Weather influences much of our lives, from what we wear on any given day to what the traffic will be like on our commute and whether or not we need to stay indoors for safety. While you might encounter some weird weather events over the course of your life, understanding the basics of everyday weather patterns is a lot simpler than you might think. If you’ve made it to adulthood without a clear understanding of what causes thunder or how rainbows form, then it’s time for a refresher.
What causes thunder and lightning?
The Greeks believed they came from Zeus hurling his lightning bolts. Followers of the Shinto faith thought that the god Raijin was beating on his drum. And Norse mythology claimed that thunder and lightning were created when Thor rode his chariot across the sky. But today, we know exactly how thunder and lightning are formed.
During a storm, warm air rises from the earth and collides with moisture in the air, which cools and forms clouds. As the clouds get bigger, they collect more and more moisture. At the very top of the clouds, temperatures can dip below freezing and form ice crystals. As more warm air travels upwards through the cloud, the ice and water molecules bump into each other and, much like rubbing a balloon on your head, create static electricity.
A little bit of static electricity won’t do much harm, but when so many small charges are put together, they can let loose more than a billion volts of electricity. That’s when a lightning bolt is created. The amount of energy is so enormous that a lightning bolt can heat the air around it to temperatures of 50,000 degrees Fahrenheit — more than five times hotter than the surface of the Sun.
You’ve probably noticed that in every storm, thunder follows lightning. That’s because thunder is a byproduct of lightning. When a lightning bolt is released, the air around it becomes superheated. The molecules in the air expand in this heat almost instantaneously. In fact, the air pressure around the lighting bolt can increase up to 100 times its original amount in a matter of milliseconds. The compressed air explodes outward, sending a shockwave in every direction and creating a loud clap of thunder.
Even though thunder and lightning are formed almost simultaneously, you will always see the lightning before you hear the thunder. That’s because the speed of sound is much slower than the speed of light. Sometimes, the lightning is so far away that the sound of the thunder fades before you can hear it. And in the case of heat lightning, the thunder occurs so high up in the atmosphere that you can’t hear the booms from the ground.
What causes rainbows?
One of the most dazzling displays that nature offers on a rainy day is a full rainbow stretching across the sky. These ephemeral daytime occurrences have captured the human imagination for centuries, inspiring stories of good luck and myths about pots of gold.
To understand how a rainbow occurs in a natural environment, you first need to understand what happens during the process of light refraction. The refractive index measures how quickly light can pass through a medium—for example, light passing through glass. When two objects have a different refractive index, the light bends when it moves from one environment to the next.
A beam of white light, or sunlight, is actually made up of many different colors. These colors — red, orange, yellow, green, blue, and violet — each have their own wavelength. When light is refracted as it passes through another medium, like glass or a raindrop, each wavelength has its own angle of bending.
On a rainy yet still sunny day, when white sunlight hits each raindrop, it is reflected off the interior of the raindrop and refracted, separating the different wavelengths of light. When they leave the raindrop and are projected, each color hits a different spot because it has been bent at a slightly different angle. This allows you to see the colors side by side.
This process also explains why rainbows always have the same color pattern. Violet has the shortest wavelength, which causes it to bend the most while red has the longest wavelength, which causes it to bend the least. This is why violet is always the bottom color of the rainbow and why red is always on the top.
So why the curved shape? Raindrops are spherical and refract light in a circle. Because of our angle relative to the Sun and the horizon, we typically only see half of that circle — the arc that we associate with normal rainbows. However, if you are in a plane flying high above the horizon and observe a rainbow from the right angle, you might have the opportunity to see the full, circular rainbow effect.
What causes seasons?
Whether you prefer summer sun, fall foliage, winter snow, or spring flowers, each season has its own natural features that transform the view outside your window.
Earth orbits around the Sun at an angle while rotating around its own axis. However, the rotation axis of the Earth is not perpendicular to its solar orbit. Rather, the Earth exhibits an axial tilt of 23.44°. Think about the Earth like a bead on a string. You hold both ends of the string in front of you at an angle, so the top of the bead is tilted slightly. Like the bead, the Earth spins on this diagonal axis, and the axial tilt does not change its orientation as the Earth orbits around the Sun. Meaning, it maintains that same position as it moves throughout space.
Because of the axial tilt, the northern and southern hemispheres receive different amounts of sunlight depending on Earth’s orbit around the Sun. When the northern hemisphere is closest to the Sun, it experiences the hot season (summer). When the northern hemisphere is farthest away, it experiences the cold season (winter). The southern hemisphere experiences the opposite amount of sunlight due to the tilt, which is why countries such as Australia experience summer from December to February and winter from June to August.
Earth’s axial tilt also affects the diurnal cycle. The portion of the Earth that is closest to the sun at any given point not only receives more heat from its proximity but also experiences a longer duration of sunlight throughout each complete rotation (one day). The opposite is true during the winter. These effects increase with latitudes diverging from the equator and are most profound at the poles. The North Pole goes through the “polar night,” a period of six months without sunlight, and the south pole goes through the “midnight sun,” during which time there is no night. The mid-latitudes are the only regions where a four-season year is experienced.
What causes wind?
Sometimes you walk outside and feel a gentle breeze blowing through your hair. Other times you step out the door and a forceful gust nearly knocks you over. In the best-case scenario, it’s just a windy day. But if it’s truly bad weather like a hurricane or Nor’easter, those strong winds can be deadly. So, where does wind come from?
It all comes down to temperature and the gases that are naturally found in our atmosphere. Though oxygen may be the dominant gas in our atmosphere, it isn’t the only thing floating around in the air. Our atmosphere is also composed of nitrogen, carbon dioxide, argon, and other trace gases.
When the temperature changes (say, from a frigid 40 degrees in the morning to a mild 65 in the afternoon), it can impact how those gas molecules interact with each other. At colder temperatures, the molecules move slower and tend to crowd together into dense packs. But when the air is warm, the molecules are more active and spread farther apart. The temperature doesn’t always change at an even rate in our atmosphere, and that can lead to uneven temperature pockets. Each type of gas will behave differently depending on the temperature. And that behavior can impact the weather by changing pressure.
Pressure is caused by the uneven heating or cooling of the Earth’s atmosphere. High pressure occurs when the air is colder while low pressure occurs when the air is warmer. These pressure systems — full of hot and cold gas molecules — will eventually meet, and that's when the fun begins. When low and high pressures converge, molecules begin to pass between the two pressure systems and cause wind. Specifically, the wind strength is determined by the difference in temperature between pressure pockets. So, if the temperature difference is minimal, you might get a light breeze or no wind at all. But when the temperatures are more extreme, that’s when you get intense gusts.
However, temperature difference isn’t the only determinant for strong winds. The distance between a high and low pressure system can also impact wind strength. Two systems that are very far apart won’t produce strong winds. However, if two systems are in close proximity, some very forceful gusts can develop.
How do clouds form?
We spend a lot of time analyzing the clouds in the sky, pointing out ones that look like rabbits and other times trying to calculate if rain is on the way. But what exactly is a cloud, and how are different clouds formed?
A cloud, in the technical sense, is a collection of water droplets and ice crystals that have gathered in one spot. These droplets or crystals are extremely tiny and light, which is why they are able to hang suspended in the air.
The first step in the formation of a cloud is evaporation. Water vapor enters the air through the evaporation of water from oceans, rivers, lakes, or other bodies of water. The gas that forms from this evaporation rises up into the atmosphere and is cooled. When this cooling process occurs, the air can't hold as much moisture as it once did. The pressure in the atmosphere is also much lower, making it even more difficult for the air to hold water. So, the vapor changes form and becomes small droplets of water or ice crystals, which then join together to form a visible cloud.
This is the basic way clouds are formed, but it’s not the only way. Sometimes when the sun heats the ground, it causes the air just above the surface to heat up as well. This warm air is lighter and not as dense as the air around it, so it rises upward. As it rises, it expands due to the pressure difference and becomes cooler. At this point, the cooler air can no longer hold all the water, and it starts to condense into a cloud, as described previously. Clouds formed from this heating and cooling process are called cumulonimbus, stratocumulus, and cumulus clouds.
Meanwhile, stratus clouds and lenticular clouds are formed when wind blows against a mountain range or other high, hard terrain and is pushed upward. As it is pushed upward, the air is forced to cool down, changing its form as it becomes a cloud. Clouds can also form due to low pressure areas pushing air upwards, forcing it, again, to go through the cooling process that makes it condense.
Finally, clouds can be formed through a weather front, when two large masses of air run into each other near the surface of the Earth, causing air to rise up higher into the atmosphere. With a warm front, during which a mass of warm air slides over a mass of cold air, the warm air gets pushed upward and forms a wide variety of cloud types, including ones that bring rain. In a cold front, heavy, cold air masses push the warm air mass upward, forming cumulus and cumulonimbus clouds, the latter of which are responsible for thunderstorms.
How do tornadoes form?
Through films like The Wizard of Oz and Twister, we’re all familiar with tornadoes, even if we’ve never seen one in person. Tornadoes are fundamentally thunderstorms that create violent air-to-ground force. They are capable of massive destruction, leveling houses, uprooting huge trees, making shambles of large buildings, and swirling vehicles into the air. Annually, the United States averages 1,200 tornadoes. These tornadoes can hit a revolving wind speed of 200 miles per hour and average 30 miles per hour of forward momentum. However, they can also remain stationary or accelerate to 70 mph, obliterating everything in their paths.
While the exact conditions for tornado formation can vary, generally tornadoes form as a result of supercell thunderstorms, the strongest type of thunderstorm. Supercells feature a combination of warm, moist air and cool, dry air. When these two elements meet, they create an unstable atmosphere that, coupled with a change in wind direction and increased wind speed, create a spinning column of air called a vortex. As warm air travels upward through the vortex, it swells with water vapor, forming a spiraling funnel cloud. The cool air then pushes downward, increasing the vortex’s speed. Eventually, the funnel cloud is forced downwards where it touches the ground, and creates a tornado.
As the wind begins moving at different speeds, directions, and altitudes, the air spins at a rapid rate, keeping the swirl in motion. In order for a tornado to be formed, the rotating air needs to be near the ground so the tornado can balance itself, like a child’s toy top.