Everything Science Grade 11

CHAPTER 10. THE ATMOSPHERE 10.2

10.2 The structure of the atmosphere

ESBDL

The Earth’s atmosphereis divided into differentlayers, each with its ownparticular characteristics(Fig-

ure 10.1).

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-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20

Height (km)

Temperature (◦C)

Troposphere

Stratosphere

Mesosphere

Thermosphere

Figure 10.1: A generalised diagram showing thestructure of the atmosphere and the changing temper-

atures up to a height of110 km

The troposphere ESBDM

The troposphere is the lowest level in the atmosphere, and it isthe part in which we live. The tro-

posphere varies in thickness, and extends fromthe ground to a height of about 7 km at the poles and

about 18 km at the equator. An important characteristic of the troposphere is that its temperature de-

creases with an increase in altitude. In other words, asyou climb higher, it will get colder. You will

have noticed this if youhave climbed a mountain, or if you have movedfrom a city at a high altitude

to one which is lower;the average temperatureis often lower where the altitude is higher. This is

FACT

Aeroplanes fly just above

the troposphere to avoid

all this turbulence. If

you have ever been in

an aeroplane and have

looked out the win-

dow once you are well

into the flight, you will

have noticed that you

are actually flying above

the level of the clouds.

Clouds and weather oc-

cur in the troposphere,

whereas the stratosphere

has very stable atmo-

spheric conditions and

very little turbulence.

because the troposphereis heated from the ’bottom up’. In other words,places that are closer tosea

level will be warmer than those at higher altitudes. The heating of the atmosphere will be discussed

in more detail later in this chapter.

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