L-3 Dynamics atmosphere and changing climate class ix

 L-3 Dynamics atmosphere and changing climate 

class ix

*Questions and Activities*

*1. What is atmosphere? Explain its composition with the help of a pie diagram.*  

The atmosphere is the layer of gases that surrounds the Earth. It protects us from harmful UV rays and maintains temperature. Its main gases are Nitrogen 78%, Oxygen 21%, Argon 0.93% and other gases 0.07%. Carbon dioxide, water vapor and dust are also present in small amounts. It helps in the survival of living beings.

*2. Draw a labelled diagram of the structure of atmosphere.*  

The atmosphere has 5 main layers. From bottom: Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere. Troposphere has weather and clouds. Stratosphere has ozone layer. Temperature decreases in troposphere, increases in stratosphere and thermosphere. Most aeroplanes fly in lower stratosphere. Each layer has different temperature and gas density.

*3. Which are the four main seasons of India?*  

The four main seasons of India are Winter, Summer, Monsoon and Post-Monsoon/Retreating Monsoon. Winter is from December to February. Summer is from March to May. South-West Monsoon is from June to September. Retreating Monsoon is from October to November. These seasons are caused by the movement of the sun and monsoon winds.

*4. Why do you not feel the pressure of the atmosphere?*  

We do not feel atmospheric pressure because our body fluids exert equal pressure outward. Our body is adapted to this pressure since birth. The pressure is distributed evenly on all sides of the body. Also, air inside our body balances the outside air pressure. So we feel comfortable.

*5. In which layer of the atmosphere do aeroplanes fly and why?*  

Aeroplanes generally fly in the lower part of the Stratosphere. This layer has very little turbulence and clouds. The air is thin, so there is less air resistance for planes. Weather changes do not occur here, making flights smooth. Flying here also saves fuel and time.

*6. Distinguish between the following:*  

*a. The troposphere and stratosphere*  

Troposphere is the lowest layer where weather occurs and temperature decreases with height. Stratosphere is above it where temperature increases with height. Ozone layer is present in stratosphere. Most weather phenomena and clouds are limited to troposphere.

*b. The south-west monsoon and north-east monsoon*  

South-West monsoon brings rainfall to most of India from June to September. It blows from sea to land. North-East monsoon blows from land to sea and gives rainfall to Tamil Nadu coast in Oct-Nov. SW monsoon is caused by heating of land, NE by cooling.

*7.3. a. Why does Shillong experience more rainfall than Kolkata?*  

Shillong lies on the windward side of Khasi hills and receives orographic rainfall. Moist monsoon winds from Bay of Bengal are forced upward here. Kolkata is on the plain and gets less orographic lift. Also, Shillong is at higher altitude. Hence Shillong gets much heavier rainfall.

*7.3. b. Why does Delhi receive more rainfall than Jodhpur?*  

Delhi is closer to the track of monsoon winds and gets moisture from Bay of Bengal branch. Jodhpur lies in the rain shadow area and is near Thar Desert. By the time winds reach Jodhpur, they become dry. Delhi also gets some western disturbances. Thus Delhi gets more rain than Jodhpur.

---

*2. Draw a labelled diagram of the structure of atmosphere.*  

*Description to draw:*  

Draw 5 horizontal layers above Earth.  

1. *Troposphere*: 0-18km, clouds, weather, temp decreases.  

2. *Stratosphere*: 18-50km, Ozone layer, temp increases, planes fly here.  

3. *Mesosphere*: 50-85km, temp decreases, meteors burn.  

4. *Thermosphere*: 85-600km, Aurora, temp increases.  

5. *Exosphere*: 600km+, outermost layer, fades into space.  

Label each layer with height and 1 main feature.

*7.1. Re-arrange the 10 stations according to their distance from the equator.*  

Since the actual Table 3.3 is not given, use this general method:  

Stations near the equator have low latitude like Thiruvananthapuram, Chennai.  

Middle latitude stations are Nagpur, Delhi, Kolkata.  

Far from equator have high latitude like Srinagar, Shillong.  

Arrange them from lowest latitude to highest latitude.  

This shows temperature decreases as we move away from equator.

*7.2 Find out:*  

*a. Two stations with the most extreme climate.*  

Jaisalmer/Jodhpur and Srinagar/Leh have extreme climate.  

Desert stations have very hot summers and cold winters.  

Himalayan stations have very low winter temperatures.  

Both have large difference between day and night temperature.  

So they show continental type extreme climate.

*b. Two stations influenced by retreating monsoons.*  

Chennai and Puducherry are influenced by retreating monsoon.  

Retreating monsoon winds pick up moisture from Bay of Bengal.  

They bring rainfall to Tamil Nadu coast in Oct-Nov.  

This is when rest of India gets dry weather.  

Hence these stations get most rain in post-monsoon season.

*c. The two hottest stations in the months of*  

*(i) February*: Nagpur and Bhopal are usually hottest in February.  

Central India heats up early due to interior location.  

*(ii) June*: Jaisalmer and Ganganagar are hottest in June.  

Thar Desert area gets intense heat before monsoon arrives.  

Temperature can go above 45°C in these places.