Circulația atmosferică - atmosferic circulation

Many components of the Earth are in motion (e.g. the atmosphere, oceans, biological systems), though some move rather slowly (e.g. continents, mantle).

Each of these systems play a role in the distribution of energy and thus the climate of the Earth. These systems can be thought of as acting on three different time scales.

1. Very short time scales (days to weeks)- surface winds…think storms and weather frontal systems.

2. Short time scales (years to decades)- tropical ocean heat pump…think El Niño.

3. Longer time scales (millennial)- deep ocean circulation…think Gulf Stream.

4. Longest time scales (10s of millions of years)- plate tectonics…think Himalayas.

Some regions receive more energy from the Sun than others. The atmosphere and oceans compensate by redistributing this excess energy by wind and water transport of heat.

Thus, both the global wind belts and ocean currents are generated and maintained because the tropics receive more insolation than the poles.

Air will also move vertically if pushed over something, or because it is more buoyant than surrounding air. Buoyancy is controlled by differences in density, usually the result of differences in temperature and moisture content between air masses.

Air moves (wind) horizontally in response to differences in pressure

Vertical movement- an air mass will rise if it is less dense than surrounding air. An air mass can become less dense if it is heated, or if it contains more moisture.

Effect of heating- air molecules move at higher rates when they heat up, spreading out and reducing density.

Effect of moisture- air with water vapor has a lower density because water molecules have a lower molecular weight.