week 4.2 australia's climate

AUSTRALIA’S CLIMATE

Week 4.2: 17 August

ESSAY DUE DATE CHANGE

Essay is now due on MONDAY the 19th of September

Hand in Essays BY 5PM

Submit essays to LearnJCU safe assign. Will be under “assessment” on LearnJCU

Townsville: Hand essays to the TRC office on the top floor of building 34.

Cairns: Hand in essays to office on top floor of A2.

Everyone: Please fill out a cover sheet with your essay. When you hand it in to the office, they will time stamp it (Cairns I know that they are sometimes not there, we will figure something out).

Australia’s Climate

What are some of the influences on Australia’s climate?

Latitudinal Zones

The subtropical ridge and blocking highs

Cut off lows, case study: Newcastle June 2007

Easterly troughs

El Niño/La Niña

Frontal systems

The Indian Ocean Dipole

The monsoon

Northwest cloud bands

Australia’s Climate

The Bureau of Meteorology website has an excellent breakdown of Australia’s weather systems.

http://www.bom.gov.au/climate/about/



http://www.rentoid.com/blog/tag/peer-to-peer/


http://www.bom.gov.au/climate/about/?bookmark=stridge

Latitudinal Zones

http://www.nature.com/nclimate/journal/v2/n4/fig_tab/nclimate1430_F2.html

• Australia lies across

three latitudinal zones:

1. Tropic zone (Darwin,

FNQ)

2. Sub-tropic zone

(Bundaberg, Brisbane)

3. Southern Temperate

Zone

The subtropical ridge and blocking highs

Australia’s Climate: The Subtropical Ridge

A string of high pressure systems across Australia.

High pressure systems generally move Eastwards along the ridge.

During summer:

the ridge sits low across Australia, brings dry and stable conditions.

The H pressure systems block cold fronts from moving North “shielding” Southern Australia from rainy weather.

In Autumn the ridge moves North, bringing dry and stable conditions North.

Southern Australia not shielded from cold fronts, more intense rain and cooler temperatures come up from the South.

The centre of Australia is affected by these H pressure systems most of the year, making it one of the driest areas on Earth.

Australia’s Climate: Blocking High


Blocking highs are strong high pressure systems which have formed further south than usual and remain near stationary for an extended period of time.

These highs essentially "block" the west to east progression of weather systems travelling Eastward across southern Australia.


Blocking highs are often, although not always, associated with a cut-off low which may form to the north of the blocking high, the two systems creating a blocking pattern.

As frontal systems approach the blocking high, they slow down, weaken and tend to slip to the south of the high pressure system.

http://www.bom.gov.au/climate/about/?bookmark=cutofflow

http://www.bom.gov.au/climate/about/?bookmark=fronts


Blocking highs have a wide range of impacts depending on their location and strength.

A blocking high can produce a hot spell, a cold spell, dry conditions or wet conditions depending on it's location and the systems around it. Blocking highs can also be associated with greater probabilities of fog and frost occurrence.

A blocking high can protect the area under it from an approaching front, but the area to the West of the BH will likely get a lot of rainfall from the front, as it is slowed down by the BH.

If the high was associated with a cut off low forming a blocking pattern, then affected areas could experience sustained heavy rainfall.


Front moving towards

Blocking High is

slowed down, wet

weather stays here

Winds are warmer above

the high

Southerly winds are

cooler below the high

Australia’s Climate: Cut off lows

Australia’s Climate: Cut off lows

Cut-off lows are low pressure systems which have broken away, or are cut-off, from the main belt of low pressure which lies to the south of Australia.

A cut-off low can also develop when a low pressure system forms on an active cold front or when an easterly flow hits the northern side of a slow-moving or blocking high.

East coast lows are a form of intense cut-off low.

Cut-off lows are associated with sustained, and often heavy, rainfall and can produce strong and gusty winds and high seas.

Australia’s Climate: East Coast lows

Australia’s Climate: East coast lows

East coast lows are intense low-pressure systems which occur on average several times each year off the eastern coast of Australia.

in particular southern Queensland,

New South Wales (NSW) and

eastern Victoria.

East coast lows will often rapidly intensify overnight making them one of the more dangerous weather systems to affect the southeast Australian coast.

East coast lows are generally associated with strong and gusty winds, sustained heavy rainfall and high seas. They can cause widespread damage over a very short period of time.

East coast lows: Newcastle June 2007

On the 7th of June 2007, a small but dangerous east coast low formed off the coast of NSW. Over the following few days it caused widespread damage along the NSW coast.

This small scale low crossed the coast of NSW near Newcastle at around 1.30am local time on the 9th of June.

This event caused widespread damage in the coastal parts of the Hunter, Central Coast and Sydney Metropolitan areas of NSW, resulting from sustained heavy rain, strong winds and large ocean waves and swell.

http://www.theherald.com.au/story/492718/artist-to-sculpt-pasha-

bulker-piece-at-nobbys/


Impacts of this east coast low included:

nine fatalities due to flooding and high winds;

major flooding in the Hunter Valley;

gale force winds and flash flooding in Newcastle and the Central Coast; and

beach erosion at many Sydney beaches caused by huge swells.

In addition, Cremorne Wharf collapsed into Sydney Harbour due to large waves and the 76,000 tonne bulk ore carrier Pasha Bulker became grounded on Newcastle Beach.


14.1 metre wave heights. This was the highest wave height recorded since records began in 1992.

Flooding and high winds caused loss of power to over 200,000 homes in the Sydney-Newcastle area.

About 6 cm of snow closed New England Highway in Murrurundi-Tamworth area and on the Northern Tablelands.

Wind gusts of up to 136 km/h were recorded.

Rainfall totals for the week were very high, with many locations setting new rainfall records

Australia’s Climate: Easterly Troughs

Easterly troughs are a dominant feature over Australia during the summer months.

The trough is located on the lee side (inland side) of the Great Dividing Range,

It extends through central Queensland and central New South Wales, sometimes extending right down into northern Victoria.


http://www.ga.gov.au/scientific-topics/hazards/flood/basics/gallery



A trough is an elongated Low pressure system .

Forms a boundary between the moist air near the coast and dry air inland.

It is partly formed by the intense heating of the land during the summer months, but the topography of the region also plays a role.

While an easterly trough forms to the west of The Great Dividing Range, a ridge of higher pressure will also form along the coast.


This pattern (windward ridge/ lee trough) is also observed in other parts of the world where wind patterns and topography are similarly aligned, such as in the South Island of New Zealand.

A trough system is also present near the west coast of Western Australia during the summer months (known as the west coast), however this trough does not have as large an impact on rainfall as the easterly trough.

Australia’s Climate: El Niño La Niña

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.

Associated with a weaker Walker Circulation (see diagram below) and brings 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.

Australia’s Climate: El Niño

Australia’s Climate: La Niña


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.

El Niño is normally associated with lower than average winter/spring rainfall over much of eastern Australia.

La Niña is normally associated with higher than average winter, spring and early summer rainfall over much of Australia.

Australia’s Climate: Frontal Systems

Australia can be affected by both warm fronts and cold fronts, however cold fronts are more common and have a greater impact on the Australian region.

Frontal systems bring rainfall to southern Australia.

These frontal systems vary in their intensity and speed, and the more intense (stronger) systems are generally associated with heavier rainfall. If frontal systems are slower moving, then rainfall may occur for extended periods and may be heavy at times.

Australia’s Climate: Indian Ocean

Sea Surface Temperatures in the Indian Ocean can influence the rainfall patterns over much of Australia.

The most commonly referred to Indian Ocean influence upon Australian climate is called the Indian Ocean Dipole (IOD).

Australia’s Climate: Indian Ocean and Frontal Systems

Australia’s Climate: The Monsoon

A monsoon is a seasonal shift in winds.

Caused by the summer heating of continents, where the land is heated faster than the ocean and causes a convection current to form, shifting wind direction.

Monsoons are also influenced by other topographic elements.


The monsoon is part of the usual evolution of the seasons in northern Australia.

In northern Australia, the prevailing wind is from the east or southeast for most of the year, but during active monsoon periods (occurring any time during November to April) the winds shift to become north-westerly at the surface.

As the Australian summer approaches, the continent heats up. Low pressure is created, which effectively draws the monsoon trough - a zone of low pressure and rising air – over northern Australia.

This trough draws in moist air from the surrounding oceans and this influx of moist air is referred to as the monsoon.


• Active phases of the monsoon bring heavy rainfall to northern Australia.

• The monsoon is associated with cloudy conditions, lengthy periods of heavy rain, occasional thunderstorms and fresh to strong squally winds. This often causes flooding in affected areas.

Australia’s Climate: Northwest Cloud bands

Northwest cloud bands bring rain to much of north western, central and south eastern Australia.

A northwest cloud band is an extensive layer of cloud which can stretch from northwest to southeast Australia.

Northwest cloud bands are formed when warm, moist tropical air originating over the Indian Ocean moves poleward (generally south eastward), and is forced to rise over colder air in the mid-latitudes. This typically occurs when tropical air to the northwest of Australia moves poleward on the western flank of a high pressure system over eastern Australia.

Northwest cloud bands can also interact with cold fronts and cut off lows over south eastern Australia to produce very heavy rainfall.

Australia’s Climate: Northwest Cloud bands

Northwest Cloudbands: 16-20 June 2005

Australia’s Climate: Summary

Australia’s climate is influenced by several global circulation systems The atmospheric currents (trade winds, subtropical highs, southern lows)

The oceans ( Indian ocean, pacific ocean)

These influences manifest themselves in several climatic events and systems including:

• blocking highs

• Cut off lows

• Easterly troughs

• El Niño/La Niña

• Frontal systems

• The Indian Ocean Dipole

• The monsoon

• Northwest cloud bands

Finish

See you all in week 6!

Next week: Olivia will look at past climate, how we measure past climate, and the tectonic history of Earth’s climate.

I will see the Cairns students tomorrow in the tutorial.

References



http://www.theherald.com.au/story/492718/artist-to-sculpt-pasha-bulker-piece-at-nobbys/

http://www.gettyimages.com.au/pictures/the-coal-ship-pasha-bulker-sits-off-nobbys-beach-june-10-news-photo-74502867#the-coal-ship-pasha-bulker-sits-off-nobbys-beach-june-10-news-photo-id74502867




http://www.theherald.com.au/story/492718/artist-to-sculpt-pasha-bulker-piece-at-nobbys/

http://www.gettyimages.com.au/pictures/the-coal-ship-pasha-bulker-sits-off-nobbys-beach-june-10-news-photo-74502867#the-coal-ship-pasha-bulker-sits-off-nobbys-beach-june-10-news-photo-id74502867


week 4.2 australia's climate

Science