A

Anti‑cyclone

Anti-cyclones are regions of higher atmospheric pressure, characterised by anti‑clockwise air circulation in the Southern Hemisphere. They’re typically linked to light winds and calm, settled weather conditions.

Atmosphere

The mixture or layers of gases that surround a planet.

Atmospheric circulation

The movement of air around the planet. It explains how thermal energy and storm systems move over the Earth’s surface.

C

Carbon dioxide

A gas (CO₂) found in the atmosphere that plays a key role in the greenhouse effect.

Climate

The long-term pattern of atmospheric conditions, usually referring to the typical or average state of the weather. It also includes expectations of weather over extended periods, such as weeks, months, or years into the future.

Climate change

Climate change refers to long-term shifts in temperatures and weather patterns, largely driven by human activities since the 1800s, especially the burning of fossil fuels. These activities release greenhouse gases like carbon dioxide and methane, which trap heat in the atmosphere and warm the planet.

Climate variability

Climate variability refers to natural fluctuations in climate elements like temperature and rainfall over months, years, or decades. These variations occur around a long-term average and are influenced by factors like ocean-atmosphere patterns (e.g. El Niño and La Niña), volcanic activity, and other natural processes.

Cloud

A collection of water droplets or ice crystals formed when water vapor in the atmosphere condenses or freezes.

Cold fronts

A weather object where cold polar air replaces warm tropical air. In some regions along the polar front, cold dense air advances towards the equator, causing warm air to be forced aloft over its sloping surface. This portion of the polar front is known as a cold front.

Convection

A process where warm air rises, often leading to cloud formation. Convection in the atmosphere can also cause local breezes, winds, and thunderstorms.

Cyclogenesis

The formation of a new low-pressure system or the strengthening of an existing one.

Cyclone

A low-pressure system with rotating air—clockwise in the Southern Hemisphere and anti-clockwise in the Northern Hemisphere. Cyclones are typically linked to stronger winds, unsettled weather, cloud cover, and rainfall.

D

Diurnal variation

The daily changes in a meteorological element, such as temperature, over the course of a solar day. It typically refers to consistent patterns observed throughout an average day.

Downburst

A powerful and damaging downward surge of air that hits the ground with force, usually linked to severe thunderstorms.

Drought

An extended period with little or no significant rainfall compared to regions typical rainfall.

Dry-bulb temperature

The air temperature measured in the shade using a thermometer placed in a white, ventilated screen about one metre above the ground.

E

East Coast Lows

Intense low-pressure systems that typically form several times a year off the eastern coast of Australia, especially affecting southern Queensland, New South Wales, and eastern Victoria.

El Niño

A large-scale warming of the central and eastern Pacific Ocean that causes significant shifts in weather patterns across the Pacific. In Australia, particularly the eastern regions, El Niño events are linked to a higher chance of drier conditions.

El Niño-Southern Oscillation (ENSO)

The natural variation in sea surface temperature and winds across the Pacific Ocean which can drive global weather patterns. There are three ENSO phases: El Nino, Neutral and La Nina

F

Flash flood

A sudden, short-lived flood characterised by a rapid increase to peak water flow.

Flooding

A flood is an overflow of water beyond the normal limits of a watercourse. Flooding occurs when water extends over what is usually dry land. This can happen when it escapes from a natural watercourse, such as a lake, river or creek. It can also happen when water is released from a reservoir, canal or dam.

Global warming

Global warming is the ongoing increase in Earth’s average surface temperature caused primarily by human activities that release greenhouse gases, such as burning fossil fuels. We often use the term climate change instead because it captures not just the warming, but also the wide range of changes in weather patterns, sea levels, and ecosystems that result from this warming.

Front

The dividing line between air masses that have different properties.

G

Greenhouse effect

A natural process that warms the Earth. When sunlight reaches the planet, some of it is reflected back into space while the rest is absorbed by the surface, warming it. The Earth then emits heat as longwave radiation, which is partly trapped by greenhouse gases like carbon dioxide, methane, and water vapor. These gases radiate heat in all directions, keeping the surface and atmosphere warm. Without this effect, the Earth’s average temperature would be about 33 degrees Celsius cooler.

Greenhouse gases

Greenhouse gases are gases in Earth’s atmosphere that trap heat from the sun, preventing it from escaping back into space and thus warming the planet. The most common greenhouse gases include carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and water vapor. These gases come from natural sources, like volcanic eruptions and wetlands, but human activities—such as burning fossil fuels, agriculture, and deforestation—have significantly increased their concentrations, intensifying the greenhouse effect and contributing to global warming and climate change.

H

Hail

Falling precipitation made up of ice particles called hailstones, which are usually spherical, conical, or irregular in shape, typically ranging from 5 to 50 millimetres in diameter. Hail can fall as individual stones or clumped together in irregular lumps.

Heat wave

A stretch of unusually hot weather lasting several days, with no temperature relief from night-time minimums.

High pressure

Areas of higher atmospheric pressure where air circulates anti-clockwise in the Southern Hemisphere. These regions, known as anticyclones, are generally associated with light winds and calm, settled weather.

High‑Impact Weather

Weather events that significantly affect communities, businesses, governments, or the natural environment, either posing risks or providing benefits. This broad definition includes more than just severe weather – such as prolonged calm that limits renewable energy generation or extensive fog that impacts aviation, even if not directly dangerous.

Humid

Air that contains a relatively high amount of water vapor, often linked to warmer temperatures. Humidity can be indicated by measures like Relative Humidity (RH) and Dewpoint Temperature.

I

Indian Ocean Dipole (IOD)

The Indian Ocean Dipole (IOD) refers to sustained changes in the difference between sea surface temperatures in the tropical western and eastern Indian Ocean. It is a major influence on Australia’s climate and can significantly impact agriculture, especially during the winter crop growing season. The IOD has three phases: neutral, positive, and negative. Events typically begin around May or June, reach their peak between August and October, and then quickly weaken when the southern hemisphere monsoon arrives near the end of spring.

J

Jet Stream

A narrow, fast-moving air current found in the tropopause, the layer between the troposphere and stratosphere. These strong winds are created by sharp pressure differences caused by large temperature contrasts at high altitudes.

L

La Niña

A large-scale cooling of the central and eastern Pacific Ocean. In Australia, especially in the east, La Niña events are linked to a higher chance of wetter weather.

Lightning

A bright flash of light caused by a sudden electrical discharge occurring within a cloud, between clouds, or less commonly, between a cloud and the ground or other structures. This happens when the buildup of opposite electrical charges inside the cloud becomes strong enough to overcome the air’s resistance, resulting in a powerful spark.

Low latitudes

In the Southern Hemisphere, low latitudes refer to areas north of about 30 degrees latitude. For Australia, this includes the region north of a line drawn roughly from midway between Perth and Geraldton (Western Australia) to Bourke (New South Wales). This zone generally experiences subtropical to tropical climates.

Low pressure

Areas of lower atmospheric pressure where air circulates clockwise in the Southern Hemisphere. These low-pressure systems, known as cyclones, are usually associated with stronger winds, unsettled weather, cloudiness, and rainfall.

M

Madden‑Julian Oscillation (MJO)

A recurring increase in rainfall across the Australian tropics that moves through tropical regions approximately every 30 to 50 days. Changes in satellite cloud patterns and atmospheric pressure help indicate when this wave passes over Australia, often triggering bursts of monsoon rainfall during the tropical wet season.

Mid latitudes

Regions between about 30 and 55 degrees latitude. For Australia, this includes the area south of a line running roughly from midway between Geraldton and Perth (Western Australia) to Bourke (New South Wales). This zone generally has a temperate climate.

Monsoon

A seasonal wind pattern, with the northern Australian monsoon typically lasting from December to March. It brings moist winds from the west to northwest into the monsoon trough, resulting in convective clouds and heavy rainfall across northern Australia. These moisture-rich winds come from the Indian Ocean and southern Asia. The northern Australian wet season mainly covers these months but can extend beyond them. For example, parts of North Queensland receive significant rainfall during cooler months, and in the Northern Territory’s Top End, the wet season is considered from October 1 to April 30, while in parts of tropical Western Australia, it’s often limited to January through March.

O

Offshore

The coastal water area located between 12 and 60 nautical miles from the shore.

Ozone

A gas in the Earth’s atmosphere composed of three oxygen atoms (triatomic oxygen). It makes up about one part in three million of all atmospheric gases. If all atmospheric ozone from the surface up to 60 km were compressed to ground level, it would form a layer roughly 3 millimeters thick and weigh around 3 billion tonnes. At high concentrations, ozone is toxic because it reacts strongly with other molecules.

P

Planetary waves

Planetary waves, also called Rossby waves, are large-scale waves in the atmosphere that move around the Earth’s mid-latitudes. They help influence weather patterns by affecting the flow of the jet stream and the movement of high and low pressure systems.

Precipitation

Any form of water particles—liquid like rain or drizzle, or solid like hail or snow—that fall from clouds and reach the ground.

R

Rainfall

A measurement of how much water falls as liquid precipitation in a certain period of time.

Relative humidity

A common measure of moisture in the air, expressed as the percentage ratio of the actual amount of moisture present to the maximum amount the air can hold at the same temperature. Since warmer air can hold more moisture, relative humidity alone doesn’t provide an exact measure of moisture content. At saturation, relative humidity is close to 100%.

Ridge

A ridge is an extended area of high pressure, shown on weather maps by rounded isobars stretching out from an anticyclone. Along the ridge line, the pressure is higher than at nearby points on either side.

S

Sea breeze

A local wind blowing from the sea onto the land. On sunny days, the land heats up faster than the sea, causing the air over the land to warm, rise, and create a pressure difference that pulls cooler air from over the sea onto the shore. At night, when the land cools faster than the sea, the wind reverses direction, creating a land breeze.

Sea Surface Temperatures (SSTs)

Refers to the temperature of the ocean’s surface. Changes in these temperatures, or anomalies, result from variations in heat exchange with the atmosphere, ocean currents, or upwelling. These temperature shifts can lead to significant changes in rainfall and atmospheric circulation, often playing a key role in climate patterns like ENSO.

Southern Annular Mode (SAM)

A climate pattern affecting rainfall and temperature in Australia, defined by the north-south movement of strong westerly winds that flow continuously in the southern hemisphere’s mid to high latitudes. This wind belt is linked to storms and cold fronts moving from west to east, bringing rain to southern Australia. The SAM has three phases: neutral, positive, and negative, each typically lasting one to two weeks but sometimes longer. The timing between phases varies from about a week to several months, and its impact on rainfall changes depending on the season and location.

Stratosphere

The atmospheric layer located roughly 10 to 50 kilometres above the Earth’s surface.

Supercell

A long-lasting thunderstorm featuring a strong, rotating updraft and downdraft occurring together.

Synoptic Scale

A horizontal scale describing large weather features in the lower atmosphere, such as high- and low-pressure systems common in mid-latitude regions.

T

Thunderstorm

Thunder is a sudden electrical discharge seen as a flash of lightning accompanied by a loud rumbling sound. Thunderstorms develop from convective clouds (Cumulonimbus) and often bring precipitation. They are usually brief and affect a relatively small area.

Trade Winds

In the Southern Hemisphere, these are east to southeasterly winds that influence tropical and subtropical regions, including northern Australia. During the northern Australian monsoon season, the easterly trade winds are replaced by moist northwesterly monsoon winds from the Indian Ocean and southern Asia. In the Northern Hemisphere, trade winds blow from east to northeasterly directions, generally moving from east to west toward the equator. Sometimes they are simply called “easterlies” to avoid specifying the hemisphere.

Tropical Cyclones

Strong low-pressure systems that develop over warm ocean waters at low latitudes. They bring powerful winds, heavy rainfall, and coastal storm surges. Tropical cyclones can cause widespread damage from wind, flooding (from rain or storm surge), and landslides in mountainous areas due to saturated soils. Known also as tropical storms in some regions, when their winds exceed 117 km/h (63 knots), they are classified as severe tropical cyclones. In the northwestern Pacific, these severe cyclones are called typhoons, while in the northeast Pacific and Atlantic/Caribbean they are called hurricanes.

Trough

An elongated area of relatively low atmospheric pressure compared to its surroundings. On weather maps, a trough is often marked by a dashed line extending from a low-pressure center. As you move toward the trough line, pressure decreases, then rises again after crossing it. A shift in wind direction usually occurs when crossing a trough. (See also Ridge and Low for comparison.)

U

Updraft

A small-scale upward-moving air current, often a fast-rising vertical wind seen in thunderstorms.

Upwelling

The movement of cold, deep ocean water rising to the surface.

W

Warm Front

In some areas along the front, warmer, less dense air moves toward the poles, sliding over the cooler air below along a sloping surface. This area is called a warm front, where warm tropical air replaces colder polar air.

Weather Change

Unexpected and unpredictable shifts in familiar weather patterns and systems, driven by human-induced climate change.

Weather Resources

The weather conditions near Earth’s surface are essential to our economy, society, ecosystems, health, and wellbeing. Elements like sunlight, wind, and rainfall support food production, provide fresh water, and increasingly supply energy for cities and homes. These are our weather resources.

Wet-bulb Temperature

Measured with a thermometer wrapped in a wet muslin cloth, the wet-bulb temperature is lower than the regular dry-bulb temperature because evaporation cools the bulb. The evaporation rate depends on air humidity – slower evaporation occurs when the air is already moist. The temperature difference between wet-bulb and dry-bulb thermometers indicates atmospheric humidity.