Monday, March 2, 2009
Geography lesson, 2nd March 2009
Today, we have started a new topic in atmosphere which is the Global Air Circulation. Basically, we have learnt how air circulate around Earth. And thus we know why desserts are not formed around the equater.Today's lesson Mr Heah introduced us a way to make our own simple model of air circulation. Firstly, we need to remove all possible variables to be able to see how only one factor affects the other. So, we romoved all the factors but HEAT from the sun. Because of the uneven distributed heat energy from the sun, for the equator part heat energy is distributed the most intensely part, thus it is the hottest. But for the poles, because energy is distributed to a largest surface area, it is the most diffused around there. And because atmosphere is liquid, convection current will be set up. Therefore, hot air will rise from equator and sink down at the poles. This model is called single cell model which has been blamed for too simplistic.
Then, Mr Heah introduced us another model called three cell model. Basically, in this model, air rise from the equator, and cold air will still sink at the poles. But, along the way that air is travelling, they will sink as well. This convection cell is called Hadley Cell. And around some where near the poles, there will be air rise as well. This cell is then called Polar cell. Then, in between those two cells, there is one more convection current cell, Ferrel cell.
And based on this diagram, we can see why desserts are always formed around from somewhere above equator. As you all can see from the diagram, for the Ferrel cell, the air rises from the terminal which is nearer to the pole and sinks at somewhere above equator. And for Hadley Cell, the air also sinks at the point that air sinks for Ferrel Cell. Thus, there is almost no air rises from that place. Furthermore, because rain is formed when hot air rises(water evaporate) and water vapor condenses then to form clouds and rainfalls. However, for that area, air won't rise, thus there would be very little percipitation here. Thus, desserts are always formed here. Whereas, although, equator recieve the most intensive heat from the sun, but because there are a lot of water evaporate as well, hence, this place recieve quite amount of precipitation every year. Also, we have talked about the cause of charatistics of dessert using air circulation to exphenlain. Because there will only be clouds formed if there is water evaporate from the grand, there will be no or little clouds in the sky. And the clouds can help reflect or keep the heat from the sun, so they can help regulate heat and temperature of a place. Therefore, in dessert, during day time, the temperature is very high whereas at night the temperature is very low.
After finding this three cell model to discribe the air circulation, we added in another affecting factor, the rotation of earth itself. Then, there is another more complicated model.
Because earth will rotate from east to west, the pathway for air flow will swing to the west a bit due to inertia.
From this lesson, the most important thing that I have learnt is how to solve a complicated question. It is just like how to generate the model for air circulation. First of all, we need to break down all the affecting factors and then concentrated on one factor. Then, after that, we should continue to add in other parts to make the model(answer) complete. Also, one more thing to notice is that when we are solving other confusing problems, we should take the easier one to do first and keep adding other harder parts to perfect your answer.
Wen Yu