooling (La Nina) in the central and eastern tropical Pacific. The ENSO cycle loosely operates over timescales from one to eight years.

Potential effects of El Nino on Australia include:

  • Reduced rainfall
  • Warmer temperatures
  • Shift in temperature extremes
  • Increased frost risk
  • Reduced tropical cyclone numbers
  • Later monsoon onset
  • Increased fire danger in southeast Australia
  • Decreased alpine snow depths

What causes an El Nino?

An El Nino occurs when sea surface temperatures in the central and eastern tropical Pacific Ocean become substantially warmer than average, and this causes a shift in atmospheric circulation. Typically, the equatorial trade winds blow from east to west across the Pacific Ocean. El Nino events are associated with a weakening, or even reversal, of the prevailing trade winds.

Warming of ocean temperatures in the central and eastern Pacific causes this area to become more favourable for tropical rainfall and cloud development. As a result, the heavy rainfall that usually occurs to the north of Australia moves to the central and eastern parts of the Pacific basin.

Monitoring El Nino

The term El Nino describes a particular phase of the ENSO climate cycle. ENSO is a coupled atmosphere-ocean phenomenon, which means that the transition between La Nina, El Nino and neutral conditions (neither El Nino nor La Nina) is governed by interactions between the atmosphere and ocean circulation.

In the ocean, ENSO is most commonly monitored through observed sea surface temperatures within a boxed region of the central and eastern tropical Pacific known as NINO3.4. In the atmosphere, ENSO is monitored via the Southern Oscillation Index (SOI), a measure of atmospheric circulation that takes the difference of atmospheric pressure between Darwin and Tahiti.

El Nino and La Nina are not turned on and off like a switch. Rather, El Nino and La Nina are a function of the strength of departures from average in NINO3.4 and the SOI.

El Nino events are typically defined when SOI values fall below 8 and NINO 3.4 temperatures are more than 0.8°C above average.

Events that maintain close to these threshold values are generally classified as moderate to weak, while those that greatly exceed them are referred to as strong. The strength of an event is not always reflected in the strength of its effects on weather, and events which don’t quite reach El Nino threshold levels may sometimes be associated with El Nino-like effects on weather.

Potential effects of El Nino

Reduced rainfall

The shift in rainfall away from the western Pacific, associated with El Nino, means that Australian rainfall is usually reduced through winter-spring, particularly across the eastern and northern parts of the continent.

Nine of the ten driest winter-spring periods on record for eastern Australia occurred during El Nino years. In the Murray-Darling Basin, winter-spring rainfall averaged over all El Nino events since 1900 was 28% lower than the long-term average, with the severe droughts of 1982, 1994, 2002 and 2006 all associated with El Nino

Australian winter spring mean rainfall deciles averaged for twelve strong El Niño events.

Australian winter spring mean rainfall deciles averaged for twelve strong El Nino events.

Although most major Australian droughts have been associated with El Nino, analysis of past El Nino events shows that widespread drought does not occur with every event, and the strength of an El Nino is not directly proportional to the rainfall impacts. For example, during the very strong El Nino that occurred in 1997–98 impacts on rainfall were generally confined to coastal southeastern Australia and Tasmania, while the relatively weak event of 2002–03 saw widespread and significant drough    

Growing season (April–November) rainfall anomalies for eastern Australian plotted against the SOI averaged for April–November for all years from 1900 to 2013, showing the varied effect of both strong and weak El Niño events on rainfall. El Niño is typically associated with sustained negative SOI values.

Growing season (April-November) rainfall anomalies for eastern Australian plotted against the SOI averaged for April–November for all years from 1900 to 2013, showing the varied effect of both strong and weak El Nino events on rainfall. El Ninois typically associated with sustained negative SOI values.

Warmer temperatures

El Niño years tend to see warmer-than-average temperatures across most of southern Australia, particularly during the second half of the year. In general, decreased cloud cover results in warmer-than-average daytime temperatures, particularly in the spring and summer months. Higher temperatures exacerbate the effect of lower rainfall by increasing evaporative demand. Prior to 2013 (a neutral ENSO year), Australia’s two warmest years for seasonal daytime temperatures for winter (2009 and 2002), spring (2006 and 2002), and summer (1982–83 and 1997–98) had all occurred during an El Niño. The warmth of recent El Niño events has been amplified by background warming trends which means that El Niño years have been tending to get warmer since the 1950s.

Australian winter–spring mean maximum temperature deciles averaged for twelve strong El Niño events.

Australian winter–spring mean maximum temperature deciles averaged for twelve strong El Niño events.

Shift in temperature extremes

For temperature extremes, there are three different measures of heat that are relevant to El Niño: wide-area heatwaves (as indicated by a very warm national area-average temperature); single-day extremes at specific point locations; and long-duration warm spells. The relationship of El Niño with each of these elements may be quite different, and location dependant.

During the warmer half of the year, there is a tendency for weather systems to be more mobile during El Niño years, with fewer blocking (stationary) high pressure systems. This means that for southern coastal locations such as Adelaide and Melbourne, individual daily heat extremes tend to be of greater intensity (hotter) during El Niño years but there is a reduced frequency of prolonged warm spells. Further north, El Niño is associated with both an increase in individual extreme hot days and multi-day warm spells.

Increased frost risk

Although maximum temperatures are generally warmer than average during El Niño years, decreased cloud cover often leads to cooler-than-average night-time temperatures during winter–spring, particularly across eastern Australia. For example, regions of southern New South Wales and northern Victoria can experience 15–30% more frost days during El Niño than the historical average; frost days which occur during spring can have significant impacts on agriculture. The Australian record cold temperature of −23.0 °C was observed at Charlotte Pass, New South Wales, on 29 June 1994 in an El Niño year.

Reduced tropical cyclone numbers

On average, there are fewer tropical cyclones in the Australian region during El Niño years. This is particularly true around Queensland, where cyclones are half as likely to cross the coast during El Niño years compared to neutral years. This means a decreased likelihood of major damage and flooding related to strong winds, high seas and heavy rains associated with tropical cyclones.

Later monsoon onset

The date of the monsoon onset in tropical Australia is generally 2–6 weeks later during El Nino years than in La Nina years. This means that rainfall in the northern tropics is typically well-below-average during the early part of the wet season for El Nino years, but close to average during the latter part of the wet season.

Australian mean rainfall deciles during October–December averaged for twelve strong El Niño events.Australian mean rainfall deciles during February–April averaged for twelve strong El Niño events.

Australian mean rainfall deciles during October–December (left) and February–April (right) averaged for twelve strong El Niño events.

Increased fire danger in southeast Australia

As a result of decreased rainfall and increased maximum temperatures, the frequency of high fire danger ratings and risk of a significant fire danger season in southeast Australia are significantly higher following an El Niño year, particularly when combined with a positive Indian Ocean Dipole (IOD) event. Some El Niño years have been followed by very severe summer fires, including Ash Wednesday (16 February 1983) and the 2002–03 and 2006–07 seasons.

However, not all major fires follow El Niño years. The spring bushfires in the Blue Mountains during October 2013 occurred during a neutral ENSO year, while Black Saturday (7 February 2009) in fact followed a weak La Niña (but notably, a positive IOD).

Decreased alpine snow depths

El Nino years (as well as positive IOD years) tend to have lower snow depths in Australia’s alpine regions. On average, the peak snow depth measured at Spencer’s Creek is 35 cm lower during El Nino years, and the season length (i.e. the period of time with snow depths greater than 100 cm) is 2.5 weeks shorter. The four lowest peak snow depths on record were all measured during El Nino years; notably, snow depths never reached 100 cm in 1982 or 2006.

However, El Nino does not guarantee a poor snow season. Indeed, three El Nino years (1972, 1977 and 1991) actually had well-above-average peak snow depths. Cooler night-time temperatures and lower rainfall during El Nino years can often mean that the snow which does fall is retained and can aid artificial snowmaking which many resorts use to supplement the natural snow they receive.

Forecasting ENSO

The significant impacts that El Nino and La Nina can have across Australia and the wider globe make the ability to forecast these events important for agriculture, businesses and communities. The Bureau of Meteorology routinely issue seasonal forecasts which include ENSO outlooks for the next several months. While the skill of these longer-range outlooks varies with the time of year and decreases the further into the future they go, the outlooks can provide useful information about when an El Nino or La Nina likely to occur and how long it might last.

Forecasts of the likelihood of ENSO events take into account temperature patterns across the tropical Pacific Ocean, both at the surface and in the sub-surface, variations in trade wind strength and atmospheric pressure, and ocean currents. The atmospheric and oceanic conditions are analysed by climate models designed for long-range seasonal outlooks. Ultimately, the occurrence of an El Nino requires ocean and atmospheric anomalies to come together and become self-reinforcing.

For the most recent information on the likelihood of El Nino or La Nina events, visit the Bureau’s ENSO Wrap-Up and ENSO tracker web pages, both updated every fortnight. For a summary of climate model outlooks for El Nino and La Nina, our Climate Model Summary page surveys eight international models, and is updated on the 16th of every month. You can sign up to email alerts for all these products.

Further information

See our website for further information about average El Nino rainfall patterns and past events, as well as current ENSO conditions.


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  • Cai W, Cowan T, Raupach M. 2009. Positive Indian Ocean Dipole events precondition southeast Australia bushfires. Geophys. Res. Lett., 36, L19710.
  • Drosdowsky W, Wheeler MC. 2014. Predicting the Onset of the North Australian Wet Season with the POAMA Dynamical Prediction System. Wea. Forecasting, 29, 150–161.
  • Kuleshov Y, Qi L, Fawcett R, Jones D. 2008. On tropical cyclone activity in the Southern Hemisphere: Trends and the ENSO connection. Geophys. Res. Lett., 35, L14S08.
  • Nicholls N, Lucas C. 2007. Interannual variation of area burnt in Tasmanian bushfires: relationships with climate and predictability. International Journal of Wildland Fire, 16(4020), 540–546.
  • Power S, Haylock M, Colman R, Wang X, 2006. The Predictability of Interdecadal Changes in ENSO Activity and ENSO Teleconnections. J. Climate, 19, 4755–4771.
  • Williams AAJ, Karoly DJ, Tapper N. 2001. The sensitivity of Australian fire danger to climate change. Climatic Change, 49, 171–191.

NASA: Earth Climate Changes Affect Earths Rotation


March 4, 2003 – (date of web publication)



image of the earth

Image 1

Click on image or here for animation.

Because of Earth’s dynamic climate, winds and atmospheric pressure systems experience constant change. These fluctuations may affect how our planet rotates on its axis, according to NASA-funded research that used wind and satellite data.

NASA’s Earth Science Enterprise (ESE) mission is to understand the Earth system and its response to natural and human-induced changes for better prediction of climate, weather and natural hazards, such as atmospheric changes or El Niño events that may have contributed to the affect on Earth’s rotation.


graph of angular momentum

Image 2


Changes in the atmosphere, specifically atmospheric pressure around the world, and the motions of the winds that may be related to such climate signals as El Nino are strong enough that their effect is observed in the Earth’s rotation signal, said David A. Salstein, an atmospheric scientist from Atmospheric and Environmental Research, Inc., of Lexington, Mass., who led a recent study.

From year to year, winds and air pressure patterns change, causing different forces to act on the solid Earth. During El Nino years, for example, the rotation of the Earth may slow ever so slightly because of stronger winds, increasing the length of a day by a fraction of a millisecond (thousandth of a second).

Issac Newton’s laws of motion explain how those quantities are related to the Earth’s rotation rate (leading to a change in the length of day) as well as the exact position in which the North Pole points in the heavens (known also as polar motion, or Earth wobble).

To understand the concept of angular momentum, visualize the Earth spinning in space. Given Earth’s overall mass and its rotation, it contains a certain amount of angular momentum. When an additional force acting at a distance from the Earth’s rotational axis occurs, referred to as a torque, such as changes in surface winds, or the distribution of high and low pressure patterns, especially near mountains, it can act to change the rate of the Earth’s rotation or even the direction of the rotational axis.

Because of the law of “conservation of angular momentum,” small but detectable changes in the Earth’s rotation and those in the rotation of the atmosphere are linked. The conservation of angular momentum is a law of physics that states the total angular momentum of a rotating object with no outside force remains constant regardless of changes within the system.

An example of this principle occurs when a skater pulls his or her arms inward during a spin (changing the mass distribution to one nearer the rotation axis, reducing the “moment of inertia,” and speeds up (increasing the skater’s spin); because the moment of inertia goes down, the spin rate must increase to keep the total angular momentum of the system unchanged.

The key is that the sum of the angular momentum (push) of the solid Earth plus atmosphere system must stay constant unless an outside force (torque) is applied, Salstein said. So if the atmosphere speeds up (stronger westerly winds) then the solid Earth must slow down (length-of-day increases).Also if more atmosphere moves to a lower latitude (further from the axis of rotation), and atmospheric pressure increases, it also gains angular momentum and the Earth would slow down as well.

Other motions of the atmosphere such as larger mass in one hemisphere than the other can lead to a wobble (like a washing machine with clothes off-balance) and the poles move, in accordance to the law of the conservation of angular momentum.

Salstein looked at wind and pressure measurements from a National Weather Service analysis that makes use of a combination of ground-based, aircraft, and space-based observations. The measurements for the Earth’s motions come from a variety of space-based measurements including satellites, like those in the Global Positioning System (GPS), the geodetic satellites that included records from NASA’s older LAGEOS satellite, and observations of distant astronomical objects using a technique known as Very Long Baseline Interferometry. Understanding the atmospheric pressure patterns, moreover, is essential to interpret results from NASA’s Gravity Recovery and Climate Experiment (GRACE).

The fact that the two vastly different systems, namely the meteorological and the astronomical, are in good agreement according to the conservation of angular momentum gives us assurance that both these types of measurements must be accurate. It shows, moreover, that changes in climate signals can have global implications on Earth’s overall rotation.

NASA’s ESE research focuses on the changes and variability in the Earth system, including atmospheric, oceanic, and geodetic areas. This research was recently presented at the annual meeting of the American Meteorological Society in Long Beach, Calif.

Make Peace With Who You Are

To make peace with who you are is the purpose of our lives. Until you find peace the world cannot change for you.  As you feel peace arise you will see the world differently. Often we project onto the world unquestioned fears. Imagine projecting inspired tears sparkling with love.