Distance Learning Module: Weather, Weather Everywhere: Part I (Earth)
What causes weather, how do we study it, and what is the weather like on other planets?
Learn all about it in this two-part series, geared toward middle-school learners! Start here to become familiar with general terms & concepts and how they apply to Earth, before moving on to Part II (Other Planets).
Typhoon parma crossing over the Philippines, on October 3, 2009. NASA image courtesy the MODIS Rapid Response Team at NASA GSFC
What is weather?
WEATHER refers to conditions in the atmosphere—the layer of gas that surrounds Earth and other planets like an “envelope.” Weather occurs in a specific area and lasts for a short time (for example, minutes or months). In contrast, climate is a term that means long-term weather patterns over an extended period of time (years, decades—even centuries or longer).
The weather on Earth is caused by the interactions between heat, air pressure, winds, and moisture. We measure and describe weather using the following vocabulary:
temperature: how much heat something contains—which is actually a measure of how fast the atoms and molecules of a substance are moving. On Earth, our heat comes in the form of solar radiation: energy from the Sun. The coldest weather usually happens near the Earth’s poles, while the warmest weather usually happens near the Equator. Why would this be?
atmospheric pressure: the weight or force of air being pulled down toward Earth’s surface by the force of gravity. Air pressure is related to altitude: as one increases, the other decreases. (In science, this is called an inverse relationship.) For instance, you would experience greater air pressure at sea level than you would on top of a tall mountain. Can you think of why that is?
wind: the movement of air. Wind forms because of differences in temperature and atmospheric pressure between nearby regions. Winds tend to blow from areas of high pressure, where it’s colder, to areas of low pressure, where it’s warmer.
Did you know:
For nearly 62 years, New Hampshire held the world record for the fastest wind gust ever recorded on Earth—231 miles per hour, recorded April 12, 1934 at the Mount Washington Observatory! In 1996, an instrument station in Australia recorded a gust of 253 miles per hour during Typhoon Olivia, breaking New Hampshire’s record.
storm: a severe weather event. There are different kinds of storms—for instance: thunderstorms usually involve wind, heavy rain, thunder and lightening; tropical cyclones are caused by wind and rain moving in a circular pattern over the ocean; and blizzards involve low temperatures, high winds, and heavy snow.
humidity: the amount of moisture, or water vapor, in the air. Water vapor is water in the form of a gas, floating in the atmosphere. When we talk about humidity and weather, we usually mean relative humidity, or the proportion of how much water the air actually holds, versus how much it could possibly hold. (We know how much water the air is able to hold based on its temperature: warmer air holds more water vapor than cooler air.)
cloudiness: as we learned in a recent Distance Learning Module, clouds are just lots of water droplets stuck together and suspended in the air. They form when warm air rises (causing water to evaporate) and then cools (causing water it to condense).
precipitation: water or ice that comes from the clouds. When a cloud is so full of water vapor that it can’t possibly hold any more (that is, it’s saturated, or has reached 100% relative humidity), some of the water condenses into drops and falls back to the Earth’s surface as rain. If a cloud is very cold, the water droplets may freeze to form ice crystals, which fall to the ground as snow, sleet, or hail.
The continual process of evaporation, condensation, and precipitation on Earth is known as the water cycle.
If you learn best through watching and listening, these two videos may help you to better understand the water cycle:
Test your understanding—fill in the blanks with one of the terms provided:
As altitude increases, air pressure _________________.
increases decreases
Winds tend to blow from areas of __________ pressure, with a _____________ temperature, to areas of ______________ pressure, where the temperature is _______________.
high low
When air warms up, it can hold ________________ water vapor than the same volume of air at a cooler temperature.
more less
When air warms up, it __________________________ in the atmosphere.
rises falls
As water moves through the water cycle, it undergoes __________________ change from a liquid to a gas; ________________________ to turn from a gas into a liquid; and ______________________ to fall to the Earth as a liquid or frozen crystals.
condensation precipitation evaporation
Answer key:
What Causes Weather?
There are several factors that affect a planet’s weather: the tilt of the planet's axis, the shape of its orbit around the sun, its atmosphere, its average distance from the Sun, and the length of its day. Let’s continue to focus on Earth’s weather for now.
Seasons & Weather Patterns
As we learned in a recent distance learning module, Earth’s seasons are the result of the tilt of our planet’s axis (the imaginary line running from the North Pole to the South Pole) and its place in its orbit (movement around the outside of the Sun).
As the Earth orbits the Sun, it constantly rotates on its axis (spins like a basketball balanced on a fingertip). The Earth’s axis is not straight up-and-down. It is tilted about 23.5 degrees, which causes sunlight to reach the Earth's surface unevenly. When the north pole of Earth's axis is pointed toward the Sun, the Northern Hemisphere receives more direct sunlight and becomes warmer: it is summer in the Northern Hemisphere. When the south pole is pointed toward the Sun, it is summer in the Southern Hemisphere and winter in the Northern Hemisphere.
As you can see, regions near the Earth’s equator face the Sun more directly and receive more solar radiation than the poles, regardless of the season. In general, this causes the Equator to be hot and the poles to be cold.
Remember that wind is simply the movement of air from an area of high pressure to an area of low pressure. For the planet Earth, this means that air likes to move from the Equator, where the air is hot and the atmospheric pressure is high, toward the poles, where the air is cooler and the atmospheric pressure is low. This movement of air across the planet is known as global wind patterns.
Global winds do not move straight up and down from south to north/north to south, because the Earth is rotating on its axis. When the Earth “spins,” it causes winds in the Northern Hemisphere to move toward the right and winds in the Southern Hemisphere to move toward the left. We call this the Coriolis effect. The video and activity below will help you to see the Coriolis effect on a smaller scale:
The processes that create weather on a global scale also create localized conditions. Differences in temperature and air pressure cause winds to move from one area to another. Water evaporates, forms clouds, and falls to Earth as precipitation. Weather in a specific area is influenced by that area’s latitude (how far it is from the Equator), its elevation (altitude), and geography—for example, how close it is to a large body of water or a mountain range.
How do scientists study weather on Earth?
Meteorology is the a branch of Earth Science that focuses on the Earth’s atmosphere and weather conditions. People who study meteorology are called meteorologists.
Meteorologists record data such as air pressure, wind speed, temperature, humidity, and precipitation to understand Earth’s weather, and to make predictions about future weather events (forecasts). Understanding and predicting weather can help us to make small everyday decisions (should I plan an outdoor picnic this afternoon? How should I dress before leaving home?) and can also save people’s lives from extreme events such as tornadoes, hurricanes, and blizzards. Weather forecasts are important for farmers, sailors, airplane pilots, and many other jobs that people perform around the world.
Have you ever seen a meteorologist reporting weather conditions on your local news?
Ancient people first predicted the weather based on their own observations. They learned to recognize patterns, and shared useful information with each orally (by talking about it). Some early tools used by meteorologists were barometers (which measure atmospheric pressure), wind vanes (which measure the direction of the wind), and thermometers (which measure temperature).
Today, meteorologists study weather conditions using information obtained from the land, sea, and upper atmosphere. They gather their data with sophisticated instruments, and use computer models to analyze and predict weather conditions throughout the world. Some tools that meteorologists use are
weather balloons—which rise into the atmosphere, gather information about conditions in their location, and transmit this information back to Earth via radio)
satellites—which use rockets to launch into the atmosphere, circle the Earth in an orbit, and record conditions (including rain, clouds, fires, dust storms, and air pollution) with sensors
and radar—which uses radio waves to detect the position of clouds and precipitation in a local area
satellite image of hurricane jeanne in the caribbean, 2004
Radar image of Hurricane rita in louisiana, 2005
A weather station is a facility with tools and technology used to forecast the weather. Different types of thermometers, barometers, and anemometers (which measure wind speed) are found at weather stations. Weather stations may also have computer equipment that allows meteorologists to create detailed maps of weather patterns, and technology that allows them to launch weather balloons.
Learn about some of the national meteorology agencies keeping us safe and informed here:
