The weather is the day-to-day condition of the atmosphere at a particular place and time – whether the air is warm or cool, moist or dry, still or moving, and whether rain or snow is falling. METEOROLOGY is the study of the weather. The Sun is the driving force behind the weather. It heats air masses in different parts of the globe unevenly, creating differences in air pressure. This causes winds as air moves from zones of high pressure to low pressure. WEATHER FRONTS occur where moving masses of air collide.


Weather fronts are border zones where masses of air of different temperatures and humidity (moisture) levels meet and push into one another. Warm air is less dense, or lighter, than cold air, and so it rises above the cold air. Rising warm air creates an area of low pressure or depression. Depressions are linked with unsettled weather conditions, including high winds and rainy spells.


A warm front occurs when a mass of warm air meets a mass of cold air. The warm air slowly rises above the cold air, forming a low pressure zone. As the rising warm air cools, the moisture in it condenses to form clouds, bringing drizzle or rain.


A cold front occurs when a mass of cold air is driven towards a mass of warm air. As they collide, a steeply sloping front is formed and the warm air is forced to rise rapidly. This produces towering thunderclouds and brings torrential rain showers.


Cold fronts often follow a few hours behind warm fronts. Earth’s rotation bends the moving masses of air, causing the fronts to spiral around one another. The warm and cold air merge to form an occluded front, which brings cloudy skies and rain.


Meteorology is the study of atmospheric conditions and weather systems. Meteorologists have the difficult task of predicting the weather for the next few days (short-term forecasts) and for a week or so ahead (long-term forecasts). We all rely on weather forecasts to help plan the day, but they are particularly important for farmers, shipping firms, and airlines, and also power stations, since the weather affects the amount of energy we use.


A synoptic chart, or weather map, shows conditions in the atmosphere at a particular place and time – here, the weather system northeast of Japan in the satellite image above. Atmospheric conditions are shown using internationally known symbols. Lines called isobars link areas of equal air pressure.


Scientists use satellites orbiting high above Earth to track weather systems. Satellites provide images of clouds, storms, and hurricanes. They also monitor temperatures and humidity using sophisticated sensors.

Copyright © 2007 Dorling Kindersley

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