Humidity and Condensation

  • Hydrosphere comprises of water in different forms. Water is present in the form of water vapour, rivers, lakes and oceans, glaciers and underground water.
  • Earth is the only planet with large amount of surface water. More than 71% of the earth’s surface is covered with water. Rivers and open lakes are the fresh water bodies.
  • Seas, oceans and closed lakes are the salt water bodies.
  • Oceans are the bodies of saline water, which form a large part of the earth’s hydrosphere. There are five major oceans in the world. These are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Arctic Ocean, and the Southern Ocean.
  • Pacific Ocean is the deepest and the largest ocean, which covers one-third of the earth’s surface. This ocean is bounded by Asia, Australia, North America and South America. Mariana Trench the deepest point of the world’s oceans is located in the Pacific Ocean.
  • Atlantic Ocean is the second largest ocean in the world. It is bounded by the North America and South America on the Western side and Europe and Africa on the Eastern side.
  • The Indian Ocean is the only ocean named after a country: India. It is the third largest ocean in the world.
  • The Arctic Ocean is the smallest and the shallowest ocean and is located within the Arctic Circle in the Northern Hemisphere. The North Pole is located in the middle of the Arctic Ocean.
  • The Southern Ocean is the fourth-largest ocean in the world. It extends from the coast of Antarctica to 60 degrees south latitude.
  • Continents and oceans are not evenly distributed between the Northern and the Southern Hemisphere.
  • This unequal distribution of land and water influences the pattern of climate on the earth. Land and water distribution influences the earth’s pattern of temperature and direction of the movement of air masses.
  • Different features associated with oceans are isthmus, bay, gulf, island, strait, and reef.
  • Isthmus is a narrow strip of land connecting two larger masses of land.
  • Bay is formed when the ocean overflows the coastline, which has sunk and eroded because of the movement in the earth’s crust.
  • Gulf is a part of ocean that penetrates into the land.
  • A strait is a narrow passage of water that connects two large water bodies.
  • Land surrounded by the water from all sides is known as an island. The group of islands is known as archipelago. Very small islands are called islets.
  • On the basis of origin, islands are classified into two categories, namely continental islands, and oceanic islands.
  • Reefs are the islands surrounded by limestone structure. Reef builds up from the skeletons of dead polyps. These islands contain the shells of small organisms known as coral. There are three types of coral reefs: fringing reefs, barrier reefs, and atoll.

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  • Q1

    ‘The proportion of humidity varies between zero upto a maximum of four to five percent.’ State the importance of this variability.


    The variability of humidity has a great importance as:
    i. It determines the amount of precipitation that a given air mass can give.
    ii. It helps in regulating the rate of heat loss by absorbing the radiation.
    iii. It determines the development and growth of disturbances and storms in the atmosphere as a result of stored latent energy.
    iv. It determines ‘sensible temperature’ or the rate of cooling of the human body.

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  • Q2

    Differentiate between weather and climate.




    Describes the atmospheric
    conditions for a short period

    Describes the atmospheric conditions for a long period of time

    Description covers a smaller area

    Description covers a larger area

    Weather data is obtained through direct observation or by the use of instruments.

    Climatic data is based on calculated averages over a period of 35 yrs.

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  • Q3

    How does convectional rainfall occur?


    The sun warms the earth and the air above it. As the heated air rises higher into the atmosphere, it expands and cools. The rapid rising of warm moist air results in the formation of cumulonimbus clouds.

    These clouds give heavy rain, usually accompanied by thunder and lightning. This type of rainfall is known as convectional rainfall, and it is very common in the equatorial regions. It occurs almost every day in the afternoon and is also called the 4’oclock rain.

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  • Q4

    The picture shows the three permanent wind systems. Identify the wind systems.
    Explain how these winds cause rainfall.



    Three permanent wind systems are:
    1. Trade winds
    2. Westerlies
    3. Polar winds

    Trade Winds:

    Trade winds blow from the cooler regions to the warmer areas and are generally dry winds. On the eastern margins of vast continental areas like that of South-East Asia, trade winds are deflected and drawn towards the continental interiors. They give rainfall more in the coastal areas and less towards the interiors. They are known as monsoon or seasonal winds. The rainfall from these winds goes on decreasing as they blow more and more into the continental interiors ending up in hot deserts like Thar Desert in India.


    Westerlies blow from warmer to cooler regions. They give rainfall throughout the year. The rainfall is more on the western margins of the continents than in the eastern where they become dry continental winds.

    In this belt on the eastern margins, seasonal convectional rainfall is experienced during summers. Southern part of this belt gets rainfall during winters.

    Polar winds:

    The polar winds blow from cold polar areas to warm regions. These winds do not give any rainfall, but contributes a lot towards causing precipitation.

    Due to frontal meeting of cold polar winds and warm westerlies, cyclones develop, which travels between 40° latitude and 65°latitude on both sides of the equator and supplements the rainfall of westerlies.

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  • Q5

    With the help of a diagram, explain the process of Relief or Orographic rainfall.


    Relief or Orographic rainfall is the most common form of rainfall. When moisture bearing wind encounters a mountain barrier it is forced to rise. As the wind rises up the mountain, it cools to its saturation point. On further cooling, rain occurs.

    The windward side of the mountains receives more rain than the leeward side. As the wind moved down the leeward side, the amount of rainfall decreases significantly. By the time, wind reaches the other side, they have lost all their moisture and have become dry. Also, the air warms up again as it moves down the slope, and this reduces the chances of rain. The leeward side of the mountain is hence, known as Rain Shadow Area.

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