Weather

Weather is the state of the Earth's atmosphere at a specific place and time, typically described in terms of temperature, humidity, cloud cover, and stability. On Earth, most weather phenomena occur in the troposphere, the lowest atmospheric layer just below the stratosphere, though weather can also occur in the stratosphere and influence conditions lower down, though the exact mechanisms are not well understood. Weather is driven by differences in air pressure, temperature, and moisture from one location to another. These differences arise primarily from variations in the Sun’s angle, which changes with latitude: areas farther from the tropics receive less direct sunlight, making them cooler. The strong temperature contrast between polar and tropical air generates large-scale atmospheric circulations, including the Hadley cell, Ferrel cell, polar cell, and the jet stream. In the middle latitudes, weather systems like extratropical cyclones are caused by instabilities in the jet stream flow, while tropical systems such as monsoons and organized thunderstorms result from different processes. Earth’s axial tilt relative to its orbital plane causes sunlight to strike at varying angles throughout the year, creating seasons. Over thousands to hundreds of thousands of years, changes in Earth’s orbital parameters alter the distribution of solar energy, influencing long-term climate. Surface temperature differences lead to pressure differences; warmer surfaces heat the air above, causing it to expand and lower pressure, which drives wind as air moves from high to low pressure, with Earth’s rotation deflecting this flow. Higher altitudes are generally cooler due to surface heating and radiational loss, though temperature inversions can occur, where temperature increases with height, sometimes capping thunderstorm development or forming fog. Different surfaces—such as oceans, forests, or ice—have varying reflectivity, roughness, and moisture content, creating local temperature differences. Weather forecasting applies science and technology to predict future atmospheric states, but Earth’s weather system is chaotic, meaning small changes can grow into large effects. Human activities like agriculture and industry have modified weather patterns, and attempts to control weather have occurred throughout history. Studying weather on other planets, such as Jupiter’s long-liv