GLOBAL AIR CIRCULATION!! --wind movements

During Geography lesson today, we learnt about the global air circulation and the movement of wind. It was an an enlightening one!

We have already learnt about the three cell diagram which includes the hadley cell, ferrel cell and the polar cell. This lesson, we focused more on the direction of the wind on the Earth.

Movement of the wind
Based on the assumption that the Earth is not rotating, the direction of the wind will move as indicated by the arrows in the picture below. They move in a straight line either downwards or upwards.

However, we know that as a fact, this is not the case. The Earth is constantly rotating in an anticlockwise direction, and this turning of the Earth brings about the Coriolis effect. What is the Coriolis effect then? It is basically the deflection of the wind to the left or right side, depending on the which hemisphere we are talking about.

Let us further analyse and understand the Coriolis effect by dividing the Earth into 6 parts.
On Earth, there are the NE polar easterlies, SE trade winds, the westerlies, NE trade winds and the SE polar easterlies. These winds are named after the direction and the origin of the wind.

The top 3 layers of the Earth are under high pressure while the bottom three layers are the low pressure belt.

Coriolis force causes the air in the the upper atmosphere to move about 30° of latitude zonally from west to east. This zonal flow causes the accumulation of air in the upper atmosphere as the direction of the wind is no longer flowing perpendicularly to its latitude. To compensate for this accumulation, some of the air in the upper atmosphere sinks back to the surface, creating the subtropical high pressure region. From this zone, a portion of the air moves back toward the equator completing the circulation system to form the Hadley cell, and creating the NE trade winds and SE trade winds. The surface air moving towards the poles from the subtropical high zone is also deflected by Coriolis force to produce the Westerlies.

In the northern hemisphere, the wind moves from the higher to lower pressure and as a result of the Earth's anti- clockwise rotation, the wind will be deflected to the right. In the Southern hemisphere, the wind moves from a lower to higher pressure, and air is deflected to the left by the Coriolis force. There is no Coriolis force at the equator.

The amount of deflection the wind makes is related to the air's speed and its latitude. Therefore, slowly blowing winds will be deflected only a small amount, while stronger winds will be deflected more. Likewise, winds blowing closer to the poles will be deflected more than winds at the same speed closer to the equator. The Coriolis force causes phenomenas like mid latitude cyclones, hurricanes and anti- cyclones.

Besides studying the Coriolis force, we also went through conceptual mind maps that were done by us in groups. We learn how to draw links between the different keywords throughout the module to explain and accout for every occurence on Earth. For example, by describing global warming to be "enhanced", we can actually stress the exarcebation and worsening of the existing problem now.

Done By: Tan Jia Min