Climatology Composition and Structure of the Atmosphere PDF

Climatology Composition and Structure of the Atmosphere

Explain the structure of atmosphere with diagram?

Climatology is the study of climate defined as weather conditions averaged over a period of time.

Structure of the Atmosphere

The atmosphere is composed of the following layers :

STRUCTURE OF THE ATMOSPHERE

  1. Troposphere
  2. Stratosphere
  3. Mesosphere
  4. Thermosphere
  5. Exosphere

All about Troposphere

Troposhpere

(i) This is the abode of all living organisms.

(ii) Almost all weather phenomena occur here.

(iii) Its average height is around 13 km. The height is roughly around 6-8 km around the poles and 16-18 km around the equator.

(iv) Upper limit of the troposphere is called as the tropopause (i.e. no turbulence) which means where the mixing stops.

Why is the height of tropopause maximum around the equator and minimum around the poles?

Reality of Equator and Poles

Height of Tropopause

Reason 1 

Temperature & Air Density at Altitude on Troposphere

At the Equator At the Poles
High heat in the equatorial area will heat up air mass in those areas. The reverse happens in the case of poles.
The heated up air parcel will expand, become less dense and consecutively rises up. Air gets very cold, becomes dense and starts sinking.
This a strong convection current is produced because of excessive heating and this will push the tropopause upward. This cause the tropopause to remain at a lower height as well.

Reason 2

Gravitational Force at Equator and Poles

(a) Gravity increases from equator to poles as the earth is not a perfect sphere (oblate spheroid). That means the gravitational force is more over poles.

(b) Hence the atmosphere is pulled with more force near the poles than at the equator leading to contraction of the atmosphere at the poles and expansion at the equator.

Reason 3 

Centrifugal Force at Equator and Poles

(a) The centrifugal force (the force acting on a body moving in a circular path which is directed away from itself) due to Earth’s rotation is maximum at Equator because the speed of the rotating earth is greater at the equator.

(b) Thus the atmosphere tends to bulge out at the equator because of the force.

Why does this temperature drop happen?

(a) As we ascend higher in the atmosphere, the amount of heat gets lost to subsecutive layer lying below.

(b) The air pressure is higher in the lower portion of the atmosphere near the earth’s surface because of the weight of all the overlying layers above. Thus density of air decreases as we move upwards.

(c) The lower layer of the air contains more water vapour and dust particles than the amount of heat radiated from the earth’s surface than the upper layers.

(d) Temperature drops with increasing altitude at the rate of 6.5 degree Celsius per 1000 m. This rate is known as Normal Lapse Rate (NLR).


Question : Normally, the temperature decreases with the increase in height from the Earth’s surface because.

  1. The atmosphere can be heated upwards only from the Earth’s surface.
  2. There is more moisture in the upper atmosphere.
  3. The air is less dense in the upper atmosphere.

Select Correct answer using the codes given below :

a). 1 only

b). 2 and 3 only

c). 1 and 3 only

d). 1,2 and 3

Explanation

  • Statement 1 is correct since atmosphere is heated by infrared radiation emitted by earth. That is, long-wave terrestrial radiation rises the temperature of the earth than incoming short-wave radiation. This source of heat is known as ground-radiation or terrestrial radiation.
  •  2nd statement is not true. In fact, it is the opposite. More than 90% of water vapour or moisture present within 5 Km from earth surface.
  • 3rd statement is true. Air is less dense, meaning it can hold less heat. Thus temperature is low in the upper atmosphere.

e). There is seasonal difference of height i.e. it varies by season. It is lower in winter and higher in summer.

What is the reason for seasonal variation of height?

Seasonal Variation of height

1). In winters, the air becomes cold i.e. becomes more dense. Therefore in general, there is drop in height.

2). Over the equator, there is no winter as there is less seasonal differences.Hence this variation is not greatly observed.

3). However, as we move towards the poles from the equator, the height increases during summer and decreases during winter.

f). There is an attitudinal variation of temperature in troposphere.

What happens at the tropospause?

Altitude vs Temperature at Troposphere

1). The zone separating the troposphere from stratosphere is known as the tropopause.

2). Tropopause is about 1.5 km thick.

3). This is isothermal layer as temperature gradient here is nearly constant.

4). The air temperature at the troposphere is about minus 80° C over the equator and about 50° C over poles.

5). Troposphere is an isothermal layer.

Note : Beware temp is lowest above equator and not the other way round.

Why is temperature lowest at the tropopause above the equator than at the poles?

Temperature at Tropopause

Since temperature decreases upward at the rate of 6.5° per 1000 m and hence it is natural that at the height of 18 km over the equator becomes much lower than at the height of 8 km over the poles.

Climatology Composition and Structure of the Atmosphere PDF

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