Essay, Paragraph or Speech on “ Climate, Atmosphere and Monsoon” Complete Essay, Speech for Class 10, Class 12 and Graduation and other classes.

 Climate, Atmosphere and Monsoon

Atmosphere is the cover or envelope of air or different gases surrounding the globe. 99% of atmosphere is within the height of 32 km from earth’s surface. It is held to the earth’s surface by the force of gravity.

Composition—The composition of atmosphere is described below :

Component Gas    Volume in percentage     

1. Nitrogen (N2) 78.08%
2. Oxygen (02) 20.94%
3. Argon (Ar) 0.93%
4. Carbon dioxide (CO2) 0.03%
5. Neon (Ne) 0.0018%
6. Helium (He) 0.0005%
7. Ozone (03) 0.00006%
8. Hydrogen (H) 0.00005%
9. Methane (CH4) Trace
10. Krypton (Kr) Trace
11. Xenon (Xe) Trace

Nitrogen and Oxygen—Nitrogen and Oxygen together constitute 99% of total volume of atmosphere. Nitrogen does not react with other substance chemically but is easily fixed into the soil working as diluent or dissolver. Oxygen can combine with all the substance and hence is most combustible.

Carbon Dioxide—It warms up the lower atmosphere by absorbing heat radiation from the sun and from the surface. Besides, in the process of photo-synthesis Green plan uses it from the atmosphere.

Ozone—Ozone, though found in very small fraction, is very important because it absorbs harmful ultraviolet rays and thus protects life. It (ozone layer) occurs between 20 to 25 km from earth’s surface.

Weather and Climate—Weather is the physical state of atmosphere at any given time. It is composed of temperature, pressure, winds, moisture and precipitation condition for a short period of time say a week or day whereas climate is the composite weather conditions for a considerable long period of time. The major elements of weather and climate are :

(1) Temperature, (2) Pressure, (3) Moisture and precipitation.

1. Temperature—Temperature denotes intensity of heat which is practically energy on the earth from isolation or incoming solar radiation.
2. Pressure—Unequal temperature in different places cause differences in atmospheric pressure. Air has the tendency to move from high pressure region to low pressure region. This movement or motion of air is horizontal and is known as wind.
3. Moisture and Precipitation—Moisture is water vapours present in the atmosphere which are often condensed into clouds. The capacity of atmosphere or air to hold water vapour or moisture depends on its temperature. This capacity increases with the increase in temperature and decreases withthe decrease in temperature. If the temperature is low it can’t retain all the mostures which it gathers while it is warm because of high temperature. This causes condensation and precipitation.

Insolation—Insolation means incoming solar radiation. It is greatest at the equator of the earth. Radiation Balance of the Earth is commonly known as heat Budget of earth. The radiation received at the poles is one fourth of the radiation received at the equator. The earth heats the atmosphere and the sun heats the earth. Thus earth’s role is akin to that of transformer in electric circuit. The sun radiate or emits short wave whereas the earth radiates long wave known as infrared radiation to space. The radiation from the sun to the earth is in short wave and is called ultraviolate radiation. It forms only 6% of Insolation. The radiation from the earth to space or atmosphere is in long waves and is known as infrared radiation. It forms 43% of insolation. It is invisible.

Light—Light is the visible part of the spectrum which lies between infrared and ultraviolet rays.

The Heat Budget of earth can be summed up in the following table :

Heat Budget of Earth

(A) Incomping Solar Radiation/Insolation   100 units

1. Absorption by 03 3 units
2. Absorption by H2O and dust particles 13 units
3. Absorption 2 units
4. Back scattered by clouds 24 units
5. Backs scattered by surface 4 units

Total = 53 units

Absorption by ground                                                      100 – 53 – 47 units

1. Absorption by the ground from sun 25 units
2. Absorption by the ground from the

atmosphere and clouds                                                                22

Total Absorption by ground                                                        Total = 47 Units

(B) Outgoing Terrestrial (Earth’s)                                              100 Units Radiation

1. Short wave radiation from earth Nil

Back radiation from H2O CO2 and

clouds to outer space                                                                    31 units

Back radiation from ground space                                            4 units

Total = 35 units

2. Long Wave Radiation from earth

Back radiation from ground                                           5 units

Back radiation from H2O, CO2 and clouds                 60 units

Total = 65 units

(C) Surface Balance of Heat

1. Incoming radiation from

(i) from the sun                                            25 units

(ii) from the atmosphere                              26 units

Total = 51 units

2. Outgoing Radiation

(i) To the Atmosphere

(ii) To Long Wave to H2O, CO2 and Clouds   13 units

(iii) Latent heat                                             24 units

(iv) Sensible heat                                5 units

                                                Total = 51 units

3. To Outer Space Radiation

(i) Back scattered from ground           4 units

(ii) Long wave                                     5 units

Total = 51 units

Direct Radiation (22 Units)—To explain the above table, out 100 units of insolation or incoming solar radiation only 22 units reach the surface directly known as direction radiation. Out of a total 35 units received at the outer margins of atmosphere 24 units are scattered back into space by clouds, 7 units by dost particles 4 units by the surface of the earth in original short wave form.

Diffuse Radiation (25 units)—A total 25 units which are scattered rays anyhow reach the surface of earth and are absorbed by it. These scattered rays are collectively called diffuse radiation.

Absorbed by Atmosphere 18 units-Out of 18 units of incoming solar radiation 3 units are absorbed by ozone, 13 units by dust and water and 2 units by clouds. Thus in total 47 units of solar incoming radiation reach the surface, 22 units through direct radiation. 25 units through diffuse radiation.

 Thus 22 units through direct radiation and 25 units through diffuse radiation and 18 units absorbed by atmosphere (in total 65 units) heats the earth and its atmosphere. In order to maintain the balance of heat 5 units in the form of long wave are radiated back from the surface of earth to space and 60 units in the same form are lost to the atmosphere from the earth. In total they are 65 units.

Effect of Incoming Radiation on Water and Land-Both land and water get affected by solar radiation but in different manner. Land cools and heats quickly because incoming solar radiation/rays can’t penetrate land to great extent which is solid surface but in case of water it can easily penetrate to a great depth and because of vertical mixing of water the penetrating heat from solar radiation get transfered in the entire mass of water easily. This is the very reason why air remain warmer in winter and cooler in summer above ocean than air on land surface.

Winds and Pressure-The air which is mixture of many gases exert pressure on the earth’s surface. The air pressure at sea level is 1013.25 millibars. The air pressure varies from region to region and is determined by temperature and density. Thus it differs vertically as well as horizontally.

Vertical Distribution of Air Pressure-According to temperature and height pressure varies. For every 10 metre there is decrease in air pressure at the rate of one millibar from above the sea level. At 5 km. above sea level pressure drops to half its value on the earths surface. Here it comes down to 540.4 millibars from 1.0132 millibars of sea level.

Horizontal Distribution of Pressure—We can distribute the air pressure zones into seven belts as given below :

Pressure Belts/Region                         Pressure-High/Low                   Location at Latitudes

1. Polar Region (North) High Pressure Belt 661/2° North and beyond
2. Sub Polar Region (North) Low Pressure Belt Between 45° to 60° lat. North
3. Sub tropical Zone (North)
4. Sub Equational Region
5. Sub Tropical Zone Southern Hemisphere
6. Sub Polar Region (South)
7. Polar Region (South)

Winds—There are three types of winds Primary, Secondary and Tertiary winds

1. Primary Winds—Primary winds blow on rotating earth’s surface in circulatory pattern under the influence of pressure winds, gradients, ceriolis effect and fractional force and remains unaffected by seasonal heating and land water contrast. Primary winds are in turn of four types.

(i) Doldrums—They on the zone lying both sides of equtor. These winds are weak with least surface movement.

(ii) Trade winds—They blow between 5° and 30° latitudes on both sides of equator. These winds are called northeast winds in northern hemisphere and in the southern hemisphere. They are called south easterly/south eastern winds. The zone near equator where they converge is called Inter Tropical Convergence Zone (ITCZ).

(iii) Westerlies—Variable in direction westerlies blow between 35° to 60° north and south latitudes. Beyond 40° latitude they become stormy and hence are called roaring forties, furious sixties and shrieking sixties.

(iv) Polar Easterlies—They blow from west to east in polar regions.

2. Secondary Winds/Periodic Winds—Those winds which change direction with the change in season are called periodic or secondary winds. Since secondary winds change their direction periodically. They are also called periodic winds. Monsoons are major periodic winds.

Monsoons—As a term Monsoon is derived from Arabic mausim meaning season. The Arabs apply this term to refer to the seasonal winds of the Arabian sea which blow about six months from the southwest and six monts from the North-East. Thus monsoon is system of winds characterized by reversal of their direction.

Formation of Monsoon—In the summer (April to September) the temperature over Indian landsmass is higher than the neighbouring Indian Ocean. It causes pressure gradiant move from South to North. Thus, this leadssouth -west monsoon (winds) blow from Indian ocean to Indian landmass causing and bringing heavy rainfall.

Formation of Winter Monsoon—In winter the landmass is colder than the sea. The pressure gradients is formed from land to sea causing north-east monsoon which is dry and does not bring rain, however a part of northeast monsoon which blows over Bay to Bengal picks up some moisture and causes rains winter rain in TamilNadu.

Sea Breeze and Land Breeze—Owing to differential heating and cooling, land and sea breezes blow. When the land is cooler than water. breeze blows from land to sea. It is known as land breeze but when land is warmer than adjacent water wind/breeze comes in form sea which is known as sea breeze. Both are diurnal monsoon.

Mountain and Valley Breezes—During the day, Mountain slope facing the sun become hatter than valley floor; the hot air rises and cool air flows up the slope. It is known as valley breeze. Mountain breeze blows after sunset when cold air slides from higher mountain to lower valley. Air after sunset. becomes cold due to loss of heat through terrestrial radiation on the mountainous slope.

Air Mass—Air mass is a large body of air with uniform properties of temperature and humidity.

Fronts—The contact line between air masses of different properties of temperature and humidity is called fronts.

Cyclone–Cyclones. on the basis of their origin are of two type

Temperat Cyclone—Concentrated in the middle latitude between 35° to 65° in both southern and northern hemisphere, temperate cyclones are caused by contrasting air from polar regions and warm moist air from tropical regions. They move from west to east along with westerlies. As soon as the cyclone approach there is drizzle followed by heavy rainfall.

Tropical Cyclone—Violent and notorious in nature, tropical cyclones cause largescale destruction. Rainfall is torrential. Characterized by steep pressure and greater wind velocity. They move west ward. Tropical Cyclone orginate over oceans near doldrums (equatorial belt of calms) when doldrums is at farthest possible point from equator.

Cyclone                                    Regions/Occurrance

1. Temperate Cyclone
2. Tropical Cyclones

(i) Typhoons                             The Pacific Ocean (eastern coast of China, Taiwan, Southern part of Japan)    

(ii) Cyclone                               Bay of Bengal (India) Eastern Coast of India

(iii) Hurricanes                                    Ethopia, Kenya (Africa), West Indies

(iv) Tornadoes—Florida                      Texas (N. America), Mexico,

(v) Willy Willies                                   Australia

Atmospheric Moisture

Humidity, Clouds and Precipitation Specific heat and Latent heat—

Water exists in three form—solid, liquid and gas (water vapour). The amountof energy required to change temperature of a substance is called specific heat whereas the heat stored in water vapour is known as latent heat.

Evaporation--The process by which liquid (water) or solid (ice) is changed into water vapour (gas).

Humidity—The water vapour content in atmosphere (air) is called humidity.

Absolute Humidity—The amount of water present in a unit volume of air is known as absolute humidity. It is expressed in grams per cubic metre.

Relative Humidity—The rates of water vapour actually present in the air (atmosphere) to the maximum water vapour reaining capacity of the air at that temperature is called relative humidity.

Dew Point/Saturation Point—When the air holds all the water vapour that it is capable of holding then air is said to be saturated. At this point relative humidity is 100 percent. This is also called dew point because from this point more cooling will lead to condensation.

Condensation—The process of water vapour (gaseous state) changing to liquid state is known as condensation. Condensation begin with addition of more water vapour to already saturated air or with decrease in its temperature.

Dew—When radiation from the earth’s surface is rapid the air in contact with the surface becomes chilled and moisture (water vapour) condenses on the leaves and grasses in the form of dew.

Frost-If the dew point is at the freezing point or below the freezing point moisture condenses in the form of tiny icy crystals known as frost.

Fog—Fog is the layer of cloud on the surface of earth with visibility of less than 1 km.

Clouds—Clouds are the condensed water vapour around the nuclei of dust particles in air. In other words cloud in aggregation of moisture droplets and ice crystals (if the temperature is below freezing point) suspended in air and are enough big to be seen by naked eyes clouds are of 3 types. They are given

(1) High Clouds (occurs between 5 to 14 km. from the ground)

(2) Middle Clouds (occurs between 2 to 7 km. from surface)

(3) Low Clouds (occurs below 2 km from the ground surface)

Precipitation–Meterologically, the fall of condensed or frozen water vapour on the ground is called precipation.

Forms of Precipitation

(i) Rain—It is the fall of liquid water drop on the surface of earth.

(ii) Drizzle—It is the fall of finer drops of water on the ground.

(iii) Snowfall—lt is fall of opaque and white grains of ice.

(iv) Sleet—It is the fall of water droplets and snow together.

(v) Hail—It is the fall of small pieces of ice. Types of Rain fall/Precipitation

(i) Conventional Rainfall—It takes place when due to intense heating moisutre laden air rises, expands, and gets cooled below a dew point and this results in rain fall. It generally occurs in equatorial region.

(ii) Orographic Rainfall—It takes place when moisture laden air is forced to rise over a mountain or elevated barrier which came in its path and becomes a hindrance in its movement, for example the moisture laden air from Arabian Sea is forced to rise by Sohyadri hills of Western Ghats. This results in expansion and cooling of air and thus causes heavy rainfall. The wind which descend on the other side of mountain (eastern side of sahyadri hills) is devoid of moisture and hence does not cause rainfall. This region (or say eastern side of Sahyadri hillts) is called rain shadow.

Monsoon Seasons of India—In Indian context the year can be divided into the four seasons :

1. The cold weather season (December to February)—During this period sun’s rays fall vertically on Tropic of Capricorn and north-west India experience low temperature, being located far inland. The mean monthly temperature during this period in north-west India is less than 10°C. This cause the development of high pressure over this region. As a result dry cold winds blow towards the region of low pressure. In north India winds blow towards the east and in peninsular India towards north east. The Ganga plains have clear skies and fine weather. Peninsular peninsular plateau has also bright weather. During this period cyclonic depresions move from Mediteranean Sea East ward towards north India causing precipitation over India. Since condensation occurs in the upper region of atmosphere precipitation is experienced on sufficiently high Himalayan torrain. This rainfall is in small amount but significant to wheat crop. Occassional rainfall also occur in southeastern part of peninsula together with cyclonie storms and depression from Bay of Bengal. But as the rainfall moves inland, it reduces in rapid manner.
2. Hot Weather Season (March to May)—There is the use in temperature and decline in atmospheric pressure in north India. The highest pressure in May (around 48°C) in north west India causes the formation of lowest pressure in this region which in turn causes the formation of local circulation of air around this low pressure creating condition for the blowing of southwest winds. The winds blow from west to north west in India and in Rajasthan they blow from the southwest to north east in Brahmputra valley from both east and west and in central India from west and north-west. They are southerly and south westerly in Peninsular and Coastal (east) areas and northerly in west coast. In India dust storm and thunder storms can be experienced with hazy atmosphere. At the meeting point of hot dry winds with humid winds from the sea, violen, storm accompanied by violent winds, torrential rain and hail are formed. They often take place in Bengal (where they are known as Kalbaisakni) and Assam (where they are known as Bordoichilla)Thunderstorm rain takes place in April and May and is called mango shower. Kerala has high rainfall in May.
3. South-West Monsoon Season—In May, with rapid rise of temperature there is decrease in air pressure. Thus deep low pressure replaces high pressure of cold weather season. This occurs from Rajasthan to West Bengal. The air is driven from Bay of Bengal and Arabian Sea to fill up this area of low pressure. The southeast trade winds from South also join this air circulation inthe form of southerly winds. Thus Kerala first experience south west monsoon in first week of June. It moves towards north and by the end of June it reaches most of the country. Thus Indian monsoon reach Indian area from Bay of Bengal as well Arabian Sea. The monsoon from the Arabian Sea causes heavy rain in Mumbai and Western ghats. These monsoon winds gets divided into two stream. One stream blows across peninsula in the south and causes heavy stormy rain fall and the other stream turn toward north and brings rain over the coastal districts of Gujrat. The Bay of Bengal winds also gets broken into two branches one travels towards India Myanmar and Thailand and other moves towards west in low pressure region. Thus in the Gangetic plains winds come from the east and causes monsoonal rain. As they move gradually west ward and reach Rajasthan because of little moisture content, give little amount of rain. About three fourth of total rain in India is received during south west monsoon season.
4. Retreating Monsoon—In the last week of September, the sun marches towards the south, as a result of which low pressure through of the Ganga plain moves towards the south. This cause weakness in southwest monsoon and finally monsoon closes by the last week of September in Rajasthan, Gujrat and W-Ganga plain. October and November are the month of transition. To conclude, over 80% rainfall is received in the four months that is from June to September.

Index of Aridity—It is the ratio of water deficiency to water need.

Index of Humidity—The ratio of water surplus to water need is known as index of humidity.

Drought—The situation in which amount of water required for maximum evapotranspiration is more than the amount available from rain (precipitation) and soil is called drought.