This chapter explains what weather is and how we measure and predict it. Weather is the state of the Earth's atmosphere at a particular time and place, and it happens mostly in the troposphere, the layer of air closest to the ground. Five elements define the weather: temperature, precipitation, atmospheric pressure, wind and humidity. The chapter shows why common standards of measurement matter — what feels chilly to someone in Chennai may feel pleasant to someone in Kashmir — and introduces the instruments scientists use: the thermometer for temperature (on the Celsius and Fahrenheit scales), the rain gauge for rainfall in millimetres, the barometer for atmospheric pressure in millibars, the wind vane and anemometer for wind direction and speed, and the hygrometer for relative humidity. It traces how people once read nature's clues — ants moving eggs, frogs croaking, pine cones opening — to forecast weather, and how meteorologists now use instruments and weather stations, including Automated Weather Stations, to collect data over time. The India Meteorological Department, set up in 1875, issues colour-coded warnings for events like heat waves, heavy rain and cyclones. The chapter stresses that accurate weather prediction helps people plan activities, lets governments prepare for disasters, and saves lives, especially as climate change makes extreme weather more frequent.
Elements of weatherWeather instrumentsReading nature's cluesWeather stations and the IMDPredicting weather and disasters
Key terms
Weather
The state of the Earth's atmosphere at a particular time and place, described by elements such as temperature, rainfall, wind and humidity.
Troposphere
The lowest layer of the atmosphere, closest to the ground, where living things breathe and where almost all weather takes place.
Precipitation
Any form of water — rain, snow, sleet or hail — that falls from the sky.
Atmospheric pressure
The weight of the air above and around us pressing on the Earth's surface, measured in millibars with a barometer.
Relative humidity
A measure of how much water vapour the air holds compared to the maximum it could hold, expressed as a percentage and measured with a hygrometer.
Meteorology
The systematic study of weather and how it changes, which forms the basis of weather forecasting.
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