VI. Paragraph Questions
1. Write a paragraph about the structure of the atmosphere.
Structure of the Atmosphere :
• The Atmosphere has 5 layers Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere.
Troposphere (Height : 8 km at the poles; 18 km at the Equator)
• The temperature decreases with increasing height. Almost all weather phenomenon take place here.
• It is called weather making layer. (upper limit - tropopause)
Stratosphere: (Height: 18 km - 50 km)
• This is a concentration of ozone molecules. It is also referred as ozonosphere. The temperature increases with increasing height. Large set planes normally fly here. (upper limit - stratopause)
Mesosphere: (Height: 50 km - 80 km)
• The temperature increases with increases with increasing height. It helps for Radio waves transmission.
Most of the meteors nearing the earth, get burned (upper limit - mesopause)
Thermosphere: (Height 80 km - 600 km)
• The composition of gases in the lower portion (Homosphere) is uniform. The composition of gases in the upper portion (Heterosphere) is uneven. The temperature increases with increasing height Ionosphere contains Ions and free electrons.
Exosphere: (Beyond broken)
• The uppermost layer of the atmosphere. This is extremely rarefied with gases and gradually merges with the outer space.
2. Explain the different types of permanent winds.
The horizontal movement of air along the surface of the earth is called the 'wind'
• Planetary winds
• Periodic winds
• Variable wind
• Local wind are the four major types of winds.
• The winds which constantly blow in the same direction throughout the year. They are called 'the prevailing winds'. Trade winds, westerlies and polar easterlies are planetary winds.
• The winds that are very helpful to traders sailing in the sees are called 'Trade wind'
• The winds that blow from south west to North East in the northern hemisphere and North West to South East in the Southern hemisphere are ‘Westerlies'
• The winds that blow from North East direction in the Northern Hemisphere and South East direction in the Southern Hemisphere are 'Polar Easterlies'
• Because of the differential heating of land and Ocean the seasonal winds that change their direction. Periodically. These are called 'monsoons'.
Ex. South West monsoon, North East monsoon.
• The disturbance and the changes in the local weather cause variations in the prevailing winds. Variable winds end up with the development of cyclones, anticyclones and storms.
• The winds from the surrounding high pressure area converge towards the centres of low pressure in a spiral form are 'cyclones'.
• The winds that blow only in a particular locality for a short period of time are 'Local winds'.
3. How are clouds classified? Explain them.
High Clouds (Height 6-20 km)
• Cirrus (8000 meters -12000 meters) These are dry; donot give rainfall, (white filaments).
• Cirro-cumulus - composed of ice crystals (White patched sheet)
• Cirro - stratus - Smooth milky transparent whitish. Composed of tiny ice crystals.
Middle clouds (Height 2.5 - 6 km)
• Alto - Stratus - thin sheets of grey or blue coloured. Consisting of frozen water droplets.
• Alto - cumulus - fitted closely together in parallel bands. They are cloud 'Sheep clouds' or 'wool pack' clouds.
• Nimbo stratus - dark colour very close to the ground surface. Associated with rain, snow or sleet.
Low clouds (Height - Ground surface - 25 km)
• Strato-cumulus (2500 meters - 3000 meters) Grey or whitish layer low clouds in rounded patches. Associated with fair or clear weather.
• Stratus - Dense, low lying fog-like clouds. Associated with rain or snow.
• Cumulus - Flat base, dome-shaped, often resembling a cauliflower. Associated with fair weather.
• Cumulo-nimbus - Fluffy thick towering thunderstorm cloud, (capable of producing heavy rain, snow, hailstorm or tornadoes)
4. How are cyclones formed? How are they classified?
Cyclones are centres of low pressure where, winds from the surrounding high pressure area converge towards the centres in a spiral form.
• Tropical cyclones
• Temperate cyclone
• Extra tropical cyclones
• Due to the differential heating of land and sea, in the inter tropical convergence zone, formed the 'Tropical Cyclones'. They cause heavy loss of life and property.
• Between 35° and 65° N and S latitudes, the front where hot and cold air masses meet, the temperate cyclones are formed. They do not become weak on reaching the land on the tropical cyclones.
• Commonly occurs over the north Atlantic ocean, North west Europe. Mediterranean basins. Mediterranean temperate cyclones extend up to Russia and India. In India it is called 'western disturbances'.
Extra tropical cyclones
• Between 30° and 60° latitudes in the both the hemispheres, occur "Extra trophical Cyclones". They collect energy from temperature differences in higher latitudes. Also called "mid latitude cyclones".
• They produce mild showers to heavy gales, thunderstorms, blizzards, and tornadoes.
5. Explain the different forms of precipitation.
Falling down of condensed water vapour in different forms is called Precipitation. Drizzle, rain, sleet, snow, hail are the main forms of precipitation.
• Drizzle : Falling of numerous uniform droplets of water with diameter of 0.5 mm is called a 'Drizzle'.
• Rain : In places having temperature above the freezing point falls 'Rain'. It is the important form of precipitation occurs only. Where there is abundant moisture in the air. (The diameter of a rain drop is more then 5 mm.)
• Sleet: Sleet is in the form of pellets made up of transparent and translucent ice.
• Snow : When condensation occours below freezing point snow is formed. It is the precipitation of opaque and semi opaque ice crystals.
• Hail: Chunks of ice falling from the sky during a rainstorm are Hails, (chunk of ice - greater then 2 cm in diameter)
VII. Activity (For Students)
1. Preparing chart of clouds at various atmospheric layers.
2. Collecting Proverbs clouds and rain related Proverbs
3. Poem on 'clouds', 'rain'
4. Report writing observe the clouds for a week, Write your report about the shape and colours of clouds.
5. Working models a) Rain Gauge b) Wind vane
6. Preparing bar diagram
a. Collect the data of temperature of Kanyakumari, Delhi, Allahabad, and Itanagar for a day. Also collect the data of rainfall received by Jaisalmer (Rajasthan), Mawsynram (Meghalaya), Nagapattinam, Coimbatore for a day.
7. Become a budding Meterologist: Record the local weather condition of your place for a week.