9th Social Science Lesson 14
Book Back Questions with Answer and Do You Know Box Content
Do You Know?
In 1772 CE Daniel Rutherford discovered Nitrogen in atmosphere. In 1774 Joseph priestly discovered oxygen in atmosphere.
Auroras are cosmic glowing lights produced by a stream of electrons discharged from the Sun’s surface due to magnetic storms that are seen as unique multi coloured fireworks hanging in the polar sky during midnight.
Magnetosphere lies beyond the exosphere. It is earth’s magnetic belt, where proton and electrons, coming out from the sun are trapped by the earth. The magnetic field extends to around 64,000 km above the Earth.
During the day, the land masses get heated more rapidly than the oceans. Heater air ascends and this causes low pressure on the adjoining ocean. Therefore, the wind blows from ocean to land in the afternoon. This is called sea breeze. Sea breeze helps in reducing the temperature of the coastal region especially during the summer season. During the night, the land cools more rapidly than the ocean. Cold air sinks and forms high pressure. The wind blows from land to sea during the night, this is called land breeze.
The windward is the side of a mountain which faces the prevailing wind. It receives heavy rainfall. The leeward side of the mountain is the side sheltered from the wind. It receives very less rainfall.
The rotation of the Earth causes deflection of winds from their original path, called the “Coriolis effect” winds are deflected to the right in the northern hemisphere and to the left in the southern hemisphere which is known as “Ferrel’s Law”. This was profounded by William Ferrel. He used “Coriolis force” named after G.G. Coriolis (1792-1843) for proving Ferrel’s law.
Super Cyclone: A violent cyclone that hit Odisha, on Friday, 29 October 1999, was one of the most devastating and strongest storm to hit the Indian coast. Winds of up to 260 kph raged for over 36 hours. The winds caused seven metre tidal wave that swept more than 20 km inland and brought massive destruction and death to a number of coastal districts in the state of Odisha. It is estimated that more than 10 million people in 12 coastal belt districts were affected by the cyclone. More than 10,000 people lost their lives.
Deliberations for naming cyclones in the Indian Ocean region began in 2000 and a formula was agreed upon in 2004. Eight countries in the region Bangladesh, India, Maldives, Myanmar, Oman, Pakistan, Sri Lanka, and Thailand contributed a set of names which our assigned sequentially whenever a cyclonic storm develops.
A front is the boundary separating warm and cold air masses. One type of air mass is usually denser than the other, with different temperatures and humidity. This meeting of air mass causes rain, snowfall, hail storm, thunder storm, lightening cold days, hot days, and windy days.
During sunset cirrus clouds look colourful hence they are called as “Mare’s Tails”.
The only sphere which contains all clouds in the atmosphere is troposphere.
Any thunderstorm which is associated with fall of hail stones is known as hailstorm. Hailstorm is one of the most feared weather phenomenons because it has the potential to destroy plant, trees, crops, animals and human life.
When the relative humidity of the air is 100%, the air is said to be saturated. Saturated air will not absorb any more water vapour. The temperature at which air gets saturated is called dew point. Humidity of the atmosphere is measured by the wet and dry bulb thermometer also called the Hygrometer.
Absolute humidity is expressed in terms of grams of water vapour present per cubic metre of air. Relative humidity is expressed in percentage.
Mawsynram is the wettest place of India as it is located in the windward side of the Purvachal hills, whereas Shillong lies on the leeward side and thus receives less rainfall. This is the same, in the case of Mumbai and Pune.
Choose the best answers:
1. _______________ is the most important gas for the survival of living organisms.
2. The lowest layer of the atmosphere is _____________
3. ____________ reflects radio waves.
4. The process of change of state of water from gaseous to liquid state is called _______________
5. The ____________ is the chief energy source of the Earth.
6. All types of clouds are found in the _______________
7. _____________ clouds are called “Sheep Clouds”
8. The monsoons are _______________
(a) Prevailing winds
(b) Periodic winds
(c) Local Winds
(d) None of the above
9. Dew in the form of ice crystals is called ___________
10. _______________ is called the eye of the storm/cyclone.
11. The vertical movement of air is called
(c) Air current
Match the following:
1. Meteorology – Wind Speed
2. Climatology – Direction of wind
3. Anemometer – Cirrus
4. Wind Vane – Study of Climate
5. Mare’s Tail – Study of Weather
6. Leeward side – Australia
7. Willy willy – Rain shadow region
Choose the correct answer:
1. Oxygen 2. Troposphere 3. Mesosphere 4. Condensation 5. Sun 6. Troposphere 7. Alto-cumulus 8. Periodic winds 9. Frost 10. Cyclones 11. Air current
Match the following:
1. Study of weather 2. Study of climate 3. Wind speed 4. Direction of wind 5. Cirrus 6. Rain shadow of rain 7. Australia