How latitude and altitude affect temperature...

***IMPORTANT! THIS IS IN THE EXAM!***

How does latitude affect temperature?

We all know by now that the Earth can be broadly divided into 3 climate types: tropical, temperate and polar. We also know by now that the further we travel from the Equator, the colder it gets. Hence, at the high latitudes, close to 90° North and South, temperatures are much lower than at the Equator.

Why is this so? Why is the temperature in Singapore so different from that in Greenland?

There are various reasons for this. The most important one has to do with what is known as the angle of solar incidence. Angle of solar incidence refers to the angle at which the Sun's rays strike the Earth's surface.

In the above diagram, N.P. represents the North Pole. 'Insolation' refers to the amount of incoming solar radiation, but that is beyond the scope of the syllabus. The dotted line represents the limit of the atmosphere.

At the Equator, the incoming solar radiation strikes the Earth at a right angle. Hence the heat from the Sun is concentrated and more intense, and is spread over a small area. Also, at this latitude, the Sun's rays travel a short distance through the atmosphere. Because of the shorter distance travelled, Less heat is lost to the atmosphere, and therefore more of the Sun's rays reach the Earth's surface.

On the other hand, at high latitudes, the incoming solar radiation strikes the Earth at an acute angle. The Sun's rays also have to pass through a longer distance in the atmosphere before reaching the Earth's surface. Hence more heat is lost to the atmosphere. Even though the rays which strike the polar regions carry the same amount of heat as the rays which strike the tropical regions, this heat is diffused and dispersed over a large area.

Let's use a flashlight as an analogy:

A represents the Sun's rays hitting the Earth at the Equator. The heat is focused and concentrated over a small area and is more intense.

B represents the Sun's rays hitting the Earth at the North Pole. The heat is diffused and dispersed over a larger area.

I hope you remember that in primary school, you learned that it is hottest at midday, when the Sun is directly overhead, whereas it is cooler in the morning and evenings, when the Sun is lower in the sky. This is the same general principle by which latitude affects temperature.

In summary:

• At different latitudes, the Sun's rays strike the Earth at different angles
• At the Equator, the Sun's rays strike the Earth at a right angle, hence the heat is more intense and concentrated over a small area. Less heat is lost to the atmosphere as the rays travel a shorter distance through the atmosphere.
• At the poles, the Sun's rays strike the Earth at an acute angle, dispersing and diffusing the heat over a larger area. More heat is lost to the atmosphere as the rays travel a longer distance through the atmosphere.

One final note: While it is hot and wet in the tropical regions, it is cold in the polar regions, so cold that most of the precipitation is frozen, and falls as snow.

How does altitude affect temperature?

Most of you would be aware that it tends to be very cold at high altitudes, such as on mountaintops, or up in the sky. Logically, one would expect that the higher the altitude, the higher the temperature, because mountaintops are closer to the Sun than objects at sea level. This is incorrect.

In actual fact, the atmosphere is NOT warmed by direct contact with the Sun's rays. What really happens is that the Earth's surface absorbs most of the heat. Then, as the Earth's surface warms up, the heat diffuses into the lower layers of the atmosphere, warming it, which in turn transfers some of the heat to the upper layers of the atmosphere.

Of course, this means that the layers of atmosphere closest to the Earth's surface receive the most heat from the Earth's surface.

What happens at high altitudes, such as on mountains, or in the upper layers of the atmosphere, is that at such great height, far from the Earth's surface, there is very little heat reaching this altitude. Most of the heat is being trapped within the lower layers of the atmosphere close to the Earth's surface.

Try and visualise a thermos flask with several layers of cloth wrapped around it. The thermos flask represents the Earth, warmed by heat from the Sun. The layers of cloth represent the layers of the atmosphere, with the layers of cloth closest to the thermos flask representing the layers of atmosphere closest to the Earth's surface. The layers of cloth on the outside would be much cooler, because most of the heat from the thermos flask is trapped in the inner layers of cloth.

In summary:

• The atmosphere is progressively warmed by the heat radiating from the Earth's surface
• The lower layers of the atmosphere closest to the Earth's surface are warmed first, and then subsequently transfer heat to the upper layers. As the heat is transferred upwards, some heat is continuously being lost.
• At high altitudes, there is very little heat left to be transferred at this height.