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What is El Nino and what might it mean for Australia?
Have you ever heard about El Niño? As you may be aware that Australia’s weather is influenced by many climate drivers. El Niño and La Niña may be two among the strongest influence on year-to-year climate variability in Australia. They are also a part of a natural cycle known as the El Niño–Southern Oscillation (ENSO) and are associated with a sustained period (many months) of warming (El Niño) or cooling (La Niña) in the central and eastern tropical Pacific. The ENSO cycle loosely operates over timescales from one to eight years.
According to the news on ABC on 14 Sep 2015, it is said man-made global warming is set to produce exceptionally high average temperatures this year and next, boosted by natural weather phenomena such as El Niño, Britain’s top climate and weather body said in a report on Monday. “It looks very likely that globally 2014, 2015 and 2016 will all be amongst the very warmest year ever recorded” Rowan Sutton of the National Centre for Atmospheric Science said. Snowman will introduce what is El Niño and what it means to Austrlians.
What is El Niño and why does it have so much influence over our weather?
El Niño is an ocean and atmospheric phenomenon which has a significant impact on our planet’s weather.
While an El Niño event influences the whole world, the main effect is on the Pacific area, which includes Australia. El Niño in Australia means hot sunny weather and drought.
“During El Niño we have the droughts in western Pacific countries like Austrlia, ” says Dr Wenju Cai, a senior principal research scientist at CSIRO Wealth from Oceans Flagship.
El Niño also results in a hotter average temperature for the whole planet by roughly 0.1 to 0.2 degrees, and this is because the associated change in winds lead to the release of heat from the ocean to the atmosphere.
The two strongest El Niño we know of were in 1982-83 and 1997-98. Dubbed ‘super El Niños’, both these evens had significant global impacts.
“In 1982-83, Australia suffered one of the biggest droughts and we had the Ash Wednesday bushfires and Melbourne was covered by the dust storm.” says Cai.
“In 1997, over 23,000 people were killed due to extreme events, droughts, floods, cyclones.”
Potential effects of El Niño on Australia include:
What causes an El Niños?
An El Niño takes place when sea surface temperatures in the central and eastern tropical Pacific Ocean become substantially warmer than average, causing a shift in atmospheric circulation. Typically, the equatorial trade winds blow from east to west across the Pacific Ocean. El Niños 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 the area to be more favourable for tropical rainfall and cloud development. As a result, the heavy rainfall that usually occurs to the norths of Australia moves to the central and eastern parts of the pacific basin.
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 causes warmer-than-average daytime temperature, 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 sumer (1982 – 83 and 1997 – 98) had all taken place during an El Niño. The warmth of recent El Niño events has been amplified by background warming trends, meaning that El Niño years have been tending to get warmer since the 1950s.
Australian winter-spring mean max. temperature deciles averaged for 12 strong El Niño events
Shift in temperature extremes
For temperature extremes, there are three different measures of heat 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 which 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.
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