Atmospheric Systems

Estimated lesson length

45 minutes - 1 hour.

Outcomes

GE-11-02 explains geographical processes and influences, at a range of scales, that form and transform places and environments

GE-11-07 applies geographical inquiry skills and tools, including spatial technologies, fieldwork, and ethical practices, to investigate places and environments

GE-11-08 applies mathematical ideas and techniques to analyse geographical data

Syllabus content

The processes, cycles and circulations connecting natural systems, including:
- - atmospheric systems
The natural processes, cycles and circulations that have shaped the land and/or water cover of ONE place

Learning intentions

Understand the phenomena of El Niño and La Niña and their effects on weather
Recognise the features of an East Coast Low
Develop knowledge of weather maps and the factors that influence weather forecasting.

Success criteria

Demonstrate an understanding of of El Niño and La Niña by writing a written response predicting the effects of current climate conditions on the Hawkesbury-Nepean catchment using real time data
Demonstrate an understanding of weather forecasting, including the features of an East Coast Low, by responding to a variety of weather map questions.

El Niño - Southern Oscillation (ENSO)

Source 1:Video - Understanding Enso (Bureau of Meteorology)

Watch the video to gain a better understanding of ENSO and its influence on weather.

El Niño and La Niña are two phases of the El Niño-Southern Oscillation (ENSO) climate pattern, which is a natural climate phenomenon. They occur when the Pacific Ocean and the atmosphere above it change from their neutral ('normal') state for several seasons.

El Niño occurs when sea surface temperatures in the central and eastern tropical Pacific Ocean become much warmer than average. As a result, a shift in atmospheric circulation occurs. Usually, equatorial trade winds blow from east to west across the Pacific Ocean. El Niño events often lead to a weakening, or even reversal, of the prevailing trade winds. When this happens, ocean temperatures become warmer in the central and eastern Pacific making these areas more favourable for cloud development and tropical rainfall. Consequently, the heavy rainfall that would normally occur in Australia, moves to the central and eastern parts of the Pacific.

In contrast, La Niña is characterised by a cooling of sea surface temperatures in the central and eastern tropical Pacific Ocean. This occurs as a result of trade winds becoming stronger which draws cooler, deep water from below. This makes the central and eastern Pacific region less favourable for cloud and rain. These sames strong trade winds help to pile up warm surface waters in the western Pacific and to the north of Australia. As a result, the western Pacific area becomes more favourable for rising air, cloud development and rainfall potentially causing heavy rainfall to occur over Australia.

Typical effects of an El Niño event on the Hawkesbury-Nepean Catchment include:

Drier and warmer conditions which can lead to prolonged periods of drought
Dry vegetation becomes susceptible to ignition. This leads to an increased bushfire risk
Greater Sydney relies on much of the Hawkesbury-Nepean Catchment for its water supply. Prolonged dry spells can lead to decreased water storage levels impacting Greater Sydney's drinking water supply
The Hawkesbury-Nepean River system supports a $259 million agriculture industry. Reduced rainfall and higher temperatures can lead to lower crop yields and poor conditions for pastoral farming.

Typical effects of a La Niña event on the Hawkesbury-Nepean Catchment include:

Above average rainfall and more intense rainfall events which can lead to flooding
Excessive rainfall can lead to waterlogging and runoff, affecting the quality of water in reservoirs
Increased rainfall also has benefits for natural ecosystems such as forests and wetlands as it supports plant growth and generally enhances river health. It also supports crop growth and creates better conditions for pastoral farming.

Source 2:A view of the extent of the July 2022 Hawkesbury River flood from the Lookout Classroom, Brewongle EEC.

Source 3:A view of the south side of the Hawkesbury River during the July 2022 flood from the Lookout Classroom, Brewongle EEC.

East Coast Lows

East Coast Lows (ECL) are intense low pressure systems which occur, on average, several times each year off the eastern coast of Australia. ECLs are more common during autumn and winter but can occur all year round. ECLs can generate heavy widespread rainfall, gale or storm force winds along the coast and adjacent waters, and very rough seas and heavy swells.

The Hawkesbury-Nepean Catchment is one of the largest coastal basins in NSW with numerous tributaries that flow into the Hawkesbury-Nepean River. The combination of the geography of the Hawkesbury-Nepean catchment and the heavy, prolonged rainfall that occurs during East Coast Lows can lead to widespread flooding. The major floods of March 2021, March 2022 and July 2022 were all preceded by an ECL. They also occurred during a triple La Niña event which lasted from late 2020 to mid 2022.

Watch the video on East Coast Lows to gain a better understanding of how this weather event impacts the Hawkesbury-Nepean Catchment.

Source 4:Video - Ask the Bureau: What is an East Coast Low? (Bureau of Meteorology)

Source 5:Weather Map of Australia. 4/8/2022http://www.bom.gov.au/australia/charts/archive/index.shtml

Activities:

Using the Bureau of Meteorology’s Climate Driver Update site: http://www.bom.gov.au/climate/enso/

a) Provide a short summary of the current climate driver update for the east coast of Australia including the causes of the current weather patterns.

b) Using the climate driver update web page and the information above on El Niño and La Niña events, predict the effects of the current climate driver update on the Hawkesbury-Nepean Catchment.

2. Source 5 shows the weather conditions in Australia on the 4th of July, 2022, the day before the worst floods recorded in the Hawkesbury in 44 years.

Using Source 5 and the below Bureau of Meteorology page 'The art of the chart: how to read a weather map' to assist you, answer the following questions to consolidate your knowledge of East Coast Lows.

https://media.bom.gov.au/social/blog/2391/the-art-of-the-chart-how-to-read-a-weather-map/

a) What type of pressure system is the east coast of NSW experiencing?

b) What kind of weather is typically associated with this type of pressure system?

c) What type of front is approaching the east coast of NSW?

d) What kind of weather is typically associated with this type of front?

e) What does the dashed line on the east coast of Australia indicate? How is it impacting the weather in this region?

f) Is the east coast of Australia experiencing strong or light winds? Explain how you know.

Sources:
http://www.bom.gov.au/climate/enso/history/ln-2010-12/ENSO-what.shtml#:~:text=They%20occur%20when%20the%20Pacific,cooling%20of%20these%20same%20areas.
http://www.bom.gov.au/weather-services/severe-weather-knowledge-centre/eastcoastlows.shtml#:~:text=ECLs%20can%20generate%20one%20or,cause%20damage%20to%20the%20coastline.
https://media.bom.gov.au/social/blog/2391/the-art-of-the-chart-how-to-read-a-weather-map/

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