Samacheer Class 8 Social Science - Weather and Climate

Weather refers to the condition of atmosphere for a short period of time, typically hours or days, including temperature, humidity, wind, and precipitation. The scientific study of weather is called Meteorology, which uses instruments and observations to understand atmospheric phenomena. The highest temperature ever recorded on the earth is 56.7°C in Death Valley, USA. Humidity is a ratio between the actual amount of water vapour and the maximum amount of water vapour the air can hold at a given temperature. Wind direction and wind speed are measured by wind vane and anemometer respectively, which are important meteorological instruments. Isotherms are imaginary lines which connect the same temperatures of different places on a map, helping to visualize temperature distribution patterns.

1. The highest temperature ever recorded on the earth is 56.7°C - True. This extreme temperature was recorded in Death Valley, California, demonstrating the intense heat that can occur in certain desert regions under specific atmospheric conditions. 2. The degree of heat present in the sun is termed as temperature - False. While temperature does measure heat, the sun's heat is more accurately described in terms of its thermal energy and the process of nuclear fusion occurring within it. 3. Rainfall is measured by Raingauge - True. A raingauge is a standard meteorological instrument used to measure the amount of precipitation that falls in a given area over a specific period of time. 4. Temperature decreases to 8°C per 1000 meters in height - False. The actual rate of temperature decrease with altitude is approximately 6.5°C per 1000 meters, known as the environmental lapse rate, though this can vary depending on atmospheric conditions. 5. Al-Balakhi prepared the first climatic Atlas of the world - True. Al-Balakhi, a Persian geographer, created one of the earliest systematic compilations of climate information organized geographically.

Weather is the day today conditions(state) of the atmosphere at any place as regards sunshine, temperature, cloud cover. Wind fog condition, air pressure, humidity, precipitation and such other elements.
2. What is insolation?
Incoming solar radiation are called Insolation.3. What is meant by atmospheric pressure?
The weight of air above a given area on the earth’s surface is called atmospheric pressure or air pressure.
4. Write a short note on “Planetary winds”
Planetary winds are the ones which blow almost in the same direction throughout the year.
So, they are called as planetary winds.
5. What are “Isolines”?
The distribution of weather elements is shown by means of Isolines on maps. Isolines are lines which join the places of equal values of weather elements.

The angle of the sun’s rays, the length of daytime, altitude, distribution of land and water bodies, location and direction of mountain ranges, air pressure, winds, and ocean currents are the major factors which affect the weather and climate of a region.

Latitude, altitude, nature of the land, ocean currents, prevailing winds, slope, shelter, and distance from the sea, natural vegetation, and soil are the major factors which affect the distribution of temperature.

The distribution of temperature is shown by means of Isotherms.
Isotherms are imaginary lines which connect the same temperatures of different places..

The angle of the sun’s rays, the length of daytime, altitude, distribution of land and water bodies, location and direction of mountain ranges, air pressure, winds, and ocean currents are the major factors which affect the weather and climate of a region.
2. Temperature decreases with an increase in altitude.
It is known as the Lapse rate which is 6.5-degree Celcius per 1000 meters is the troposphere.
3. Mountain climbers carry Oxygen cylinders while ascending peaks.
With decreasing air pressure, the availability of oxygen to breathe also decreases. At very high altitudes, atmospheric pressure and available oxygen get so low that people can become sick and even die. Mountain climbers use bottled oxygen when they ascend very high peaks.

Artificial pressure is created in aircraft because at very high altitudes, atmospheric pressure becomes extremely low and the available oxygen decreases significantly. When an aircraft climbs to cruising altitude, typically between 30,000 to 40,000 feet, the external atmospheric pressure is only a fraction of what it is at sea level. Without pressurization, passengers and crew would experience rapid decompression sickness, also known as the bends, which occurs when there is a sudden transition from high pressure to low pressure. This condition can cause nitrogen bubbles to form in the bloodstream and tissues, leading to severe pain, paralysis, and even death. To prevent this dangerous situation, modern aircraft are equipped with pressurization systems that maintain an artificial cabin pressure equivalent to an altitude of about 6,000 to 8,000 feet. This allows passengers to remain comfortable and safe during flight while the aircraft operates at much higher altitudes where fuel efficiency is optimal. The pressurization system continuously regulates cabin pressure and oxygen levels, ensuring a safe and comfortable environment for all occupants throughout the flight.

Measuring Temperature:
1. The temperature of a unit volume of air at a given time is measured in scales like Celsius, Fahrenheit, and Kelvin. Meteorologist measures the temperature by the Thermometer, Stevenson screen and minimum and maximum Thermometer.
2. The energy received by the earth through insolation is lost by outgoing radiation.
3. Atmosphere is mainly heated by outgoing radiation from 2 to 4 pm. So the maximum temperature is recorded between 2 and 4 pm regularly and the minimum temperature is recorded around 4 am before sunrise.
Mean Temperature:
1. The average of the maximum and minimum temperatures within 24 hours is called mean daily temperature [(87°F + 73°F)/2=80°F].
2. Diurnal range of temperature is the difference between the maximum and minimum temperatures of a day. The annual range of temperature is the difference between the highest and lowest mean monthly temperatures of a year.
2. Write about the wind and its types.
The horizontal movement of air is called wind. The wind systems are broadly categorized into three as follows.
Planetary winds
Seasonal winds
Local winds
1. Planetary Winds are the ones which blow almost in the same direction throughout the year. So, they are called as Permanent or planetary winds. Trade winds, Westerlies, and polar easterlies are the types of prevailing winds.
2. Seasonal winds are those which change their direction according to the season in a year. They are called as monsoon winds. These winds blow from sea to land during summer and land to sea during winter.
3. Local winds are the winds that blow over a small area only during a particular time of a day or a short period of a year. Land and sea breezes are examples of these winds.
3. List out the weather elements and associated measuring instruments.
Weather elements
Measuring instruments
Temperature
Celsius, Fahrenheit, Kelvin
Rainfall
Rain gauge
Air Pressure
Aneroid Barometer
Humidity
Hygrometer
Wind
Anemometer

Solar radiation
2. ……………. and soil are the major factors which affect the distribution of temperature.
Natural vegetation3. The distribution of temperature is shown by means of ………………..
Isotherms
4. Temperature zone lies between tropic of …………… circle in the Northern Hemisphere and the ………………. circle in the Southern Hemisphere.
Arctic, Antarctic
5. Frigid zone is known as …………………
polar region
6. ………………… is a major component of the water cycle.
Rain
7. Generally rainfall is high in the …………….. region.
Equatorial
8. The average of ……………. and ……………. temperatures within 24 hours is called mean daily temperature.
maximum, minimum
9. …………………. is a diagram used to depict the direction and periods of prevailing winds on a map.
Wind rose
10. Weather is the day to day conditions of the ………………………..
atmosphere
11. The amount of carbon dioxide in the atmosphere is ………………..
0.03%
12. The amount of argon in the atmosphere is …………….
0.97%
13. The word Klimo means ……………….
Inclination
14. Climate is the average atmospheric conditions usually for ………………..
35 years
15. The Scientific Study of Climate is called …………….
Climatology