Q. 1 Define the term Humidity. Give the different types of Humidity.
Answer Key Points: -
The amount of water vapor present in the atmosphere is called Humidity. There are three main types of humidity: -
1) Absolute Humidity: - The actual amount of the water vapour present in the atmosphere is known as the absolute humidity. It is the weight of water vapour per unit volume of air and is expressed in terms of grams per cubic meter.
2) Relative Humidity: - The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity.
Q. 2 Why does the amount of water vapour decreases rapidly with altitude?
Answer Key Points: -
1) Lack of water bodies on higher altitudes.
2) Due to less temperature evaporation also decreases.
3) Water vapours depend upon density of air and temperature, at high altitudes, Air density is less and thin water vapours are heavier and heavy things are pulled down and lighter things float above it.
Q. 3 Give the importance of Humidity.
Answer Key Points: -
1) Water vapour present in the air causes precipitation.
2) Water vapour absorbs and reflects much part of the insolation from the sun and preserve the Earth from heating.
3) Water molecules have high surface tension they can attract the adjoining water molecules and are able to form droplets, dew, fog and mist.
4) Humidity decides the quantity of latent heat energy stored in the atmosphere for the growth of storms.
Q. 4 Explain the process of evaporation.
Answer Key Points: -
1) Evaporation is a process by which water is transformed from liquid to gaseous state. Heat is the main cause for evaporation. The temperature at which the water starts evaporating is referred to as the latent heat of vapourisation.
2) Increase in temperature increases water absorption and retention capacity of the given parcel of air. Similarly, if the moisture content is low, air has a potentiality of absorbing and retaining moisture.
3) Movement of air replaces the saturated layer with the unsaturated layer. Hence,
the greater the movement of air, the greater is the evaporation.
Q. 5 What factors influence the process of condensation?
Answer Key Points: -
The transformation of water vapour into water is called condensation. Condensation is influenced by the volume of air, temperature, pressure and humidity. Condensation takes place: -
1) When the temperature of the air is reduced to dew point with its volume remaining constant.
2) When volume of air is increased without any addition of heat.
3) When both the volume and the temperature are reduced.
4) When additional moisture is added to the air through evaporation.
Q. 6 What are forms of condensation? Describe the process of dew and frost formation.
Answer Key Points: -
Condensation is caused by the loss of heat. Forms of condensation can be classified on the basis of temperature and location. Condensation takes place when the dew point is lower than the freezing point as well as higher than the freezing point. The moisture in the atmosphere takes one of the following forms: -
1) Dew: - When the moisture is deposited in the form of water droplets on cooler surfaces of solid objects (rather than nuclei in air above the surface) such as stones, grass blades and plant leaves, it is known as dew. The conditions for the formation of the dew are clear sky, high relative humidity and long cold nights. It is also very necessary that dew point is above the freezing point.
2) Frost: - Frost forms on cold surfaces when condensation takes place below freezing point. The moisture of atmosphere deposited in the form of minute ice crystals. The conditions for the formation of frost are clear sky, high relative humidity; long cold nights and the air temperature must be below freezing point.
3) Fog and Mist: - When the temperature of an air mass containing a large quantity of water vapour falls all of a sudden, condensation takes place within itself on fine dust particles. So, the fog is a cloud with its base at or very near to the ground. Thin fog is called mist.
4) Smog: - When fog is mixed with smoke such a condition is called smog. Smog is mainly formed in urban and industrial areas during winters where the level of air pollution is high.
5) Clouds: - Cloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of the water vapour in free air at considerable elevations. As the clouds are formed at some height over the surface of the Earth, they take various shapes.
Q. 7 Give the difference between Fog and Mist.
Answer Key Points: -
Fog
Mist
1. Meaning
Fogs are drier than mist.
The mist contains more moisture than the fog.
2. Prevalent
They are prevalent where warm currents of air come in contact with cold currents.
Mists are frequent over mountains as the warm air rising up the slopes meets a cold surface.
3. Structure
Fogs are mini clouds in which condensation takes place around nuclei provided by the dust, smoke, and the salt particles.
In mist each nuclei contains a thicker layer of moisture.
4. Visibility
Fog is denser than mist. In fog one can see less than 1,000 meters away.
Mist is less dense and quicker to dissipate when wind, temperature, or relative humidity changes. In mist one can see more than 1000 meters away.
5. Duration
The duration of fog is comparatively longer than mist.
The duration of mists is comparatively shorter than fog.
Q. 8 What is a Cloud? Explain different types of clouds.
Answer Key Points: -
Cloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of the water vapour in free air at considerable elevations. As the clouds are formed at some height over the surface of the Earth, they take various shapes. According to their height, expanse, density and transparency or opaqueness clouds are grouped under four types: -
1) Cirrus: - Cirrus clouds are formed at high altitudes (8,000-12,000m). They are thin and detatched clouds having a feathery appearance. They are always white in colour.
2) Cumulus: - Cumulus clouds look like cotton wool. They are generally formed at a height of 4000-7000 m. They exist in patches and can be seen scattered here and there. They have a flat base.
3) Stratus: - As their name implies, stratus are layered clouds covering large portions of the sky. These clouds are generally formed either due to loss of heat or the mixing of air masses with different temperatures.
4) Nimbus: - Nimbus clouds are black or dark gray. They form at middle levels or very near to the surface of the Earth. These are extremely dense and opaque to the rays of the sun. Sometimes, the clouds are so low that they seem to touch the ground. Nimbus clouds are shapeless masses of thick vapour.
Q. 9 Define the term ’Precipitation’. Give its process of formation and different forms or types.
Answer Key Points: -
The word presentation is derived from the Latin word ‘Precipitation’ meaning a headlong falling down. The presentation is defined as falling down of condensed water vapour on the surface of the Earth in any form such as rain, snow, sleet, and hail. The other forms of precipitation include Drizzle, Dew, Fog, Ice pellets and Graupel.
Process of Formation: -
When the humid air rises up and it cools and the process of condensation take place the condensed air is unable to hold the moisture at the temperature then the condensed water starts falling down in different forms.
Major types of precipitation are: -
1) Rainfall: - Rain or Rainfall is a process by which liquid water in the forms of droplets from sky, with diameters greater than 0.5 mm (0.02 inch) falls on the surface of the Earth.
2) Snowfall: - When the temperature is lower than the 0°C, the water vapour in the atmosphere returns directly into very small ice crystals precipitation takes place in the form of fine flakes of snow and is called snowfall.
3) Sleet: - Sleet is a regionally variant (type) term for some forms of precipitation in which snowflakes and rain water droplets falling together on the surface of the Earth. This is formed when a layer of air with the temperature above freezing point over lie a sub-freezing layer near the ground.
4) Hailstones: - Sometimes, drops of rain after being released by the clouds become solidified into small rounded solid pieces of ice and which reach the surface of the Earth are called hailstones.
5) Drizzle: - It is a light liquid precipitation consisting of liquid water drops smaller than those of rain generally smaller than 0.5 mm (0.02 in) in diameter. Drizzle is normally produced by low stratiform clouds and stratocumulus clouds. Drizzle tends to be the most frequent form of precipitation over large areas of the world's oceans, particularly in the colder regions of the subtropics.
6) Sun-Shower: - A sun-shower or sun shower is a meteorological phenomenon in which rain falls while the sun is shining. A sun-shower is usually the result of accompanying winds associated with a rain storm sometimes miles away, blowing the airborne raindrops into an area where
there are no clouds, therefore causing a sun-shower.
7) Freezing Rain: - It is the name given to rain maintained at temperatures below freezing by the ambient air mass that causes freezing on contact with surfaces. Unlike a mixture of rain and snow, ice pellets, or hail, freezing rain is made entirely of liquid droplets. The raindrops become super cooled while passing through a sub-freezing layer of air hundreds of meters above the ground, and then freeze upon impact with any surface they encounter, including the ground, trees, electrical wires, aircraft, and automobiles. The resulting ice, called glaze ice, can accumulate to a thickness of several centimeters and cover all exposed surfaces.
Q. 10 Explain different types of rainfall.
Answer Key Points: -
On the basis of origin, rainfall may be classified into three types: -
1) Convectional Rain: - The air on being heated becomes light and rises up in convection currents. As it rises, it expands and loses heat and consequently, condensation takes place and cumulous clouds are
formed. With thunder and lightning, heavy rainfall takes place but this does not last for long.
Such rain is common in the summer or in the hotter part of the day. It is very common in the equatorial regions and interior parts of the continents, particularly in the northern hemisphere. In the late afternoon, the clouds burst into a heavy rainfall along with thunder and lighting. It usually occurs daily at about 4 pm, so convectional rain is called 'Four o'clock Rain' in the equatorial regions.
2) Orographic Rain: - ‘Orographic Rain’ (snow, or other precipitation) also known as the ‘Relief Rain’ produced when moist air is lifted as it moves over a mountain range. As the air rises and cools, orographic clouds form and serve as the source of the precipitation, most of which falls upwind of the mountain ridge.
the warm Westerlies. In higher latitudes it is also known as the frontal rainfall.
Q. 11 Discuss the salient features of the world distribution of precipitation.
Answer Key Points: -
1) Different places on the Earth’s surface receive different amounts of rainfall in different seasons within a year. In general, as we move from the equator towards the poles, rainfall goes on decreasing steadily.
2) The coastal areas of the world receive greater amounts of rainfall than the interior parts of the continents. The rainfall is more over the oceans than on the landmass.
3) Between the latitudes 35° and 40° N and S of the equator, the rain is heavier on the eastern coasts and goes on decreasing towards the west. But, between 45° and 65° N and S of equator, the rainfall is first received on the western margins of the continents and it goes on decreasing towards the east.
4) In some regions rainfall is distributed evenly throughout the year such as in the equatorial belt and in the western parts of cool temperate regions.
Q. 12 Give the major precipitation regimes of the world.
Answer Key Points: -
Rainfall is the main form of precipitation. Based on the total amount of annual precipitation, major precipitation regimes of the world are identified as follows: -
1) Areas of Heavy Rainfall: - Areas receiving over 200 cm of annual rainfall are termed as areas of heavy rainfall. These areas include the equatorial belt in Africa, Asia, and South America, the windward slopes of the mountains along the western coasts in the cool temperate zone and the coastal areas of the monsoon lands.
2) Areas of Moderate Rainfall: - This includes areas having 100 to 200 cm of annual rainfall. The interior of continents and the coastal areas of the continents receive moderate rainfall.
3) Areas of Inadequate Rainfall: - The central parts of the tropical lands and eastern and interior parts of temperate lands receive inadequate rainfall, i.e., between 50 and 100 cm of annual rainfall.
4) Areas of Low Rainfall: - Areas receiving less than 50 cm of annual rainfall are known as areas of low rainfall. The rain shadow areas in the interior of the continents and high latitudes receive very low rainfall.
