Air: Weather Climate

Learning Goals:

Weather: It is the hour to hour, day to day conditions of the atmosphere. It changes dramatically from day to day. Even metaphorically it is said ‘as changeable as the weather ’. Weather may be: Hot, Humid, Pleasant or Breezy.

The first two weather conditions might make us irritable and make it impossible to go for an outing with friends. The third and fourth weather conditions are welcome and acceptable by all. We get to hear the weather report across the world on News channels. Weather forecast is also important for us to plan our day. It is especially important for fishermen who are warned not to venture into the sea due to high tide forecast, for cricket fans and players speculating the outcome of a One Day match etc.


The average weather condition of a place for a longer period of time is called the climate of the place. Weather pattern of more than 20 years is considered for defining the climate of a place.

Meteorology: It is the study of the atmosphere. An operational forecaster analyzes weather conditions and issues forecasts or alerts the public of severe weather for their area.

The following are the aspects to be studied while studying the concept of weather and climate:


It is the degree of hotness or coldness of the air. It changes between day and night and from season to season. Thermometer is a device for measuring temperature.

Insolation: It is an important factor that influences the distribution of temperature. The incoming solar energy intercepted by the earth is called insolation. The amount of insolation decreases from the equator to the poles. This is the reason why the poles are much colder than the equator.

If the temperature of the earth becomes too high, it will be too warm for some crops to grow. The temperature in the cities is much higher than that in villages. This is because the concrete and metals in buildings and the asphalt of roads get heated up during the day and this trapped heat is released during the night. Some of our big and highly populated cities like Mumbai are slowly turning into ‘concrete jungle’. The lack of greenery is responsible for warmer climate in cities.

Air Pressure

The air above us presses us with great force. But we do not feel it at all. This is because it presses us from all directions and our body exerts a counter pressure. Air pressure is defined as the pressure exerted by the weight of air on the earth’s surface.

Nature of vertical air pressure: The pressure falls rapidly as we go up the layers of the atmosphere. Therefore, the pressure is the highest at sea level and decreases with altitude.

Nature of horizontal air pressure: Horizontally, the distribution of air pressure is influenced by the temperature of the air at a given place.

Where the temperature is high, the air gets heated up and rises, thus creating a low pressure area. This is associated with cloudy skies and wet weather.

Where the temperature is low, the air is cold and therefore heavy. This heavy air sinks and creates a high pressure area. High pressure is associated with clear and sunny skies.

The movement of air is always from areas of high pressure to areas of low pressure.

Barometer is used to measure atmospheric pressure.


The moving air is called wind. Winds can be gentle or very strong. Gentle winds blow away smoke or fine dust. An extremely strong wind is in the nature of a storm which can even uproot trees. A wind can be strong enough to make it difficult to walk against it.

Types of Wind

  1. Permanent winds: These blow constantly throughout the year in a particular direction. For example – the trade winds, westerlies and easterlies.
  2. Seasonal winds: These winds change their direction in different seasons. For example, monsoons in India.
  3. Local winds: These winds blow only during a particular period of the day or year in a small area. Land and sea breeze are examples of this.


When water evaporates from land and different water bodies, it becomes water vapour. Moisture in the air at any time is called humidity. A humid day is a day in which the air is full of water vapour. The capacity of the air to hold water increases as the air gets warmer.

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