water balance 31 March 09

31 March 09

In this lesson, the water balance P= E + Q +∆ S, as well as several other factors involved were taught.

Precipitation is measured by the summation of the level of Evapotranspiration (E) summed with the Runoff (Q) and rate of change in the levels of the initial Soil moisture and final soil moisture.

The water balance is usually used by hydrologists to plan and manage water supply within a drainage basin. It can be applied to predict possible water shortages, irrigation patterns, pollution control and flooding.

Additional factors that are involved with Infiltration were also discussed, with Interception by vegetation being the concentration of the discussion. Most drainage basins are clothed by one or more forms of vegetation. This vegetation will to some extent intercept precipitation. Water may be held on the leaves to then be evaporated or flow down from leaf to leaf as throughfall. It may also flow down from tree trunks or plant stems as stemflow.

Vegetation also reduces rainsplash, by absorbing the impact of raindrops by preventing them from landing directly on the ground. This reduces soil erosion and soil compaction (which may encourage overland flow.) Plants also reduce the amount of water available in the system by the use of water as they grow (absorption of water through roots). Its rate of transfer is also slowed as the roots encourage water to pass into the soil and rock.

Another item discussed was the possible variations to the equation by human activity, mainly by deforestation or reforestation. If P stays the same, and E becomes more (more trees), S decreases. If P stays the same, and E decreases (less trees), Q would become more. S does not necessarily increase as there would be rivalling factors involved such as, less absorption yet more rainsplash.etc.

CHESTER LAU jh40614

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

GLOBAL AIR CIRCULATION!!

❤Global Air Circulation, yeah!!

Me- Haha, hello everybody!!

Class- Haha, hello hello!!

Okay, let’s talk about our Geo lesson on Mon :)

Firstly, we shall remember “GEOG”:

❤G- Good Attitude

❤E- Engagement

❤O- Ownership

❤G- Growth

This is very important for our Geo lessons❤

Now, let's talk about the following question:

“Why aren’t deserts found at equator???”

We all know deserts are very warm but…

Does it mean that deserts are located at the warmest region of the earth which is known as “equator”?

The answer is NO.

A desert is a landscape or region that receives very little precipitation. Deserts can be defined as areas that receive an average annual precipitation of less than 250 mm (10 in), or as areas in which more water is lost than falls as precipitation.

Thus, the real answer to the question is related closely with Global Air Circulation!! Now, let’s talk about the global air circulation, yeah!!

Firstly, we assume the earth is at rest. As what we have learnt before, air flows from the cold parts to the warm parts because cold air is heavier than worm air. Therefore, it should flow from the poles to the equator. However, because of the influences of convection and convergence, when the air reaches the equator, it will be lifted vertically and then flows horizontally. Finally, the air will flow back to the poles from the equator. The upper air at the poles then will sink as it is cooler. By doing so, air circulation is completed!!vvvvv

However, as the earth is rotating from the west to the east all the time, the first model is not completely correct. The rotation will develop the one-cell circulation to three. The three cells are known as: the Polar cell, the Ferrel cell and the Hadley cell.

Both of the Polar cell and the Hadley cell are driven by heat while the Ferrel cell is driven by the other two!! From the model above we can see that the air is sinking at the shaded region. As what we have learnt before, air will keep rising when it is warm. It will finally form clouds and make RAIN!! However, there is no adiabatic cooling of the air of the shaded region and it sinks so that there will not be clouds thus there is not RAIN!! Therefore there is very little precipitation there. Thus, deserts are formed there!!!

So, this is why deserts are found at those areas instead of at the equator!!!

Haha, done, yeah!!!
:D

Done by Liu Tong :P

The 10 minutes question.

To what extent should we be concerned about Carbon Dioxide emissions?

We should be very concerned about carbon dioxide emissions because it would cause dire consequences on Earth and living things. Carbon dioxide is a greenhouse gas. Hence, when too much of it is emitted into the atmosphere, the amount of greenhouse gases increases. Greenhouse gases trap heat on earth causing the average temperature all around the globe to increase.

This will result in the melting of ice caps in the south and North Pole. When the ice bergs melt, the animals living there will lose their natural habitat. One good example would be the polar bears. Polar bears need ice to live on. They need to come ashore on ice to hunt and rest. Hence when most of the ice bergs melt, they have no choice but to keep swimming in water looking for another ice berg. When they cannot find one and they become too tired after swimming for long hours, they will all drown. This would cause extinction of several species like the polar bear.

When more ice melt, the water level of oceans and seas would increase and low lying beautiful cities like Bangkok and Venice would be submerged under water. The beautiful monuments and tourists attractions there would disappear and the people living there would have to move to another country or city. Also, when the average global temperature increases, sensible heat would be higher and there would be an increased chance of getting heat stroke.

All these effects are caused by too much carbon dioxide emitted. It will cause extinction of animals and disrupt the food chain. It will also cause changes to human beings and their lifestyles. Hence, we should be very concerned about carbon dioxide emissions.

I read on the internet that currently, the oceans and land absorbs half the amount of carbon dioxide emitted by human beings. It acts as a carbon basin and absorbs carbon dioxide. Some scientist predict that the oceans and land would continue to absorb even more carbon dioxide in the future. However, some scientitsts disagree and predicts that when it reaches a certain limit, the oceans and land will not be able to keep up with the ever increasing amounts of carbon dioxide emission.

A simple reason based on the oceans is because the organism that absorbs carbon dioxide in the oceans are mostly the plants when they need carbon dioxide for photosynthesis. I agree that with the increased concentration of carbon dioxide in the oceans, rate of photosynthesis would increase too!However, they can only increase to a certain limit as it is now affected by other factors such as metabolic reactions in the plant, water, nutrients availibility etc.

done by: JIAYI!