SOCIAL SCIENCE -VII- CHAPTER 2: UNDERSTANDING THE WEATHER (LESSON NOTES)

 

SOCIAL SCIENCE -VII- CHAPTER 2:

UNDERSTANDING THE WEATHER

(LESSON NOTES)

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 v Introduction to Weather

Ø Weather refers to the state of the Earth’s atmosphere at a particular time and place.

Ø The atmosphere is the layer of gases (air) that surrounds the Earth.

§  The troposphere is the lowest layer of the atmosphere where:

·       Humans, animals, and plants live.

·       Almost all-weather phenomena occur.

Ø The height troposphere is 6 to 18 kilometres from the ground. Its thickness varies:

§  It is thinner at the poles due to cold air.

§  It is thicker in tropical regions due to warm air.

v Elements of Weather

 

Ø We use many words to describe the weather — hot, cold, rainy, cloudy, humid, snowy, windy, and so on. It is described using five main elements:

(1) Temperature: The hotness or coldness the atmosphere is called as temperature.

(2) Precipitation: Any form of water, as rain, snow, sleet or hail, falls from the sky.

(3) Atmospheric Pressure: The weight of the air above us, felt on the Earth’s surface.

(4) Wind: The movement of air, including its speed and direction.

(5) Humidity: The amount of water vapour in the air.

v Traditional Weather Prediction

Ø In earlier times, people predicted (Forecast) weather by observing nature.

Ø Common signs included:

§ Birds flying low.

§ Ants carrying eggs to higher ground.

§ Frogs croaking loudly.

§ Pine cones opening or closing.

Ø These traditional methods are still used in many parts of India.

 

v Meteorology

Ø The scientific study of weather and its changes is called as meteorology.

Ø Meteorologists use:

§  Scientific instruments.

§  Data collection methods.

Ø They predict weather for:

§  Hours.

§  Days.

§  Weeks.

 

v Weather Instruments

 

v Thermometer (Temperature Measurement)

   Ø A thermometer is used to measure temperature.

   Ø Types of thermometers:

·       Clinical thermometer.

·       Laboratory thermometer.

·       Digital thermometer.

   Ø Temperature is measured in:

·       Celsius (°C).

·       Fahrenheit (°F).

   Ø Important Calculations:

§  Range of temperature = Maximum temperature − Minimum temperature.

§  Mean daily temperature = (Maximum + Minimum) ÷ 2.

 

v Rain Gauge (Precipitation Measurement)

   Ø The amount of rainfall is measured with the help of an instrument called a rain gauge

Ø Structure:

§  Funnel collects rainwater.

§  Cylinder stores water.

§  Scale measures depth.

Ø Rainfall is measured in millimetres (mm).

 

v Barometer (Atmospheric Pressure Measurement)

Ø The instrument used to measure atmospheric pressure is called a barometer. Pressure is measured in millibars (mb).

Ø Key Points:

§  Normal pressure at sea level ≈ 1013 mb.

§  Pressure below 1000 mb indicates a low-pressure system or depression (possible storm).

§  Pressure decreases with increase in altitude.

 

v Wind Instruments

 

Ø Wind Vane

§  Measures wind direction.

§  It rotates and points in the direction from which the wind blows.

Ø Anemometer

§  The simplest instrument to measure the wind direction and speed is the anemometer. It has rotating 3 or 4 cups. And attached meter. Faster rotation indicates stronger wind. (KM/H)

 

v Hygrometer (Humidity Measurement)

Ø A hygrometer measures humidity (water vapour in air).

Ø It also depends on factors like temperature, wind, pressure and location

Ø Humidity is expressed as relative humidity (%).

Ø Key Points:

§  0% = No water vapour (ideal condition, not real).

§  100% = Air is fully saturated.

§  Dry weather: 20%–40% humidity.

§  Humid weather: 60%–80% humidity.

 

v Weather Stations

Ø A weather station is a place where all weather instruments are kept together.  It records weather data regularly.

Ø Automated Weather Station (AWS)

Ø AWS is a self-operating system with sensors.

Ø It measures:

§  Temperature.

§  Humidity.

§  Wind speed and direction.

§  Rainfall.

§  Atmospheric pressure.

Ø It provides accurate and real-time data.

 

v Predicting the Weather

Ø Meteorologists collect and analyse weather data over time.

Ø Predictions are made using scientific methods and technology.

Ø Importance of Weather Prediction:

§  Helps prepare for:

·       Floods.

·       Droughts.

·       Cyclones.

·       Heat waves.

§  Assists:

·       Farmers in planning crops.

·       Fishermen in avoiding storms.

·       Governments in disaster management.

Ø Weather Warnings

§  Weather departments issue alerts such as:

·       Watch (Be updated).

·       Alert (Be prepared).

·       Warning (Take action).

v Key Concepts

Ø Weather is determined by the combined effect of all five elements.

Ø Different elements dominate at different times:

§  Rainfall in monsoon.

§  Temperature in summer and winter.

§  Pressure during cyclones.

§  Wind during storms or hot winds (loo).

Ø Weather is closely related to climate.

 

v Summary of the Lesson (Bullet Points)

Ø Weather is the condition of the atmosphere at a specific time and place.

Ø The troposphere is the layer where all weather changes occur.

Ø The main elements of weather are:

§  Temperature.

§  Precipitation.

§  Atmospheric pressure.

§  Wind.

§  Humidity.

Ø Traditional methods of weather prediction are based on observing nature.

Ø Meteorology is the scientific study of weather.

Ø Weather instruments include:

§  Thermometer for temperature.

§  Rain gauge for rainfall.

§  Barometer for pressure.

§  Anemometer and wind vane for wind.

§  Hygrometer for humidity.

• Ø Weather stations collect and record weather data regularly.
• Ø Automated Weather Stations provide real-time and accurate data.
• Ø Weather prediction helps in disaster preparedness and planning.
• Ø Weather warnings help people take preventive actions.
• Ø Weather and climate are closely connected concepts.