Atmosphere

A precious shield

The atmosphere is a component of the climate system. It is the gaseous envelope that surrounds Earth and shields the biosphere from potentially harmful ultraviolet solar radiation. It has a layered structure in which water vapour decreases and the air becomes progressively thinner with altitude. Roughly three-quarters of the atmosphere’s mass lies in the layer closest to Earth’s surface—the troposphere—which has an average thickness of about 11 km.

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Curious by nature

The engine of weather

Atmospheric phenomena are driven by the Sun. Part of the Sun’s energy is absorbed by Earth’s surface, part by the atmosphere, and another portion is reflected back into space.

Uneven heating of Earth’s surface triggers strong convective motions in the troposphere (from the Greek tropos, “turn/change”), which—together with Earth’s rotation—produce the prevailing wind systems and the circulation of air masses.

Ocean waters move more slowly than air, but they can store far more heat than the atmosphere, and that heat is transported by ocean currents.

The prevailing wind system transfers heat from equatorial to polar regions. When air warms, it becomes less dense, expands, and rises; cooler air sinks, creating a circular pathway called a circulation cell.

Near the surface, airflow within these cells sets up the planet’s major wind belts.

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