WBBSE Class 6 Geography Chapter 7 Weather and Climate Introduction
1. Weather refers to the atmospheric conditions (air temperature, precipitation, humidity, pressure, wind, cloudiness) of a particular place at a given point in time.
2. Climate is defined as the average weather conditions of a greater extent of the area over a long period of time, say 30-35 years.
3. Only 1 in 20 billion parts of sunlight reaches the Earth. This is known as incoming solar radiation or insolation.
4. Only 51% of the insolation heats the Earth’s surface. This is called effective solar radiation.
5. About 35% of the insolation is reflected back to outer space by clouds, dust particles, and water vapour without heating the Earth’s surface. This is called the albedo.
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6. At night, almost 51% of the insolation which heats up the Earth’s surface during the day, radiates back to the atmosphere or space from the Earth’s surface. This is terrestrial radiation.
7. The process of heat transfer from the Sun, directly to the Earth’s surface and back to the atmosphere again, is called radiation.
8. The process by which heat energy is transferred from a warmer surface to some other cooler surface is called conduction. The incoming solar radiation heats up the Earth’s surface.
Thus, the lowest strata of air close to the Earth’s surface get heated up first. This warm air rises upwards and the cool air above settles downwards to take its place.
This cool air then gets similarly heated up and moves upwards. The process of heat transfer through the movement of air currents is known as convection.
WBBSE Class 6 Elements of Weather Notes
9. The incoming solar radiation heats up the Earth’s surface. Thus, the lowest strata of air close to the Earth’s surface get heated up
first. This warm air rises upwards and the cool air above settles downwards to take its
10. Heat is an energy that can warm up any object and temperature is the measure of heat.
Class 6 Geography WBBSE
11. The difference between the maximum and the minimum temperature of any place in a day is called the diurnal range of temperature.
12. The difference between the average temperature of the coldest month and the hottest month in a year is known as the annual range of temperature.
13. The water vapour content in a particular volume of air in a place, at a particular temperature is known as the humidity of that air.
14. The pressure exerted by the air on the Earth’s surface is called air pressure.
15. The horizontal movement of air is known as the wind or airflow.
16. The measurable proportion of clouds in the sky is called cloud cover or cloudiness.
17. The moisture-laden air being light moves upwards. The temperature and air above is less and thus the moisture cools down and turns into little droplets of water. This is the process of condensation.
18. Water vapour in the air condenses around dust particles to form tiny water droplets which collectively form clouds.
Small water droplets merge with each other and become heavy droplets. These water droplets then fall as rain on the Earth’s surface under the influence of gravity.
19. The angle at which sunlight strikes the Earth’s surface is called the angle of incidence of sunlight on Earth.
20. Isotherms are imaginary lines on the Earth’s surface that connect all points on a map with equal temperatures.
21. The temperature decreases gradually from the Earth to the poles due to the difference in the angle of incidence of sunlight.
The division of the Earth into three belts on the basis of the amount of heat received from the Sun is called the heat belts.
22. The region between the Tropic of Cancer and the Tropic of Capricorn on either side of the Equator is known as Torrid Zone.
23. The regions from the Tropic of Cancer to the Arctic Circle and from the Tropic of Capricorn to the Antarctic Circle in the northern and southern hemispheres respectively are known as Temperate Zones.
24. The regions from the Arctic Circle to the North Pole in the northern hemisphere and from the Antarctic Circle to the South Pole in the southern hemisphere are known as the Frigid Zones.