Explorer's Guide to World Weather

Explorer's Guide to World Weather

Introducing Earth Oceans and air swirl around Earth. Ocean waters that wash the shores of North America also wash the shores of Asia. The breeze that blows curtains in South America rustles leaves in Africa's trees. Yet regions on Earth can be very different from one another. In some places, people never need a heavy coat. In other places, people never go without one. Farmers pray for rain in some places. In other places, rain falls every day. Let's look at why different parts of our planet have such different weather.

How Scientists Measure Weather How many words can you think of to describe weather? Hot, cold, warm, chilly, rainy, sunny, snowy, foggy-the list could go on and on. All these words describe two things: temperature and precipitation. Temperature is how hot or cold a place is. Precipitation is moisture that falls to the ground in the form of rain, snow, sleet, or hail. To track the weather of a place, we measure two conditions. How hot is it? How wet is it? Climate is simply the average weather in a place over long periods of time.

Weather information can be recorded on graphs. Look at the temperature graph below. The graph shows information on the weather in Sydney, Australia, for the first six months of the year. The numbers on the left side show the degrees of temperature. Now look at the precipitation graph. It is very similar except that, on the left side, the numbers show amounts of precipitation in inches. By collecting weather information over time at many places, scientists have discovered that Earth has many different climate patterns.

Climate Field Guide What determines Earth's climate patterns? It all starts with the Sun. The Sun warms our planet, but its warmth is spread unevenly over Earth's surface. The equator is an imaginary line that circles the middle of Earth like a belt. Areas near the equator tend to be much warmer than areas far to the north or south. Because Earth is shaped like a ball, the Sun's rays hit Earth at different angles in different places. The Sun's rays are most direct around Earth's middle and least direct at the North and South Poles.

Try This! Mark an X in the center of a sheet of paper. Have a friend hold the paper so it's facing you. Shine a flashlight at the paper so it makes a circle of light on the paper around the X. Have your friend slowly tilt the paper away from you. As the paper is tilted away, the circle of light will stretch to become an oval. The same amount of light is being spread over more of the paper. As a result, even though the X on the paper is still in the light, it is now getting less light than it was before. In the same way, because Earth is shaped like a ball, as you move north or south away from the equator, Earth curves more and more away from the Sun. Earth's polar regions are cold because they receive less direct sunlight than areas near the equator.