Patterns of Climate
Introduction
Climate is the study of weather over time. Weather is the short-term study of temperature, precipitation
rates, humidity, sun and wind. Some factors that affect the climate of an area include global air
circulation, topography and ocean currents. These factors all work together to create the climate found in
Australia, which is drier than all the other continents, with the exception of Antarctica.
Australian climate zones
Precipitation patterns across Australia are seasonal in nature. In northern Australia, most of the year's
rain falls in the summer months, while the winter months are dry. Due to this region's closeness to the
equator, however, the temperature tends to remain constant year-round. In eastern Australia, rain also
falls mostly during the summer, although rain can also fall during the winter months. Since this part of
Australia is further from the equator, however, summer months are warmer than winter months. In the
southern part of Australia, rain tends to fall more in the winter than in the summer. In eastern and central
Australia, little rain falls at all.
Temperature patterns in Australia differ depending on their latitude. At lower latitudes, that is, areas
closer to the equator, warmer temperatures are experienced year-round. As you move further south into
higher latitudes, however, the overall temperatures become cooler, while the seasonal variation, that is,
the difference between temperatures in summer and winter months, increases.
Global air circulation
The circulation of air throughout the world is very important because it stops the equatorial area from
becoming too hot and the polar regions from becoming too cold. The temperature of the air dictates
whether a region is humid or dry, hot or cold.
Air masses are large areas of air that are very similar in their temperature and humidity. These air masses
are linked to the global wind patterns. Atmospheric circulation is controlled by six regions of winds across
the globe and three major pressure cells.
The constant movement of air masses changes air temperature and pressure with latitude and altitude.
Changes in temperature and pressure create different patterns of weather. Areas of low pressure often
create condensation and result in storms. Areas of high pressure often create clear skies and warm, dry
air. Due to Australia's position on the Earth, Australia's air circulation is dominated by high pressure
systems, which lead to a warm, dry climate. These high pressure systems move with the season, which
leads to the seasonal rainfall patterns seen in Australia.
Topography
On top of tall mountains, it is cooler than at sea level. This happens because temperature decreases with
increasing altitude. This is called the lapse rate. Temperatures usually fall about 2o to 3oC for every 300
metres of altitude. Low, flat areas are warmer than high, mountainous regions of the same latitude. So
although the Himalayan Mountain Range is located along the Tropic of Cancer, the mountains are covered
with snow. Since Australia is a very flat continent, it stays very warm.
Landforms, such as mountains, act as barriers that force air masses to move up and over them. When
warm, moist air meets a mountain it is forced to rise. As this warm air rises, it begins to cool down with
increased altitude and condensation occurs. Once the air is saturated, precipitation occurs. The rain or
snow released on the windward side (the side from which the wind is blowing) of the mountain is known as
orographic rainfall. Since Australia's mountains have much lower altitudes than mountains on other
continents, the effects of orographic rainfall are not as strong as they are elsewhere. This, however,
explains why the coastal plains receive more rainfall than other parts of the continent.
After precipitation, the air mass is dry and flows down the opposite side of the mountain. This dry air
heats up as it descends down the leeward side (the side shielded from the wind) of the mountain. This is
called a rain shadow effect. It is on this side of mountains that desert climates are often found. The
Great Dividing Range in eastern Australia has a rain shadow effect on the Central Lowlands on its west
side, causing the Central Lowlands to be dry.
Ocean currents
The oceans make up about 70 percent of the Earth's surface. These huge bodies of water absorb solar
radiation and store it on the surface. Because the oceans heat up and cool down more slowly than the land,
areas near oceans experience a more stable climate than those further inland. Places not near an ocean or
other large body of water, such as central Australia, tend to have an arid climate.
Oceanic surface currents transport water around the globe. These giant surface water rotations are
called gyres. There is a major gyre in every major ocean. Water is warmed at the equator and travels
toward the poles, distributing heat. Once at the poles, water is cooled and then travels back to the
equator. Where there are cold currents, the coastal climate is dry. Where the currents are warm, the
coastal climate is moist because of higher evaporation rates. Off the western coast of Australia, there is a
cold water current. Therefore, rainfall rates in Western Australia are low.
El Niño and La Niña
El Niño is another oceanic phenomenon that affects the climate of Australia. El Niño is when normally cool
areas of the ocean along the western coast of South America are allowed to be warmed by the tropical sun.
This has varying effects in different places but it causes droughts in northern and eastern Australia.
Conversely, when the cold water currents are colder than they usually are, a phenomenon called La Niña
occurs. La Niña causes heavy rainfall and often flooding in northern and eastern Australia.
The effects of El Niño and La Niña on the Australian climate are also referred to as the southern
oscillation. This effect occurs because the ocean's surface temperature affects global air circulation
patterns. Normally, there is an area of high pressure over the central Pacific Ocean. During El Niño years,
however, the area of high pressure moves over the northern part of Australia. La Niña years, however, see
abnormally low air pressure over Australia, causing increased rainfall.