1. Introduction
Have you ever noticed that the weather can change during the same day? A morning may be sunny, the afternoon may become cloudy, and rain may arrive in the evening.
We experience weather every day. We may describe it as hot, cold, rainy, cloudy, humid, windy, pleasant or snowy.
Understanding weather is important because it affects our daily activities, agriculture, transport, travel and safety. Accurate weather information can also help people prepare for heavy rain, storms, droughts and heat waves.
- How can we measure and monitor the weather around us?
- How do weather predictions help us prepare for heavy rain, storms, drought and heat waves?
📚 Table of Contents
- Introduction
- What is Weather?
- Atmosphere and Troposphere
- Elements of Weather
- Traditional Weather Forecasting
- Meteorology
- Temperature
- Precipitation and Rainfall
- Atmospheric Pressure
- Wind
- Humidity
- Weather Stations
- Automated Weather Stations
- India Meteorological Department
- Modern Weather Prediction
- Importance of Weather Forecasting
- Important Terms
- Weather Instruments at a Glance
- Chapter Summary
- Quick Revision
- Important Questions
- MCQs
- Chapter Activities
- FAQs
2. What is Weather?
Weather is the state of the Earth's atmosphere at a particular time and place.
In simple words, weather tells us what the atmosphere is like at a certain place and at a certain moment.
We use words such as hot, cold, rainy, cloudy, humid, snowy and windy to describe weather.
Examples of Weather
- It is raining in Mumbai.
- It is very hot in Jaipur.
- A cold wind is blowing in a hill station.
- The sky is cloudy before a storm.
- The air feels humid near the coast.
3. Atmosphere and the Troposphere
The atmosphere is the layer of gases that surrounds the Earth. We commonly call this mixture of gases “air”.
The atmosphere has several layers. The layer closest to the Earth's surface is called the troposphere.
The Troposphere
Almost all weather phenomena that we experience take place in the troposphere.
The troposphere extends approximately from 6 to 18 kilometres above the ground. It is thinner near the poles and thicker in tropical regions.
4. Elements of Weather
Weather is described using several measurable elements. This chapter focuses on five important elements:
| Element | What it tells us | Main Instrument |
|---|---|---|
| Temperature | How hot or cold the air is. | Thermometer |
| Precipitation | Water falling from the atmosphere, such as rain. | Rain gauge |
| Atmospheric Pressure | The pressure exerted by the air. | Barometer |
| Wind | Direction and speed of moving air. | Wind vane and anemometer |
| Humidity | Amount of water vapour present in the air. | Hygrometer |
5. Traditional Weather Forecasting
Humans have observed nature for thousands of years and tried to identify signs that indicate changes in weather.
Traditional knowledge has often been passed from one generation to another.
Examples of Nature's Weather Signals
- Ants may move their eggs to higher ground before heavy rain.
- Frogs may croak loudly before rainfall.
- Birds may behave differently before changes in weather.
- Squirrels may gather food according to seasonal conditions.
- Pine cones respond to changes in environmental humidity.
However, modern weather forecasting uses scientific measurements, instruments, computers and weather observations from many locations.
6. What is Meteorology?
Meteorology is the systematic study of weather and how weather changes.
Scientists who study weather are called meteorologists.
Meteorologists collect weather data, analyse it and use it to understand and predict future weather conditions.
Meteorology = scientific study of weather.
Meteorologists = scientists who study weather.
7. Temperature
Temperature tells us how hot or cold the air is at a particular place.
Temperature is commonly measured using a thermometer.
Thermometer
Traditional thermometers may use a coloured liquid that expands when temperature increases.
Digital thermometers are increasingly used because they can provide precise readings and can record more data.
Temperature Scales
Temperature can be expressed using different scales. The Celsius scale is commonly used for weather reports in India.
Maximum and Minimum Temperature
Weather reports often tell us the maximum and minimum temperatures recorded during a day.
Temperature Range
The range of temperature is the difference between the maximum and minimum temperature during a given period, usually 24 hours.
Mean Daily Temperature
The mean daily temperature can be calculated by adding the maximum and minimum temperatures and dividing the result by two.
Example
Suppose the maximum temperature is 32°C and the minimum temperature is 18°C.
Mean = (32°C + 18°C) ÷ 2 = 25°C
8. Precipitation and Rainfall
Precipitation means water falling from the atmosphere to the Earth's surface.
It can occur in different forms, including:
- Rain
- Snow
- Sleet
- Hail
Rain Gauge
Rainfall is measured using an instrument called a rain gauge.
Rainwater falls through a funnel and collects in a container. A scale is used to measure the depth of the collected water.
Rainfall is usually expressed in millimetres (mm).
Where should a rain gauge be placed?
A rain gauge should be placed in an open location where buildings, trees or walls do not block rainfall. It should also be stable and properly positioned.
Why measure rainfall?
- To monitor rainfall patterns.
- To help farmers plan agricultural activities.
- To monitor floods and drought conditions.
- To support weather forecasting.
- To understand long-term rainfall patterns.
9. Atmospheric Pressure
Air has weight. The force exerted by the weight of air on a surface is called atmospheric pressure.
Barometer
A barometer is an instrument used to measure atmospheric pressure.
Atmospheric pressure is commonly expressed in millibars (mb).
Pressure and Height
Atmospheric pressure generally decreases as we go higher above sea level because there is less air above us.
This is why pressure at a high mountain location can be much lower than pressure near sea level.
Atmospheric Pressure and Weather
Changes in atmospheric pressure are important for understanding weather systems. Meteorologists monitor pressure to help understand conditions such as storms and cyclones.
10. Wind
Wind is moving air.
Weather reports often tell us two important things about wind:
- Direction from which the wind is blowing.
- Speed at which the wind is moving.
Wind Vane
A wind vane shows the direction from which the wind is coming.
At airports, a windsock is often used to provide a quick indication of wind direction and strength.
Anemometer
An anemometer is used to measure wind speed.
A common type of anemometer has cups that rotate when wind blows. Stronger winds make the cups rotate faster.
Wind speed is commonly measured in kilometres per hour (km/h).
Anemometer → Wind speed
11. Humidity
Humidity refers to the amount of water vapour present in the air.
Humidity is influenced by factors such as temperature, wind, atmospheric pressure and location.
Relative Humidity
Humidity is commonly expressed as relative humidity.
Air with no water vapour would be considered 0% humidity, while air saturated with water vapour would have 100% relative humidity.
In practice, dry weather may have relative humidity around 20–40%, while humid weather commonly falls around 60–80%.
Hygrometer
A hygrometer is an instrument used to measure humidity.
Humidity and Evaporation
When water evaporates, it causes a cooling effect.
When the air already contains a large amount of water vapour, evaporation occurs more slowly.
This is why wet clothes generally dry more slowly on a very humid day.
Humidity and Sweating
When humidity is high, sweat evaporates more slowly. This can make us feel hotter and more uncomfortable even when the temperature is the same.
12. Weather Stations
Measuring weather requires several instruments. A weather station brings different weather instruments together at one location.
Weather stations measure and record weather conditions at regular intervals.
Weather Elements Recorded
- Temperature
- Precipitation
- Atmospheric pressure
- Wind speed
- Wind direction
- Humidity
The collected data can be used to monitor weather, create weather maps and prepare forecasts.
13. Automated Weather Stations
An Automated Weather Station (AWS) is a self-operating system that uses sensors to measure and record weather conditions.
What can an AWS measure?
- Temperature
- Humidity
- Wind speed
- Wind direction
- Precipitation
- Atmospheric pressure
Why are AWS useful?
Automated weather stations can collect information without requiring a person to take every measurement manually.
They are useful in areas such as:
- Agriculture
- Aviation
- Navigation
- Environmental monitoring
- Disaster management
14. India Meteorological Department (IMD)
The India Meteorological Department (IMD) is India's national meteorological service.
The IMD was established in 1875.
It collects and analyses weather information and provides forecasts and warnings for different parts of India.
IMD Motto
The chapter mentions the IMD motto: ādityāt jāyate vriṣhti, meaning “From the sun arises rain.”
The phrase is associated with the ancient text Manusmṛiti. The fuller idea is that from the Sun comes rain, from rain comes food, and from food come living beings.
- IMD = India Meteorological Department
- Established = 1875
- Main role = weather observation, forecasting and warnings
15. Modern Weather Prediction
Modern weather forecasting does not depend on simply looking at the sky. Meteorologists use observations from instruments, weather stations, satellites and other sources.
Weather data is collected from different places and at different times. Scientists analyse this information to understand current weather conditions and predict what may happen in the future.
How Weather Forecasting Works
- Weather conditions are measured using instruments.
- Data is collected from weather stations and other sources.
- The data is recorded and analysed.
- Meteorologists study weather patterns.
- Forecasts are prepared.
- Warnings are issued when dangerous weather is expected.
16. Why is Weather Forecasting Important?
Weather forecasts help people make better decisions and prepare for changing weather conditions.
Agriculture
Farmers use weather information to plan sowing, irrigation, harvesting and other agricultural activities.
Travel and Transport
Weather information is important for road, rail, sea and air transport. Dangerous weather can affect travel plans and safety.
Disaster Preparedness
Forecasts can provide early warnings for events such as heavy rainfall, storms, cyclones and heat waves.
Daily Life
Weather forecasts help us decide what clothes to wear, whether to carry an umbrella, whether to plan outdoor activities and how to prepare for extreme temperatures.
Industries
Many industries depend on weather information for planning and safe operation.
17. Important Terms and Definitions
18. Weather Instruments at a Glance
🌡️ Thermometer
Measures temperature.
🌧️ Rain Gauge
Measures precipitation/rainfall.
📊 Barometer
Measures atmospheric pressure.
🧭 Wind Vane
Shows wind direction.
💨 Anemometer
Measures wind speed.
💧 Hygrometer
Measures humidity.
| Instrument | Weather Element | Common Unit/Information |
|---|---|---|
| Thermometer | Temperature | °C |
| Rain Gauge | Rainfall | mm |
| Barometer | Atmospheric Pressure | millibars (mb) |
| Wind Vane | Wind Direction | Direction |
| Anemometer | Wind Speed | km/h |
| Hygrometer | Humidity | % relative humidity |
19. Important Data to Remember
| Fact | Answer |
|---|---|
| Lowest layer of atmosphere discussed in the chapter | Troposphere |
| Approximate height of troposphere | 6–18 km |
| Number of major elements of weather discussed | Five |
| IMD established | 1875 |
| Rainfall unit | Millimetres (mm) |
| Wind speed commonly measured in | Kilometres per hour (km/h) |
| Dry-weather relative humidity range mentioned | About 20–40% |
| Humid-weather relative humidity range mentioned | About 60–80% |
20. Chapter Summary
Weather is the state of the Earth's atmosphere at a particular time and place. Most weather phenomena occur in the troposphere, the lowest layer of the atmosphere.
The five important elements discussed in this chapter are temperature, precipitation, atmospheric pressure, wind and humidity.
Temperature is measured with a thermometer, rainfall with a rain gauge, atmospheric pressure with a barometer, wind direction with a wind vane, wind speed with an anemometer and humidity with a hygrometer.
People have traditionally observed natural signs to predict weather, but modern meteorology uses scientific instruments, weather stations and technology to collect and analyse data.
Weather stations bring several instruments together to record weather conditions. Automated Weather Stations use sensors to collect data automatically.
The India Meteorological Department, established in 1875, plays an important role in weather observation, forecasting and warnings in India.
21. Quick Revision
22. Important Questions and Answers
Long Answer Questions
23. MCQs – Class 7 SST Chapter 2
24. Fill in the Blanks
25. True or False
26. Match the Following
| Instrument | Weather Element |
|---|---|
| 1. Hygrometer | Humidity |
| 2. Anemometer | Wind speed |
| 3. Barometer | Atmospheric pressure |
| 4. Thermometer | Temperature |
| 5. Rain gauge | Precipitation |
27. Chapter Activities – Learn by Doing
Activity 1: Make a Simple Rain Gauge
You can make a simple rain gauge using a suitable container and measuring scale.
Place it in an open area away from buildings, trees and other objects that may obstruct rainfall. Keep it stable and record the amount of water collected at the same time each day.
Continue recording for several days or weeks and compare the rainfall amounts.
Activity 2: Keep a Temperature Record
Record the maximum and minimum temperatures of your city for 7–10 days.
Calculate the temperature range for each day.
Activity 3: Observe Weather Signs
Ask older members of your family or community about traditional signs they use to understand approaching rain or changes in weather.
Record the signs they mention and discuss them with your classmates.
Activity 4: Weather Report
Look at a weather report for your city and identify:
- Maximum temperature
- Minimum temperature
- Humidity
- Rainfall
- Wind direction
- Wind speed
- Weather warnings
28. Frequently Asked Questions
29. Final Revision Challenge ⭐
Try answering these questions without looking at your notes. If you can answer all of them confidently, you have understood the main ideas of the chapter.
- Define weather.
- What is the atmosphere?
- What is the troposphere?
- Name the five elements of weather.
- What is meteorology?
- What does a thermometer measure?
- What does a rain gauge measure?
- What does a barometer measure?
- What does a wind vane measure?
- What does an anemometer measure?
- What does a hygrometer measure?
- What is humidity?
- Why does high humidity affect evaporation?
- What is an Automated Weather Station?
- When was the IMD established?
- Why is weather forecasting important?
🌡️ Temperature → Thermometer
🌧️ Precipitation → Rain Gauge
📊 Pressure → Barometer
🧭 Wind Direction → Wind Vane
💨 Wind Speed → Anemometer
💧 Humidity → Hygrometer