The air will be still one day, and the next, powerful gusts of wind can knock down trees. What is going on here? The main cause of wind is a little surprising. The gases that make up our atmosphere do interesting things as the temperatures change. When gases warm up, the atoms and molecules move faster, spread out, and rise. When air is colder, the gases get slower and closer together. Colder air sinks. The sun warms up the air, but it does so unevenly.
Because the sun hits different parts of the Earth at different angles, and because Earth has oceans, mountains, and other features, some places are warmer than others. Because of this, we get pockets of warm air and cold air. In the northern hemisphere this wind spiral flows in an anticlockwise direction around areas of low pressure and in a clockwise direction around areas of high pressure - the opposite is the case in the southern hemisphere as the Coriolis force acts in the opposite direction.
Wind flow. How does wind flow around areas of high and low pressure? You might also like. Read more. This rising and sinking of air in the atmosphere takes place both on a global scale and a local scale. As the atmosphere heats, the warmer air rises which creates areas of lower pressure. The colder, denser air forming adjacent high pressure systems moves to fill in the space left by the rising warmer air. The warm air cools when it nears the top of the troposphere and sinks back toward the Earth's surface, creating convection currents in the atmosphere.
High pressure weather systems typically result from colder air patterns while low pressure weather systems generally result from warmer air patterns. If the Earth didn't spin, the convection currents in the atmosphere could develop winds that would blow from the poles all the way to the equator. The Earth's rotation around its axis, however, causes the Coriolis effect. The spinning Earth deflects the wind from a straight line into a curve.
The stronger the wind, the greater the curve. In the northern hemisphere the deflection curves to the right. In the southern hemisphere the deflection curves to the left. Another way to consider the direction of the Coriolis effect is from the perspective of an astronaut floating directly above the North pole. A helium balloon released north of the equator would travel in a counterclockwise direction. If the astronaut were above the South pole instead and the balloon was released south of the equator, the balloon would appear to travel in a clockwise direction.
Meanwhile, returning to the equator, the cooling air at the top of the column of rising air is pushed aside and begins to fall back to the Earth's surface.
The Coriolis effect twists the rising and falling air nearest the equator into the pattern of wind called the trade winds. In the northern hemisphere the trade winds flow from the northeast to the southwest while in the southern hemisphere the trade winds flow from the southeast to the northwest.
The wind pattern in the mid-latitudes flows in the opposite direction, generally west to east. Weather patterns in the U. These winds are called the westerlies. Early explorers learned about these general patterns and used them to explore the world. These wind patterns provided a steady source of propulsion for sailing ships traveling from Europe and Africa to the New World and back again.
The pressure differences that make wind happen are caused by differences in temperature.
0コメント