Understanding the Weather

Class 07 Social Science

Weather is a state of the Earth’s atmosphere at a particular time and place. Atmosphere is the layer of gases (air) that surround the Earth.

The layer closest to the surface of the Earth is called the troposphere, and that is where all land-based plants and animals live and breathe. It is also where almost all weather phenomena take place. The troposphere extends to a height of 6 to 18 kilometres from the ground. It is less thick at the poles (where the cold air contracts) and thicker in the tropical zone (where the warmer air expands).

Elements of Weather

The elements of weather are:

1. ƒTemperature: How hot or cold the atmosphere is.
2. Precipitation: Any form of water, such as rain, snow, sleet or hail, that falls from the sky.
3. ƒAtmospheric Pressure: The weight of the air above us, felt on the Earth’s surface.
4. ƒWind: The movement of air, including its speed and direction.
5. Humidity: The amount of water vapour in the air.

From early times, humans have closely observed Nature and learnt to read her signals to forecast the weather. Observing birds flying low, ants carrying eggs, squirrels gathering nuts, frogs croaking loudly, or even the opening and closing of pine cones, provided valuable information about coming rain or storms. This knowledge has been passed down from generation to generation. Even today, in many parts of India, people use traditional ways to predict the weather, especially the arrival of the monsoon.

In the last few centuries, scientists have worked out methods to measure and monitor the elements of the weather with great precision. Based on those inputs, meteorologists try to predict how the weather will behave in a particular region after a few hours or a few days, or even a few weeks.

Weather Instruments

Temperature

There are several types of thermometers. Some measure the ambient temperature and others record the maximum and minimum temperatures during a day. Thermometers often use a coloured liquid which expands when the temperature increases. However, more and more, digital thermometers are preferred as they are more precise and can record more data. 

Temperature recordings can be used to collect some useful statistics, including:

• ƒRange of temperature or the maximum temperature minus the minimum temperature during a particular period of time (usually 24 hours).
• ƒMean daily temperature or the maximum temperature plus the minimum temperature of the day divided by two.

Precipitation

The amount of rainfall is measured with the help of an instrument called a rain gauge. When it rains, the water falls into a funnel and is collected in a cylinder. A scale is attached to the cylinder to measure the depth of rainwater collected. For example, when the height of the water collected is 5 mm, we say that the area received 5 mm of rainfall.

Atmospheric Pressure

Atmospheric pressure is the pressure exerted by the weight of the air above and around us.

The atmospheric pressure is higher near the sea coast and lower as we go higher up into the mountains. When you climb a mountain, the air gets thinner than in the plain below. As a result, the air pressure is lower, and there is less oxygen available for lungs to take in. With less oxygen getting into the blood, the body has to work harder to keep moving. That’s why people sometimes feel breathless, dizzy or tired at high altitudes.

The atmospheric pressure is not always high in the plains below or on the coast. It sometimes drops dramatically, resulting in 'depression’ or ‘low-pressure system’, which can sometimes develop into a storm or even a cyclone.

The instrument used to measure atmospheric pressure is called a barometer. As with thermometers, there are several types of barometers. The unit they display is generally the millibar (abbreviated as mb). The normal atmospheric pressure at the sea coast is around 1013 mb; a pressure below 1000 mb indicates a depression.

Wind

Wind is the movement of air from areas of high pressure to areas of low pressure. Speed and direction are two important factors to describe the wind. The wind is an important element of the weather. Its direction and speed help in weather forecasting. Besides, air pilots and sailors need to be aware of wind data, as the wind has a great influence on flying or sailing. Farmers also use the wind direction to predict where rain might come from. Also, a greater wind speed will cause the soil to dry faster.

A wind vane has a rotating arm with a pointer at one end and a tail at the other. When the wind blows, the tail is pushed, and the pointer turns in the direction of the wind. It responds even to a light breeze.

The simplest instrument to measure the wind direction and speed is the anemometer. It has three or four metal cups that rotate on a vertical shaft when the wind blows - the stronger the wind, the faster the rotation. A meter attached at the bottom counts how many times the anemometer spins in a certain period of time and calculates the wind speed in kilometres per hour (km/h).

Humidity

Humidity refers to the amount of water vapour present in the air. It also depends on factors like temperature, wind, pressure and location.

Humidity of the air is measured as relative humidity: air that would contain absolutely no water vapour (which is impossible
in natural conditions) is rated at 0%, while air saturated with water vapour will have a humidity of 100%. In practice, dry weather has a relative humidity range between 20% and 40%, while humid weather usually falls between 60% and 80% relative humidity.

Humidity is measured through an instrument called a hygrometer. There are several types of hygrometers, depending on the principle they are based on. The measurement of humidity is of great importance in many industrial processes, such as food processing. Museums also monitor humidity as they need to maintain a dry environment to preserve their exhibit.

Weather Stations

We need several instruments to measure the weather at a particular place and time. A weather station brings all these instruments together, making it easy to measure and track the weather. Readings of all the measurements are taken at regular intervals, which helps in mapping and forecasting the weather.

Automated Weather Station

An Automated Weather Station (AWS) is a self-operating system that uses various sensors to measure and record weather data, such as temperature, humidity, wind speed and direction, precipitation, and atmospheric pressure. Such stations are widely used in fields like agriculture, aviation, navigation, environmental monitoring, and so on, providing accurate and timely weather information without the need for human intervention.

Predicting the Weather

Meteorologists collect data using these instruments over long periods of time. They study the data and use scientific methods to try and predict the weather. Such predictions are very important nowadays, as climate change makes extreme weather, such as droughts, floods, cyclones, etc., more frequent.

Accurate predictions help us to be ready for such events. They also enable local governments to mobilise resources and prepare for any disasters. For example, if stormy weather is expected at sea, fishermen are warned about venturing out in their boats, or an entire coastal area might have to be evacuated if a cyclone is expected.