Unit - 3 (Climatology)
- Weather and Climate
- Composition of atmosphere
- Structure of atmosphere
- Insolation, Heat budget and Albedo
- Temperature and Inversion of Temperature
- Pressure and Pressure belts
- Winds
- Planetary winds
- Seasonal winds and Local winds
- Humidity, Evaporation and Condensation
- Types of clouds and Precipitation
- Air masses
- Jet Streams
- Temperate cyclones and Tropical cyclones
- Climatic regions
Previous Unit - Geomorphology
Next Unit - Oceanography
Weather and Climate -
- Weather is the day to day state of the atmosphere.
- Climate is the average atmospheric condition of an area over a considerable period of time. It is calculated for a minimum period of 30 years. It includes factors such as rainfall, temperature, humidity, pressure, wind, etc.
Atmosphere - The layer of air surrounding the Earth, held by gravity is the atmosphere. It is a thick gaseous envelop which surrounds the Earth from all sides and is attached to the Earth's surface due to Gravitational force.
Composition of Atmosphere - Atmosphere is composed of many gases, water vapour and dust particles.
Gases present in the Atmosphere (as percentage of volume)
- Nitrogen - 78.08%
- Oxygen - 20.95%
- Argon - 0.93%
- Carbon di-oxide - 0.0036%
- Neon - 0.002%
- Helium - 0.0005%
- Krypton - 0.0001%
- Xenon - 0.00009%
- Hydrogen - 0.00005%
Nitrogen -
- It is the most abundant gas present in the Atmosphere.
- Leguminous plants use it for their growth.
- Nitrogen gas is used in food packing.
- Nitrogen is the basic component of Amino Acids and Proteins.
- Nitrogen gas is used in the manufacture of fertilizers.
Oxygen -
- It is the second most abundant gas present in the Atmosphere.
- It was released in the Atmosphere by the plants during photosynthesis and is consumed by both plants and animals during respiration.
- It is negligible above 120 KM.
Carbon di-oxide -
- It was absorbed by the plants during photosynthesis.
- It is called Green House gas because it holds heat for a longer period of time.
- It is negligible above 90 KM.
Noble Gases -
- Argon, Neon, Helium, Krypton and Xenon are noble gases.
- They are chemically inactive.
Water Vapour -
- It is water in the gaseous form present in the Atmosphere.
- The amount of Water Vapour present in the Atmosphere depends on many factors and varies from place to place and from time to time.
- It is concentrated mainly upto 16 KM (16KM - 99% & upto 6 KM- 90%)
- It is also a Green House gas.
Dust Particles -
- It varies from place to place.
- It is hygroscopic in nature, i.e., it has the capacity to absorb the moisture and helps in condensation and cloud formation.
Variation in composition -
1. With time
- Amount of Carbon di-oxide increases because of Human activities and burning of fossil fuels.
- Amount of Ozone gas decreases because of increase in CFC (Chlorofluorocarbon)
2. With altitude
- Water Vapour and Dust Particles decreases with increase in altitude.
- Ozone is concentrated in a particular belt (35-50 KM)
3. With latitude
- Amount of Water Vapour in Tropical and Equatorial region is more because of high temperature.
- Dust Particles is more in Sub-tropical region because of dry winds.
Structure of Atmosphere
Homosphere -
- It is present upto 80 KM above the sea level.
- Uniform mixture of all the gases are present in this sphere.
- Gases are present in molecular form.
- Very high concentration of Water Vapour and Dust Particles are present.
Heterosphere -
- It is found above 80 KM.
- Different layers of gases are present (Nitrogen layer → Oxygen layer → Helium layer → Hydrogen layer)
- Gases are present in atomic form (ionic form).
- Negligible amount of Water Vapour and Dust Particles are present.
Layers of Atmosphere
1. Troposphere
- Troposphere is the layer which is very near to the surface.
- Its height is not uniform. It is maximum at Equator (16 KM) and minimum at poles (6 KM).
- Reason - Equatorial region → high temperature → high convection → gases rise, that's why it is higher at Equator.
- Its average height is (12-13 KM)
- It is called Zone of Turbulence and Zone of Convection (because of high convection).
- Temperature decreases as we move away from the surface.
- The rate of decrease of temperature is 6.5°C/KM or 1°C/165 m. This rate is known as Normal lapse rate.
- All the weather phenomenon is restricted to troposphere due to the presence of water vapour and dust particles.
- Tropopause is the boundary between troposphere and stratosphere. The temperature here is nearly constant that's why it is named so.
- From tropopause, temperature starts to increase which is known as Temperature inversion.
2. Stratosphere
- It extends from tropopause to 50 KM.
- It is called so because the layers are stratified and are non-convective in nature (i.e., no vertical movement of gases).
- Temperature increases in stratosphere due to the absorption of UV lights by Ozone layer which is concentrated between 35-50 KM.
- The conditions are extremely dry except few rare cloud which is known as Mother of Pearl or Nacreous. It looks colourful due to the absorption of Sunlight. They are the one of the most beautiful phenomena observed on the Earth.
- Stratosphere ends at Stratopause which is the boundary between Stratosphere and Mesosphere.
3. Mesosphere
- It extends from Stratopause to 80 KM.
- Temperature decreases with height and reaches upto -100℃ at 80 KM which is the lowest temperature experienced in the Atmosphere.
- It ends at Mesospause.
4. Thermosphere
- It extends from Mesospause to 500-700 KM.
- It consists on lower Nitrogen layer upto 200 Km and higher Oxygen layer in atomic form.
- Temperature rises rapidly due to the absorption of high energy radiation and reaches upto 1000℃ at the height of 350 KM.
- However, the heat is not felt due to the absence of molecular collision.
- Auroras are found in Thermosphere. It is called Aurora Borealis or Northern lights at North Pole and Aurora Australis or Southern lights at South Pole.
5. Exosphere
- It extends from 500-600 Km to the end of the Atmosphere.
- It contains atomic Oxygen, Helium and Hydrogen.
- It contains Magnetosphere which is composed of electrons and protons derived from solar winds and other charged particles and they are arranged in two bands at 3000 KM and 10000 KM which are called as Van Allen Radiation belts. It protects us from harmful solar winds (high energy rays).
Ionosphere
- It extends from 80 to 650 KM and it is formed due to the ionisation by solar radiation.
- It is made up of different layers such as d, e, f, g layer, etc.
- Ionosphere reflects the long wavelength radio waves back to the Earth which helps in Radio communication.
Change in Temperature with change in altitude
Previous Article - Landforms
Next Article - Insolation and Heat Budget
Notes on other subjects
Optional Notes
Note - This is my Vision IAS Notes (Vision IAS Class Notes) and Ashutosh Pandey Sir's Public Administration Class notes. I've also added some of the information on my own.
Hope! It will help you to achieve your dream of getting selected in Civil Services Examination 👍
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