Measuring Weather

How does the weather change from day to day? How can we measure weather?

By using different instruments and technology, we are able to accurately describe and predict weather. We can measure and predict temperature, the strength and direction of wind, or when it will rain. We are also able to predict extreme weather events like thunderstorms and hurricanes.

Temperature

Temperature is a measure of how hot or cold the air around us is. It is measured in degrees Celsius (oC) or degrees Fahrenheit (oF). Temperature is measured using a thermometer. When the temperature is high, the weather can be described as warm or hot. When the temperature is low, the weather can be described as cool or cold.

thermometer

Think Deeply

The summit of Mount Everest is almost 9,000 meters. How would the air pressure at that height compare to the air pressure on the ground?

barometer

Air Pressure and Wind

Like all matter, the air in the Earth’s atmosphere has mass. Air pressure is caused by the weight of the air pressing down on the Earth’s surface. In lower areas of the Earth’s surface there is more air pressing down than high areas. So air pressure is higher at sea level and decreases with height. Air pressure changes with temperature. When the heat from the Sun heats the surface of the Earth, the air surrounding the Earth is heated. This causes the air to rise and the air pressure decreases.

The weather changes as the air pressure in an area changes. Generally, low air pressure will result in bad weather such as strong winds and rain. High air pressure is associated with calmer weather with clearer skies and little wind.

Air pressure is measured using a barometer.

wind sock

Wind is moving air. When the heat from the Sun warms the air in one area, the air rises and the air pressure decreases. In places where the air is cooler, the air falls and the air pressure increases. Wind is caused when air moves from an area of high pressure to an area of low pressure. The greater the difference in air pressure, the stronger the wind. We can measure the speed of wind using an anemometer or a wind sock. These tools can also be used to measure the direction the wind is blowing.

anemometer

A Closer Look Sea Breezes and Land Breezes

A good example to help understand the relationship between temperature, air pressure and wind is to look at sea breezes and land breezes.

During the day, the Sun heats both the land and ocean, but the land gets heated faster. This causes the air above the land to become warmer than the air above the ocean. The air above the land rises and the cool air from the ocean moves to take its place. This causes wind to blow from the ocean to the land. This movement of the air is called a sea breeze.

During a sea breeze, wind blows from the ocean onto land.

near-shore wind farm

During the night, there is no Sun in the sky to warm the surface of the Earth. Both the land and the ocean begin to cool. The land cools down faster than the ocean. The warmer air above the ocean rises and the cooler air from the land moves to takes its place. This causes the wind to blow from the land to the ocean. This movement of the air is called a land breeze.

Did You Know?

Wind farms are often located near the coast. They use the energy in sea breezes and land breezes to generate electricity.

During a land breeze, wind blows from the land to the ocean.

Think Deeply

Earth is the only known planet to contain water in three states. What are these three states and where can they be found on Earth?

Precipitation

Water that falls from clouds in the sky is called precipitation. There are four main types of precipitation – rain, sleet, snow and hail.

The air in our atmosphere contains water in the form of a gas called water vapor. When warm air rises, it begins to cool and the water vapor forms tiny water droplets in clouds. The droplets attach to dust and other particles. As more water droplets form and combine, they form larger drops. The drops fall to Earth as rain.

sleet

In very cold temperatures, falling rain may freeze into small pieces of ice before reaching the ground. This type of precipitation is called sleet. If the air in the clouds is cold enough, the water vapor can rapidly freeze and form snowflakes. Snowflakes fall to the ground as snow.

During a thunderstorm, raindrops in storm clouds can freeze to form balls of ice. These balls of ice fall to the ground as hail.

How is rain different from sleet, snow and hail?

AB Activity 9.2

hailstones

A Closer Look The Water Cycle

Water on Earth is constantly being heated and cooled. As this happens, water moves in a cycle between the surface of the Earth and the atmosphere. This process is called the water cycle. The heat from the Sun causes the water in the ocean, lakes and rivers to change into a gas called water vapor. This process of changing from a liquid to a gas is called evaporation. The water vapor in the air cools as it rises and changes to liquid water in the form of tiny water droplets in clouds. This process of changing from a gas to a liquid is called condensation.

evaporation condensation

The water droplets combine with other water droplets and eventually fall back to the surface of the Earth as precipitation. The precipitation flows on and under the ground into rivers, lakes and the ocean.

AB Activity 9.3

precipitation Try This!

How long does it take for water to evaporate outside? Plan and conduct an investigation to find out. What factors affect the rate of evaporation?

Go Online!

Watch the water cycle in action in a video on the NGScience website. QuickCode: C4D6

Weather satellites orbit the Earth collecting and sending weather information back to Earth.

Weather Forecasting

Weather scientists, called meteorologists, are constantly using technology to gather information about the weather. Weather stations all over the Earth collect data on temperature, the movement of wind, air pressure and precipitation. Buoys in the ocean collect data about currents, water temperature and wave height. Radars collect data about the movements of clouds and precipitation. In space, weather satellites are constantly orbiting the Earth, collecting and sending information about the weather back to Earth.

Meteorologists use powerful computers to analyze and interpret weather information. By observing patterns in the weather, they are able to predict what the weather will be like in the future. These predictions are called weather forecasts. Weather forecasts are very helpful to people. They can help us to plan our day or week. They can also warn and help us to prepare for severe weather events, such as thunderstorms, hurricanes, floods and droughts.

What information do meteorologists communicate to people during a weather forecast?

AB Activity 9.4

Meteorologists analyze and interpret patterns in the weather to predict what the weather will be like in the future.

Weather radars are able to monitor the movement of clouds and precipitation.