Weather refers to the condition of the atmosphere at a particular place and time. It can change from hour to hour and day to day. Climate, on the other hand, is the average weather pattern of a place over a long period — usually 30 years or more.
Elements of Weather
- 1.The main elements that describe weather are:
- 2.Temperature – The degree of hotness or coldness of the air, measured in degrees Celsius (°C) using a thermometer.
- 3.Humidity – The amount of water vapour present in the air. High humidity makes weather feel sticky and muggy. Measured using a hygrometer.
- 4.Precipitation – Any form of water that falls from clouds — rain, snow, sleet, or hail. Rainfall is measured using a rain gauge.
- 5.Wind – The movement of air from areas of high pressure to areas of low pressure. Wind direction is shown by a wind vane; wind speed by an anemometer.
- 6.Cloud cover – The fraction of the sky covered by clouds, measured in oktas (eighths).
- 7.Atmospheric pressure – The weight of the air above a point, measured with a barometer.
How Weather Is Recorded
Meteorological departments collect weather data every day from weather stations across the country. This data is used to prepare weather forecasts — predictions about future weather — which are important for farmers, sailors, pilots, and disaster management teams.
Water Cycle (Hydrological Cycle)
- 1.Weather is closely linked to the water cycle:
- 2.Evaporation – Water from oceans, rivers, and lakes changes into water vapour due to solar heat.
- 3.Transpiration – Plants release water vapour through their leaves.
- 4.Condensation – Water vapour cools as it rises and turns into tiny water droplets, forming clouds.
- 5.Precipitation – Water falls back to Earth as rain, snow, etc.
- 6.Collection/Runoff – Water collects in oceans, rivers, and groundwater, restarting the cycle.
Factors Affecting Weather
- Latitude – Areas near the equator are hotter; areas near the poles are colder.
- Altitude – Temperature decreases with increase in altitude (about 6.5°C per 1000 m rise — called the normal lapse rate).
- Distance from the sea – Coastal areas have moderate weather; inland areas experience extremes.
- Wind direction – Winds blowing from the sea bring moisture; winds from land are dry.
- Cloud cover – Clouds trap heat at night (warming effect) and reflect sunlight during the day (cooling effect).
Types of Rainfall
- Convectional rainfall – Intense solar heating causes warm air to rise rapidly, cool, and form clouds; common in tropical areas.
- Relief (orographic) rainfall – Moist air forced to rise over a mountain cools and rains on the windward side.
- Cyclonic (frontal) rainfall – Occurs when warm and cold air masses meet along a front.
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On a clear summer afternoon in Delhi, the temperature is 42°C. By the next morning it drops to 28°C. This daily (diurnal) temperature variation happens because there are no clouds to trap heat at night, so energy radiates away rapidly — illustrating how cloud cover affects temperature.
A farmer in Maharashtra checks the weather forecast and learns that a cyclone is approaching the coast. He harvests his crops early to avoid loss. This shows why accurate weather forecasting is vital for agriculture and livelihoods.
Mawsynram in Meghalaya (near Cherrapunji) is among the wettest places on Earth. This is because moisture-laden southwest monsoon winds are forced upward by the Khasi Hills (relief rainfall), dropping enormous amounts of rain on the windward side.
A wet towel dries faster on a sunny, windy day than on a humid, still day. This is because high humidity reduces the rate of evaporation — the air is already saturated with moisture, so it cannot absorb more water vapour easily.
At an altitude of 3000 m in the Himalayas, the temperature is about 20°C cooler than at sea level (3 x 6.5 = 19.5°C). This explains why hill stations like Shimla and Mussoorie are pleasantly cool in summer while the plains are sweltering.
Coastal cities like Mumbai have smaller differences between summer and winter temperatures compared to inland cities like Delhi. The sea acts as a temperature buffer — it warms slowly and cools slowly, moderating coastal climates. This is called the maritime effect.
A barometer reading that drops sharply usually signals the approach of a storm or low-pressure system. Sailors have used barometers for centuries to anticipate bad weather. A rising barometer indicates clearing skies and improving weather.
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Key Terms
- Weather – Atmospheric conditions at a specific place and time.
- Climate – Average weather of a place over 30+ years.
- Meteorology – The scientific study of the atmosphere and weather.
- Normal lapse rate – Temperature drop of 6.5°C per 1000 m rise in altitude.
- Humidity – Amount of water vapour in the air.
Common mistakes
- Students often confuse weather (short-term, local) with climate (long-term, regional average). Remember: "Climate is what you expect; weather is what you get."
- The rain gauge measures depth of rainfall in mm, NOT the total volume — it catches rain in a standard-sized cylinder and measures the depth of water collected.
Summary
Weather is determined by temperature, humidity, precipitation, wind, pressure, and cloud cover, all of which are measured by specialised instruments. The water cycle drives much of our weather. Factors like latitude, altitude, distance from sea, and wind patterns create the variety of weather we observe. Understanding weather helps us prepare for natural hazards and manage agriculture effectively.