Worldwide Wind Currents Weather Dynamics Science 10

The Flow of Air Due to the uneven heating of the Earth’s surface, the temperatures of the air above it are also uneven. When air warms it expands and becomes less dense. Cooler air is denser than warm air and exerts more pressure on its surroundings. Cool air flows toward and under warm air, pushing the warm air up and away. Hence, warm air rises and cold air falls.

At the Equator The air that is close to Earth’s surface warms to nearly the same temperature as the land or water. As air warms it becomes less dense and begins to rise. Cooler air moves in below and then it warms. The denser, colder air at the poles moves along the Earth’s surface and moves the warm air toward the poles. This is the concept of convection.

Wind Patterns on Earth Technically, if the Earth was rotating and the atmosphere was not, we would all feel wind of 300m / s (1080 km / hr). Since this is not the case, the atmosphere must be moving with the Earth. In fact, for the most part the atmosphere spins with the Earth at the same speed as the surface below it. Different places of the Earth are moving at quite different speeds. Think about someone living in Nova Scotia versus someone who is living on the Equator. Both people need to move around the Earth completely in 24 hours.

Coriolis Effect Due to the rotating of the Earth, any object moving on the Earth’s surface does not move in a perfectly straight line. It too rotates! This influence on moving object due to the rotating of the Earth is known as the Coriolis Effect. Scientists, Meteorologists, as well as military personnel all need to take the Coriolis Effect in to consideration. If the military are trying to fire a missile a large distance, they need to consider that the Earth is moving and therefore the object will move counter- clockwise with the Earth.

Prevailing Westerlies The Coriolis effect causes wind to blow from west to east. These winds are called prevailing westerlies and are generally why weather systems move from the west toward the east in Canada.

Jet Stream Ribbons of extremely fast moving air near the top of the atmosphere are known as jet streams. They are found at the boundaries of temperate and polar zones and temperate and tropical zones. The jet streams vary from 100 km/h to 300km/h, are thousands of kilometres long and a few hundred kilometres wide. In general the weather north of the jet stream is cold and the weather south of the jet stream is warmer. The jet streams change quite often and are not perfect circles which is why they are usually a part of weather forecasts.

Do You Understand? 1.Why does air over the equator tend to rise? 2.How do we know that the atmosphere rotates with Earth and does not remain stationary while Earth rotates under it? 3.What property of Earth causes the Coriolis Effect? 4.Describe the overal result of the Coriolis Effect in the Northern and Southern Hemispheres. 5.Where would you expect to find a jet stream? 6.A round-trip airplane ticket between Calgary and Toronto states that the actual flying time in the air is 3h 38min from Calgary to Toronto and 4h 6min from Toronto to Calgary. From your knowledge about winds explain why it is half an hour longer to fly west than east.