Weather

Weather is what happens in the air.

It can be sunny or rainy.

Sunlight hits the Earth. This makes some places warm. Other places stay cool.

Heat and air move around. This movement makes wind. It also makes clouds.

Weather can change quickly. Even a small change can have a big effect. We use science to guess what the weather will be like tomorrow.

Weather is what happens in the air around us.

Most weather occurs in the troposphere. This is the lowest part of our atmosphere. Weather changes every day. It includes things like rain, snow, and wind.

Weather is driven by differences in heat and air pressure. The Sun hits the Earth at different angles. This happens because the Earth is tilted. Some places get more direct sunlight. This makes them warmer. Warm air rises and creates low pressure. Cooler air moves in to take its place. This movement of air is what we call wind.

Weather is a chaotic system. This means small changes can lead to huge effects. Because of this, it is hard to predict. Forecasters use science to guess future weather. However, they cannot predict the weather more than two weeks ahead. Weather also shapes our world. Rain can break down rocks into soil. This is a way the Earth changes over time.

Weather is the state of the air at a specific place and time. It includes things like temperature, humidity, and cloud cover. Most of these events happen in the troposphere. This is the lowest layer of our atmosphere. We often talk about weather as what happens day-to-day. This is different from climate, which is the average of weather over long periods.

Weather works because of differences in heat, moisture, and air pressure. The Sun hits different parts of Earth at different angles. This happens because our planet is tilted on its axis. Near the tropics, sunlight hits more directly and makes things warm. In the poles, the sunlight spreads out and stays cooler. Warm air rises and creates low pressure. Cooler air moves in to fill that space, which creates wind.

Scientists have studied these patterns for a long time. They know that the strong temperature difference between polar and tropical air creates huge air movements. These include the Hadley cell, the Ferrel cell, and the polar cell. They also found the jet stream, which is a fast flow of air. Changes in Earth's orbit can even change the climate over thousands of years. These shifts affect how much solar energy we receive.

Weather is a chaotic system, which means small changes can lead to huge effects. This makes it very hard to predict exactly what will happen. Forecasters use science to guess the future, but they have limits. It is theoretically impossible to make useful daily predictions more than two weeks ahead. We can see massive storms elsewhere, too. For example, Jupiter has a huge storm called the Great Red Spot. It has lasted for at least 300 years.

Weather also shapes the very ground we walk on. Rain can absorb carbon dioxide from the air. This makes the water slightly acidic. This acidic rain helps break down rocks into smaller pieces of soil. This process is called weathering. Weather can also change human history. In 1281, winds called the Kamikaze helped save Japan from an invasion. In 1565, a hurricane helped Spain take control of Florida.

Weather is the state of the Earth's atmosphere at a specific place and time. It is usually described by looking at temperature, humidity, cloud cover, and stability. Most weather phenomena occur in the troposphere. This is the lowest layer of the planet's atmosphere, located just below the stratosphere. It is important to distinguish weather from climate. Weather refers to day-to-day conditions like precipitation and temperature. Climate is the term used for the average of these atmospheric conditions over much longer periods of time.

Weather is driven by differences in air pressure, temperature, and moisture between different locations. These differences often begin with the Sun's angle at a specific spot. Because Earth's axis is tilted relative to its orbital plane, known as the ecliptic, sunlight hits the surface at different angles. This tilt also causes the seasons. In the tropics, sunlight hits more directly, while at higher latitudes, the light spreads out and makes locations cooler. These temperature differences cause pressure differences. When a surface is hot, it warms the air above it. This causes the air to expand, which lowers its density and the resulting surface air pressure.

Air moves to balance these pressure differences. A horizontal pressure gradient moves air from higher pressure regions to lower pressure regions, which creates wind. As the air moves, the Earth's rotation causes a deflection of the airflow due to the Coriolis effect. On a large scale, the strong temperature contrast between polar and tropical air creates massive atmospheric circulations. These include the Hadley cell, the Ferrel cell, and the polar cell, as well as the jet stream. In the middle latitudes, weather systems like extratropical cyclones are caused by instabilities in the jet stream flow.

Temperature also changes with altitude. Higher altitudes are typically cooler than lower altitudes because most atmospheric heating comes from contact with the Earth's surface. However, sometimes an inversion occurs. An inversion is when the temperature actually increases with height. This can make mountaintops warmer than the valleys below. Inversions can lead to fog and can act as a cap that stops thunderstorms from developing. On a local scale, different surfaces like oceans, forests, or ice sheets can cause temperature differences because they have different levels of moisture or reflectivity.

Earth's weather is a chaotic system. This means that small changes in one part of the system can grow to have massive effects on the whole system. This instability makes weather forecasting difficult. While scientists use technology to predict the atmosphere, it is theoretically impossible to make useful day-to-day predictions more than about two weeks ahead. We can see similar processes in space, too. Jupiter has a famous anticyclonic storm called the Great Red Spot. This landmark storm has existed for at least 300 years.

Weather is also a fundamental process that shapes the physical Earth through weathering. This process breaks down rocks and soils into smaller fragments and substances. During rain, water droplets absorb carbon dioxide from the air. This makes the rainwater slightly acidic, which helps the water erode surfaces. This released sediment and chemicals can then participate in further chemical reactions. Over time, geological forces can turn this sediment back into rocks or soils.

Weather has also played a direct role in human history. Extreme weather can cause populations to move or change the outcome of events. For example, the Kamikaze winds helped save Japan from a Mongol invasion in 1281. In 1565, a hurricane destroyed a French fleet, allowing Spain to conquer Fort Caroline. More recently, Hurricane Katrina redistributed over one million people across the United States. In the U.S., the National Weather Service tracks the impact of weather. In 2019, tornadoes caused over 3 billion dollars in crop and property damage.