Air – The mixture of gases which from the earth is atmosphere and which we breathe is called air.
Atmosphere – The thick envelope of air surrounding the earth is called the atmosphere.
It is one of the natural components of the environment.
The survival of all the living beings on this planet depends on the atmosphere.
Functions of Atmosphere:
It provides us the air we breathe.
It protects us from the harmful effects of sun’s rays.
It prevents the earth from becoming too hot or too cold.
Composition of Air:
The air that we breathe is a mixture of many gases like oxygen, nitrogen, carbon dioxide, argon etc.
The majority of the atmosphere is made up of nitrogen (78%) and oxygen (21%).
The other gases that are present in small quantities are: Carbon dioxide (0.03%), Argon (0.93%) and others (helium, hydrogen, ozone).
Tiny dust particles are also present in the air, apart from the above gases.
Nitrogen:
It is the gas that is most abundant in the air.
Plants need nitrogen to make protein.
Plants cannot take the gaseous nitrogen from air.
Some bacteria live in soil and in roots of some plants.
Oxygen:
It is the second most plentiful gas in the air.
Oxygen plays an important role for human beings, animals and plants in the following ways.
Most of the living beings need oxygen for respiration.
Green plants produce oxygen during photosynthesis.
The consumption of oxygen by human beings and animals is replenished by the production of the same by plants.
Carbon dioxide:
It is another important gas.
Green plants need carbon dioxide to carry out photosynthesis.
Most of the living beings release carbon dioxide during respiration.
Structure of the atmosphere:
Our atmosphere is divided into five layers which are:
Troposphere, stratosphere, mesosphere, thermosphere and exosphere
Troposphere: It is the most important layer of the atmosphere.
Its average height is 13 km.
The air we breathe exists here
Almost all the weather phenomena occur in this layer.
The weather phenomena include: Rainfall, Fog, Hailstorm etc.
Stratosphere: This layer is just above the troposphere.
It extends to a height of 50 km.
It is almost free from clouds and associated weather phenomena that occur in the troposphere.
It is most ideal for flying aeroplanes since it is free from weather phenomena.
It contains a layer of ozone gas which protects us from the harmful effect of ultraviolet rays from the sun.
The depletion of the ozone layer of late is a serious concern for all of us.
Mesosphere: It is the third layer of the atmosphere and it lies above the stratosphere.
It extends up to a height of 80 km.
The burning of meteorites on entering from space occurs in this layer.
Thermosphere: It is the fourth layer and the layer above the mesosphere.
In this layer, temperature rises very rapidly with increase in height.
Ionosphere is a part of this layer. It extends between 80 to 400 km
It helps in radio transmission. This layer is responsible for reflecting back of the radio waves that are transmitted from the earth.
Exosphere: It is the uppermost layer of the atmosphere.
It has very thin air.
Light gases like helium and hydrogen float into the space from here
Weather: The condition of the atmosphere in one area at a particular time is called weather.
It changes dramatically from day to day.
Even metaphorically it is said ‘as changeable as the weather ’.
Weather may be: Hot, Humid, Pleasant or Breezy.
Climate: The average weather condition of a place for a longer period of time is called the climate.
Weather pattern of more than 20 years is considered for defining the climate of a place.
Meteorology:
It is the study of the atmosphere.
An operational forecaster analyzes weather conditions and issues forecasts or alerts the public of severe weather for their area.
Following are the aspects to be studied while studying the concept of weather and climate:
Temperature
Air Pressure
Wind
Moisture
Temperature – The degree of hotness or coldness measured on a definite scale is called temperature.
It changes between day and night and from season to season.
Thermometer is a device for measuring temperature.
Insolation – The amount of energy from the sun that reaches the earth is called insolation.
It is an important factor that influences the distribution of temperature.
The incoming solar energy intercepted by the earth is called insolation.
The amount of insolation decreases from the equator to the poles.
This is the reason why the poles are much colder than the equator.
Air Pressure – The force exerted onto a surface by the weight of the air is called air pressure.
The air above us presses us with great force.
But we do not feel it at all.
This is because it presses us from all directions and our body exerts a counter pressure.
Air pressure is defined as the pressure exerted by the weight of air on the earth’s surface.
Nature of vertical air pressure:
The pressure falls rapidly as we go up the layers of the atmosphere.
Therefore, the pressure is the highest at sea level and decreases with altitude.
Nature of horizontal air pressure:
Horizontally, the distribution of air pressure is influenced by the temperature of the air at a given place.
Where the temperature is high, the air gets heated up and rises, thus creating a low pressure area.
This is associated with cloudy skies and wet weather.
Where the temperature is low, the air is cold and therefore heavy. This heavy air sinks and creates a high pressure area.
High pressure is associated with clear and sunny skies.
The movement of air is always from areas of high pressure to areas of low pressure.
Wind: The moving air is called wind.
Winds can be gentle or very strong.
Gentle winds blow away smoke or fine dust.
An extremely strong wind is in the nature of a storm which can even uproot trees.
A wind can be strong enough to make it difficult to walk against it.
Types of Wind:
Permanent winds: The air which always blows constantly throughout the year in a particular direction is called a permanent air. For example – the trade winds, westerlies and easterlies.
Seasonal winds: The air which always changes their direction in different seasons is called seasonal winds. For example, monsoons in India.
Local winds: The air which always blows only during a particular period of the day or year in a small area is called local winds. For example: Land and sea breeze.
Cyclone: A large scale of air masses that rotates around a strong centre of low atmospheric pressure is called cyclone.
Wind Velocity:
Winds of up to 260 km. per hour lasted for about 36 hours.
These winds uprooted trees and damaged the kutcha houses.
Power supply and telecom line snapped completely.
Rain: Heavy rain occurred under the influence of cyclone for three days and led to the flooding of major rivers.
Tidal Surge: The cyclonic winds caused tidal waves that swept 20 km inland and brought massive destruction to the coastal areas.
Damage caused by the cyclone:
About 13 million people were affected. A large number of livestock were killed.
Standing crops of paddy, vegetables and fruits were severely damaged.
Large tracts of agricultural lands have turned infertile due to the salinisation caused by the surge. Large tracts of sal, bamboo and teak plantations have disappeared.
The mangrove forests between Paradip and Konark vanished.
Moisture – A liquid such as water in the form of very small drops, either in the air, in a substance, or on a surface is called moisture.
When water evaporates from land and different water bodies, it becomes water vapour.
Moisture in the air at any time is called humidity.
A humid day is a day in which the air is full of water vapour.
The capacity of the air to hold water increases as the air gets warmer.
AIR: RAIN CYCLONE:
Precipitation: The water droplets form clouds which become heavy and fall from the sky in the form of rain is called precipitation.
Evaporation causes the formation of water vapour and condensation causes the formation of droplets of water.
Condensation occurs when the water vapour cools on rising.
Precipitation that comes down to the earth in the liquid form is called rain.
On the basis of the mechanism, there are three types of rainfall, as shown below.
Convectional Rainfall
Cyclonic Rainfall
Orographic Rainfall
Convectional Rainfall:
When a portion of the earth becomes heated more than it’s surrounding, it creates significant amount of evaporation.
Convection currents then push up the moist air and cumulonimbus clouds are formed.
These clouds result in convectional rainfall.
Convectional rainfall is in the form of showers with rapidly changing intensity.
This type of rainfall happens for a short duration because horizontal expanse of a cumulonimbus cloud is small.
Cyclonic Rainfall or Stratiform Rainfall:
This type of rainfall is formed by frontal system surrounding extra tropical cyclones.
Cyclone is formed when warm air meets cold air.
Stratiform rainfall usually occurs from nimbostratus cloud.
Orographic Rainfall:
Orographic rainfall occurs when a mass of air is pushed up because of a structure with very high elevation; such as a mountain.
The lifted air cools down and precipitation occurs.
Rain shadow area is formed on the other side of the elevation.
Importance of reasonable amount of rainfall:
Rainfall is essential for the mere survival of plants and animals.
It brings fresh water to the earth’s surface.
If it is less, we face water scarcity and resultantly severe drought.
