NCERT-GEOGRAPHY-CLASS-07-CHAPTER-04

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What is Air?

  • A mixture of various gases, we find on the Earth is air.
  • And please note there is a difference between air and the atmosphere, which we are going to discuss in the next heading.

 

Composition of the atmosphere

 


  • A huge mass of air, as a blanket we find around the earth, is known as the atmosphere.
  • In the composition of the atmosphere, we have

  1. nitrogen 78%,
  2. oxygen 21%,
  3. carbon dioxide 0.36 per cent and
  4. rest of the gases, including ozone, hydrogen-helium, and neon.
  • In addition, we also have two main components-
  1. Water Vapour, and
  2. Dust particles.



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Gases we inhale?


The gases we inhale are,
  1. a large amount of oxygen
  2. a little bit of nitrogen.

 

The mechanism through which plants take in nitrogen

   


  • Plants do not directly intake nitrogen but through bacteria, which are found in the soil and roots of a plant.
  • This bacterium is a microorganism that transforms atmospheric nitrogen into fixed nitrogen, which is the inorganic compound usable by plants. 


What is air circulation?

 


  • In the atmosphere at a particular place, we have the heating and the cooling of air.
  • When the air gets heated up, it becomes lighter and starts to rise, known as "air currents".
  • On the other hand, cold air, which sinks down, fills the place vacated by rising hot air.
  • It is an ongoing process, and that's how the heated air and cold air change their respective places simultaneously in a circular manner, known as Air Circulation.



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The utility of carbon dioxide  

       

  1. The main task of carbon dioxide is to trap the heat radiated by the Earth's surface.
  2. The plant Kingdom uses carbon dioxide to make their food and, as a by-product, releases oxygen.
  3. On the other hand, the Animal Kingdom and human beings inhale oxygen and release carbon dioxide as a by-product.
  4. That's how a perfect balance is maintained in the Earth's atmosphere.
  5. Burning fossil fuels more than the proportional requirement results in the addition of more carbon dioxide to the atmosphere.
  6. As a result, that atmosphere traps more terrestrial radiation, causing the increment of average atmospheric temperature known as global warming.


Pictorial presentation of "Greenhouse Gas"


  

layers of the Earth's Atmosphere

    




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Ozone layer


  • We found the ozone layer in the second atmospheric layer of the Earth, which is the "stratosphere".
  • The main task of the ozone layer is to absorb ultraviolet radiation from the Sun.

 

Ionosphere

  • The ionised zone of the Earth's upper atmosphere, which we find in the thermosphere.

 

What is temperature

  • The measurement of the degree of heat with a unit of a given place is known as the temperature of that place.
  • Variation in the temperature is  "mainly subjected to"
  1. latitudinal position,
  2. degree of insolation,
  3. location, and
  4. relief feature.
Rest factors are explained in the following image.



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Insolation

   


  • The incoming solar radiation, in the form of energy, which is coming to the Earth's surface in the "short wavelength form" and is intercepted by the Earth through its atmosphere and crust known as insolation.

 

Decreasing pattern of insolation - Latitudinal Heat Budget



  • Based on it, we calculate the latitudinal heat budget of the Earth.
  • Details we will discuss in the 11th class, physical geography.

 

Why is the temperature of the city (Heat Island) higher than that of a village

     

  • A city is a compact unit and an example of a human-made modified environment, whereas a village, a nature dependent habitate, is a much more open unit.
  • The city has construction material in bulk quantities, which is more prone to intercept higher amounts of solar insolation.
  • So, during the night, the back radiation or terrestrial radiation takes a long time for the cooling effect and maintains the city's average temperature at about 30 degrees centigrade or more than 30 degrees centigrade, then we say the city is a heat Island.
  • On the other hand, in the village, this amount is less in quantity.

 

The atmosphere of the moon


  • On the moon, we don't have the atmosphere just because the moon does not have the required amount of gravitational pull to hold atmosphere like what we have on earth.
  • It does not mean that the Moon has no gases at all.
  • On the Moon, a very small amount of gases is present, but these gases are extremely thin and scattered. Therefore, the Moon does not have a proper atmospheric composition like the Earth.
  • It simply means that the presence of gases alone does not form an atmosphere. As we discussed earlier, there is a difference between air and atmosphere. Air is a mixture of gases, while an atmosphere is a thick gaseous envelope held around a celestial body by gravity.

Air pressure


  • The exerted pressure/weight of air on a given unit place of the earth is known as air pressure.

 

Distribution of air pressure


  • As we move up in the atmosphere, in a proportional manner, the air pressure starts to reduce.
Note- 
  • But horizontally pressure also reduces, so why do we not count the horizontal pressure gradient 🤔
  • This we will discuss 11th class physical geography 👍
  • Air pressure is highest at the sea level/ sea surface.
  • The temperature of a given place -&- its latitude position are major factors that determine the air pressure of a given place.

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Low-pressure area


  • In the presence of high-temperature air becomes lighter and starts to lift up, creating a low-pressure area.
  • The low-pressure area of a given place is characterised by cloudy weather and moist air.
 

Wind

       

The
  1. the horizontal movement of air,
  2. from a high-pressure zone towards a low-pressure zone,
  3. in a particular direction known as wind.

 

Types of winds

 

  1. Permanent winds - Equatorial winds are an example
  2. seasonal winds - The southwest monsoon of India is the classic example, and
  3. Local winds - The Loo, which blows during the May and June months, is an example of local wind.

 

Land breeze and sea breeze

  

  1. When the wind blows from the sea toward the land known as the sea breeze.
  2. Opposite of it is known as a land breeze.
  • The sea breeze blows during the daytime while the land breeze blow during the nighttime?


👉NCERT-GEOGRAPHY-CLASS-6-NOTES 👀


 

Moisture

  • Through the process of evaporation, the transformation of water into two vapours is known as moisture.

 

Humidity

  

  • At a given place and time, the amount of moisture present in the air is known as humidity.
  • When the humidity is less than a hundred per cent we called as relative humidity

 

Humid day

     

  • On a humid day, the air is full of water vapour, which is why it cannot hold any more water vapour.
  • That's why we are sweating all day when it is a humid day.

 

Clouds?

  



  1. The rising water vapour, simultaneously, starts to cool down 
  2. causing the process of condensation around hygroscopic nuclei (Surface to water vapour condensation), which transforms water vapour into water droplets.
  3. The mass of that water droplet around hygroscopic nuclei is known as a cloud.

 

Precipitation


  • A cloud has a relative capacity to hold water droplets.
  • When the cloud loses its holding capacity and the droplets start to come down, the process is known as precipitation.

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Rain


  • When the precipitation comes to the Earth's surface in the form of water droplets known as rain.

 

Types of rainfall


We have three kinds of rainfall: one is
  1. Convectional rainfall, 
  2. Orographic rainfall and
  3. Cyclonic rainfall. 



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