Weather

Lore & Background

Weather is driven by differences in air pressure, temperature, and moisture, which result from the Sun's angle varying with latitude. The strong temperature contrast between polar and tropical air gives rise to large-scale circulations like the Hadley cell, Ferrel cell, polar cell, and jet stream. Weather systems in the middle latitudes, such as extratropical cyclones, are caused by instabilities of the jet stream flow. Because Earth's axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year, causing seasons. Over thousands of years, changes in Earth's orbit affect the amount and distribution of solar energy, influencing long-term climate.

Reader's Guide

Weather is a fundamental process that shapes the Earth through weathering, breaking down rocks and soils. Rainwater absorbs carbon dioxide, becoming slightly acidic, which aids erosion. The released sediment and chemicals participate in chemical reactions that affect the surface, such as acid rain, and deposit salts in oceans. Weather also has direct effects on humans, with tornadoes causing significant fatalities and property damage. The atmosphere is a chaotic system, making weather forecasting difficult beyond a few days, and it is theoretically impossible to make useful day-to-day predictions more than about two weeks ahead. Studying weather on other planets, such as Jupiter's Great Red Spot, has helped understand Earth's weather. Human activities like agriculture and industry have modified weather patterns.

Did You Know?

• Most weather phenomena occur in the troposphere, just below the stratosphere.
• The strong temperature contrast between polar and tropical air gives rise to the Hadley cell, Ferrel cell, polar cell, and jet stream.
• It is theoretically impossible to make useful day-to-day weather predictions more than about two weeks ahead.