Indian ocean dipole iod weather systems

What Is The Indian Ocean Dipole

The Indian Ocean Dipole is a sustained change or difference in the sea surface temperatures of the eastern and western Indian Ocean waters.

It is similar to La Nina and El Nino which are large-scale weather phenomena that affect the western and eastern Pacific Oceans. The IOD is a key driver of Australia’s climate and can have a significant effect on agriculture.

This is because the events coincide with winter crop growing seasons. There are three phases to the IOD: neutral, positive, and negative.

These events usually begin in May or June and peak between August-October. Then, they rapidly decline when the monsoon arrives in the southern hemisphere towards the end of spring.

Sea Surface Temperatures

Temperature patterns and rainfall patterns in Australia are affected by Indian Ocean sea surface temperatures. Higher than average sea surface temperatures may provide more moisture to frontal systems and lows that cross Australia.

The Indian Ocean Dipole Phases

Neutral IOD phase

Iod neutral

The Pacific water flows between the Indonesian islands, keeping the northwest coast of Australia warm. The Indian Ocean basin’s western half is covered by air, which rises and falls above the area. This creates westerly winds that blow along the equator.

The tropical Indian Ocean has temperatures that are very close to the normal range. Therefore, the neutral IOD does not affect Australia’s climate.

Positive IOD Phase

Iod positive

The equator is where westerly winds become weaker, allowing warm water toward Africa. Cool water can also rise from the eastern deep oceans due to changes in winds. This creates a temperature differential across the tropical Indian Ocean, with water that is cooler than normal in the east and more warm than usual in the west.

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This means that there is generally less moisture in the atmosphere to the northwest than usual. This alters the flow of weather systems from Australia’s West, which often results in lower rainfall and higher temperatures than usual over parts of Australia during winter or spring.

Positive IOD Phase Effects

Rainfall is lower than the average in parts of Australia.

Negative IOD Phase

Iod negative

The equator is where westerly winds are strongest, which allows warmer waters to condense near Australia. This creates a temperature differential across the tropical Indian Ocean with warmer water to the east and cooler water to the west.

Negative IODs are more common in parts of southern Australia than the average winter-spring rainfall. This is because the warmer waters off Northwest Australia offer more moisture for weather systems that cross the country.

Negative IOD Phase Impacts

Sometimes, rainfall is higher than the average in southeastern Australia.

When the Pacific and Indian oceans work together

When La Nina/El Nino and An IOD

The major climate driver for the Pacific Ocean is the El Nino-Southern Oscillation. It can have a significant impact on Australia’s climate. El Nino years are more humid and warmer in eastern Australia than La Nina years, which tend to be wetter and cooler across most of the country.

If El Nino occurs in conjunction with a positive IOD the two phenomena can increase their dry effects. The same applies to La Nina when it coincides with a negative IOD.  IOD  The likelihood of receiving above-average winter-spring rains usually increases.

Indian Ocean Dipole years

From 1960, when reliable records of the IOD began, to 2016 there have been 11 negative IOD and 10 positive IOD events.

Negative IOD years

There have only been 5 years in total since 1960 that the IOD and La Nina have coincided in the same year

  • 1960
  • 1964 – Negative IOD/La Nina
  • 1974 – Negative IOD/La Nina
  • 1981
  • 1989 – Negative IOD/La Nina
  • 1992
  • 1996
  • 1998 – Negative IOD/La Nina
  • 2010 – Negative IOD/La Nina
  • 2014
  • 2016 – Negative IOD/El Nino

Positive IOD years

  • 1961
  • 1963 – Positive IOD/El Nino
  • 1972 – Positive IOD/El Nino
  • 1982 – Positive IOD/El Nino
  • 1983
  • 1994 – Positive IOD/El Nino
  • 1997 – Positive IOD/El Nino
  • 2006 – Positive IOD/El Nino
  • 2015 – Positive IOD/El Nino

Further Reading

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