Weather

Weather refers to the state of the Earth's atmosphere at a specific place and time, typically described in terms of temperature, humidity, cloud cover, and stability. It includes day-to-day changes in temperature, precipitation, and other atmospheric conditions. While weather focuses on short-term changes, climate describes the average conditions over longer periods.

Weather is driven by differences in air pressure, temperature, and moisture between places. These differences arise from the Sun's angle, which varies with latitude and leads to large-scale atmospheric circulations like the Hadley cell, Ferrel cell, polar cell, and the jet stream. Because Earth's axis is tilted, sunlight hits different parts of the planet at different angles throughout the year, influencing weather patterns.

Weather forecasting uses science and technology to predict future atmospheric conditions. Because Earth's weather system is a chaotic system, small changes can lead to big effects. Humans have tried to control the weather throughout history, and activities like agriculture and industry have changed weather patterns. Studying weather on other planets, like Jupiter's Great Red Spot, helps us understand our own planet's weather.

Causes

On Earth, common weather phenomena include wind, cloud formation, rain, snow, fog, and dust storms. Larger events such as tornadoes, hurricanes, typhoons, and ice storms are also part of Earth's weather system. Most of these events happen in the troposphere, the lowest layer of the atmosphere.

Weather happens mainly because of differences in air pressure, temperature, and moisture. These differences are caused by how directly the sunlight hits a place, which changes depending on where you are on Earth. The contrast between very cold polar air and warm tropical air creates big air movements, like the jet stream. These movements influence weather patterns far away. Small changes in the atmosphere can lead to big changes in the weather, which is why forecasting is tricky.

Shaping the planet Earth

Weather is one of the key processes that helps shape our planet. It breaks down rocks and soils into smaller pieces through a process called weathering. When it rains, water droplets pick up carbon dioxide from the air, making the rainwater slightly acidic. This acidity helps water wear away surfaces over time. The tiny bits of rock and chemicals washed away can later form new rocks and soils, showing how weather helps change the Earth’s surface.

Effect on humans

Further information: Biometeorology

Weather is something everyone experiences when they go outside. People often talk about the weather and how it changes. Extreme weather, like tornadoes, can cause a lot of damage and affect many lives.

Weather has also influenced important events in history. For example, strong winds helped save Japan from an invasion in 1281. Hurricanes have changed where people live, like after Hurricane Katrina in 2005, which caused many people to move from the Gulf coast. Cold periods, such as the Little Ice Age, led to crop failures and difficult times for people in Europe and Finland.

Forecasting

Weather forecasting is the science of predicting what the air will be like in the future at a certain place. People have tried to guess the weather for thousands of years, but today we use computers and science to make better guesses.

We collect information about the air right now and use what we know about how air moves to figure out what will happen later. Even with powerful computers, it's hard to be exact because the air changes in complicated ways. That's why forecasts are more accurate for the next few days than for a week or more away. People use weather forecasts for many reasons, like knowing if they need an umbrella or planning farm work.

Modification

People have always wanted to control the weather. Ancient cultures performed rituals to bring rain for their crops. In modern times, efforts have included cloud seeding to clear fog at airports, increase winter rain in mountains, and prevent hail.

Human activities have also changed the weather without meaning to. Factories release pollutants that cause acid rain, harming lakes and plants. Emissions of greenhouse gases contribute to climate change, which can lead to more extreme weather like floods and storms. Even big cities can create their own weather patterns by heating up the air around them.

Microscale meteorology

Microscale meteorology is the study of short-lived atmospheric phenomena that are smaller than mesoscale, about 1 km or less. These small weather events include tiny cloud "puffs" and other brief cloud features. Together with mesoscale meteorology, they are sometimes called "mesoscale and microscale meteorology" (MMM). These tiny weather patterns are too small to show up on a weather map.

Extremes on Earth

Main articles: Extremes on Earth and List of weather records

Earth experiences a wide range of temperatures. The coldest temperature ever recorded was −89.2 °C at Vostok Station, Antarctica, in 1983. The hottest recorded temperature was 57.7 °C in Libya in 1922, though this record is no longer considered official.

Some places on Earth are known for extreme weather. In Antarctica, winds can reach speeds of up to 199 miles per hour. Mount Rainier in Washington, US, holds the record for the most snowfall in a year, with over 31,000 mm of snow.

Extraterrestrial weather

Studying weather on other planets helps us understand Earth’s weather better. These planets follow similar physical rules but have very different conditions. For example, the Cassini–Huygens mission to Titan found clouds made from methane that create rain of liquid methane.

One famous feature is Jupiter’s Great Red Spot, a huge storm that has lasted for over 300 years. On planets like Neptune, winds can blow up to 600 meters per second, much faster than on Earth. Scientists are still learning why these distant worlds have such extreme weather.

Space weather

Main article: Space weather

Weather isn't just something that happens on Earth—it can also happen in space! The Sun sends out a stream of particles called the solar wind, which travels through the Solar System. Sometimes, big events on the Sun, like coronal mass ejections, send even more particles out. These space weather events can create beautiful lights in the sky called aurorae, and they can sometimes mess with things like electricity grids and radio signals. Scientists study these space weather patterns to understand how they affect our planet.