24 March

Hi class, so do you remember 24 March was one of the super hot days? We were complaining to Ms Kavi that the weather was so hot and that we were all perspiring like crazy? Ms Kavi told us that there was an uneven heating in localized environment. Basically she said that there were many different factors that actually affect the uneven heating. One of the factors was due to El-Nino (worsening effect).

El-Nino is a climate pattern that occurs across the tropical Pacific Ocean on average every five years, but over a period which varies from three to seven years, and is therefore, widely and significantly, known as "quasi-periodic." Also, we were taught of what is the global circulation of air. Net heat will tend to lose or gain.

Net heat loss: Higher albedo, ice reflects insolation (mostly occurs at polar area/ regions)

This means that the air is more dense, sinks, contracts and has a higher pressure.

Net heat gain: Mostly occurs at equatorial regions/temperate regions: Angle of incidence refers to the amount of solar insolation received is higher than that lose to atmosphere.

This means that the air is less dense, expands, rises, and has a lower pressure.

Lastly we learnt about the convection cell. Convection cell is a concept in plate tectonics that accounts for the lateral or the upward and downward movement of subcrustal mantle material as due to heat variation in the earth. We were taught till here for today’s lesson. So if you are interested to find out what exactly is the convection cells named as and what happen in the different cells, stay tuned for the next post!:)


Geraldine Lim (09)

Geog Field Trip around NJC!

Hellooo everyone!

Today we started learning about the hydrosphere, and how the drainage basin system (drainage basin hydrological cycle) works as a system, with flows, outputs, inputs and stores. (reminds me of our essay! haha)

Well we went around and had a mini field trip around the school and pictures are shown below. We learnt about how the saturation of the different kinds of soil (like say, with vegetation and without) have different zones of aeration in terms of size. In barren land, air gaps in zones of aeration are smaller, as the soil is being compacted. With this compaction, the gaps in the Earth cannot hold as much water as compared to those with vegetation, and thus surface runoff increases. This causes the water table to drop in it's level.

When zone of saturation increases in size, the water table will be raised, and those causes flooding.

Here the water is being collected by the drainage system.

Surface runoff from the canvas sheet!

Raining raining.

Here what's happening is the water is being collected as 1) the land cannot take in anymore (reached it's maximum point of saturation) and 2) the drain is higher than the ground level. So water is collected and does not flow into the drain as quickly.

yay. haha here's a video on serious surface runoff.

QUESTION OF THE LESSON: How do urban settlements affect the hydrological cycle?

L(ots)O(f)L(ove),

SAM! (register 13)

Solstices and Equinoxes

Hi, all! Sorry for the late post. This post is about solstice and equinox, which we learned on 23rd Feb.

Equinoxes are the two days in the year when the day and night are exactly the same length. The vernal equinox (spring equinox) is on 20 or 21 March ( This year the vernal equinox is on 20 March which is 6 more days from now!) while the autumnal equinox is on 22 or 23 September.

Winter solstice is when the sun is above the horizon for the shortest amount of time on 21 or 22 Dec while summer solstice has the longest amount of time receiving sunlight on 20 or 21 June.

However the dates mentioned above are with respect to the northern hemisphere where we live in. For the southern hemisphere the seasons are different which means when we are having summer solstice, southern hemisphere is at winter solstice and vice versa. Quite common sense, right?

The variation of the dates is because that the revolution of earth is not exactly 365 days. It is actually 365 days 5 hours 48 minutes and 46 seconds and…… yup. So we have to include the 5 hours for calculating the exact dates.

Here is the classical picture in explaining the rationale of equinox and solstice though I think we’ve already had enough discussion on the day itself. Comparing the shaded area with the bright ones you can see the different lengths of day and night. For equinoxes we can see that when the sun directly shines on the equator, it is divided equally by day and night.

Why is it so? The earth is tilted! That causes the sun shines directly on tropic of cancer or tropic of Capricorn at different times and thus results of differences in length of the day and night.

OK. This is the most important part that we all need to understand about that lesson. Any questions please refer to the notes or leave me a comment below.

Lan Tu (8)

Global Circulation of Air

Hellos! Today, we learnt more about the global circulation of air. (OK, sorry, there will be no diagrams)

The global model consists of the tropical cell (Hadley cell), the mid-lattitude cell (Ferrel cell) and the Polar cell.

The Hadley Cell
The Hadley cell is the in the area of zero degrees and thirty degrees north as well as zero degrees and thirty degrees south. What happens at the Hadley cell is that warm air rises and moves away from the earth and the air cools to the temperature of surrounding air. The air movement is unstable and there is convection rain. At the equator, due to insoluation from the sun - the intensity of heat received along the equator is high, the air rises. This air is warm air at low pressure.

The Ferrel Cell
The Ferrel cell is from thirty degrees north to sixty degrees north or thirty degrees south to sixty degrees south. At the Ferrel cell, the cold air (from Polar and sub-Polar regions) sinks and the decending air warms by compression, resulting in cloudless and stable conditions. At thirty degrees north/south, there is high pressure so the air seems to 'come in' as opposed to 'rise away' like at zero degrees.

The Polar cell
The Polar cell ranges from sixty degrees north to nienty degrees north or sixty degrees south to ninety degrees south. At the Polar cell, around the sixty degree north/south area, warm air from the tropics meets cold air from the Polar areas. The warm air rises quickly and compes into contact with the cold parcels of air. This results in instability and depressions. The cold air sinks at ninety degrees north/south and is at high pressure, resulting in dry and stable conditions at nienty degrees north/south.

Air moves from areas of higher pressure to lower pressure, however the air movement is not straight. Why is this so? This is due to the movement of the earth - remember the Coriolis Effect? On top of that, the land mass distribution is uneven, with more land in the Northern Hemisphere. This results in a differential temperature since land absorbs and gives out more heat than water. So what about monsoon winds? The cross over oceans and carry moisture. What path do they take?

Don't forget to read the notes! Especially on the Surface Features of the Global Atmospheric Circulation System (because I didn't write anything about that since it is there...)

<3 Huiling XD (10)